Comparative assessment of genetic and morphological variation at an extensive hybrid zone between two wild cats in southern Brazil

Evaluating hybrid speciation and swamping in wild carnivores with a decision-tree approach

Hybridization is an important evolutionary force with a principal role in the origin of new species, known as hybrid speciation. However, ongoing hybridization can create hybrid swamping, in which parental genomes are completely lost. This can become a biodiversity threat if it involves species that have adapted to certain environmental conditions and occur nowhere else. Because conservation scientists commonly have a negative attitude toward hybrids, it is important to improve understanding of the influence of interspecific gene flow on the persistence of species. We reviewed the literature on species hybridization to build a list of all known cases in the order Carnivora. To examine the relative impact, we also noted level of introgression, whether fertile offspring were produced, and whether there was mention of negative or positive evolutionary effects (hybrid speciation and swamping). To evaluate the conservation implications of hybrids, we developed a decision-making tree with which to determine which actions should be taken to manage hybrid species. We found 53 hybrids involving 68 unique taxa, which is roughly 23% of all carnivore species. They mainly involved monophyletic (83%) and sympatric species (75%). For 2 species, the outcome of the assessment was to eliminate or restrict the hybrids: Ethiopian wolf (Canis simensis) and Scottish wildcat (Felis silvestris silvestris). Both species hybridize with their domestic conspecifics. For all other cases, we suggest hybrids be protected in the same manner as native species. We found no evidence of genomic extinction in Carnivora. To the contrary, some species appear to be of hybrid origin, such as the Asiatic black bear (Ursus thibetanus) and African golden wolf (Canis lupaster). Other positive outcomes of hybridization are novel genetic diversity, adaptation to extreme environments, and increased reproductive fitness. These outcomes are particularly valuable for counterbalancing genetic drift and enabling adaptive introgression in a human-dominated world.

Extensive Phylogenomic Discordance and the Complex Evolutionary History of the Neotropical Cat Genus Leopardus

Even in the genomics era, the phylogeny of Neotropical small felids comprised in the genus Leopardus remains contentious. We used whole-genome resequencing data to construct a time-calibrated consensus phylogeny of this group, quantify phylogenomic discordance, test for interspecies introgression, and assess patterns of genetic diversity and demographic history. We infer that the Leopardus radiation started in the Early Pliocene as an initial speciation burst, followed by another in its subgenus Oncifelis during the Early Pleistocene. Our findings challenge the long-held notion that ocelot (Leopardus pardalis) and margay (L. wiedii) are sister species and instead indicate that margay is most closely related to the enigmatic Andean cat (L. jacobita), whose whole-genome data are reported here for the first time. In addition, we found that the newly sampled Andean tiger cat (L. tigrinus pardinoides) population from Colombia associates closely with Central American tiger cats (L. tigrinus oncilla). Genealogical discordance was largely attributable to incomplete lineage sorting, yet was augmented by strong gene flow between ocelot and the ancestral branch of Oncifelis, as well as between Geoffroy's cat (L. geoffroyi) and southern tiger cat (L. guttulus). Contrasting demographic trajectories have led to disparate levels of current genomic diversity, with a nearly tenfold difference in heterozygosity between Andean cat and ocelot, spanning the entire range of variability found in extant felids. Our analyses improved our understanding of the speciation history and diversity patterns in this felid radiation, and highlight the benefits to phylogenomic inference of embracing the many heterogeneous signals scattered across the genome.

