Genetic and morphometric variation in the potamonautid river crab Potamonautes parvispina (Decapoda: Potamonautidae) from two Western Cape rivers,South Africa

Patterns of genetic and morphometric variation amongst five populations of Potamonautes parvispina from two rivers in the Western Cape, were examined. Genetic variation at 14 loci was investigated using protein gel electrophoresis. The results showed that the populations were genetically invariant within and between the two drainage systems. Discriminant functions analyses of seven carapace variables demonstrated regional differentiation between the population groups in the two drainage systems. Other morphometric characters exhibited a significant degree of variation within drainage systems. Morphometric data were highly variable and were discordant with the genetic data, which suggests that environmental factors may be responsible for the large degree of phenotypic plasticity. Results from the present study are discussed in terms of widespread gene flow and recent population divergence.     

Biochemical differentiation in the Idaho ground squirrel, Spermophilus brunneus (Rodenta: Scuridae)

Spermophilus brunneus is restricted to a 90 × 125-km area of west central Idaho, with two distinct (northern and southern) groups of populations within this limited range. Morphological differences in pelage length and coloration, external and cranial measurements, and bacula suggest that these groups are either very distinct subspecies or species. We used starch-gel electrophoresis to estimate the amount of genetic differentiation accompanying these morphological differences by assaying genetic variation at 31 loci in the two geographic groups. Fifteen loci were polymorphic (13 in the northern group, 12 in the southern), and mean heterozygosity (H) was high (12.3% northern and 10.8% southern). Nei's genetic distance (0.057) is in the range usually associated with subspecific differences. However, Jaccard's association coefficient (0.893) is about the same as that found between several ground squirrel taxa currently recognized as species. The high levels of heterozygosity suggest that S. brunneus is a neoendemic rather than a paleoendemic species.     

Traditional and geometric morphometric analyses reveal homogeneity in European Scutacarus acarorum Goeze, 1780 populations (Acari: Scutacaridae: Heterostigmatina)

The mite Scutacarus acarorum (Scutacaridae, Heterostigmatina) is one of the dominant bumblebee inquilines in the Holarctic. The wide distribution and the host generalist behaviour of S. acarorum suggest that it could be a group of multiple cryptic species. European S. acarorum populations and a small population from New York were studied using traditional and geometric morphometric methods to detect possible geographical or host-dependent variation. The analyses revealed homogeneity of all populations, suggesting that the species experienced a bottleneck during the last ice age and that gene flow between the populations is maintained. High variability within populations indicates a high genetic diversity. No host-related morphological differences were detected, suggesting that S. acarorum is a true generalist. Fresh mite samples from locations all over the Holarctic are needed to draw further conclusions on the species’ phylogeography and also on its population genetic structure.     

Genetic differentiation and gene flow of Porcellionides pruinosus (Crustacea: Isopoda: Oniscidea) in Tunisia

Iso-enzymatic polymorphism analysis was carried out on Tunisian populations of Porcellionides pruinosus to clarify their confused taxonomic status, previously revealed by reproductive and morphological approaches. Seventeen allozyme loci were studied, using horizontal starch gel electrophoresis, in 230 adult specimens belonging to nine populations of P. pruinosus located in north, central and south Tunisia, to assess the levels of their intra-genetic and inter-genetic diversity, and to analyse their genetic structure. Our results indicate a low genetic variability with a polymorphism ratio ranging from 29.4% in Tabarka to 47.1% in the Garat Nâam and Raccada populations, and the mean number of alleles per locus was estimated at 1.51 ± 0.15. The direct-count of heterozygosity ranged between 8.1% and 15%. Substantial estimates of demic structuring were found at the total population (F_ST = 0.198), with a generalized and significant heterozygote deficiency detected in every population (with a mean value for all populations of F_IS = 0.372). Genetic distances between the studied populations were low, indicating that they belong to the same species. Nevertheless, the genetic analyses showed the divergence of the population of Tabarka from all the other studied populations, with the lowest mean gene flow, 0.58, and the highest mean genetic distance, (0.182) obtained also by the morphological and reproductive approaches.     

