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PubMed1990

The dystrophin gene is autosomally located on a microchromosome in chicken.

The dystrophin gene has been mapped to a pair of microchromosomes in Gallus domesticus. In situ hybridization using a pool of biotinylated human cDNA probes allowed detection of this huge single-copy sequence without having to employ isotopic labeling. The autosomal nature of the DMD gene in chicken is supported by molecular data from quantitative Southern blot analysis and is in sharp contrast to that in all eutherian mammals studied, where it is a characteristically X-linked locus. With previous data taken into consideration, these results should prove significant in understanding the evolution of sex chromosomes during speciation as well as highlighting the importance of avian microchromosomes.

Animals↗
PubMed1996

Rapid Speciation of the Five Most Medically Relevant Candida Species Using PCR Amplification and a Microtiter Plate-Based Detection System.

Background: Diagnosis of disseminated candidiasis can be difficult, as patient symptoms are often vague and blood cultures negative despite systemic involvement. Rapid detection of Candida would be advantageous, as delays in initiating antifungal therapy increase mortality. Conventional blood culturing methods require at least 3-7 days for detecting and speciating isolates, especially non-albicans species. In contrast, DNA amplification techniques make it possible to detect Candida DNA directly from clinical samples, thus eliminating the need to culture. Methods and Results: This study describes a polymerase chain reaction (PCR)-based assay, which permits amplification and speciation of the five most medically relevant Candida species, which cause over 95% of all Candida infections, namely, C. albicans, C. tropicalis, C. (Torulopsis) glabrata, C. parapsilosis, and C. krusei. Speciating these isolates has become more important recently with the introduction of fluconazole, and antifungal drug that has lower nephrotoxicity than fungizone but a narrower host range. Conclusions: By using this PCR-based assay in conjunction with a rapid microtiter plate-based detection system, samples can be analyzed for Candida DNA from five species in a single day. This represents a significant time saving as compared with the more lengthy but commonly used techniques of agarose gel electrophoresis and Southern blot hybridization for PCR product detection.

Journal Article↗
PubMed2026

Admixture and Selection Driven by El Niño-Southern Oscillation Events Shape the Genetic Structure of Octopus mimus-O. hubbsorum Complex Across the Humboldt and South Equatorial Current Transition Zone.

Marine transition zones, where contrasting water masses converge, can function as natural laboratories for studying admixture and early stages of speciation. The genomic structure of the eastern Pacific Octopus mimus-O. hubbsorum complex was investigated by analyzing whole-genome sequencing data from 67 individuals sampled along the west coast of the Americas, spanning Mexico and the Peruvian coast. This includes the South Equatorial Current, the transition zone, and the Humboldt Current System. The mitochondrial genomes fell into two major genetic clades that largely corresponded to the warm-water northern (O. hubbsorum) and cold-water southern (O. mimus) lineages. Analyses of the nuclear genomes revealed the same bipartite structure but also identified a broad admixture zone characterized by two different admixed clades (Admixed-Cold and Admixed-Warm). The results suggest that episodic relaxation of oceanographic barriers during El Niño-Southern Oscillation (ENSO) events promotes secondary contact and gene flow, resulting in admixed individuals recurrently during ENSO years. However, the survival of these admixed individuals depends on the adaptive genetic composition of each organism and the prevailing environmental conditions. Outlier SNP analysis supports these findings, where the Admixed-Cold cluster shares mainly the adaptive genetic component identified as outliers in O. mimus, while Admixed-Warm is linked to those in O. hubbsorum. The O. mimus-O. hubbsorum complex is currently occupying a gray zone of speciation, in which selection and climate-driven connectivity act in tandem to shape genomic divergence.

gene flow↗
PubMed2002

Sequence variation and genomic amplification of a family of Gypsy-like elements in the oomycete genus Phytophthora.

A family of sequences resembling Gypsy retroelements was identified and shown to be widely distributed throughout the genus Phytophthora, a member of the algallike oomycete fungi. Polymerase chain reaction (PCR) using specific and degenerate primers detected the family in 29 of 37 species tested. DNA hybridization also failed to detect the sequences in the eight species that were negative in PCR. The element appears to have been a major force in the shaping of Phytophthora genomes because its abundance varied drastically from about 10 to more than 10,000 copies per genome within the species containing the element. Family members diverged from each other by single-base changes, insertions, and deletions, with a mean nucleotide divergence of 16.7%. By constructing phylogenies of the elements, lineages were identified that predated speciation events within Phytophthora and subfamilies that had diverged more recently. The element was studied in detail in Phytophthora infestans, in which about 30 copies are dispersed throughout the genome. Phylogenetic comparisons of the reverse transcriptases placed the family within the Ty3/Gypsy group of long terminal repeat (LTR) retrotransposons, with the closest affinities to elements from plants. However, each of 12 family members sequenced contained defects that would render their protein products inactive, including frameshift mutations within reverse transcriptase domains and truncations that appeared to eliminate gag, protease, and terminal repeat sequences.

