Not what it looks like : mate-searching behaviour, mate preferences and clutch production in wandering and territory-holding female fiddler crabs

Risks inherent in mate-searching have led to the assumption that females moving sequentially through populations of courting males are sexually receptive, but this may not be true. We examined two types of fiddler crab females: wanderers moving through the population of courting males and residents that were occupying and defending their own territories. Sometimes residents leave territories to look for new burrows and we simulated this by displacing wanderers and residents and observing their behaviour while wandering. We predicted that the displaced wanderers would exhibit more mate-searching behaviours than resident females. However, wandering and resident females behaved nearly identically, displaying mate-searching behaviours and demonstrating matching mate preferences. Also, males behaved the same way towards both female types and similar proportions of wanderers and residents stayed in a male's burrow to mate. But more wanderers than residents produced egg clutches when choosing a burrow containing a male, suggesting females should be categorized as receptive and non-receptive. Visiting and rejecting several males is not the defining feature of female mate choice. Moving across the mudflat by approaching and leaving a succession of burrows (mostly occupied by males) is an adaptive anti-predator behaviour that is useful in the contexts of mate-searching and territory-searching.9 page(s

Fighting in fiddler crabs Uca mjoebergi: what determines duration?

Contest duration in animals is often interpreted as being a consequence of mutual assessment of the difference in the competitors' resource-holding potential (RHP), allowing the inferior individual to avoid costly interactions it is likely to lose. Duration is thus predicted by the relative size of the competitors, and increases as the difference between them decreases. Alternatively, each individual may persist in accordance with thresholds determined by its own RHP, and weaker rivals retreat because they have lower thresholds. Contest duration depends on the RHP of the contestant that gives up first. Recent work suggests that even though duration is determined by the loser's size, this hypothesis also predicts a negative correlation between duration and the relative RHP of the contestants. However, it predicts (unlike the mutual assessment hypothesis) that contest duration should increase with the mean size of the contestants. We studied the determinants of fighting duration in the fiddler crab Uca mjoebergi. Fight duration increased with increasing size of the loser, and decreased, but to a lesser extent, with increasing size of the winner. Fights between size-matched individuals increased in duration with increasing mean size of the competitors. Neither the mutual assessment nor own-RHP-dependent persistence hypotheses can accurately explain the data. Instead, we present a modification of recent modelling work, and suggest that in U. mjoebergi individual cost thresholds may determine duration, but that larger opponents may inflict those costs more rapidly, consistent with the cumulative assessment game of animal conflict.&nbsp