A quantitative synthesis of and predictive framework for studying winter warming effects in reptiles

Abstract

Increases in temperature related to global warming have important implications for organismal fitness. For ectotherms inhabiting temperate regions, ‘winter warming’ is likely to be a key source of the thermal variation experienced in future years. Studies focusing on the active season predict largely positive responses to warming in the reptiles; however, overlooking potentially deleterious consequences of warming during the inactive season could lead to biased assessments of climate change vulnerability. Here, we review the overwinter ecology of reptiles, and test specific predictions about the effects of warming winters, by performing a meta-analysis of all studies testing winter warming effects on reptile traits to date. We collated information from observational studies measuring responses to natural variation in temperature in more than one winter season, and experimental studies which manipulated ambient temperature during the winter season. Available evidence supports that most reptiles will advance phenologies with rising winter temperatures, which could positively affect fitness by prolonging the active season although effects of these shifts are poorly understood. Conversely, evidence for shifts in survivorship and body condition in response to warming winters was equivocal, with disruptions to biological rhythms potentially leading to unforeseen fitness ramifications. Our results suggest that the effects of warming winters on reptile species are likely to be important but highlight the need for more data and greater integration of experimental and observational approaches. To improve future understanding, we recap major knowledge gaps in the published literature of winter warming effects in reptiles and outline a framework for future research.

Climate change-induced shifts in survival and size of the worlds’ northernmost oviparous snake: A 68-year study

“…Our model predictions suggest that male and female body length increased by 5 and 7 cm, respectively, over the study period 1945-2006. This is line with climate warming permitting a longer annual period of foraging activity and earlier hatching dates [32,57]. Our data also suggest that grass snakes in the study population now emerge from hibernation approximately 10 days earlier in spring than they did 60 years ago.…”

“…To our knowledge this is the first documentation of long-term survival trends across seasons in a temperate reptile. An obvious implication is that research as well as conservation efforts about effects of climate change on temperate ectotherms need to address seasonal survival patterns separately in order to better understand causality of population change [ 56 , 57 ]. Teasing apart mortality by season is also crucial for devising counter-measures for declining populations.…”

Demographic history and genomic signatures of selection in a widespread vertebrate ectotherm

“…Thermosensitive traits such as temperature‐dependent sex determination (TSD) and anoxia tolerance make these species particularly vulnerable. Temperature changes of only a few degrees could destabilize sex ratios, especially in small populations (Mitchell et al., 2010; Mitchell & Janzen, 2010), or influence individuals' ability to prepare adequately for warming winter conditions (Moss & MacLeod, 2022). In reptiles, most studies investigating potential responses to climate change suggest that plasticity plays an important, and perhaps predominant, role in mediating organismal responses to temperature (e.g., Janzen et al., 2018; Refsnider & Janzen, 2012, 2016; Urban et al., 2014).…”