| Given the unprecedented waves of species extinctions in the Anthropocene,generating knowledge on large clades of organisms has become essential for their conservation.This requires a better understanding of the evolutionary and ecological processes at both a macro and a micro scale,which includes life histories,diversification processes,genetic composition of populations,historical distribution patterns,how ecosystems and biomes develop over time and responses to past climatic events.Among vertebrates,amphibians are known to show the highest propensity to go extinct.This dissertation focuses on the remarkable diversification of rhacophorid frogs(family Rhacophoridae)commonly known as ?old world tree frogs‘,which represent 6% of global amphibian diversity,utilize four distinct reproductive modes,and span a climatically variable area across mainland Asia,associated continental islands,and Africa.To date,out of the 426 rhacophorid species described,17 extinct,26 critically endangered,40 endangered,26 near threatened and 36 vulnerable species have been recorded.As a proportion of extinct species in an amphibian family,rhacophorids holds a higher proportion(4%)which depicts the importance of generating knowledge for their conservation.Here,I intend to generate knowledge on their species boundaries,evolutionary ecology,climatic niche evolution,biogeography,population genetics and morphological evolution to facilitate conservation.In a macro-evolutionary scale analysis,I investigated the climatic niches of rhacophorid frogs and their correlates of evolution to get a deeper understanding on how their climatic niches evolved over time.I built a complete,species-level phylogeny for Rhacophoridae by integrating phylogenomic/Sanger sequence data and phylogenetic imputation to delineate patterns of their diversification.Lineage through time plots and subsequent spatial-mapping revealed near-constant diversification rates and highly uneven distributions of species richness,respectively in this group.Montane regions on islands and some mainland regions had higher phylogenetic diversity and unique assemblages of taxa.These regions represented tropical and subtropical broad leaf forest ecosystems and rainforests which comprised of cool-wet climatic conditions.These regions can be regarded as the refugia contributing towards generation and maintenance of their diversity across time.Climatic niche and phylogeography analyses explained how spatial and temporal structuring is shaped by the evolution of the climatic niches of these frogs.The results showed that starting from a center of origin,rhacophorids dispersed among distant refugia by adapting to new climatic conditions(?niche evolution‘-dominant),especially following the origin of key evolutionary innovations such as terrestrial reproduction(in the Late Eocene)or by dispersal during periods of favourable climate(?niche conservatism‘-dominant).Next,the biogeographical history and diversification of Rhacophoridae,distributed in five biogeographical regions was investigated.Using a biogeographical model-based approach,the role of dispersal by testing for alternative biogeographical hypotheses suggesting different centers of origin was investigated.Further,for fifteen diversification models,the effect of lineage isolation time,diversity-dependence,paleotemperatures,speciation and extinction rates,and major extinction events on the diversification of Rhacophoridae was tested.The biogeographical model testing approach confirmed an East/Southeast Asian center of origin(out of Asia),with dispersal likely mediated by plate tectonic evolution,sea level fluctuations and climate changes.The best-fitting diversification models explained that the diversification of Rhacophoridae were also mediated by lineage isolation time and paleotemperatures.However,diversity-dependent diversification models had low support.Speciation was linearly dependent on time and paleotemperatures,while extinction rates were either linearly or exponentially dependent in the best fitting diversification models.These results demonstrated that episodic major extinction events in the Indian Plate may have played a major role in shaping rhacophorid‘s early evolution thus favoring an Out of Asia hypothesis among the empirical models.Furthermore,in a micro-evolutionary scale,to identify genetic as well as environmental factors that limit the dispersal of Rhacophorids,I looked at the population structure,genetic variation,gene flow,phylogeography and climatic niche of Polypedates megacephalus(a foam nesting rhacophorid with high dispersal capabilities)in China.I combined multilocus genomic analyses of RAD-seq loci with an extensive compilation of climatic data,complemented by molecular species delimitation,species distribution modeling,climatic niche characteristics and phylogeography.I carried out field work within southern China and collected genomic tissue samples of 77 individuals of P.megacephalus belonging to 18 different localities spread across southern China.The collected tissue samples were subjected to Rad-sequencing and SNP based phylogenetic analyses.These results revealed a shallow but significant genetic structure of P.megacephalus in southern China.It was found that P.megacephalus originated around the Tibetan plataue during the late Pliocene and subsequently gave rise to six genetically distinct populations in southern China.Historically,complex changes in the region‘s geology(including formation of river barriers and formation of mountains)and climate altered the topology and environmental conditions,resulting in an initial fragmentation of habitat generating the several populations today.The populations seem to be in geneflow to a certain extent but are almost isolated by geographical distance.They seem to have experienced three severe population bottleneck events during their evolution and currently are in a phase of declining their effective population size.The stable climate envelopes in southern China appear to be climate refuges for P.megacephalus as well as barriers promoting population isolation.To further investigate the evolutionary correlates and patterns of dispersal in direct developing rhacophorids in a micro-evolutionary scale,the genus Pseudophilautus in Sri Lanka was used as a representative genus and carried out a study utilizing molecular systematics,morphological and climatic niche evolution.First,the species boundaries of Pseudophilautus in the context of the phylogenetic species concept was tested.A well resolved phylogeny included with several molecular loci(n DNA–Rag-1;mt-DNA– 12 S r RNA,16 S r RNA)was subjected to a molecular species delimitation analyses using the ABGD,b PTP,m PTP and b GMYC species delimitation methods.The study synonymized 16 previously described species and recovered 14 unidentified potential new species as well.The geophylogeny affirmed a species distribution across the island‘s aseasonal ?wet zone‘ and its three principal hill ranges,suggestive of allopatric speciation playing a dominant role,especially between mountain masses.Among the species that are merged by the delimitation analyses,a pattern leading towards a model of parapatric speciation(ongoing speciation in the presence of gene flow)emerged.Pseudophilautus also exhibited five different ecomorph categories—Tree-shrub dwellers,Leaf-litter forms,Rock-boulder forms,Generalists and Canopy forms—which showed a remarkable array of morphological specializations.Body size was a major determinant in their ecomorphological evolution,and their evolution supported a dynamic fitness landscape with larger bodies favoring over smaller bodies at a certain period time.Results further suggested that these ecomorphs likely evolved independently across the phylogeny,in different geographic regions,and at different altitudes,with accelerated morphological evolution during late Miocene to mid Pliocene,possibly owing to favorable cold and wet climates associated with Himalayan-Tibetan orogeny.The results further suggest that although direct developers have the capacity to live independent on water and become widespread,they may alternatively utilize their potential to specialize within their habitats thus limiting their spatial distribution.The knowledge generated in this study helps in broadening the knowledge on the evolution of old world tree frogs,their patterns of diversification,biogeography,climate correlates,population genetics,species boundaries and ecomorphological evolution.This further provides a deeper understanding on how the climatic niches of differently breeding rhacophorid frogs evolved towards shaping their diversity and distribution and will help facilitate the conservation of this remarkable diversification of tree-frogs. |
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