Natural selection on thermal performance in a novel thermal environment

Abstract

Tropical ectotherms are thought to be especially vulnerable to climate change because they are adapted to relatively stable temperature regimes, such that even small increases in environmental temperature may lead to large decreases in physiological performance. One way in which tropical organisms may mitigate the detrimental effects of warming is through evolutionary change in thermal physiology. The speed and magnitude of this response depend, in part, on the strength of climate-driven selection. However, many ectotherms use behavioral adjustments to maintain preferred body temperatures in the face of environmental variation. These behaviors may shelter individuals from natural selection, preventing evolutionary adaptation to changing conditions. Here, we mimic the effects of climate change by experimentally transplanting a population of Anolis sagrei lizards to a novel thermal environment. Transplanted lizards experienced warmer and more thermally variable conditions, which resulted in strong directional selection on thermal performance traits. These same traits were not under selection in a reference population studied in a less thermally stressful environment. Our results indicate that climate change can exert strong natural selection on tropical ectotherms, despite their ability to thermoregulate behaviorally. To the extent that thermal performance traits are heritable, populations may be capable of rapid adaptation to anthropogenic warming. Bahamas | thermoregulationA nthropogenic climate change may be the single most dramatic physical change our planet has experienced during human history (1). In the tropics, where species are adapted to relatively stable climates, the impacts of climate change are predicted to be especially severe (2-5) (but see refs. 6, 7). Because many species maintain a body temperature (T b ) that is already close to their thermal limits, even small increases in environmental temperature (T e ) may produce large decreases in physiological performance that could push populations toward extinction (4).In tropical environments, evolutionary adaptation may be one of the most important mechanisms by which populations can avoid extinction (8). As climates shift, fitness for many species will become increasingly linked to variation in traits important for performance in a warmer and more thermally variable world (4). Numerous theoretical, laboratory, and field studies demonstrate a capacity for rapid evolution on time scales similar to those over which global warming is predicted to occur (9-11). Indeed, recent work on lizards (12) and butterflies (13) has revealed rapid shifts in thermal physiology that appear to be directly associated with changing thermal environments. Despite mounting evidence that the capacity for evolution may fundamentally alter extinction probabilities in the face of anthropogenic climate change, the potential for rapid evolution is usually not considered in models that attempt to predict the impact of climate change on biological populations (8).The rate at which ...

Limited tolerance by insects to high temperatures across tropical elevational gradients and the implications of global warming for extinction

“…This pattern of high evolvability of critical thermal minimum but low potential for adaptation of CT max has also been described for several endo-and ectotherms (30). Adaptation to warmer temperatures in ecological time is also possible; there is evidence of rapid evolution of thermal tolerance to warm temperatures in anurans and lizards (7,31).…”

“…The thermal adaptation hypothesis proposes that because adaptation to a broad range of temperatures has a high physiological cost, the thermal limits of populations and species will be selected to match temperatures that characterize their geographic ranges (2,4). As a result, tolerance to high temperatures is assumed to be a conservative trait with limited phenotypic plasticity and evolvability (5,6) [but an example of rapid evolution of CT max is provided by Logan et al (7)]. This limitation in phenotypic and evolutionary responses poses a serious threat to organisms under projected global warming (2).…”

Reversal of response to artificial selection on body size in a wild passerine

“…Generally, our results fit well with the idea that natural populations often are well adapted, with few individuals in the phenotypic space of very low fitness Schluter, 1988;Haller and Hendry, 2014). In such cases the detection of selection and the underlying fitness function might be difficult, and could be approached by experimental manipulations of the phenotype (Flux and Flux, 1982;Cresswell, 2000;Brakefield, 2003;Postma et al, 2007;Vignieri et al, 2010) or the ambient biotic or abiotic environmental conditions (Endler, 1980;Snaydon and Davies, 1982;Wade and Kalisz, 1990;Losos et al, 1997Losos et al, , 2001Svensson and Sinervo, 2000;Calsbeek and Smith, 2007;Barrett et al, 2008;Calsbeek et al, 2009;Logan et al, 2014).…”

Evolution caused by extreme events

“…When lizards were forcibly introduced onto a hot Caribbean island, survival was highest in individuals that ran relatively quickly at high temperature [38]. Similarly, when marine stickleback fish were transferred to (relatively cold) freshwater ponds, their cold tolerance evolved within 3 years [39].…”