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William H Karasov - One of the best experts on this subject based on the ideXlab platform.
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warmer temperature increases toxicokinetic elimination of pcbs and pbdes in Northern Leopard Frog larvae lithobates pipiens
Aquatic Toxicology, 2021Co-Authors: Cherry T Brown, Jeremiah M Yahn, William H KarasovAbstract:Abstract We studied the temperature dependence of accumulation and elimination of two polychlorinated biphenyls (PCBs; PCB-70 and PCB-126) and a commercial mixture of congeners of polybrominated diphenyl ethers (PBDEs; DE-71™)) in Northern Leopard Frog (Lithobates pipiens) tadpoles. We reared tadpoles at 18, 23, or 27 °C for 5.3 or up to 13.6 weeks (longer at cooler temperature where development is slower) on diets containing the toxicants, each at several different toxicant concentrations, and compared tissue concentrations as a function of food concentration and rearing temperature. Following > 1 month of accumulation, tissue concentrations of all three toxicants in exposed tadpoles were linearly related to dietary concentrations as expected for first order kinetics, with no significant effect of rearing temperature.We also raised free-swimming L. pipiens tadpoles for 14 days on foods containing either toxicant at 18 or 27 °C during an accumulation phase, and then during depuration (declining toxicant) phase of 14 days we provided food without toxicants and measured the decline of toxicants in tadpole tissue. All the congeners were eliminated faster at warmer rearing temperature, as expected. Using Arrhenius’ equation, we calculated that the apparent activation energy for elimination of both PCB congeners by tadpoles was 1.21 eV (95% confidence interval 0.6–1.8 eV). We discuss how this value was within the range of estimates for metabolic reactions generally (range 0.2 – 1.2 eV), which might include metabolic pathways for biotransformation and elimination of PCBs. Furthermore, we discuss how the lack of an effect of rearing temperature on tadpole near-steady-state tissue residue levels suggests that faster elimination at the warmer temperature was balanced by faster uptake, which is plausible considering the similar temperature sensitivities (i.e., activation energies) of all these processes. Although interactions between toxicants and temperature can be complex and likely toxicant-dependent, it is plausible that patterns observed in tadpoles might apply to other aquatic organisms. Published data on depuration in 11 fish species eliminating 8 other organic toxicants indicated that they also had similar apparent activation energy for elimination (0.82 ± 0.12 eV; 95% confidence interval 0.56 – 1.08 eV), even though none of those studied toxicants were PCBs or PBDEs. Additional research on toxicant-temperature interactions can help improve our ability to predict toxicant bioaccumulation in warming climate scenarios.
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digestive efficiency of Northern Leopard Frog lithobates pipiens tadpoles during development reared on a laboratory diet
Herpetologica, 2016Co-Authors: Sarah M Gleason, Jeremiah M Yahn, William H KarasovAbstract:Abstract: In rasping aquatic feeders, like many tadpoles, it is challenging to measure both the food consumed and excreta produced and thereby calculate digestive efficiency. The goals of this study were to measure the apparent digestive efficiency of Northern Leopard Frog (Lithobates pipiens) tadpoles on an artificial laboratory diet and test the use of putative inert markers to calculate digestibility. The diet used was commercial ground rabbit chow (primary ingredient: alfalfa meal) suspended in agar and gelatin. If dietary ash (8.35% of diet dry mass) were a perfect inert marker, then its concentration in digesta, excreta, or both, should increase as organic matter is absorbed from the food, making the ratio of ash in food to ash in digesta or excreta an index of how much of the food mass is indigestible. Ash content in digesta dissected from the distalmost portion of the tadpoles’ intestine was about twice as concentrated as in food, indicating a 50% dry matter digestibility (DMD). This compared wel...
