Geographical variations in waving display and barricade‐building behaviour, and genetic population structure in the intertidal brachyuran crab Ilyoplax pusilla (de Haan, 1835)

Abstract

Geographic variations in two social behavioural characters, waving display and barricade building, and genetic population structure were examined in the tidal‐flat‐inhabiting dotillid crab Ilyoplax pusilla (de Haan, 1835), in six localities between the northern and southern limits of its distributional range (four localities from the Japanese mainland and two southern localities from the Ryukyu Islands). Although waving motion followed the same lateral–circular pattern in all of the local populations, cheliped‐extension at the wave peak was most prominent in the Yakugachi River population (near the distribution's southern limit in the Rykukyu Islands), followed by Haneji Inlet (the southern limit in the Ryukyu Islands) and four localities on the Japanese mainland in that order. The frequency of barricade building showed a similar trend, namely lowest in Yakugachi River, followed by Haneji Inlet and the four mainland localities. Genetic relationships among the six local populations revealed that the two southernmost populations (Yakugachi River and Haneji Inlet), particularly the former, differed significantly from the mainland populations. The similar geographic trend between social behaviour and genetic structure suggests a relationship at some level between the two.