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Carlos Garcia de Leaniz

Swansea University, Biosciences, Faculty Member

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ISI Research ID: B-4396-2011
H-index 21 (Google Scholar)
http://scholar.google.com/citations?user=HJK5CzYAAAAJ

My group works mostly on salmonid ecology and conservation, as well as on the impacts of aquaculture escapes. We are currently working on the freshwater pearl mussel and its relation to salmonid hosts, on anti-predatory behaviour and fish welfare in relation to captive breeding, and on the ecology of salmonid invasions. We use a variety of techniques to address clearly formulated questions and to test hypotheses. For example, we use image analysis and behavioural conditioning to quantify changes in fish shape and welfare due to domestication and to see how these changes can be reversed using environmental enrichment. We also use stable isotopes, scale analysis, and molecular markers to identify fish escaping from fish farms, to infer what they eat, and to try to quantify their potential impacts upon native fish. Some of our projects are carried out in collaboration with external agencies both in the UK (EA, NRW) and abroad (Chile, Spain, Falklands).

I offer placements for motivated students and volunteers in our lab and we are always looking for exceptional post-graduate students (MRes, MPhil, PhD) to join our group. If you are research-driven, willing to work hard, and interested in finding out why things are the way they are, drop me a line. Funding opportunities might be available.

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Diego Garcia de Jalon

Universidad Politécnica de Madrid

University of Melbourne

DIEGO JOSE OLIVA CUEVA

Luis Huachaca Santos

Universidad Nacional Federico Villarreal

Universidad Nacional de San Antonio Abad del Cusco

La Carraila (Valle de Ricote)

Maria Pilar Gomez

Irenes Calderon Muñoz

Universidad Central de Venezuela

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Papers by Carlos Garcia de Leaniz

La fragmentación de los ríos

Investigación y Ciencia, 2022

Carlos García de Leániz | Un sinfín de barreras interrumpe el flujo de los ríos europeos y altera... more

Silver spoons in the rough: can environmental enrichment improve survival of hatchery Atlantic salmon Salmo salar in the wild

Journal of Fish Biology

This study tested the 'silver spoon' hypothesis which posits that individuals that develop under ... more This study tested the 'silver spoon' hypothesis which posits that individuals that develop under favourable conditions should enjoy a fitness advantage later in life because they are more likely to recognize and settle in high-quality habitats. Atlantic salmon Salmo salar of two age classes (0+ and 1+ years) were reared in environmentally enriched or standard hatchery tanks for a short period (c. 10 weeks), were then released into a natural river and sampled on repeated occasions to test for silver-spoon effects. Compared with controls, enriched fish had a 6⋅4% higher recapture rate and settled in higher velocity habitats when they were stocked as 0+ year fry, but not when they were stocked as 1+ year parr. The opportunity for selection was generally higher for environmentally enriched fish than for controls, and also higher for 0+ than for 1+ year fish. Selection favoured individuals with high condition factor, extensive fat reserves and longer than average pectoral fins in both age classes but favoured a small body size in 1+ year and a large body size in 0+ year releases. Stomach analysis showed that enriched fish ate more, and adapted quicker to natural prey than controls. These results provide support for silver-spoon effects in fish and indicate that enrichment can improve post-release performance in conservation programmes, but seemingly only if fish are not kept in captivity for too long.

Maladaptation and phenotypic mismatch in hatchery-reared Atlantic salmon Salmo salar released in the wild

Journal of Fish Biology

Changes in body shape, fluctuating asymmetry (FA) and crypsis were compared among Atlantic salmon... more Changes in body shape, fluctuating asymmetry (FA) and crypsis were compared among Atlantic salmon Salmo salar fry kept as controls in captivity and those released and subsequently recaptured in the wild according to a before-after-control-impact (BACI) design. Hatchery fish that survived in the wild became more cryptic and displayed a much lower incidence of fin erosion and of asymmetric individuals than control fish kept in captivity. Significant differences in body shape were also apparent, and survivors had longer heads, thicker caudal peduncles and a more streamlined body shape than hatchery controls as early as 20 days following stocking, most likely as a result of phenotypic plasticity and non-random, selective mortality of maladapted phenotypes. Hatchery-reared fish typically perform poorly in the wild and the results of this study indicate that this may be due to phenotypic mismatch, i.e. because hatcheries generate fish that are phenotypically mismatched to the natural environment.

Contrasting patterns of genetic and phenotypic differentiation in two invasive salmonids in the southern hemisphere

Evolutionary Applications

Invasion success may be expected to increase with residence time (i.e., time since first introduc... more Invasion success may be expected to increase with residence time (i.e., time since first introduction) and secondary releases (i.e., those that follow the original introduction), but this has rarely been tested in natural fish populations. We compared genetic and phenotypic divergence in rainbow trout and brown trout in Chile and the Falkland Islands to test the prediction that adaptive divergence, measured as P ST /F ST , would increase with residence time and secondary releases. We also explored whether interspecific competition between invaders could drive phenotypic divergence. Residence time had no significant effect on genetic diversity, phenotypic divergence, effective population size, or signatures of expansion of invasive trout. In contrast, secondary releases had a major effect on trout invasions, and rainbow trout populations mostly affected by aquaculture escapees showed significant divergence from less affected populations. Coexistence with brown trout had a positive effect on phenotypic divergence of rainbow trout. Our results highlight an important role of secondary releases in shaping fish invasions, but do not support the contention that older invaders are more differentiated than younger ones. They also suggest that exotic trout may not have yet developed local adaptations in these recently invaded habitats, at least with respect to growth-related traits.