Phylogenetic divergence in a desert fish: differentiation of speckled dace within the Bonneville, Lahontan, and upper Snake river basins

Historical events have had a great impact on the biogeography of fishes of western North America. We examined the genetic variation of the speckled dace ( Rhinichthys osculus ) to determine the effects on this species of extensive hydrological changes during the last 10 million years in the Bonneville and Lahontan basins of the Great Basin and the upper Snake River Basin. Eight hundred sixty-nine base pairs of the mitochondrial gene cytochrome b were sequenced from 97 individuals representing 22 populations within these 3 basins, as well as from 2 individuals of longnose dace ( Rhinichthys cataractae ) that served as outgroups. Additionally, 13 speckled dace sequences representing 3 Bonneville populations were used from GenBank. Phylogenetic relationships were reconstructed using maximum parsimony and maximum likelihood criteria. Analysis of molecular variance was used to determine population structure and to estimate the amount of gene flow across the community boundaries. Three distinct clades were reconstructed representing the Lahontan Basin, the northern Bonneville and upper Snake River basins, and the southern Bonneville Basin. Additionally, most of the population structuring was explained by variation among basins (65.33%). Speckled dace demonstrated high genetic variation. As hypothesized, the northern and southern Bonneville specimens formed separate clades; however, the southern Bonneville clade was basal to a sister clade formed by the northern Bonneville/upper Snake River and Lahontan clades. These relationships indicate that Pliocene connections between the Snake, Lahontan, and Bonneville drainages, rather than more recent Pleistocene connections, best explain population structuring in speckled dace.     

Evolutionary differentiation within the northern Great Basin pocket gopher, Thomomys townsendii I. Morphological variation

Geographic and nongeographic variation in morphology was examined in Thomomys townsendii . A univariate analysis of external and cranial characters from a large population sample (66 adults; fusion of cranial sutures used as aging criteria) was used to assess variation among three adult age classes and between sexes. Only minor variation is apparent among age classes; however, sexual dimorphism is pronounced. Univariate and multivariate techniques were used to analyze external and cranial measurements and pelage characters for adults throughout the species range. These analyses show little to support the seven subspecific designations recognized by Davis (1937). The general pattern is one of homogeneity throughout the range of Thomomys townsendii . With the possible exception of T. t. nevadensis samples, current subspecies are not defined as morphological units. In fact, differentiation is found among populations within some subspecies. The most apparent pattern seen in these analyses is the divergence between the Humboldt River (including Honey Lake Valley samples) and Snake River systems. These results will be considered with those of a companion paper on the genetic variation in this species to more adequately assess the patterns of differentiation in Thomomys townsendii .     

Revisiting the saproxylic beetle ‘Propomacrus cypriacus Alexis & Makris, 2002’ (Coleoptera: Euchiridae) using molecular,morphological and ecological data

Propomacrus cypriacus a saproxylic beetle endemic to Cyprus, was described as a species distinct from P. bimucronatus on the basis of a few morphological characters and has been evaluated as Critically Endangered by IUCN, as it depends on veteran trees and has a restricted distribution. Herein we explored the distribution, ecology, morphology and genetic variation of the populations from Cyprus, and we attempted a phylogenetic analysis including related species based on two mitochondrial and one nuclear DNA markers. We also used published mtDNA divergence rates to date cladogenetic events. Despite extensive sampling, we found only a small number of individuals, adding a few additional localities to the known distribution of the species, and we identified two more host species to those previously reported. Morphological examination showed that only the form of male protibiae differs consistently in Cyprus populations compared to those of P. bimucronatus from Turkey and the Lebanon. Nevertheless, genetic analyses do not support a distinct species status for populations from Cyprus, which should instead be considered as a subspecies of P. bimucronatus. Morphological and ecological data further support this conclusion. Cyprus populations have diverged from nearby continental ones in mid to late Pleistocene.     

Evolutionary differentiation within the northern Great Basin pocket gopher, Thomomys townsendii II. Genetic variation and biogeographic considerations

Geographic and nongeographic variation in morphology was examined in Thomomys townsendii . A univariate analysis of external and cranial characters from a large population sample (66 adults; fusion of cranial sutures used as aging criteria) was used to assess variation among three adult age classes and between sexes. Only minor variation is apparent among age classes; however, sexual dimorphism is pronounced. Univariate and multivariate techniques were used to analyze external and cranial measurements and pelage characters for adults throughout the species range. These analyses show little to support the seven subspecific designations recognized by Davis (1937). The general pattern is one of homogeneity throughout the range of Thomomys townsendii . With the possible exception of T. t. nevadensis samples, current subspecies are not defined as morphological units. In fact, differentiation is found among populations within some subspecies. The most apparent pattern seen in these analyses is the divergence between the Humboldt River (including Honey Lake Valley samples) and Snake River systems. These results will be considered with those of a companion paper on the genetic variation in this species to more adequately assess the patterns of differentiation in Thomomys townsendii .     

