Genetic Polymorphism and Evolution in Parthenogenetic Animals. II. Diploid and Polyploid SOLENOBIA TRIQUETRELLA (Lepidoptera: Psychidae)

Genic polymorphism at sixteen enzyme loci of four different chromosomal races of Solenobia triquetrella (bisexual, two diploid parthenogenetic races and tetraploid parthenogenetic) has been studied by starch gel electrophoresis. Isolated small diploid bisexual populations have rather uniform allele frequencies at all loci which we have studied. Diploid and tetraploid parthenogenetic individuals of this species are in general as heterozygous as bisexual ones. All parthenogenetic local populations are different from each other in the Alps. These parthenogenetic genotypes cannot be derived from a common ancestor through single mutations but rather bear evidence for a polyphyletic origin of parthenogenesis in Solenobia triquetrella. In the marginal distribution areas of the species in northern Europe single genotypes are spread over far larger areas than in the mountain regions of central Europe. This may be due to the old origin of parthenogenesis and polyploidy in northern Europe. No new parthenogenetic and polyploid strains have lately arisen in the regions outside of the Alps.     

The Organization of Genetic Diversity in the Parthenogenetic Lizard CNEMIDOPHORUS TESSELATUS

The parthenogenetic lizard species Cnemidophorus tesselatus is composed of diploid populations formed by hybridization of the bisexual species C. tigris and C. septemvittatus, and of triploid populations derived from a cross between diploid tesselatus and a third bisexual species, C. sexlineatus. An analysis of allozymic variation in proteins encoded by 21 loci revealed that, primarily because of hybrid origin, individual heterozygosity in tesselatus is much higher (0.560 in diploids and 0.714 in triploids) than in the parental bisexual species (mean, 0.059). All triploid individuals apparently represent a single clone, but 12 diploid clones were identified on the basis of genotypic diversity occurring at six loci. From one to four clones were recorded in each population sampled. Three possible sources of clonal diversity in the diploid parthenogens were identified: mutation at three loci has produced three clones, each confined to a single locality; genotypic diversity at two loci apparently caused by multiple hybridization of the bisexual species accounts for four clones; and the remaining five clones apparently have arisen through recombination at three loci. The relatively limited clonal diversity of tesselatus suggests a recent origin. The evolutionary potential of tesselatus and of parthenogenetic forms in general may be less severely limited than has generally been supposed.     

Potential for parthenogenesis of virgin females in a bisexual population of the geographically parthenogenetic mayfly Ephoron shigae (Insecta: Ephemeroptera,Polymitarcyidae)

The burrowing polymitarcyid mayfly Ephoron shigae is a geographically parthenogenetic species. Interestingly, the distributions of the bisexual and unisexual populations overlap broadly in their respective geographic ranges. In this mayfly, obligatory diploid thelytoky appears within unisexual populations. In the present study, we examined the potential for parthenogenesis or the parthenogenetic ability of females in a bisexual population aiming to understand the emergence of unisexual populations. The results obtained revealed that females in the examined bisexual populations showed a potential for diploid thelytoky as also seen in the unisexual populations, although, in females from bisexual populations, the development success rates of their unfertilized eggs were considerably lower than those of virgin females from unisexual populations. In the three bisexual reproducing species (Ephemera japonica, Ephemera strigata, and Ephemera orientalis) in the closely‐related family Ephemeridae, diploid thelytoky (i.e. tychoparthenogenesis; < 3%) was also observed. However, in this case, the parthenogenetic development success rates of unfertilized eggs were significantly lower than those of virgin females in the bisexual (Hino‐yosui Irrigation Canal) population of E. shigae. Accordingly, we suggest that parthenogenetic ability (i.e. tychoparthenogenesis or facultative parthenogenesis) in bisexual populations of E. shigae may facilitate the evolutionary transition to unisexual populations with fully obligatory parthenogenesis. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 326–334.     

Morphological characterization of adult Artemia (Crustacea, Branchiopoda) from different geographical origin. Mediterranean populations

Twelve morphological parameters have been measured in Artemiaindividuals belonging to 27 different populations located aroundthe Western Mediterranean basin. An analysis, through multivariatediscriminant procedures, allows us to establish relationshipsamong different populations. The three different types of populationstudied (bisexual diploid, parthenogenetic diploid and parthenogenetictetraploid) are thoroughly characterized by their morphologicalcharacteristics. This simple method is shown to be useful ingrouping different populations and to have predictive valuein assigning new populations to the groups previously analyzed.     

