Research Article |
Corresponding author: Simeon Borislavov Borissov ( borissovsb@gmail.com ) Academic editor: Monika Eberhard
© 2021 Simeon Borislavov Borissov, Georgi Hristov Hristov, Dragan Petrov Chobanov.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Borissov SB, Hristov GH, Chobanov DP (2021) Phylogeography of the Poecilimon ampliatus species group (Orthoptera: Tettigoniidae) in the context of the Pleistocene glacial cycles and the origin of the only thelytokous parthenogenetic phaneropterine bush-cricket. Arthropod Systematics & Phylogeny 79: 401-418. https://doi.org/10.3897/asp.79.e66319
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Abstract
Parthenogenetic lineages are known to rapidly colonize large areas that become available after glacial periods as parthenogenetic reproduction is beneficial over mating when the favorable season is very short. The only obligatory parthenogenetic species of the largest bush-cricket subfamily Phaneropterinae is Poecilimon intermedius. It belongs to the Anatolio-Balkan lineage Poecilimon ampliatus species group and in contrast has a remarkably broad distribution from Central Europe to China, following the pattern of geographical parthenogenesis. In this study we provide a systematic revision of the P. ampliatus group based on mitochondrial (ND2) and nuclear (ITS) phylogeny. We estimate divergence times by applying secondary calibration on the ND2 tree to test for congruence between recent splits in the group and the Pleistocene climatic oscillations. We use ecological niche modelling to analyze the ecological requirements of the parthenogenetic P. intermedius and its sexually reproducing sister species P. ampliatus. By projecting on the conditions during the Last Glacial Maximum we outline the suitable areas for both species during the glacial cycles and discuss range shifts in response to climate change. Based on all results we hypothesize that the drought-tolerant P. intermedius originated during the recent glaciations in the southwestern part of its current range and rapidly radiated in a northeastern direction. Its sister species P. ampliatus, which is adapted to higher levels of precipitation, remained in the western Balkans, where populations retreated to higher altitudes during warming.
ecological niche modelling, evolution, parthenogenesis, phylogeny, Poecilimon intermedius, systematics
Poecilimon Fischer, 1853 is the most diverse genus of the Eurasian bush-cricket tribe Barbitistini with more than 140 currently described species (
Diversity of Poecilimon is concentrated in the southern Balkans, Anatolia and the Caucasus with very few taxa spreading outside this range. Nevertheless, the parthenogenetic species P. intermedius (Fieber, 1853) has a remarkably broad range stretching from Central Europe to western China, reaching well over the 55th parallel north in Middle Asia (
Large distribution areas are reported for various asexual organisms (
It was argued that the advantage of parthenogenetic lineages in the colonization of new areas, such as formerly glaciated territories, is a consequence of hybridization rather than of parthenogenesis itself (
Our study aims to explore the origin of the only known obligatory parthenogenetic member of the richest bush-cricket subfamily Phaneropterinae (over 2,600 species; Mugleston et al. 2018) through reconstructing the molecular phylogeny of the P. ampliatus group. We test the hypothesis of a recent origin of the parthenogenetic lineage P. intermedius, triggered by the rapidly changing environmental conditions during the Pleistocene (e.g.
Material was collected during various field trips in the period 2014–2020. Collected specimens were conserved in absolute ethanol and kept at -20 C to preserve DNA. A total of 11 taxa from the P. ampliatus group sensu
Total DNA was isolated from the hind femur applying a salt-ethanol extraction protocol (e.g.
Visualization, trimming and assembly of sequences were performed with CodonCode Aligner v. 8.0.2 (CodonCode, Dedham, MA, USA). Alignments were prepared in Mega X (
Maximum likelihood (ML) analyses were run using RAxML ver. 8.2.12 (
Choosing calibrations for molecular dating could be challenging, especially when fossil data is unavailable. A recent study estimated divergence dates in Poecilimon, using the isolation of Crete as a source of age constraint (
BEAST 2.6.3 (
The two sister species Poecilimon ampliatus and P. intermedius diverged recently (Lehmann et al. 2010;
The area accessible via dispersal (M) for a particular taxon is an important component of niche modeling and needs to be carefully estimated, considering landscape changes over time, evolutionary history and relations with other species (
The sexually reproducing P. ampliatus is mainly distributed in the western Balkans reaching in an isolated locality Romania to the north (
Occurrence data was collected from literature (
The occurrence datasets were thinned with the R package spThin (
Layers with the 19 bioclimatic variables available at Worldclim v. 1.4 (Hjimans et al. 2005; www.worldclim.org) were downloaded at 2.5 minutes resolution, together with the downscaled data from two alternative General Circulation Models (GCM) for the LGM: The Community Climate System Model (CCSM4;
The presence-only algorithm implemented in Maxent v. 3.4.3 (
European representatives of the Poecilimon ampliatus species-group A,B: P. ampliatus (male, female), Montenegro, Durmitor National Park, 1500 m; C,D: P. pechevi (male, female), Bulgaria/North Macedonia border, Vlakhina Mt., 1900 m; E,F: P. ebneri (male, female), Bulgaria, Belassitsa Mt., 1850 m; G: P. klisuriensis (male), North Macedonia, Pelister Mt., Gjavato Pass, 1100 m; H: P. intermedius (female), Russia, Saratov, 300 m; I,J: P. marmaraensis (male, female), Bulgaria, E Stara Planina Mts, 950 m.
