Male and female developmental temperature modulate post-copulatory interactions in a beetle

Sexual selection theory has proven to be fundamental to our understanding of the male-female 15 (sperm-egg) interactions that characterise fertilisation. However, sexual selection does not operate 16 in a void and abiotic environmental factors have been shown to modulate the outcome of pre17 copularory sexual interactions. Environmental modulation of post-copulatory interactions are 18 particularly likely because the form and function of primary reproductive traits appears to be acutely 19 sensitive to temperature stress. Here we report the effects of developmental temperature on female 20 reproductive architecture and the interaction between male and female developmental 21 temperature on the outcome of sperm competition in the bruchid beetle Callosobruchus maculatus. 22 When females were reared at developmental temperatures above and below typical temperatures 23 the bursa copulatrix (site of spermatophore deposition) were smaller and, were either shorter and 24 broader (high temperatures) or longer and thinner (low temperatures) than those reared at 25 intermediate temperatures. Males and females reared at low developmental temperatures were 26 less likely to mate than those reared at higher temperatures. Where copulation occurred, females 27 reared at the highest temperature copulated for longest, whilst males reared at the lowest 28 temperature spent longer in copula. Male developmental temperature had a significant impact on 29 the outcome of sperm competition: males reared at 17oC were largely unsuccessful in sperm 30 competition against control (27oC) males, although some of the variation in the outcome of sperm 31 competition was a product of the interaction between male and female developmental 32 temperature. Our results demonstrate that male-female interactions that characterise pre- and post33 copulatory outcomes are sensitive to developmental temperature and that plasticity in cryptic 34 female preferences could lead to heterogeneous selection on the male reproductive phenotype.