Contrasting patterns of molecular diversity and Wolbachia infection in bisexual and parthenogenetic Strophosoma weevils (Coleoptera: Curculionidae)

It has been postulated that parthenogenesis in weevil species is of hybrid origin, but some have speculated that Wolbachia infection plays a role through the modification of host breeding systems. Here we focus on Strophosoma weevils, which are known to be pests in young forest stands. Using molecular data, we investigated the diversity of the two most common Strophosoma species in Europe: S. capitatum, which reproduces bisexually, and S. melanogrammum, which is parthenogenetic. Also researched were their associations with the endosymbiotic bacterium Wolbachia. These species of weevil were found to be clearly distinguishable based on their mitochondrial DNA, with the bisexual taxa being more diverse. However, the nuclear DNA divergence of the two species was very low, and the parthenogenetic taxon was found to be heterozygous. Wolbachia infection was detected in all individuals of the S. melanogrammum populations and less than half of the S. capitatum populations. Moreover, multiple Wolbachia strains were found in both taxa (two in the former and three in the latter). The results of this research suggest that parthenogenesis in this genus is of hybrid origin and that Wolbachia could have played a role in speciation of these weevils.     

Molecular and genetic characterization of the allelic variants of Du215, Du281, Du323, and Du47G microsatellite loci in parthenogenetic lizard <Emphasis Type="Italic">Darevskia armeniaca</Emphasis> (Lacertidae)

A key issue in the study of unisexual (parthenogenetic) vertebrate species is the determination of their genetic and clonal diversity. In pursuing this aim, various markers of nuclear and mitochondrial genomes can be used. The most effective genetic markers include microsatellite DNA, characterized by high variability. The development and characterization of such markers is a necessary step in the genetic studies of parthenogenetic species. In the present study, using locus-specific PCR, for the first time, an analysis of allelic polymorphism of four microsatellite loci is performed in the populations of parthenogenetic species Darevskia armeniaca. In the studied populations, allelic variants of each locus are identified, and the nucleotide sequences of each allele are determined. It is demonstrated that allele differences are associated with the variation in the structure of microsatellite clusters and single nucleotide substitutions at fixed distances in flanking DNA regions. Structural allele variations form haplotype markers that are specific to each allele and are inherited from their parental bisexual species. It is established which of the parental alleles of each locus were inherited by the parthenogenetic species. The characteristics of the distribution and frequency of the alleles of microsatellite loci in the populations of D. armeniaca determining specific features of each population are obtained. The observed heterozygosity of the populations at the studied loci and the mutation rates in genome regions, as well as Nei’s genetic distances between the studied populations, are determined, and the phylogenetic relationships between them are established.     

THE ORIGIN AND EVOLUTION OF PARTHENOGENESIS IN HETERONOTIA BINOEI (GEKKONIDAE): EXTENSIVE GENOTYPIC DIVERSITY AMONG PARTHENOGENS

Variation at 18 allozyme loci was assayed among representatives of the geographically widespread, triploid parthenogenetic form of Heteronotia binoei. A minimum of 52 different genotypes were observed among 143 individuals. Virtually all localities sampled had multiple genotypes among the unisexuals. This represents unusually high genotypic diversity for a unisexual vertebrate. Heterozygosity in the triploids was higher than in diploid bisexual populations of H. binoei. Comparison with the alleles present in the diploid bisexuals confirms that the parthenogens are hybrids and indicates that most of the genotypic diversity stems from repetitive hybrid origins. However, the presence of some alleles unique to the parthenogens suggests that mutation adds to their genetic diversity. The genetic structure of this geographically widespread parthenogen suggests the hypothesis that the persistence and spread of the unisexual lineages is facilitated by genotypic diversity.     

Density dependent selection in parthenogenetic and self-mating populations

The consequences of density dependent selection on genetically heterogeneous, diploid populations reproducing by self-mating or various parthenogenetic mechanisms is investigated. A logistic fitness function that depends upon both the genotype of an individual and the density of the population is used. Such a fitness function simultaneously determines the population size and the genotype frequencies. The equilibrium solutions to a one locus and two locus model are given as well as some generalizations to n loci and nonlogistic fitness functions. Conditions are found that maintain several different genotypes simultaneously in the equilibrium population. The interaction of such selection with the genetic mechanisms which determine mode of reproduction in parthenogenetic populations is also discussed.     

Identification and biological role of the endosymbionts Wolbachia in rice water weevil (Coleoptera: Curculionidae)

Wolbachia spp. are obligate intracellular bacteria present in reproductive tissues of many arthropod species. Wolbachia infection status and roles in host reproduction were studied in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera, Curculionidae), an introduced species in China. We examined Wolbachia infection status in five populations in China where it reproduces parthenogenetically, and one native population in Southeast Texas, where it reproduces bisexually. All populations were infected by Wolbachia, and all specimens in each population were infected by Wolbachia of a single strain. Phylogenetic analyses based on multilocus sequence typing system indicated that Wolbachia in non-native L. oryzophilus weevils diverges evidently from those in native weevils. After treatments with tetracycline, parthenogenetic weevils reduced the fecundity significantly and eggs were not viable. Our results suggest that Wolbachia are necessary for oocyte production in L oryzophilus.     

