Are we losing common and widespread species? Implications from the phylogeography of the floating frog (Occidozyga lima)

Background/Question/Methods

Conservation efforts generally focus on species that are rare and restricted in distribution, while those considered common and widespread are often overlooked. However, it is becoming apparent that commonness does not protect a species from extinction in this age of rapid environmental change. Moreover, the phenomenon of cryptic diversity raises the question of whether any truly widespread species exist at all. A cryptic species complex appearing to be widespread and unthreatened may obscure declines or extinctions of some species within the complex. The floating frog (Occidozyga lima) is a common lowland frog with a vast distributional range across tropical East Asia, but populations in South China have been undergoing declines recently due to extensive habitat loss. In order to determine whether these populations were distinct and potentially in need of conservation, we evaluated the genetic variation of O. lima based on 4650bp of DNA data (12S, 16S, 28S, ND1, tyrosinase and histone H3 genes) from 114 individuals representing multiple populations ranging from South China to Indonesia. Analyses were conducted using maximum parsimony, maximum likelihood and Bayesian inference.

Results/Conclusions

We discovered at least four distinct, well-supported lineages (South China, Myanmar, Indochina, Indonesia) across the species’ range, and the phylogenetic pattern matches the geographical pattern of mountain ranges. Our results suggest that O. lima is a cryptic species complex. Despite documented population declines in South China, O. lima is not regarded as threatened, because populations of its counterparts in other area of tropical East Asia are considered stable, and there is currently no regulatory protection for the species. The findings of this study provide an example of how a threatened species may be masked within a cryptic species complex and raise the specter of a loss of evolutionarily significant units before they are fully understood. These results have significant conservation implications for rapidly declining amphibian populations in tropical East Asia, where many species are still poorly known.