Seasonal dynamics of social spacing and mate choice in Ulvaria subbifurcata

Abstract

The seasonal dynamics of aggression and social spacing; and mate choice of the radiated shanny, Ulvaria subbifurcata was examined using both laboratory and field observations. In addition, the role of aggression was examined in the context of territoriality and reproduction. -- A 12 month study demonstrated adult U. subbifurcata hold and defend a crevice site year-round. Hence, adults can be considered territorial. The field study also demonstrated that adults hold and and defend crevice sites from April to November. However, adult U. subbifurcata moved slightly offshore during winter months (December to March). Although not observed, it is suspected that while offshore adults also hold territories. It is thought that territoriality in U. subbifurcata is for shelter and reproduction. -- The laboratory and field observations also demonstrated that aggression in both sexes increased during the pre-reproductive period (March to May) and peaked during the reproductive period (May to July). A proportion of the increase in aggression in the pre-reproductive period can be attributed to territory establishment in the field. However, the increase in aggression during the reproductive period can be attributed to increased GSI and hormonal levels. Hence, aggression is important in the reproductive behaviour of the radiated shanny. -- To examine the role of aggression in reproduction in U. subbifurcata additional laboratory and field observations were performed. Observations indicated that there was variance in male spawning success. It was discovered that a high level of male aggression and large body size were both important criteria for female mate choice and subsequent male spawning success. Laboratory observations also indicated that female choice of spawning partners was based on active examination of all experimental males and nest sites before spawning. In addition, field observations indicated positive assortative mating. -- Aggression in U. subbifurcata changes temporally and appears to play an important role in territoriality and sexual selection, two important aspects of sociability.