The ITS1+ITS2 matrix (ITS hereafter) contained 27 sequences. The total length of the alignment was 708 bp, including 170 variable sites, 88 parsimony-informative sites and 12 gaps. The ND2 dataset included 29 DNA sequences and consisted of 936 bp from which 481 variable and 391 parsimony-informative sites. No signs of significant saturation or NUMTs were found.
Nuclear data. ML analyzes provided poor bootstrap support, though generally agreed with the BI topology (results not shown). The ITS BI-tree (Fig.
Bayesian inference phylogenetic trees of the Poecilimon ampliatus species group. A: ITS; B: ND2. Posterior probabilities are represented as numbers next to nodes. Colored branches correspond to the Poecilimon ampliatus species complex (yellow), the rest of P. ampliatus group (blue) and outgroups (black), respectively.
Mitochondrial data. The ND2 BI-tree showed the best node support (Fig.
According to our divergence times estimation, all splits within P. ampliatus s.l. happened during the Pliocene and Pleistocene (Fig.
Mitochondrial chronogram based on the ND2 phylogenetic reconstruction of the Poecilimon ampliatus species group. Blue line indicates climate fluctuations over time (by Robert A. Rohde, based on data from
After the thinning procedure a total of 58 localities for P. intermedius (Fig.
The variables with the highest contribution to the model of P. intermedius were precipitation of warmest quarter (BIO18) and precipitation of driest quarter (BIO17). The highest gain from a single variable was obtained from BIO17 and maximum temperature of warmest month (BIO5) (see jackknife test Fig.
Importance of environmental variables. A: response of Poecilimon intermedius to precipitation of driest quarter (BIO17); B: Response of P. ampliatus to BIO17; C: Jackknife test of regularized training gain of the P. intermedius model; D: Jackknife test of regularized training gain of the P. ampliatus model.
The most contributing variable in the P. ampliatus model was precipitation of driest quarter (BIO17) with 65 % relative contribution to the model. BIO17 also obtained the highest gain when used in isolation (Fig.
The phylogenetic reconstructions presented in this study support the P. ampliatus species group in a broad sense as defined by
The ITS phylogeny suggests that the P. armeniacus species group after
As a result, the Poecilimon ampliatus groupings sensu
The nuclear phylogeny strongly supports that P. davisi is a sister taxon to the P. ampliatus species complex, which was not supported by the mitochondrial phylogeny (compare Fig.
Тhe Pleistocene climatic oscillations caused well-studied dramatic range shifts and shaped genetic diversity and speciation of numerous lineages on a world scale (
Two splits at the tip of the tree:1) between P. ebneri and P. klisuriensis and 2) between P. pechevi and P. intermedius+P. ampliatus, were estimated at 0.40–0.45 Ma (also matching the 95 % HPD intervals). These splits coincide with the Mid-Brunhes Transition, an increase in the amplitude of climatic cycles ca. 0.43 Ma, that resulted in significantly warmer interglacials (
Molecular dating showed that P. intermedius, P. ampliatus and P. pechevi shared a common ancestor 0.43 Ma. The split between P. ampliatus and P. intermedius was estimated at 0.37 Ma (Fig.
Though obligately thelytokous lineages are not rare in insects, these usually have a recent origin and are not expected to have long evolutionary history (
Decay of sexual traits and mating behavior is expected and has been reported in parthenogenetic females (
Parthenogenetic lineages are known to rapidly colonize large areas that become available after glacial periods (
The main characteristic of our ecological niche model of P. intermedius is that the projection on the LGM conditions significantly reduces suitable area (Fig.
Precipitation variables were the most informative for the models of both species. For P. ampliatus precipitation of driest quarter (BIO17) was the most important variable. The projection of the P. ampliatus ecological niche model on the CCSM4 demonstrated that during glaciations suitable habitats for the species extended on a large area including lowland and mountain areas over the Dinarides, while populations retreated to higher latitudes in response to warming (compare Fig.