Heleobia maltzani (Westerlund, 1886) (Caenogastropoda: Truncatelloidea: Cochliopidae) from Crete and species-level diversity of Heleobia Stimpson, 1865 in Europe

Morphological characters and partial cytochrome oxidase (COI) DNA sequences were used to investigate intra- and interpopulation differences among three Cretan brackish-water populations of Heleobia maltzani snails. The morphology of male and female reproductive organs of H. maltzani did not differ within studied populations or in comparison with closely related species. In contrast, analysis of shell morphology revealed substantial variation not supported by the genetic data. Genetics results showed surprisingly low differentiation between all Cretan populations and also mainland populations of Heleobia. They also showed that H. maltzani is conspecific with four other European species of Heleobia, thus implying that there is only one species of brackish-water Heleobia in Europe. Such a low level of genotypic differentiation is unusual for typical island species and is most probably the consequence of recent colonization of Crete. Possible scenarios of such processes are discussed.     

Morphological and genetic variation among populations of the rare Kachina daisy ( Erigeron kachinensis ) from southeastern Utah

Erigeron kachinensis , the Kachina daisy, is a rare species restricted to canyons in southeastern Utah. The species is known to exhibit low fecundity due to low percent fertilization of ovules and high percent abortion of fertilized ovules. Previous reproductive studies suggest that low fecundity is a consequence of small population size and inbreeding depression. This study examines genetic diversity within and among populations of E. kachinensis in Natural Bridges National Monument using enzyme electrophoresis. Field populations are found to have significantly different morphologies. However, morphological differences were less pronounced among populations grown in the greenhouse. The Kachina daisy exhibits levels of genetic variability in its populations similar to that of other outcrossed species. Genetic diversity statistics demonstrate that only 22.8% of genetic variation is distributed among populations. Genetic distance could not be correlated with geographic distance. Most of the populations showed significant deviation of fixation indices from zero for multiple loci. Observation of genotype frequencies demonstrates that populations are fixing on different genotypes and may be experiencing initial stages of genetic drift. Mean observed heterozygosity was 0.166 and was found to increase with increasing size and/or age in populations.     

Genetic structuring at a fine scale in the russet-crowned motmot ( Momotus mexicanus ) in a tropical dry forest in central Mexico

Because of their high dispersal abilities, birds are expected to manifest marked genetic structuring only at relatively large geographic scales. However, it is not well known how factors like nest site fidelity in a largely resident species could limit gene flow and increase genetic structuring in birds. In this study we use RAPD markers to estimate genetic structuring in a strongly sedentary species of the American tropics, the Russet crowned Motmot ( Momotus mexicanus ), within a tropical dry forest in central Mexico. Genetic structuring was assessed among 3 populations separated by a mean distance of only 25 km. We report that 12.9% of the total genetic variation is explained by differences among sites, which is quite high for a bird at this geographic scale. We propose that high nest site fidelity, brought on by a scarcity of suitable nest substrates, may be responsible for high genetic structuring in this species.     

Genetic structure in striped skunks ( Mephitis mephitis ) on the Southern High Plains of Texas

Genetic variation within populations reflects population-level social and demographic processes and influences how a population behaves as an evolutionary unit. We examined partitioning of genetic variation in striped skunks ( Mephitis mephitis ) from the Southern High Plains of Texas during 1994-1995. Sixty-nine male and 35 female skunks were sampled on four 12.8-km 2 study plots. Plot centers ranged from 17.6 to 61.6 km apart. We used multi-locus DNA fingerprinting with 2 probes, pV47 and CTTxAGG, to test 3 hypotheses: (1) females are more genetically similar to other females than males are to other males on the same plot (indicating greater female philopatry than male philopatry), (2) genetic similarity is greater within plots than among plots (indicating partitioning of genetic variation in space), and (3) genetic similarity of males decreases as the distance separating males increases (indicating geographic distance affects rates of gene flow). In general, males on a plot had lower average genetic similarity than females. Genetic similarity within plots was not different from genetic similarity among plots for males or for females. Genetic similarity of males did not decrease with increasing distance among plots. The lack of geographical genetic structure in striped skunks suggests at the scale of this study (< 60 km) that gene flow of biparentally inherited genes is not distance-mediated. However, the higher similarity values for females than for males on the same plot supports an effect of male-biased dispersal and female philopatry on partitioning of genetic variation between sexes.     

