Temperature variations affect postcopulatory but not precopulatory sexual selection in the cigarette beetle

The ambient temperature varies on several timescales such as year, season and day and affects many reproductive traits of ectotherms. Thus, the direction and intensity of sexual selection should be affected by thermal conditions. However, the effects of temperature variation during mating events have sometimes been overlooked. We assessed traits associated with pre- and postcopulatory sexual selection in the cigarette beetle, Lasioderma serricorne, using three thermal mating conditions: 19 °C, 25 °C and 31 °C. Thermal conditions did not affect precopulatory traits (mating rate, mating latency and courtship intensity). Mating duration increased with decreasing temperature, whereas the number of sperm transferred and female fecundity were greatest at 25 °C. To investigate whether these thermal differences affected the risk of sperm competition (remating rate) and fitness consequences for both sexes, we conducted double-mating experiments using a black colour mutant. Females that had first mated at low or high temperatures were more likely to accept remating and exhibited higher fecundity compared to females that rejected remating; when females remated, the paternity of the first male was highest at 25 °C. Thermal conditions at the first mating event affected the fitness consequences for both sexes, irrespective of the females' remating acceptance. Changes to the thermal conditions for the female remating event caused no difference in the female remating rate or fecundity; however, the paternity of the second mate was highest at the intermediate temperature, and this could be attributed to the decreased sperm transfer at low and high temperatures. Our results suggest that temperature conditions during mating affect postcopulatory processes in L. serricorne. In particular, when females first mated at extreme temperatures, polyandry was promoted, potentially favouring males with higher sperm competitive ability through increased likelihood and intensity of sperm competition.