Animals↗
PubMedDate not supplied

A new taxon in the genus Neisseria.

Among 3,520 strains of Neisseria and Branhamella received in the laboratory during the last seven years, 13 could not be speciated. These 13 strains (Neisseria sp. group) were isolated from the throats of healthy children in Europe and Africa. The Neisseria sp. group oxidized glucose and maltose similarly to N. meningitidis. The observation of polysaccharide synthesis prompted the authors to examine the genomic relationship between the Neisseria sp. group and the type strains of all species of Neisseria and Branhamella. Additional phenotypic characteristics were also examined. Results indicated that the 13 strains in this study belong to the genus Neisseria, in which they constitute one homogenous hybridization group. They belong to the same genospecies as N. gonorrhoeae, N. meningitidis, N. flavescens and N. lactamica. However, they differ from N. meningitidis in production of polysaccharides, growth requirements and the lack of gamma-glutamyl transferase activity.

Genotype↗
PubMed2000

Cytogenetics of the Anopheles gambiae complex in Sudan, with special reference to An. arabiensis: relationships with East and West African populations.

The species composition of malaria vector mosquitoes belonging to the Anopheles gambiae complex (Diptera: Culicidae) from >40 localities in Sudan, representing most ecological situations, was determined by analysis of ovarian polytene chromosomes. Of 2162 females, 93% were identified as An. arabiensis Patton and 7% were An. gambiae Giles sensu stricto. No hybrids were found between the two species. Anopheles arabiensis occurred in all but two sites, whereas An. gambiae s.s. was effectively limited to the southernmost, more humid localities. For chromosomal paracentric inversions, the degree of polymorphism was low in An. gambiae s.s. (inversions 2La, 2Rb and 2Rd), higher in An. arabiensis (inversions Xe, 2Ra, b, bc, d1, s; 3Ra, d). Anopheles gambiae samples from Sudan were all apparently panmictic, i.e. they did not show restricted gene flow such as observed among West African populations (interpreted as incipient speciation). Chromosomal inversion patterns of An. gambiae in southern Sudan showed characteristics of intergrading Savanna/Forest populations similar to those observed in comparable eco-climatic situations of West Africa. Anopheles arabiensis was polymorphic for inversion systems recorded in West Africa (2Ra, 2Rb, 2Rdl, 3Ra) and for a novel 2Rs polymorphism, overlapping with inversion systems 2Rb and 2Rd1. Samples carrying the 2Rs inversion were mostly from Khashm-el-Girba area in central-eastern Sudan. In the great majority of the samples all polymorphic inversions were found to be in Hardy-Weinberg equilibrium. Sudan populations of An. arabiensis should therefore be considered as generally panmictic. Anopheles arabiensis shows more inversion polymorphism in west than in east African populations. Sudan populations have more evident similarities with those from westwards than those from eastwards of the Great Rift Valley. The possible influence of the Rift on evolution of An. arabiensis is discussed.

Africa, Eastern↗
PubMed2004

Nonallopatric and parallel origin of local reproductive barriers between two snail ecotypes.

Theory suggests that speciation is possible without physical isolation of populations (hereafter, nonallopatric speciation), but recent nonallopatric models need the support of irrefutable empirical examples. We collected snails (Littorina saxatilis) from three areas on the NW coast of Spain to investigate the population genetic structure of two ecotypes. Earlier studies suggest that these ecotypes may represent incipient species: a large, thick-shelled 'RB' ecotype living among the barnacles in the upper intertidal zone and a small, thin-shelled 'SU' ecotype living among the mussels in the lower intertidal zone only 10-30 m away. The two ecotypes overlap and hybridize in a midshore zone only 1-3 m wide. Three different types of molecular markers [allozymes, mitochondrial DNA (mtDNA) and microsatellites] consistently indicated partial reproductive isolation between the RB and the SU ecotypes at a particular site. However, each ecotype was related more closely to the other ecotype from the same site than to the same ecotype from another site further along the Galician coast (25-77 km away). These findings supported earlier results based solely on allozyme variation and we could now reject the possibility that selection produced these patterns. The patterns of genetic variation supported a nonallopatric model in which the ecotypes are formed independently at each site by parallel evolution and where the reproductive barriers are a byproduct of divergent selection for body size. We argue that neither our laboratory hybridization experiments nor our molecular data are compatible with a model based on allopatric ecotype formation, secondary overlap and introgression.