Genetic diversity in the Carabodes marginatus species group (Acarida,Oribatida, Carabodidae) as inferred from allozymes

Ten populations representing four species of the ‘Carabodes marginatus’ group, as C. marginatus, C. affinis, C. quadrangulus and C. montanus from central Italy have been studied for genetic variation at 16 enzymatic loci by electrophoresis. Morphotypes close to C. marginatus but easily distinguishable by the shorter marginal notogastral setae were also included in the analysis to evaluate their systematic status. Carabodes arduinii, a very different species from the ‘coriaceus’ group, was employed as an out-group. Phylogenetic relationships among different species were studied and inferred data demonstrated that cladogenetic events occurred, even though rates of molecular and morphological evolution do not correlate. Morphotypes related to C. marginatus were genetically very close to the type specimens, but a different pattern of allele frequency was observed in sympatric populations of the two setal forms. Possible explanations for this finding are suggested in relation to historical processes. The rate of gene flow among populations of the two morphs was estimated by both Wright's F _st and Slatkin's Nm methods. These two different procedures yielded contradictory results.     

Taxonomy of Sphaeromeria, Artemisia , and Tanacetum (Compositae, Anthemideae) based on randomly amplified polymorphic DNA (RAPD)

Relationships within, between, and among the Anthemideae genera Sphaeromeria, Artemisia , and Tanacetum were investigated using 238 randomly amplified polymorphic DNA (RAPD) markers obtained from twenty 10-mer primers amplified on genomic DNA. Forty-one populations from 16 taxa (15 species) were studied. Jaccard's coefficient of similarity and UPGMA clustering analysis were used to construct phenograms. T tests were used to make comparisons between samples at various systematic levels. DNA markers were 75% similar for conspecific populations. Sixteen Sphaeromeria populations (5 species) showed an average interspecific similarity of 21%. Interspecific similarity among 23 Artemisia populations (8 species with 2 subspecies of A. tridentata included) averaged 27%. Two Tanacetum species (1 population each) were 89% similar. The high similarity of Tanacetum species was in the range of observed values for conspecific populations; indeed those 2 species ( T. vulgare and T. boreale ) have been considered conspecific by some authors. The 3 subgenera of Artemisia studied ( Artemisia, Dracunculus , and Tridentatae ) formed separate groups. In comparison among the genera, Sphaeromeria was 18% similar to Artemisia (more similar to subgenus Tridentatae than the other Artemisia subgenera); intergeneric comparisons of Sphaeromeria and Artemisia and Tanacetum , which supports previously established morphological distinctions. Sphaeromeria potentilloides may be misplaced in the genus Sphaeromeria based on DNA marker results. It is likely that North American Anthemideae are circumboreal derivatives of ancestral Eurasian stock and that Sphaeromeria is derived from an Artemisia -like ancestor.     

Hybridization between a rare and introduced Oenothera along the north Pacific Coast

Interspecific hybridization has increasingly become regarded as a serious threat to the genetic integrity and persistence of rare plants. Oenothera glazioviana (Onagraceae) is a horticultural species that has escaped cultivation and now threatens the narrow Pacific coastal endemic O. wolfii with hybridization. Reports of morphologically intermediate and ecologically aggressive forms prompted this investigation into the extent of hybridization over the range of O. wolfii . In particular, this study identifies populations of pure and hybrid origins. We used multivariate methods to characterize the morphological variation of Oregon and northern California coastal Oenothera populations. Putatively pure O. wolfii and O. glazioviana individuals do not overlap in many floral characteristics. We found morphologies ranging between the 2 species in northern California populations, however, supporting the inference of hybridization. Remote O. wolfii populations in Oregon were smaller in almost all characters, and discriminant analysis was able to distinguish the rare species from both hybrids and O. glazioviana . However, 5 of 10 O. wolfii populations overlapped significantly with hybrid populations for individual traits and composite morphology, and trait values outside the range of O. wolfii were discovered in 2 populations previously considered to be pure. We also discuss the morphological evidence in light of these species’ chromosomal complexes and environmental factors.     