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restructuring of the amphibian gut microbiota through metamorphosis
Environmental Microbiology Reports, 2013Co-Authors: Kevin D Kohl, William H Karasov, Tawnya L Cary, Denise M DearingAbstract:Summary Vertebrates maintain complex symbioses with a diverse community of microbes residing within their guts. The microbial players in these symbioses differ between major taxa of vertebrates, such that fish and amniotes maintain notably different communities. To date, there has not been a culture-independent inventory of an amphibian gut microbial community. Here, we compared gut microbial communities of tadpoles and Frogs of the Northern Leopard Frog (Lithobates pipiens). We utilized Illumina sequencing, which allowed us to inventory more than 450 000 microbial sequences. We found that tadpoles and Frogs differ markedly in the composition of their gut microbial communities, with tadpoles maintaining a community more similar to fish, whereas the Frog community resembles that of amniotes. Additionally, Frogs maintain a community with lower phylogenetic diversity compared with tadpoles. The significant restructuring ofthemicrobiotaislikelyduetochangesindietaswell as the large reorganization of the intestinal organ during metamorphosis. Overall, we propose that amphibians represent an important system in which to study regulation and selection of gut microbial communities.
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toxicokinetics of polybrominated diphenyl ethers across life stages in the Northern Leopard Frog lithobates pipiens
Environmental Toxicology and Chemistry, 2013Co-Authors: Tawnya L Cary, William H KarasovAbstract:Polybrominated diphenyl ethers (PBDEs), a class of flame retardants, are bioaccumulative toxins that can biomagnify in food webs. However, little is known about the toxicokinetics of total and congener-specific BDEs in lower vertebrates. The authors exposed Northern Leopard Frog (Lithobates (Rana) pipiens) tadpoles to diets containing DE-71 (a pentabromodiphenyl ether mixture (0 ng/g as control, 71.4 ng/g, and 634 DE-71 ng/g wet mass)) for 50 d, followed by a period of depuration during which they were fed only undosed (control) food. After 28 d, tadpoles eliminated over 94% of the ΣPBDEs from their tissues (t½ = 5.9 ± 1.9 d) with no significant differences in elimination rates for the predominant congeners. Elimination of BDE-99 was independent of dose, indicating first-order kinetics. It did not fit a biexponential model significantly better than a monoexponential model, indicating single-compartment elimination. To compare developmental life-stage kinetics following larval exposure, the authors collected individuals at the beginning and end of metamorphosis and at 70 d postmetamorphosis. During metamorphosis, total-body residues per individual did not significantly change, implying little to no elimination. After 70 d, juvenile Frogs eliminated 89.7% of the ΣPBDEs from their tissues, and BDE-47 was eliminated at a faster rate (t½= 17.3 d) than BDE-99 and BDE-100 (t½ = 63.0 d and 69.3 d, respectively). Because the kinetics of PBDEs in L. pipiens differed among life stages, developmental life stage—especially for species that undergo metamorphosis—should be considered when determining the toxicity of persistent organic pollutants. Environ Toxicol Chem 2013;32:1631–1640. © 2013 SETAC
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effects of chronic polybrominated diphenyl ether exposure on gonadal development in the Northern Leopard Frog rana pipiens
Environmental Toxicology and Chemistry, 2012Co-Authors: Nathan D Van Schmidt, Tawnya L Cary, Manuel E Ortizsantaliestra, William H KarasovAbstract:Polybrominated diphenyl ethers (PBDEs) are bioaccumulative, persistent organic pollutants used as flame retardants in consumer goods. Concentrations of PBDEs in North American wildlife have been increasing for decades and been shown to have estrogenic effects on sexual development. No studies, however, have examined the effects of PBDEs on the sexual development of North American Frogs at ecologically relevant concentrations. This study examined the effects of five dietary concentrations of DE-71 (0, 1.1, 6.1, 71.4, and 634 ng ΣPBDEs/g diet), a technical PBDE mixture, on the gonadal development of the Northern Leopard Frog, Rana pipiens. Tadpoles were exposed chronically from the time they became free-swimming until metamorphosis. Frogs were killed either at metamorphic climax or 10 weeks after completing metamorphosis, processed for histology, and examined for alterations in sexual development. The experimental group exposed to PBDEs at 1.1 ng/g had a significantly larger proportion of females compared with the expected 50:50 sex ratio. At 10 weeks post-metamorphosis, male Frogs exposed to 6.1 and 71.4 ng/g had significantly smaller testes, but all other measure of gonadal development tested showed no effects. No intersex or increased incidence of gonadal abnormality were detected. These findings indicate that PBDEs may disrupt sexual differentiation in Frogs at low, environmentally relevant concentrations. Environ. Toxicol. Chem. 2012;31:347–354. © 2011 SETAC
Jason T Hoverman - One of the best experts on this subject based on the ideXlab platform.
