Genetic diversity patterns across habitats and forms of a morphologically cryptic South Asian frog (Sphaerotheca...

Sphaerotheca maskeyi (Dicroglossidae) is a medium-sized South Asian frog. It is of conservation concern due to its global declining population trend. This study aimed to (1) determine the phylogenetic placement of S. maskeyi, (2) assess genetic variation across contrasting habitat types (natural vs. degraded), and (3) compare genetic diversity between two distinct morphotypes (dotted and rusty forms) by using mitochondrial (16 S rRNA) and nuclear (RAG-1) gene markers.

Phylogenetic analyses using both Maximum Likelihood and Bayesian inference consistently placed all sampled individuals within the Sphaerotheca maskeyi clade, clearly distinct from its congeners. Comparisons of genetic diversity between habitat types revealed that populations from natural habitats showed numerically higher but statistically non-significant values for both mitochondrial and nuclear markers (16 S: Hd = 0.963, π = 0.063; RAG-1: Hd = 0.9818, π = 0.0237) than those from degraded habitats (16 S: Hd = 0.760, π = 0.054; RAG-1: Hd = 0.9556, π = 0.0175). Analysis of molecular variance (AMOVA) for both loci indicated that most genetic variation was partitioned within populations rather than among them. Similarly, comparisons between morphotypes showed that the rusty form exhibited numerically higher but statistically non-significant nucleotide diversity for both genes (16 S rRNA: Hd = 0.222, π = 0.00210; RAG-1: Hd = 1.000, π = 0.01258) than the dotted form (16 S rRNA: Hd = 1.000, π = 0.00059; RAG-1: Hd = 0.933, π = 0.00517). AMOVA indicated moderate but marginal and statistically non-significant genetic differentiation between the two morphotypes (FST = 0.09057, p = 0.058), suggesting weak genetic structuring and providing no strong evidence for pronounced genetic divergence between the two forms.

Frogs from natural habitats and of the rusty morphotype showed higher but statistically non-significant genetic diversity, with most variation occurring within populations and only weak, non-significant genetic structuring between morphotypes, indicating no strong genetic divergence.