title: Why are some species older than others? A large-scale study of vertebrates.
abstract: BACKGROUND
  Strong variations are observed between and within taxonomic groups in the age of extant species and these differences can clarify factors that render species more vulnerable to extinction. Understanding the factors that influence the resilience of species is thus a key component of evolutionary biology, but it is also of prime importance in a context of climate change and for conservation in general. We explored the effect of extrinsic and intrinsic factors on the timing of the oldest diversification event in over 600 vertebrate species distributed worldwide. We used phylogenetic comparative methods to show that color polymorphism, latitude and reproduction (the latter through its interaction with latitude) affected the timing of the oldest diversification event within a species.
  
  
  RESULTS
  Species from higher latitudes tended to be younger, and colour-polymorphic species were older than monomorphic species. Mode of reproduction was important also, in that the age of oviparous species decreased with latitude, whereas no pattern was apparent for viviparous species. Organisms which have already persisted for a long time may be more likely to deal with future modifications of their environment.
  
  
  CONCLUSIONS
  Species that are colour polymorphic, viviparous, and/or live at low latitudes have exhibited resilience to past environmental changes, and hence may be better able to deal with current climate change.
authors.affiliation: Department of Ecology and Evolution, Biophore Building, University of Lausanne, 1015, Lausanne, Switzerland.
authors.forename: Laure
authors.initials: L
authors.lastname: Cattin
authors.affiliation: Department of Ecology and Evolution, Biophore Building, University of Lausanne, 1015, Lausanne, Switzerland.
authors.forename: Johan
authors.initials: J
authors.lastname: Schuerch
authors.affiliation: Department of Ecology and Evolution, Biophore Building, University of Lausanne, 1015, Lausanne, Switzerland.|Swiss Institute of Bioinformatics, Quartier Sorge, 1015, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Salamin
authors.affiliation: Department of Ecology and Evolution, Biophore Building, University of Lausanne, 1015, Lausanne, Switzerland. sylvain.dubey@unil.ch.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Dubey
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D057231:Climate Change; D004777:Environment; D049810:Genetic Speciation; D010802:Phylogeny; D012098:Reproduction; D014714:Vertebrates / Q000235:genetics*
keywords: Colour polymorphism; Intraspecific diversification; Latitude; Oviparity; Species age; Viviparity