Shrinking fish: comparisons of prehistoric and contemporary salmonids indicate decreasing size at age across millennia

Royal Society Open Science

Eco-immunology of fish invasions: the role of MHC variation

Immunogenetics

The relationship between invaders and the pathogens encountered in their new environment can have... more The relationship between invaders and the pathogens encountered in their new environment can have a large effect on invasion success. Invaders can become free from their natural pathogens and reallocate costly immune resources to growth and reproduction, thereby increasing invasion success. Release from enemies and relaxation of selective pressures could render newly founded populations more variable at immune-related genes, such as the major histocompatibility complex (MHC), particularly when they have different origins. Using rainbow and brown trout, two of the world's most successful fish invaders, we tested the general hypothesis that invaders should display high intrapopulation immunogenetic diversity and interpopulation divergence, due to the interplay between genetic drift and successive waves of genetically divergent introductions. We analysed genetic diversity and signatures of selection at the MHC class II β immune-related locus. In both species, MHC diversity (allelic richness and heterozygosity) for southern hemisphere populations was similar to values reported for populations at their native range. However, MHC functional diversity was limited, and population immunogenetic structuring weaker than that observed using neutral markers. Depleted MHC functional diversity could reflect a decrease in immune response, immune-related assortative mating or selection for resistance to newly encountered parasites. Given that the role of MHC diversity in the survival of these populations remains unclear, depleted functional diversity of invasive salmonids could compromise their long-term persistence. A better understanding of the eco-immunology of invaders may help in managing and preventing the impact of biological invasions, a major cause of loss of biodiversity worldwide.

Less can be more: loss of MHC functional diversity can reflect adaptation to novel conditions during fish invasions

Ecology & Evolution

"The ability of invasive species to adapt to novel conditions depends on population size and envi... more "The ability of invasive species to adapt to novel conditions depends on population size and environmental mismatch, but also on genetic variation. Away from their native range, invasive species confronted with novel selective pressures may display different levels of neutral vs. functional genetic variation. Yet, the majority of invasion studies have only examined genetic variation at neutral markers, which may reveal little about how invaders adapt to novel environments. Salmonids are good model systems
to examine adaptation to novel pressures because they have been translocated all over the world and represent major threats to freshwater biodiversity in the Southern Hemisphere, where they have become invasive. We examined patterns of genetic differentiation at seven putatively neutral (microsatellites) loci and one immune-related (MHC class II-β) locus among introduced rainbow trout living in captivity (farmed) or
under natural conditions (naturalised) in Chilean Patagonia. A significant positive association was found between differentiation at neutral and functional markers, highlighting the role of neutral evolutionary forces in shaping genetic variation at immune-related genes in salmonids. However, functional (MHC) genetic diversity (but not microsatellite diversity) decreased with time spent in the wild since introduction, suggesting that
there was selection against alleles associated with captive rearing of donor populations that do not provide an advantage in the wild. Thus, although high genetic diversity may initially enhance fitness in translocated populations, it does not necessarily reflect invasion success, as adaptation to novel conditions may result in rapid loss of functional MHC diversity."

Can migrants escape from density-dependence?

1. Migration is thought to maximize growth by enabling individuals to escape from density-depende... more 1. Migration is thought to maximize growth by enabling individuals to escape from density-dependence, but this has rarely been tested at the individual level in natural populations.

2. We employed linear mixed modelling of the spacing between
consecutive scale growth rings to reconstruct individual growth profiles of a paradigmatic fish migrant, the sea trout (Salmo trutta) and related these to estimates of year class strength over a 13-year period.

3. Variation in scale growth was 1.3 times greater among individuals than within individuals in freshwater, and 10 times greater at sea. Scale growth was inversely related to year class strength, both in freshwater (before migration) and at sea (after migration).

4. Competition for patchily distributed resources is the most plausible explanation for the negative density-dependent growth observed in freshwater and, to a lesser extent, in the marine environment.

5. Our study provides some of the strongest evidence for a role of density-dependence in determining partial migrations because although migrants can maximize growth by moving into the sea, they do not appear to become free from density-dependence constraints completely. This has implications for conservation and suggests that sea trout and other anadromous fish displaying partial migrations may not be best managed on a river by river basis, but rather from a broader, coastal perspective"

Does the parasitic freshwater pearl mussel M. margaritifera harm its host?

Many parasites have strong negative impacts on their hosts, but the effects of single-host, non-t... more Many parasites have strong negative impacts on their hosts, but the effects of single-host, non-trophically transmitted parasites can be subtle and are not well understood. We examined the physiological response of juvenile brown trout (Salmo trutta) to encystment by the parasitic larvae (glochidia) of the freshwater pearl mussel, Margaritifera margaritifera. Glochidia abundance was positively correlated to host body size and was accompanied by significant spleen enlargement at 31 days postexposure, but not before (15 days) or after (160 days). Compared to controls, encysted gill lamellae were significantly thicker and longer, and tended to have fewer mucous cells which may have facilitated encystment. There were no significant difference in mean blood haematocrit between encysted and uninfected trout, but encysted trout took c. 6 h longer to reach basal ventilation rate than controls suggesting that glochidiosis may impose a respiratory burden to brown trout. These findings may have implications for the artificial propagation of the freshwater pearl mussel because the effects of glochidia on host respiratory performance appear to be additive. Therefore, aiming for high glochidia loads may not be the best option for mussel propagation programmes, if this compromises host fitness and hence the probability of successful glochidia excystment

