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Gregory P Brown - One of the best experts on this subject based on the ideXlab platform.
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genetic analysis of the mating system and opportunity for sexual selection in northern water snakes Nerodia sipedon
Behavioral Ecology, 2002Co-Authors: Melanie R Prosser, Lisle H. Gibbs, Gregory P BrownAbstract:We used data collected over 3 years at two study sites to quantify the rates and consequences of multiple paternity and to determine the opportunity for selection on male and female northern water snakes (Nerodia sipedon). We sampled litters from 45 females that gave birth to 811 offspring. Using eight microsatellite DNA loci (probability of exclusion of nonparental males 0.99), we assigned paternity to 93% of neonates from one study population and 69% of neonates from the other population. Observations of participation in mating aggregations predicted individual reproductive success poorly for two reasons. First, males regularly courted nonreproductive females. Second, more than half of all sexually mature males obtained no reproductive success each year, despite the fact that many of them participated in mating aggregations. The number of sires per litter ranged from one to five, with 58% of all litters sired by more than one male. Multiple paternity increased with female size, apparently both because bigger females mated with more males and because the larger litters of big females provide paternity opportunities to more males. Multiple paternity was also more prevalent in years with shorter mating seasons. We detected no advantage to multiple paternity in reducing either the number of unfertilized ovules or stillborn young. Despite the majority of males siring no young each year, some males fathered young with as many as three different females in one year. Male reproductive success increased by more than 10 offspring for each additional mate, whereas female success increased by fewer than 2 offspring for each additional mate. The opportunity for sexual selection was more than five times higher in males than females. Key words: mating system, microsatellites, multiple paternity, Nerodia sipedon, paternity analysis, sexual selection, snakes. [Behav Ecol 13: 800–807 (2002)]
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factors affecting neonate size variation in northern water snakes Nerodia sipedon
Journal of Herpetology, 1999Co-Authors: Gregory P Brown, Melanie R Prosser, Kelley J KissnerAbstract:The theoretical construct of an optimal offspring size remains widely cited in life history literature, despite the regular failure of the central prediction of that theory, that offspring size should not vary within populations. Here we used data from 77 litters collected over four years from captive and free- living northern water snakes (Nerodia sipedon) to test several hypotheses proposed to explain within-pop- ulation variation in offspring size. Neonate mass varied from 1.5 to 6.1 g. Neonate mass did not increase as a simple function of maternal size, contrary to the hypothesis that maternal body size physically constrains offspring size. Holding litter size constant, larger females and females in better condition produced larger offspring. The variance in neonate size greatly exceeded the maximum that could be accounted for by the fractional-offspring hypothesis. We found some evidence that females that acquire food during the pro- tracted period of follicular enlargement can invest that energy into those follicles, and thus increase offspring size. We found no evidence that embryos trade off condition with body size when they are born earlier. The strongest correlate of offspring size was litter size: offspring were smaller in larger litters. Because larger litters were born earlier, we propose that large females (i.e, those producing large litters) may have an energetic advantage that allows them to ovulate earlier. If early birth increases neonate fitness, then a small offspring born early may have the same fitness as a larger offspring born later, thereby allowing larger females to trade off offspring size against offspring number. Collectively, our results suggest that offspring size in northern water snakes varies as a consequence of constraints imposed by reproductive
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demography and sexual size dimorphism in northern water snakes Nerodia sipedon
Canadian Journal of Zoology, 1999Co-Authors: Gregory P BrownAbstract:We used data from a 9-year mark-recapture study to determine whether demographic factors could explain female-biased sexual size dimorphism in northern water snakes (Nerodia sipedon). Most males re...
