Repeated evolution of terrestrial lineages in a continental lizard radiation

• Published in: Journal of evolutionary biology 2020-01, Vol.33 (1), p.57-66
• Main Authors: Lajmi, Aparna, Verma, Anjali, Karanth, K. Praveen
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Adaptive radiation; Animals; Body size; climate; Diversification; ecological opportunity; Ecosystem; Evolution; Genetic Speciation; Grasslands; Hemidactylus; India; late Miocene aridification; Lizards - anatomy & histology; Lizards - classification; Microhabitats; Morphology; Peninsular India; Phylogeny; Small mammals; Terrestrial environments
• ISSN: 1010-061X; 1420-9101
• DOI: 10.1111/jeb.13544

The “early‐burst” model of adaptive radiation predicts an early increase in phenotypic disparity concurrent with lineage diversification. Although most studies report a lack of this coupled pattern, the underlying processes are not identified. The continental radiation of Hemidactylus geckos from Peninsular India includes morphologically diverse species that occupy various microhabitats. This radiation began diversifying ~36 Mya with an early increase in lineage diversification. Here, we test the “early‐burst” hypothesis by investigating the presence of ecomorphs and examining the pattern of morphological diversification in a phylogenetic framework. Two ecomorphs—terrestrial and scansorial species—that vary significantly in body size and toepad size were identified. Unlike the prediction of the “early‐burst” model, we find that disparity in toepad morphology accumulated more recently ~14 Mya and fit the Ornstein‐Ulhenbeck model. Ancestral state reconstruction of the two ecomorphs demonstrates that terrestrial lineages evolved independently at least five times from scansorial ancestors, with the earliest diversification in terrestrial lineages 19–12 Mya. Our study demonstrates a delayed increase in morphological disparity as a result of the evolution of terrestrial ecomorphs. The diversification of terrestrial lineages is concurrent with the establishment of open habitat and grasslands in Peninsular India, suggesting that the appearance of this novel resource led to the adaptive diversification. Morphological differences often accumulate late in adaptive radiations, however, the underlying processes are often not identified. We demonstrate a delayed increase in morphological disparity in a radiation of Hemidactylus geckos as a result of multiple independent evolution of ground‐dwelling lineages, in this group of largely climbing geckos. These ground‐dwelling geckos are predominantly distributed in open savanna habitats and their diversification is concurrent with the expansion of these habitats in the Late Miocene in the dry zone of Peninsular India.