Morphological and Genetics Support for a Hitherto Undescribed Spotted Cat Species (Genus Leopardus; Felidae, Carnivora) from the Southern Colombian Andes

In 1989, a skin of a small spotted cat, from the Galeras Volcano in southern Colombia (Nariño Department), was donated to the Instituto Alexander von Humboldt (identification, ID 5857) at Villa de Leyva (Boyacá Department, Colombia). Although originally classified as Leopardus tigrinus, its distinctiveness merits a new taxonomic designation. The skin is distinct from all known L. tigrinus holotypes as well as from other Leopardus species. Analysis of the complete mitochondrial genomes from 44 felid specimens (including 18 L. tigrinus and all the current known species of the genus Leopardus), the mtND5 gene from 84 felid specimens (including 30 L. tigrinus and all the species of the genus Leopardus), and six nuclear DNA microsatellites (113 felid specimens of all the current known species of the genus Leopardus) indicate that this specimen does not belong to any previously recognized Leopardus taxon. The mtND5 gene suggests this new lineage (the Nariño cat as we name it) is a sister taxon of Leopardus colocola. The mitogenomic and nuclear DNA microsatellite analyses suggest that this new lineage is the sister taxon to a clade formed by Central American and trans-Andean L. tigrinus + (Leopardus geoffroyi + Leopardus guigna). The temporal split between the ancestor of this new possible species and the most recent ancestor within Leopardus was dated to 1.2-1.9 million years ago. We consider that this new unique lineage is a new species, and we propose the scientific name Leopardus narinensis.

Detecting introgressive hybridization to maintain genetic integrity in endangered large waterbird: a case study in milky stork

Hybridization between milky stork (Mycteria cinerea) and painted stork (M. leucocephala) occurs frequently in captivity. Dusit Zoo is a captive breeding facility where storks with phenotypically ambiguous patterns have recently been observed, and their status remaining inconclusive. Here, we used a combination of phenotypic characters and genetic markers (cytochrome b and 14 microsatellite markers) to distinguish and identify hybrids from the two parental species (n = 114). Haplotype analysis revealed asymmetric mtDNA introgression from M. cinerea to M. leucocephala, with twelve morphologically classified M. leucocephala individuals carrying heterospecific mtDNA. Comprehensive biparental genetic assessments identified 33% of all three genetic clusters as admixed individuals, of which most were either F2 hybrids, backcrosses with M. leucocephala, or hybrids of unknown generation, implying weak premating isolation with the absence of intrinsic postzygotic isolation between parentals. Morphological analysis demonstrated that the absence or indistinctness of a black bar across the breast is the most noticeable trait to identify these hybrids. The endangered M. cinerea was found to have genomic contamination from M. leucocephala and vice versa, with at least 41 hybrid individuals being identified. These findings provide critical information for detecting hybrids and identifying suitable breeding stocks with genetic purity for future reintroduction and conservation management.

Comparative phylogeography among eight Neotropical wild cat species: no single evolutionary pattern

The felid species of South America are thought to have arrived on the continent during the Great American Biotic Interchange (GABI) in the Pleistocene. However, molecular and palaeontological data do not agree on how this event affected speciation in felids. Here, we determine both the number of colonization events and the period when felines first migrated from North America to South America. In addition, we evaluate whether similar evolutionary events could have affected the eight Neotropical cat species in their levels of genetic diversity, spatial genetic structure and demographic changes. We analysed four concatenated mitochondrial genes of the jaguar, ocelot, margay, tigrina, pampas cat, Andean cat, puma and jaguarundi. The samples were representative of a wide distribution of these species in Central and South America. Our analysis suggests either three or four colonization events from North America to South America over the past 3 Myr, followed by subsequent speciation events and the attainment of high or very high genetic diversity levels for seven of the species. No unique evolutionary process was detected for any of the current Neotropical cat species.

Genome-wide SNPs clarify a complex radiation and support recognition of an additional cat species

Phylogenetic reconstruction and species delimitation are often challenging in the case of recent evolutionary radiations, especially when postspeciation gene flow is present. Leopardus is a Neotropical cat genus that has a long history of recalcitrant taxonomic problems, along with both ancient and current episodes of interspecies admixture. Here, we employ genome-wide SNP data from all presently recognized Leopardus species, including several individuals from the tigrina complex (representing Leopardus guttulus and two distinct populations of Leopardus tigrinus), to investigate the evolutionary history of this genus. Our results reveal that the tigrina complex is paraphyletic, containing at least three distinct species. While one can be assigned to L. guttulus, the other two remain uncertain regarding their taxonomic assignment. Our findings indicate that the “tigrina” morphology may be plesiomorphic within this group, which has led to a longstanding taxonomic trend of lumping these poorly known felids into a single species.

