Group-spawning and Simultanous Polyandry of a Stream-dwelling Frog Feirana kangxianensis

Here we provide an example of simultaneous polyandry based on genetic evidence in Feirana kangxianensis. This stream-dwelling species occurs only in Kangxian County, southern Gansu Province, where it is sympatric with its sibling species F quadranus. During the breeding season the sex ratio of F kangxianensis was marginally female-biased (44 male:59 female) and the encounter rate in a relatively pristine habitat was significantly higher than that in heavily quarried habitats (9.6 +/- 4.8 indiv./km vs. 3.2 +/- 2.5 indiv./km). Three egg masses containing an average of 698 eggs were deposited on the underside of one or two adjacent flat rocks, 6.0-10.0 cm under the water surface and 1.0-3.5 cm above the streambed. Using Bayesian sibship clustering of nine polymorphic microsatellite genotypes, two females were detected as group-spawning in one oviposition site, with three males fertilizing each female's eggs simultaneously. We also discuss the conservation requirements of this range-restricted species and the evolutionary implication of its unusual reproductive strategy.