Dierking et al 2014 Evolutionary Applications

Evolutionary applications, 2014

Natural hybridization plays a key role in the process of speciation. However, anthropogenic (human induced) hybridization of historically isolated taxa raises conservation issues. Due to weak barriers to gene flow and the presence of endangered taxa, the whitefish species complex is an excellent study system to investigate the consequences of hybridization in conservation. We focused on three naturally reproductively isolated whitefish taxa in Germany: the endangered, anadromous North Sea houting (NSH) and Baltic houting (BH), which were reintroduced after local extinction, and the commercially stocked European whitefish (EW). To evaluate the genetic integrity of each taxon, source and reintroduced populations of NSH and BH, and EW populations were characterized based on two mitochondrial and 17 microsatellite loci. Additionally, we investigated gill raker counts as an adaptive phenotypic trait. Even though clear genetic and phenotypic differentiation confirmed the houtings as separ...

Hereditas, 2008

The amount of genetic differentiation at DNA microsatellite loci in European whitefish (Coregonus lavaretus) was assessed among ecotypes, populations and run-timing types. The magnitude of genetic changes potentially caused by hatchery broodstock rearing were also compared with those observed in corresponding natural populations. A total of 35 populations were studied, including 33 Coregonus lavaretus populations and two samples of Coregonus peled. Five of the six whitefish ecotypes in Finland were represented within C. lavaretus populations. Genetic diversity among C. lavaretus populations proved to be high compared to two C. peled populations. The genetic D A distance between these two species was as high as 0.86. The genetic differentiation among ecotypes was generally low and thus gives support for the hypothesis of one native European whitefish species in Scandinavia. Among the ecotypes the northern, large sparsely-rakered, bottom-dwelling whitefish was most unique. Thus, observed genetic differences in quantitative traits have either developed independently of phylogenetic lineages, or have mixed and later changed according to environments and selection pressures. Overall genetic distances between the anadromous whitefish populations along the Finnish coast, especially in the Bothnian Bay area, were small. Populations of this area have been heavily influenced by human activities, and they also have the highest probability of mixing by natural means. In two cases, the Rivers Iijoki and Tornionjoki, statistically significant genetic differences could be observed between summer-and autumn-run spawning-time types. Wild populations had slightly higher allelic diversity than hatchery-reared populations of corresponding rivers. Although some reduction in genetic diversity during hatchery rearing is possible, it is an important aid in maintaining endangered populations.

Molecular Ecology, 2010

Translocations of Baltic whitefish (Coregonus sp.) into Austrian Alpine lakes have created 'artificial hybrid zones', threatening the genetic integrity of native lineages. We evaluate the genetic structure of Coregonus in Austrian lakes and characterize hybridization and introgression between native and introduced lineages. Fifteen populations (N = 747) were assessed for allelic variation at eight microsatellite loci and a reduced set (N = 253) for variation across two mtDNA genes (cyt b and NADH-3). Bayesian approaches were used to estimate individual admixture proportions (q-values) and classify genotypes as native, introduced or hybrids. q-value distributions varied among populations highlighting differential hybridization and introgression histories. Many lakes revealed a clear distinction between native and introduced genotypes despite hybridization, whereas some locations revealed hybrid swarms. Genetic structure among lakes was congruent with morphological divergence and novelty raising speculation of multiple taxa, including a population south of the Alps, outside the putative native range of Coregonus. Although statistically congruent with inferences based on nuclear markers, mitochondrial haplotype data was not diagnostic with respect to native and non-native lineages, supporting that the Alpine region was colonized post-glacially by an admixture of mtDNA lineages, which coalesce >1 Ma. Mechanisms promoting or eroding lineage isolation are discussed, as well as a high potential to conserve native Alpine lineages despite the extensive historical use of introduced Baltic stocks.