Mixed-effects modelling of scale growth profiles predicts the occurrence of early and late fish migrants

Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth v... more Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth variation can be interpreted in relation to conspecifics’ performance. Unfortunately, assessing individual variation in growth rates is problematic under natural conditions because subjects typically need to be marked, repeated measurements of body size are difficult to obtain in the field, and recaptures may be limited to a few time events which will generally vary among individuals. The analysis of consecutive growth rings (circuli) found on scales and other hard structures offers an alternative to mark and recapture for examining individual growth variation in fish and other aquatic vertebrates where growth rings can be visualized, but accounting for autocorrelations and seasonal growth stanzas has proved challenging. Here we show how mixed-effects modelling of scale growth increments (inter-circuli spacing) can be used to reconstruct the growth trajectories of sea trout (Salmo trutta) and correctly classify 89% of individuals into early or late seaward migrants (smolts). Early migrants grew faster than late migrants during their first year of life in freshwater in two natural populations, suggesting that migration into the sea was triggered by ontogenetic (intrinsic) drivers, rather than by competition with conspecifics. Our study highlights the profound effects that early growth can have on age at migration of a paradigmatic fish migrant and illustrates how the analysis of inter-circuli spacing can be used to reconstruct the detailed growth of individuals when these cannot be marked or are only caught once.

Inbred and furious: negative association between aggression and genetic diversity in a highly inbred fish.

Aggressive behaviour plays an important role in securing resources, defending against predators a... more Aggressive behaviour plays an important role in securing resources, defending against predators and shaping social interactions. Although aggression can have positive effects on growth and reproductive success, it is also energetically costly and may increase injury and compromise survival. Individual genetic diversity has been positively associated with aggression but the cause for such an association is not clear, and it might be related to the ability to recognise kin. In order to disentangle the relationships between genetic diversity, kinship and aggression, we quantified aggressive behaviour in a wild, self-fertilising fish (Kryptolebias marmoratus) with naturally variable degrees of genetic diversity, relatedness and familiarity. We found that, in contrast to captive fish, levels of aggression among wild K. marmoratus are positively associated with individual homozygosity, but not with relatedness or familiarity. We suggest that the higher aggression shown by homozygous fish could be related to better kin discrimination and may be facilitated by hermaphrodite competition for scarce males, given the fitness advantages provided by outcrossing in terms of parasite resistance. It seems likely that the relationships between aggression and genetic diversity are largely influenced by both the environment and population history.

A genetic marker for the maternal identification of Atlantic salmon x brown trout hybrids.

"Interspecific hybridization between Atlantic salmon and brown trout is well documented, but why ... more "Interspecific hybridization between Atlantic salmon and brown trout is well documented, but why it should vary so much among populations is not clear.
Determining the maternal origin of hybrids can provide insights into the mechanisms underlying interspecific hybridization, but this information is lacking in many studies. Here we present a species-specific mitochondrial
DNA marker for the identification of the maternal origin of hybrids. This marker involves only one PCR step followed by fragment analysis, can be integrated within PCR multiplexing for existing nuclear markers for hybrid identification, and is therefore faster and more cost-effective than
previous methods. Keywords Interspecific hybridization Atlantic salmon
Brown trout Mitochondrial DNA"

And the last shall be first: heterochrony and compensatory marine growth in sea trout (Salmo trutta).

Early juvenile growth is a good indicator of growth later in life in many species because larger ... more Early juvenile growth is a good indicator of growth later in life in many species because larger than average juveniles tend to have a competitive advantage. However, for migratory species the relationship between juvenile and adult growth remains obscure. We used scale analysis to reconstruct growth trajectories of migratory sea trout (Salmo trutta) from six neighbouring populations, and compared the size individuals attained in freshwater (before migration) with their subsequent growth at sea (after migration). We also calculated the coefficient of variation (CV) to examine how much body size varied across populations and life stages. Specifically, we tested the hypothesis that the CV on body size would differ between freshwater and marine environment, perhaps reflecting different trade-offs. Neighbouring sea trout populations differed significantly in time spent at sea and in age-adjusted size of returning adults, but not on size of seaward migration, which was surprisingly uniform and may be indicative of strong selection pressures. The CV on body size decreased significantly over time and was highest during the first 8 months of life (when juvenile mortality is highest) and lowest during the marine phase. Size attained in freshwater was negatively related to growth during the first marine growing season, suggesting the existence of compensatory growth, whereby individuals that grow poorly in freshwater are able to catch up later at sea. Analysis of 61 datasets indicates that negative or no associations between pre- and post-migratory growth are common amongst migratory salmonids. We suggest that despite a widespread selective advantage of large body size in freshwater, freshwater growth is a poor predictor of final body size amongst migratory fish because selection may favour plasticity during transitions to a novel environment, and marine compensatory growth may negate any initial size advantage acquired in freshwater.

