Thermal preference of male Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) reflects higher sexual performance at warmer temperatures (#354)
The reproductive interactions of females and males have evolved as a consequence of the confluence of interests but asymmetric costs borne by each sex. The two sexes have divergent strategies of energy investment that correspond with different life strategies. Due to this, it is possible that differing modes of reproductive investment between the sexes in insects are reflected by the thermal preference of each sex because metabolic energy release in ectotherms is dependent on temperature. The critical role of energy in male reproductive success is evident in male Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), where signaling and participation in leks or fruit guarding depends on stored lipid and sugar levels. Using thermal gradient assays, we found that male C. capitata preferred a temperature of 23.8±0.3˚C but females preferred 22.1±0.3˚C, and these preferences were significantly different. To explain this result, we tested a range of non-mutually exclusive explanations related to the energetic demands of sexual activity and reproductive output over the temperature range of 18-28˚C. We found that the frequency, total duration and mean length of calling bouts by male C. capitata were optimal at 26˚C. Mating propensity, mating latency and mean copula duration were optimised over the range of 22-28˚C, but when mating occurred, temperature had no effect on the incidence of sperm storage or the number of sperm stored by females. Female longevity was highest at 28˚C, but lifetime egg production was optimal at 24˚C. These results illustrate that there are differences in the reproductive fitness of the sexes in C. capitata at different temperatures, although the optima of measured traits do not align well with the thermal preference of each sex. It appears that higher average environmental temperatures may improve male sexual performance and female longevity, but fecundity may decline in the absence of adaptation or thermoregulatory behaviour.