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Matthew J. Parris - One of the best experts on this subject based on the ideXlab platform.
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A stable niche assumption-free test of ecological divergence.
Molecular phylogenetics and evolution, 2014Co-Authors: Mizuki K. Takahashi, Matthew J. Parris, Jonathan M. Eastman, Duane A. Griffin, Jason Baumsteiger, Andrew StorferAbstract:Understanding the impact of geological events on diversification processes is central to evolutionary ecology. The recent amalgamation between ecological niche models (ENMs) and phylogenetic analyses has been used to estimate historical ranges of modern lineages by projecting current ecological niches of organisms onto paleoclimatic reconstructions. A critical assumption underlying this approach is that niches are stable over time. Using Notophthalmus viridescens (Eastern Newt), in which four ecologically diverged subspecies are recognized, we introduce an analytical framework free from the niche stability assumption to examine how refugial retreat and subsequent postglacial expansion have affected intraspecific ecological divergence. We found that the current subspecies designation was not congruent with the phylogenetic lineages. Thus, we examined ecological niche overlap between the refugial and modern populations, in both subspecies and lineage, by creating ENMs independently for modern and estimated last glacial maximum (LGM) Newt populations, extracting bioclimate variables by randomly generated points, and conducting principal component analyses. Our analyses consistently showed that when tested as a hypothesis, rather than used as an assumption, the niches of N. viridescens lineages have been unstable since the LGM (both subspecies and lineages). There was greater ecological niche differentiation among the subspecies than the modern phylogenetic lineages, suggesting that the subspecies, rather than the phylogenetic lineages, is the unit of the current ecological divergence. The present study found little evidence that the LGM refugial retreat caused the currently observed ecological divergence and suggests that ecological divergence has occurred during postglacial expansion to the current distribution ranges.
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rapid change in life cycle polyphenism across a subspecies boundary of the Eastern Newt notophthalmus viridescens
Journal of Herpetology, 2011Co-Authors: Mizuki K. Takahashi, Yukiko Y Takahashi, Matthew J. ParrisAbstract:Abstract Life-cycle polyphenism has been hypothesized to facilitate ecological speciation in salamanders. A recent study demonstrated that the Eastern Newt (Notophthalmus viridescens) subspecies genetically differ in expression of life-cycle polyphenism. However, we currently lack direct evidence that the life-history divergence among the Newt subspecies is associated with the suggested ecological parameters, namely availability of wetlands and suitable terrestrial habitats. To test such associations, we examined life-history traits of two subspecies, Notophthalmus viridescens viridescens and Notophthalmus viridescens dorsalis, across the subspecies boundary, which corresponds with changes in those ecological parameters between the Piedmont Plateau and the Coastal Plain. We reared larval Newts derived from the two focal subspecies across the contact zone in outdoor mesocosms under two different hydroperiod treatments (three-month drying and permanent water). We found striking genetically based differences...
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on the role of sexual selection in ecological divergence a test of body size assortative mating in the Eastern Newt notophthalmus viridescens
Biological Journal of The Linnean Society, 2010Co-Authors: Yukiko Y Takahashi, Mizuki K. Takahashi, Matthew J. ParrisAbstract:Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body-size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two Eastern Newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life-cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body-size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body-size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life-cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 884–897.
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On the role of sexual selection in ecological divergence: a test of body‐size assortative mating in the Eastern Newt Notophthalmus viridescens
Biological Journal of the Linnean Society, 2010Co-Authors: Mizuki K. Takahashi, Yukiko Y Takahashi, Matthew J. ParrisAbstract:Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body-size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two Eastern Newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life-cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body-size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body-size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life-cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 884–897.
