Resolving species boundaries in the phenotypically diverse Bradypodion ventrale group
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2023-01-16
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Dwarf chameleons of the genus Bradypodion are a phenotypically diverse group of southern African endemics that underwent a rapid radiation beginning approximately 6 Mya. The phenotypic variation characterizing the youngest clades is thought to be due to ecologically driven diversification, resulting in convergent ecomorphological states across the different clades, but with divergent ecomorphological states between closely related taxa. For example, the Bradypodion ventrale species complex includes several described species (B. ventrale occurring in diverse shrubby habitats, and B. taeniabronchum, B. baviaanense and B. barbatulum occurring in montane fynbos), with an undescribed candidate species from the fynbos habitat at Groendal Nature Reserve in the Eastern Cape Province, South Africa. Mitochondrial DNA was able to fully resolve the status of most species in the complex; however, the status of the Groendal population is unclear. This population is parapatric with B. ventrale but occupies a very different habitat and has a seemingly different morphology. Nevertheless, because the two are closely related, there may still be sufficient gene flow detected between them, blurring species boundaries. To investigate whether the two populations could be considered separately evolving lineages, we combined fine-scale genetic markers (microsatellites) and a suite of morphological measurements to assess the differences between these populations. Data from 18 microsatellite loci revealed distinct genetic structure between B. ventrale and the Groendal chameleons, suggesting there is no present-day gene flow between them. The morphological evidence showed the Groendal chameleons to be similar to B. ventrale for overall head shape, but diverse in terms of tail, casque and limb size showing more similarity to B. taeniabronchum. Given that Groendal chameleons are genetically and morphologically different from B. ventrale, we suggest that gene flow between these species has ceased due to an ecological barrier, allowing the Groendal chameleons to undergo ecological diversification and placing them as a separately evolving population that is in the early stage of speciation.
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Dwarf chameleons of the genus Bradypodion are a phenotypically diverse group of southern African endemics that underwent a rapid radiation beginning approximately 6 Mya. The phenotypic variation characterizing the youngest clades is thought to be due to ecologically driven diversification, resulting in convergent ecomorphological states across the different clades, but with divergent ecomorphological states between closely related taxa. For example, the Bradypodion ventrale species complex includes several described species (B. ventrale occurring in diverse shrubby habitats, and B. taeniabronchum, B. baviaanense and B. barbatulum occurring in montane fynbos), with an undescribed candidate species from the fynbos habitat at Groendal Nature Reserve in the Eastern Cape Province, South Africa. Mitochondrial DNA was able to fully resolve the status of most species in the complex; however, the status of the Groendal population is unclear. This population is parapatric with B. ventrale but occupies a very different habitat and has a seemingly different morphology. Nevertheless, because the two are closely related, there may still be sufficient gene flow detected between them, blurring species boundaries. To investigate whether the two populations could be considered separately evolving lineages, we combined fine-scale genetic markers (microsatellites) and a suite of morphological measurements to assess the differences between these populations. Data from 18 microsatellite loci revealed distinct genetic structure between B. ventrale and the Groendal chameleons, suggesting there is no present-day gene flow between them. The morphological evidence showed the Groendal chameleons to be similar to B. ventrale for overall head shape, but diverse in terms of tail, casque and limb size showing more similarity to B. taeniabronchum. Given that Groendal chameleons are genetically and morphologically different from B. ventrale, we suggest that gene flow between these species has ceased due to an ecological barrier, allowing the Groendal chameleons to undergo ecological diversification and placing them as a separately evolving population that is in the early stage of speciation.
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