Serendipity and adaptation in New World marsupial evolution

Abstract

This is the frst study analyzing the distribution of New World marsupials and their relationship to climatic zones on a continental scale. We describe the distribution at diferent taxonomic categories (order, subfamily, tribe, genus) and their presence within climates, and discuss these patterns considering two diferent processes: serendipity or adaptation (i.e., a serendipitous process afects a taxon older than the climate it inhabits, or afects a taxon younger than the climate it inhabits but without the evolution of new traits; an adaptation process afects a taxon in a climate with the evolution of new traits). Living Didelphimorphia included the highest richness and least functional redundancy in Tropical climates at the four taxonomic categories studied; living Paucituberculata was mostly represented in Temperate climates, and living Microbiotheria was exclusively represented in Temperate climates. The most restrictive climates grouped generalized forms (e.g., scansorial animalivores) with a high order richness, but high functional redundancy and low richness for all the other taxonomic categories (i.e., subfamily, tribe, genus). Also, climates which favor complex habitats (e.g., tropical, subtropical and temperate forests) have a higher richness and functional redundancy, while simple habitats resulting from drier and/or colder climates have less specialized forms, albeit taxonomically singular (e.g., Lestodelphys, Chacodelphys, Caenolestes). Highly seasonal climates grouped generalized taxa with high functional redundancy, and convergent adaptations (e.g., caudal fat storage, torpor or hibernation), while stable climates over long periods of time, acted as diversifcation centers for New World marsupials, especially Didelphimorphia.