Physiological climatic limits inDrosophila: patterns and implications

Abstract

SummaryPhysiological limits determine susceptibility to environmental changes, and can be assessed at the individual, population or species/lineage levels. Here I discuss these levels in Drosophila, and consider implications for determining species susceptibility to climate change. Limits at the individual level in Drosophila depend on experimental technique and on the context in which traits are evaluated. At the population level, evidence from selection experiments particularly involving Drosophila melanogaster indicate high levels of heritable variation and evolvability for coping with thermal stresses and aridity. An exception is resistance to high temperatures, which reaches a plateau in selection experiments and has a low heritability/evolvability when temperatures are ramped up to a stressful level. In tropical Drosophila species, populations are limited in their ability to evolve increased desiccation and cold resistance. Population limits can arise from trait and gene interactions but results from different laboratory studies are inconsistent and likely to underestimate the strength of interactions under field conditions. Species and lineage comparisons suggest phylogenetic conservatism for resistance to thermal extremes and other stresses. Plastic responses set individual limits but appear to evolve slowly in Drosophila. There is more species-level variation in lower thermal limits and desiccation resistance compared with upper limits, which might reflect different selection pressures and/or low evolvability. When extremes are considered, tropical Drosophila species do not appear more threatened than temperate species by higher temperatures associated with global warming, contrary to recent conjectures. However, species from the humid tropics may be threatened if they cannot adapt genetically to drier conditions.

Extreme cost of rivalry in a monandrous species: male–male interactions result in failure to acquire mates and reduced longevity

“…The data are notable because D. subobscura is commonly used as a model of stress tolerance in nature [41][42][43]. However, stress tolerance studies in this species have focused on thermal effects on genetic and phenotypic polymorphisms of wings and desiccation resistance [43 -45].…”

Thermal variation, thermal extremes and the physiological performance of individuals

“…displacement competition, sudden weather changes) and then probably only for short periods of time. Ultimately, brief extreme events near (or beyond) the nominal performance bounds may have greater effect on overall performance (Hoffmann, 2010) (see next section).…”

Natural selection on thermal performance in a novel thermal environment

“…The rate at which thermal physiology can evolve in response to a changing climate depends on generation time (5), the additive genetic variances and covariances underlying phenotypic variation (14), and the strength of selection on traits that influence performance (15,16). Strong selection is a prerequisite for rapid evolutionary adaptation to global warming, but many ectothermic species may shelter themselves from selection by using behavioral adjustments to maintain a preferred T b in the face of environmental variation (17,18).…”