Environmentally caused dwarfism or a valid species—Is Testudo weissingeri Bour, 1996 a distinct evolutionary lineage? New evidence from mitochondrial and nuclear genomic markers

Abstract

We examine the evolutionary relationships of the five traditionally recognized species of the western Palearctic tortoise genus Testudo ( T. graeca, T. hermanni, T. horsfieldii, T. kleinmanni, and T. marginata) and the newly described dwarfed species T. weissingeri by using sequence data of the mitochondrial cytochrome b gene and nuclear genomic fingerprints with inter-simple sequence repeats (ISSR). Testudo weissingeri differs from T. marginata mainly by its smaller size and some color-pattern characteristics. T. weissingeri lives in the driest, poorest and hottest part of the distributional range of T. marginata. While both data sets demonstrated phylogenetic distinctness of the five traditionally recognized species of Testudo, some subspecies and even some local populations, we detected no differentiation between T. marginata and T. weissingeri. We conclude that T. weissingeri is not a distinct evolutionary unit. We suggest that its small size is the result of suboptimal environmental conditions with limited resources and synonymize it with T. marginata. T. marginata and T. kleinmanni form a clade that is supported both by our mtDNA and nuclear genomic data sets. According to mtDNA data, this clade is the sister taxon to the T. graeca complex. A sister group relationship of T. hermanni and (( T. marginata + T. kleinmanni) + T. graeca) is moderately to weakly supported by mtDNA data; T. horsfieldii is the sister taxon to a clade comprising all other Testudo species.