Bidirectional hybridisation and introgression between introduced European brown hare, Lepus europaeus and the endemic Irish hare, L. timidus hibernicus

Introduced non-native species can threaten native species through interspecific hybridisation and genetic introgression. We assessed the prevalence of hybridisation and introgression between introduced European brown hare, Lepus europaeus, and the endemic Irish hare, L. timidus hibernicus. Roadkill hares (n = 56) were sequenced for a 379bp section of the mitochondrial DNA D-loop and a 474bp segment of the nuclear transferrin (Tf) gene. A species-specific indel in the transferrin gene was present in L.t. hibernicus and absent in L. europaeus. Excluding three hares from which molecular data could not be recovered, 28 hares (53%) were native L.t. hibernicus, 7 (13%) were non-native L. europaeus and 18 (34%) were hybrids; of which 5 (28%) were first generation (F1) involving bidirectional crosses with mismatched nuclear and mtDNA (3 ♂ europaeus x ♀ hibernicus and 2 ♂ hibernicus x ♀ europaeus). Mixed nuclear transferrin sequences suggested 13 (72%) of hybrids were at least 2nd generation (F2) with 9 (69%) possessing L.t. hibernicus and 4 (31%) L. europaeus mtDNA (the latter indicative of hybrid backcrossing with the non-native). The prevalence of hybridisation at similar mountain-brown hare contact zones throughout Europe is notably lower (4–16%) and typically unidirectional (♂ europaeus x ♀ timidus). A high prevalence of bidirectional hybridisation and introgression (in association with projected climate change) may favour the introduced species over the native. Genetic surveillance and population monitoring are needed to further explore the potential conservation implications of European brown hare in Ireland.

The distribution of lagomorph syphilis caused by Treponema paraluisleporidarum in Europe

Treponema paraluisleporidarum infects both rabbits (ecovar Cuniculus) and hares (ecovar Lepus). While the occurrence of the bacterium has previously been reported for European brown hares (Lepus europaeus) and domestic rabbits (Oryctolagus cuniculus f. domestica), there are no data available that report infection in the European context. We tested a total of 1,995 serum samples and 287 genital swabs from opportunistically sampled European brown hares (Lepus europaeus; n = 2135), Mountain hares (Lepus timidus; n = 4), European rabbits (Oryctolagus cuniculus; n = 138), and pet rabbits (O. cuniculus f. domestica; n = 5). The samples originated from eight European countries. In case only serum was available, we tested the samples for the presence of anti-treponemal antibodies. For this, we utilized the Treponema pallidum-particle agglutination test (TP-PA), which is suited for the use in lagomorphs due to the antigenic cross-reactivity of anti-T. pallidum and anti-T. paraluisleporidarum antibodies. In addition, the results of 380 sera were confirmed using the fluorescent-Treponema antibody absorption test (FTA-ABS). In all cases where swab samples were available, DNA was extracted and tested using quantitative PCR to test for the presence of the lagomorph syphilis-bacterium. We were able to detect antibodies in 825 of 1,995 lagomorph sera (41.4%; brown hare: 825/1,868; rabbit: 0/127) and obtained positive qPCR results from 182 of 287 swab samples (63.4%; European brown hare: 167/267; mountain hare: 4/4; rabbit: 11/16). While all rabbit sera (n = 127) tested negative for anti-treponemal antibodies, the presence of the bacterium was confirmed in eight wild (n = 8/11) and three domestic rabbits (n = 3/5) from Germany using qPCR.