Genetic analysis of the rare species Salix arizonica (Salicacea) and associated willows in Arizona and Utah

Management decisions affecting the rare plant Arizona willow ( Salix arizonica ) will be aided by understanding genetic similarities among populations of this species. Random Amplified Polymorphic DNA (RAPD) analysis was conducted on 20 populations of S. arizonica , 12 populations of 5 congeners, and 2 samples of outgroup, Populus tremuloides . A phenogram based on DNA markers shows clear separation of populations of S. arizonica from those of co-occurring willow species, but similarity is low (～ 37%) between Utah and Arizona populations of S. arizonica . Evaluation of the relationship of habitat characteristics and geographic distance to genetic similarity reveals that environment and genetic similarity are poorly correlated. Considering Arizona versus Utah populations, we found a significant negative relationship between geographic distance and genetic similarity ( r = 0.936), but no significant relationship between interpopulation distance and genetic similarity within Arizona or Utah. The wide geographic disjunction of S. arizonica populations in Utah and Arizona appears to have existed for a long period during which genetic drift, random mutations, and selection for somewhat different habitats have pushed the 2 regional complexes along separate evolutionary trajectories. Preservation of genetic variation within S. arizonica will require protection of multiple populations in Arizona and Utah.     

Effects of habitat fragmentation and differing mobility on the population structures of a Great Basin dragonfly ( Sympetrum corruptum ) and damselfly ( Enallagma carunculatum )

The population structure of 2 Great Basin odonate species was assessed using protein electrophoresis. Analyses included 7 populations of Sympetrum corruptum (suborder Anisoptera), a migratory and highly mobile dragonfly, and 8 populations of Enallagma carunculatum (suborder Zygoptera), a weak flier that is not known to migrate far from natal water sources. Though we expected the damselfly ( E. carunculatum ) to show greater genetic isolation than the dragonfly ( S. corruptum ), both species apparently had high levels of gene flow (theta = 0.0604 for S. corruptum , theta = 0.0485 for E. carunculatum ) and showed no evidence for isolation by distance. These results suggest that both species are highly vagile and that the most important factors affecting population structure of these odonates may be ecological conditions such as habitat patchiness and the ephemerality of water sources.     

On the taxonomic status of Eriogonum robustum (Polygonaceae), a rare endemic in western Nevada

Evidence from the morphology, genetics, and biogeography of a rare endemic from western Nevada, Erigonum robustum , is presented to determine the most accurate taxonomic classification. Previous authors have classified E. robustrum Greene both as a species and as a variety E. lobbii Torrey & Gray. However, results of a morphometric comparison for 9 characters establish that significant morphological differentiation exists between E. robustum and E. lobbii . In addition, results of a genetic study using protein electrophoresis indicated that genetic differentiation may exist between these 2 taxa. Furthermore, the 2 taxa are geographically, ecologically, and reproductively isolated. Finally, the selective pressures that act on E. robustum in a narrowly restricted cold-desert environment are different from those that act on E. lobbii in subalpine environment. Thus, all available data support a species-level taxonomic classification for E. robustum .     

Native plant community composition and genetic diversity associated with long-term weed invasions

Many studies have assessed genetic changes in exotic plant species in their native and introduced ranges, but none have focused on genetic variation in native plant species in response to exotic invasion. We examine characteristics of native plant communities within and outside old (> 25 year) invasions of Acroptilon repens (Russian knapweed) and Cardaria draba (hoary cress). We also document genetic variability of 4 native grass populations ( Hesperostipa comata [needle and thread], Achnatherum hymenoides [Indian ricegrass], Sporobolus airoides [alkali sacaton], and Poa secunda [Sandberg bluegrass]) from 2 areas: adjacent to and within weed invasions. Native plant species richness and diversity did not differ between invaded and noninvaded areas. Inter-simple sequence repeat (ISSR) analysis of individual native perennial grasses of each of the 4 species suggests that populations exposed to long-term coexistence with exotics may differ from adjacent noninvaded populations. We suggest that future research efforts should focus on intraspecific diversity of native plant species to identify possible candidates for restoration following weed control.     

A plasma protein marker for population genetic studies of the desert tortoise ( Xerobates agassizi )

Fifty-seven individual plasma samples from desert tortoises ( Xerobates agassizi ) representing 10 separate populations were analyzed by polyacrylamide gel electrophoresis using alkaline buffers. An albumin-like protein was found to be polymorphic for two electromorphs in northern populations inhabiting the Mohave Desert Province while Sonoran Desert populations to the south were monomorphic. The genetic divergence demonstrated in this survey is similar to earlier studies and provides evidence for the Colorado River as a potential barrier to gene flow among tortoise populations. These data suggest that tortoise plasma, examined by various electrophoretic methods, may provide a nondestructive means of determining the broad regional origin of desert tortoises.