Effect of temperature on sexual size dimorphism during the developmental period in the broad-horned flour beetle.

Adult size in numerous insects is strongly dependent on temperature. In several cases, a temperature-size rule is observed in which developmental temperature and adult size tradeoff. Although several previous studies have demonstrated the temperature-size rule, only a few have explored the relationship between developmental temperature and weapon traits or sexual size dimorphism. This study was conducted to investigate the size of the broad-horned flour beetle Gnatocerus cornutus when it was developed under different temperatures. G. cornutus males possess weapon traits for male-male combat and exhibit sexual size dimorphism in other morphological traits. Results showed that male weapon size and body size complied with the temperature-size rule. Furthermore, the extent of sex dimorphism in genae width, a weapon-supportive trait, were larger at lower temperatures. Our findings suggest that the temperature-size rule also influences the size of sexual traits.