Abstract
This study explored the extent to which the hermaphroditic and reproductive characteristics vary among five congeneric (Choerodon) and co-occurring species of the Labridae, a family in which hermaphroditism is widespread. Sampling was located in the large sub-tropical Shark Bay (26° S, 113° E), one of only twenty World Heritage Properties in Australia. Choerodon cephalotes, C. cyanodus, C. cauteroma and C. schoenleinii live within the main body of the embayment, which approaches the southern limit of their tropical, geographical ranges, whereas C. rubescens lives along its outer western boundary, close to the northern limit of its warm, temperate distribution. A combination of comprehensive length and age compositions, histological analyses of gonads and logistic regressions of lengths and ages at maturity and sex change are consistent with all five species being monandric protogynous hermaphrodites. Choerodon cephalotes, C. rubescens and C. schoenleinii are sexually dichromatic, with the lengths and ages of males at the extreme upper end of those of females and low proportions of males among adults (adult sex ratios, ASR: 11–33%). It is proposed that these species have polygynous mating systems, such as leks or harems. Although C. cauteroma has an ASR of essentially parity, its pronounced sexual dichromatism and the ages of its males typically lying at the upper end of those of its females indicate that this species also has a polygynous mating system. Limited sexual dichromatism and an ASR as high as 71% suggest that C. cyanodus is not polygynous. As the timing of the main spawning period of the four species within Shark Bay increases sequentially between early spring and late summer, the temperature trigger for spawning by those species also presumably increases progressively. This phasing of spawning, allied with some interspecific spatial variation, reduces the potential for competition among the larvae and early juveniles of the five Choerodon species. Choerodon rubescens spawns earlier in Shark Bay than in the cooler waters of the Abrolhos Islands, 230 km further south. The management implications of data for Choerodon species, and particularly of the size compositions and the ASRs of the two largest species, C. rubescens and C. schoenleinii, are discussed. The variations in the hermaphroditic and reproductive features of five congeneric species of labrid, in the region in which their distributions overlap, highlight the evolutionary/biological plasticity of this family and thereby contributes to its diversity and success.
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