Regional mtDNA SNP differentiation in European Atlantic salmon (Salmo salar): an assessment of potential utility for determination of natal origin

The Atlantic salmon, Salmo salar, shows geographically structured differentiation at various clas... more The Atlantic salmon, Salmo salar, shows geographically structured differentiation at various classes of molecular genetic variation, among and within river stocks. Nuclear microsatellite locus variation at multiple loci has been exploited for more than a decade as a marker for the continental origin of fish caught at sea in distant-water fisheries. However, a simpler, more cost-effective, but still accurate, assignment can be obtained using a single microsatellite locus in combination with a mitochondrial DNA (mtDNA) single-nucleotide polymorphism (SNP) detected by restriction enzyme digestion. Following on from this, a preliminary study was made of the potential for using mtDNA SNP variation to enhance the resolving power and cost-effectiveness of within-continent assignment of European salmon as determined using microsatellites. Variation in 20 mtDNA regions, encompassing ?43% of this genome, in 330 salmon from 29 rivers across Europe, was analysed. High levels of inter-individual and inter-river variation were found, as well as evidence of regional differentiation paralleling observed microsatellite differentiation. The observations indicate scope for using mtDNA SNPs along with microsatellites for genetically based assignment of European salmon to region and river of natal origin, but further study is needed. Key words: Atlantic salmon, genetic stock identification, marine ecology, mitochondrial DNA, 454 sequencing

Metapopulation dynamics of a diadromous galaxiid fish and potential effects of salmonid aquaculture

1.Direct ecological effects of biological invasions have been widely documented, but indirect gen... more 1.Direct ecological effects of biological invasions have been widely documented, but indirect genetic effects on native species are poorly known. In many cases this is due to lack of information on the genetic structure of species affected by invasions.
2. We used microsatellite DNA loci to estimate the genetic structure and gene flow patterns of Galaxias maculatus, a galaxiid fish endemic to the Southern Hemisphere which is increasingly being threatened by salmonid invasions.
3. Analysis of nine diadromous populations of G. maculatus in Chilean Patagonia (an area heavily impacted by farming of non-native salmonids) indicates that dispersal is mostly a passive process, seemingly driven by wind and currents, and resulting in high gene flow and weak population structuring. 4.Gene flow was asymmetrical, with three populations acting as sources and six populations acting as sinks. Sinks had lower habitat quality and had a greater incidence of adults than sources, which consisted mostly of juveniles.
5.Rivers invaded by salmonid escapees experienced significantly higher aquaculture pressure than rivers where salmonid escapees were apparently absent, but no effect on genetic diversity of G. maculatus could be detected.
6.We discuss whether salmonid aquaculture might affect the demography and connectivity of galaxiid metapopulations: indirectly through habitat alteration and directly through escapes of predatory fish."

DNA barcoding and microsatellites help species delimitation and hybrid identification in endangered galaxiid fishes.

The conservation of data deficient species is often hampered by inaccurate species delimitation. ... more The conservation of data deficient species is often hampered by inaccurate species delimitation. The galaxiid fishes Aplochiton zebra and Aplochiton taeniatus are endemic to Patagonia (and for A. zebra the Falkland Islands), where they are threatened by invasive salmonids. Conservation of Aplochiton is complicated because species identification is hampered by the presence of resident as well as migratory ecotypes that may confound morphological discrimination. We used DNA barcoding (COI, cytochrome b) and a new developed set of microsatellite markers to investigate the relationships between A. zebra and A. taeniatus and to assess their distributions and relative abundances in Chilean Patagonia and the Falkland Islands. Results from both DNA markers were 100% congruent and revealed that phenotypic misidentification was widespread, size-dependent, and highly asymmetric. While all the genetically classified A. zebra were correctly identified as such, 74% of A. taeniatus were incorrectly identified as A. zebra, the former species being more widespread than previously thought. Our results reveal, for the first time, the presence in sympatry of both species, not only in Chilean Patagonia, but also in the Falkland Islands, where A. taeniatus had not been previously described. We also found evidence of asymmetric hybridisation between female A. taeniatus and male A. zebra in areas where invasive salmonids have become widespread. Given the potential consequences that species misidentification and hybridisation can have for the conservation of these endangered species, we advocate the use of molecular markers in order to reduce epistemic uncertainty. Keywords: Aplochiton zebra, Aplochiton taeniatus, hybridisation, barcoding, biological invasions, conservation;

Obituary. William Crozier Jordan (Bill) 1962-2011

Something smells fishy: predator-naïve salmon use diet cues, not kairomones, to recognize a sympatric mammalian predator

The ability to recognize predators is one of the most important lines of defence in a prey’s arse... more

Winning the invasion roulette: escapes from fish farms increase admixture and facilitate establishment of non-native rainbow trout

Aquaculture is a major source of invasive aquatic species, despite the fact that cultured organis... more Aquaculture is a major source of invasive aquatic species, despite the fact that cultured organisms often have low genetic diversity and tend to be maladapted to survive in the wild. Yet, to what extent aquaculture escapees become established by means of high propagule pressure and multiple origins is not clear. We analysed the genetic diversity of 15 established populations and 4 farmed stocks of non-native rainbow trout in Chile, a species first introduced for recreational fishing around 1900, but which has in recent decades escaped in large numbers from fish farms and become widespread. Aquaculture propagule pressure was a good predictor of the incidence of farm escapees, which represented 16% of all free-ranging rainbow trout and were present in 80% of the study rivers. Hybrids between farm escapes and established trout were present in all rivers at frequencies ranging between 7 and 69%, and population admixture was positively correlated with genetic diversity. We suggest that non-native salmonids introduced into the Southern Hemisphere could benefit from admixture because local adaptations may not have yet developed and there may be initially little fitness loss resulting from outbreeding depression.

