COS 32-3
Plasticity of breeding in Foothill Yellow-legged Frog (Rana boylii) linked to predictable environmental cues observed across species’ range
Variability in ecosystems provides heterogeneity through time and space, and organisms in stochastic systems such as rivers must evolve physiological or life history adaptations that allow flexible responses to seasonal and annual variability. This biological plasticity may be tied to environmental cues that forecast stable conditions suitable for sensitive life history stages. The lotic Rana boylii (foothill yellow-legged frog) breeds in very similar hydrologic conditions across watersheds and years, despite a highly variable geographical and environmental gradient across its range from southern Oregon to northern Baja California. We suggest R.boylii utilize specific environmental cues (flow recession rate and water temperature) to project the onset of suitable and stable hydraulic and thermal periods for initiation of spring egg deposition (oviposition) because these signals remain consistent across spatial and temporal scales. We believe that R. boylii have adapted a plastic response (breeding timing) to these environmental signals to ‘forecast’ life history periods critical to reproductive success. We compare and analyze R. boylii breeding data in conjunction with flow recession rates and water temperature to demonstrate differences in inter-annual breeding timing between wet years and dry years, as well as regional differences observed in coastal and Sierra Nevada watersheds in California.
Results/Conclusions
Rana boylii shows high plasticity in the timing of breeding, but remains strongly correlated with hydrological cues such as the rate of the natural spring snowmelt recession in the Sierra Nevada (approximately 10 cm per week) and mean weekly water temperatures that exceed 10 °C. On average, rain-driven watersheds in coastal R. boylii populations initiate breeding in early March, over a month earlier than snowmelt-dominated systems in the Sierra Nevada. Summary of over 10 years of breeding data for R. boylii across California shows the range in breeding timing can vary by 4 months, from early March to early July. For R. boylii, breeding plasticity may be viewed as a behavioral response to environmental cues from predictable recession rates, timing of receding flows, and water temperature. Conservation management in regulated rivers for crucial breeding and rearing periods may be enhanced by more accurately mimicking environmental cues like the timing and consistency of flow recession rates in the spring. This research helps expand current knowledge about breeding phenology for this species and informs future management planning and climate change monitoring efforts by more accurately defining the environmental cues required for R. boylii breeding.