Temperature drives pre‐reproductive selection and shapes the biogeography of a female polymorphism

Abstract

Conflicts of interests between males and females over reproduction is a universal feature of sexually reproducing organisms and has driven the evolution of intersexual mimicry, mating behaviours and reproductive polymorphisms. Here, we show how temperature drives pre‐reproductive selection in a female colour polymorphic insect that is subject to strong sexual conflict. These species have three female colour morphs, one of which is a male mimic. This polymorphism is maintained by frequency‐dependent sexual conflict caused by male mating harassment. The frequency of female morphs varies geographically, with higher frequency of the male mimic at higher latitudes. We show that differential temperature sensitivity of the female morphs and faster sexual maturation of the male mimic increases the frequency of this morph in the north. These results suggest that sexual conflict during the adult stage is shaped by abiotic factors and frequency‐independent pre‐reproductive selection that operate earlier during ontogeny of these female morphs.

Changes in gene expression during female reproductive development in a colour polymorphic insect

“…The male-mimicking A-females of I. elegans develop their final colour pattern at an earlier age than the other female morphs (Svensson et al 2020; Fig. 1b; S1).…”

“…1b; Svensson et al 2009). Morph differences in the direction, magnitude or timing of gene expression changes during this developmental period could suggest direct or indirect interactions between the colour-morph locus and loci underlying the multitude of phenotypic traits that differentiate the adult female morphs Lancaster et al 2017;Willink and Svensson 2017;Willink et al 2019;Svensson et al 2020). Elucidating these interactions is important for a better understanding of the mechanisms behind pleiotropy of majoreffect loci, and how these loci can produce phenotypically divergent and co-adapted morphs in damselflies and other insects.…”

“…However, the results in the present study do not permit us to pinpoint the specific physiological or molecular mechanisms 22 555 560 565 570 behind such a cost. The accelerated reproductive development in A-females might however be advantageous, especially at northern latitudes where mating seasons are cooler and shorter (Svensson et al 2020).…”

“…This blue abdominal patch is initially present in sexually immature individuals of all three female morphs development, but there are pronounced differences between A-females and the two other female morphs (I-and O-females). These colour changes occur continuously over the span of a few days (Svensson et al 2020;Fig. 1b; S1).…”

“…Two of the female morphs in I. elegans differ phenotypically from males in their sexually mature colouration, while the third morph is considered to be a male-mimic, with a colour pattern strikingly similar to that of males ). Male-mimicking females also differ from the other two morphs in their ontogenetic trajectories of colour change and in several other phenotypic traits, including fecundity Willink et al 2019), mating rates ), parasite resistance and tolerance (Willink and Svensson 2017), cold tolerance (Lancaster et al 2017) and adult development times (Svensson et al 2020). Some of these phenotypic differences between the morphs are likely to be adaptive and a result of correlational selection (Svensson 2017).…”