ABSTRACT Background/Question/Methods A central tenet of classical biogeography is that taxonomic ... more ABSTRACT Background/Question/Methods A central tenet of classical biogeography is that taxonomic similarity among ecological communities declines with increasing geographical distance due to both historical factors and contemporary environmental constraints. While this tenet has been well demonstrated for many plants and animals, there has been a lack of agreement as to whether it holds true for microorganisms. The question of microbial biogeography is further complicated for microorganisms that form symbioses, because the distributions of their hosts may themselves be limited by the aforementioned factors. To examine the geographic patterns in Alnus (alder)-associated microbial assemblages and determine how they may relate to host plant biogeography, we studied ectomycorrhizal (ECM) fungal and N-fixing Frankia bacterial assemblages associated with two Alnus species in montane central Mexico and compared them with Alnus-associated ECM and Frankia assemblages located throughout the Pacific Northwestern United States and beyond. ECM root samples and Frankia root nodules were collected from four sites in Mexico. ECM samples were identified with ITS and LSU rRNA gene sequences, while Frankia samples were identified using nifH (nitrogenase) gene sequences. Each microbial assemblage was assessed using both taxon- (richness, diversity, evenness indices) and sequence divergence-based (UniFrac clustering and significance) analyses to facilitate comparison to Alnus-associated ECM and Frankia assemblages found elsewhere. Results/Conclusions Among the ECM fungal samples collected in Mexican forests, only 23 taxa were encountered, reflecting the relatively low richness and distinctive composition of Alnus-associated ECM assemblages found elsewhere in the Americas and in Europe. Clavulina, an ECM lineage never before reported with Alnus, contained the dominant taxon overall. However, there was a strikingly high sequence similarity among many of the other ECM taxa found in Mexico and those in Alnus forests in the United States, supporting a host-ECM fungi co-migration hypothesis from a common north temperate origin. Likewise, although two novel Frankia genotypes were found among the Mexican samples, the Frankia assemblages were overall highly similar to those associated with Alnus species in the Pacific Northwest. Genotype- and phylogenetic distance-based community analyses, however, indicated that neither geographic location nor the phylogenetic relationships among hosts is a strong predictor of Frankia assemblage structure at the continental scale. Thus, in contrast to ECM assemblages, our results suggest that factors other than classical biogeography are more influential in determining the continental-scale distribution and diversity of Alnus-associated Frankia bacteria.
ABSTRACT Background/Question/Methods “Enemy escape” is often cited as a key biotic contributor to... more ABSTRACT Background/Question/Methods “Enemy escape” is often cited as a key biotic contributor to the invasion success of non-indigenous species, but the presence or absence of specialized mutualists may also play a significant role in determining invasional outcomes. This study examines how mutualistic specificity is influencing the invasion of two European ectomycorrhizal (EM) angiosperms in New Zealand: Alnus glutinosa (black alder) and Salix fragilis (crack willow). In their native ranges, Alnus species associate with a small, host-specific set of EM fungi, while Salix species usually associate with a broader group of generalist EM fungi. As such, we hypothesized that A. glutinosa would retain a limited, specific EM fungal community as it invaded, while S. fragilis would associate with a broader subset of its usual EM fungi, perhaps acquiring some native New Zealand associates. To test our hypothesis, we performed a field study at two invaded riverbeds in New Zealand, using molecular techniques to identify both EM fungi (species-level taxa) and plant roots. Results/Conclusions Alnus glutinosa and Salix fragilis were both well colonized by EM fungi in New Zealand, but associated with distinctive EM fungal communities at both field sites. The A. glutinosa-associated community was taxon poor (6-7 EM fungal taxa per site) and was nearly identical at both locations, while the S. fragilis community was more taxon rich (19-25 EM fungal taxa) and differed substantially from site to site. Both of these communities had lower taxon richness than they typically would have in the native ranges of the host plants. A phylogenetic analysis of the best-represented EM fungal family (Thelephoraceae) in the data set suggested that neither A. glutinosa nor S. fragilis has acquired native New Zealand EM fungi in that family, even though the family is abundantly associated with native New Zealand trees (genus Nothofagus). Taken together, our data indicate that, despite having left many of their mutualists behind in their native European ranges, A. glutinosa and S. fragilis are relying primarily on EM fungal partners from those areas, and are not acquiring new associates as they invade New Zealand.
