Strong Genetic Divergence Research Articles

On the taxonomic status of the harvest mouse Micromys minutus (Rodentia: Muridae) from Vietnam

The taxonomic status of the harvest mouse Micromys minutus from Vietnam is re-evaluated. The mtDNA analysis shows that the harvest mice from Lao Cai Province of northern Vietnam belongs to a distinct phylogenetic lineage, previously known only from a haplotype from Chengdu, Sichuan Province, southern China (Yasuda et al. 2005). The mtDNA analysis shows a strong genetic divergence among this lineage and all the other known haplotypes of Micromys minutus (11.68% for cytochrome b gene sequences). Canonical discriminant analysis of cranial and dental data, as well as of some external characters, also separate the Vietnam – South China group (also including an Indian specimen) from other Palaearctic populations. The skull of southern populations is relatively large, with a longer and broader palatine. The dorsal pelage of the Vietnamese specimens is grey, tinged with brown in comparison with the red-brown dorsal colouration sharply contrasting with the white underside in the majority of Euro-Siberian adults. The harvest mice of the Vietnam – South China group are distinguished from the typical European ones by their rather long tail that is about 120% of the body length (82 to 95% in the Palaearctic populations). Both genetic and morphological data suggest the existence of a second Micromys species, occurring at least in North Vietnam and South China. The available name for this species is Micromys erythrotis (Blyth, 1856).

A new species of cryptically coloured day gecko (Phelsuma) from the Tsingy de Bemaraha National Park in western Madagascar

Phelsuma borai sp. nov. (Squamata: Gekkonidae) is described from the Tsingy de Bemaraha National Park, a deciduous dry forest on a karstic limestone massif in western Madagascar. The new species, known from a single specimen only, has a greyish-brown ground colouration and the ability of remarkable colour change. In terms of colouration and morphology it most closely resembles Phelsuma mutabilis, which might occur in sympatry, but differs by scalation, colouration and strong genetic divergence.

Nuclear and cytoplasmic genetic diversity in weed beet and sugar beet accessions compared to wild relatives: new insights into the genetic relationships within the Beta vulgaris complex species

Hybridization between cultivated species and their wild relatives is now widely considered to be common. In the Beta vulgaris complex, the sugar beet seed multiplication areas have been the scene of inadvertent pollination of sugar beet seed bearers by wild ruderal pollen donors, generating a weedy form of beet which infests sugar beet fields in European countries. Up to now, investigations of evolutionary dynamics of genetic diversity within the B. vulgaris complex were addressed using few genetical markers and few accessions. In this study, we tackled this issue using a panel of complementary markers: five nuclear microsatellite loci, four mitochondrial minisatellite loci and one chloroplastic PCR-RFLP marker. We sampled 1,640 individuals that illustrate the actual distribution of inland ruderal beets of South Western France, weed beets and wild sea beets of northern France as well as the diversity of 35 contemporary European diploid cultivars. Nuclear genetic diversity in weed beets appeared to be as high as those of ruderal beets and sea beets, whereas the narrowness of cultivar accessions was confirmed. This genetic bottleneck in cultivars is even more important in the cytoplasmic genome as only one haplotype was found among all sugar beet cultivars. The large majority of weed beet populations also presented this unique cytoplasmic haplotype, as expected owing to their maternal cultivated origin. Nonetheless, various cytoplasmic haplotypes were found within three populations of weed beets, implying wild-to-weed seed flows. Finally, our findings gave new insights into the genetical relationships between the components of the B. vulgaris complex: (1) we found a very strong genetic divergence between wild sea beet and other relatives, which was unexpected given the recent evolutionary history and the full cross-compatibility of all taxa and (2) we definitely confirmed that the classification into cultivated, wild, ruderal and weed forms according to their geographical location, phenotype or their domesticated status is clearly in accordance with genetic clustering despite the very recent domestication process of sugar beet.

Population response to habitat fragmentation in a stream-dwelling brook trout population.