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Life cycle polyphenism as a factor affecting ecological divergence within Notophthalmus viridescens
Oecologia, 2008Co-Authors: Mizuki K. Takahashi, Matthew J. ParrisAbstract:Polyphenism, which allows a single genotype to express multiple discrete phenotypes in response to environmental cues, is an adaptive trait in heterogeneous environments. Pond hydroperiod is an important ecological parameter affecting amphibian life history, and variation in local pond hydrology has been hypothesized to play a role in species divergence via changes in polyphenism. The Eastern Newt ( Notophthalmus viridescens ) expresses life cycle polyphenism. Larvae develop along three possible pathways: metamorphosis to aquatic lunged adult via a terrestrial juvenile (eft) stage, metamorphosis directly to an aquatic lunged adult, or maturation directly to an aquatic gilled adult without metamorphosis (i.e., paedomorphosis). Subspecies of N. viridescens vary in their polyphenic patterns, suggesting possible adaptation to different environments. However, no studies have experimentally tested how genetic and environmental components contribute to the observed differences among subspecies and whether such differences may facilitate divergence. We tested whether adaptation to local pond hydrology via polyphenic changes existed among subspecies by rearing larvae of three subspecies ( N. v. dorsalis , N. v. louisianensis , and N. v. viridescens ) along three hydroperiod regimes (short, long, and constant) in outdoor artificial ponds. We found that larval N. v. viridescens obligately metamorphosed to efts under all hydroperiods, whereas N. v. dorsalis and N. v. louisianensis exhibited plasticity: larvae metamorphosed to efts under drying conditions but metamorphosed directly to aquatic adults or became paedomorphic in constant water. Also, N. v. viridescens metamorphosed to efts faster and at a smaller body size than the other two subspecies. These data suggest that subspecies of N. viridescens are adapted to different pond hydroperiods, supporting the potential for polyphenism to facilitate divergence. Canalizing selection for certain alternative phenotypes within a single species in which other populations remain plastic may play an important role in the initiation of ecological divergence.
Mizuki K. Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Facultative Oviposition of Eastern Newt (Notophthalmus viridescens) in Response to Water Reduction of Aquatic Habitats
The American Midland Naturalist, 2016Co-Authors: Mizuki K. Takahashi, Carolyn McpheeAbstract:Plastic responses by amphibian larvae to various pond hydroperiods have received much theoretical and empirical attention. In contrast few studies examined maternal plasticity in oviposition in response to different hydroperiods. Using the Eastern Newts as a model, we tested a hypothesis that mothers respond to water reduction of aquatic habitats and alter life history traits such as timing of oviposition, clutch size, and egg size. Alternatively, females may entirely forgo oviposition if aquatic habitats are unsuited for larval survival, in which case we predicted greater body-mass gain of females that forgo oviposition. We daily monitored oviposition of 20 females for 38 d, 10 in constant water treatment and 10 in water reduction treatment. Six females deposited a total of 265 eggs in the constant water treatment whereas only one female deposited 17 eggs in the water reduction treatment, suggesting females facultatively altered oviposition behavior in response to water reduction. Contrary to the prediction, oviposited females gained significantly more body mass, suggesting those females that skipped oviposition stopped vitellogenesis during the experiment; whereas, oviposited females still contained yolk-laden ova at the end of the experiment. We could not test maternal plasticity in timing of oviposition, egg size, and clutch size because only one female from the water reduction treatment deposited eggs. The present study demonstrates that the Eastern Newt is a potentially useful model to further explore maternal plasticity in amphibians.
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A stable niche assumption-free test of ecological divergence.
Molecular phylogenetics and evolution, 2014Co-Authors: Mizuki K. Takahashi, Matthew J. Parris, Jonathan M. Eastman, Duane A. Griffin, Jason Baumsteiger, Andrew StorferAbstract:Understanding the impact of geological events on diversification processes is central to evolutionary ecology. The recent amalgamation between ecological niche models (ENMs) and phylogenetic analyses has been used to estimate historical ranges of modern lineages by projecting current ecological niches of organisms onto paleoclimatic reconstructions. A critical assumption underlying this approach is that niches are stable over time. Using Notophthalmus viridescens (Eastern Newt), in which four ecologically diverged subspecies are recognized, we introduce an analytical framework free from the niche stability assumption to examine how refugial retreat and subsequent postglacial expansion have affected intraspecific ecological divergence. We found that the current subspecies designation was not congruent with the phylogenetic lineages. Thus, we examined ecological niche overlap between the refugial and modern populations, in both subspecies and lineage, by creating ENMs independently for modern and estimated last glacial maximum (LGM) Newt populations, extracting bioclimate variables by randomly generated points, and conducting principal component analyses. Our analyses consistently showed that when tested as a hypothesis, rather than used as an assumption, the niches of N. viridescens lineages have been unstable since the LGM (both subspecies and lineages). There was greater ecological niche differentiation among the subspecies than the modern phylogenetic lineages, suggesting that the subspecies, rather than the phylogenetic lineages, is the unit of the current ecological divergence. The present study found little evidence that the LGM refugial retreat caused the currently observed ecological divergence and suggests that ecological divergence has occurred during postglacial expansion to the current distribution ranges.
