Assessing the genetic landscape of a contact zone: the case of European hare in northeastern Greece

From refugia to contact: Pine processionary moth hybrid zone in a complex biogeographic setting

Contact zones occur at the crossroad between specific dispersal routes and are facilitated by biogeographic discontinuities. Here, we focused on two Lepidoptera sister species that come in contact near the Turkish Straits System (TSS). We aimed to infer their phylogeographic histories in the Eastern Mediterranean and finely analyze their co-occurrence and hybridization patterns in this biogeographic context. We used molecular mitochondrial and nuclear markers to study 224 individuals from 42 localities. We used discordances between markers and complementary assignment methods to identify and map hybrids and parental individuals. We confirmed the parapatric distribution of Thaumetopoea pityocampa (Lepidoptera: Notodontidae) in the west and Thaumetopoea wilkinsoni in the east and identified a narrow contact zone. We identified several glacial refugia of T. wilkinsoni in southern Turkey with a strong east-west differentiation in this species. Unexpectedly, T. pityocampa crossed the TSS and occur in northern Aegean Turkey and some eastern Greek islands. We found robust evidence of introgression between the two species in a restricted zone in northwestern Turkey, but we did not identify any F1 individuals. The identified hybrid zone was mostly bimodal. The distributions and genetic patterns of the studied species were strongly influenced both by the Quaternary climatic oscillations and the complex geological history of the Aegean region. T. pityocampa and T. wilkinsoni survived the last glacial maximum in disjoint refugia and met in western Turkey at the edge of the recolonization routes. Expanding population of T. wilkinsoni constrained T. pityocampa to the western Turkish shore. Additionally, we found evidence of recurrent introgression by T. wilkinsoni males in several T. pityocampa populations. Our results suggest that some prezygotic isolation mechanisms, such as differences in timing of the adult emergences, might be a driver of the isolation between the sister species.

Positive selection and precipitation effects on the mitochondrial NADH dehydrogenase subunit 6 gene in brown hares (Lepus europaeus) under a phylogeographic perspective

Previous studies in hares and jackrabbits have indicated that positive selection has shaped the genetic diversity of mitochondrial genes involved in oxidative phosphorylation, which may affect cellular energy production and cause regional adaptation to different environmental (climatic) pressures. In the present study, we sequenced the NADH dehydrogenase subunit 6 (MT-ND6) gene of 267 brown hares (L. europaeus) from Europe and Asia Minor and tested for positive selection and adaptations acting on amino acid sequences (protein variants). Molecular diversity indices and spatial clustering were assessed by DnaSP, Network, and Geneland, while the presence of selection signals was tested by codeml in PAML, and by using the Datamonkey Adaptive Evolution web server. The SPSS software was used to run multinomial regression models to test for possible effects of climate parameters on the currently obtained protein variants. Fifty-eight haplotypes were revealed with a haplotype diversity of 0.817, coding for 17 different protein variants. The MT-ND6 phylogeographic pattern as determined by the nucleotide sequences followed the earlier found model based on the neutrally evolving D-loop sequences, and reflected the earlier found phylogeographic Late Pleistocene scenario. Based on several selection tests, only one codon position consistently proved to be under positive selection. It did occur exclusively in the evolutionarily younger hares from Europe and it gave rise to several protein variants from the southeastern and south-central Balkans. The occurrence of several of those variants was significantly favored under certain precipitation conditions, as proved by our multinomial regression models. Possibly, the great altitudinal variation in the Balkans may have lead to bigger changes in precipitation across that region and this may have imposed an evolutionarily novel selective pressure on the protein variants and could have led to regional adaptation.

Islands and hybrid zones: combining the knowledge from "Natural Laboratories" to explain phylogeographic patterns of the European brown hare

Background

The aim of the study was to use hybrid populations as well as island populations of the European brown hare (Lepus europaeus) to explore the effect of evolutionary events, such as the post-deglaciation translocations, spontaneous and human-mediated, local adaptation and the genetic drift in the shaping of the phylogeographic patterns of the species. For this purpose, we used molecular markers, both nuclear and mitochondrial, that are indicative for local adaptation as well as neutral markers to elucidate the patterns of population differentiation based on geographic isolation and the clade of origin. To broaden our analysis, we included data from our previous studies concerning mainland populations, to explore the genetic differentiation in the base of the geographic origin (mainland/island) of the populations.

