Temperature-dependent life history and transcriptomic responses in
heat-tolerant versus heat-sensitive Brachionus rotifers
Abstract
A species’ response to thermal stress is an essential physiological
trait that can determine occurrence and temporal succession in nature,
including response to climate change. Environmental temperature affects
zooplankton performance by altering life-spans and population growth
rates, but the molecular mechanisms underlying these alterations are
largely unknown. To compare temperature-related demography, we performed
cross-temperature life-table experiments in closely related
heat-tolerant and heat-sensitive Brachionus rotifer species that occur
in sympatry. Within these same populations, we examined the genetic
basis of physiological variation by comparing gene expression across
increasing temperatures. We found significant cross-species and
cross-temperature differences in heat response, with the heat-sensitive
species adopting a strategy of high survival and low population growth,
while the heat-tolerant followed an opposite strategy. Comparative
transcriptomic analyses revealed both shared and opposing responses to
heat. Most notably, expression of heat shock proteins (hsps) is
strikingly different in the two species. In both species, hsp responses
mirrored differences in population growth rates, showing that hsp genes
are likely a key component of a species’ adaptation to different
temperatures. Temperature induction caused opposing patterns of
expression in further functional categories such as energy, carbohydrate
and lipid metabolism, and in genes related to ribosomal proteins. In the
heat-sensitive species, elevated temperatures caused up-regulation of
genes related to induction of meiotic division as well as genes
responsible for post-translational histone modifications. This work
demonstrates the sweeping reorganizations of biological functions that
accompany temperature adaptation in these two species and reveals
potential molecular mechanisms that might be activated for adaptation to
global warming.