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rapid change in life cycle polyphenism across a subspecies boundary of the Eastern Newt notophthalmus viridescens
Journal of Herpetology, 2011Co-Authors: Mizuki K. Takahashi, Yukiko Y Takahashi, Matthew J. ParrisAbstract:Abstract Life-cycle polyphenism has been hypothesized to facilitate ecological speciation in salamanders. A recent study demonstrated that the Eastern Newt (Notophthalmus viridescens) subspecies genetically differ in expression of life-cycle polyphenism. However, we currently lack direct evidence that the life-history divergence among the Newt subspecies is associated with the suggested ecological parameters, namely availability of wetlands and suitable terrestrial habitats. To test such associations, we examined life-history traits of two subspecies, Notophthalmus viridescens viridescens and Notophthalmus viridescens dorsalis, across the subspecies boundary, which corresponds with changes in those ecological parameters between the Piedmont Plateau and the Coastal Plain. We reared larval Newts derived from the two focal subspecies across the contact zone in outdoor mesocosms under two different hydroperiod treatments (three-month drying and permanent water). We found striking genetically based differences...
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on the role of sexual selection in ecological divergence a test of body size assortative mating in the Eastern Newt notophthalmus viridescens
Biological Journal of The Linnean Society, 2010Co-Authors: Yukiko Y Takahashi, Mizuki K. Takahashi, Matthew J. ParrisAbstract:Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body-size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two Eastern Newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life-cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body-size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body-size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life-cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 884–897.
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On the role of sexual selection in ecological divergence: a test of body‐size assortative mating in the Eastern Newt Notophthalmus viridescens
Biological Journal of the Linnean Society, 2010Co-Authors: Mizuki K. Takahashi, Yukiko Y Takahashi, Matthew J. ParrisAbstract:Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body-size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two Eastern Newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life-cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body-size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body-size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life-cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 884–897.
Matthew J. Gray - One of the best experts on this subject based on the ideXlab platform.
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Frequency‐dependent transmission of Batrachochytrium salamandrivorans in Eastern Newts
Transboundary and emerging diseases, 2021Co-Authors: Adrianna Tompros, Andrew Dean, Andy Fenton, Mark Q. Wilber, Edward Davis Carter, Matthew J. GrayAbstract:Transmission is the fundamental process whereby pathogens infect their hosts and spread through populations, and can be characterized using mathematical functions. The functional form of transmission for emerging pathogens can determine pathogen impacts on host populations and can inform the efficacy of disease management strategies. By directly measuring transmission between infected and susceptible adult Eastern Newts (Notophthalmus viridescens) in aquatic mesocosms, we identified the most plausible transmission function for the emerging amphibian fungal pathogen Batrachochytrium salamandrivorans (Bsal). Although we considered a range of possible transmission functions, we found that Bsal transmission was best explained by pure frequency-dependence. We observed that >90% of susceptible Newts became infected within 17 days post-exposure to an infected Newt across a range of host densities and initial infection prevalence treatments. Under these conditions, we estimated R0 = 4.9 for Bsal in an Eastern Newt population. Our results suggest that Bsal has the capability of driving Eastern Newt populations to extinction, and that managing host density may not be an effective management strategy. Intervention strategies that prevent Bsal introduction or increase host resistance or tolerance to infection may be more effective. Our results add to the growing empirical evidence that transmission of wildlife pathogens can saturate and be functionally frequency-dependent.
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Experimental methodologies can affect pathogenicity of Batrachochytrium salamandrivorans infections.