Development of 13 microsatellite markers for the threatened galaxiid fish Aplochiton zebra (Jenyns, 1842)

Aplochiton zebra (peladilla, zebra trout) is a galaxiid fish endemic to Patagonia and the Falklan... more Aplochiton zebra (peladilla, zebra trout) is a galaxiid fish endemic to Patagonia and the Falkland Islands, where populations are threatened by salmonid introductions. Here we describe the isolation and characterization of 13 polymorphic microsatellite DNA markers that can be used for assessing the genetic variation and conservation status of this species. The variability of these markers was assessed in six rivers in Chilean Patagonia. The number of alleles ranged from 5 to 80 per locus and observed heterozygosities varied between 0.168 and 0.910. A protocol for multiplexing these markers is described.

La fragmentación de los ríos

Investigación y Ciencia, 2022

Carlos García de Leániz | Un sinfín de barreras interrumpe el flujo de los ríos europeos y altera... more

Silver spoons in the rough: can environmental enrichment improve survival of hatchery Atlantic salmon Salmo salar in the wild

Journal of Fish Biology

This study tested the 'silver spoon' hypothesis which posits that individuals that develop under ... more This study tested the 'silver spoon' hypothesis which posits that individuals that develop under favourable conditions should enjoy a fitness advantage later in life because they are more likely to recognize and settle in high-quality habitats. Atlantic salmon Salmo salar of two age classes (0+ and 1+ years) were reared in environmentally enriched or standard hatchery tanks for a short period (c. 10 weeks), were then released into a natural river and sampled on repeated occasions to test for silver-spoon effects. Compared with controls, enriched fish had a 6⋅4% higher recapture rate and settled in higher velocity habitats when they were stocked as 0+ year fry, but not when they were stocked as 1+ year parr. The opportunity for selection was generally higher for environmentally enriched fish than for controls, and also higher for 0+ than for 1+ year fish. Selection favoured individuals with high condition factor, extensive fat reserves and longer than average pectoral fins in both age classes but favoured a small body size in 1+ year and a large body size in 0+ year releases. Stomach analysis showed that enriched fish ate more, and adapted quicker to natural prey than controls. These results provide support for silver-spoon effects in fish and indicate that enrichment can improve post-release performance in conservation programmes, but seemingly only if fish are not kept in captivity for too long.

Maladaptation and phenotypic mismatch in hatchery-reared Atlantic salmon Salmo salar released in the wild

Journal of Fish Biology

Changes in body shape, fluctuating asymmetry (FA) and crypsis were compared among Atlantic salmon... more Changes in body shape, fluctuating asymmetry (FA) and crypsis were compared among Atlantic salmon Salmo salar fry kept as controls in captivity and those released and subsequently recaptured in the wild according to a before-after-control-impact (BACI) design. Hatchery fish that survived in the wild became more cryptic and displayed a much lower incidence of fin erosion and of asymmetric individuals than control fish kept in captivity. Significant differences in body shape were also apparent, and survivors had longer heads, thicker caudal peduncles and a more streamlined body shape than hatchery controls as early as 20 days following stocking, most likely as a result of phenotypic plasticity and non-random, selective mortality of maladapted phenotypes. Hatchery-reared fish typically perform poorly in the wild and the results of this study indicate that this may be due to phenotypic mismatch, i.e. because hatcheries generate fish that are phenotypically mismatched to the natural environment.

Contrasting patterns of genetic and phenotypic differentiation in two invasive salmonids in the southern hemisphere

Evolutionary Applications

Invasion success may be expected to increase with residence time (i.e., time since first introduc... more Invasion success may be expected to increase with residence time (i.e., time since first introduction) and secondary releases (i.e., those that follow the original introduction), but this has rarely been tested in natural fish populations. We compared genetic and phenotypic divergence in rainbow trout and brown trout in Chile and the Falkland Islands to test the prediction that adaptive divergence, measured as P ST /F ST , would increase with residence time and secondary releases. We also explored whether interspecific competition between invaders could drive phenotypic divergence. Residence time had no significant effect on genetic diversity, phenotypic divergence, effective population size, or signatures of expansion of invasive trout. In contrast, secondary releases had a major effect on trout invasions, and rainbow trout populations mostly affected by aquaculture escapees showed significant divergence from less affected populations. Coexistence with brown trout had a positive effect on phenotypic divergence of rainbow trout. Our results highlight an important role of secondary releases in shaping fish invasions, but do not support the contention that older invaders are more differentiated than younger ones. They also suggest that exotic trout may not have yet developed local adaptations in these recently invaded habitats, at least with respect to growth-related traits.