Genetic diversity and structure of the hedgehogs Erinaceus europaeus and Erinaceus roumanicus: evidence for ongoing hybridization in Eastern Europe

Secondary contact zones between related species are key to understanding speciation mechanisms. The Central European sympatry zone of West European (Erinaceus europaeus) and northern white-breasted (Erinaceus roumanicus) hedgehogs is well studied, whereas data on the Eastern European sympatry zone are scarce. We examined the genetic variation in Russian populations using the mitochondrial Cytb gene, TTR intron 1 and 11 microsatellites to assess genetic variability and distribution patterns. In contrast to the Central European sympatry zone, we found evidence of ongoing hybridization between the two species in the sympatry zone of European Russia, where the proportion of individuals with mixed ancestry was c. 20%. Our data indicate bi-directional mtDNA introgression, but with a higher frequency of E. europaeus haplotypes in hybrids. The proportion of pure specimens with introgressed mitotypes is higher in E. roumanicus than in E. europaeus. Nuclear data showed the prevalence of the genetic contribution from E. roumanicus in admixed individuals. Demographic analyses indicated recent population growth in E. europaeus and little change in E. roumanicus, suggesting that E. europaeus colonized East Europe later than E. roumanicus.

Hare's affairs: Lessons learnt from a noninvasive genetic monitoring for tracking mountain hare individuals

Systematic monitoring of individuals and their abundance over time has become an important tool to provide information for conservation. For genetic monitoring studies, noninvasive sampling has emerged as a valuable approach, particularly so for elusive or rare animals. Here, we present the 5-year results of an ongoing noninvasive genetic monitoring of mountain hares (Lepus timidus) in a protected area in the Swiss Alps. We used nuclear microsatellites and a sex marker to identify individuals and assign species to noninvasively collected feces samples. Through including a marker for sex identification, we were able to assess sex ratio changes and sex-specific demographic parameters over time. Male abundance in the area showed high fluctuations and apparent survival for males was lower than for females. Generally, males and females showed only little temporary migration into and out of the study area. Additionally, using genotyped tissue samples from mountain hares, European hares (Lepus europaeus) and their hybrids, we were able to provide evidence for the first occurrence of a European hare in the study area at an elevation of 2,300 m a.s.l. in spring 2016. For future monitoring studies, we suggest to include complementary analysis methods to reliably infer species identities of the individuals analyzed and, thus, not only monitor mountain hare individual abundance, but also assess the potential threats given through competitive exclusion by and hybridization with the European hare.

Widespread introgression of mountain hare genes into Fennoscandian brown hare populations

In Fennoscandia, mountain hare (Lepus timidus) and brown hare (Lepus europaeus) hybridize and produce fertile offspring, resulting in gene flow across the species barrier. Analyses of maternally inherited mitochondrial DNA (mtDNA) show that introgression occur frequently, but unavailability of appropriate nuclear DNA markers has made it difficult to evaluate the scale- and significance for the species. The extent of introgression has become important as the brown hare is continuously expanding its range northward, at the apparent expense of the mountain hare, raising concerns about possible competition. We report here, based on analysis of 6833 SNP markers, that the introgression is highly asymmetrical in the direction of gene flow from mountain hare to brown hare, and that the levels of nuclear gene introgression are independent of mtDNA introgression. While it is possible that brown hares obtain locally adapted alleles from the resident mountain hares, the low levels of mountain hare alleles among allopatric brown hares suggest that hybridization is driven by stochastic processes. Interspecific geneflow with the brown hare is unlikely to have major impacts on mountain hare in Fennoscandia, but direct competition may.

Mitochondrial and nuclear DNA reveals reticulate evolution in hares (Lepus spp., Lagomorpha, Mammalia) from Ethiopia