Http Dx Doi Org 10 1080 03610919008812870, Oct 24, 2007
ABSTRACT A Monte Carlo study is used to examine the size and power of t tests formed using a vari... more ABSTRACT A Monte Carlo study is used to examine the size and power of t tests formed using a variety of estimation procedures appropriate in the context of heteroskedasticity when there are no replicated observations. There are three main results: (1) the ordinary least squares estimator is quite robust with respect to inference; (2) an estimated generalized least squares estimator, formed using a possibly-erroneous assumption that the functional form of the heteroskedasticity is multiplicative, has highest power among the estimators considered, but has a too-large size; and (3) the advantages of the jackknife do not appear until the degree of heteroskedasticity is unrealistically large
ABSTRACT Current pesticide risk assessment for honey bees is based on laboratory tests and on sem... more ABSTRACT Current pesticide risk assessment for honey bees is based on laboratory tests and on semi-field and field studies. Risk assessment schemes focus on quotients of the hazard imposed by a compound and the predicted exposure to this compound in the field. This chapter gives a brief introduction into the rationale and approaches of ecological modeling of population dynamics. It presents an example model to demonstrate the potential insights that can be gained from such ecological models, summarizes current modeling practice, and describes recent attempts to establish good modeling practice (GMoP), which is needed to make mechanistic effect models applicable for regulatory risk assessment. It provides an overview of existing models of honey bee colonies and gives recommendations for the potential use of these models for pesticide risk assessment. The chapter briefly discusses how ecological modeling could support risk assessment of non-Apis pollinators.
To simulate effects of pesticides on different honeybee (Apis mellifera L.) life stages, the BEEH... more To simulate effects of pesticides on different honeybee (Apis mellifera L.) life stages, the BEEHAVE model was used to explore how increased mortalities of larvae, in-hive workers and foragers, as well as reduced egg-laying rate, could impact colony dynamics over multiple years. Stresses were applied for 30 days, both as multiples of the modelled control mortality and as set percentage daily mortalities to assess the sensitivity of the modelled colony both to small fluctuations in mortality and periods of low to very high daily mortality. These stresses simulate stylised exposure of the different life stages to nectar and pollen contaminated with pesticide for 30 days. Increasing adult bee mortality had a much greater impact on colony survival than mortality of bee larvae or reduction in egg laying rate. Importantly, the seasonal timing of the imposed mortality affected the magnitude of the impact at colony level. In line with the LD50, we propose a new index of 'lethal imposed ...
Despite widespread concern over possible adverse effects of pesticides on nontarget arthropods, t... more Despite widespread concern over possible adverse effects of pesticides on nontarget arthropods, the scientific basis for evaluating and interpreting such risks is still hotly debated. Using examples drawn largely from work on carabid beetles and aphid parasitoids, this paper reviews some critical aspects of trials conducted at different levels in the testing hierarchy. For laboratory tests, multiple dose bioassays offer considerable advantages over ones at a single dose, providing a more precise comparison of effects between species and chemicals, and a more objective basis for decision making. The transition from simple laboratory bioassays to more realistic trials poses additional challenges that are best addressed in the short-term by focusing on 'semi-field' tests (conducted in the laboratory or field), allowing adequate replication and some insight into mechanisms underlying observed results. Although the primary objective is to assess mortality, such experiments can relatively easily be extended to investigate indirect and sublethal effects, providing an added benefit.