Animals↗
PubMed2004

Revisiting the role of introgression vs shared ancestral polymorphisms as key processes shaping genetic diversity in the recently separated sibling species of the Anopheles gambiae complex.

The role of interspecific hybridisation in the evolution of pest species is poorly understood. In mosquito disease vectors this is of particular importance due to the evolution of insecticide resistance and the proposed release of transgenic strains that are refractory to the malaria parasite. In this study, we apply population genetic methods in a novel manner to determine whether mitochondrial DNA sequences have introgressed between the closely related African malaria vectors Anopheles gambiae and A. arabiensis. Our results suggest that speciation was geologically recent and ancestral haplotypes at the ND5 locus are retained in both species. In addition, comparing haplotype frequencies in allopatric and sympatric populations, suggest locale specific unidirectional introgression of mitochondria from A. arabiensis into A. gambiae.

Africa↗
PubMed2000

Evolution of nucleotide substitutions and gene regulation in the amylase multigenes in Drosophila kikkawai and its sibling species.

In order to determine evolutionary changes in gene regulation and the nucleotide substitution pattern in a multigene family, the amylase multigenes were characterized in Drosophila kikkawai and its sibling species. The nucleotide substitution pattern was investigated. Drosophila kikkawai has four amylase genes. The Amy1 and Amy2 genes are a head-to-head duplication in the middle of the B arm of the second chromosome, while the Amy3 and Amy4 genes are a tail-to-tail duplication near the centromere of the same chromosome. In the sibling species of D. kikkawai (Drosophila bocki, Drosophila leontia, and Drosophila lini), sequencing of the Amy1, Amy2, Amy3, and Amy4 genes revealed that the Amy1 and Amy2 gene group diverged from Amy3 and Amy4 after duplication. In the Amy1 and Amy2 genes, the divergent evolution occurred in the flanking regions; in contrast, the coding regions have evolved in concerted fashion. The electrophoretic pattern of AMY isozymes was also examined. In D. kikkawai and its siblings, two or three electrophoretically different isozymes are encoded by the Amy1 and Amy2 genes (S isozyme) and by the Amy3 and Amy4 genes (F (M) isozymes). The S and F (M) isozymes show different patterns of band intensity when larvae and flies were fed in different media. Amy1 and Amy2, which encode the S isozyme, are more strikingly regulated than Amy3 and Amy4, which encode the F (M) isozyme. The GC content and codon usage bias were higher for the Amy1 and Amy2 genes than for the Amy3 and Amy4 genes. Although the ratio of synonymous and replacement substitutions within the Amy1 and Amy2 gene group was not significantly different from that within the Amy3 and Amy4 gene group, the synonymous substitution rate in the lineage of Amy1 and Amy2 was lower than that of Amy3 and Amy4. In conclusion, after the first duplication but before speciation of four species, the synonymous substitution rate between the two lineages and the electrophoretic pattern of the isozymes encoded by them changed, although we do not know whether there was any evolutionary relationship between the two.

Amino Acid Substitution↗
PubMed1978

Conservation and chromosomal localization of DNA satellites in balenopterid whales.

DNA satellites were isolated from three balenopterid species, viz. the minke, sei, and fine whales. In each of them at least two DNA satellites were recognizable with buoyant densities in neutral CsCl of rho = 1.702/1.703 and rho = 1.710/1;711, respectively. cRNAs from each satellite group were used for filter and in situ hybridisations. Homo-and heterologous DNA-cRNA hybrids within each satellite group yielded virtually identical melting curve profiles showing conservation of at least a considerable part of the DNA satellite sequences. There was no evident sequence homology between the rho = 1.702/1.703 and the rho = 1.710/1;711 satellites by filter hybridisation.--The in situ hybridisation showed that in each species the rho = 1.702/1.703 satellite was located in centromeric-paracentromeric C-bands in a few pairs, whereas the rho = 1.710/1.711 satellite was located in terminal C-bands throughout the karyotypes.--The data on the whale DNA satellites indicate that the quantitative evolution of the sateliite DNA sequences preceded species divergence of the balenopterids and that the satellite sequences have remained relatively unaltered since the divergence took place. The function of satellite DNA is considered to imply the introduction of both chromosomal and genic polymorphisms and thus being of great importance in speciation, Based upon these concepts a model is postulated for the function of satellite DNA. According to this model at meiotic pairing euchromatinheterochromatin overlapping between homologous chromosomes is considered to be of a general occurrence. This overlapping is presumed to be accentuated by the size heteromorphism frequently observed between homologous heterochromatic segments (C-bands). In the region of such euchromatinheterochromatin overlapping, cross-over would be excluded. The overlapping is suggested to be rectified progresssively in the chromosome arms, leaving unaffected crossing-over distant to the euchromatin-heterochromatin junctions. The consequence of this will be that genes in the proximity of the junctions are collectively inherited and selected, whereas genes distant to the the heterochromatin will be independently assorted and selected.

