Zone Of Parapatry Research Articles

The contribution of hybridization to range-wide population genetic structure in a Pacific coastal dune plant.

Interspecific hybridization can cause genetic structure across species ranges if the mating system and degree of sympatry/parapatry with close relatives varies geographically. The coastal dune endemic Camissoniopsis cheiranthifolia (Onagraceae) exhibits genetic subdivisions across its range, some of which are associated with shifts in mating system from outcrossing to selfing, while others are not. For instance, strong differentiation between large-flowered, self-incompatible (LF-SI) and large-flowered, self-compatible (LF-SC) populations occurs without much reduction in outcrossing or obvious barriers to gene flow. We hypothesized that LF-SI diverged from LF-SC via hybridization with the predominantly inland SI sister species C. bistorta. We analyzed spatial proximity using 1460 herbarium records and genetic variation at 12 microsatellites assayed for 805 and 404 individuals from 32 C. cheiranthifolia and 18 C. bistorta populations, respectively. We also assayed nine chloroplast microsatellites for 124 and 111 individuals from 27 and 19 populations, respectively. Closer parapatry was associated with unexpectedly high genetic continuity between LF-SI C. cheiranthifolia and C. bistorta. LF-SI genotypes clustered with C. bistorta exclusive of other C. cheiranthifolia genotypes. Similarly, pairwise FST among SI C. cheiranthifolia and C. bistorta, adjusted for geographic proximity, was not higher between heterospecific than conspecific populations. The lack of genetic differentiation between LF-SI C. cheiranthifolia and C. bistorta populations, even those located away from the zone of parapatry, suggests that, instead of hybridizing with C. bistorta, LF-SI C. cheiranthifolia is rather an ecotype of C. bistorta that has adapted to coastal dune habitat independent of other lineages in C. cheiranthifolia proper.

Species limits and biogeography of Rhynchospiza sparrows

The genus Rhynchospiza comprises two species, the monotypic Tumbes Sparrow (R. stolzmanni) and the Stripe-crowned Sparrow (R. strigiceps) with subspecies strigiceps and dabbenei. In the study reported here we evaluated the taxonomic status of these taxa and discussed key features involved in speciation. All three taxa exhibited multiple differences in plumage, morphology, and vocalizations, supporting the recognition of three species in Rhynchospiza. The very large-billed R. stolzmanni has a song composed of a succession of faster complex trilled phrases, shows a small black loral line and dark-chestnut head stripes with large dark central-stripe to individual feathers, and is resident in the Tumbes region. The large and heavy dabbenei has a song consisting of a series of simple chirping notes, shows a large black loral crescent and chestnut head stripes with a reduced to absent dark center to feathers, and inhabits the Austral Yungas as a year-round resident. The small and pale strigiceps has a song consisting of a succession of complex trilled phrases, shows a small black loral line and rufous-brown head stripes with large dark central-stripe to feathers, and inhabits Dry and Sierran Chaco where it is a partial migrant. Locality data and ecological niche modeling show that dabbenei and strigiceps are allo-parapatric and use different altitudinally segregated habitats at their zone of parapatry. Molecular phylogenetic analyses (NADH dehydrogenase 2 [ND2] gene) revealed R. stolzmanni to be sister (11.5% divergent) to a recently diverged dabbenei and strigiceps clade (1.6% divergent). We conclude that the genus Rhynchospiza comprises three species-level entities, each restricted to a major biogeographic region, and that vocalizations and facial patterns provide key evidence on species limits in these otherwise similarly plumaged taxa. The evolutionary–cultural differences in songs, with complex phrases in those of R. strigiceps and R. stolzmanni, and single notes in the songs of R. dabbenei, suggest changes in the innate vocal learning template during speciation in the latter.