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single and mixture per and polyfluoroalkyl substances accumulate in developing Northern Leopard Frog brains and produce complex neurotransmission alterations
Neurotoxicology and Teratology, 2020Co-Authors: Rachel M Foguth, Jason T Hoverman, Linda S Lee, T D Hoskins, G C Clark, M Nelson, R W Flynn, C De Perre, Maria S SepulvedaAbstract:Abstract Per- and polyfluoroalkyl substances (PFAS) are present in water and >99% of human serum. They are found in brains of wildlife; however, little is known about effects on the developing brain. To determine the effects of PFAS on brain and cardiac innervation, we conducted an outdoor mesocosm experiment with Northern Leopard Frog larvae (Rana pipiens) exposed to control, 10 ppb perfluorooctane sulfonate (PFOS), or a PFAS mixture totaling 10 ppb that mimicked aqueous film forming foam-impacted surface water (4 ppb PFOS, 3 ppb perfluorohexane sulfonate, 1.25 ppb perfluorooctanoate, 1.25 ppb perfluorohexanoate, and 0.5 ppb perfluoro-n-pentanoate). Water was spiked with PFAS and 25 larvae (Gosner stage (GS) 25) added to each mesocosm (n = 4 mesocosms per treatment). After 30 days, we harvested eight brains per mesocosm and remaining larvae developed to GS 46 (i.e. metamorphosis) before brains and hearts were collected. Weight, length, GS, and time to metamorphosis were recorded. Brain concentrations of all five PFAS were quantified using LC/MS/MS. Dopamine and metabolites, serotonin and its metabolite, norepinephrine, γ-aminobutyric acid, and glutamate were quantified using High Performance Liquid Chromatography with electrochemical detection while acetylcholine and acetylcholinesterase activity were quantified with the Invitrogen Amplex Red Acetylcholine Assay. PFOS accumulated in the brain time- and dose-dependently. After 30 days, the mixture decreased serotonin while both PFAS treatments decreased glutamate. Interestingly, acetylcholine increased in PFAS treatments at GS 46. This research shows that developmental environmentally relevant exposure to PFAS changes neurotransmitters, especially acetylcholine.
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chronic per polyfluoroalkyl substance exposure under environmentally relevant conditions delays development in Northern Leopard Frog rana pipiens larvae
Environmental Toxicology and Chemistry, 2020Co-Authors: Wesley R Flynn, Chloe De Perre, Linda S Lee, Maria S Sepulveda, Michael Iacchetta, Jason T HovermanAbstract:Per-/polyfluoroalkyl substances (PFAS) are pervasive in aquatic systems globally and capable of causing detrimental effects on human and wildlife health. However, most studies are conducted under artificial conditions that are not representative of environmental exposures. Environmental exposures are characterized by multiple routes of exposure, low aquatic PFAS levels, and greater environmental variability than laboratory tests. Determining whether these factors influence toxicity is critical for understanding the effects of PFAS on aquatic life, including amphibians. Our goal was to assess the impact of PFAS on an amphibian under semirealistic conditions. We reared Northern Leopard Frog (Rana pipiens) larvae in outdoor mesocosms containing sediment spiked to low, medium, and high levels (nominally 10, 100, or 1000 ppb dry wt) of perfluorooctanesulfonic acid (PFOS) or perfluorooctanoic acid (PFOA) for 30 d. Larvae in all PFOS treatments and the medium-PFOA treatment were approximately 1.5 Gosner stages less developed than control animals after 30 d. Notably, these developmental delays were observed at PFOS concentrations in the water as low as 0.06 ppb, which is considerably lower than levels associated with developmental effects in laboratory studies. Our results suggest that deriving toxicity values from laboratory studies examining aquatic exposure only may underestimate the effects of environmental PFAS exposure. Environ Toxicol Chem 2020;00:1-6. © 2020 SETAC.
