Biology subjects

Pettersen, A. K.

Publications and source records attributed to Pettersen, A. K..

3 recordsLinked to original sources

bioRxiv2023

How do fluctuating temperatures alter the cost of development?

O_LIQuantifying how variable temperature regimes affect energy expenditure during development is crucial for understanding how future thermal regimes may impact early life survival and population persistence. C_LIO_LIDevelopmental Cost Theory (DCT) suggests that there is an optimal temperature (Topt) that minimises energy expenditure during development (the "cost of development"). Exposure to fluctuating temperatures around an average of Topt are anticipated to increase either development time or metabolic rate. As a result, embryos will rapidly deplete yolk reserves, and consequently hatch at a smaller size or with less residual yolk to support postnatal survival and growth. C_LIO_LIHere, we studied total embryonic energy expenditure (development time and rate of CO2 production) and conversion of yolk into tissue in common wall lizards (Podarcis muralis) under three incubation treatments anticipated, based on DCT, to increase the cost of development: no variance (Topt constant, 24 {degrees}C), low variance (22 - 26 {degrees}C), and high variance (18 - 30 {degrees}C). C_LIO_LIAs predicted, we found that increasing variance around Topt increased the cost of development, despite reducing time to hatching. As a consequence, embryos on average hatched with 59% lower residual yolk reserves under high variance versus constant incubation temperatures. C_LIO_LIOur results highlight how the relative temperature sensitivities of development time and metabolic rate determine the cost of development, which in turn may predict the ability of egg-laying ectotherms to persist in variable environments. We show that DCT can provide a mechanistic framework for understanding the widespread, but often seemingly idiosyncratic, effects of fluctuating incubation temperatures on hatchling tissue and residual yolk mass. C_LI

physiology↗

bioRxiv2022

Population divergence in maternal investment and embryo energy use and allocation reveals adaptive responses to cool climates

The thermal sensitivity of early life stages can play a fundamental role in constraining species distribution. For egg-laying ectotherms, cool temperatures often extend development time and exacerbate developmental energy cost. Despite these costs, egg laying is still observed at high latitudes and altitudes. How embryos overcome the developmental constraints posed by cool climates is crucial knowledge for explaining the persistence of oviparous species in such environments and for understanding thermal adaptation more broadly. Here, we studied maternal investment, and embryo energy use and allocation in wall lizards spanning altitudinal regions, as potential mechanisms of local adaptation to development in cool climates. Specifically, we compared population-level differences in (1) investment from mothers (egg mass, embryo retention and thyroid yolk hormone concentration), (2) embryo energy expenditure during development, and (3) embryo energy allocation from yolk towards tissue. We found evidence that energy expenditure was greater under cool compared with warm incubation temperatures. Females from relatively cool regions did not compensate for this energetic cost of development by producing larger eggs or increasing thyroid hormone concentration in yolk. Instead, embryos from the high-altitude region used less energy to complete development, i.e., they developed faster without a concomitant increase in metabolic rate, compared with those from the low-altitude region. Embryos from high altitudes also allocated relatively more energy towards tissue production, hatching with lower residual yolk:tissue ratios than low-altitude region embryos. These results suggest that local adaptation to cool climate in wall lizards involves mechanisms that regulate embryonic utilisation of yolk reserves and its allocation towards tissue, rather than shifts in maternal investment of yolk content or composition.

evolutionary biology↗

bioRxiv2021

Behavioural adaptations in egg laying ancestors facilitate evolutionary transitions to live birth

Live birth is a key innovation that has evolved from egg laying ancestors over 100 times in reptiles. However, egg-laying lizards and snakes often possess preferred body temperatures that are lethal to developing embryos, which should select against egg retention. Here, we demonstrate that thermal mismatches between mothers and offspring are widespread across the squamate phylogeny. This mismatch is resolved by gravid females adjusting their body temperature towards the thermal optimum of embryos. Importantly, phylogenetic reconstructions suggest this thermoregulatory behaviour evolved in egg-laying species prior to the evolution of live birth. Maternal thermoregulatory behaviour therefore bypasses the constraints imposed by a slowly evolving thermal physiology and has likely been a key facilitator in the repeated transitions to live birth.

evolutionary biology↗