Molecular Ecology (2013) 22, 3318–3332 doi: 10.1111/mec.12296 Divergent evolutionary histories of two sympatric spruce bark beetle species CORALIE BERTHEAU,* HANNES SCHULER,* WOLFGANG ARTHOFER,† DIMITRIOS N. AVTZIS,‡ 1 1 FRANCßOIS MAYER,§ SUSANNE KRUMBOCK,*€ YOSHAN MOODLEY¶ and CHRISTIAN STAUFFER* *Department of Forest and Soil Sciences, Institute of Forest Entomology, Forest Pathology and Forest Protection, Boku, University of Natural Resources and Life Sciences, Vienna, Austria, †Molecular Ecology Group, University of Innsbruck, Innsbruck, Austria, ‡Forest Research Institute, NAGREF, Vasilika, Thessaloniki, Greece, §Lutte Biologique et Ecologie Spatiale, Universite Libre de Bruxelles, Brussels, Belgium, ¶Department of Integrative Biology and Evolution, Konrad Lorenz Institute of Ethology, University of Veterinary Medicine, Vienna, Austria Abstract Ips typographus and Pityogenes chalcographus are two sympatric Palearctic bark beetle species with wide distribution ranges. As both species are comparable in biology, life history, and habitat, including sharing the same host, Picea abies, they provide excellent models for applying a comparative approach in which to identify common historical patterns of population differentiation and the influence of species-specific ecological characteristics. We analysed patterns of genetic diversity, genetic structure and demographic history of ten I. typographus and P. chalcographus populations co-distributed across Europe using both COI and ITS2 markers. Rather than similari- ties, our results revealed striking differences. Ips typographus was characterised by low genetic diversity, shallow population structure and strong evidence that all extant haplogroups arose via a single Holocene population expansion event. In contrast, genetic variation and structuring were high in P. chalcographus indicating a longer and more complex evolutionary history. This was estimated to be five times older than I. typographus, beginning during the last Pleistocene glacial maximum over 100 000 years ago. Although the expansions of P. chalcographus haplogroups also date to the Holocene or just prior to its onset, we show that these occurred from at least three geographically separated glacial refugia. Overall, these results suggest that the much longer evolutionary history of P. chalcographus greatly influenced the levels of phylogeographic subdivision among lineages and may have led to the evolution of dif- ferent life-history traits which in turn have affected genetic structure and resulted in an advantage over the more aggressive I. typographus. Keywords: comparative phylogeography, COI, Ips typographus, ITS2, Pityogenes chalcographus, species-specific characters Received 25 June 2012; revision received 7 February 2013; accepted 13 February 2013 Comparative phylogeography is a powerful approach Introduction to match historical patterns of gene flow, divergence An important issue in evolutionary biology is whether and speciation mechanisms among co-distributed taxa general and predictable relationships exist between the that overlap in space and time, but which are indepen- phylogeographic structure of species, their environmental dently confronted with the same historical events, requirements and species-specific ecology (Avise 2000). submitted to the same or different ecological processes and presenting similar or distinct intrinsic life-history Correspondence: Coralie Bertheau, Fax: +43 1 3686352/97; traits (Taberlet et al. 1998; Avise 2000; Hickerson et al. E-mail: [email protected] 2010). This multispecies approach offers a deeper 1Equally contributing senior authors. understanding of the evolutionary processes affecting © 2013 John Wiley & Sons Ltd COMPARATIVE GENETIC STUDY OF BARK BEETLES 3319 phylogeographic patterns among sympatric species and develop in other Pinaceae species (Fuhrer€ & (Bermingham & Moritz 1998; Zink 2002). Concordant Muehlenbrock 1983; Bertheau et al. 2009a,b). Conse- geographic distributions among species lineages have quently, after strong storms across Europe in 1990, enabled the detection of climatic refugia, postglacial P. chalcographus was responsible for the destruction of re-colonization routes or zones of contact (Taberlet et al. eight million m3 timber of spruce and other conifers, 1998; Hewitt 2000), while unrelated phylogeographic whereas the monophagous I. typographus destroyed patterns among species highlighted the influence of four times that amount exclusively in spruce (Gregoire environmental factors, life-history and/or ecological & Evans 2004). traits which affect dispersal capacities, host specializa- The phylogeography of both species has been rela- tion or adaptability to new environments (Avise et al. tively well investigated in Europe (see Avtzis