Phylogenetic and phylogeographic evidence for a Pleistocene disjunction between Campanula jacobaea (Cape Verde Islands) and C. balfourii (Socotra)

Abstract

Our understanding of processes that led to biogeographic disjunct patterns of plant lineages in Macaronesia, North Africa and Socotra remains poor. Here, we study a group of Campanula species distributed across these areas integrating morphological and reproductive traits with phylogenetic and phylogeographic data based on the obtention of sequences for 4 highly variable cpDNA regions and AFLP data. The phylogeny obtained shows a sister relationship between Campanula jacobaea (endemic to Cape Verde Islands) and C. balfourii (endemic to Socotra), thus revealing a striking disjunct pattern (8300 km). These species diverged around 1.0 Mya; AFLP and haplotype data suggest that no genetic interchange has occurred since then. Their closest taxon, C. hypocrateriformis, is endemic to SW Morocco. The archipelagos of Macaronesia and Socotra have probably acted as refugia for North-African species, leading to speciation through isolation. Although C. balfourii has a restricted distribution, its genetic variability suggests that its populations have suffered no bottlenecks. C. jacobaea is also genetically rich and its distribution across Cape Verde Islands seems to have been influenced by the NE-SW trade winds, which may also have favoured the admixture found among the populations of the three southern islands. Floral features of the morphologically hypervariable C. jacobaea were also measured to assess whether the taxon C. bravensis, described for some of the southeast populations of C. jacobaea, corresponds to a different evolutionary entity. We show that morphological variation in C. jacobaea does not correspond to any genetic or geographic group.

Keywords: Biogeography; Campanula bravensis; Climatic fluctuations; Colonisers; Macaronesia; Phylogeny.