Let's wait for the evening: nocturnal copulation in a tropical damselfly Phylolestes ethelae (Odonata, Synlestidae)

Abstract

Sexual selection is one of the main causes of the diversity of reproductive behaviours observed intra- and interspecifically. Here we study the reproductive behaviour of a unique species, Phylolestes ethelae, the only member of the family Synlestidae (Odonata) found in America. Our hypothesis was that the phylogenetic uniqueness of this species and the fact that it lives on an island would produce novel behaviours worth protecting as they are a part of the biodiversity. Between 2017 and 2019 we studied a population of P. ethelae in the National Park Armando Bermúdez in the Dominican Republic by means of mark-recapture techniques and focal observations. The survival rate was estimated as 0.953 ± 0.012 (SE), which translates into an expected lifespan of 20.6 days. We found that some males showed high site fidelity but very little activity, and territorial disputes were almost inexistent. Females, on the other hand, were rarely observed on the river, and were found mainly on the nearby paths and forest. We recorded 28 tandems and observed a total of 17 copulations, lasting an average of 18.6 min. Examination of sperm volumes in females interrupted during copulation indicated that males removed most of the sperm from the female bursa copulatrix during stage I of copula, but they could not remove sperm from the paired spermathecae. The duration of precopulatory tandem was highly variable (from 3 min to 7.8 h). In some cases, copulation was observed shortly (3 min) after tandem formation, mainly during the morning. However, some pairs formed during the morning, remained in tandem for several hours, and mated late, after dusk. Females laid eggs not accompanied by the male. Mating after the main peak of activity might be a strategy which protects sperm investment because females laying eggs after dusk are unlikely to be mated again that day. Further studies are needed to decipher phenotypic correlates of the males that mate after dusk.