et al. 2012 1987; Bowen & Avise 1990; Peterson & Dennot 1998). for review). Ips typographus has been the subject of sev- Although the number of comparative genetic studies on eral studies using a variety of molecular markers. An insects has increased in recent years, most deal with original analysis of a fragment of the mitochondrial host-parasite interactions (Whiteman et al. 2007; Ren gene cytochrome c oxidase subunit I (COI) from 18 et al. 2008; Borer et al. 2012; among others) or closely spruce populations revealed only eight haplotypes but related species (Solomon et al. 2008; Papadopoulou et al. identified two potential glacial refugia—one in the 2009; Morgan et al. 2011; among others), and few have south Alps and the other in the Moscow region (Stauffer been carried out in Europe (Brouat et al. 2004; Hayward et al. 1999). Contrary to knowledge that spruce recolon- & Stone 2006; Kerdelhue et al. 2006; Espındola & ized Scandinavia from a refuge on the Russian plain Alvarez 2011). (Tollefsrud et al. 2008), Stauffer et al. (1999) concluded Here, we present a comparative study of two sympatric that I. typographus re-colonized Scandinavia only from insect species with similar life histories, biology and southern Europe because Russian and Lithuanian popu- habitats to determine how these have been influenced lations did not share haplotypes with Scandinavia. by their evolutionary histories. Ips typographus (L.) and Nuclear allozyme and microsatellite studies highlighted Pityogenes chalcographus (L.) are two Palearctic scolytid low diversity and lack of structure in I. typographus beetles belonging to the tribe Ipini. They have a wide populations due to high gene flow (Stauffer et al. 1999; distribution range concordant with the distribution of Salle et al. 2007; Gugerli et al. 2008). However, the their main host, the Norway spruce, Picea abies (L. H. recent discovery of cryptic nuclear copies (numts) that Karst.) (Pfeffer 1995). The two species specialize in appear very similar to authentic mitochondrial DNA exploiting weakened spruce trees especially after (mtDNA) in I. typographus (Bertheau et al. 2011) created extreme climatic events, such as storms, snow breakage doubts in the interpretation of Stauffer et al. (1999). Avt- and droughts. These events favour population growth zis et al. (2008) studied P. chalcographus in 39 European that can lead to extensive ecological and economical spruce populations, sequencing almost the complete damage, making the beetles the most serious pests to COI gene, and discovered 58 haplotypes that were par- spruce forests in Europe (Gregoire & Evans 2004). titioned into three major clades. Two of these clades are Among the reasons for their breeding success are their thought to have diverged 70 000–100 000 years ago efficient pheromone-mediated infestation and aggrega- (kya) from central to northeastern European refugia and tion behaviour (Byers 2004), their strong association are now found in northern and central Europe with with blue stain fungus (Kirisits 2004; Six & Wingfield unidirectional reproductive incompatibility (Fuhrer€ 2011) and their flexible reproductive cycles which allow 1976; Avtzis et al. 2008). Southern Europe comprised for up to three generations in particularly warm years the remaining genetic variation with glacial refugia sug- (Jurc et al. 2006; Jonsson€ et al. 2011). Both species are gested in the Apennines and the Dinaric Alps. polygamous with an endophytic life cycle as they bore While much work has been carried out, the numt galleries into the bark of their host where larval devel- problem, the lack of a fully comparative assessment opment and most often adult maturation take place. and of an informative nuclear DNA (nuDNA) marker They are mostly found together on the same trees currently preclude a common synthesis of bark beetle (Bertheau et al. 2009a). Ips typographus is confined to the phylogeography in Europe. mid- and lower parts of the trunk (Hedgren 2004; Ips typographus and P. chalcographus share many eco- Wermelinger 2004), whereas P. chalcographus segregates logical and life characteristics, but they show variable preferentially into the thinner bark of the tree’s upper levels of specialization to P. abies. As the geographic reaches and branches but it is not rare to find it in the distribution of phytophagous insects is necessarily thicker bark (Grunwald€ 1986). While both species embedded within the range of their host plants preferentially infest P. abies, only P. chalcographus is (Simonato et al. 2007), one might expect the genetic considered oligophagous, with the ability to colonize structure of the monophagous I. typographus to more © 2013 John Wiley & Sons Ltd 3320 C. BERTHEAU ET AL. closely resemble that of P. abies than the oligophagous