PloS one, 2020Co-Authors: Rajeev Kumar, Edward Davis Carter, Daniel A. Malagon, Anna C. Peterson, Debra L. Miller, Markese L. Bohanon, Joseph Patrick W. Cusaac, Matthew J. GrayAbstract:Controlled experiments are one approach to understanding the pathogenicity of etiologic agents to susceptible hosts. The recently discovered fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has resulted in a surge of experimental investigations because of its potential to impact global salamander biodiversity. However, variation in experimental methodologies could thwart knowledge advancement by introducing confounding factors that make comparisons difficult among studies. Thus, our objective was to evaluate if variation in experimental methods changed inferences made on the pathogenicity of Bsal. We tested whether passage duration of Bsal culture, exposure method of the host to Bsal (water bath vs. skin inoculation), Bsal culturing method (liquid vs. plated), host husbandry conditions (aquatic vs. terrestrial), and skin swabbing frequency influenced diseased-induced mortality in a susceptible host species, the Eastern Newt (Notophthalmus viridescens). We found that disease-induced mortality was faster for Eastern Newts when exposed to a low passage isolate, when Newts were housed in terrestrial environments, and if exposure to zoospores occurred via water bath. We did not detect differences in disease-induced mortality between culturing methods or swabbing frequencies. Our results illustrate the need to standardize methods among Bsal experiments. We provide suggestions for future Bsal experiments in the context of hypothesis testing and discuss the ecological implications of our results.
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Experimental methodologies can affect pathogenicity of Batrachochytrium salamandrivorans infections
2020Co-Authors: Rajeev Kumar, Edward Davis Carter, Daniel A. Malagon, Anna C. Peterson, Debra L. Miller, Markese L. Bohanon, Joseph Patrick W. Cusaac, Matthew J. GrayAbstract:Controlled experiments are one approach to understanding the pathogenicity of etiologic agents to susceptible hosts. The recently discovered fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has resulted in a surge of experimental investigations because of its potential to impact global salamander biodiversity. However, variation in experimental methodologies could thwart knowledge advancement by introducing confounding factors that make comparisons difficult among studies. Thus, our objective was to evaluate if variation in experimental methods changed inferences made on the pathogenicity of Bsal. We tested whether passage duration of Bsal culture, exposure method of the host to Bsal (water bath vs. skin inoculation), Bsal culturing method (liquid vs. plated), host husbandry conditions (aquatic vs. terrestrial), and skin swabbing frequency influenced diseased-induced mortality in a susceptible host species, the Eastern Newt (Notophthalmus viridescens). We found that disease-induced mortality was faster for Eastern Newts when exposed to a low passage isolate, when Newts were housed in terrestrial environments, and if exposure to zoospores occurred via water bath. We did not detect differences in disease-induced mortality between culturing methods or swabbing frequencies. Our results illustrate the need to standardize methods among Bsal experiments; we provide suggestions for future experiments in the context of hypothesis testing.
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Host density and habitat structure influence host contact rates and Batrachochytrium salamandrivorans transmission
Scientific Reports, 2020Co-Authors: Daniel A. Malagon, Edward Davis Carter, Luis A. Melara, Olivia F. Prosper, Suzanne Lenhart, J. A. Fordyce, Anna C. Peterson, Debra L. Miller, Matthew J. GrayAbstract:Batrachochytrium salamandrivorans ( Bsal ) is an emerging invasive pathogen that is highly pathogenic to salamander species. Modeling infection dynamics in this system can facilitate proactive efforts to mitigate this pathogen's impact on North American species. Given its widespread distribution and high abundance, the Eastern Newt ( Notophthalmus viridescens ) has the potential to significantly influence Bsal epidemiology. We designed experiments to 1) estimate contact rates given different host densities and habitat structure and 2) estimate the probability of transmission from infected to susceptible individuals. Using parameter estimates from data generated during these experiments, we modeled infection and disease outcomes for a population of Newts using a system of differential equations. We found that host contact rates were density-dependent, and that adding habitat structure reduced contacts. The probability of Bsal transmission given contact between Newts was very high (>90%) even at early stages of infection. Our simulations show rapid transmission of Bsal among individuals following pathogen introduction, with infection prevalence exceeding 90% within one month and >80% mortality of Newts in three months. Estimates of basic reproductive rate (R_0) of Bsal for Eastern Newts were 1.9 and 3.2 for complex and simple habitats, respectively. Although reducing host density and increasing habitat complexity might decrease transmission, these management strategies may be ineffective at stopping Bsal invasion in Eastern Newt populations due to this species’ hyper-susceptibility.
