Heat hardening in a tropical lizard: geographic variation explained by the predictability and variance in environmental temperatures

Abstract

Summary Over the coming decades, our planet will experience a dramatic increase in average temperatures and an increase in the variance around those temperatures leading to more frequent and harsher heat waves. These changes will impact most species and impose strong selection on physiological traits. Rapid acclimation is the most direct way for organisms to respond to such extreme events, but we currently have little understanding of how the capacity to mount such plastic responses evolves. Accordingly, there is some urgency to determine how the physiological response to high temperatures varies within species, and how this variation is driven by the environment. Here, we investigate heat‐hardening capacity – a rapid physiological response that confers a survival advantage under extreme thermal stress – across 13 populations of a rain forest lizard, Lampropholis coggeri, from the tropics of north‐eastern Australia. Our results reveal that heat hardening is constrained in these lizards by a hard upper thermal limit for locomotor function (approximately 43 °C). Further, hardening response shows strong geographic variation associated with thermal environment: lizards from more predictable and more seasonal thermal environments exhibited greater hardening compared with those from more stochastic and less seasonal habitats. This finding – that predictability in thermal variation influences hardening capacity – aligns closely with theoretical expectations. Our results suggest that tropical species may harbour adaptive variation in physiological plasticity that they can draw from in response to climate change, and this variation is spatially structured in locally adapted populations. Our results also suggest that, by using climatic data, we can predict which populations contain particular adaptive variants; information critical to assisted gene flow strategies.

Basking behavior predicts the evolution of heat tolerance in Australian rainforest lizards

“…; Phillips et al. ) and broader meta‐analyses of acclimation (Gunderson and Stillman ) all find that physiological traits typically only shift by 1–2°C in response to acute or sustained environmental shifts (but see meta‐analysis of CT min acclimation in Pintor et al. ), whereas our measurements often differed by up to 12°C (Fig.…”

“…Indeed, Phillips et al. () found that one of our target species, L. coggeri , exhibits a marked heat hardening response. However, they also found that organisms in environments that are already approaching thermal limits have a reduced capacity to shift heat tolerance, which has also been observed in flies (Kristensen et al.…”

Thermoregulatory behaviour explains countergradient variation in the upper thermal limit of a rainforest skink

“…Indeed, many other thermal traits are regularly measured in ectotherms, including the optimal temperature and performance breadth for whole‐animal performances (e.g. sprint speed and gut passage time), critical thermal minimum, and heat shock response (Angilletta et al , Clusella‐Trullas, S. et al , Phillips et al , ). Given the pressing need to understand how species adjust to different climates, studying the interactions between these traits and their association with thermoregulatory behavior and thermal environment should be a high priority.…”

Spatial and temporal heterogeneity in climate change limits species' dispersal capabilities and adaptive potential

“…Similarly, rapid plastic and evolutionary responses to global climate change have already been observed across taxa ranging from migratory birds (Gill et al 2013) to anadromous fish (Kovach et al 2012), arthropods (Krehenwinkel et al 2016), annual plants (Franks et al 2016), and soil (Bataillon et al 2016) and aquatic invertebrates (Oexle et al 2016). In fact, rapid, directional climatic changes may even facilitate rapid responses (Phillips et al 2016). Thus, although niche conservatism may ultimately constrain the extent and rate at which populations can adapt evolutionarily to climate change (Quintero and Wiens 2013), rapid climate-driven adaptations may not be as rare as once thought (Moran and Alexander 2014).…”