With similar ecological niches, coexisting closely related species usually differentiate to avoid competition for resources. However, the reproduction mode behind the coexistence remains unknown. Platyrhina tangi Iwatsuki, Zhang & Nakaya, 2011 and P. sinensis (Bloch & Schneider, 1801) are sister-species with similar morphologies and ecological niches. Both species have widespread distributions that overlap in southern Taiwan Strait and hence are ideal for the study of sympatric coexistence mechanism of closely related species. In this study, the reproductive biology of P. tangi and P. sinensis coexisting in the southern Taiwan Strait were analyzed and compared, including size at sexual maturity, reproductive cycle and reproductive activity season, fecundity, and size at birth, to assess the overlapping degree and differentiation of their reproductive niches. The two species possess similar sexual maturity lengths in the study area and had both shown distinct sexual dimorphism. The reproductive cycle of both species was about one year. Still, the childbirth behavior of P. tangi took place half a year later than P. sinensis, proofing the occurrence of reproductive periods differentiation. Both species have adopted embryonic diapause as a reproductive strategy, but the duration of diapause is different. Compared to P. sinensis, P. tangi possesses a higher fecundity. Results have shown that although the two species overlapped highly in reproductive traits, there are significant temporal differences between their reproductive periods. This temporal differentiation of reproductive biology may be the key factor driving the coexistence of two niche-similar species in the study area, which is conducive to related studies.

comparative reproductive biology, sympatric, closely related species, southern Taiwan Strait