Les colonies d’abeilles peuvent être assimilées à un système complexe possédant une résilience pr... more Les colonies d’abeilles peuvent être assimilées à un système complexe possédant une résilience propre face aux perturbations. Comme toutes espèces vivantes, la survie d’une colonie d’abeilles dépendra de sa qualité individuelle, de sa capacité adaptative et de son seuil de résilience face aux stress émergeants. De nombreux stress résultants des changements globaux sont soupçonnés d’agir en synergie pour provoquer le déclin des populations d’abeilles. On peut entre autres citer les stress biotiques comme les parasites, pathogènes et prédateurs, mais également les stress environnementaux comme les pesticides et la raréfaction des ressources florales. La multiplicité des stress et de leurs interactions rend trop complexe l’approche empirique pour étudier le déclin des abeilles. Dans ces conditions particulières, nous proposons une démarche intégrative combinant des suivis de terrain (approche empirique) avec des outils de modélisation de dynamique de colonie (approche mécaniste). L’app...
Bubble activity has been found to play a key role in many HIFU applications, ranging from thermal... more Bubble activity has been found to play a key role in many HIFU applications, ranging from thermal ablation to histotripsy. A combined active‐passive cavitation detection system is presented, which enables localization of bubble activity with respect to the HIFU focus during HIFU ...
Background/Question/Methods The importance of microbial symbioses for plant nutrition is well doc... more Background/Question/Methods The importance of microbial symbioses for plant nutrition is well documented, however the mechanisms driving these partnerships are not clear. For example, the plant genus Alnus forms a tripartite symbiosis with both mycorrhizal fungi and nitrogen-fixing actinobacteria, and it has been shown that the relationship between Alnus and its ectomycorrhizal (ECM) fungal partners is uncommonly specific. We hypothesized that the specificity of the Alnus-ECM assemblage was shaped partly by the physiology of fungal symbionts. Specifically, we proposed that the fungi forming ectomycorrhizas with Alnus are proficient at obtaining nutrients other than nitrogen (e.g. phosphorus) for their host. To analyze this hypothesis, we compared the enzyme activity of ECM root tips sampled from the fine roots of Alnus rubra and Pseudotsuga menziesii in pure stands at the Cascade Head Experimental Forest in Western Oregon. Nine root tips were sampled from each of eight soil cores ta...
ABSTRACT Background/Question/Methods A central tenet of classical biogeography is that taxonomic ... more ABSTRACT Background/Question/Methods A central tenet of classical biogeography is that taxonomic similarity among ecological communities declines with increasing geographical distance due to both historical factors and contemporary environmental constraints. While this tenet has been well demonstrated for many plants and animals, there has been a lack of agreement as to whether it holds true for microorganisms. The question of microbial biogeography is further complicated for microorganisms that form symbioses, because the distributions of their hosts may themselves be limited by the aforementioned factors. To examine the geographic patterns in Alnus (alder)-associated microbial assemblages and determine how they may relate to host plant biogeography, we studied ectomycorrhizal (ECM) fungal and N-fixing Frankia bacterial assemblages associated with two Alnus species in montane central Mexico and compared them with Alnus-associated ECM and Frankia assemblages located throughout the Pacific Northwestern United States and beyond. ECM root samples and Frankia root nodules were collected from four sites in Mexico. ECM samples were identified with ITS and LSU rRNA gene sequences, while Frankia samples were identified using nifH (nitrogenase) gene sequences. Each microbial assemblage was assessed using both taxon- (richness, diversity, evenness indices) and sequence divergence-based (UniFrac clustering and significance) analyses to facilitate comparison to Alnus-associated ECM and Frankia assemblages found elsewhere. Results/Conclusions Among the ECM fungal samples collected in Mexican forests, only 23 taxa were encountered, reflecting the relatively low richness and distinctive composition of Alnus-associated ECM assemblages found elsewhere in the Americas and in Europe. Clavulina, an ECM lineage never before reported with Alnus, contained the dominant taxon overall. However, there was a strikingly high sequence similarity among many of the other ECM taxa found in Mexico and those in Alnus forests in the United States, supporting a host-ECM fungi co-migration hypothesis from a common north temperate origin. Likewise, although two novel Frankia genotypes were found among the Mexican samples, the Frankia assemblages were overall highly similar to those associated with Alnus species in the Pacific Northwest. Genotype- and phylogenetic distance-based community analyses, however, indicated that neither geographic location nor the phylogenetic relationships among hosts is a strong predictor of Frankia assemblage structure at the continental scale. Thus, in contrast to ECM assemblages, our results suggest that factors other than classical biogeography are more influential in determining the continental-scale distribution and diversity of Alnus-associated Frankia bacteria.