BMC Evolutionary Biology, 2008

Background Adaptive radiation within fishes of the Coregonus lavaretus complex has created numerous morphs, posing significant challenges for taxonomy and conservation priorities. The highly endangered North Sea houting (C. oxyrhynchus; abbreviated NSH) has been considered a separate species from European lake whitefish (C. lavaretus; abbreviated ELW) due to morphological divergence and adaptation to oceanic salinities. However, its evolutionary and taxonomic status is controversial. We analysed microsatellite DNA polymorphism in nine populations from the Jutland Peninsula and the Baltic Sea, representing NSH (three populations, two of which are reintroduced) and ELW (six populations). The objectives were to: 1) analyse postglacial recolonization of whitefish in the region; 2) assess the evolutionary distinctiveness of NSH, and 3) apply several approaches for defining conservation units towards setting conservation priorities for NSH. Results Bayesian cluster analyses of genetic differentiation identified four major groups, corresponding to NSH and three groups of ELW (Western Jutland, Central Jutland, Baltic Sea). Estimates of historical migration rates indicated recolonization in a north-eastern direction, suggesting that all except the Baltic Sea population predominantly represent postglacial recolonization via the ancient Elbe River. Contemporary gene flow has not occurred between NSH and ELW, with a divergence time within the last 4,000 years suggested from coalescence methods. NSH showed interbreeding with ELW when brought into contact by stocking. Thus, reproductive isolation of NSH was not absolute, although possible interbreeding beyond the F1 level could not be resolved. Conclusion Fishes of the C. lavaretus complex in the Jutland Peninsula originate from the same recolonization event. NSH has evolved recently and its species status may be questioned due to incomplete reproductive isolation from ELW, but it was shown to merit consideration as an independent conservation unit. Yet, application of several approaches for defining conservation units generated mixed outcomes regarding its conservation priority. Within the total species complex, it remains one among many recently evolved unique forms. Its uniqueness and high conservation priority is more evident at a local geographical scale, where conservation efforts will also benefit populations of a number of other endangered species.

Journal of Evolutionary Biology, 2009

For free-spawning estuarine taxa, gene flow among estuaries may occur via hybridization with mobile congeners. This phenomenon has rarely been investigated, but is probably susceptible to anthropogenic disturbance. In eastern Australia, the estuarine Black Bream Acanthopagrus butcheri and marine Yellowfin Bream Acanthopagrus australis have overlapping distributions and the potential to hybridize. We used surveys of microsatellite and mtDNA variation in 565 adults from 25 estuaries spanning their distributional range to characterize the species and their putative hybrids. Hybrids were widespread (68% of estuaries) and hybrid frequencies varied greatly among estuaries (0-58%). Most (88%) were classed as advanced generation backcrosses with A. butcheri and displayed A. butcheri mtDNA haplotypes. We found most hybrids in the three estuaries within the zone of sympatry (57%). Our study highlights the underemphasized importance of estuaries as sites of hybridization and suggests that hybridization is driven both by opportunity for contact and human activity.

PLOS ONE, 2019

Artificial transplantation of organisms and consequent invasive hybridization can lead to the extinction of native species. In Matsuyama, Japan, a native bitterling fish, Tanakia lanceolata, is known to form hybrids with another bitterling species, T. limbata, which was recently introduced from western Kyushu, Japan. These bitterlings spawn in the gills of two freshwater unionid species, Pronodularia japanensis and Nodularia douglasiae nipponensis, which have rapidly declined on the Matsuyama Plain in the past 30 years. To gauge the effect of invasive hybridization, we determined the genetic introgression between T. lanceolata and T. limbata and analyzed the morphology of these species and their hybrids to infer their niche overlap. We collected adult individuals of Tanakia spp. and genotyped them based on six microsatellite loci and mitochondrial cytochrome b sequences. We analyzed their meristic characters and body shapes by geometric morphometrics. We found that 10.9% of all individuals collected were hybrids. Whereas T. lanceolata were more densely distributed downstream and T. limbata were distributed upstream, their hybrids were widely distributed, covering the entire range of native T. lanceolata. The body height and anal fin length of T. limbata were greater than those of T. lanceolata, but their hybrids were highly morphologically variable, covering both parental morphs, and were widely distributed in the habitats of both parental species. Hybridization has occurred in both directions, but introduced T. limbata females and native T. lanceolata males are more likely to have crossed. This study shows that invasive hybridization with the introduced T. limbata is a potential threat to the native population of T. lanceolata via genetic introgression and replacement of its niche in streams.