For hares (Lepus spp., Leporidae, Lagomorpha, Mammalia) from Ethiopia no conclusive molecular phylogenetic data are available. To provide a first molecular phylogenetic model for the Abyssinian Hare (Lepus habessinicus), the Ethiopian Hare (L. fagani), and the Ethiopian Highland Hare (L. starcki) and their evolutionary relationships to hares from Africa, Eurasia, and North America, we phylogenetically analysed mitochondrial ATPase subunit 6 (ATP6; n = 153 / 416bp) and nuclear transferrin (TF; n = 155 / 434bp) sequences of phenotypically determined individuals. For the hares from Ethiopia, genotype composition at twelve microsatellite loci (n = 107) was used to explore both interspecific gene pool separation and levels of current hybridization, as has been observed in some other Lepus species. For phylogenetic analyses ATP6 and TF sequences of Lepus species from South and North Africa (L. capensis, L. saxatilis), the Anatolian peninsula and Europe (L. europaeus, L. timidus) were also produced and additional TF sequences of 18 Lepus species retrieved from GenBank were included as well. Median joining networks, neighbour joining, maximum likelihood analyses, as well as Bayesian inference resulted in similar models of evolution of the three species from Ethiopia for the ATP6 and TF sequences, respectively. The Ethiopian species are, however, not monophyletic, with signatures of contemporary uni- and bidirectional mitochondrial introgression and/ or shared ancestral polymorphism. Lepus habessinicus carries mtDNA distinct from South African L. capensis and North African L. capensis sensu lato; that finding is not in line with earlier suggestions of its conspecificity with L. capensis. Lepus starcki has mtDNA distinct from L. capensis and L. europaeus, which is not in line with earlier suggestions to include it either in L. capensis or L. europaeus. Lepus fagani shares mitochondrial haplotypes with the other two species from Ethiopia, despite its distinct phenotypic and microsatellite differences; moreover, it is not represented by a species-specific mitochondrial haplogroup, suggesting considerable mitochondrial capture by the other species from Ethiopia or species from other parts of Africa. Both mitochondrial and nuclear sequences indicate close phylogenetic relationships among all three Lepus species from Ethiopia, with L. fagani being surprisingly tightly connected to L. habessinicus. TF sequences suggest close evolutionary relationships between the three Ethiopian species and Cape hares from South and North Africa; they further suggest that hares from Ethiopia hold a position ancestral to many Eurasian and North American species.

Variation of partial transferrin sequences and phylogenetic relationships among hares (Lepus capensis, Lagomorpha) from Tunisia

North African hares are currently included in cape hares, Lepus capensis sensu lato, a taxon that may be considered a superspecies or a complex of closely related species. The existing molecular data, however, are not unequivocal, with mtDNA control region sequences suggesting a separate species status and nuclear loci (allozymes, microsatellites) revealing conspecificity of L. capensis and L. europaeus. Here, we study sequence variation in the intron 6 (468 bp) of the transferrin nuclear gene, of 105 hares with different coat colour from different regions in Tunisia with respect to genetic diversity and differentiation, as well as their phylogenetic status. Forty-six haplotypes (alleles) were revealed and compared phylogenetically to all available TF haplotypes of various Lepus species retrieved from GenBank. Maximum Likelihood, neighbor joining and median joining network analyses concordantly grouped all currently obtained haplotypes together with haplotypes belonging to six different Chinese hare species and the African scrub hare L. saxatilis. Moreover, two Tunisian haploypes were shared with L. capensis, L timidus, L. sinensis, L. yarkandensis, and L. hainanus from China. These results indicated the evolutionary complexity of the genus Lepus with the mixing of nuclear gene haplotypes resulting from introgressive hybridization or/and shared ancestral polymorphism. We report the presence of shared ancestral polymorphism between North African and Chinese hares. This has not been detected earlier in the mtDNA sequences of the same individuals. Genetic diversity of the TF sequences from the Tunisian populations was relatively high compared to other hare populations. However, genetic differentiation and gene flow analyses (AMOVA, F_ST, Nm) indicated little divergence with the absence of geographically meaningful phylogroups and lack of clustering with coat colour types. These results confirm the presence of a single hare species in Tunisia, but a sound inference on its phylogenetic position would require additional nuclear markers and numerous geographically meaningful samples from Africa and Eurasia.

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.