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Perfluoroalkyl substances increase susceptibility of Northern Leopard Frog tadpoles to trematode infection
Environmental Toxicology and Chemistry, 2020Co-Authors: Sophia R. Brown, R. Wesley Flynn, Jason T HovermanAbstract:Per/polyfluoroalkyl substances (PFAS) are contaminants of emerging concern that can impair immune function, yet few studies have tested whether exposure increases infection risk. Using laboratory experiments, we found that exposure to 10 ppb of perfluorohexanesulfonic acid increased trematode (Echinoparyphium lineage 3) infections in larval Northern Leopard Frogs (Lithobates pipiens). However, there was no effect of perfluorooctanesulfonic acid. Our results demonstrate that PFAS can potentially enhance infection risk in natural systems. Environ Toxicol Chem 2020;00:1-6. © 2020 SETAC.
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uptake and depuration of four per polyfluoroalkyl substances pfass in Northern Leopard Frog rana pipiens tadpoles
Environmental Science and Technology Letters, 2017Co-Authors: Gary M Hoover, Michael F Chislock, Brian J Tornabene, Samuel C Guffey, Youn Jeong Choi, Chloe De Perre, Jason T Hoverman, Linda S Lee, Maria S SepulvedaAbstract:Per/polyfluoroalkyl substances (PFASs) are persistent organic contaminants that are ubiquitous in surface waters. To date, their effects on aquatic systems, especially amphibians, are poorly understood. We examined the uptake and depuration of perfluorooctanesulfonate (PFOS), perfluorohexanesulfonate (PFHxS), perfluorooctanoic acid (PFOA), and 6:2 fluorotelomer sulfonate (6:2 FTS) in Northern Leopard Frog (Rana pipiens) tadpoles. Whole-body concentrations were examined every 10 d during constant aqueous exposure to targeted concentrations of 10, 100, and 1000 μg/L for 40 d and for 30 d during depuration. Effects of PFAS exposure on length and development were also examined. Rapid uptake led to steady state concentrations by 10 d for most exposures. PFOS accumulated to the highest levels with whole-body bioconcentration factor (BCF) values at 40 d ranging from 19.6 to 119.3. The remaining PFASs were not found to bioconcentrate (BCF < 1.0 at 40 d). Furthermore, some BCF values decreased during the exposure ...
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Uptake and Depuration of Four Per/Polyfluoroalkyl Substances (PFASS) in Northern Leopard Frog Rana pipiens Tadpoles
2017Co-Authors: Gary M Hoover, Michael F Chislock, Brian J Tornabene, Samuel C Guffey, Youn Jeong Choi, Chloe De Perre, Jason T Hoverman, Linda S Lee, Maria S. SepúlvedaAbstract:Per/polyfluoroalkyl substances (PFASs) are persistent organic contaminants that are ubiquitous in surface waters. To date, their effects on aquatic systems, especially amphibians, are poorly understood. We examined the uptake and depuration of perfluorooctanesulfonate (PFOS), perfluorohexanesulfonate (PFHxS), perfluorooctanoic acid (PFOA), and 6:2 fluorotelomer sulfonate (6:2 FTS) in Northern Leopard Frog (Rana pipiens) tadpoles. Whole-body concentrations were examined every 10 d during constant aqueous exposure to targeted concentrations of 10, 100, and 1000 μg/L for 40 d and for 30 d during depuration. Effects of PFAS exposure on length and development were also examined. Rapid uptake led to steady state concentrations by 10 d for most exposures. PFOS accumulated to the highest levels with whole-body bioconcentration factor (BCF) values at 40 d ranging from 19.6 to 119.3. The remaining PFASs were not found to bioconcentrate (BCF < 1.0 at 40 d). Furthermore, some BCF values decreased during the exposure phase, suggesting dilution due to growth and/or changes in toxicokinetics over ontogeny. During depuration, half-lives ranged from 1.2 to 3.3 d for all compounds. All PFASs tended to induce developmental delays, though statistical significance was only seen for PFOS and PFHxS. These sublethal effects observed at environmentally relevant concentrations are concerning and merit further study
Dennis L Murray - One of the best experts on this subject based on the ideXlab platform.
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tissue specific transcriptome characterization for developing tadpoles of the Northern Leopard Frog lithobates pipiens
Genomics, 2016Co-Authors: Michael E Donaldson, Jessica N Longhi, Barry J Saville, Dennis L MurrayAbstract:Abstract A potential cause of amphibian population declines are the impacts of environmental degradation on tadpole development. We conducted RNA sequencing on developing Northern Leopard Frog tadpoles and through de novo transcriptome assembly we annotated a large number of open reading frames comparable in number and extent to genes identified in Xenopus. Using our transcriptome, we found transcript level changes between early (Gosner 26–31) and late (Gosner 36–41) stage tadpoles were the greatest in the tail, which is reabsorbed throughout development. There was an up-regulation of immunity genes in both the head and tail of the late tadpoles and a down-regulation of genes associated with the energy pathways of the mitochondria and the production of myosin. Overall, transcript level changes across development were consistent with studies on Xenopus and our findings highlight the broader utility of using RNA-seq to identify genes differentially expressed throughout development and in response to environmental pressures.
