Biology session

Same-generation individuals of an insect population spend their adult life more or less synchronously, but due to the variance in timing of emergence and lifespan, the synchrony is not perfect. Protandry, when males emerge earlier than females, is also typical. Between-sex asynchrony results in reduced mating opportunities, while within-sex asynchrony reduces mating and resource competition. However, no metrics exist that characterise this (a)synchrony between individuals in a population.

We define a reproductive synchrony index (RSi) to gauge individual-level mating opportunities for insect imagoes. RSi was calculated as a ratio of the number of days overlapping between the ith imago's lifespan and all opposites-sex individual's lifespan to the maximum number of days they could have shared, had they emerged the same day. Similarly, we computed a competitive synchrony index, CSi, to measure within-sex competition for mating, experienced by the ith individual. Finally, the synchrony of the whole population can be defined between-sex (RSp) to describe how individuals of a population exploit mating opportunities and within-sex (CSp) to measure the strength of mating competition.

RSi and CSi can be estimated from mark-recapture data that cover the entire reproductive period. We tested these indices on simulated and real mark-recapture data of the Clouded Apollo butterfly (Parnassius mnemosyne).

In contrast to adult and operational sex ratio, these indices emphasise individual differences in mating opportunities and competition. RSi and CSi declined over the reproductive period, and increased with lifespan. RSp and CSp can be used to compare synchronicity across different reproductive periods, populations, or species.