Yukiko Y Takahashi - One of the best experts on this subject based on the ideXlab platform.
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rapid change in life cycle polyphenism across a subspecies boundary of the Eastern Newt notophthalmus viridescens
Journal of Herpetology, 2011Co-Authors: Mizuki K. Takahashi, Yukiko Y Takahashi, Matthew J. ParrisAbstract:Abstract Life-cycle polyphenism has been hypothesized to facilitate ecological speciation in salamanders. A recent study demonstrated that the Eastern Newt (Notophthalmus viridescens) subspecies genetically differ in expression of life-cycle polyphenism. However, we currently lack direct evidence that the life-history divergence among the Newt subspecies is associated with the suggested ecological parameters, namely availability of wetlands and suitable terrestrial habitats. To test such associations, we examined life-history traits of two subspecies, Notophthalmus viridescens viridescens and Notophthalmus viridescens dorsalis, across the subspecies boundary, which corresponds with changes in those ecological parameters between the Piedmont Plateau and the Coastal Plain. We reared larval Newts derived from the two focal subspecies across the contact zone in outdoor mesocosms under two different hydroperiod treatments (three-month drying and permanent water). We found striking genetically based differences...
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on the role of sexual selection in ecological divergence a test of body size assortative mating in the Eastern Newt notophthalmus viridescens
Biological Journal of The Linnean Society, 2010Co-Authors: Yukiko Y Takahashi, Mizuki K. Takahashi, Matthew J. ParrisAbstract:Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body-size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two Eastern Newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life-cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body-size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body-size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life-cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 884–897.
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On the role of sexual selection in ecological divergence: a test of body‐size assortative mating in the Eastern Newt Notophthalmus viridescens
Biological Journal of the Linnean Society, 2010Co-Authors: Mizuki K. Takahashi, Yukiko Y Takahashi, Matthew J. ParrisAbstract:Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body-size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two Eastern Newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life-cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body-size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body-size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life-cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 884–897.
Edward Davis Carter - One of the best experts on this subject based on the ideXlab platform.
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Frequency‐dependent transmission of Batrachochytrium salamandrivorans in Eastern Newts
Transboundary and emerging diseases, 2021Co-Authors: Adrianna Tompros, Andrew Dean, Andy Fenton, Mark Q. Wilber, Edward Davis Carter, Matthew J. GrayAbstract:Transmission is the fundamental process whereby pathogens infect their hosts and spread through populations, and can be characterized using mathematical functions. The functional form of transmission for emerging pathogens can determine pathogen impacts on host populations and can inform the efficacy of disease management strategies. By directly measuring transmission between infected and susceptible adult Eastern Newts (Notophthalmus viridescens) in aquatic mesocosms, we identified the most plausible transmission function for the emerging amphibian fungal pathogen Batrachochytrium salamandrivorans (Bsal). Although we considered a range of possible transmission functions, we found that Bsal transmission was best explained by pure frequency-dependence. We observed that >90% of susceptible Newts became infected within 17 days post-exposure to an infected Newt across a range of host densities and initial infection prevalence treatments. Under these conditions, we estimated R0 = 4.9 for Bsal in an Eastern Newt population. Our results suggest that Bsal has the capability of driving Eastern Newt populations to extinction, and that managing host density may not be an effective management strategy. Intervention strategies that prevent Bsal introduction or increase host resistance or tolerance to infection may be more effective. Our results add to the growing empirical evidence that transmission of wildlife pathogens can saturate and be functionally frequency-dependent.
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Experimental methodologies can affect pathogenicity of Batrachochytrium salamandrivorans infections.