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growth and sexual size dimorphism in northern water snakes Nerodia sipedon
Copeia, 1999Co-Authors: Gregory P BrownAbstract:Understanding the evolutionary basis for sexual size dimorphism (SSD) in a species first requires determining the extent to which observed SSD is a result of sex differences in growth or in size at maturity, as opposed to being a consequence of factors such as differential survival or catchability of the sexes. We used data from a nine-year study to assess how these factors contribute to female-biased SSD in Nerodia sipedon in eastern Ontario. Females grew substantially faster and larger than males, although both sexes approached their asymptotic size at the same rate. Smaller individuals of both sexes grew faster, and snakes grew faster in years with higher mean air temperatures during the activity season. Variation in growth rate was unrelated to relative fat content of individuals in the spring. We found no evidence that either the sex or size of individuals affected their probability of capture. However, comparisons of estimated ages of males and females, and a null growth-based analysis, both indicated that large, old males were overrepresented in capture samples, probably as a result of differential survival of males and females. The overrepresentation of large males caused us to slightly underestimate SSD caused by sex differences in growth. A comparison of sex-specific growth patterns in our population of N. sipedon with those in two other N. sipedon populations suggests that intraspecific variation in SSD in this species may be primarily a consequence of differences between populations in selection pressures on males.
Lisle H. Gibbs - One of the best experts on this subject based on the ideXlab platform.
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DOI 10.1007/s00265-005-0026-7 ORIGINAL ARTICLE
2014Co-Authors: Lisle H. Gibbs, H. L. Gibbs, P. J. Weatherhead, K. J. KissnerAbstract:Experimental assessment of ecological and phenotypic factors affecting male mating success and polyandry in northern watersnakes, Nerodia sipedo
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genetic analysis of the mating system and opportunity for sexual selection in northern water snakes Nerodia sipedon
Behavioral Ecology, 2002Co-Authors: Melanie R Prosser, Lisle H. Gibbs, Gregory P BrownAbstract:We used data collected over 3 years at two study sites to quantify the rates and consequences of multiple paternity and to determine the opportunity for selection on male and female northern water snakes (Nerodia sipedon). We sampled litters from 45 females that gave birth to 811 offspring. Using eight microsatellite DNA loci (probability of exclusion of nonparental males 0.99), we assigned paternity to 93% of neonates from one study population and 69% of neonates from the other population. Observations of participation in mating aggregations predicted individual reproductive success poorly for two reasons. First, males regularly courted nonreproductive females. Second, more than half of all sexually mature males obtained no reproductive success each year, despite the fact that many of them participated in mating aggregations. The number of sires per litter ranged from one to five, with 58% of all litters sired by more than one male. Multiple paternity increased with female size, apparently both because bigger females mated with more males and because the larger litters of big females provide paternity opportunities to more males. Multiple paternity was also more prevalent in years with shorter mating seasons. We detected no advantage to multiple paternity in reducing either the number of unfertilized ovules or stillborn young. Despite the majority of males siring no young each year, some males fathered young with as many as three different females in one year. Male reproductive success increased by more than 10 offspring for each additional mate, whereas female success increased by fewer than 2 offspring for each additional mate. The opportunity for sexual selection was more than five times higher in males than females. Key words: mating system, microsatellites, multiple paternity, Nerodia sipedon, paternity analysis, sexual selection, snakes. [Behav Ecol 13: 800–807 (2002)]
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microgeographic population genetic structure in the northern water snake Nerodia sipedon sipedon detected using microsatellite dna loci
Molecular Ecology, 1999Co-Authors: Melanie R Prosser, Lisle H. GibbsAbstract:We describe the isolation and genetic characterization of eight microsatellite DNA loci from the northern water snake, Nerodia sipedon sipedon and use these loci to analyse levels of genetic differentiation between local (<2km apart) populations of these snakes in Ontario. These loci are variable, with expected heterozygosities ranging from 0.28 to 0.91, and can correctly exclude nonsires in parentage analyses with a high probability (0.998). Population analyses reveal significant deviation from expected heterozygosity levels for one population, probably a result of a null allele(s) at a single locus and small but significant levels of genetic differentiation among all three populations. This demonstrates that microgeographic genetic structure exists in this species, possibly due to limited dispersal.
James R Dixon - One of the best experts on this subject based on the ideXlab platform.
