Phenotypic plasticity of nest timing in a post‐glacial landscape: how do reptiles adapt to seasonal time constraints?

Abstract

Life histories evolve in response to constraints on the time available for growth and development. Nesting date and its plasticity in response to spring temperature may therefore be important components of fitness in oviparous ectotherms near their northern range limit, as reproducing early provides more time for embryos to complete development before winter. We used data collected over several decades to compare air temperature and nest date plasticity in populations of painted turtles and snapping turtles from a relatively warm environment (southeastern Michigan) near the southern extent of the last glacial maximum to a relatively cool environment (central Ontario) near the northern extent of post-glacial recolonization. For painted turtles, population-level differences in reaction norm elevation for two phenological traits were consistent with adaptation to time constraints, but no differences in reaction norm slopes were observed. For snapping turtle populations, the difference in reaction norm elevation for a single phenological trait was in the opposite direction of what was expected under adaptation to time constraints, and no difference in reaction norm slope was observed. Finally, among-individual variation in individual plasticity for nesting date was detected only in the northern population of snapping turtles, suggesting that reaction norms are less canalized in this northern population. Overall, we observed evidence of phenological adaptation, and possibly maladaptation, to time constraints in long-lived reptiles. Where present, (mal)adaptation occurred by virtue of differences in reaction norm elevation, not reaction norm slope. Glacial history, generation time, and genetic constraint may all play an important role in the evolution of phenological timing and its plasticity in long-lived reptiles.

Countergradient Variation in Reptiles: Thermal Sensitivity of Developmental and Metabolic Rates Across Locally Adapted Populations

“…Temperature poses a strong influence on physiological rates underlying energy acquisition and utilization in ectotherms that often misalign with the direction of selection. For example, an acute decrease in environmental temperature increases development time, yet cold climates often select for faster development so that embryos can complete development and commence feeding and growth before the onset of winter (Edge et al, 2017). CnGV can enable populations to compensate for the direct effects of temperature on physiological rates, to ensure persistence of populations under extreme climatic regimes (Angilletta, 2009;Conover et al, 2009).…”

Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

“…First, seasonality favours indeterminate growth, as energy should be diverted towards growth at times of year when offspring prospects are poor, provided that larger body size increases future fecundity (Ejsmond et al., ; Kozłowski, ). Indeed, snapping turtles in our study population are near their species’ northern range limit, and inhabit a highly seasonal and time‐constrained environment; in fact, many nests exhibit total failure for lack of sufficient thermal energy for embryos to develop and hatch, suggesting that eggs laid early in the season are more likely to be successful (Edge et al., ). Second, indeterminate growth tends to be favoured when life expectancy is relatively long (Ejsmond et al., , ; Perrin et al., ).…”

Use of field‐portable ultrasonography reveals differences in developmental phenology and maternal egg provisioning in two sympatric viviparous snakes

“…Recently, there has been increasing interest in the dynamics of development in the wild, particularly with rising concern regarding effects of climate change on reproductive phenology (Abouheif et al, 2014;Gilbert, Bosch, & Ledón-Rettig, 2015;Ledón-Rettig & Pfennig, 2011;Parmesan, 2007;Sultan, 2007;Telemeco, Elphick, & Shine, 2009;Walther et al, 2002;Winkler, Dunn, & McCulloch, 2002). Shifts in the onset of breedings seasons, length of developmental periods, and hatching times have been documented in a wide range of species, including insects, amphibians, turtles, lizards, and birds (e.g., Edge et al, 2017;Parmesan, 2007;Rutschmann et al, 2016;Urban, Richardson, & Freidenfelds, 2014;Valtonen, Latja, Leinonen, & Pöysä, 2017). Yet much remains to be learned regarding plasticity and phylogenetic constraints on developmental life history in natural populations with varying reproductive modes, including viviparity (live-bearing) and oviparity (eggbearing) species (Sultan, 2007).…”