PloS one, 2020Co-Authors: Rajeev Kumar, Edward Davis Carter, Daniel A. Malagon, Anna C. Peterson, Debra L. Miller, Markese L. Bohanon, Joseph Patrick W. Cusaac, Matthew J. GrayAbstract:Controlled experiments are one approach to understanding the pathogenicity of etiologic agents to susceptible hosts. The recently discovered fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has resulted in a surge of experimental investigations because of its potential to impact global salamander biodiversity. However, variation in experimental methodologies could thwart knowledge advancement by introducing confounding factors that make comparisons difficult among studies. Thus, our objective was to evaluate if variation in experimental methods changed inferences made on the pathogenicity of Bsal. We tested whether passage duration of Bsal culture, exposure method of the host to Bsal (water bath vs. skin inoculation), Bsal culturing method (liquid vs. plated), host husbandry conditions (aquatic vs. terrestrial), and skin swabbing frequency influenced diseased-induced mortality in a susceptible host species, the Eastern Newt (Notophthalmus viridescens). We found that disease-induced mortality was faster for Eastern Newts when exposed to a low passage isolate, when Newts were housed in terrestrial environments, and if exposure to zoospores occurred via water bath. We did not detect differences in disease-induced mortality between culturing methods or swabbing frequencies. Our results illustrate the need to standardize methods among Bsal experiments. We provide suggestions for future Bsal experiments in the context of hypothesis testing and discuss the ecological implications of our results.
-
Experimental methodologies can affect pathogenicity of Batrachochytrium salamandrivorans infections
2020Co-Authors: Rajeev Kumar, Edward Davis Carter, Daniel A. Malagon, Anna C. Peterson, Debra L. Miller, Markese L. Bohanon, Joseph Patrick W. Cusaac, Matthew J. GrayAbstract:Controlled experiments are one approach to understanding the pathogenicity of etiologic agents to susceptible hosts. The recently discovered fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has resulted in a surge of experimental investigations because of its potential to impact global salamander biodiversity. However, variation in experimental methodologies could thwart knowledge advancement by introducing confounding factors that make comparisons difficult among studies. Thus, our objective was to evaluate if variation in experimental methods changed inferences made on the pathogenicity of Bsal. We tested whether passage duration of Bsal culture, exposure method of the host to Bsal (water bath vs. skin inoculation), Bsal culturing method (liquid vs. plated), host husbandry conditions (aquatic vs. terrestrial), and skin swabbing frequency influenced diseased-induced mortality in a susceptible host species, the Eastern Newt (Notophthalmus viridescens). We found that disease-induced mortality was faster for Eastern Newts when exposed to a low passage isolate, when Newts were housed in terrestrial environments, and if exposure to zoospores occurred via water bath. We did not detect differences in disease-induced mortality between culturing methods or swabbing frequencies. Our results illustrate the need to standardize methods among Bsal experiments; we provide suggestions for future experiments in the context of hypothesis testing.
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Host density and habitat structure influence host contact rates and Batrachochytrium salamandrivorans transmission
Scientific Reports, 2020Co-Authors: Daniel A. Malagon, Edward Davis Carter, Luis A. Melara, Olivia F. Prosper, Suzanne Lenhart, J. A. Fordyce, Anna C. Peterson, Debra L. Miller, Matthew J. GrayAbstract:Batrachochytrium salamandrivorans ( Bsal ) is an emerging invasive pathogen that is highly pathogenic to salamander species. Modeling infection dynamics in this system can facilitate proactive efforts to mitigate this pathogen's impact on North American species. Given its widespread distribution and high abundance, the Eastern Newt ( Notophthalmus viridescens ) has the potential to significantly influence Bsal epidemiology. We designed experiments to 1) estimate contact rates given different host densities and habitat structure and 2) estimate the probability of transmission from infected to susceptible individuals. Using parameter estimates from data generated during these experiments, we modeled infection and disease outcomes for a population of Newts using a system of differential equations. We found that host contact rates were density-dependent, and that adding habitat structure reduced contacts. The probability of Bsal transmission given contact between Newts was very high (>90%) even at early stages of infection. Our simulations show rapid transmission of Bsal among individuals following pathogen introduction, with infection prevalence exceeding 90% within one month and >80% mortality of Newts in three months. Estimates of basic reproductive rate (R_0) of Bsal for Eastern Newts were 1.9 and 3.2 for complex and simple habitats, respectively. Although reducing host density and increasing habitat complexity might decrease transmission, these management strategies may be ineffective at stopping Bsal invasion in Eastern Newt populations due to this species’ hyper-susceptibility.