Axel Moehrenschlager - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Seasonal Differences in Extinction and Colonization Drive Occupancy Dynamics of an Imperilled Amphibian
2016Co-Authors: Lea A. R, Des H. V. Smith, Breana L. Jones, David R. C. Prescott, Axel MoehrenschlagerAbstract:A detailed understanding of the population dynamics of many amphibian species is lacking despite concerns about declining amphibian biodiversity and abundance. This paper ex-plores temporal patterns of occupancy and underlying extinction and colonization dynamics in a regionally imperiled amphibian species, the Northern Leopard Frog (Lithobates pipiens) in Alberta. Our study contributes to elucidating regional occupancy dynamics at Northern lat-itudes, where climate extremes likely have a profound effect on seasonal occupancy. The primary advantage of our study is its wide geographic scale (60,000 km2) and the use of re-peat visual surveys each spring and summer from 2009–2013. We find that occupancy var-ied more dramatically between seasons than years, with low spring and higher summer occupancy. Between spring and summer, colonization was high and extinction low; inverse-ly, colonization was low and extinction high over the winter. The dynamics of extinction and colonization are complex, making conservation management challenging. Our results re-veal that Northern Leopard Frog occupancy was constant over the last five years and thus there is no evidence of decline or recovery within our study area. Changes to equilibrium oc-cupancy are most sensitive to increasing colonization in the spring or declining extinction in the summer. Therefore, conservation and management efforts should target actions that are likely to increase spring colonization; this could be achieved through translocations or improving the quality or access to breeding habitat. Because summer occupancy is already high, it may be difficult to improve further. Nevertheless, summer extinction could be re-duced by predator control, increasing water quality or hydroperiod of wetlands, or increasing the quality or quantity of summer habitat
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Annual Northern Leopard Frog occupancy trends from 2009–2013 in spring (20 April–02 June) and summer (21 July–30 August) in southern Alberta.
2015Co-Authors: Lea A. Randall, Des H. V. Smith, Breana L. Jones, David R. C. Prescott, Axel MoehrenschlagerAbstract:-2 LL = -2 log likelihood; K = number of parameters; AIC = Akaike Information Criterion; wi = Akaike weight; ψ = occupancy; ɣ = colonization; ε = extinction. Variance inflation factor ĉ = 1.Annual Northern Leopard Frog occupancy trends from 2009–2013 in spring (20 April–02 June) and summer (21 July–30 August) in southern Alberta.
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Seasonal and annual Northern Leopard Frog occupancy dynamics in southern Alberta from 2009–2013 spring (20 April–02 June) and summer (21 July–30 August) visual surveys.
2015Co-Authors: Lea A. Randall, Des H. V. Smith, Breana L. Jones, David R. C. Prescott, Axel MoehrenschlagerAbstract:-2 LL = -2 log likelihood; K = number of parameters; AIC = Akaike Information Criterion; wi = Akaike weight; ψ = occupancy; ɣ = colonization. Variance inflation factor ĉ = 1.Seasonal and annual Northern Leopard Frog occupancy dynamics in southern Alberta from 2009–2013 spring (20 April–02 June) and summer (21 July–30 August) visual surveys.
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Annual Northern Leopard Frog occupancy trends with site selection criteria (SSC) from 2009–2013 in spring (20 April–02 June) and summer (21 July–30 August) in southern Alberta.
2015Co-Authors: Lea A. Randall, Des H. V. Smith, Breana L. Jones, David R. C. Prescott, Axel MoehrenschlagerAbstract:-2 LL = -2 log likelihood; K = number of parameters; AIC = Akaike Information Criterion; wi = Akaike weight; ψ = occupancy; ɣ = colonization; ε = extinction. Variance inflation factor ĉ = 1.Annual Northern Leopard Frog occupancy trends with site selection criteria (SSC) from 2009–2013 in spring (20 April–02 June) and summer (21 July–30 August) in southern Alberta.
