Stage-Specific Demographic Effects of Hydrologic Variation in a Stream Salamander

Differences in Larval Microhabitat Between Two Cryptic, Sympatric Salamander Species (Desmognathus folkertsi and D. amphileucus) in Northeastern Georgia, USA

Sympatric species often exhibit habitat differences that promote coexistence. Two cryptic, sympatric salamander species, Desmognathus folkertsi and D. amphileucus, occupy streams across the Appalachian Mountains of northeastern Georgia, USA. Although frequently occurring together, the adults exhibit differences in microhabitat with D. folkertsi predominating in smaller streams and D. amphileucus more abundant in larger streams. Our purpose was to test for possible differences in larval habitat. Using a stream in which the two species coexist, we collected larvae from riffles, and biotic and abiotic variables associated with the stream and adjacent riparian zone were recorded. Because adults partially segregate by stream size, we noted the entry of a tributary that increased stream size and flow rate. Results showed a significant distribution of the two species upstream compared to downstream of the tributary, with no D. amphileucus found upstream; D. folkertsi was found throughout the study stream. We also found a significant difference between species in flow rate. We found no differences in any other variable that explained larval distribution patterns. We hypothesize that D. folkertsi nest in lower-flow riffles than D. amphileucus, resulting in the distribution of larvae, a pattern that may reflect selection on larval survival.

Outbreeding reduces survival during metamorphosis in a headwater stream salamander

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 salamander Gyrinophilus porphyriticus. The life cycle of G. porphyriticus includes 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.