Adaptive significance of long mating with repeated intromissions in Zygogramma bicolorata

Long matings are abundant in insects despite the range of the costs involved. The causes and consequences of the evolution of long mating remain an interesting problem for behavioural ecologists. We studied extraordinarily long mating that involves repeated intromissions interspersed with latent periods in the Parthenium beetle (Zygogramma bicolorata). We conducted a series of interrupted mating assays to examine the fitness consequences of different components of this curious mating behaviour. We tested multiple adaptive hypotheses concerning male fertility and competitive ability. We found that sperm transfer and fertility did not exhibit a linear increase with the number of intromissions. There was also no evidence of nutrient transfer by the males. Interestingly, our results showed that both sexes suffered a significant cost of long mating. Further, female remating behaviour was found to be modulated by the length of previous mating. Additionally, males were observed performing a curious leg rubbing behaviour during the inter-intromission latent period, putatively serving as a copulatory courtship function that reduced female resistance to the continuance of mating. Therefore, we show that while the long mating may still serve a mate guarding role, there are additional fitness effects of such behaviour that need careful consideration. Our study provides insights into the adaptive significance of long mating and its fitness consequences.

Methods
The beetles were brought to the laboratory to setup a breeding population. Once established, the experiments were conducted by setting up mating trials. Most of the experiments were conducted in the laboratory. A few experiments, especially for mating behaviour characterization, were done outside the laboratory - under semi-natural setup.