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Top five Northern Leopard Frog detection probability models for 2009–2013 spring (20 April–02 June) or summer (21 July–30 August) visual surveys in southern Alberta.
2015Co-Authors: Lea A. Randall, Des H. V. Smith, Breana L. Jones, David R. C. Prescott, Axel MoehrenschlagerAbstract:-2 LL = -2 log likelihood; K = number of parameters; AIC = Akaike information criterion; wi = Akaike weights; p = probability of detection; wind chill (Wchill); air temperature (AT); maximum (Wmax) and average (Wavg) wind speed; water surface temperature (WT); humidity (HM); Julian date of survey (JD). Variance inflation factor ĉ = 1.Top five Northern Leopard Frog detection probability models for 2009–2013 spring (20 April–02 June) or summer (21 July–30 August) visual surveys in southern Alberta.
Michael S. Blouin - One of the best experts on this subject based on the ideXlab platform.
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variations in the expressed antimicrobial peptide repertoire of Northern Leopard Frog rana pipiens populations suggest intraspecies differences in resistance to pathogens
Developmental and Comparative Immunology, 2009Co-Authors: Jacob A Tennessen, Michael S. Blouin, Douglas C Woodhams, Pierre Chaurand, Laura K Reinert, David D Billheimer, Yu Shyr, Richard M Caprioli, Louise A RollinssmithAbstract:The Northern Leopard Frog (Rana pipiens or Lithobates pipiens) is historically found in most of the provinces of Canada and the Northern and southwest states of the United States. In the last 50 years, populations have suffered significant losses, especially in the western regions of the species range. Using a peptidomics approach, we show that the pattern of expressed antimicrobial skin peptides of Frogs from three geographically separated populations are distinct, and we report the presence of four peptides (brevinin-1Pg, brevinin-1Pl, ranatuerin-2Pb, and ranatuerin-2Pc) that have not previously been found in skin secretions. The differences in expressed peptides reflect differences in the distribution of alleles for the newly described Brevinin1.1 locus in the three populations. When enriched peptide mixtures were tested for their ability to inhibit growth of the pathogenic amphibian chytrid (Batrachochytrium dendrobatidis), peptides from Minnesota or Vermont Frogs were more effective that peptides from Michigan Frogs. Four of the purified peptides were tested for their ability to inhibit growth of two bacterial pathogens (Aeromonas hydrophila and Staphylococcus epidermidis) and B. dendrobatidis. Three of the four were effective inhibitors of B. dendrobatidis and S. epidermidis, but none inhibited A. hydrophila. We interpret these differences in expression and activity of antimicrobial peptides as evidence to suggest that each population may have been selected to express a suite of peptides that reflects current and past encounters with skin microbes.
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an analysis of selection on a colour polymorphism in the Northern Leopard Frog
Molecular Ecology, 2006Co-Authors: Eric A. Hoffman, Frederick W Schueler, Adam Jones, Michael S. BlouinAbstract:In this study, we investigated the role of selection in the maintenance of a dorsal colour polymorphism in natural populations of the Northern Leopard Frog, Rana pipiens. We determined genetic structure both spatially and temporally from a suite of putatively neutral molecular markers and tested whether or not the colour locus exhibited patterns of genetic variation that differed from those of the neutral loci. Spatial genetic structure at the colour locus was indistinguishable from structure at neutral loci [95% confidence intervals of F(ST) (neutral) = (0.07, 0.35), F(ST) (colour locus) = 0.114]. In the temporal analysis, we found that the variance among populations in the change in allele frequency at the colour locus (equal to 0.004) lies within the 95% confidence intervals for the variance among populations in changes in allele frequencies at neutral loci. In light of our inability to show evidence for the selective maintenance of the colour polymorphism, we used computer simulations to infer the power of our spatial and temporal techniques to detect selection. The computer simulations showed that although the strength of selection (s) would need to be relatively strong to have been detected by the temporal approach (s = 0.1-0.4, depending on the model tested), the spatial analysis would have detected all but weak selection (s = 0.01-0.04, depending on the model tested). This study illustrates the importance of using a locus comparison approach to detect evidence for selective maintenance before conducting studies to measure the selective mechanisms maintaining a polymorphism.
