Anagenetic evolution in island plants

Abstract

Aim Plants in islands have often evolved through adaptive radiation, providing the classical model of evolution of closely related species each with strikingly different morphological and ecological features and with low levels of genetic divergence. We emphasize the importance of an alternative (anagenetic) model of evolution, whereby a single island endemic evolves from a progenitor and slowly builds up genetic variation through time. Location Continental and oceanic islands. Methods We surveyed 2640 endemic angiosperm species in 13 island systems of the world, both oceanic and continental, for anagenetic and cladogenetic patterns of speciation. Genetic data were evaluated from a progenitor and derivative species pair in Ullung Island, Korea, and Japan. Results We show that the anagenetic model of evolution is much more important in oceanic islands than previously believed, accounting for levels of endemic specific diversity from 7% in the Hawaiian Islands to 88% in Ullung Island, Korea, with a mean for all islands of 25%. Examination of an anagenetically derived endemic species in Ullung Island reveals genetic (amplified fragment length polymorphism) variation equal or nearly equal to that of its continental progenitor. Main conclusions We hypothesize that, during anagenetic speciation, initial founder populations proliferate, and then accumulate genetic variation slowly through time by mutation and recombination in a relatively uniform environment, with drift and/or selection yielding genetic and morphological divergence sufficient for the recognition of new species. Low‐elevation islands with low habitat heterogeneity are highly correlated with high levels of anagenetic evolution, allowing prediction of levels of the two models of evolution from these data alone. Both anagenetic and adaptive radiation models of speciation are needed to explain the observed levels of specific and genetic diversity in oceanic islands.

Speciation Has a Spatial Scale That Depends on Levels of Gene Flow

“…We found strong evidence for a general positive relationship between area and the probability of in situ spe- (1) shows in situ, cladogenetic speciation (Stuessy et al 2006) in which a mainland species reaches an island and subsequently splits within the island into two new species. (2) shows how multiple colonization followed by anagenetic change, with no diversification within the island, can create the same pattern of multiple species within one genus that are endemic to the same island (Coyne and Price 2000;Stuessy et al 2006).…”

“…We considered the number of genera with at least one endemic species to represent the number of endemic lineages and the number of genera with two or more endemic species to represent the number of lineages that have diversified in situ (Coyne and Price 2000;Stuessy et al 2006). Therefore, our measure of the probability of speciation on a particular island was the number of genera with two or more endemic species divided by the number of genera with one or more endemic species.…”

“…(2) shows how multiple colonization followed by anagenetic change, with no diversification within the island, can create the same pattern of multiple species within one genus that are endemic to the same island (Coyne and Price 2000;Stuessy et al 2006). (3) shows in situ, anacladogenetic speciation (Stuessy et al 2006), in which a mainland species reaches an island and remains unchanged while budding off an endemic daughter species. b, Phylogenetic patterns resulting from these three modes of island diversification.…”

An island view of endemic rarity—Environmental drivers and consequences for nature conservation

“…Besides phylogenetic effects (e.g., niche conservatism) and biogeographical history, environmental settings (e.g., climate, topography, disturbance regimes, species interactions) determine the range size of species (Brown et al, 1996). On high-elevation islands, which are often environmentally diverse but of small area, endemic species have evolved to realize niches in a wide range of habitats and environmental settings (Stuessy et al, 2006;Whittaker & Fernández-Palacios, 2007).…”

Assessing the role of cladogenesis in macroevolution by integrating fossil and molecular evidence

“…5,14,15). Addressing this question is challenging due to insufficient fossil data for most taxa and the difficulties in relating morphological change to genetic divergence and the evolution of reproductive isolation (16).…”