Molecular inference of a Late Pleistocene diversification shift inNigellas. lat. (Ranunculaceae) resulting from increased speciation in the Aegean archipelago

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Abstract
Aim To infer the temporal course and geographical mode of speciation in Mediterranean/Southwest AsianNigellas. lat.Location Mediterranean Basin, Aegean archipelago.Methods Phylogenies forNigellaL. andGaridellaL. (= Nigellas. lat.) were obtained from maximum‐likelihood analyses of internal transcribed spacer (ITS) sequences. Diversification through time was analysed by log lineages‐through‐time (LTT) plots and survival analyses. Relative node age estimates were regressed against the degree of sympatry between sister clades to infer the predominant mode of geographical speciation inNigellas. lat.Results The Late Pleistocene radiation of theNigella arvensiscomplex in the Aegean region caused a significant departure from a stochastic speciation/extinction process of diversification during the evolution ofNigellas. lat., a lineage of (at least) Late Miocene origin. Speciation withinNigellas. lat. predominantly took place in allopatry.Main conclusions No significant effect on diversification rate was found regarding the establishment of a Mediterranean‐type climate, or the onset of the Quaternary climatic oscillations. Rather, the accelerated rate of speciation in theN. arvensiscomplex is plausibly related toincreasedopportunities for allopatric speciation afforded by the (palaeo)geographical complexity of the Aegean archipelago combined with Late Pleistocene changes in climate and sea level. The evolution of self‐pollination and associated changes in habitat preference and flowering time further augmented speciation and niche differentiation within the complex, but these changes did not act as the primary promoters of the radiation process.