Uncovering overlooked island diversity: colonization and diversification of the medically important spider genus Loxosceles (Arachnida: Sicariidae) on the Canary Islands

Abstract

Aim Our aim was to assess the evolutionary history of the spider genus Loxosceles on the Canary Islands. We unravelled its present diversity within the archipelago, and investigated its origin, mode and tempo of colonization to and between the islands using a phylogenetic framework.Location Canary Islands, Madeira, Iberian Peninsula, North Africa, Mediterranean region, Guinea.Methods We conducted extensive sampling across the Canary Islands, and examined the phylogenetic relationships among the Canary Island representatives of the genus Loxosceles and with regard to species from western Africa and the Mediterranean Basin. We used an evolutionary criterion (general mixed Yule coalescent) to delimit the evolutionary lineages, and applied fossil and biogeographical calibration points to estimate dates for major cladogenetic events within the Canary Islands using a Bayesian framework.Results Phylogenetic analyses revealed the existence of a well-supported clade formed exclusively by Canarian Loxosceles specimens, comprising seven allopatrically distributed evolutionary lineages. Major dispersal events between the islands occurred during the late Miocene. Representatives of the cosmopolitan Loxosceles rufescens were also found on the archipelago. Main conclusionsWe have revealed the existence of an overlooked endemic group of medically important spiders. The pattern of diversity of this group fits well with the general dynamic theory of oceanic island biogeography, where maximum diversity is found on islands of intermediate age. The colonization pathway of the group is compatible with a stepping-stone model. Betweenislands dispersal was the major driving force for diversification in the group, but a few within-island speciation events were also inferred, such as on Gran Canaria, where the Roque Nublo volcanic event acted as a vicariant agent, promoting the split between the two Gran Canarian lineages. The recently introduced L. rufescens is cohabiting with the endemic lineages.

Extant primitively segmented spiders have recently diversified from an ancient lineage

“…While extant liphistiids indeed possess arachnid plesiomorphies (figure 1a,b) not shared with any other spiders, and the Mesothelae lineage traces back as far as the Carboniferous, the origin of Liphistiidae and its diversification are surprisingly much more recent than once thought, repeating the patterns recently detected also in other textbook living fossils [1,4]. We trace the origin of the family in Southeast or East Asia to the Late Palaeogene and Eocene (39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58), and the origins of all eight genera to the Late Oligocene and Neogene (figure 3a; electronic supplementary material, figure S1 and table S3). However, liphistiids do belong to a very long evolutionary branch that connects them with the only mesothelean fossil known from Eurasia ( figure 3a), and consequently, some of their phenotypic traits resemble the hypothetically ancestral spiders.…”

“…All phylogenetic analyses support the monophyly of Liphistiidae and of eight genera. As the fossil evidence supports a Carboniferous Euramerican origin of Mesothelae, our dating analyses postulate a long eastward over-land dispersal towards the Asian origin of Liphistiidae during the Palaeogene (39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58). Contrary to expectations, diversification within extant liphistiid genera is relatively recent, in the Neogene and Late Palaeogene .…”

Comparative phylogeography of oceanic archipelagos: Hotspots for inferences of evolutionary process

“…However, species may, at least sometimes, also disperse from younger to older islands, even when these islands are occupied by close relatives (70). Among spiders, a progression rule has been documented for Loxosceles (73) and Dysdera (74, 75), whereas Pholcus and Spermophorides probably colonized the older Fuerteventura and Lanzarote from the younger Gran Canaria (76,77). The mixed support for a progression across the Canary Islands presents the possibility of an alternative explanation for the origin of the endemics of the oldest islands, which could be the result of secondary replacement of its original fauna by new colonists better adapted to increasingly arid conditions (78).…”

Complex inter‐island colonization and peripatric founder speciation promote diversification of flightless Pachyrhynchus weevils in the Taiwan–Luzon volcanic belt

“…The "stepping-stone by island age model" of asymmetric colonization from geologically older to younger islands is one of the common modes of colonization in several well-documented archipelagos, showing a clear linear age sequence of the origin of islands, such as the Hawaiian and Gal apagos Islands in the Pacific Ocean (Funk & Wagner, 1995;Gillespie, 2004;Parent, Caccone, & Petren, 2008) and the Canary Islands in the Atlantic (Juan et al, 2000;Planas & Ribera, 2014). However, some observations of stochastic dispersal have suggested that the unpredictability of interisland colonization can be linked to the geological history of the islands in a more complex manner (Gillespie et al, 2012).…”