Shrinking fish: comparisons of prehistoric and contemporary salmonids indicate decreasing size at age across millennia

Royal Society Open Science

Eco-immunology of fish invasions: the role of MHC variation

Immunogenetics

The relationship between invaders and the pathogens encountered in their new environment can have... more The relationship between invaders and the pathogens encountered in their new environment can have a large effect on invasion success. Invaders can become free from their natural pathogens and reallocate costly immune resources to growth and reproduction, thereby increasing invasion success. Release from enemies and relaxation of selective pressures could render newly founded populations more variable at immune-related genes, such as the major histocompatibility complex (MHC), particularly when they have different origins. Using rainbow and brown trout, two of the world's most successful fish invaders, we tested the general hypothesis that invaders should display high intrapopulation immunogenetic diversity and interpopulation divergence, due to the interplay between genetic drift and successive waves of genetically divergent introductions. We analysed genetic diversity and signatures of selection at the MHC class II β immune-related locus. In both species, MHC diversity (allelic richness and heterozygosity) for southern hemisphere populations was similar to values reported for populations at their native range. However, MHC functional diversity was limited, and population immunogenetic structuring weaker than that observed using neutral markers. Depleted MHC functional diversity could reflect a decrease in immune response, immune-related assortative mating or selection for resistance to newly encountered parasites. Given that the role of MHC diversity in the survival of these populations remains unclear, depleted functional diversity of invasive salmonids could compromise their long-term persistence. A better understanding of the eco-immunology of invaders may help in managing and preventing the impact of biological invasions, a major cause of loss of biodiversity worldwide.

Less can be more: loss of MHC functional diversity can reflect adaptation to novel conditions during fish invasions

Ecology & Evolution

"The ability of invasive species to adapt to novel conditions depends on population size and envi... more "The ability of invasive species to adapt to novel conditions depends on population size and environmental mismatch, but also on genetic variation. Away from their native range, invasive species confronted with novel selective pressures may display different levels of neutral vs. functional genetic variation. Yet, the majority of invasion studies have only examined genetic variation at neutral markers, which may reveal little about how invaders adapt to novel environments. Salmonids are good model systems
to examine adaptation to novel pressures because they have been translocated all over the world and represent major threats to freshwater biodiversity in the Southern Hemisphere, where they have become invasive. We examined patterns of genetic differentiation at seven putatively neutral (microsatellites) loci and one immune-related (MHC class II-β) locus among introduced rainbow trout living in captivity (farmed) or
under natural conditions (naturalised) in Chilean Patagonia. A significant positive association was found between differentiation at neutral and functional markers, highlighting the role of neutral evolutionary forces in shaping genetic variation at immune-related genes in salmonids. However, functional (MHC) genetic diversity (but not microsatellite diversity) decreased with time spent in the wild since introduction, suggesting that
there was selection against alleles associated with captive rearing of donor populations that do not provide an advantage in the wild. Thus, although high genetic diversity may initially enhance fitness in translocated populations, it does not necessarily reflect invasion success, as adaptation to novel conditions may result in rapid loss of functional MHC diversity."

Can migrants escape from density-dependence?

1. Migration is thought to maximize growth by enabling individuals to escape from density-depende... more 1. Migration is thought to maximize growth by enabling individuals to escape from density-dependence, but this has rarely been tested at the individual level in natural populations.

2. We employed linear mixed modelling of the spacing between
consecutive scale growth rings to reconstruct individual growth profiles of a paradigmatic fish migrant, the sea trout (Salmo trutta) and related these to estimates of year class strength over a 13-year period.

3. Variation in scale growth was 1.3 times greater among individuals than within individuals in freshwater, and 10 times greater at sea. Scale growth was inversely related to year class strength, both in freshwater (before migration) and at sea (after migration).

4. Competition for patchily distributed resources is the most plausible explanation for the negative density-dependent growth observed in freshwater and, to a lesser extent, in the marine environment.

5. Our study provides some of the strongest evidence for a role of density-dependence in determining partial migrations because although migrants can maximize growth by moving into the sea, they do not appear to become free from density-dependence constraints completely. This has implications for conservation and suggests that sea trout and other anadromous fish displaying partial migrations may not be best managed on a river by river basis, but rather from a broader, coastal perspective"

Does the parasitic freshwater pearl mussel M. margaritifera harm its host?

Many parasites have strong negative impacts on their hosts, but the effects of single-host, non-t... more Many parasites have strong negative impacts on their hosts, but the effects of single-host, non-trophically transmitted parasites can be subtle and are not well understood. We examined the physiological response of juvenile brown trout (Salmo trutta) to encystment by the parasitic larvae (glochidia) of the freshwater pearl mussel, Margaritifera margaritifera. Glochidia abundance was positively correlated to host body size and was accompanied by significant spleen enlargement at 31 days postexposure, but not before (15 days) or after (160 days). Compared to controls, encysted gill lamellae were significantly thicker and longer, and tended to have fewer mucous cells which may have facilitated encystment. There were no significant difference in mean blood haematocrit between encysted and uninfected trout, but encysted trout took c. 6 h longer to reach basal ventilation rate than controls suggesting that glochidiosis may impose a respiratory burden to brown trout. These findings may have implications for the artificial propagation of the freshwater pearl mussel because the effects of glochidia on host respiratory performance appear to be additive. Therefore, aiming for high glochidia loads may not be the best option for mussel propagation programmes, if this compromises host fitness and hence the probability of successful glochidia excystment

Mixed-effects modelling of scale growth profiles predicts the occurrence of early and late fish migrants

Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth v... more Fish growth is commonly used as a proxy for fitness but this is only valid if individual growth variation can be interpreted in relation to conspecifics’ performance. Unfortunately, assessing individual variation in growth rates is problematic under natural conditions because subjects typically need to be marked, repeated measurements of body size are difficult to obtain in the field, and recaptures may be limited to a few time events which will generally vary among individuals. The analysis of consecutive growth rings (circuli) found on scales and other hard structures offers an alternative to mark and recapture for examining individual growth variation in fish and other aquatic vertebrates where growth rings can be visualized, but accounting for autocorrelations and seasonal growth stanzas has proved challenging. Here we show how mixed-effects modelling of scale growth increments (inter-circuli spacing) can be used to reconstruct the growth trajectories of sea trout (Salmo trutta) and correctly classify 89% of individuals into early or late seaward migrants (smolts). Early migrants grew faster than late migrants during their first year of life in freshwater in two natural populations, suggesting that migration into the sea was triggered by ontogenetic (intrinsic) drivers, rather than by competition with conspecifics. Our study highlights the profound effects that early growth can have on age at migration of a paradigmatic fish migrant and illustrates how the analysis of inter-circuli spacing can be used to reconstruct the detailed growth of individuals when these cannot be marked or are only caught once.

