Molecular dating and biogeography of fig-pollinating wasps

Figs and fig-pollinating wasps are obligate mutualists that have coevolved for over 60 million years. But when and where did pollinating fig wasps (Agaonidae) originate? Some studies suggest that agaonids arose in the Late Cretaceous and the current distribution of fig-wasp faunas can be explained by the break-up of the Gondwanan landmass. However, recent molecular-dating studies suggest divergence time estimates that are inconsistent with the Gondwanan vicariance hypothesis and imply that long distance oceanic dispersal could have been an important process for explaining the current distribution of both figs and fig wasps. Here, we use a combination of phylogenetic and biogeographical data to infer the age, the major period of diversification, and the geographic origin of pollinating fig wasps. Age estimates ranged widely depending on the molecular-dating method used and even when using the same method but with slightly different constraints, making it difficult to assess with certainty a Gondwanan origin of agaonids. The reconstruction of ancestral areas suggests that the most recent common ancestor of all extant fig-pollinating wasps was most likely Asian, although a southern Gondwana origin cannot be rejected. Our analysis also suggests that dispersal has played a more important role in the development of the fig-wasp biota than previously assumed. (C) 2009 Elsevier Inc. All rights reserved.

Cyclamen: time, sea and speciation biogeography using a temporally calibrated phylogeny

Aim The Mediterranean region is a species-rich area with a complex geographical history. Geographical barriers have been removed and restored due to sea level changes and local climatic change. Such barriers have been proposed as a plausible mechanism driving the high levels of speciation and endemism in the Mediterranean basin. This raises the fundamental question: is allopatric isolation the mechanism by which speciation occurs? This study explores the potential driving influence of palaeo-geographical events on the speciation of Cyclamen (Myrsinaceae), a group with most species endemic to the Mediterranean region. Cyclamen species have been shown experimentally to have few genetic barriers to hybridization. Location The Mediterranean region, including northern Africa, extending eastwards to the Black Sea coast. Methods A generic level molecular phylogeny of Myrsinaceae and Primulaceae is constructed, using Bayesian approximation, to produce a secondary age estimate for the stem lineage of Cyclamen. This estimate is used to calibrate temporally an infrageneric phylogeny of Cyclamen, built with nrDNA ITS, cpDNA trnL-F and cpDNA rps16 sequences. A biogeographical analysis of Cyclamen is performed using dispersal-vicariance analysis. Results The emergence of the Cyclamen stem lineage is estimated at 30.1-29.2 Ma, and the crown divergence at 12.9-12.2 Ma. The average age of Cyclamen species is 3.7 Myr. Every pair of sister species have mutually exclusive, allopatric distributions relative to each other. This pattern appears typical of divergence events throughout the evolutionary history of the genus. Main conclusions Geographical barriers, such as the varying levels of the Mediterranean Sea, are the most plausible explanation for speciation events throughout the phylogenetic history of Cyclamen. The genus demonstrates distributional patterns congruent with the temporally reticulate palaeogeography of the Mediterranean region.

Diversification of a large genus in a continental biodiversity hotspot: temporal and spatial origin of Muraltia (Polygalaceae) in the Cape of South Africa

Phylogenetic relationships in the largely South African genus Muraltia (Polygalaceae) are assessed based on DNA sequence data (nuclear ribosomal ITS, plastid atpB-rbcL spacer, trnL intron, and trnL-F spacer) for 73 of the 117 currently recognized species in the genus. The previously recognised subgenus Muraltia is monophyletic, but the South African endemic genus Nylandtia is embedded in Muraltia subgenus Psiloclada. Subgenus Muraltia is found to be sister to subgenus Psiloclada. Estimates show the beginning of diversification of the two subgenera in the early Miocene (Psiloclada, 19.3+/-3.4 Ma; Muraltia, 21.0+/-3.5 Ma) pre-dating the establishment of the Benguela current (intermittent in the middle to late Oligocene and markedly intensifying in the late Miocene), and summer-dry climate in the Cape region. However, the later increase in species numbers is contemporaneous with these climatic phenomena. Results of dispersal-vicariance analyses indicate that major clades in Muraltia diversified from the southwestern and northwestern Cape, where most of the species are found today.

An extreme case of plant-insect co-diversification: figs and fig-pollinating wasps

It is thought that speciation in phytophagous insects is often due to colonization of novel host plants, because radiations of plant and insect lineages are typically asynchronous. Recent phylogenetic comparisons have supported this model of diversification for both insect herbivores and specialized pollinators. An exceptional case where contemporaneous plant insect diversification might be expected is the obligate mutualism between fig trees (Ficus species, Moraceae) and their pollinating wasps (Agaonidae, Hymenoptera). The ubiquity and ecological significance of this mutualism in tropical and subtropical ecosystems has long intrigued biologists, but the systematic challenge posed by >750 interacting species pairs has hindered progress toward understanding its evolutionary history. In particular, taxon sampling and analytical tools have been insufficient for large-scale co-phylogenetic analyses. Here, we sampled nearly 200 interacting pairs of fig and wasp species from across the globe. Two supermatrices were assembled: on average, wasps had sequences from 77% of six genes (5.6kb), figs had sequences from 60% of five genes (5.5 kb), and overall 850 new DNA sequences were generated for this study. We also developed a new analytical tool, Jane 2, for event-based phylogenetic reconciliation analysis of very large data sets. Separate Bayesian phylogenetic analyses for figs and fig wasps under relaxed molecular clock assumptions indicate Cretaceous diversification of crown groups and contemporaneous divergence for nearly half of all fig and pollinator lineages. Event-based co-phylogenetic analyses further support the co-diversification hypothesis. Biogeographic analyses indicate that the presentday distribution of fig and pollinator lineages is consistent with an Eurasian origin and subsequent dispersal, rather than with Gondwanan vicariance. Overall, our findings indicate that the fig-pollinator mutualism represents an extreme case among plant-insect interactions of coordinated dispersal and long-term co-diversification.