Estimating the propagule size of a cryptogenic crested newt population

AbstractEncountering cryptogenic populations that are either native or introduced is a common but underreported phenomenon in field biology. Such local species' occurrences of unknown origin hamper our understanding of species' natural distribution ranges, and pose a problem to conservation management decisions. Genetic tools are frequently used to infer the ancestry of natural or invasive populations based on spatial geographical variation. Here we describe the occurrence of cryptogenic crested newts Triturus cristatus c. 25 km away from their main range and situated in an area where an introduction has taken place half a century ago. We first verify the suitability of a coalescent‐based analysis that reconstructs the number of founder individuals of a putative propagule from a source pool, based on previously published data documenting a well‐known introduction (the Laysan finch on the Hawaiian archipelago). After showing the validity of the approach, we apply this analysis to the case of T. cristatus, revealing that the number of effective founders would have been of the same order as the current effective carrying capacity of the population. We thus argue that the local T. cristatus occurrence is in fact of natural origin, with the documented introduction having little or no impact to the current gene pool. The result has major implications to our understanding of the species' habitat requirements in a zone of parapatry with a closely related species.

Nuclear and Mitochondrial Patterns of Introgression between the Parapatric European TreefrogsHyla arboreaandH. intermedia

Postglacial northward expansions from distinct southern European refugia have lead to the formation of several secondary contact zones between species. These zones are providing growing insights into the relevance of introgressive hybridization in shaping patterns of genetic diversity, and into the evolutionary processes involved in the completion of reproductive isolation barriers. Using both nuclear (9 allozyme loci) and mitochondrial (PCR-RFLP of a cytochrome b gene fragment) diagnostic markers we investigated the genetic patterns of variation across a zone of parapatry between the two European treefrogs Hyla arborea and H. intermedia. Neither F1 and F2 hybrids nor backcrosses were identified, indicating the lack of current gene exchange between the two species. However, introgressed alleles were observed in both species and in all markers analysed, which testifies to the occurrence of past events of introgressive hybridization. A wide variation in the frequencies of introgressed alleles was observed b...

The distribution of two medically and agriculturally important cryptic rodent species, Mastomys natalensis and M. coucha (Rodentia: Muridae) in South Africa

The medically and agriculturally important Natal multimammate mouse, Mastomys natalensis (A. Smith, 1834) and the multimammate mouse, M. coucha (A. Smith, 1836), are sibling species and cannot easily be distinguished morphologically. As a consequence, their respective distributional ranges across South Africa remain uncertain. Consequently, locality data of positively identified (karyotyped and/or electrophoretically determined) specimens from South Africa were collated from museum records, the literature, and recently collected material in an attempt to: 1) delimit geographic distributions using positively identified specimens; 2) predict the most likely areas of occurrence of the two sibling species using a variety of selected eco geographic variables (EGVs) associated with verified locality data; and 3) assess both verified and predicted geographic distributions with reference to previously reported incidents of plague in South Africa. Both verified and predicted distributions are broadly similar and show a geographic separation along the eastern escarpment of South Africa that seems to be influenced by altitude and rainfall. M. natalensis occurs in the low altitude/high rainfall eastern coastal region, extending to northeastern South Africa, while M. coucha keeps to the high altitude/moderate rainfall central and northeastern South Africa. Although the two species were shown to be either sympatric or to occur in close proximity at four localities, additional research is needed to determine the zone of parapatry. Univariate and multivariate analyses showed statistically significant differences between eco geographic characteristics of collecting localities associated with each of the two species in South Africa. The derived distributions indicate previously reported cases of plague in South Africa, to some extent, coincide with the distributional range of M. coucha rather than M. natalensis.

Distribution of veld rat sibling species Aethomys chrysophilus and Aethomys ineptus (Rodentia: Muridae) in southern Africa

Sibling species Aethomys chrysophilus (de Winton) and Aethomys ineptus Thomas and Wroughton are indistinguishable in external morphology. Although their combined geographic range extends over a large area of southern Africa, their respective distributions are uncertain. We have assembled a database that includes all known positively identified specimens from the literature, as well as those recently collected by the authors in South Africa. Based on these specimens, we suggest that A. chrysophilus occupies most of the combined range, reaching its southern limit in northern South Africa, primarily in low elevations of the Limpopo River drainage. The remainder of South Africa is occupied by A. ineptus, which occurs at higher elevations in north central South Africa but expands into lower elevation habitats in the southern portion of its range. Although mostly parapatric, their ranges are known to overlap west of Pretoria (Magaliesberg region of North West Province) and west of the Soutpansberg in Limpopo Province. However, they are known with certainty to be syntopic at only one locality (Langjan Nature Reserve, Limpopo Province). Further research is needed to determine the zone of parapatry in Mozambique, Botswana and Namibia.