Fragmentation can strongly influence population persistence and expression of life-history strategies in spatially-structured populations. In this study, we directly estimated size-specific dispersal, growth, and survival of stream-dwelling brook trout in a stream network with connected and naturally-isolated tributaries. We used multiple-generation, individual-based data to develop and parameterize a size-class and location-based population projection model, allowing us to test effects of fragmentation on population dynamics at local (i.e., subpopulation) and system-wide (i.e., metapopulation) scales, and to identify demographic rates which influence the persistence of isolated and fragmented populations. In the naturally-isolated tributary, persistence was associated with higher early juvenile survival (∼45% greater), shorter generation time (one-half) and strong selection against large body size compared to the open system, resulting in a stage-distribution skewed towards younger, smaller fish. Simulating barriers to upstream migration into two currently-connected tributary populations caused rapid (2–6 generations) local extinction. These local extinctions in turn increased the likelihood of system-wide extinction, as tributaries could no longer function as population sources. Extinction could be prevented in the open system if sufficient immigrants from downstream areas were available, but the influx of individuals necessary to counteract fragmentation effects was high (7–46% of the total population annually). In the absence of sufficient immigration, a demographic change (higher early survival characteristic of the isolated tributary) was also sufficient to rescue the population from fragmentation, suggesting that the observed differences in size distributions between the naturally-isolated and open system may reflect an evolutionary response to isolation. Combined with strong genetic divergence between the isolated tributary and open system, these results suggest that local adaptation can ‘rescue’ isolated populations, particularly in one-dimensional stream networks where both natural and anthropogenically-mediated isolation is common. However, whether rescue will occur before extinction depends critically on the race between adaptation and reduced survival in response to fragmentation.

DIFFERENTIATION BETWEEN TWO SALT MARSH BEETLE ECOTYPES: EVIDENCE FOR ONGOING SPECIATION

The plausibility of trait divergence under divergent natural selection in the presence of gene flow in natural populations is a contentious issue in evolutionary research. Its importance lies in the fact that this process is thought to be one of the key triggers in ecological speciation in which a species splits into ecologically distinct forms when separate niches are occupied. In this study we demonstrate strong genetic divergence at the IDH1 locus between pond- and canal-inhabiting individuals of the salt marsh beetle Pogonus chalceus from the Guérande salt fields. Moreover, wing size, a trait that has a heritable basis in this species, was significantly larger in the pond populations, which is in concordance with the unstable nature of this habitat. The relationship between IDH1 allele frequencies and wing size variation was consistent with patterns seen across western European populations. By means of neutral allozymes and microsatellites we detected a small but significant degree of sexual isolation between ecotypes. We conclude that speciation is ongoing and that divergence reflects a balance between selection and gene flow.

Protecting evolutionary significant units for the remnant populations of Berchemiella wilsonii var. pubipetiolata (Rhamnaceae)

Berchemiella wilsonii var. pubipetiolata (Rhamnaceae) is an endangered tree in eastern China. Habitat destruction has resulted in fragmentation of remnant populations and extinction of local populations. AFLP and cpDNA markers were used to determine the population structure of remnant populations of B. wilsonii var. pubipetiolata. Moderate nuclear genomic diversity was found within each of the four remnant populations (H-S = 0.141-0.172), while the cpDNA haplotype diversity in each population ranged from 0.356 to 0.681. Six haplotypes were identified by a combined cpRFLP and cpSSR analysis in a total of 89 individuals. AMOVA revealed significantly AFLP genetic differentiation within and between regions (Phi(SC) = 0.196, Phi(CT) = 0.396, respectively), and a high cpDNA haplotype differentiation between regions (Phi(CT) = 0.849). The results suggest low gene flow between populations of B. wilsonii var. pubipetiolata. Strong genetic divergence between two regional populations as revealed by both AFLP and cpDNA markers provided convincing evidence that two distinct evolutionary lineages existed, and should be recognized as 'evolutionary significant units' (ESUs) for conservation concerns.

