Temporal and spatial variation in female mating preferences in a fiddler crab

Abstract

Female mating preferences can vary temporally, with females choosing different males at different times; and spatially, with females in different populations preferring different males. This level of complexity is now well established, but we know of no evidence for a mosaic of female preferences within a single population. Here we show that, in the banana fiddler crab, Uca mjoebergi, female preferences vary both temporally and spatially. Females living in the high intertidal zone changed their mating preference for male size over the duration of the 9-day mating period every semi-lunar cycle: early mating females selected larger males with cooler burrows, slowing embryonic development; those mating later, selected smaller males with warmer burrows, accelerating development. Females living lower in the inter-tidal zone, however, did not show this temporal variation: they select the same sized males throughout the mating period. It is only in the high inter-tidal zone, at the start of the fortnightly mating period, that large size confers a mating advantage to males.

Mate choice and the operational sex ratio: an experimental test with robotic crabs

“…Male claw size in the population at the time of our study ranged from 4.6 to 25.4 mm (mean AE SD: 14.97 AE 4.29 mm; n = 222; based on transects). This is consistent with three recent estimates from the same study area [14.84 mm (n = 82), 14.95 mm (n = 199) and 14.9 mm (n = 177); Clark & Backwell, 2015]. Even though males within this size range all produce courtship waves, it is possible that the smaller males have burrows that are too narrow for females.…”

“…The results from female choice trials using robotic crabs have largely been corroborated by field studies of correlates of male mating success (e.g. Reaney & Backwell, ; Clark & Backwell, ). Given the large numbers of mate‐searching females and that females mate on the day that they begin to search (Clark & Backwell, ), it is highly improbable that we tested a female more than once.…”

“…The smallest, median and largest claw sizes we used were always the same (Table ). The mean ‘male’ claw size (18.2 mm) was larger than the mean for males whose burrows are inspected (16.0 mm; Clark & Backwell, ): 10 of the 15 ‘males’ had claws greater than 16.0 mm. This makes tests for a directional mating preference conservative, although only moderately so given that naturally 7 of 15 males are larger than average (assuming the median and the mean are the same).…”

“…Our mate choice experiments were conservative with respect to female choice for larger males as the mean test claw size (18.2 mm) was larger than the population mean (14.9 mm). The disparity was smaller when using the estimated mean of 16.0 mm based on males naturally visited by females (from Clark & Backwell, ). Ten of the 15 ‘males’ available across the three OSR treatments were larger than this mean.…”

Multimodal communication in courting fiddler crabs reveals male performance capacities

“…Female U. mjoebergi exhibit variation in their preference for male size, hence burrow volume (as the two are correlated), over the 9-day semi-lunar mating period [30]. It might, therefore, sometimes be detrimental for a male to provide additional information about burrow volume by drumming.…”