Island hopping, long‐distance dispersal and species radiation in the Western Indian Ocean: historical biogeography of the Coffeeae alliance (Rubiaceae)

Abstract

Aim The Western Indian Ocean region (WIOR) is home to a very diverse and largely unique flora that has mainly originated via long‐distance dispersals. The aim of this study is to gain insight into the origins of the WIOR biodiversity and to understand the dynamics of colonization events between the islands. We investigate spatial and temporal hypotheses of the routes of dispersal, and compare the dispersal patterns of plants of the Coffeeae alliance (Rubiaceae) and their dispersers. Rubiaceae is the second most species‐rich plant family in Madagascar, and includes many endemic genera. The neighbouring archipelagos of the Comoros, Mascarenes and Seychelles also harbour several endemic Rubiaceae. Location The islands of the Western Indian Ocean. Methods Phylogenetic relationships and divergence times were reconstructed from plastid DNA data of an ingroup sample of 340 species, using Bayesian inference. Ancestral areas and range evolution history were inferred by a maximum likelihood method that takes topological uncertainty into account. Results At least 15 arrivals to Madagascar were inferred, the majority of which have taken place within the last 10 Myr. Most dispersal events were supported as being from mainland Africa, but Catunaregam may have dispersed from Asia. Although most Coffeeae alliance lineages are zoochorous, the general pattern of dispersals from Africa is incongruent with the biogeographic origins of the extant Malagasy volant frugivores. Several out‐of‐Madagascar dispersals were inferred to the neighbouring islands, as well as back‐colonizations of Africa. Main conclusions The African flora has been of foremost importance as source of dispersal to the islands of the Western Indian Ocean. Following the colonization of Madagascar, rapid radiations appear to have taken place in some clades, and Madagascar has also been an important source area for subsequent dispersal to the Comoros, Mascarenes and Seychelles.

Historical biogeography and phylogeny of the pantropical Psychotrieae alliance (Rubiaceae), with particular emphasis on the Western Indian Ocean Region

“…The Comoros, Mascarenes, and Seychelles have been postulated to serve as stepping‐stones for recent dispersal events toward Madagascar (e.g., angiosperms, Schatz, 1996; chamaeleons, Raxworthy et al, 2002). Our analyses of the Psychotrieae alliance, consistent with those by Wikström et al (2010) and Kainulainen et al (2017), do not support this hypothesis, but instead reveal that Madagascar has served as a stepping‐stone for subsequent colonization events to the rest of the WIOR (e.g., Craterispermeae, Fig. 3; the WIOR Psychotria lineage, Fig.…”

“…However, it does not tell us anything about the timing and direction or sequence of the island colonization within the WIOR, as well as the colonization events between the region and the rest of the tropics. Further, the high level of endemism and wide distribution of the alliance across the WIOR make this group of plants and the region an ideal model and geographic setting, respectively, for investigating the origins of insular biodiversity and dynamics of island colonization (see also Wikström et al, 2010; Kainulainen et al, 2017).…”

Ancestral range reconstruction of remote oceanic island species of Plantago (Plantaginaceae) reveals differing scales and modes of dispersal

“…Similarly, differing dispersal modes have also been inferred in explaining the historical biogeographies of other bird‐dispersed plant families with unique taxa on multiple oceanic islands (i.e. Asteliaceae [Birch & Keeley, ], Rubiaceae [Kainulainen et al., ]), and thus, evidence is building that there is not a single LDD model that fits all, but rather that a combination of stepping stone dispersal and extreme LDD can both shape insular floras within closely related plant groups, and that multiple floristic areas can be the sources of closely related island taxa.…”

“…The nearest landmasses are often implicated as the primary sources for island taxa, yet, as a result of bird-mediated LDD across extreme distances such as via the Pacific or Asia-Australian bird flyways, thousands of kilometres can separate some of the most closely related taxa (Baldwin & Wagner, 2010;Gillespie et al, 2012). Thus, LDD events mediated by bird vectors can result in multiple theories of biogeographic origins for island plant lineages (Birch & Keeley, 2013;de Queiroz, 2005;Kainulainen, Razafimandimbison, Wikstrom, & Bremer, 2017; le Roux et al, 2014). Applying biogeographical models and using molecular phylogenetic relationships to reconstruct source areas for island taxa can help resolve complex biogeographical histories, identify important areas of floristic exchange and elucidate dispersal routes that shape island floras (Bacon, Simmons, Archer, Zhao, & Andriantiana, 2016;Bouckaert et al, 2014;Ho et al, 2015;Johnson, Clark, Wagner, & McDade, 2017;Matzke, 2014).…”

Out of Africa? A dated molecular phylogeny of the cicada tribe Platypleurini Schmidt (Hemiptera: Cicadidae), with a focus on African genera and the genusPlatypleuraAmyot & Audinet‐Serville

“…This was followed by India colliding with Asia in the Eocene (50-35 Ma;Karanth, 2006;Aitchison et al, 2007;Ali & Aitchison, 2008), facilitating the transfer of lineages of Gondwanan origin into Asia (Karanth, 2006). Although Madagascar has been separated from Africa for 160 Ma, its proximity to the East African coast is thought to have allowed faunal interchange (Yoder & Nowak, 2006;Kainulainen et al, 2017;Bourguignon et al, 2018). Similarly, the proximity of India to the East African coast (Briggs, 2003) is thought to have facilitated faunal interchange before its eventual collision with Eurasia (Briggs, 2003).…”