DOI: 10.5061/dryad.gf1vhhmkn
title: Additive and mostly adaptive plastic responses of gene expression to multiple stress in Tribolium castaneum

description: Gene expression is known to be highly responsive to the environment and
 important for adjustment of metabolism but there is also growing evidence
 that differences in gene regulation contribute to species divergence and
 differences among locally adapted populations. However, most studies so
 far investigated populations when divergence had already occurred.
 Selection acting on expression levels at the onset of adaptation to an
 environmental change has not been characterized. Understanding the
 mechanisms is further complicated by the fact that environmental change is
 often multivariate, meaning that organisms are exposed to multiple
 stressors simultaneously with potentially interactive effects. Here we use
 a novel approach by combining fitness and whole-transcriptome data in a
 large-scale experiment to investigate responses to drought, heat and their
 combination in Tribolium castaneum . We found that fitness was reduced by
 both stressors and their combined effect was almost additive. Expression
 data showed that stressor responses were acting independently and did not
 interfere physiologically.  Since we measured expression and
 fitness within the same individuals, we were able to estimate selection on
 gene expression levels. We found that variation in fitness can be
 attributed to gene expression variation and that selection pressures were
 environment dependent and opposite between control and stress conditions.
 We could further show that plastic responses of expression were largely
 adaptive, i.e.  in the direction that should increase fitness.
description: We used a <i>T. castaneum </i>strain (Cro1) which was
 collected from a wild population in 2010 and adapted to standard control
 conditions (CTL: 33 °C, 70% relative humidity (r.h.)) since then. To
 assess the fitness changes caused by stressful environmental conditions,
 we exposed the beetles to a drought, a heat, and a combined heat-drought
 treatment (conditions: Dry (=D) : 33°C, 30% r.h.; Hot (=H): 37 °C, 70 %
 r.h; Hot-Dry (=HD): 37°C, 30% r.h.). Parents of the experimental beetles
 were reared in control conditions and beetles used for this fitness assay
 were transferred to treatments at the egg stage. Males and females were
 separated at the pupal stage. We mated each virgin female with one
 unrelated male from the same condition in a 15 mL tube with 1 g medium
 (organic wheat flour mixed with 10% organic baker's yeast). The male
 was removed after 24 h. Females were removed from the tubes after one week
 of egg laying, and 9 g medium was added to provide food for the developing
 offspring. After five weeks the number of offspring was counted. At this
 time, all offspring had reached the adult stage. Some females did not
 produce any offspring. Data was collected in 2015.
description: First column: female ID = female that produced offspring; second
 column: male ID = mating partner of female, father of offspring; third
 column: number of adult offspring; fourth column: condition in the climate
 chamber: CTL=control, D=dry, H=hot, HD=hot-dry