Inbred and furious: negative association between aggression and genetic diversity in a highly inbred fish.

Aggressive behaviour plays an important role in securing resources, defending against predators a... more Aggressive behaviour plays an important role in securing resources, defending against predators and shaping social interactions. Although aggression can have positive effects on growth and reproductive success, it is also energetically costly and may increase injury and compromise survival. Individual genetic diversity has been positively associated with aggression but the cause for such an association is not clear, and it might be related to the ability to recognise kin. In order to disentangle the relationships between genetic diversity, kinship and aggression, we quantified aggressive behaviour in a wild, self-fertilising fish (Kryptolebias marmoratus) with naturally variable degrees of genetic diversity, relatedness and familiarity. We found that, in contrast to captive fish, levels of aggression among wild K. marmoratus are positively associated with individual homozygosity, but not with relatedness or familiarity. We suggest that the higher aggression shown by homozygous fish could be related to better kin discrimination and may be facilitated by hermaphrodite competition for scarce males, given the fitness advantages provided by outcrossing in terms of parasite resistance. It seems likely that the relationships between aggression and genetic diversity are largely influenced by both the environment and population history.

A genetic marker for the maternal identification of Atlantic salmon x brown trout hybrids.

"Interspecific hybridization between Atlantic salmon and brown trout is well documented, but why ... more "Interspecific hybridization between Atlantic salmon and brown trout is well documented, but why it should vary so much among populations is not clear.
Determining the maternal origin of hybrids can provide insights into the mechanisms underlying interspecific hybridization, but this information is lacking in many studies. Here we present a species-specific mitochondrial
DNA marker for the identification of the maternal origin of hybrids. This marker involves only one PCR step followed by fragment analysis, can be integrated within PCR multiplexing for existing nuclear markers for hybrid identification, and is therefore faster and more cost-effective than
previous methods. Keywords Interspecific hybridization Atlantic salmon
Brown trout Mitochondrial DNA"

And the last shall be first: heterochrony and compensatory marine growth in sea trout (Salmo trutta).

Early juvenile growth is a good indicator of growth later in life in many species because larger ... more Early juvenile growth is a good indicator of growth later in life in many species because larger than average juveniles tend to have a competitive advantage. However, for migratory species the relationship between juvenile and adult growth remains obscure. We used scale analysis to reconstruct growth trajectories of migratory sea trout (Salmo trutta) from six neighbouring populations, and compared the size individuals attained in freshwater (before migration) with their subsequent growth at sea (after migration). We also calculated the coefficient of variation (CV) to examine how much body size varied across populations and life stages. Specifically, we tested the hypothesis that the CV on body size would differ between freshwater and marine environment, perhaps reflecting different trade-offs. Neighbouring sea trout populations differed significantly in time spent at sea and in age-adjusted size of returning adults, but not on size of seaward migration, which was surprisingly uniform and may be indicative of strong selection pressures. The CV on body size decreased significantly over time and was highest during the first 8 months of life (when juvenile mortality is highest) and lowest during the marine phase. Size attained in freshwater was negatively related to growth during the first marine growing season, suggesting the existence of compensatory growth, whereby individuals that grow poorly in freshwater are able to catch up later at sea. Analysis of 61 datasets indicates that negative or no associations between pre- and post-migratory growth are common amongst migratory salmonids. We suggest that despite a widespread selective advantage of large body size in freshwater, freshwater growth is a poor predictor of final body size amongst migratory fish because selection may favour plasticity during transitions to a novel environment, and marine compensatory growth may negate any initial size advantage acquired in freshwater.

Regional mtDNA SNP differentiation in European Atlantic salmon (Salmo salar): an assessment of potential utility for determination of natal origin

The Atlantic salmon, Salmo salar, shows geographically structured differentiation at various clas... more The Atlantic salmon, Salmo salar, shows geographically structured differentiation at various classes of molecular genetic variation, among and within river stocks. Nuclear microsatellite locus variation at multiple loci has been exploited for more than a decade as a marker for the continental origin of fish caught at sea in distant-water fisheries. However, a simpler, more cost-effective, but still accurate, assignment can be obtained using a single microsatellite locus in combination with a mitochondrial DNA (mtDNA) single-nucleotide polymorphism (SNP) detected by restriction enzyme digestion. Following on from this, a preliminary study was made of the potential for using mtDNA SNP variation to enhance the resolving power and cost-effectiveness of within-continent assignment of European salmon as determined using microsatellites. Variation in 20 mtDNA regions, encompassing ?43% of this genome, in 330 salmon from 29 rivers across Europe, was analysed. High levels of inter-individual and inter-river variation were found, as well as evidence of regional differentiation paralleling observed microsatellite differentiation. The observations indicate scope for using mtDNA SNPs along with microsatellites for genetically based assignment of European salmon to region and river of natal origin, but further study is needed. Key words: Atlantic salmon, genetic stock identification, marine ecology, mitochondrial DNA, 454 sequencing

