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Grass diversification in Madagascar: In situ radiation of two large C3 shade clades and support for a Miocene to Pliocene origin of C4 grassy biomes

Author:
Hackel, Jan, Vorontsova, Maria S., Nanjarisoa, Olinirina P., Hall, Russell C., Razanatsoa, Jacqueline, Malakasi, Panagiota, Besnard, Guillaume
Source:
Journal of biogeography 2018 v.45 no.4 pp. 750-761
ISSN:
0305-0270
Subject:
C3 plants, C4 plants, Miocene epoch, Pliocene epoch, Poaceae, bamboos, data collection, ecosystems, flora, forests, grasses, grasslands, habitats, immigration, indigenous species, models, phylogeny, Africa, Madagascar
Abstract:
AIM: Grasses (Poaceae) are found in all major habitats of Madagascar and have a particular importance in C₄ grasslands, whose origins are controversial. We aimed to estimate the number, age and origins of endemic grass lineages in the Madagascar region, and to compare the diversification of C₃ and C₄ taxa. LOCATION: Madagascar and the surrounding Indian Ocean islands, integrated within a global dataset. METHODS: We estimated 11 time‐calibrated molecular phylogenies including 73% of Madagascar's known grass flora (65% of endemics), using two calibration scenarios. Integrating the available sequences from worldwide grass species, a total of 1928 accessions were analysed. We tested range evolution models, estimated ancestral ranges, and compared the patterns of lineage accumulation between endemic C₃ and C₄ grasses. RESULTS: We recovered 69 lineages endemic to or with an estimated origin in the Madagascar region, 25 of them C₃ and 44 C₄. Range evolution analysis suggests widespread distance‐scaling of dispersal and strongest historical links to Africa. Extant grass diversity largely accumulated since the Miocene, with parallel increases in C₃ and C₄ taxa. Two large C₃ groups in the “Forest shade clade” (Paniceae: Boivinellinae) and the bamboos (subtribe Hickeliinae) have an estimated origin in the Madagascar region. Divergences and crown ages of endemic C₄ lineages largely coincide with the Miocene grassland expansion. MAIN CONCLUSIONS: Madagascar's extant grass flora is the result of multiple overseas dispersals, predominantly from Africa, and diversified from the Miocene onwards. C₃ grasses are characterized by two large presumed in situ radiations of shade grasses in the Paniceae and bamboos. Endemic C₄ lineages result from twice as many immigration events, resulting in smaller clades. Ages of C₄ lineages are consistent with a Pliocene or Late Miocene origin of grasslands in Madagascar, but estimating the nature and expanse of such early grasslands will require further research.
Agid:
5921566