Mating behaviour of the leucosiid crabPyrhila pisum(De Haan, 1841)

Abstract

Mating behaviour of the leucosiid crab Pyrhila pisum was studied in the laboratory and tidal flats in Japan. Most males actively approached females. Males started guarding females without any courtship behaviour (pre-copulatory guarding). Males began copulation within several minutes. The copulation continued for about 1–2 h, following which males began post-copulatory guarding. This guarding lasted from almost 0 to over 3 days, but its duration was generally much longer than that prior to copulation. Release of guarding was not linked to ovulation by females. Long-term rearing experiments revealed that both sexes of P. pisum could copulate multiple times with various mates. Developmental stages of the embryos recorded from copulating ovigerous females widely varied; their timing of copulation may not be fixed. In the tidal flat, wandering males frequently contacted with other individuals, but without distinguishing single males, single females and pairs of P. pisum, or Hemigrapsus takanoi. Male P. pisum cannot recognize female conspecifics, and they approach their mates relying only on vision, without using any attractive cues from females. In cases in which males encountered pairing crabs, they successfully stole the females when the guardians were smaller than the challengers, suggesting that effectiveness of guarding depends on male size. Among the mating pairs, males tended to be larger than females, and the tendency of size-assortative mating was weak or absent. Therefore, the mating behaviour of P. pisum is not elaborate, although their guarding behaviour may contribute to improve success to some degree.

Sexual traits and reproductive strategy of the leucosiid crabPyrhila pisum

“…The process of copulation and guarding behaviour of P . pisum was confirmed in our previous paper (Kobayashi & Vazquez Archdale, 2020). Female adult P. pisum copulated during their intermoult phase including in ovigerous condition.…”

“…Large seminal receptacles suggest that females copulate multiple times and accumulate semen. Under rearing conditions for about a month, females copulated at most six times with six mates (Kobayashi & Vazquez Archdale, 2020). No significant correlation between carapace width and the weight of the seminal receptacles means that the times of copulation varied irrespective of the female's body size.…”

“…The tendency that growth is more markedly expressed in the merus than in the propodus may suggest their importance for securing mates rather than for fighting with competitors in their mating strategy. More precisely, males did not contact competitors for a long time and spent much more time guarding their mates (Kobayashi & Vazquez Archdale, 2020).…”

“…This is shown in their mating behaviour. Although males of both groups guard females after copulation, the larger challengers with large chelipeds win during combat and successfully steal the females (Kobayashi & Vazquez Archdale, 2020).…”

“…They are found during the daytime actively wandering for long distances on sandy or muddy substrates along the shoreline, and often exhibit their mating behaviour without using shelters or burrows. Thus we have studied the ecology of this crab and recently reported its feeding habit, occurrence pattern in the intertidal area, reproductive ecology and mating behaviour (Kobayashi 2013; Kobayashi & Vazquez Archdale, 2017, 2020). We have revealed that the mating behaviour of P. pisum is not elaborate.…”