Degrees of change: between and within population variation in thermal reaction norms of phenology in a viviparous lizard

Abstract

As the earth warms, populations will be faced with novel environments to which they may not be adapted. In the short term, populations can be buffered against the negative effects, or maximize the beneficial effects, of such environmental change via phenotypic plasticity and, in the longer term, via adaptive evolution. However, the extent and direction of these population-level responses will be dependent on the degree to which responses vary among the individuals within them (i.e., within population variation in plasticity), which is, itself, likely to vary among populations. Despite this, we have estimates of among-individual variation in plastic responses across multiple populations for only a few systems. This lack of data limits our ability to predict the consequences of environmental change for population and species persistence accurately. Here, we utilized a 16-yr data set from climatically distinct populations of the viviparous skink Niveoscincus ocellatus tracking over 1,200 litters from more than 600 females from each population to examine inter-and intrapopulation variability in the response of parturition date to environmental temperature. We found that these populations share a common population-mean reaction norm but differ in the degree to which reaction norms vary among individuals. These results suggest that even where populations share a common mean-level response, we cannot assume that they will be affected similarly by altered environmental conditions. If we are to assess how changing climates will impact species and populations accurately, we require estimates of how plastic responses vary both among and within populations.

Individual telomere dynamics and their links to life history in a viviparous lizard

“…We found strong differences in telomere length between our populations, with longer telomeres in the cool highland population compared to the warm lowland population. While more populations are needed to definitively link these differences to life histories, the results are consistent with divergent patterns of growth reflecting thermal opportunity and affecting age and size at reproduction, with females in cool highland populations maturing at a larger size and on average 1 year later than individuals from warm lowland populations [52] (see electronic supplementary material, for information on the consistency of these traits across highland and lowland regions). This suggests cellular maintenance in warm lowland individuals may be traded off against the benefits of greater short-term reproductive success during the early years of life.…”

“…The two populations used in this study are at climatic extremes of the species distribution and exhibit substantial differences in life history. Warm lowland populations grow faster, mature on average 1 year earlier (at a smaller size) and produce fewer offspring per litter than cool highland populations [50][51][52]. These life-history traits are consistent across several warm and cold populations [51,53,54] (see electronic supplementary material, figure S1).…”

“…While the relationships between thermal environment and telomeres dynamics are complex [23], the faster developmental rate exhibited as a result of exposure to more extreme developmental temperatures can have negative effects on telomere attrition (although see [78]). That these effects were not observed in the highlands may have to do with the fact that birth date is substantially more canalized in that population-either as a result of selection, variation in microhabitat or variation in behaviour [52,53]. Therefore, there may not be sufficient variation in birth date between individuals to generate differences in telomeres.…”

“…faster life histories) compared to the cool highlands [50,51,55,56]. Temperature variation within and between years influences birth date and reproductive timing in this species [52,53] which has consequences for the success of offspring later in life [57,58]. Thus, we use the birth date of offspring as a proxy for the thermal environment experienced during gestation [52,57] and the consequent effects on the developmental rate of offspring.…”

Pleistocene divergence in the absence of gene flow among populations of a viviparous reptile with intraspecific variation in sex determination

“…On the other hand, close examination of the life history of this species has not revealed strong evidence for population‐specific local adaptation in traits that may explain their genetic isolation (Cadby et al., 2014; Caldwell et al., 2017; Cliff et al., 2015; Wapstra & Swain, 2001; Wapstra et al., 1999). For example, temperature reaction norms for gestation length and offspring development are remarkably similar in each population (Cunningham et al., 2020), however, further studies will reveal if local thermal adaptation has occurred since isolation resulting in population‐specific thermosensitivity of sex determination. Regardless, whether sex determination isolated populations or occurred subsequent to their isolation, our estimate of divergence time places a lower limit on the timeframe of their divergence.…”