Rates of Molecular Evolution in Nuclear Genes of East Mediterranean Scorpions

Abstract

Scorpions of the genus Mesobuthus represent a useful terrestrial model system for studying molecular evolution. They are distributed on several Aegean islands and the adjacent mainland, they are believed to have low rates of dispersal, and evolutionary divergence dates of taxa are available based on biogeographic events that separated islands from each other and the mainland. Here, we present data on polymorphism and synonymous (Ks) and non-synonymous (Ka) substitution rates for nine nuclear protein-coding genes of two east Mediterranean scorpion species, Mesobuthus gibbosus and M. cyprius (Buthidae). Levels of polymorphism tend to be lower in populations from islands (mean nucleotide diversity pi = 0.0071 +/- 0.0028) than in mainland populations (mean pi = 0.0201 +/- 0.0085). By using linear regression of genetic divergence versus isolation time, we estimate Ks to be 3.17 +/- 1.54 per (site x 10(9) years), and Ka to be 0.39 +/- 0.94 per (site x 10(9) years). These estimates for both Ks and Ka are considerably lower than for many other invertebrates, such as Drosophila, and may be attributed to scorpions' mammal-like generation times (approximately 2 years) and low metabolic rates. Phylogenetic analysis using maximum likelihood revealed a phylogeny that is congruent with that expected based on biogeographic events and in which divergences at synonymous sites are proportional to the dates that the taxa are believed to have split. Tests of equality of branch lengths for the Cyprus and Crete lineages revealed that Ks-estimates are about the same in both lineages, as expected from the biogeographic events that separated the islands, but Ka was increased in the Cyprus lineage compared to the Cretan lineage.

Species Delimitation and Morphological Divergence in the Scorpion Centruroides vittatus (Say, 1821): Insights from Phylogeography

“…The estimate T div was calculated with the formula T div  = TΘ/(2μ). Here Θ and T, the scaled divergence specify Θ and T (time), were estimated with MDIV; a μ value of ∼1% divergence per million years for scorpion mtDNA COI was obtained from rate estimates from the Mediterranean Mesobuthus scorpion genus as it represents a robust rate estimate for this mitochondrial gene [29], [64].…”

Microallopatry Caused Strong Diversification in Buthus scorpions (Scorpiones: Buthidae) in the Atlas Mountains (NW Africa)

“…Buthus scorpions are widely distributed over large parts of Africa and show a circum-Mediterranean stronghold including the Mediterranean islands, with extraordinarily high diversity in North Africa [10]–[14]. Yet, molecular studies showed that diversity may still be underestimated and additional cryptic species may be abundant [14]. Most buthid scorpions are strictly territorial and philopatric and have low dispersal abilities.…”

A new species of Buthus Leach, 1815 from Cyprus (Scorpiones, Buthidae)

“…On the other hand, the other discussions about endemism of some snake species occurring in the two island origin of Cyprus (Troodos and Kyrenia island); Hierophis cypriensis , in only southern Cyprus (i.e., Throodos island) while Platyceps najadum (non-endemic)and Natrix tessellata (non-endemic) is distributed only in northern Cyprus (i.e., Kyrenia island) and also on the mainland (Göçmen et al 2009). Gantenbein and Keightley (2004) stated his analyses shows that Mesobuthus cyprius occurring in Cyprus is autochthonous. Mesobuthus cyprius recorded in both southern and northern Cyprus.…”

“…According to widely accepted theory is Mediterranean salinity crisis that the Mediterranean sea dried out and these two island or the Trodos island and southern Tauruian-Kyrenian peninsula connected via landbridges about 5.6 Myrs (Hsü et al 1977; Cavazza and Wezel 2003). When the refilling of the Mediterranean basin, Cyprus terrestrial animals was isolated for around 5.2 – 5.3 Myrs (Robertson 1998; Gantenbein and Keightley 2004 ). This isolation played a major role in forming actual scorpion fauna of Cyprus and molecular and morphological phylogenetic analysis has revealed that populations of the island of Cyprus represent a divergent lineage; so these have been assigned to the species rank (i.e., Mesobuthus cyprius Gantenbein and Kropf, 2000).…”