ABSTRACT Background/Question/Methods “Enemy escape” is often cited as a key biotic contributor to... more ABSTRACT Background/Question/Methods “Enemy escape” is often cited as a key biotic contributor to the invasion success of non-indigenous species, but the presence or absence of specialized mutualists may also play a significant role in determining invasional outcomes. This study examines how mutualistic specificity is influencing the invasion of two European ectomycorrhizal (EM) angiosperms in New Zealand: Alnus glutinosa (black alder) and Salix fragilis (crack willow). In their native ranges, Alnus species associate with a small, host-specific set of EM fungi, while Salix species usually associate with a broader group of generalist EM fungi. As such, we hypothesized that A. glutinosa would retain a limited, specific EM fungal community as it invaded, while S. fragilis would associate with a broader subset of its usual EM fungi, perhaps acquiring some native New Zealand associates. To test our hypothesis, we performed a field study at two invaded riverbeds in New Zealand, using molecular techniques to identify both EM fungi (species-level taxa) and plant roots. Results/Conclusions Alnus glutinosa and Salix fragilis were both well colonized by EM fungi in New Zealand, but associated with distinctive EM fungal communities at both field sites. The A. glutinosa-associated community was taxon poor (6-7 EM fungal taxa per site) and was nearly identical at both locations, while the S. fragilis community was more taxon rich (19-25 EM fungal taxa) and differed substantially from site to site. Both of these communities had lower taxon richness than they typically would have in the native ranges of the host plants. A phylogenetic analysis of the best-represented EM fungal family (Thelephoraceae) in the data set suggested that neither A. glutinosa nor S. fragilis has acquired native New Zealand EM fungi in that family, even though the family is abundantly associated with native New Zealand trees (genus Nothofagus). Taken together, our data indicate that, despite having left many of their mutualists behind in their native European ranges, A. glutinosa and S. fragilis are relying primarily on EM fungal partners from those areas, and are not acquiring new associates as they invade New Zealand.
Http Dx Doi Org 10 1080 03610919008812870, Oct 24, 2007
ABSTRACT A Monte Carlo study is used to examine the size and power of t tests formed using a vari... more ABSTRACT A Monte Carlo study is used to examine the size and power of t tests formed using a variety of estimation procedures appropriate in the context of heteroskedasticity when there are no replicated observations. There are three main results: (1) the ordinary least squares estimator is quite robust with respect to inference; (2) an estimated generalized least squares estimator, formed using a possibly-erroneous assumption that the functional form of the heteroskedasticity is multiplicative, has highest power among the estimators considered, but has a too-large size; and (3) the advantages of the jackknife do not appear until the degree of heteroskedasticity is unrealistically large
ABSTRACT Current pesticide risk assessment for honey bees is based on laboratory tests and on sem... more ABSTRACT Current pesticide risk assessment for honey bees is based on laboratory tests and on semi-field and field studies. Risk assessment schemes focus on quotients of the hazard imposed by a compound and the predicted exposure to this compound in the field. This chapter gives a brief introduction into the rationale and approaches of ecological modeling of population dynamics. It presents an example model to demonstrate the potential insights that can be gained from such ecological models, summarizes current modeling practice, and describes recent attempts to establish good modeling practice (GMoP), which is needed to make mechanistic effect models applicable for regulatory risk assessment. It provides an overview of existing models of honey bee colonies and gives recommendations for the potential use of these models for pesticide risk assessment. The chapter briefly discusses how ecological modeling could support risk assessment of non-Apis pollinators.
