Ihlow, F., C. Spitzweg, M. Flecks, N. A. Poyarkov, P. P. Mohapatra, V. Deepak & U. Fritz

Unexpected lack of genetic and morphological divergence in a widespread tortoise – Phylogeography of Indotestudo elongata. pp. 183-194 plus Supplementary document 1.

Abstract. The diverse climatic and geological history of Southeast Asia has been a driving force behind significant Pleistocene and Holocene range dynamics and the consequent biological diversification in the region. Among the species exhibiting wide distributions, extending across several well-known zoogeographic barriers, the Elongated Tortoise (Indotestudo elongata) is noted for its extensive variability in size, shape, and colouration. To examine phylogeographic differentiation within I. elongata, we analysed three mitochondrial gene fragments (ND4, cyt b, and COI) for 52 individuals including fourteen historic specimens and 25 sequences obtained from GenBank. Phylogenetic analyses of the concatenated alignment revealed genetic homogeneity across the range, supported by a shallow mean uncorrected p distance of 1.2% in cyt b. This corresponds to a surprising lack of biogeographic structuring. Concordantly, multivariate statistical analyses of morphometric and colouration-related characters of 166 adult tortoises (79 males and 87 females) from Myanmar, Thailand, Cambodia, and Vietnam showed no statistically significant differences between biogeographic units. The lack of any phylogeographic signal and morphological differentiation despite the presence of significant biogeographic barriers is unusual for a terrestrial vertebrate from this region. Archaeological evidence suggests that Elongated Tortoises have been used as a food item for millennia. It could be that their current wide distribution and the absence of genetic differentiation are the result of a significant range expansion caused by extensive human-mediated dispersal over the prehistoric and historic tortoise trade. The observed lack of phylogeographic structure considerably simplifies conservation measures such as conservation breeding, reintroduction, and population reinforcement.

Key words. Testudines, Testudinidae, biogeography, geographic variation, historical DNA, human-mediated transport, mitochondrial DNA, molecular genetics, morphology, museum specimens, Southeast Asia.