Animals↗
PubMed2001

A genetic map in the Mimulus guttatus species complex reveals transmission ratio distortion due to heterospecific interactions.

As part of a study of the genetics of floral adaptation and speciation in the Mimulus guttatus species complex, we constructed a genetic linkage map of an interspecific cross between M. guttatus and M. nasutus. We genotyped an F(2) mapping population (N = 526) at 255 AFLP, microsatellite, and gene-based markers and derived a framework map through repeated rounds of ordering and marker elimination. The final framework map consists of 174 marker loci on 14 linkage groups with a total map length of 1780 cM Kosambi. Genome length estimates (2011-2096 cM) indicate that this map provides thorough coverage of the hybrid genome, an important consideration for QTL mapping. Nearly half of the markers in the full data set (49%) and on the framework map (48%) exhibited significant transmission ratio distortion (alpha = 0.05). We localized a minimum of 11 transmission ratio distorting loci (TRDLs) throughout the genome, 9 of which generate an excess of M. guttatus alleles and a deficit of M. nasutus alleles. This pattern indicates that the transmission ratio distortion results from particular interactions between the heterospecific genomes and suggests that substantial genetic divergence has occurred between these Mimulus species. We discuss possible causes of the unequal representation of parental genomes in the F(2) generation.

Alleles↗
PubMed1994

Structure and genetics of the partially duplicated gene RP located immediately upstream of the complement C4A and the C4B genes in the HLA class III region. Molecular cloning, exon-intron structure, composite retroposon, and breakpoint of gene duplication.

The correlation of many HLA-associated autoimmune and genetic diseases with the polymorphic complement C4 genes may be attributed to the presence of disease susceptibility genes in the close proximity of C4. We have cloned and characterized a pair of partially duplicated genes, RP1 and RP2, located 611 base pairs upstream of the human C4A and C4B genes, respectively. The putative RP protein, consisting of 364 amino acid residues, is basic and highly hydrophilic. There is a bipartite nuclear localization signal at residues 114-131 and therefore RP may be a nuclear protein. Northern blot analysis suggested that RP is ubiquitously expressed. The 5' region of the RP1 gene is CpG rich, which is a characteristic of housekeeping genes. The RP1 gene contains nine exons. Located in the fourth intron is a cluster of Alu elements, and a newly defined composite retroposon SVA with a SINE, multiple copies of GC-rich VNTRs and an Alu element altogether enclosed by direct terminal repeats. Members of SVA are also present in the complement C2 gene located about 20 kilobases upstream of RP1 in the HLA and in the cytochrome CYP1A1 gene. Determination of the DNA sequences for RP2 from two different HLA haplotypes revealed identical hybrid sequences which resulted from fusion of RP with the tenascin-like Gene X and truncation of the 5' regions of both genes. Cumulative data suggest that the four tandemly arranged genes RP, complement C4, steroid 21-hydroxylase (CYP21), and Gene X altogether form a modular structure, RCCX. The number of RCCX modules varies from one to three or more in the population. Absence of the truncated genes RP2 and Gene XA have been detected in genomes with single RCCX modules. Duplication of the RCCX modules probably occurred before the speciation of great apes and humans as they contain the same breakpoint region of RP and Gene X gene duplication.

Alleles↗
PubMed1999

Studies on karyotype evolution in higher primates in relation to human chromosome 14 and 9 by comparative mapping of immunoglobulin C epsilon genes with fluorescence in situ hybridization.

