What drives diversification in a pantropical plant lineage with extraordinary capacity for long‐distance dispersal and colonization?

Abstract

AimColonization of new areas may entail shifts in diversification rates linked to biogeographical movement (dispersification), which may involve niche evolution if species were not exapted to new environments. Scleria (Cyperaceae) includes c. 250 species and has a pantropical distribution suggesting an extraordinary capacity for long‐distance dispersal and colonization. We investigate patterns of diversification in Scleria, and whether they are coupled with colonization events, climate niche shifts or both.LocationTropics and subtropics.TaxonNutrushes Scleria (Cyperaceae).MethodsWe used molecular data from three DNA regions sequenced for 278 accessions representing 140 Scleria taxa (53% of species) to develop a chronogram, model ancestral ranges and measure rates of diversification. Integrating data from 12,978 digitized and georeferenced herbarium records, we investigated niche evolution.ResultsHigh dispersal rates in Scleria, a genus with multiple dispersal syndromes, make reconstruction of ancestral ranges at deep nodes in the phylogeny highly equivocal. Main dispersal and colonization events involve movements from South to Central America (c. 19), from Africa to Madagascar (c. 12), from Asia to Oceania (c. 7), from Africa to South America (c. 7) and Central America to South America (c. 6). The two main shifts in diversification rates happened during the warm period of the Miocene.Main conclusionsDispersification from South America to Africa without climate niche shift seems to explain the diversification shift in section Hypoporum implying that species were exapted. Shifts in climate niche evolution predate the second shift in diversification rates suggesting lineages were exapted prior to biogeographical movements. Within subgenus Scleria, colonizations of Asia and Madagascar by sections Elatae and Abortivae, respectively, are coupled with niche shifts suggesting that these colonizations involved climate niche adaptation.

The evolutionary history of sedges (Cyperaceae) in Madagascar

“…An increase in subgenus Scleria has also been detected before (Larridon et al., 2020). These shifts in diversification rates were related to climate niche evolution (Larridon et al., 2020). Four further increases in diversification rates were detected: in a subclade within the crown clade of Rhynchospora ; a subclade within the crown clade of Eleocharis ; the Isolepis + Ficinia Clade; and the Schoenoplectus Clade.…”

“…The increase in diversification rates in Scleria section Hypoporum has been detected in a study focused on this genus (Larridon et al., 2020), but the additional increase in its crown clade was not. An increase in subgenus Scleria has also been detected before (Larridon et al., 2020). These shifts in diversification rates were related to climate niche evolution (Larridon et al., 2020).…”

“…Colonization after long‐distance dispersal (LDD) has been suggested as a common process to explain the disjunct distribution of many Cyperaceae species and lineages (Larridon et al., 2020; Martín‐Bravo et al., 2019; Spalink et al., 2016; Viljoen et al., 2013; Villaverde et al., 2017). Cyperaceae originated in South America in the late Cretaceous, and subsequently dispersed to reach their current cosmopolitan distribution (Spalink et al., 2016; current results).…”

“…Contrarely Carex originated in the Northern Hemisphere (Eastern Palaearctic) in the late Eocene and repeatedly colonized the Southern Hemisphere as well as a number of continental and volcanic islands (Martín‐Bravo et al., 2019). In Scleria , the rate of dispersal is so high that it is not possible to infer the ancestral range distribution with confidence (Larridon et al., 2020). The current study agrees with previous studies that Cyperaceae have colonized Madagascar repeatedly through LDD from the late Eocene (the timing of the biogeographic events are after the split of Madagascar from Africa) and from all continental land masses (Table 3).…”

Global dispersal and diversification of the genus Schoenus (Cyperaceae) from the Western Australian biodiversity hotspot

“…A genus that has received considerable taxonomic attention in recent years is Schoenus L. (Cyperaceae, tribe Schoeneae; Fig. 1), which is one of the ten most species-rich genera in the family (Govaerts et al, 2020;Larridon et al, 2020Larridon et al, , 2021. Schoenus is predominately an austral genus, with most of its species in Australia, New Zealand, southeast Asia, and southern Africa (Govaerts et al, 2020).…”