COURTSHIP AND THE EVOLUTION OF UNDERGROUND MATING IN UCA TETRAGONON (DECAPODA, OCYPODIDAE)

Uca tetragonon is an Indo-West Pacific species of fiddler crab in the narrow-front (NF) species group. Male Uca tetragonon used display by c law-waving to attract females into burrows of males for mating. Pairin g attempts by male Uca tetragonon attracting conspecific females into their burrows occurred in 2 different ways. In type 1, males entered t heir burrows after their mates did, and, in type 2, males entered thei r burrows first and their mates followed. Both types occurred with sim ilar frequencies. Rate of pair formation and spawning rate of paired f emales were not significantly different between the 2 types. Nine of 2 0 females spawned in the pooled data from both types. In Indo-West Pac ific fiddlers, type 1 pair formation (female first) has been found in the 5 subgenera (NF and the broad-front species (BF) group) and type 2 (male first) previously only in the BF group, but now also in Uca tet ragonon. Type 1 is common to all subgenera of Uca in the Indo-West Pac ific, a criterion typical of ancestral characters. Since NF and BF gro ups are distinctly different in phylogenesis as well as in their ecolo gy, type 2 pair formation is supposed to be a derived behavioral chara cter in NF fiddlers, having evolved independently from the BF group.