Wright et al. (2006): The road from Santa Rosalia: A faster tempo of evolution in tropical climates.

Wright, S. D., J. Keeling, and L. N. Gillman. 2006. The road from Santa Rosalia: A faster tempo of evolution in tropical climates. Proceedings of the National Academy of Sciences, USA 103:7718-7722.

This study has demonstrated for the first time that molecular evolution proceeds at a faster tempo in the tropics than at higher latitudes. Forty-five woody rainforest plant genera were identified that have species occurring in both tropical and temperate climates. Numerous New Zealand species were included, in part because New Zealand carries into high latitudes a large number of woody plant genera that also occur in lowland tropical rainforest assemblages. For each genus one species was selected from the highest latitude and altitude possible and another selected from the lowest latitude and altitude possible. The ITS region of rDNA was then sequenced and substitution rates for each species pair were compared using a confamiliar outgroup. The rate of molecular evolution in the tropical species was found to be, on average, twice that in temperate species. Probably the most fundamental ecological pattern in nature is the declining species richness with increasing distance from the equator. It is suggested that differential rates of molecular evolution might provide the mechanism responsible for this pattern.