Genetic impacts of hybrid catfish farming ( Clarias macrocephalus× C. gariepinus) on native catfish populations in central Thailand

Escaped hybrid catfish (female Thai walking catfish, Clarias macrocephalus×male African catfish, C. gariepinus) from farms in central Thailand may interbreed with C. macrocephalus individuals in the wild. We assessed genetic introgression of C. gariepinus genes into four wild and two broodstock populations of C. macrocephalus based on diagnostic alleles at six allozyme loci and one microsatellite locus. A total of 22 out of 515 C. macrocephalus individuals examined had C. gariepinus alleles. One individual had C. gariepinus alleles at all six loci while the 21 remaining individuals had C. gariepinus alleles at one to two loci. In each population, the diagnostic markers detected between one and five individuals (1% to 11% of the sample) bearing hybrid genotypes. Farmers' inadvertent use of introgressed C. macrocephalus individuals as broodstock in producing hybrid catfish could result in loss of hybrid vigor for growth or disease resistance. We also evaluated existing genetic diversity within and among wild and broodstock C. macrocephalus populations using three microsatellite DNA markers. Compared to other Clarias species, C. macrocephalus had moderately high genetic variation within and among populations. Within each population, the number of alleles per locus ranged from 4 to 18 and heterozygosities ranged from 0.34 to 0.89. Narathivas, a southern population had the lowest microsatellite variation, allelic diversity (three alleles per locus) and heterozygosity ( H O=0.34). Within the central Thailand populations, the Ang Thong broodstock population expressed the lowest genetic diversity. Pair-wise exact tests suggested genetic divergence among most studied populations (31 of 36 tests, p<0.01). Cavalli–Sforza's chord genetic distances indicated strong genetic divergence between the Narathivas population (i.e., southern Thailand) and the rest of the sampled populations. Within central and northern Thailand, the Ang Thong Broodstock (central), Ayutthaya (central), Phitsanulok 1(northern) and Phitsanulok 2 (northern) populations were genetically diverged from the rest of the central populations. Our results suggested low levels of genetic introgression within examined wild and broodstock populations of C. macrocephalus and moderately high genetic diversity within and among these populations. Therefore, these populations could still be properly managed to prevent further genetic introgression and to maintain existing genetic diversity.

Resource-associated divergence in the arctic marine amphipod Paramphithoe hystrix

Host specialization has played an important role in the speciation of groups such as herbivorous insects and parasitic invertebrates. In this study, we provide evidence for its role in the diversification of the amphipod Paramphithoe hystrix Ross 1835 in Arctic marine waters. This species lives and feeds on the tissues of varied invertebrate hosts that are much larger than itself, including poriferans, hydrozoans and echinoderms, acting as a 'micropredator'. We examined the genetic structure of P. hystrix at sites in the Canadian Arctic where it is represented by a white form found on the light-coloured sea star Solaster endeca, a red form on the pink soft coral Gersemia rubriformis and by a spotted form with an unidentified host. These phenotypes occur in microallopatry, sometimes occupying alternate hosts just a few metres apart. Although their variation in host associates might have arisen from ingested host tissue, our results indicate that these morphs are genetically distinct. Mitochondrial (cytochrome c oxidase I) and nuclear (28S ribosomal RNA) gene sequences, as well as allozyme data all show strong genetic divergence between the three colour morphs, demonstrating their reproductive isolation. These results suggest that P. hystrix is a complex of at least three species, which may have arisen as a result of disruptive selection following host switches. Moreover, the depths of genetic divergence indicate that diversification of this complex was complete prior to the Pleistocene.

