The effects of developmental temperature and inbreeding on sexually selected traits of male guppies ( Poecilia reticulata )

Global temperatures are rising and inbreeding is increasingly common in wild animals as populations decline. There is extensive research on inbreeding and temperature stress, but little is known about how they interact to affect sexually selected traits. We therefore investigated how developmental temperature (26°C or 30°C) and inbreeding affect male guppies (Poecilia reticulata). We reciprocally cross-bred full-siblings to create inbred and outbred fish, then measured traits under either pre-copulatory (i.e., coloration, gonopodium length, sexual attractiveness, mating behavior) or post-copulatory (i.e., sperm number, velocity) sexual selection for ∼120 adult males. There was no evidence that temperature and inbreeding interact to affect trait expression; instead, their effects were additive. Males reared at 30°C were significantly less attractive to females, and made fewer sigmoid mating displays, than males reared at 26 °C. Inbred males were also less attractive, but their mating behavior did not differ from that of outbred males. Sperm number and velocity were unaffected by inbreeding or developmental temperature. Unexpectedly, males reared at 30 °C and inbred males both had significantly more orange coloration. Our results show that inbreeding and developmental temperature independently influence some sexually selected male traits, suggesting that climate change and habitat fragmentation might alter evolution under sexual selection.