Aim: To infer historical-biogeographical patterns and processes in South America based on estimated divergence times and ancestral distributions for a diverse clade of small marsupials (Monodelphis). Location: South America. Methods: We estimated a time-scaled phylogeny using sequence data from four nuclear genes and one mitochondrial gene for most currently recognized species, which we also scored for biome occupancy. We used maximum-likelihood methods that explicitly model historical-biogeographical processes to estimate ancestral distributions. Results: The earliest cladogenetic events in the genus occurred in the late Miocene, with subsequent diversification from the early Pliocene to the late Pleistocene. Model selection suggests an important role for founder-event speciation, a process seldom accounted for in previous biogeographical analyses of continental clades. Two equivalently optimal models that incorporate this process each reconstruct the most recent common ancestor of Monodelphis as occurring in both Amazonia and the Atlantic Forest, from which the Andes, the Arid Diagonal (Caatinga, Cerrado, Chaco) and other neighbouring biomes were colonized during the Pliocene and Pleistocene. Main Conclusions: The diversification of Monodelphis was not restricted to a narrow time interval, suggesting that speciation cannot be attributed to a single leading factor such as tectonism or Pleistocene climatic fluctuations. In particular, speciation within the Atlantic Forest biome appears to have occurred in the Neogene, whereas most Amazonian speciation events are substantially younger. Amazonia and/or the Atlantic Forest hosted most diversification events within Monodelphis and were the historical sources of lineages that subsequently colonized other areas. Founder-event speciation, a concept traditionally associated with long-distance dispersal among islands, must sustain other interpretations in historical-biogeographical analyses of non-vagile organisms in continental contexts. Possible mechanisms for founder-event speciation in Monodelphis include historically transient connections between currently disjunct biomes and rapid reproductive isolation of populations colonizing adjacent but ecologically disparate biomes.
Bibliographical noteFunding Information:
We are grateful to Nick Matzke for help with ancestral-range analyses, and to Ana Pavan, Andr? Carvalho, Bernardo Santos and Ivan Prates for suggestions on previous versions of the manuscript. The manuscript benefited from comments by three anonymous referees. The many friends and colleagues who donated tissues and other resources that were crucial for our sequencing work are acknowledged in Pavan et?al. (). That work was funded, in part, by National Science Foundation grants DEB-743062 (to S.A.J.) and DEB-743039 (to R.S.V), whereas S.E.P. was supported by fellowships from the City University of New York and the American Museum of Natural History. A grant from Labex CEBA (Centre d'?tude de la biodiversit? amazonienne) allowed S.E.P. to attend the Thematic School on Advanced Methods in Neotropical Biogeography (French Guiana, 2013).
- Atlantic Forest
- South America
- ancestral-range estimation
- dated phylogeny
- founder-event speciation