Long mounting with repeated copulations in Zygogramma bicolorata: A test of adaptive significance of a curious mating behaviour

Long matings are abundant in insects despite the range of the costs involved. The causes and consequences of the evolution of long matings remain an interesting problem for behavioural ecologists. We studied the Parthenium beetle (Zygogramma bicolorata), which is known to show extraordinarily long copulations. Our detailed investigation showed, for the first time, that the long mounting in this species entails repeated copulation. Each of these copulations is preceded and succeeded by a leg-rubbing behaviour. We found the same characteristic pattern in laboratory and semi-natural conditions. We conducted a series of interrupted mounting assays to examine the fitness consequences of the duration of mounting. We tested multiple hypotheses regarding the transfer of sperm and non-sperm components, and the function of leg rubbing in modulating the female copulatory behaviour. Sperm transfer and fertility did not exhibit a linear increase with the number of copulations. There was also no evidence of nutrient transfer by the males. In contrast, our experiments reveal significant cost of long mounting in these beetles. We showed female remating behaviour can be modulated by the long previous mounting. Our data also suggest that leg rubbing may reduce female resistance to mating. While the long mating possibly serves as copulatory mate guarding, the males may increase their competitive ability through modulating female remating. We also propose leg rubbing to be a copulatory courtship behaviour. Our study provides preliminary insights into the evolution of long mating in such systems and necessitates further research on sexual selection.