Introduction Amphibians are one of the most endangered groups of animals in semiarid regions (Stuart et al., 2004; Rissler and Apodaca, 2007; D' Amen and Bombi, 2009) and loss of their biodiversity is currently a major international concern (Blaustein and Kiesecker, 2002). This global concern regarding amphibians' decline is mainly due to their role as indicators of environmental stress and their impact on other animals (Blaustein et al., 1994; Blaustein and Wake, 1995; Fouquet et al., 2010). Amphibians are more sensitive to environmental toxins and changes in patterns of temperature or rainfall than other terrestrial vertebrate groups because of their highly permeable skins and because they inhabit both terrestrial and aquatic habitats during their life cycles at different stages (Alford and Richards, 1999). They are important components of many ecosystems where they may constitute the highest fraction of vertebrate biomass (Blaustein et al., 1994). Currently, 475 (7.7%) out of 6200 known amphibian species worldwide are classified as "Critically Endangered" (D' Amen and Bombi, 2009) and biologists believe that alarming declines of amphibians have occurred (Alford and Richards, 1999; Wake and Vredenburg, 2008; D' Amen and Bombi, 2009). Overall, complex causes including diseases, invasive species, pollution, climate change, solar radiation, and habitat fragmentation are associated with amphibian population declines that vary across species and areas (Alford and Richards, 1999; Blaustein and Kiesecker, 2002; Guisan and Thuiller, 2005; D' Amen and Bombi, 2009). Preservation of species requires an understanding of their biodiversity patterns. Knowledge about history, biology, and the relationship between species occurrence and climate condition can greatly support conservation planning (Rissler and Apodaca, 2007). Tree frogs of the genus Hyla Laurenti, 1768 are widely distributed throughout the Middle East. These small and semiaquatic vertebrates are generally dependent on open waters for their reproduction (e.g., pools, springs, artificial water reservoirs). Therefore, their distribution is limited by the availability of such habitats. Because of their relatively low mobility, the high and cold mountain ridges of Anatolia or the Iranian highlands and deserts in central Iran, the eastern Levant, or most of the Arabian Peninsula might be effective barriers to their dispersal (

Secondary contact zones have been formed between several pairs of avian species and subspecies in northern and north-eastern Iran during the post-Pleistocene and Holocene periods. Three subspecies groups out of the four in the great tit (Parus major), major, bokharensis and cinereus, are believed to have come into local or regional secondary contact in north-eastern Iran. Parus major intermedius is also known from this region and has long been suggested to have a hybrid origin from hybridization between the yellow western (major) subspecies group and the grey-coloured eastern (bokharensis or cinereus) subspecies group based on its intermediate plumage coloration. Here, we investigated the evidence of intergradation between subspecies groups and the evolutionary origin of P. m. intermedius using mitochondrial DNA sequences and microsatellites, and approximate Bayesian computation to test competing scenarios for the demographic history of the populations. Our analyses indicate a divergence origin for intermedius that resulted from expansion of the major subspecies group. Low mitochondrial diversity and high genetic differentiation in comparison with central populations suggest that intermedius is a peripheral population. Microsatellite data show no signs of nuclear admixture between the bokharensis and major subspecies groups. However, one phenotypically intermedius specimen had bokharensis mtDNA and major nuclear DNA in the assumed hybrid zone (Lotf Abad), supporting past introgression.