Abstract
L. aenigmamus is endemic to the limestone formations of the Khammuan Province (Lao PDR), and is strongly specialized ecologically. From the survey of 137 individuals collected from 38 localities, we studied the phylogeography of this species using one mitochondrial (Cyt b) and two nuclear genes (BFIBR and GHR). Cyt b analyses reveal a strong mtDNA phylogeographical structure: 8 major geographical clades differing by 5–14% sequence divergence were identified, most of them corresponding to distinct karst areas. Nuclear markers display congruent results but with a less genetic structuring. Together, the data strongly suggest an inland insular model for Laonastes population structure. With 8 to 16 evolutionary significant units in a small area (about 200×50 km) this represents an exceptional example of micro-endemism. Our results suggest that L. aenigmamus may represent a complex of species and/or sub-species. The common ancestor of all Laonastes may have been widely distributed within the limestone formations of the Khammuan Province at the end of Miocene/beginning of the Pliocene. Parallel events of karst fragmentation and population isolation would have occurred during the Pleistocene or/and the end of the Pliocene. The limited gene flow detected between populations from different karst blocks restrains the likelihood of survival of Laonastes. This work increases the necessity for a strict protection of this rare animal and its habitat and provides exclusive information, essential to the organization of its protection.
Highlights
Eroded limestone outcrops form a prominent part of the landscape in Southeast Asia
In a previous study we presented a preliminary analysis of the genetic diversity of L. aenigmamus [16]: 52 specimens were sampled and the population structure was surveyed by sequencing 887 base pairs of the Cytochrome b (Cyt b) gene
Given that: (1) private haplotypes are found for all clades, (2) Snn tests indicate that mtDNA defined clades are significantly differentiated for both nuclear genes, (3) pattern of differentiation between clades is clearer when both nDNA genes are combined, and (4) between clade divergence events mostly occurred recently; incomplete lineage sorting of the nuclear markers could explain the low genetic differentiation observed in nDNA
Summary
Eroded limestone outcrops form a prominent part of the landscape in Southeast Asia. Because of high limestone weathering [1,2] erosion in these areas resulted in scattered, isolated limestone hills with steep flanks called karsts towers. Despite a high diversity of habitat specialists and endemic taxa [3,4,5,6,7,8,9], these limestone karsts remain among the least studied ecosystems in Southeast Asia. Further studies demonstrated: first, that L. aenigmamus is a member of the Diatomyidae, a fossil family known from early Oligocene to late Miocene in Pakistan, India, Thailand, China, and Japan [14]; second, that the Diatomyidae are the sister group of the Ctenodactylidae, a family of small rodents found in rocky deserts across the northern parts of Africa; third, that together with the Hystricognathi, the Diatomyidae and the Ctenodactylidae form the suborder Ctenohystrica [15]
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