Karyotypic homologies in relation to human chromosome 14 and 9 were studied through comparative mapping of the immunoglobulin C epsilon genes in higher primates by fluorescence in situ hybridization (FISH) technique. The C epsilon genes will be suitable probes for the analysis of evolutionary rearrangements due to that the multiple recombinational events such as gene duplications and deletions have occurred repeatedly in the immunoglobulin CH gene family (IGH@) during the course of primate evolution. IGH@ locating on the terminal region of human chromosome 14 (HSA14), at band HSA14q32.33, has generated multiple pseudogenes and among subclasses of IGH@ the C epsilon genes have shown most dynamic changes with generating both truncated type (C epsilon 2) and processed type (C epsilon 3) pseudogenes. In this study, chromosomal homologies and rearrangements on HSA14 (C epsilon 1) and HSA9 (C epsilon 3) in relation to the evolutionary genesis of their primate homologous chromosomes in speciation were investigated by comparative mapping with FISH and chromosome painting (ZOO-FISH) techniques. Comparative mapping of the C epsilon 1 gene at HSA14q32.33 was carried out in seven species of nonhuman primates: common chimpanzee (PTR), pygmy chimpanzee (PPA), gorilla (GGO), orangutan (PPY), white-handed gibbon (HLA), agile gibbon (HAG), and Japanese macaque (MFU). The C epsilon 1 gene was assigned to the telomeric region of HSA14 homologues in each species, namely, PTR15q32, PPA15q32, GGO18q16, PPY15q32, HLA17qter, HAG17qter, and MFU7q29, respectively. These results suggested that HSA14 has high degree of syntenic organization with its primate homologues confirmed by ZOO-FISH. Concerning HSA9, comparative mapping of the C epsilon 3 gene at HSA9p24.2-->p24.1 was performed. The mapped positions indicated the HSA9 homologous regions detected by ZOO-FISH in each species, namely, PTR11q34, PPA11q34, GGO13q22, PPY13q16, HLA8qter, HAG8qter, and MFU14q22, respectively, suggesting that several dynamic chromosomal rearrangements including at least twice pericentric inversions have occurred during the course of hominoid evolution. The comparison of syntenic groups and painting results has provided a hypothesis of the evolutionary genesis of HSA9 and its homologues with defined breakpoints on the present chromosomes. Likewise, studies on karyotype evolution will be promoted by combining comparative mapping with ZOO-FISH that can more clearly define the chromosomal rearrangements among species.

Animals↗
PubMed2002

Evidence for a conserved polydnavirus gene family: ichnovirus homologs of the CsIV repeat element genes.

In Campoletis sonorensis Ichnovirus (CsIV), the repeat element genes constitute a gene family of 28 members. In the present work, we document the presence of members of this gene family in two additional ichnoviruses, Hyposoter didymator Ichnovirus (HdIV) and Tranosema rostrale Ichnovirus (TrIV). Two repeat element genes, representing at least one functional gene, were identified in TrIV, whereas HdIV was found to contain at least three such genes. In both HdIV and TrIV, the known repeat element genes are encoded on single genome segments, with hybridization studies suggesting the presence of other, related but as yet uncharacterized genes. The HdIV and TrIV repeat element genes are all transcribed in infected caterpillars, although differences exist among genes in levels and in tissue specificity of expression. A heuristic tree was generated indicating that the repeat element genes are more similar within a species of wasp than between species, with TrIV genes being more closely related to the CsIV than to the HdIV genes. These results suggest that the most significant duplication, divergence, and expansion of the repeat element genes occurred after speciation. The finding that repeat element genes form an interspecific family within the genus Ichnovirus supports the view that the proteins they encode play an important role in ichnovirus biology.

Amino Acid Sequence↗
PubMed1988

MHC polymorphism pre-dating speciation.

Two features distinguish the polymorphism of the major histocompatibility complex (MHC) loci from that of other loci: its high diversity and the large genetic distance between MHC alleles. More than 100 alleles exist in natural populations in the mouse at each of the functional class I and class II alleles, all alleles occurring at frequencies that cannot be explained by recurrent mutations. Some of the alleles differ by approximately 70 nucleotides in the coding region alone and some of the products of the allelic genes differ by more than 50 amino acids. It has generally been assumed that these differences accumulated after species inception. Here, we present evidence for an alternative explanation of the origin of MHC polymorphism: a large part of the MHC polymorphism pre-dates speciation and is passed on from species to species. We describe allelic differences that must have arisen before the separation of mice and rats from a common ancestor more than 10 million years ago.

