Hydrologic variability contributes to reduced survival through metamorphosis in a stream salamander

Abstract

Changes in the amount, intensity, and timing of precipitation are increasing hydrologic variability in many regions, but we have little understanding of how these changes are affecting freshwater species. Stream-breeding amphibians—a diverse group in North America—may be particularly sensitive to hydrologic variability during aquatic larval and metamorphic stages. Here, we tested the prediction that hydrologic variability in streams decreases survival through metamorphosis in the salamander Gyrinophilus porphyriticus, reducing recruitment to the adult stage. Using a 20-y dataset from Merrill Brook, a stream in northern New Hampshire, we show that abundance of G. porphyriticus adults has declined by ∼50% since 1999, but there has been no trend in larval abundance. We then tested whether hydrologic variability during summers influences survival through metamorphosis, using capture–mark–recapture data from Merrill Brook (1999 to 2004) and from 4 streams in the Hubbard Brook Experimental Forest (2012 to 2014), also in New Hampshire. At both sites, survival through metamorphosis declined with increasing variability of stream discharge. These results suggest that hydrologic variability reduces the demographic resilience and adaptive capacity of G. porphyriticus populations by decreasing recruitment of breeding adults. They also provide insight on how increasing hydrologic variability is affecting freshwater species, and on the broader effects of environmental variability on species with vulnerable metamorphic stages.

A review of hydrologic signatures and their applications

“…For example, Jowett and Duncan (1990) analyze 130 sites in New Zealand and find that high flow variability is negatively correlated with mean water velocity and relative bed stability, and positively correlated with trout habitat. In other species, flow variability reduces abundance, such as in stream salamanders where variability reduces survival through metamorphosis (Lowe, Swartz, Addis, & Likens, 2019). Clausen and Biggs (1997) find that the "Fre3" signature, that is, the frequency of floods higher than three times the median flow, predicts periphyton and invertebrate density because Fre3 flows have sufficient energy to disturb sand and gravel riverbed sediments.…”

Metamorphosis imposes variable constraints on genome expansion through effects on development

“…Rather, trait evolution is described by moderate stochastic noise around an equilibrium value that we interpret as a balance between TE accumulation and a constraint imposed by metamorphosis. Although the animals are able to feed, there are other ways in which fitness can be lowered during salamander metamorphosis; for example, metamorphosing individuals are less able to exploit stream habitat refugia than either larvae or adults, which increases their mortality (Lowe, et al 2019). Our results indicate that feeding metamorphosis imposes a less severe constraint on genome size than non-feeding metamorphosis, and we infer that the constraint is mediated by vulnerabilities other than depletion of energetic stores.…”

Reflections on the Ecology of Landscapes

“…• Salamander loss occurs in streams because of increased variability in streamflow (Lowe et al 2019).…”