Host plant associations and geographical factors in the diversification of the Macaronesian Rhopalomesites beetles (Coleoptera: Curculionidae)

Abstract

[Aim] To obtain nuclear and mitochondrial phylogenies of Macaronesian Rhopalomesites weevils and test the monophyly and time of origin of two species groups feeding on Euphorbiaceae and other plants. Additionally, to investigate the population structure within species, and its associations with geographical isolation versus trophic selection.

[Location] Macaronesian Islands and the British Isles.

[Methods] Maximum likelihood and Bayesian phylogenetic analyses were undertaken using mitochondrial (cox1 and cytb) and nuclear (ITS-2 and 28S RNA) genomic sequences. Ancestral Rhopalomesites host plant associations and divergence times were inferred from Bayesian analyses and population data.

[Results] Evidence was found for two Rhopalomesites clades. One was associated with Euphorbia host plants, having vicariant species in the Madeira and Canary archipelagos. In this lineage, an ancestral association with Euphorbia mellifera in the two island groups was deduced, which has subsequently undergone shifts to related host plant species in marginal areas. The second clade was found to be an ecological generalist, exploiting decaying wood from the Lauraceae or other forest trees – is also present on such islands along with the Azores and parts of Atlantic Western Europe.

[Main conclusions] The results point to a quasi-parallel colonization by the two ecologically distinct lineages in Macaronesia, dating to the early Pliocene, followed by allopatric isolation according to the presence of suitable habitats on particular islands in more recent times.