Explaining extreme differences in species richness among co-occurring palm clades in Madagascar

Evolutionary Journal of the Linnean Society, vol. 3

Abstract

Abstract Imbalance in species richness among related clades is a pervasive, yet incompletely understood feature of biodiversity. Comparison of species-poor and species-rich clades that have evolved within the same region can shed light on the mechanisms underlying this phenomenon. The long-isolated island of Madagascar is an ideal place for doing this. Madagascar harbours at least ten clades of palms (Arecaceae) that have colonized the island independently and diversified to widely differing degrees, ranging from one to 180 known species. We estimated colonization times and diversification rates for these clades based on an extensive phylogenomic dataset and tested the degree to which clades that arrived in Madagascar earlier have more species (time-for-speciation effect), finding a moderate effect. For context, we tested for time-for-speciation effects in other plant and animal lineages, finding variable but qualitatively similar results. Our findings suggest that variation in diversification rate (i.e. speciation and/or extinction rate) is a major driver of species richness imbalance among Malagasy clades, both in palms and elsewhere. We demonstrate that in palms, differences in diversification rates originated long before colonization of the island, suggesting a minor role of classical ‘island radiation’ and a stronger role of heritable traits driving diversification rate. Ability to colonize new climates also appears to play a role. Future work should address the interplay between the dynamic environment of Madagascar and the inherited traits of colonizing lineages to fully explain the island’s intriguing mix of species-poor and species-rich clades.

Authors 8

1. Wolf L. Eiserhardt corresponding

   Aarhus University · Royal Botanic Gardens, Kew

   Affiliation as printed

   Department of Biology, Aarhus University , Aarhus ,

   Royal Botanic Gardens , Kew, Richmond ,

   Department of Biology, Aarhus University, Aarhus, Denmark

   Royal Botanic Gardens, Kew, Richmond, UK

2. Lars Emil Svejgaard F Hansen

   Aarhus University

   Affiliation as printed

   Department of Biology, Aarhus University , Aarhus ,

   Department of Biology, Aarhus University, Aarhus, Denmark

3. Thomas L. P. Couvreur Aachen Naturalis Biodiversity Center Botany Section

   Naturalis Biodiversity Center · Centre de Coopération Internationale en Recherche Agronomique pour le Développement · Université de Montpellier · Diversité, adaptation et développement des plantes · Institut de Recherche pour le Développement

   Affiliation as printed

   DIADE, Université de Montpellier, IRD, CIRAD , Montpellier ,

   Naturalis Biodiversity Centre, Botany Section , Leiden ,

   Naturalis Biodiversity Centre, Botany Section, Leiden, The Netherlands

4. John Dransfield

   Royal Botanic Gardens, Kew

   Affiliation as printed

   Royal Botanic Gardens , Kew, Richmond ,

   Royal Botanic Gardens, Kew, Richmond, UK

5. Paola de Lima Ferreira

   Aarhus University

   Affiliation as printed

   Department of Biology, Aarhus University , Aarhus ,

   Department of Biology, Aarhus University, Aarhus, Denmark

6. Mijoro Rakotoarinivo

   University of Antananarivo

   Affiliation as printed

   Department of Plant Biology and Ecology, Faculty of Sciences, University of Antananarivo , Antananarivo , 

7. Sidonie Bellot

   Royal Botanic Gardens, Kew

   Affiliation as printed

   Royal Botanic Gardens , Kew, Richmond ,

   Royal Botanic Gardens, Kew, Richmond, UK

8. William J. Baker

   Aarhus University · Royal Botanic Gardens, Kew

   Affiliation as printed

   Department of Biology, Aarhus University , Aarhus ,

   Royal Botanic Gardens , Kew, Richmond ,

   Department of Biology, Aarhus University, Aarhus, Denmark

   Royal Botanic Gardens, Kew, Richmond, UK