Temperature‐induced multi‐species cohort effects in sympatric snakes

Abstract

In reptiles, reproductive maturity is often determined by size rather than age. Consequently, growth early in life may influence population dynamics through effects on generation time and survival to reproduction. Because reproductive phenology and pre‐ and post‐natal growth are temperature dependent, environmental conditions may induce multi‐species cohort effects on body size in sympatric reptiles. I present evidence of this using 10 years of neonatal size data for three sympatric viviparous snakes, Dekay's Brown snakes (Storeria dekayi), Red‐bellied Snakes (S. occipitomaculata), and Common Garter snakes (Thamnophis sirtalis). End‐of‐season neonatal size varied in parallel across species such that snout–vent length was 36%–61% greater and mass was 65%–223% greater in years when gestating females could achieve higher April–May (vs. June–July or August–September) operative temperatures. Thus, temperature had a larger impact during follicular enlargement and ovulation than during gestation or post‐natal growth. Multi‐species cohort effects like these may affect population dynamics and the magnitude of these effects may increase with climate change.

Increased offspring size and reduced gestation length in an ectothermic vertebrate under a worst-case climate change scenario

“…However, this increase in ambient temperature had no impact on successful birth rate or the number of offspring in each litter. The observed decrease in gestation length is consistent with those previously observed among a number of other viviparous ectotherms (Blanchard and Blanchard, 1940;Ji et al, 2006;Wang et al, 2017;King, 2022).…”

“…This behavioral tradeoff serves to illustrate the importance of an organism's thermal environment, and that maintaining proper temperature is vital for the survival and optimal development of offspring and therefore directly 4 impacts the individual fitness of reproducing adults. Temperatures experienced during gestation are often observed to impact neonate size in viviparous squamates (Mathies and Andrews, 1997;Lourdais et al, 2004;Gao et al, 2010;King, 2022). Both greater neonate body length (Brown and Shine, 2004;Kissner and Weatherhead, 2005;Addis et al, 2017) and greater body mass (Jayne and Bennett, 1990;Bronikowski, 2000;Kissner and Weatherhead, 2005) are associated with significantly increased rates of survival to adulthood in viviparous snakes.…”

“…Changes to environmental thermal conditions during gestation have been observed to impact both physiology and behavior of viviparous ectotherms to alter characteristics such as maternal energy use and basking and foraging behavior (Lourdais et al, 2002;Ladyman et al, 2003;Wang et al, 2017), gestation length (Blanchard and Blanchard, 1940;Ji et al, 2006;Wang et al, 2017;King, 2022), litter size (Lourdais et al, 2004;Zhang et al, 2010;Tang et al, 2012), and body condition and viability of neonates (Lourdais et al, 2004;Wang et al, 2017;King, 2022). Although there is often agreement regarding the influence of warmer temperatures on gestation, neonate survival, and body condition, the specific effects observed differ between studies and depend on the biological system examined.…”

Patterns of tropical forest understory temperatures

“…Microclimate also controls the seasonal movements of species within an ecosystem and thus directly impacts distribution capacity and populations especially in fragmented terrains 57,58 . Comprehending how these activities function with microclimate to shape species' cohorts 59 and their exposure to climate change is essential to forecasting range dynamics 60,61 .…”