SEX ALLOCATION IN A SIMULTANEOUS HERMAPHRODITE, THE ZEBRA GOBY LYTHRYPNUS-ZEBRA - INSIGHTS GAINED THROUGH A COMPARISON WITH ITS SYMPATRIC CONGENER, LYTHRYPNUS-DALLI

The sexual pattern of the zebra goby, Lythrypnus zebra, is an apparent exception to sex allocation theory. Most L. zebra are simultaneous he rmaphrodites (i.e., have active female and male gonadal tissue), yet i t appears they do not reproduce as males and females simultaneously. U nderstanding the maintenance of simultaneous hermaphroditism in L. zeb ra could expand sex allocation theory. In this study, I used a compari son with the blue-banded goby, Lythrypnus dalli, a sympatric congener with a qualitatively similar sexual pattern, to investigate the role o f male spawning rate, body size and sexual flexibility in determining the sexual pattern of L. zebra and to isolate differences between the species that might explain their differing sexual patterns. Using fiel d measurements of male nesting success, I found no differences between the species in the body size of nesting males suggesting that large s ize is associated with successful male reproduction in both species. I n addition, nesting males spawned at approximately three times the rat e of females in both species; thus, reproduction via male function can be equally advantageous relative to adopting the female role. However , the nest longevity of L. zebra males was shorter than that of L. dal li males, suggesting reproduction via male function may be less reliab le in L. zebra. Finally, under laboratory conditions, L. zebra females tended to prefer large mates, and L. zebra were able to re-allocate i n both directions, exhibiting a greater capacity to switch than L. dal li. Given these results, I suggest that switching between the sexes pl ays a greater role in maintaining simultaneous hermaphroditism in L. z ebra than L. dalli, perhaps because male reproduction is not as consis tent in L. zebra. Sexual flexibility may be an important factor affect ing patterns of sex allocation, generally.