Diallel crossing among maize populations for resistance to fall armyworm

Among the insects infecting the maize (Zea mays L.) crop in Brazil, the fall armyworm (Spodoptera frugiperda Smith, 1797, Lepdoptera: Noctuidae) is considered one of the most important because it causes the highest damage to yield. Genetic resistance to the fall armyworm has be an effective control strategy. The main objective of this work was to evaluate new germplasm sources for resistance to the fall armyworm, the key pest for the maize crop in Brazil. A partial diallel design between 20 varieties of Brazilian germplasm and nine exotic and semi-exotic varieties of different origin was used. The 180 crosses and 29 parental varieties along with two commercial checks were evaluated in three locations in the State of São Paulo State (Brasil). Fall armyworm resistance (FAWR) under artificial and natural infestations, grain yield (GY), and plant height (PH) were analyzed. The populations CMS14C and MIRT, and hybrid São José x MIRT showed the highest resistance, with values of 1.8, 1.7 and 1.4, respectively. Populations PMI9401 and PR91B, and the hybrid CMS14C x (B97xITU) had best yields, with 4893, 3858 and 5677 kg ha-1, respectively. Heterosis ranged from -28% to 47% for FAWR and from -21% to 125% for GY, with mean values of -0,43% and 31%, respectively. Genotype by environment interaction was not significant for FAWR. The effects of varieties and heterosis were significant for all traits, showing that both additive and dominance effects may be important as sources of variation. For FAWR, only specific heterosis presented significance, suggesting strong genetic divergence between specific pairs of parental populations. Brasilian populations PMI9302 and São José, and the exotic population PR91B presented high performance per se, and also in croses for FAWR and GY. Crosses PMI9401 x (Cuba110 x EsalqPB1) and São José x MIRT presented high specific heterosis effects for both characters. These populations can be useful to be introgressed in maize breeding programs.

SYSTEMATICS OF THE EUROPEAN ENDANGERED CRAYFISH SPECIES AUSTROPOTAMOBIUS PALLIPES (DECAPODA: ASTACIDAE) WITH A RE-EXAMINATION OF THE STATUS OF AUSTROPOTAMOBIUS BERNDHAUSERI

Abstract The status of Austropotamobius berndhauseri (Crustacea, Decapoda) was re-examined by the combination of two recent genetic studies based on the analysis of the mitochondrial 16S rRNA gene obtained from sampling across the entire range of the white-clawed crayfish species complex. From the phylogenetic tree obtained, the results clearly demonstrate two clusters (A and B) separated by a strong genetic divergence (5.0 ± 1.0%) corresponding to A. italicus and A. pallipes species. Within A. italicus, three mtDNA lineages were found corresponding to A. i. italicus, A. i. carinthiacus, and A. i. carsicus. Austropotamobius berndhauseri specimens are not genetically distinct from A. i. carinthiacus distributed in Austria. This group is more closely related to A. i. italicus (1.4 ± 0.5%) than A. i. carsicus (3.6 ± 0.7%) which is concordant with allozyme data. These data support the redefinition of A. berndhauseri as being A. italicus carsicus.

Systematics of the European Endangered Crayfish Species Austropotamobius Pallipes (Decapoda: Astacidae) with a Re-Examination of the Status of Austropotamobius Berndhauseri

The status of Austropotamobius berndhauseri (Crustacea, Decapoda) was re-examined by the combination of two recent genetic studies based on the analysis of the mitochondrial 16S rRNA gene obtained from sampling across the entire range of the white-clawed crayfish species complex. From the phylogenetic tree obtained, the results clearly demonstrate two clusters (A and B) separated by a strong genetic divergence |$(5.0 \pm 1.0\%)$| corresponding to A. italicus and A. pallipes species. Within A. italicus, three mtDNA lineages were found corresponding to A. i. italicus, A. i. carinthiacus, and A. i. carsicus. Austropotamobius berndhauseri specimens are not genetically distinct from A. i. carinthiacus distributed in Austria. This group is more closely related to A. i. italicus|$(1.4 \pm 0.5\%)$| than A. i. carsicus|$(3.6 \pm 0.7\%)$| which is concordant with allozyme data. These data support the redefinition of A. berndhauseri as being A. italicus carsicus.

Can a Place of Origin of the Main Cystic Fibrosis Mutations Be Identified?