Results

Our results suggest that local adaptation shapes the differentiation in both genomes, favoring specific alleles in nuclear genes (e.g. DQA) or haplotypes in mtDNA (e.g. Control Region, CR). mtDNA variation was found to be in a higher level and was able to give a phylogeographic signal for the populations. Furthermore, the degree of variation was influenced not only by the geographic origin, but also by the clade of origin, since specific island populations of Anatolian origin showed a greater degree of variation compared to specific mainland populations of the European clade. Concerning the hybrid population, we confirmed the existence of both clades in the territory and we provided a possible explanation for the lack of introgression between the clades.

Conclusion

Our results indicate that the Quaternary’s climatic oscillations played a major role in the shaping of the phylogeographic patterns of the species, by isolating populations in the distinct refugia, where they adapted and differentiate in allopatry, leading to genome incompatibilities observed nowadays.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1354-y) contains supplementary material, which is available to authorized users.

Genetic analyses of brown hare (Lepus europaeus) support limited migration and translocation of Greek populations

Numerous studies have shown that the phylogeography of many species, including European brown hare, has been affected by the climatic oscillations of the Pleistocene. During this period the Balkans acted as a major refugium offering habitable conditions for many species. However, few studies have focused on the specific role of the Greek peninsula in the phylogeographic history of species in this southernmost margin of Balkans. We, therefore analyzed a 528 bp fragment of the D-loop region of mitochondrial DNA in 154 wild brown hare individuals from unsampled areas from both mainland and island Greece and compared it to 310 available brown hare sequences (including 110 Greek samples). Newly identified haplotypes show characteristic distribution in specific Greek areas reinforcing the theory that Greece can be considered as a subrefuge within Balkans for a number of species, with several “refugia within refugia” spots, holding significant genetic diversity. No haplotypes from wild Greek individuals clustered with the Central and Western Europe group revealing a minimal contribution of this area to the colonization of central Europe. One hundred and ten reared brown hares were also analyzed to elucidate the impact of introductions on local populations. Most of these samples presented close genetic affinity with haplotypes from Central and Western Europe indicating that farms in Greece use breeders from those areas. Therefore, despite human translocation of individuals, the genetic structure of brown hare has mostly been influenced by paleoclimatic conditions and minimally by human actions.

Large-scale mitochondrial DNA analysis reveals new light on the phylogeography of Central and Eastern-European Brown hare (Lepus europaeus Pallas, 1778)

European brown hare, Lepus europaeus, from Central and Eastern European countries (Hungary, Poland, Serbia, Lithuania, Romania, Georgia and Italy) were sampled, and phylogenetic analyses were carried out on two datasets: 1.) 137 sequences (358 bp) of control region mtDNA; and 2.) 105 sequences of a concatenated fragment (916 bp), including the cytochrome b, tRNA-Thr, tRNA-Pro and control region mitochondrial DNA. Our sequences were aligned with additional brown hare sequences from GenBank. A total of 52 and 51 haplotypes were detected within the two datasets, respectively, and assigned to two previously described major lineages: Anatolian/Middle Eastern (AME) and European (EUR). Furthermore, the European lineage was divided into two subclades including South Eastern European (SEE) and Central European (CE). Sympatric distribution of the lineages of the brown hare in South-Eastern and Eastern Europe revealed contact zones there. BAPS analysis assigned sequences from L. europaeus to five genetic clusters, whereas CE individuals were assigned to only one cluster, and AME and SEE sequences were each assigned to two clusters. Our findings uncover numerous novel haplotypes of Anatolian/Middle Eastern brown hare outside their main range, as evidence for the combined influence of Late Pleistocene climatic fluctuations and anthropogenic activities in shaping the phylogeographic structure of the species. Our results support the hypothesis of a postglacial brown hare expansion from Anatolia and the Balkan Peninsula to Central and Eastern Europe, and suggest some slight introgression of individual haplotypes from L. timidus to L. europaeus.

Can secondary contact following range expansion be distinguished from barriers to gene flow?

Secondary contact is the reestablishment of gene flow between sister populations that have diverged. For instance, at the end of the Quaternary glaciations in Europe, secondary contact occurred during the northward expansion of the populations which had found refugia in the southern peninsulas. With the advent of multi-locus markers, secondary contact can be investigated using various molecular signatures including gradients of allele frequency, admixture clines, and local increase of genetic differentiation. We use coalescent simulations to investigate if molecular data provide enough information to distinguish between secondary contact following range expansion and an alternative evolutionary scenario consisting of a barrier to gene flow in an isolation-by-distance model. We find that an excess of linkage disequilibrium and of genetic diversity at the suture zone is a unique signature of secondary contact. We also find that the directionality index ψ, which was proposed to study range expansion, is informative to distinguish between the two hypotheses. However, although evidence for secondary contact is usually conveyed by statistics related to admixture coefficients, we find that they can be confounded by isolation-by-distance. We recommend to account for the spatial repartition of individuals when investigating secondary contact in order to better reflect the complex spatio-temporal evolution of populations and species.

