Assortative mating in a fiddler crab

in Behaviour
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Non-random mating, particularly positive size-assortative mating, is common and can have major evolutionary consequences. The causes of size-assortative mating, however, are rarely examined. Here we explore the possibility of sexual selection, mate availability and mating constraints causing the strong correlation between male and female sizes in the fiddler crab Uca mjoebergi. We show that the full size range of males is available to females throughout the mating period, so mate availability is unlikely to cause size-assortative mating in this species. We also show that mechanical constraints do not prevent females from entering the burrows or mating with the full size range of males. We suggest that the strong size assortative mating that we observed throughout the mating cycle is driven by sexual selection. Both males and females prefer large partners. The benefit to mating with large partners needs further investigation.

Assortative mating in a fiddler crab

in Behaviour



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  • View in gallery

    (a) The size of the female and the male she selected as a mate. (b) The size of the females that mated on different days of the mating period. (c) The size of the rejected males over the duration of the mating cycle. (d) The distribution of visited but rejected males (grey lines) and males in the general population (black lines).

  • View in gallery

    The size of mated pairs (solid dots) and the size of pairs in which females were able to fit into the males’ burrows (open dots). Note that, for each solid dot, there are hollow dots below it; this indicates that females were able to fit into smaller burrows than the ones they selected.

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