Budding speciation via peripheral isolation: the Psorodonotus venosus (Orthoptera, Tettigoniidae) species group example

Abstract

Kaya S, C ß ıplak B. (2016). Budding speciation via peripheral isolation: the Psorodonotus venosus (Orthoptera, Tettigoniidae) species group example. --Zoologica Scripta, 45, 521-537. The peripatric or budding species model has remained theoretical until recently. The habitat preference and range pattern of the mountainous Psorodonotus venosus species group, distributed in Anatolia and Caucasus, offered potential to test the predictions of the model. The study aimed to confirm the parameters and to provide evidence for peripatric speciation in a terrestrial group. Fourteen populations representing the total range of the group were studied. Sequences of two mitochondrial fragments including four loci (12S rDNA+tDNAval+16S rDNA and COI) and a nuclear fragment including three loci (ITS1+5.8S rDNA+ITS2) were obtained and used in phylogenetic, time estimation, population genetics and demographic analyses. Additionally, phenotypical data were provided for the group. Phylogenetic analyses supported the monophyly of the PVG and suggested similar intralineage relationships, but did not support the monophyly of each of the species in the group. The molecular chronograms indicated radiation of the group throughout the Pleistocene. Demographic analyses suggested constant population sizes for the populations in the centre of the range but a significant departure from constancy in four peripheral populations. Genetic diversity is significantly reduced in peripheral populations, but not in others. We arrived to following conclusions. The data suggest that P. venosus is the ancestral species and P. rugulosus, P. tendurek and P. hakkari are bud species, as their haplotypes are nested within P. venosus. As expected under the budding speciation model, (i) in contrast to ancestral species, genetic diversity is reduced, and there are signs of departure from constant population size in bud species; (ii) bud species have isolated and restricted ranges, while the ancestral species does not, (iii) the relative ages of ancestral and bud species are the most reliable data to confirm the model, and chronograms of PVG well support this prediction, and (iv) the divergence events in the group co-occurred with major climatic transformations of the Pleistocene. Corresponding author: C ß ıplak B,

Phylogeography and taxonomy of the Psorodonotus caucasicus (Orthoptera, Tettigoniidae) group: independent double invasion of the Balkans from the Caucasus

“…The present results confirm previous studies which show ITS1‐5.8S rDNA‐ITS2 nuclear fragments to be uninformative for species‐level phylogenetics of Orthopteran lineages (Kuperus & Chapco, ; Çıplak et al , ; Kaya & Çıplak, ). Although phylogentically uninformative, ITS sequences, on their own or in combination with another marker, can still be used as candidate genes for DNA barcoding, as haplotypes are almost always consistently species‐specific with species delimitation tests.…”

“…For molecular clock estimates, the COI and 12S–16S matrices were analysed separately using beast v1.8.0 (Drummond et al , ) as previously reported divergence rates for each marker differ considerably (Kaya & Çıplak, ). The nodes of the main clades were dated using a Bayesian coalescence approach, as implemented in beast .…”

“…The time to the most recent common ancestor (TMRCA) for each clade was estimated under the model parameters suggested in jmodeltest v1.0 (http://darwin.uvigo.es/) and/or partitionfinder v1.1.1 (Lanfear et al , ) (File S1). To calibrate time estimation analyses, we used substitution rates reported specifically for Psorodonotus (Kaya & Çıplak, ). Kaya & Çıplak () estimated 0.0182 substitutions per site/Ma for COI .…”

“…To calibrate time estimation analyses, we used substitution rates reported specifically for Psorodonotus (Kaya & Çıplak, ). Kaya & Çıplak () estimated 0.0182 substitutions per site/Ma for COI . This rate is slightly higher than several previous estimates for insects (Papadopoulou et al , ) but similar to that reported for Tettigoniidae (Shapiro et al , ).…”

“…This rate is slightly higher than several previous estimates for insects (Papadopoulou et al , ) but similar to that reported for Tettigoniidae (Shapiro et al , ). The divergence rate for 12S–16S (0.0119 site/Ma) by Kaya & Çıplak () is the only rate reported previously for this fragment; consequently this rate was set to calibrate the analysis of the 12S–16S matrix (for application details, see File S1).…”