Metapopulation dynamics of a diadromous galaxiid fish and potential effects of salmonid aquaculture

1.Direct ecological effects of biological invasions have been widely documented, but indirect gen... more 1.Direct ecological effects of biological invasions have been widely documented, but indirect genetic effects on native species are poorly known. In many cases this is due to lack of information on the genetic structure of species affected by invasions.
2. We used microsatellite DNA loci to estimate the genetic structure and gene flow patterns of Galaxias maculatus, a galaxiid fish endemic to the Southern Hemisphere which is increasingly being threatened by salmonid invasions.
3. Analysis of nine diadromous populations of G. maculatus in Chilean Patagonia (an area heavily impacted by farming of non-native salmonids) indicates that dispersal is mostly a passive process, seemingly driven by wind and currents, and resulting in high gene flow and weak population structuring. 4.Gene flow was asymmetrical, with three populations acting as sources and six populations acting as sinks. Sinks had lower habitat quality and had a greater incidence of adults than sources, which consisted mostly of juveniles.
5.Rivers invaded by salmonid escapees experienced significantly higher aquaculture pressure than rivers where salmonid escapees were apparently absent, but no effect on genetic diversity of G. maculatus could be detected.
6.We discuss whether salmonid aquaculture might affect the demography and connectivity of galaxiid metapopulations: indirectly through habitat alteration and directly through escapes of predatory fish."

DNA barcoding and microsatellites help species delimitation and hybrid identification in endangered galaxiid fishes.

The conservation of data deficient species is often hampered by inaccurate species delimitation. ... more The conservation of data deficient species is often hampered by inaccurate species delimitation. The galaxiid fishes Aplochiton zebra and Aplochiton taeniatus are endemic to Patagonia (and for A. zebra the Falkland Islands), where they are threatened by invasive salmonids. Conservation of Aplochiton is complicated because species identification is hampered by the presence of resident as well as migratory ecotypes that may confound morphological discrimination. We used DNA barcoding (COI, cytochrome b) and a new developed set of microsatellite markers to investigate the relationships between A. zebra and A. taeniatus and to assess their distributions and relative abundances in Chilean Patagonia and the Falkland Islands. Results from both DNA markers were 100% congruent and revealed that phenotypic misidentification was widespread, size-dependent, and highly asymmetric. While all the genetically classified A. zebra were correctly identified as such, 74% of A. taeniatus were incorrectly identified as A. zebra, the former species being more widespread than previously thought. Our results reveal, for the first time, the presence in sympatry of both species, not only in Chilean Patagonia, but also in the Falkland Islands, where A. taeniatus had not been previously described. We also found evidence of asymmetric hybridisation between female A. taeniatus and male A. zebra in areas where invasive salmonids have become widespread. Given the potential consequences that species misidentification and hybridisation can have for the conservation of these endangered species, we advocate the use of molecular markers in order to reduce epistemic uncertainty. Keywords: Aplochiton zebra, Aplochiton taeniatus, hybridisation, barcoding, biological invasions, conservation;

Obituary. William Crozier Jordan (Bill) 1962-2011

Something smells fishy: predator-naïve salmon use diet cues, not kairomones, to recognize a sympatric mammalian predator

The ability to recognize predators is one of the most important lines of defence in a prey’s arse... more

Winning the invasion roulette: escapes from fish farms increase admixture and facilitate establishment of non-native rainbow trout

Aquaculture is a major source of invasive aquatic species, despite the fact that cultured organis... more Aquaculture is a major source of invasive aquatic species, despite the fact that cultured organisms often have low genetic diversity and tend to be maladapted to survive in the wild. Yet, to what extent aquaculture escapees become established by means of high propagule pressure and multiple origins is not clear. We analysed the genetic diversity of 15 established populations and 4 farmed stocks of non-native rainbow trout in Chile, a species first introduced for recreational fishing around 1900, but which has in recent decades escaped in large numbers from fish farms and become widespread. Aquaculture propagule pressure was a good predictor of the incidence of farm escapees, which represented 16% of all free-ranging rainbow trout and were present in 80% of the study rivers. Hybrids between farm escapes and established trout were present in all rivers at frequencies ranging between 7 and 69%, and population admixture was positively correlated with genetic diversity. We suggest that non-native salmonids introduced into the Southern Hemisphere could benefit from admixture because local adaptations may not have yet developed and there may be initially little fitness loss resulting from outbreeding depression.

Development of 13 microsatellite markers for the threatened galaxiid fish Aplochiton zebra (Jenyns, 1842)

Aplochiton zebra (peladilla, zebra trout) is a galaxiid fish endemic to Patagonia and the Falklan... more Aplochiton zebra (peladilla, zebra trout) is a galaxiid fish endemic to Patagonia and the Falkland Islands, where populations are threatened by salmonid introductions. Here we describe the isolation and characterization of 13 polymorphic microsatellite DNA markers that can be used for assessing the genetic variation and conservation status of this species. The variability of these markers was assessed in six rivers in Chilean Patagonia. The number of alleles ranged from 5 to 80 per locus and observed heterozygosities varied between 0.168 and 0.910. A protocol for multiplexing these markers is described.