Mitogenomic analysis in European brown hare (Lepus europaeus) proposes genetic and functional differentiation between the distinct lineages

European brown hare is a small game species spreading across Europe to Asia Minor, with important economic traits. Population genetics studies using mitochondrial DNA markers have revealed the existence of two major phylogeographic lineages, the European and the Anatolian. European lineage is further divided in the European type halpogroup and south-eastern European type halpogroup, while Anatolian consists only by the Anatolian/Middle Eastern type halpogroup. All three haplogroups show a discrete geographical distribution, with an overlapping zone forming in North-East Greece and Bulgaria, forming a contact zone. Despite the existence of a contact zone, European haplotype was never detected in Anatolia and vice versa, proposing the presence of genetic barriers responsible for this phenomenon. In this study, we analyzed the whole mitochondrial genomes of specimens originating from both lineages, aiming to detect the genetic and functional differentiation of the oxidative phosphorylation complexes that are encoded by mtDNA that could lead gradually to the reproductive isolation of the lineages.

SNP Identification through Transcriptome Analysis of the European Brown Hare (Lepus europaeus): Cellular Energetics and Mother's Curse

The European brown hare (Lepus europaeus, Pallas 1778) is an important small game species in Europe. Due to its size and position in the food chain, as well as its life history, phenotypic variation and the relatively recent speciation events, brown hare plays an important role in the structure of various ecosystems and has emerged as an important species for population management and evolutionary studies. In order to identify informative SNPs for such studies, heart and liver tissues of three samples from the European lineage and a three-sample pool from the Anatolian lineage were subjected to RNA-Sequencing analysis. This effort resulted in 9496 well-assembled protein-coding sequences with close homology to human. After applying very stringent filtering criteria, 66185 polymorphic sites were identified in 7665 genes/cds and 2050 of those polymorphic sites are potentially capable of distinguishing the European from the Anatolian lineage. From these distinguishing mutations we focused on those in genes that are involved in cellular energy production, namely the glycolysis, Krebs cycle and the OXPHOS machinery. A selected set of SNPs was also validated by Sanger sequencing. By simulating the three European individuals as one pool, no substantial informative-SNP identification was lost, making it a cost-efficient approach. To our knowledge this is the first attempt to correlate the differentiation in both nuclear and mitochondrial genome between the two different lineages of L. europaeus with the observed spatial partitioning of the lineages of the species, proposing a possible mechanism that is maintaining the reproductive isolation of the lineages.

Mammals and habitat disturbance: the case of brown hare and wildfire

Ecosystem disturbances, such as wildfires, are driving forces that determine ecology and conservation measures. Species respond differentially to wildfires, having diverse post-fire population evolution. This study reports, for first time, the responses of brown hare (Lepus europaeus Pallas, 1778) to wildfires. Hare relative abundance, age ratio, diet quality, body condition, and diseases were studied. Fire influence on vegetation was calculated at a micro-scale level. Hare abundance was lower the first year after wildfires in burned relative to unburned areas. The reverse was found in the second year when hare abundance was higher in burned areas. Hare abundance in burned areas was also higher in the third and fourth years. In the fifth and sixth years after wildfire no significant difference was found in abundance. At a micro-scale level, higher numbers of hare feces were counted in places with greater wildfire influence on vegetation. Age ratio analysis revealed more juveniles in burned areas, but the same number of neonates in burned and unburned areas, indicating lower mortality of juveniles in burned areas. Reduced predation in burned areas provides the most plausible explanation for our findings.

Diet adaptability by a generalist herbivore: the case of brown hare in a Mediterranean agroecosystem

BACKGROUND

Brown hares (Lepus europaeus) were collected before and after autumn rains from a mixed farmland and scrubland area. The age and sex of each specimen were determined, and microhistological technique was applied to analyze the stomach contents.

RESULTS

Hares consumed a higher number of plant species in comparison with other studies in continental European farmlands. A different pattern in diet of hare was found, where from a partial herbivory, frugivory, and granivory during the dry period, hares turn to primarily herbivory during the wet period. An expansion of diet breadth and an increase in food consumption was found in the dry season. Farming contributes to the enrichment of diet especially during the dry season. Diet composition was differed between ages, but no significant difference was found between the two sexes.

CONCLUSIONS

Hare is a facultative generalist herbivore that adapts its diet to the seasonal vegetation changes. In Mediterranean ecosystems, the seeds, fruits, and grapes are important additions to the diet. Results suggest that during the dry period juveniles cannot exploit all the available food resources, such as fruits and seeds, as effectively as adults.