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Abstract Assessing direct fitness effects of individual genetic diversity is challenging due to the intensive and long‐term data needed to quantify survival and reproduction in the wild. But resolving these effects is necessary to determine how inbreeding and outbreeding influence eco‐evolutionary processes. We used 8 years of capture–recapture data and single nucleotide polymorphism genotypes for 1906 individuals to test for effects of individual heterozygosity on stage‐specific survival probabilities in the salamanderGyrinophilus porphyriticus. The life cycle ofG. porphyriticusincludes an aquatic larval stage followed by metamorphosis into a semi‐aquatic adult stage. In our study populations, the larval stage lasts 6–10 years, metamorphosis takes several months, and lifespan can reach 20 years. Previous studies showed that metamorphosis is a sensitive life stage, leading us to predict that fitness effects of individual heterozygosity would occur during metamorphosis. Consistent with this prediction, monthly probability of survival during metamorphosis declined with multi‐locus heterozygosity (MLH), from 0.38 at the lowest MLH (0.10) to 0.06 at the highest MLH (0.38), a reduction of 84%. Body condition of larvae also declined significantly with increasing MLH. These relationships were consistent in the three study streams. With evidence of localised inbreeding within streams, these results suggest that outbreeding disrupts adaptations in pre‐metamorphic and metamorphic individuals to environmental gradients along streams, adding to evidence that headwater streams are hotspots of microgeographic adaptation. Our results also underscore the importance of incorporating life history in analyses of the fitness effects of individual genetic diversity and suggest that metamorphosis and similar discrete life stage transitions may be critical periods of viability selection.
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Life-Stage Differences in Microhabitat Use by Hellbenders (Cryptobranchus alleganiensis)
Hellbenders (Cryptobranchus alleganiensis) are long-lived, fully aquatic salamanders that inhabit cool, well-oxygenated streams and rivers in the eastern United States. Although once abundant, C. alleganiensis populations have experienced major declines across the historical range. Habitat degradation, siltation, aquatic contaminants, and infectious diseases are commonly suggested as contributors to these declines. Although Tennessee provides areas of high-quality habitat for C. alleganiensis, microhabitat differences among life stages are not well documented. We evaluated microhabitat use of larval, subadult, and adult C. alleganiensis at three streams in east Tennessee by comparing sites occupied by C. alleganiensis to random sites within each stream. We used multivariate analysis to evaluate microhabitat use differences among larval, subadult, and adult C. alleganiensis. We completed habitat assessments for 60 individuals. We detected an association between C. alleganiensis presence (regardless of life stage) and the percentage of large rock, the percentage of low embedded rocks, and the number of rocks above 500 mm. Furthermore, the volume of cover rock, the number of rocks above 500 mm, the distance to bank, and the percentage of low embedded rocks, gravel, and sand were the most important microhabitat attributes to discriminate life-stage distributions. Overall, our analyses identify microhabitat attributes that are potentially important for long-term C. alleganiensis conservation and provide guidance for stream protection and restoration practices that might mitigate sedimentation and habitat degradation in impacted streams.
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- Award ID(s):
- 1831988
- PAR ID:
- 10100477
- Date Published:
- Journal Name:
- Herpetologica
- Volume:
- 75
- Issue:
- 1
- ISSN:
- 0018-0831
- Page Range / eLocation ID:
- 21-29
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Detecting declines and quantifying extinction risk of long‐lived, highly fecund vertebrates, including fishes, reptiles, and amphibians, can be challenging. In addition to the false notion that large clutches always buffer against population declines, the imperiled status of long‐lived species can often be masked by extinction debt, wherein adults persist on the landscape for several years after populations cease to be viable. Here we develop a demographic model for the eastern hellbender (Cryptobranchus alleganiensis), an imperiled aquatic salamander with paternal care. We examined the individual and interactive effects of three of the leading threats hypothesized to contribute to the species' demise: habitat loss due to siltation, high rates of nest failure, and excess adult mortality caused by fishing and harvest. We parameterized the model using data on their life history and reproductive ecology to model the fates of individual nests and address multiple sources of density‐dependent mortality under both deterministic and stochastic environmental conditions. Our model suggests that high rates of nest failure observed in the field are sufficient to drive hellbender populations toward a geriatric age distribution and eventually to localized extinction but that this process takes decades. Moreover, the combination of limited nest site availability due to siltation, nest failure, and stochastic adult mortality can interact to increase the likelihood and pace of extinction, which was particularly evident under stochastic scenarios. Density dependence in larval survival and recruitment can severely hamper a population's ability to recover from declines. Our model helps to identify tipping points beyond which extinction becomes certain and management interventions become necessary. Our approach can be generalized to understand the interactive effects of various threats to the extinction risk of other long‐lived vertebrates. As we face unprecedented rates of environmental change, holistic approaches incorporating multiple concurrent threats and their impacts on different aspects of life history will be necessary to proactively conserve long‐lived species.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/0018-0831-75.1.21