The genetic background of the mutations that most often cause cystic fibrosis (CF) is different from that of non-CF chromosomes in populations of European origin. It is not known whether these haplotype backgrounds could be found at high frequencies in populations in which CF is, at present, not common; such populations would be candidates for the place of origin of CF mutations. An analysis of haplotypes of CF transmembrane conductance regulator, together with their variation in specific CF chromosomes, in a worldwide survey of normal chromosomes shows (1) a very low frequency or absence of the most common CF haplotypes in all populations analyzed and (2) a strong genetic variability and divergence, among various populations, of the chromosomes that carry disease-causing mutations. The depth of the gene genealogy associated with disease-causing mutations may be greater than that of the evolutionary process that gave rise to present-day human populations. The concept of "population of origin" lacks either spatial or temporal meaning for mutations that are likely to have been present in Europeans before the ethnogenesis of present populations; subsequent population processes may have erased the traces of their geographic origin.

Strong genetic divergence among populations of a marine fish with limited dispersal, Acanthochromis polyacanthus, within the Great Barrier Reef and the Coral Sea.

Acanthochromis polyacanthus is an unusual tropical marine damselfish that uniquely lacks pelagic larvae and has lost the capacity for broad-scale dispersal among coral reefs. On the modern Great Barrier Reef (GBR), three color morphs meet and hydridize at two zones of secondary contact. Allozyme electrophoreses revealed strong differences between morphs from the southern zone but few differences between morphs from the northern counterpart, thus suggesting different contact histories. We explore the phylogeography of Acanthochromis polyacanthus with mitochondrial cytochrome b region sequences (alignment of 565 positions) obtained from 126 individuals representing seven to 12 fish from 13 sites distributed over 12 reefs of the GBR and the Coral Sea. The samples revealed three major clades: (1) black fish collected from the southern GBR; (2) bicolored fish collected from the GBR and one reef (Osprey) from the northern Coral Sea; (3) black and white monomorphs collected from six reefs in the Coral Sea. All three clades were well supported (72-100%) by bootstrap analyses. Sequence divergences were very high between the major clades (mean = 7.6%) as well as within them (2.0-3.6%). Within clades, most reefs segregated as monophyletic assemblages. This was revealed both by phylogenetic analyses and AMOVAs that showed that 72-90% of the variance originated from differences among groups, whereas only 5-13% originated within populations. These patterns are discussed in relation to the known geological history of coral reefs of the GBR and the Coral Sea. Finally, we ask whether the monospecific status of Acanthochromis should be revisited because the sequence divergences found among our samples is substantially greater than those recorded among well-recognized species in other reef fishes.

WHEN MORPHOLOGY MISLEADS: INTERPOPULATION UNIFORMITY IN SEXUAL SELECTION MASKS GENETIC DIVERGENCE IN HARLEQUIN BEETLE-RIDING PSEUDOSCORPION POPULATIONS.

Differences in secondary sexual characteristics of males often provide the most conspicuous means of distinguishing between closely related species. Does this therefore imply that the absence of differentiation in exaggerated male traits between allopatric populations provides evidence of a single, genetically cohesive species? We addressed this question with a comprehensive investigation of two populations (French Guiana and Panama) of the harlequin beetle-riding pseudoscorpion, Cordylochernes scorpioides. This highly sexually dimorphic pseudoscorpion is currently described as a single species, ranging throughout the Neotropics. Our morphometric analyses detected minimal differentiation between the two populations in all nine external morphological characters measured, including sexually dimorphic traits in males. Only in traits of the spermatophore was there any appreciable level of differentiation. Behavior differentiation and prezygotic reproductive isolation were also limited: 78.3% of males successfully transferred sperm to "foreign" females, and in 63.9% of these cases, females' eggs were successfully fertilized. By contrast, extensive divergence existed in two of nine electrophoretic loci, including an essentially fixed-allele difference at the Ldh locus. Most significantly, postzygotic reproductive isolation was complete, with heteropopulation zygotes invariably aborting early in development. These results strongly suggest that the two populations are, in fact, sibling species, a conclusion supported by our recently published findings on their marked divergence in minisatellite DNA. How can such interpopulation homogeneity in male sexually dimorphic traits exist in the face of strong genetic divergence? We propose that sexual selection, oscillating between favoring small and then large males, maintains such high levels of male variability within each population that it has obscured a speciation event in which genetic divergence and postzygotic incompatibility have clearly outpaced the evolution of prezygotic reproductive isolation.