Has Vicariance or Dispersal Been the Predominant Biogeographic Force in Madagascar? Only Time Will Tell

Abstract

Madagascar is one of the world's hottest biodiversity hot spots due to its diverse, endemic, and highly threatened biota. This biota shows a distinct signature of evolution in isolation, both in the high levels of diversity within lineages and in the imbalance of lineages that are represented. For example, chameleon diversity is the highest of any place on Earth, yet there are no salamanders. These biotic enigmas have inspired centuries of speculation relating to the mechanisms by which Madagascar's biota came to reside there. The two most probable causal factors are Gondwanan vicariance and/or Cenozoic dispersal. By reviewing a comprehensive sample of phylogenetic studies of Malagasy biota, we find that the predominant pattern is one of sister group relationships to African taxa. For those studies that include divergence time analysis, we find an overwhelming indication of Cenozoic origins for most Malagasy clades. We conclude that most of the present-day biota of Madagascar is comprised of the descendents of Cenozoic dispersers, predominantly with African origins. Ignoring temporal information obscures the connection between biogeographic patterns and their underlying causes. Donoghue & Moore, 2003 You're either on the bus, or off the bus.

A well-sampled phylogenetic analysis of the polystichoid ferns (Dryopteridaceae) suggests a complex biogeographical history involving both boreotropical migrations and recent transoceanic dispersals

“…The alternative hypothesis, involving island-hopping across the Indian Ocean, should also be considered, as recent investigations have highlighted the critical role archipelagos that are currently immersed but were likely above water when the sea-level was low (but see Sheth et al, 2003 andThébaud et al, 2009) in the biogeography of the southwestern Indian Ocean region (Cuenca et al, 2008;Le Péchon et al, 2015;Renner et al, 2010;Strijk et al, 2014). An Asian origin of the Southwestern Indian Ocean Polystichum species is in line with the view that a large part of biota of Madagascar and nearby islands share strong biogeographical affinities with Asia (Warren et al, 2010;Yoder and Nowak, 2006). Polystichum subg.…”

Is the sword moss (Bryoxiphium) a preglacial Tertiary relict?

“…Furthermore, bryophytes may be prone to biotic dispersal across continents and oceans (Lewis et al, 2014). Altogether, these observations support the hypothesis that, in spore-producing plants (van Zanten and Pócs, 1981;Wolf et al, 2001) and other mobile organisms (Sanmartín and Ronquist, 2004;Yoder and Nowak, 2006;Perrie and Brownsey, 2007;Sanmartín et al, 2007;De Queiroz, 2014), dispersal has obscured any signature of vicariance. In fact, recent re-analysis of the only study inferring geographic vicariance due to continental drift in mosses (McDaniel and Shaw, 2003) yielded much younger ages for the relevant split that are incompatible with a continental drift scenario (Villarreal and Renner, 2014).…”

Large-scale phylogeny of chameleons suggests African origins and Eocene diversification

“…Oceanic dispersal has become fundamental to many biogeographic and diversification hypotheses [28,[73][74][75][76][77][78] even for taxa which were traditionally considered poor dispersers, such as amphibians [79][80][81]. Consideration of oceanic palaeo-currents and the timing of diversification events are both necessary components of many biogeographic scenarios.…”