Abstract
The Great American Biotic Interchange (GABI) was greatly influenced by the completion of the Isthmus of Panama and impacted the composition of modern faunal assemblages in the Americas. However, the contribution of preceding events has been comparatively less explored, even though early immigrants in the fossil records are evidence for waif dispersals. The cricetid rodents of the subfamily Sigmodontinae are a classic example of a species-rich South American radiation resulting from an early episode of North American invasion. Here, we provide a temporal and spatial framework to address key aspects of the historical biogeography and diversification of this diverse mammal group by using mitochondrial and nuclear DNA datasets coupled with methods of divergence time estimation, ancestral area reconstruction and comparative phylogenetics. Relaxed-clock time estimates indicate that divergence of the Sigmodontinae began in the middle–late Miocene (ca. 12–9 Ma). Dispersal-vicariance analyses point to the arrival of a single lineage of northern invaders with a widespread ancestral distribution and imply that the initial differentiation between Central and South America gave rise to the most basal groups within the subfamily. These two major clades diversified in the late Miocene followed by the radiation of main tribes until the early Pliocene. Within the Oryzomyalia, tribes diverged initially in eastern South America whereas multiple dispersals into the Andes promoted further diversification of the majority of modern genera. A comparatively uniform background tempo of diversification explains the species richness of sigmodontines across most nodes, except for two akodontine genera with recent increases in diversification rates. The bridging of the Central American seaway and episodes of low sea levels likely facilitated the invasion of South America long before the onset of the post-Isthmian phase of the GABI.
Highlights
The Great American Biotic Interchange (GABI) is one of the major biogeographic events that shaped modern faunal communities in the Americas
The role of the GABI in shaping the historical biogeography and diversification of sigmodontine rodents has been debated on the basis of extensive paleontological work during the last few decades and, more recently, in the light of molecular phylogenetics
The oldest South American fossil remains found in Argentina and that can be undoubtedly ascribed to sigmodontines date from the late Miocene to early Pliocene [51,52,53], whereas previous phylogenetic studies using different molecular clock methods and sampling strategies place the origin of the sigmodontine radiation in the middle to late Miocene [37,57,58,59,103]
Summary
The Great American Biotic Interchange (GABI) is one of the major biogeographic events that shaped modern faunal communities in the Americas. As a consequence of asymmetrical dispersal dynamics and speciation and extinction rates between northern and southern contingents [3], more than half of the present-day mammalian genera in South America were derived from northern immigrants, contrasted with only 10% of North American genera that have southern ancestry [12] Possible explanations for this asymmetry involve dissimilar taxon pools, surface area, habitat availability and resource use [2,13]. Facilitated since the completion of the Isthmus of Panama at around 3.5 Ma [14,15,16], overseas dispersals prior to the main pulses of the GABI (starting at ,2.7 Ma) had an impact on the composition of terrestrial mammal communities as evidenced in mammal-bearing units of North and South America [17] The first of these records correspond to ground sloths that arrived in North America ca. These dates set only minimum ages for the initiation of the land mammal interchange [21]
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