Population structure and gene flow of Geoffroy’s cat (Leopardus geoffroyi) in the Uruguayan Savanna ecoregion

Felids are among the species most threatened by habitat fragmentation resulting from land-use change. In the Uruguayan Savanna ecoregion, about 30% of natural habitats have been lost, large felids have been eradicated from most of the region, and the impact of anthropogenic threats over the smaller species that remain is unknown. To develop management strategies, it is important to enhance knowledge about species population structure and landscape connectivity, particularly when land-use change will continue and intensify in the next years. In this study, we evaluate the population structure and gene flow of Geoffroy’s cat in the Uruguayan Savanna ecoregion. We generated a matrix of 11 microsatellite loci for 70 individuals. Based on Bayesian approaches we found that within the Uruguayan Savanna, Geoffroy’s cat shows high levels of genetic variability and no population structure. However, we observed genetic differences between individuals from the Uruguayan Savanna and those from the contiguous ecoregion, the Argentinian Humid Pampa. Four first-generation migrants from Humid Pampa were identified in the Uruguayan Savanna, suggesting a stronger gene flow in the west-east direction. We detected a past bottleneck followed by a subsequent recovery in Geoffroy’s cat populations in both ecoregions. These results lay the groundwork to understand the population dynamics and conservation status of Geoffroy’s cat in the Uruguayan Savanna ecoregion, and provide baseline data to establish population monitoring.

Skin deep: The decoupling of genetic admixture levels from phenotypes that differed between source populations

OBJECTIVES

In genetic admixture processes, source groups for an admixed population possess distinct patterns of genotype and phenotype at the onset of admixture. Particularly in the context of recent and ongoing admixture, such differences are sometimes taken to serve as markers of ancestry for individuals-that is, phenotypes initially associated with the ancestral background in one source population are assumed to continue to reflect ancestry in that population. Such phenotypes might possess ongoing significance in social categorizations of individuals, owing in part to perceived continuing correlations with ancestry. However, genotypes or phenotypes initially associated with ancestry in one specific source population have been seen to decouple from overall admixture levels, so that they no longer serve as proxies for genetic ancestry. Here, we aim to develop an understanding of the joint dynamics of admixture levels and phenotype distributions in an admixed population.

METHODS

We devise a mechanistic model, consisting of an admixture model, a quantitative trait model, and a mating model. We analyze the behavior of the mechanistic model in relation to the model parameters.

RESULTS

We find that it is possible for the decoupling of genetic ancestry and phenotype to proceed quickly, and that it occurs faster if the phenotype is driven by fewer loci. Positive assortative mating attenuates the process of dissociation relative to a scenario in which mating is random with respect to genetic admixture and with respect to phenotype.

CONCLUSIONS

The mechanistic framework suggests that in an admixed population, a trait that initially differed between source populations might serve as a reliable proxy for ancestry for only a short time, especially if the trait is determined by few loci. It follows that a social categorization based on such a trait is increasingly uninformative about genetic ancestry and about other traits that differed between source populations at the onset of admixture.

The role of the environment in the spatial dynamics of an extensive hybrid zone between two neotropical cats

