Adaptive radiations as windows to the evolution of diversity: the spider genera Dysdera and Hogna in the Madeira archipelago

Abstract

Dysdera and Hogna are the most speciose spider genera of the Madeira archipelago. I have extensively revised their taxonomy, describing a total of eleven new species, establishing five synonyms and revalidating one name, using illustrations, SEM and stereomicroscope imaging for descriptions. I tested their phylogenetic placement and their monophyly with a multi‐locus target gene phylogeny using both mitochondrial (cox1, 16S+L1, ND1, 12S) and nuclear markers (28S, H3, ITS‐2), while at the same time running single gene (cox1) based species delimitation methods, which, in turn, would be integrated with the morphological data to infer on species boundaries. In the case of Hogna, I have generated haplotype networks for two genes (cox1 and ITS‐2) to show the structure of haplotypes across species. I performed time‐calibrated phylogenetic analyses for both genera using different frameworks.

Results indicate that Madeira was colonized by Dysdera at least twice, with a speciose clade represented by ten species and another represented by a single species, in both cases with Iberian or Moroccan ancestry. The single species lineage shares a common ancestor with congenerics found in the remote archipelago of Azores, being adapted to coastal habitats, which probably favoured oceanic long‐distance dispersal by means of rafting. The Madeiran clade of Hogna appears monophyletic, although methodological support is low. Species delimitation methods did reveal geographic structure for several Dysdera species, but in general agreed with morphological data to assess species boundaries. In Hogna, however, we have uncovered a remarkable case of two species, H. insularum (Kulczynski, 1899) and H. maderiana (Walckenaer, 1837), which cannot be differentiated by either morphology or any molecular based species

delimitation method. I discuss the possibility of hybridization as reported in other members of the genus, and we are developing a more thorough genomic approach to understand this pattern.

Finally, building on the extensive sampling across the archipelago for most species, I delved into conservation problems and possible protection measures for threatened species. Given the restricted range of most species in these two genera and the multiple anthropogenic threats they face, only targeted conservation programs can prevent future population extirpation and species extinctions.