To simulate effects of pesticides on different honeybee (Apis mellifera L.) life stages, the BEEH... more To simulate effects of pesticides on different honeybee (Apis mellifera L.) life stages, the BEEHAVE model was used to explore how increased mortalities of larvae, in-hive workers and foragers, as well as reduced egg-laying rate, could impact colony dynamics over multiple years. Stresses were applied for 30 days, both as multiples of the modelled control mortality and as set percentage daily mortalities to assess the sensitivity of the modelled colony both to small fluctuations in mortality and periods of low to very high daily mortality. These stresses simulate stylised exposure of the different life stages to nectar and pollen contaminated with pesticide for 30 days. Increasing adult bee mortality had a much greater impact on colony survival than mortality of bee larvae or reduction in egg laying rate. Importantly, the seasonal timing of the imposed mortality affected the magnitude of the impact at colony level. In line with the LD50, we propose a new index of 'lethal imposed ...
Despite widespread concern over possible adverse effects of pesticides on nontarget arthropods, t... more Despite widespread concern over possible adverse effects of pesticides on nontarget arthropods, the scientific basis for evaluating and interpreting such risks is still hotly debated. Using examples drawn largely from work on carabid beetles and aphid parasitoids, this paper reviews some critical aspects of trials conducted at different levels in the testing hierarchy. For laboratory tests, multiple dose bioassays offer considerable advantages over ones at a single dose, providing a more precise comparison of effects between species and chemicals, and a more objective basis for decision making. The transition from simple laboratory bioassays to more realistic trials poses additional challenges that are best addressed in the short-term by focusing on 'semi-field' tests (conducted in the laboratory or field), allowing adequate replication and some insight into mechanisms underlying observed results. Although the primary objective is to assess mortality, such experiments can relatively easily be extended to investigate indirect and sublethal effects, providing an added benefit.
Les colonies d’abeilles peuvent être assimilées à un système complexe possédant une résilience pr... more Les colonies d’abeilles peuvent être assimilées à un système complexe possédant une résilience propre face aux perturbations. Comme toutes espèces vivantes, la survie d’une colonie d’abeilles dépendra de sa qualité individuelle, de sa capacité adaptative et de son seuil de résilience face aux stress émergeants. De nombreux stress résultants des changements globaux sont soupçonnés d’agir en synergie pour provoquer le déclin des populations d’abeilles. On peut entre autres citer les stress biotiques comme les parasites, pathogènes et prédateurs, mais également les stress environnementaux comme les pesticides et la raréfaction des ressources florales. La multiplicité des stress et de leurs interactions rend trop complexe l’approche empirique pour étudier le déclin des abeilles. Dans ces conditions particulières, nous proposons une démarche intégrative combinant des suivis de terrain (approche empirique) avec des outils de modélisation de dynamique de colonie (approche mécaniste). L’app...
Bubble activity has been found to play a key role in many HIFU applications, ranging from thermal... more Bubble activity has been found to play a key role in many HIFU applications, ranging from thermal ablation to histotripsy. A combined active‐passive cavitation detection system is presented, which enables localization of bubble activity with respect to the HIFU focus during HIFU ...
Background/Question/Methods The importance of microbial symbioses for plant nutrition is well doc... more Background/Question/Methods The importance of microbial symbioses for plant nutrition is well documented, however the mechanisms driving these partnerships are not clear. For example, the plant genus Alnus forms a tripartite symbiosis with both mycorrhizal fungi and nitrogen-fixing actinobacteria, and it has been shown that the relationship between Alnus and its ectomycorrhizal (ECM) fungal partners is uncommonly specific. We hypothesized that the specificity of the Alnus-ECM assemblage was shaped partly by the physiology of fungal symbionts. Specifically, we proposed that the fungi forming ectomycorrhizas with Alnus are proficient at obtaining nutrients other than nitrogen (e.g. phosphorus) for their host. To analyze this hypothesis, we compared the enzyme activity of ECM root tips sampled from the fine roots of Alnus rubra and Pseudotsuga menziesii in pure stands at the Cascade Head Experimental Forest in Western Oregon. Nine root tips were sampled from each of eight soil cores ta...
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