Distribution of haplotypes and microsatellite alleles among Asian elephants (Elephas maximus) in Thailand

Abstract

Habitat fragmentation often promotes increased inbreeding depression due to interrupted gene flow between populations. In this study, we demonstrate that Asian elephants most likely also suffer from outbreeding depression due to cryptic speciation. We analysed mitochondrial and nuclear DNA loci from 78 Asian elephants. Haplotype genealogy and analysis of molecular variance revealed two matrilinear clades (αh, βh). Microsatellite analyses of individuals grouped according to their haplotype clade (corresponding group of nuclear genotypes called αnucand βnuc) revealed significant genotypic differentiation between αnucand βnuc. Such genealogically differentiated forms in a morphologically uniform species are considered indicative of cryptic speciation. The differentiation was caused by bulls, whereas considering cows only resulted in no differentiation. Such result is best explained by Haldane's rule whereby hybrid formation between genealogical forms causes lower viability and fertility of heterogametic hybrids. Although the lack of hybrid-specific morphological characteristics renders direct testing of reduced hybrid fitness under natural conditions unfeasible, the effects of Haldane's rule are demonstrated by reduced male-mediated gene flow between genealogical forms under sympatric conditions, as was indeed suggested by the data found in Asian elephants: male-mediated gene flow between groups αnucand βnucwas much lower than female-mediated gene flow. © 2007 Springer-Verlag.