Alleles↗
PubMed2006

Assignment of 204 genes localized on HSA17 to a porcine RH (IMpRH) map to generate a dense comparative map between pig and human/mouse.

Bi- and uni-directional chromosome painting (ZOO-FISH) and gene mapping have revealed correspondences between human chromosome (HSA) 17 and porcine chromosome (SSC) 12 harboring economically important quantitative trait loci. In the present study, we have assigned 204 genes localized on HSA17 to SSC12 to generate a comprehensive comparative map between HSA17 and SSC12. Two hundred fifty-five primer pairs were designed using porcine sequences orthologous with human genes. Of the 255 primer pairs, 208 (81.6%) were used to assign the corresponding genes to porcine chromosomes using the INRA-Minnesota 7000-rad porcine x Chinese hamster whole genome radiation hybrid (IMpRH) panel. Two hundred three genes were integrated into the SSC12 IMpRH linkage maps; and one gene, PPARBP, was found to link to THRA1 located in SSC12 but not incorporated into the linkage maps. Three genes (GIT1, SLC25A11, and HT008) were suggested to link to SSC12 markers, and the remaining gene (RPL26) did not link to any genes/expressed sequence tags/markers registered, including those in the present study. A comparison of the gene orders among SSC12, HSA17, and mouse chromosome 11 indicates that intra-chromosomal rearrangements occurred frequently in this ancestral mammalian chromosome during speciation.

Acetyltransferases↗
PubMed2004

Chromosomal speciation: a reply.

The "genic" and the "non-genic" (chromosomal) hypotheses for the predominant mechanism by which species diverge into two have long been in contention. In 1998 Coyne and Orr attacked certain formulations of the chromosomal hypothesis on the grounds that they required macromutations (structural changes in chromosomes). In 1999 I replied that numerous independent micromutations (single DNA base changes) should suffice (GC% hypothesis). Kliman et al., with the support of Coyne and Charlesworth, have presented various counterarguments, to which the present paper responds with evidence that GC% differences are primary to genic differences and would operate by changing the structure of stem-loops extruded from duplex DNAs. Chromosomes attempting to align by means of complementary loop-loop interactions would fail if GC% differences exceeded a critical threshold. This would disrupt meiosis (hybrid sterility) and the parents of organisms with failed meiosis would be reproductively isolated from each other. If they could find new mates with which they were GC-compatible, then new species could emerge. The model leads to predictions consistent with several lines of evidence. The GC% version of the chromosomal hypothesis has a sound basis and deserves at least as much attention as its genic rival.

Animals↗
PubMed2006

Speciation in reverse: morphological and genetic evidence of the collapse of a three-spined stickleback (Gasterosteus aculeatus) species pair.

Historically, six small lakes in southwestern British Columbia each contained a sympatric species pair of three-spined sticklebacks (Gasterosteus aculeatus). These pairs consisted of a 'benthic' and 'limnetic' species that had arisen postglacially and, in four of the lakes, independently. Sympatric sticklebacks are considered biological species because they are morphologically, ecologically and genetically distinct and because they are strongly reproductively isolated from one another. The restricted range of the species pairs places them at risk of extinction, and one of the pairs has gone extinct after the introduction of an exotic catfish. In another lake, Enos Lake, southeastern Vancouver Island, an earlier report suggested that its species pair is at risk from elevated levels of hybridization. We conducted a detailed morphological analysis, as well as genetic analysis of variation at five microsatellite loci for samples spanning a time frame of 1977 to 2002 to test the hypothesis that the pair in Enos Lake is collapsing into a hybrid swarm. Our morphological analysis showed a clear breakdown between benthics and limnetics. Bayesian model-based clustering indicated that two morphological clusters were evident in 1977 and 1988, which were replaced by 1997 by a single highly variable cluster. The most recent 2000 and 2002 samples confirm the breakdown. Microsatellite analysis corroborated the morphological results. Bayesian analyses of population structure in a sample collected in 1994 indicated two genetically distinct populations in Enos Lake, but only a single genetic population was evident in 1997, 2000, and 2002. In addition, genetic analyses of samples collected in 1997, 2000, and 2002 showed strong signals of 'hybrids'; they were genetically intermediate to parental genotypes. Our results support the idea that the Enos Lake species pair is collapsing into a hybrid swarm. Although the precise mechanism(s) responsible for elevated hybridization in the lake is unknown, the demise of the Enos Lake species pair follows the appearance of an exotic crayfish, Pascifasticus lenisculus, in the early 1990s.

Animals↗