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.

Incorporating Topological and Age Uncertainty into Event-Based Biogeography of Sand Spiders Supports Paleo-Islands in Galapagos and Ancient Connections among Neotropical Dry Forests

“…This scenario is similar to the metapopulation vicariance model that has been proposed to explain the presence of ancient, poorly dispersing groups in recent volcanic archipelagos, particularly in the Galapagos [57,58]. It could also explain other instances of clades whose estimated ages are older than the islands they occupy, such as sheet-web weavers in the Juan Fernández Islands [59].…”

Solenysa, a Cretaceous Relict Spider Group in East Asia

“…The oldest linyphiid fossil was originally described as an undetermined linyphiid [16]. Several studies have used it as a calibration point based on different assumptions: as a stem linyphiid, a crown linyphiid, a crown clade containing all linyphiids except Stemonyphantes [7,8,19,20,49,50], or even as a stem araneoid [51]. Herein, following Arnedo and Hormiga [7], we assigned the age of the fossil to the most recent common ancestor (MRCA) of Linyphiidae and applied an exponential prior with a mean of 10.0 and offset = 125.0 for this calibration, which gave a 95% confident interval of 125-155 Myr.…”

“…Several studies have used it as a calibration point based on different assumptions: as a stem linyphiid, a crown linyphiid, a crown clade containing all linyphiids except Stemonyphantes [7,8,19,20,49,50], or even as a stem araneoid [51]. Herein, following Arnedo and Hormiga [7], we assigned the age of the fossil to the most recent common ancestor (MRCA) of Linyphiidae and applied an exponential prior with a mean of 10.0 and offset = 125.0 for this calibration, which gave a 95% confident interval of 125-155 Myr. According to Hormiga et al [52], the Hawaiian spiders Orsonwelles malus is endemic to Kaui Island (formed 5.1 million years ago), and Orsonwelles polites is endemic to the adjacent O'ahu Island (formed 2.6-3.7 million years ago).…”

“…It is common in systematics that a high-level molecular phylogeny may significantly conflict with the established taxonomic system based on morphological characters [1][2][3][4]. Understanding the evolutionary past that shaped the species diversity of lineages always attracts the interest of biologists [5][6][7][8]. Spiders are generalist predators, forming a successful terrestrial animal group, and their high species diversity is distributed unevenly across lineages [9], even extremely asymmetrically between sister groups [4,10].…”

“…The classical taxonomic system of Linyphiidae consists of seven subfamilies [18]. However, this was not supported by molecular phylogenetic analyses [1,4,7]. Four of them, Linyphiinae, Erigoninae, Micronetinae, and Ipainae, were not monophyletic groups; the representatives of Mynogleninae and Dubiaraneinae fell into Linyphiinae; the Stemonyphantinae taxa were often clustered with pimoids, the sister group of linyphiids [1,4,[19][20][21].…”