Phylogenetic and Ecogeographic Analyses of Selected Asclepiads of Pakistan

Abstract

This study covers phylogenetic and ecogeographic analyses of wild Asclepiadoideae taxa (commonly refened to as Asclepiads) using fresh field collections, herbarium specimens and in silico data obtained from European molecular biology laboratory databases. The basic aim of the study was to improve the understanding of various taxa (especially the subsubtribe Cynanchinae and Tylophorineae) through sample/species representation from Asia thus filling in the gaps in phylogeny of these asclepiads at global level; also to observe the distribution pattern of Asclepiads in Pakistan and assessing the impact of climate change on selected medicinal species of this group. The phylogenetic analysis of both subtribes were done using earlier defined methods but with modifications and addition of various molecular markers. (for e.g At2g06530, At2g34620) range from ITS, ETS, TrnT-F etc. The phylogenetic analysis covers two large subtribes of Asclepiadoideae i.e. Cynanchinae and Tylophorineae. The subtribe Cynanchinae (with 117 taxa and 4,168 characters) was treated with ITS, cpDNA and combined datasets analysed through Maximum Likelihood (ML), Maximum Parsimony (MP) and Bayesian Probability (BP) revealing improved support in major clades within Cynanchinae. The sub subtribe Tylophorineae (with 107 taxa and 3,659 characters) treated in a combined datasets (due to non-significant partition homogeneity. and no discordance between the cpDNA and the mDNA datasets) evidently showed Pentatropis as sister to rest of the clades, with improved support in BI and ML analyses. Both Vincetoxicum and Tylophora were confined not to be monophyletic. FLUihermore the ecogeogrphic data was treated for moisture relation, rarest species and impact of climatic changes through Maxent modeling. For this purpose, the passport data associated with 726 herbarium and field records of Asclepiads from Pakistan were studied. Altogether twenty eight wild species were recorded; the species richness and rarity patterns were recorded at 1 X 1 grid cells. The species-wise analyses showed the presence of Cynanchum and Vincetoxicum in the Northern parts of the country and maximum diversity and overlap among species was found in the n0l1heastern pmis of country: i.e. Rawalpindi, Islamabad and adjoining areas of Potohar platue. Ecologically, the percentage precipitation and seasonal temperatures were found as viii indirect indicators for species OCCUlTence. Similarly, most of the species were found concentrated at altitudes between 2000 and 4000ft. Ecological Niche Modeling (implemented In Maxent) was used to predict the potential ecological niches of three medicinally important Asclepiad species: Pentatropis spiralis, Tylophora hirsuta, and Vincetoxicum arnottianum. All three species differ in their ecological requirements, biogeographic importance and conservation value. The Maxent model based on herbarium and field data performed well for the three species with an average test AUC value of 0.84 for P. sp ira lis , 0.77 for V arnottianum, and 0.72 for T hirsuta. Under the future climate change scenario, the Maxent model predicted habitat gains for P. spiralis in southem Punjab and Tylophora hirsuta was predicted to lose habitat in patches in north em Punjab and Gilgit Baltistan. In conclusion, the attempt at understanding the phylogeny of selected taxa has improved the resolution for all clades and obtained cOlTespondence with the geographical occurrence of taxa. It provides sound evidences for inclusion of all related genera into larger genus Cynanchum. Further it is evident that Pentatropis maintained its position as sister ' to Vincetoxicum in Tylophorineae. Both Vincetoxicum and Tylophora are confined not to be monophyletic and the small genus Biondia is nested inside Tylophora clade. Furthermore the distributional pattem shows that most of the Asclepiads occur in Rawalpindi, Islamabad and adjoining areas of Potohar; species are concentrated between altitudinal range of 2000-4000ft. Pentatropis spiralis, Telosma cordata and Calotropis procera are most widely distributed species. Cynanchum petrense, Holostemma sp, Vincetoxicum canescens, Orthanthera sp, Ceropegia macrantha are designated rare and required immediate consideration for conservation. Modelling shows that Pentatropis spiralis and Vincetoxicum arnotianum will gain some habitats while temperature dependent Tylophora hirsuta will suffer lose in habitats in patches. The only possible further work in Cynanchinae would be lacking in this research is on type species of the American genus Metalepis and molecular dating for datasets. From ecological perspective, targeted studies for the respective areas for rare sp could be planned that will elaborate more facts.