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low genetic diversity and evidence of population structure among subspecies of Nerodia harteri a threatened water snake endemic to texas
Conservation Genetics, 2012Co-Authors: David Rodriguez, Michael R J Forstner, Dustin L Mcbride, Llewellyn D Densmore, James R DixonAbstract:Nerodia harteri is a threatened small-bodied water snake that occupies one of the most restricted ranges of any snake within the continental United States. It is found closely associated with rivers and tributaries in the Colorado and Brazos river basins, which flow through north-central Texas. Nerodia harteri has been at the center of debate owing to conflicts between conservation efforts and the construction of dams that change or destroy its preferred habitat. Additionally, its taxonomic status has also been under contention with some authors recognizing two subspecies, the Brazos water snake (N. h. harteri) and the Concho water snake (N. h. paucimaculata), whereas other authors consider each separate species. Despite its relatively recent discovery during the 1940s, N. harteri has been the subject of several ecological studies, yet no population genetic assessment of either subspecies has been performed to date. We first evaluated the phylogenetic placement of both subspecies among other North American Nerodia using partial sequence data from the mitochondrial gene cytochrome-b. We then tested for population subdivision among four rivers encompassing the range of N. harteri and tested for the presence of admixture between river basins using mitochondrial sequence data (920 bp of cyt-b) and five cross-species amplified microsatellite loci. We found low mitochondrial haplotype diversity represented by two unique haplotypes in each river basin, which were separated by no more than four nucleotide changes. Nuclear loci showed low genetic diversity and population structuring within and among river basins. We did not find conclusive evidence of admixture between basins, and we support the presence of two separate evolutionarily significant units and two separate management units corresponding to each major river basin. Given increasing natural and anthropogenic threats, we recommend continued ecological and genetic monitoring of both subspecies.
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reproductive ecology of the concho water snake Nerodia harteri paucimaculata
Copeia, 1999Co-Authors: Brian D. Greene, James M. Mueller, Martin J. Whiting, James R DixonAbstract:The reproductive biology of the Concho water snake (Nerodia harteri paucimaculata) was studied from 1988 to 1992 in central Texas. Minimum snout-vent lengths (SVL) at maturity were 380 mm in males and 460 mm in females. Mating occurred primarily in late April and early May, although we observed some evidence of fall mating. Gestation was approximately three months. Parturition occurred predominantly in mid-August, ranging from 29 July to 22 September. Approximately 85% (range 79.5-88.8) of adult females were gravid each year with the proportion of reproductive females varying as a function of body size. Litter size averaged 11.1 (range 4-29) and varied both among and within study sites. Maternal SVL was correlated with litter size and mass but not offspring SVL or mass with litter size held constant. Litter size had no effect on offspring SVL or mass when female SVL was held constant. Relative clutch mass averaged 0.46 and was independent of female size. Mean offspring length and mass were 175 mm SVL and 3.8 g, respectively, showing no overall sexual differences. However, mean SVL was typically greater for females within litters.
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Feeding Ecology of the Concho Water Snake, Nerodia harteri paucimaculata
Journal of Herpetology, 1994Co-Authors: Brian D. Greene, James M. Mueller, Martin J. Whiting, James R Dixon, Okla W. ThorntonAbstract:The diet of the Concho water snake Nerodia harteri paucimaculata was investigated from 1987 to 1990 by palpation of stomach contents. Prey remains representing 304 prey items were recovered from 192 individual snakes. Concho water snakes were almost completely piscivorous, feeding on 19 species of fish from nine families with minnows (Cyprinidae) dominating numerically. Cricket frogs (Acris crepitans) represented the only non-piscine prey. Diet diversity increased ontogenetically according to snake body size. Observations of foraging snakes suggest an ontogenetic change in foraging sites concurrent with a change in diet composition. Prey size was positively correlated with snake body size although some snakes occasionally ingested numerous small prey, possibly due to opportunistic feeding on small prey aggregations. Snakes occasionally attempted to handle prey too large to be ingested. Feeding occurred from mid-March to early November. Gravid females fed throughout the spring into mid-July and resumed feeding after parturition. Neonate and juvenile riverine snakes ingested prey in proportion to apparent availability while adults consumed a disproportionate amount of larger prey species. Lacustrine snakes primarily consumed prey associated with benthic or shallow water habitats. However, few individuals of open water and top water species were ingested, suggesting that prey habitat preference strongly influences catchability in lake systems.