Identifying factors that create and maintain a hybrid zone is of great interest to ecology, evolution and, more recently, conservation biology. Here, we investigated the role of environmental features in shaping the spatial dynamics of a hybrid zone between the southern tigrina, Leopardus guttulus, and Geoffroy's cat, L. geoffroyi, testing for exogenous selection as the main force acting on its maintenance. These Neotropical felid species are mainly allopatric, with a restricted area of sympatry in the ecotone between the Atlantic Forest and Pampa biomes. As both biomes have experienced high rates of anthropogenic habitat alteration, we also analysed the influence of habitat conversion on the hybrid zone structure. To do this, we used 13 microsatellite loci to identify potential hybrids and generated ecological niche models for them and their parental species. We compared the influence of variables on parental species and hybrid occurrence and calculated the amount of niche overlap among them. Parental species showed different habitat requirements and predicted co-occurrence was restricted to the forest-grassland mosaic of the ecotone. However, hybrids were found beyond this area, mainly in the range of L. geoffroyi. Hybrids demonstrated higher tolerance to habitat alteration than parental types, with a probability of occurrence that was positively related with mosaics of cropland areas and remnants of natural vegetation. These results indicate that exogenous selection alone does not drive the dynamics of the hybrid zone, and that habitat conversion influences its structure, potentially favouring hybrids over parental species.

Breeding behaviour predicts patterns of natural hybridization in North American minnows (Cyprinidae)

Premating barriers such as variation in reproductive behaviour can evolve quickly, but because gametic and postzygotic incompatibilities often evolve more slowly, circumstances that bring gametes into contact can breach the boundaries of premating isolation. In aquatic environments, the gametes of organisms with external fertilization are released into a constantly moving environment and may come into contact with heterospecific gametes. In fishes, nest association (spawning in another species' nest) is a behaviour that brings gametes from different species into close spatiotemporal proximity. These interactions might increase chances of hybridization, especially when multiple species associate with a single nest builder. This study addresses these interactions in the largest clade of North American freshwater fishes, the minnows (Cyprinidae). We compiled a list of over 17,000 hybrid specimens in conjunction with species distribution data, breeding behaviours, and an inferred phylogeny to test if breeding behaviour, in addition to evolutionary history, is an important predictor of hybridization. We find that breeding behaviour is a significant predictor of hybridization, even when phylogenetic relatedness and divergence time are accounted for. Specifically, nest associates are more likely to hybridize with other nest associates whereas non-nesting species had relatively low rates of hybridization.

Taxonomic revision of the pampas cat Leopardus colocola complex (Carnivora: Felidae): an integrative approach

The pampas cat Leopardus colocola has been subject to conflicting classifications over the years. Currently, one polytypic species with seven subspecies is recognized, but integrative taxonomic study for this debated group has never been done. Here, we combine the broadest morphological coverage of the pampas cat to date with molecular data and ecological niche models to clarify its species composition and test the validity of recently proposed subspecies. The multiple lines of evidence derived from morphology, molecular, biogeography and climatic niche datasets converged on the recognition of five monotypic species: L. braccatus, L. colocola, L. garleppi (including thomasi, budini, steinbachi, crespoi and wolffsohni as synonyms), L. munoai and L. pajeros (including crucina as synonym). These five species are morphologically diagnosable based on skin and skull traits, have evolved in distinct climatic niche spaces and were recovered in molecular species delimitation. Contrary to previous taxonomic arrangements, we do not recognize subspecies in pampas cats. To objectively define the two most controversial species, we designate neotypes for L. colocola and L. pajeros. The diversification of pampas cats is associated with Middle Pleistocene glaciations, but additional genetic samples from the central Andean region are still needed to conclusively reconstruct its evolutionary history.

ISSR Analysis of Genetic Diversity and Structure of Plum Varieties Cultivated in Southern China

Plums (Prunus spp.) are important deciduous fruit crops in the world. China is a major producer of P. salicina Lindl., but the genetic relationship of Chinese plums in key production regions remain unclear. In this study, 14 University of British Columbia (UBC) inter simple sequence repeats (ISSR) primers were used to analyze 33 plum varieties cultivated in Fujian Province to determine their genetic diversity and population structure. A total of 146 bands were generated, of which 130 were polymorphic. Mean percentage of polymorphic bands was 89.04%, Shannon’s information index value was 0.38, and the Nei’s genetic index value was 0.24. Using unrooted trees (Neighbor-Joining method), 33 varieties were classified into four groups. Split graph separated them into two major groups, each with two subgroups. The two phylogenetic trees indicate that environmental or natural selection pressure is an important factor influencing their genetic relationship. Analysis of population structure revealed that they have frequent genetic exchanges among closed subpopulations; thus, genetic variation mainly occurs within the population. Additionally, based on the phylogenetic analysis and unique morphological characteristics of fruits, we propose that the Chinese landrace Nai could contribute significantly to development of the famous variety Wickson.

