A study in contrasts: two extensive Neotropical radiations

Lessa et al. (2014) make a compelling case for systematic exploration of genomes in the diverse South American rodent fauna. Not only do the caviomorph and sigmodontine rodents comprise a sizable portion of the continental fauna, but they have radiated into virtually all available habitats and have adopted practically all of the life modes exploited by rodents elsewhere. Both are diverse and demonstrably monophyletic, offering great insights into the evolutionary transitions underlying these presumably adaptive radiations. Here we comment on the non-South American portions of these radiations, as well as the broader phylogenetic context of these rodents, recent work on Caribbean taxa, and historical biogeography. Although both rodent radiations flourished in South America, neither is confined there, as clearly noted by the authors. Both groups extend far into North America, reaching the Arctic Ocean in the case of the caviomorph Erethizon and the central Great Plains in the cases of the sigmodontines Sigmodon and Oryzomys (IUCN, 2014), although only these three genera range north of Mexico (see Caviomorpha distribution in Figure 1). Both also underwent important, endemic radiations in the Caribbean, mainly on the Greater Antilles (Dávalos and Turvey, 2012). The Caribbean region constitutes one of three principal regions of endemism FIGURE 1 | Species richness of caviomorph rodents in the New World tropics (modified from Upham and Patterson, in press).