J D Rouse - One of the best experts on this subject based on the ideXlab platform.
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chlorinated hydrocarbon concentrations in plasma of the lake erie water snake Nerodia sipedon insularum and northern water snake Nerodia sipedon sipedon from the great lakes basin in 1998
Archives of Environmental Contamination and Toxicology, 2000Co-Authors: Christine A Bishop, J D RouseAbstract:From the Great Lakes basin, concentrations of 59 congener-specific polychlorinated biphenyls (PCBs) and 14 organochlorine pesticides were measured in blood plasma of northern water snake (Nerodia sipedon sipedon) and Lake Erie water snake (Nerodia sipedon insularum), which is endangered in Canada. In 1998, four male adult Lake Erie water snakes were sampled from Pelee Island, western Lake Erie; four male northern water snakes were sampled at Little Lake, about 20 km north of Parry Sound in central Ontario; and four adult gravid female northern water snakes were sampled from Garden Island, eastern Lake Ontario. The blood plasma was pooled by site for a total of three samples analyzed. The Pelee Island sample from male Lake Erie water snakes contained less than half the lipid concentration (0.349%) than samples from the other sites, but it was the most contaminated with PCBs, even on a wet weight basis. Summed concentration of individual PCBs in the Pelee Island sample was 167 ng/g (wet weight), which was 14-fold higher than the next most contaminated sample, which was from Little Lake. The plasma sample from Little Lake contained 12 ng/g (WW) and was four times more contaminated with PCBs than the sample from female snakes from Garden Island, Lake Ontario. Organochlorine pesticide concentrations in plasma were relatively similar among sites. None of the pesticides was found above trace concentrations (0.1-0.9 ng/g) except pp'-DDE, which occurred at 2-5 ng/g among sites. PCB congener patterns in the Lake Erie water snakes were compared to PCB patterns in plasma of common snapping turtle (Chelydra serpentina serpentina) from Lake Ontario, herring gull eggs (Larus argentatus) from western Lake Erie, and mudpuppy eggs (Necturus maculosus) from the Detroit River. The PCB patterns in water snake and herring gull sample were most similar, followed by the pattern in snapping turtle plasma. The presence of more lower-chlorinated chlorobiphenyls in the mudpuppy eggs relative to the other species made this sample distinct from the water snake, gull, and turtle.
Victor H Hutchison - One of the best experts on this subject based on the ideXlab platform.
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lack of postprandial thermophily in diamondback water snakes Nerodia rhombifera
Comparative Biochemistry and Physiology Part A: Physiology, 1995Co-Authors: Victor H HutchisonAbstract:Abstract We compared the preferred body temperature ( T b ) of fasted and satiated diamondback water snakes ( Nerodia rhombifera ) in linear thigmothermal gradients. We found no significant postprandial thermophily. Thermoregulatory precision varied among 6 days of testing and was most precise during the first day (24–48 hr after feeding).
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influence of pregnancy on thermoregulation of water snakes Nerodia rhombifera
Journal of Thermal Biology, 1994Co-Authors: Victor H HutchisonAbstract:Abstract 1. 1. We compared preferred body temperatures ( T b s ) of gravid, nongravid and postparturient diamondback water snakes ( Nerodia rhombifera ) in linear thigmothermal gradients 2. 2. Gravid females had a significantly higher mean preferred T b (27.7 ± 0.3°C) than nongravid (24.8 ± 0.8°C), postparturient winter (22.3 ± 2.2°C) and postparturient summer (24.1 ± 1.2°C) snakes 3. 3. Gravid snakes spent longer periods at higher temperatures and had no diel cycle in T b , but nongravid and postparturient winter snakes had higher T b in the scotophase than in the photophase 4. 4. The selected T b s of gravid snakes varied less than that of nongravid and postparturient groups