Morphometric difference between the Novosibirsk and Tomsk chromosome races ofSorex araneus in a zone of parapatry

A hybrid zone between the Novosibirsk and Tomsk chromosome races of the common shrewSorex araneus Linnaeus, 1758 was found near Novosibirsk city (West Siberia, Russia) in an area unimpeded by geographic barriers. In this zone, the shrews of both races and their hybrids were trapped and karyotyped and 22 features of their cranial and postcranial skeleton were measured. Canonical discriminant analysis revealed 3 distinct groups of individuals, which corresponded to the 3 karyotypic categories involved in the analysis. The first discriminant function reflected the differences in the size of skeletal elements. The Novosibirsk shrews and the hybrids were significantly smaller than the Tomsk shrews. The second discriminant function was interpreted as a parameter of skeletal proportionality. The hybrids were significantly less proportional than the parental races. This study revealed one of the clearest examples of morphological differentiation between chromosome races of the common shrew.

Dynamic Change of a Zone of Parapatry between Two Species of Pholidobolus (Sauria: Gymnophthalmidae)

cently on groups of closely-related species that are distributed parapatrically (for a recent review see Barton and Hewitt, 1980). Parapatrically distributed organisms usually meet at narrow hybrid zones, although in some cases hybridization may be rare or unobserved (Montanucci, 1973; Selander et al., 1974; Nevo et al., 1974; Caire and Zimmerman, 1975; Greenbaum and Baker, 1976; Hillis et al., 1983). These zones of sympatry often occur along ecotones and are generally considered to be relatively stable, especially if selection against hybridization is strong (Barton, 1979). Montanucci's (1973) systematic review of lizards of the genus Pholidobolus revealed that the five species are distributed parapatrically in the Andes of Ecuador (Fig. 1). Areas of sympatry are extremely limited; overlap occurs only between the ranges of three species-pairs (Fig. 1): (1) P. montium and P. affinis in the upper end of the Latacunga Basin (Hoya del Rio Cutuchi) in the vicinity of Mulal6; (2) P. affinis and P. prefrontalis at the edge of the Palmira Desert; and (3) P. prefrontalis and P. macbrydei on the east side of the Cuenca Valley (Hoya del Rio Paute). All of these zones are in ecotonal situations.

Biochemical Systematics of the Atherinid Genus Menidia

Species of the atherinid genus Menidia were compared electrophoretically for enzymes representing an apparent 24 gene loci and for nonenzymatic skeletal muscle proteins. Average allelic frequency similarities between conspecific populations range from 0.84 to 0.99, averaging 0.94. The greatest allelic frequency similarity between two populations definitely representing separate species is 0.82. At a given locus, pairs of species tend to have either essentially identical or completely different allelic frequencies. Consistent with current taxonomic treatment, M. menidia and M. extensa were found to be quite distinctive from each other and from each of the other species in the genus. Populations of M. peninsulae were consistently distinct from M. beryllina, with which they were formerly considered conspecific. These two species co-occur from Florida to Texas, and genetic discontinuity was verified in four areas of local sympatry. Morphological and ecological differences also were found between M. peninsulae and M. beryllina. Contrasting with all other species comparisons in the genus, no electrophoretic differences were found between M. audens and M. beryllina. Morphological analysis revealed an intermediate population in Lake Palourde, southern Louisiana, the region where the ranges of these two species approach one another. Although the structure of this population suggests hybridization, the reproductive relationships of M. audens and M. beryllina remain in doubt. Hybridization is possible between all three of the coastal species, M. beryllina, M. peninsulae and M. menidia, but is common only in the zone of parapatry of M. menidia and M. peninsulae in northeastern Florida. Very little or no gene exchange between species occurs in this hybrid zone. Hybridization in Menidia appears to be related more to ecological similarity than to genetic similarity.