Small spotted bodies with multiple specific mitochondrial DNAs: existence of diverse and differentiated tigrina lineages or species (Leopardus spp: Felidae, Mammalia) throughout Latin America

We analysed two sets of mitochondrial (mt) DNA data from tigrinas (traditionally, Leopardus tigrinus) we sampled in Costa Rica, Venezuela, Colombia, Ecuador, Peru, Bolivia, northwestern and northeastern Argentina and southern Brazil. Additionally, the analysis included some GenBank sequences from southern, central and northeastern Brazil. The first mt set (mt ATP8+mt 16S rRNA with 41 tigrina) revealed the existence of seven different tigrina-like haplogroups. They could represent, at least, 4-6 different tigrina species following the Phylogenetic Species Concept (PSC). In the second mt set (mitogenomics with 18 tigrinas), we detected six different tigrina-like haplogroups. They could represent 4-5 different tigrina species - including a possible full new species, which has gone previously unnoticed to the world of science both morphologic and molecularly. Coat patterns of several of these different tigrinas support the molecular differences. We also detected intense hybridization in many Andean tigrina with margays (Leopardus wiedii) and ocelots (Leopardus pardalis) as well as hybridization of one Bolivian tigrina with Leopardus geoffroyi. Similar hybridization was found for many of the southern Brazilian tigrina (Leopardus guttulus). All of the temporal split estimates for these tigrina haplogroups, together with those of the Leopardus species recognized to date, began in the late Pliocene but mostly occurred during the Pleistocene. In agreement with the existence of multiple species within the traditional L. tigrinus species, we detected strong and significant spatial structure in the two mt data sets. There were clear circular clines. A major part of the analyses detected more genetic resemblance between the Central American + trans Andean Colombian and Ecuadorian tigrina (L. oncilla) with the most geographically distant tigrina from central and southern Brazil (L. guttulus; pure individuals not hybridized with L. geoffroyi). In comparison, the Andean tigrina taxa had intermediate geographical origins but were highly genetically differentiated both from the Central American + trans Andean Colombian-Ecuadorian tigrina and from the central and southern Brazilian tigrina.

Phylogenomic evidence for ancient hybridization in the genomes of living cats (Felidae)

Inter-species hybridization has been recently recognized as potentially common in wild animals, but the extent to which it shapes modern genomes is still poorly understood. Distinguishing historical hybridization events from other processes leading to phylogenetic discordance among different markers requires a well-resolved species tree that considers all modes of inheritance and overcomes systematic problems due to rapid lineage diversification by sampling large genomic character sets. Here, we assessed genome-wide phylogenetic variation across a diverse mammalian family, Felidae (cats). We combined genotypes from a genome-wide SNP array with additional autosomal, X- and Y-linked variants to sample ∼150 kb of nuclear sequence, in addition to complete mitochondrial genomes generated using light-coverage Illumina sequencing. We present the first robust felid time tree that accounts for unique maternal, paternal, and biparental evolutionary histories. Signatures of phylogenetic discordance were abundant in the genomes of modern cats, in many cases indicating hybridization as the most likely cause. Comparison of big cat whole-genome sequences revealed a substantial reduction of X-linked divergence times across several large recombination cold spots, which were highly enriched for signatures of selection-driven post-divergence hybridization between the ancestors of the snow leopard and lion lineages. These results highlight the mosaic origin of modern felid genomes and the influence of sex chromosomes and sex-biased dispersal in post-speciation gene flow. A complete resolution of the tree of life will require comprehensive genomic sampling of biparental and sex-limited genetic variation to identify and control for phylogenetic conflict caused by ancient admixture and sex-biased differences in genomic transmission.