LaGomiCs-Lagomorph Genomics Consortium: An International Collaborative Effort for Sequencing the Genomes of an Entire Mammalian Order

The order Lagomorpha comprises about 90 living species, divided in 2 families: the pikas (Family Ochotonidae), and the rabbits, hares, and jackrabbits (Family Leporidae). Lagomorphs are important economically and scientifically as major human food resources, valued game species, pests of agricultural significance, model laboratory animals, and key elements in food webs. A quarter of the lagomorph species are listed as threatened. They are native to all continents except Antarctica, and occur up to 5000 m above sea level, from the equator to the Arctic, spanning a wide range of environmental conditions. The order has notable taxonomic problems presenting significant difficulties for defining a species due to broad phenotypic variation, overlap of morphological characteristics, and relatively recent speciation events. At present, only the genomes of 2 species, the European rabbit (Oryctolagus cuniculus) and American pika (Ochotona princeps) have been sequenced and assembled. Starting from a paucity of genome information, the main scientific aim of the Lagomorph Genomics Consortium (LaGomiCs), born from a cooperative initiative of the European COST Action "A Collaborative European Network on Rabbit Genome Biology-RGB-Net" and the World Lagomorph Society (WLS), is to provide an international framework for the sequencing of the genome of all extant and selected extinct lagomorphs. Sequencing the genomes of an entire order will provide a large amount of information to address biological problems not only related to lagomorphs but also to all mammals. We present current and planned sequencing programs and outline the final objective of LaGomiCs possible through broad international collaboration.

Characterizing the physical and genetic structure of the lodgepole pine × jack pine hybrid zone: mosaic structure and differential introgression

Understanding the physical and genetic structure of hybrid zones can illuminate factors affecting their formation and stability. In north-central Alberta, lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia) and jack pine (Pinus banksiana Lamb) form a complex and poorly defined hybrid zone. Better knowledge of this zone is relevant, given the recent host expansion of mountain pine beetle into jack pine. We characterized the zone by genotyping 1998 lodgepole, jack pine, and hybrids from British Columbia, Alberta, Saskatchewan, Ontario, and Minnesota at 11 microsatellites. Using Bayesian algorithms, we calculated genetic ancestry and used this to model the relationship between species occurrence and environment. In addition, we analyzed the ancestry of hybrids to calculate the genetic contribution of lodgepole and jack pine. Finally, we measured the amount of gene flow between the pure species. We found the distribution of the pine classes is explained by environmental variables, and these distributions differ from classic distribution maps. Hybrid ancestry was biased toward lodgepole pine; however, gene flow between the two species was equal. The results of this study suggest that the hybrid zone is complex and influenced by environmental constraints. As a result of this analysis, range limits should be redefined.

DNA barcodes and morphology reveal a hybrid hawkmoth in Tahiti (Lepidoptera : Sphingidae)

Interspecific hybridisation is a rare but widespread phenomenon identified as a potential complicating factor for the identification of species through DNA barcoding. Hybrids can, however, also deceive morphology-based taxonomy, resulting in the description of invalid species based on hybrid specimens. As the result of an unexpected case of discordance between barcoding results and current morphology-based taxonomy, we discovered an example of such a hybrid ‘species’ in hawkmoths. By combining barcodes, morphology and a nuclear marker, we show that Gnathothlibus collardi Haxaire, 2002 is actually an F1 hybrid between two closely related species that co-occur on Tahiti. In accordance with the International Code of Zoological Nomenclature, the taxon G. collardi is thus invalid as a species. This study demonstrates the potential of DNA barcodes to detect overlooked hybrid taxa. With the growth of sequence libraries, we anticipate that more unsuspected hybrid species will be detected, particularly among those taxa that are very rare, such as those known from only the type specimen.

Reticulate evolution: frequent introgressive hybridization among Chinese hares (genus lepus) revealed by analyses of multiple mitochondrial and nuclear DNA loci

BACKGROUND

Interspecific hybridization may lead to the introgression of genes and genomes across species barriers and contribute to a reticulate evolutionary pattern and thus taxonomic uncertainties. Since several previous studies have demonstrated that introgressive hybridization has occurred among some species within Lepus, therefore it is possible that introgressive hybridization events also occur among Chinese Lepus species and contribute to the current taxonomic confusion.