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effective population sizes and temporal stability of genetic structure in rana pipiens the Northern Leopard Frog
Evolution, 2004Co-Authors: Eric A. Hoffman, Frederick W Schueler, Michael S. BlouinAbstract:Although studies of population genetic structure are very common, whether genetic structure is stable over time has been assessed for very few taxa. The question of stability over time is particularly interesting for Frogs because it is not clear to what extent Frogs exist in dynamic metapopulations with frequent extinction and recolonization, or in stable patches at equilibrium between drift and gene flow. In this study we collected tissue samples from the same five populations of Leopard Frogs, Rana pipiens, over a 22-30 year time interval (11-15 generations). Genetic structure among the populations was very stable, suggesting that these populations were not undergoing frequent extinction and colonization. We also estimated the effective size of each population from the change in allele frequencies over time. There exist few estimates of effective size for Frog populations, but the data available suggest that ranid Frogs may have much larger ratios of effective size (Ne) to census size (Nc) than toads (bufonidae). Our results indicate that R. pipiens populations have effective sizes on the order of hundreds to at most a few thousand Frogs, and Ne/Nc ratios in the range of 0.1-1.0. These estimates of Ne/Nc are consistent with those estimated for other Rana species. Finally, we compared the results of three temporal methods for estimating Ne. Moment and pseudolikelihood methods that assume a closed population gave the most similar point estimates, although the moment estimates were consistently two to four times larger. Wang and Whitlock's new method that jointly estimates Ne and the rate of immigration into a population (m) gave much smaller estimates of Ne and implausibly large estimates of m. This method requires knowing allele frequencies in the source of immigrants, but was thought to be insensitive to inexact estimates. In our case the method may have failed because we did not know the true source of immigrants for each population. The method may be more sensitive to choice of source frequencies than was previously appreciated, and so should be used with caution if the most likely source of immigrants cannot be identified clearly.
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evolutionary history of the Northern Leopard Frog reconstruction of phylogeny phylogeography and historical changes in population demography from mitochondrial dna
Evolution, 2004Co-Authors: Eric A. Hoffman, Michael S. BlouinAbstract:This study uses a combined methodological approach including phylogenetic, phylogeographic, and demographic analyses to understand the evolutionary history of the Northern Leopard Frog, Rana pipiens. We tested hypotheses concerning how (or if) known geological events and key features of the species biology influenced the contemporary geographic and genetic distribution of R. pipiens. We assayed mitochondrial DNA variation from 389 individuals within 35 populations located throughout the species range. Our a priori expectations for patterns and processes influencing the current genetic structure of R. pipiens were supported by the data. However, our analyses revealed specific aspects of R. pipiens evolutionary history that were unexpected. The phylogenetic analysis indicated that R. pipiens is split into populations containing discrete eastern or western haplotypes, with the Mississippi River and Great Lakes region dividing the geographic ranges. Nested clade analysis indicated that the biological process most often invoked to explain the pattern of haplotype position is restricted gene flow with isolation by distance. Demographic analyses showed evidence of both historical bottlenecks and population expansions. Surprisingly, the genetic evidence indicated that the western haplotypes had significantly reduced levels of genetic diversity relative to the eastern haplotypes and that major range expansions occurred in both regions well before the most recent glacial retreat. This study provides a detailed history of how a widespread terrestrial vertebrate responded to episodic Pleistocene glacial events in North America. Moreover, this study illustrates how complementary methods of data analysis can be used to disentangle recent and ancient effects on the genetic structure of a species.
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Nine polymorphic microsatellite loci for the Northern Leopard Frog ( Rana pipiens )
Molecular Ecology Notes, 2003Co-Authors: Eric A. Hoffman, W. R. Ardren, Michael S. BlouinAbstract:We describe the cloning and characterization of nine microsatellite loci from the Northern Leopard Frog. Seven loci consist of tetranucleotide repeats, one locus consists of a dinucleotide repeat and one locus consists of a GT repeat juxtaposed with a GATA repeat. In a sample of 36 Frogs from a natural population, polymorphism at these loci ranged from two to 13 alleles per locus with expected heterozygosities ranging from 0.5 to 0.91. These loci will be useful to researchers since this species is used for a broad range of studies.