Models of current distribution of Poecilimon intermedius and P. ampliatus mapped in relation to precipitation of driest quarter (BIO17). A: color-coded map of BIO17 (
All the above speculations call for a comparatively recent climate-driven origin of P. intermedius out of a high humidity-dependent ancestor. The latter might have been an isolated population of P. ampliatus or a common ancestor of both taxa, subjected to isolation during climate and habitat deterioration and population decline. Based on dating the main lineage splits within the P. ampliatus species complex, shrinking of the eco-niche of P. ampliatus during interglacial periods, and poor genetic distinction between distant populations of P. intermedius, we suggest that the current vast population of P. intermedius evolved in a single evolutionary event ca. 0.4 Ma, shortly after the Mid-Brunhes Transition. The warmer interglacials that followed were suitable for P. intermedius to colonize the vast territories to the east. The distance on land between the Dinarides and China is ca. 5000 km which gives an average colonization speed of ca. 0.01 km per year. Colonization was rapid during interglacials followed by retreat to refugia during glacials. Thus, the expansion of the species must have had a pulsate stepping stone character with successive cycles forward and back. Even though considering that the expansion periods were shorter than retraction, a significantly larger speed (>>10 meters/year) combined with dispersal from the refugial stepping stone-populations allowed this vast ‘migration’. According to our ecological niche models P. intermedius suffered a significant population crisis during the Last Glacial Maximum and is suspected to be in a current expansion following the expansion of open habitats, increase of temperature and decrease of humidity.
Poecilimon klisuriensis was initially described as a species, differing from P. ebneri in the shape of the male cercus tip, length of the subgenital plate and the shape of the lower valve of the ovipositor (
The present study also supports the species status of P. pechevi that was recently questioned based on its similarity with P. ebneri (
A general systematic implication of the presented phylogenies is the monophyly of the group as basically proposed by
Poecilimon amissus species complex
Poecilimon amissus Brunner von Wattenwyl, 1878
Poecilimon marmaraensis marmaraensis Naskrecki, 1991
Poecilimon marmaraensis nalbanti Ünal, 2005
Poecilimon orbelicus species complex (= P. luschani species group sensu Boztepe, Kaya & Çiplak 2013)
Poecilimon egrigozi Ünal, 2005
Poecilimon helleri Boztepe, Kaya & Çiplak, 2013
Poecilimon ledereri Ramme, 1933
Poecilimon luschani birandi Karabag, 1950
Poecilimon luschani chobanovi Boztepe, Kaya & Çiplak, 2013
Poecilimon luschani luschani Ramme, 1933
Poecilimon orbelicus Pančić, 1883
Poecilimon tuncayi Karabag, 1953
Poecilimon armeniacus species complex (partly sensu Ünal, 2010; still in need of revision)
Poecilimon armeniacus (Uvarov, 1921)
Poecilimon eskishehirensis Ünal, 2003
Poecilimon ferwillemsei Ünal, 2010
Poecilimon harveyi Karabag, 1964
Poecilimon haydari Ramme, 1951
Poecilimon guichardi Karabag, 1964
Poecilimon inopinatus Ünal, 2010
Poecilimon karabagi (Ramme, 1942)
Poecilimon ampliatus species complex
Poecilimon ampliatus Brunner von Wattenwyl, 1878;
Poecilimon ebneri Ramme, 1933
Poecilimon intermedius (Fieber, 1853);
Poecilimon klisuriensis Willemse, 1982, stat. rev.;
Poecilimon pechevi Andreeva, 1978
Species with distant relationships (ungrouped):
Poecilimon davisi Karabag, 1953
Poecilimon doga Ünal, 2004;
Poecilimon excisus Karabag, 1950.
This study was supported by the National Science Fund (MES) of Bulgaria – project DN11/14–18.12.2017 to Dragan Chobanov (sampling, DNA, isolation, amplification and sequencing), and by the Bulgarian Ministry of Education and Science under the National Research Program “Young scientists and postdoctoral students” approved by DCM Nº577 / 17.08.2018 – a grant to Simeon Borissov (data processing and analyses). We thank the reviewers Klaus-Gerhard Heller and Gerlind Lehmann, as well as the editor Marianna Simões, for their valuable corrections, comments and contribution in improving the manuscript.
File 1
Data type: .xlsx
Explanation note: Table S1. Localities and accession numbers of sequences used in the analyses.
File 2
Data type: .pdf
Explanation note: Table S2. List of 95 % HPD intervals of the ND2 chronogram. Node numbers correspond to the numbers on Fig.
File 3
Data type: .xlsx
Explanation note: Table S3. Model parameters estimated with ENMeval (