Biological Conservation

The success of conservation programs for genetically depleted species is challenging because survival and adaptive potential are thought to be promoted by genetic factors. Such programs are thus generally designed to minimize the risks associated with the loss of genetic diversity and inbreeding. However, few empirical studies have explored the outcomes of these strategies in released individuals once they are in the wild. The only remaining population of the critically endangered European sturgeon, Acipenser sturio, is located in the Gironde estuary (France) after continued demographic decline over the last century. A restoration program that was initiated 20 years ago has resulted in more than one and a half million individuals being stocked in the last decade. Because the captive broodstock is composed of a small number of breeders (N = 78 in 2007, which decreased to N = 21 in early 2017), maintaining genetic diversity and minimizing inbreeding are crucial for the successful recovery of this species. Based on the analysis of 18 microsatellite markers, we examined the patterns of genetic diversity of fish from the last wild cohorts and broodstock as well as of captive-born fish recaptured after stocking. Our results support the hypothesis of a genetic bottleneck with low genetic diversity and a highly reduced effective population size in wild-born A. sturio. While the original diversity is depleted, clearly challenging conservation strategies, we found that genetic erosion has been limited during restocking (96% of the broodstock and 90% of the wild fish original diversity has been maintained in recaptured individuals). Results further suggest that the genetics of the parents is not the main factor explaining recapture probability: progeny issued from both related and not related parent pairs were found in recaptures years after their release. For broodstock management, kinship between parents is identified as a relevant parameter to be considered to avoid inbreeding. This study suggests that a multi-year stocking strategy associated with sufficiently high numbers of unrelated parent pairs may be the best strategy for the successful reintroduction and preservation of genetic diversity for A. sturio. These findings are encouraging for the species and further highlights the relevance of careful genetic monitoring for the long-term conservation of genetically depleted species, which are more vulnerable to genetic effects.

Acta Biologica, 2017

Common whitefish (Coregonus maraena) in Poland belongs to the endangered species. The degradation of the environment causes common whitefish to lose its natural reproduction sites. The natural genetic structure of whitefish has been compromised by anthropogenetic activities involving eutrophication, river regulation, the introduction of non-native species and as well as excessive exploitation of the species. The genetic variability of common whitefish (Coregonus maraena) from 2 sites: Pomeranian Bay and the lower Oder river, was assessed using microsatellite markers. A total of 45 caught individuals were analysed (26 from Pomeranian Bay and 19 from the Oder river). Polymorphism at nine loci, Str60INRA,

2001

Hatchery broodstocks used for genetic conservation or aquaculture may represent their ancestral gene pools rather poorly. This is especially likely when the fish that found a broodstock are close relatives of each other. We re-analysed microsatellite data from a breeding experiment on red sea bream to demonstrate how lost genetic variation might be recovered when gene frequencies have been distorted by consanguineous founders in a hatchery. A minimal-kinship criterion based on a relatedness estimator was used to select subsets of breeders which represented the maximum number of founder lineages (i.e., carried the fewest identical copies of ancestral genes). UPGMA clustering of Nei's genetic distances grouped these selected subsets with the parental gene pool, rather than with the entire, highly 'drifted' offspring generation. The selected subsets also captured much of the expected heterozygosity and allelic diversity of the parental gene pool. Independent pedigree data on the same fish showed that the selected subsets had more contributing parents and more founder equivalents than random subsets of the same size. The estimated mean coancestry was lower in the selected subsets, meaning that inbreeding in subsequent generations would be lower if they were used as breeders. The procedure appears suitable for reducing the genetic distortion due to consanguineous and over-represented founders of a hatchery gene pool.

Molecular Ecology, 2010

Populations of obligately estuarine taxa are potentially small and isolated and may lack genetic variation and display regional differentiation as a result of drift and inbreeding. Hybridization with a wide-ranging marine congener should introduce genetic variation and reduce the effects of inbreeding depression and genetic drift. However, high levels of hybridization can cause demographic and genetic swamping. In southeastern Australia hybridization occurs between obligately estuarine Black bream (Acanthopagrus butcheri) and migratory marine Yellowfin bream (Acanthopagrus australis). Here, we surveyed genetic variation at eight microsatellite loci and the mitochondrial control region of juvenile fish from five coastal lagoons (including temporal replication in two lagoons) (total n = 970) to determine the frequency and persistence of hybridization, and its likely consequence for the estuarine restricted A. butcheri. Of 688 juvenile fish genotyped 95% were either A. australis (347) or hybrids (309); only 5% (32) were A. butcheri. Most hybrids were later generation hybrids or A. butcheri backcrosses, which are likely multi-generational residents within lagoons. Far greater proportions of hybrid juveniles were found within two lagoons that are generally closed to the ocean (>90% hybrid fish within generally closed lagoons vs. 12-27% in permanently or intermittently open lagoons). In both lagoons, this was consistent across multiple cohorts of fish [79-97% hybrid fish (n = 282)]. Hybridization and introgression represent a major threat to the persistence of A. butcheri and have yet to be investigated for large numbers of estuarine taxa.