Repeated colonization, adaptive radiation and convergent evolution in the sheet-weaving spiders (Linyphiidae) of the south Pacific Archipelago of Juan Fernandez.

Abstract

We report on the colonization and diversification of linyphiid spiders in the Pacific oceanic archipelago of Juan Fernandez. About 50 spider species occur naturally in these islands, most of them endemic and about half of them are linyphiids. Linyphiidae includes no fewer than 15 species of Laminacauda and three of Neomaso (with several additional undescribed species in the latter genus), all of them single island endemics. There are three additional linyphiid endemic genera, two monotypic and one, Juanfernandezia, with two species. Unlike the rather uniform somatic morphology and small ground sheet webs of the continental Laminacauda and Neomaso species, the Juan Fernandez endemics exhibit morphological features and life history traits that are very rare or unknown in any other linyphiids. A multi-locus phylogenetic analysis confirms at least five independent Juan Fernandez colonizations of Linyphiidae, two within the same genus, and three of which underwent subsequent local diversification. Different calibrations suggest alternative colonization timelines, some at odds with island ages, but all agree on similar diversification timings of the endemic lineages. Rare phenotypic traits (e.g. gigantism, massive chelicerae or elongated legs) evolved multiple times independently within the islands. Based on the remarkable levels of eco-phenotypic differentiation in locally diversified species showing densely packed distributions, we propose that Laminacauda, and probably Neomaso, constitute a case of adaptive radiation.