RESULTS

Data from four mtDNA genes, from 116 individuals, and one nuclear gene, from 119 individuals, provides the first evidence of frequent introgression events via historical and recent interspecific hybridizations among six Chinese Lepus species. Remarkably, the mtDNA of L. mandshuricus was completely replaced by mtDNA from L. timidus and L. sinensis. Analysis of the nuclear DNA sequence revealed a high proportion of heterozygous genotypes containing alleles from two divergent clades and that several haplotypes were shared among species, suggesting repeated and recent introgression. Furthermore, results from the present analyses suggest that Chinese hares belong to eight species.

CONCLUSION

This study provides a framework for understanding the patterns of speciation and the taxonomy of this clade. The existence of morphological intermediates and atypical mitochondrial gene genealogies resulting from frequent hybridization events likely contribute to the current taxonomic confusion of Chinese hares. The present study also demonstrated that nuclear gene sequence could offer a powerful complementary data set with mtDNA in tracing a complete evolutionary history of recently diverged species.

Mountain pine beetle host-range expansion threatens the boreal forest

The current epidemic of the mountain pine beetle (MPB), an indigenous pest of western North American pine, has resulted in significant losses of lodgepole pine. The leading edge has reached Alberta where forest composition shifts from lodgepole to jack pine through a hybrid zone. The susceptibility of jack pine to MPB is a major concern, but there has been no evidence of host-range expansion, in part due to the difficulty in distinguishing the parentals and their hybrids. We tested the utility of a panel of microsatellite loci optimized for both species to classify lodgepole pine, jack pine and their hybrids using simulated data. We were able to accurately classify simulated individuals, and hence applied these markers to identify the ancestry of attacked trees. Here we show for the first time successful MPB attack in natural jack pine stands at the leading edge of the epidemic. This once unsuitable habitat is now a novel environment for MPB to exploit, a potential risk which could be exacerbated by further climate change. The consequences of host-range expansion for the vast boreal ecosystem could be significant.

Conservation implications of hybridization in Hawaiian picture-winged Drosophila

In this review, we discuss the importance of hybridization among species for the conservation of Hawaiian picture-winged Drosophila. Hybridization can be a positive evolutionary process that creates new species and increases the adaptation of populations and species through the spread of adaptive alleles and traits. Conversely, hybridization can disrupt the genetic integrity of species or populations and this may be most detrimental among taxa that are recently hybridizing due to recent ecological changes. The loss of biodiversity in Hawaiian Drosophila through hybridization may be facilitated by habitat alteration and introduced species that reduce population sizes and alter geographic distributions of native species. We briefly review the evidence for hybridization in the genus Drosophila and then focus on hybridization in the Hawaiian picture-winged Drosophila. We examine three general approaches for identifying hybrids and for assessing the factors that appear to contribute to hybridization and the potential ecological and evolutionary outcomes of hybrids in natural populations. Overall, the potential for hybridization among species will likely increase the risk of extinction for Hawaiian picture-winged Drosophila species. Thus, it is important to consider the potential for hybridization among species when developing plans for the conservation of Hawaiian Drosophila.

Introgression from Lepus europaeus to L. timidus in Russia revealed by mitochondrial single nucleotide polymorphisms and nuclear microsatellites

Hybridisation among wild mammal populations may lead to introgression of genes and genomes over the species barrier. In Sweden, in northern Europe, and on the Iberian Peninsula in southern Europe, mitochondrial DNA from L. timidus occurs among L. europaeus specimens, presumably as a result of interspecific hybridisation. In Russia, the species are believed to hybridise as well, but no investigations have confirmed introgression. Here we develop species diagnostic single nucleotide polymorphisms in the mitochondrial genomes and combine them with analysis of nuclear microsatellite markers to investigate hybridisation and introgression in 71 Lepus specimens from Russia. A total of 58 specimens are typical representatives of either species. An additional nine specimens have slightly intermediate genotypes, potentially as a result of introgression of nuclear genes. Finally, we find three specimens with L. europaeus mitochondrial genome and apparent L. timidus nuclear genome. This indicates that the reciprocal transfer of mtDNA occur among Russian populations of these species. Our observation differs from previous observations of mtDNA introgression in Sweden and Iberia, and provides further support for a reticulated mode of introgression within the genus Lepus.