Phylogeography and seed dispersal in islands: the case of Rumex bucephalophorus subsp. canariensis (Polygonaceae)

Abstract

Background and aims: Rumex bucephalophorus subsp. canariensis is an endemic taxon to Macaronesia with diaspore polymorphism. The origin and colonizing route of this taxon in Macaronesia was studied using molecular data and information on diaspore types.

Methods: Amplified fragment length polymorphism (AFLP) was used in 260 plants from 22 populations of R. bucephalophorus subsp. canariensis, four from the Madeiran archipelago and 18 from the Canary archipelago. Diaspore production was analysed in 9-50 plants from each population used for AFLP analysis. One hundred and one plants from the Madeiran archipelago and 375 plants from the Canary Islands were studied. For each plant the type of diaspore produced was recorded.

Key results: Overall populations had low genetic diversity but they showed a geographical pattern of genetic diversity that was higher in the older eastern islands than in the younger western ones. Two types of dispersible diaspores were found: in the eastern Canary islands (Lanzarote, Fuerteventura and Gran Canaria), plants produced exclusively long-dispersible diaspores, whereas in the western Canary islands (Tenerife, La Gomera, El Hierro) and the Madeiran archipelago plants produced exclusively short-dispersible diaspores. Genetically, the studied populations fell into four main island groups: Lanzarote-Fuerteventura, Gran Canaria, Tenerife-El Hierro and La Gomera-Madeira archipelago.

Conclusions: A Moroccan origin of R. bucephalophorus subsp. canariensis is hypothesized with a colonization route from the eastern to the western islands. In addition, at least one gene flow event from La Gomera to the Madeiran archipelago has taken place. During the colonization process the type of dispersible diaspore changed so that dispersability decreased in populations of the westernmost islands.

Fig 1.

The Macaronesian region. For each archipelago, the period of formation is indicated in parentheses; zero indicates volcanic eruptions that have continued through historical times. The minimum distance separating the islands from each other is also indicated. (A) The locations of the four sampled populations of Rumex bucephalophorus subsp. canariensis in the Madeiran archipelago. (B) The locations of the sampled populations of Rumex bucephalophorus subsp. canariensis in the Canary archipelago.

Fig. 2.

(A) The tree generated by SplitsTree composition, based on the genetic distances of Nei and Li, for 22 populations of Rumex bucephalophorus subsp. canariensis, and four populations of R. bucephalophorus that are representatives of the two closest subspecies (R. bucephalophorus subsp. hispanicus and R. bucephalophorus subsp. gallicus). The population numbers correspond to those in Table 1. The branches indicate the value of the support (10 000 replicates) if >50 %. (B) The genetic structure of Rumex bucephalophorus subsp. canariensis inferred by Bayesian clustering of AFLP data, with assignment of 260 K into individual genetically distinguishable groups. Each individual is represented by a coloured vertical bar assigned according to the group(s). Populations are identified in Table 1. The band shows the most stable and likely assignment estimated by the structure (at K = 4) (see text). (C) Naperian logarithm of the posterior probability of the AFLP data, lnP(D), according to the different possible clusters (K) in R. bucephalophorus subsp. canariensis. The most probable K value is indicated by an arrow.