Gone with the plate: the opening of the Western Mediterranean basin drove the diversification of ground-dweller spiders

Abstract

BackgroundThe major islands of the Western Mediterranean--Corsica, Sardinia, and the Balearic Islands--are continental terrenes that drifted towards their present day location following a retreat from their original position on the eastern Iberian Peninsula about 30 million years ago. Several studies have taken advantage of this well-dated geological scenario to calibrate molecular rates in species for which distributions seemed to match this tectonic event. Nevertheless, the use of external calibration points has revealed that most of the present-day fauna on these islands post-dated the opening of the western Mediterranean basin. In this study, we use sequence information of the cox1, nad1, 16S, L1, and 12S mitochondrial genes and the 18S, 28S, and h3 nuclear genes, along with relaxed clock models and a combination of biogeographic and fossil external calibration points, to test alternative historical scenarios of the evolutionary history of the ground-dweller spider genus Parachtes (Dysderidae), which is endemic to the region.ResultsWe analyse 49 specimens representing populations of most Parachtes species and close relatives. Our results reveal that both the sequence of species formation in Parachtes and the estimated divergence times match the geochronological sequence of separation of the main islands, suggesting that the diversification of the group was driven by Tertiary plate tectonics. In addition, the confirmation that Parachtes diversification matches well-dated geological events provides a model framework to infer substitution rates of molecular markers. Divergence rates estimates ranged from 3.5% My-1 (nad1) to 0.12% My-1 (28S), and the average divergence rate for the mitochondrial genes was 2.25% My-1, very close to the "standard" arthropod mitochondrial rate (2.3% My-1).ConclusionsOur study provides the first unequivocal evidence of terrestrial endemic fauna of the major western Mediterranean islands, whose origin can be traced back to the Oligocene separation of these islands from the continent. Moreover, our study provides useful information on the divergence rate estimates of the most commonly used genes for phylogenetic inference in non-model arthropods.

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 .…”

Ancient lineage, young troglobites: recent colonization of caves by Nesticella spiders

“…This rate was comparable to that estimated by Papadopoulou et al [44], who through an extensive survey of tenebrionid beetles obtained a divergence rate of 3.54% per MY for cox1 . Our estimated rates for mitochondrial genes were higher than those of Bidegaray-Batista et al [45], probably because of our inclusion of population level comparisons [46]. The estimated substitution rates for H3, 28S, and 18S were 0.066%, 0.16%, and 0.076%, respectively, with 18S and 28S showing high rate heterogeneity among lineages.…”

Phylogeography of a good Caribbean disperser: Argiope argentata (Araneae, Araneidae) and a new ‘cryptic’ species from Cuba

“…We then ran BEAST (Drummond and Rambaut 2007; Drummond et al 2012) for dating analyses of the mtDNA data. The BEAST run comprised 40,000,000 generations, using a lognormal relaxed clock with fixed estimated substitution rate (mean = 0.0112, SD = 0.001) (Bidegaray-Batista and Arnedo 2011), assuming a birth-death speciation model for the tree prior, with the best fit substitution models, and default options for all other prior and operator settings. The final consensus tree was produced in TreeAnnotator v1.8.0, with 25% burn-in.…”