Selection for Mating Reluctance in Females of a Diploid Parthenogenetic Strain of DROSOPHILA MERCATORUM

A diploid parthenogenetic strain of Drosophila mercatorum was outcrossed to produce genetic variance among the impaternate female offspring. Selection experiments were carried out for reluctance of the parthenogenetic females to mate.After only two cycles of selection, a parthenogenetic strain which is significantly less receptive to males from three different bisexual strains was obtained. It was also found that there is some degree of sexual isolation among the three bisexual strains used. The results support the idea that selection can render a newly produced diploid parthenogenetic strain behaviorally different from its bisexual ancestor. This appears to provide a framework which can explain the natural coexistence of diploid bisexual and diploid parthenogenetic biotypes in some species of insects.     

Reproductive modes and genetic polymorphism in the tardigrade Richtersius coronifer (Eutardigrada, Macrobiotidae)

Abstract. Allozymes were assessed by starch gel electrophoresis in 3 populations of a eutardigrade, Richtersius coronifer , with different reproductive modes. One population from Italy (with 2 sub-populations) was amphimictic and 2 populations (1 from Italy and 1 from Sweden) were parthenogenetic. All populations, irrespective of their reproductive mode, were diploid with the same chromosome number (2n=12) and had bivalents in the oocytes. Of the 14 loci analyzed, only 3 were polymorphic. The amphimictic population had a higher degree of genetic variability (mean heterozygosity >0.25) than the parthenogenetic populations (mean heterozygosity of the 2 populations <0.01). In all female populations, allele frequencies at all 3 loci deviated from Hardy-Weinberg equilibria due to heterozygote deficiency. These results support a hypothesis of automictic parthenogenesis in R. coronifer .     

The bacterial community associated with adult vine weevil (Otiorhynchus sulcatus) in UK populations growing on strawberry is dominated by Candidatus Nardonella

Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), commonly known as black vine weevil or simply vine weevil, is an important pest of soft fruit and ornamental crops. This species is endemic to temperate areas of Europe but has spread to many other areas over the last century, including North America and Australasia. The ability of vine weevils to adapt to such different environments is difficult to reconcile with the parthenogenetic reproduction strategy, which is likely to underpin a low genetic diversity. It is therefore tempting to hypothesize that weevil adaptation to different environments is mediated, at least partly, by the microbial communities inhabiting these insects. As a first step towards testing this hypothesis we characterized the composition of the bacterial microbiota in weevils from populations feeding on strawberry plants across four geographically separate locations in the UK. We performed 16S rRNA gene Illumina amplicon sequencing, generating 2 882 853 high‐quality reads. Ecological indices, namely Chao1 and Shannon, revealed that the populations used for this study harboured a low diversity and an uneven bacterial microbiota. Furthermore, β‐diversity analysis failed to identify a clear association between microbiota composition and location. Notably, a single operational taxonomic unit phylogenetically related to Candidatus Nardonella accounted for 81% of the total sequencing reads for all tested insects. Our results indicate that vine weevil bacterial microbiota resembles that of other insects as it has low diversity and it is dominated by few taxa. A prediction of this observation is that location per se may not be a determinant of the microbiota inhabiting weevil populations. Rather, other or additional selective pressures, such as the plant species used as a food source, ultimately shape the weevil bacterial microbiota. Our results will serve as a reference framework to investigate other or additional hypotheses aimed at elucidating vine weevil adaptation to its environment.     

Population differentiation and intraspecific genetic admixture in two Eucryptorrhynchus weevils (Coleoptera: Curculionidae) across northern China

Increasing damage of pests in agriculture and forestry can arise both as a consequence of changes in local species and through the introduction of alien species. In this study, we used population genetics approaches to examine population processes of two pests of the tree‐of‐heaven trunk weevil (TTW), Eucryptorrhynchus brandti (Harold) and the tree‐of‐heaven root weevil (TRW), E. scrobiculatus (Motschulsky) on the tree‐of‐heaven across their native range of China. We analyzed the population genetics of the two weevils based on ten highly polymorphic microsatellite markers. Population genetic diversity analysis showed strong population differentiation among populations of each species, with F _ST ranges from 0.0197 to 0.6650 and from −0.0724 to 0.6845, respectively. Populations from the same geographic areas can be divided into different genetic clusters, and the same genetic cluster contained populations from different geographic populations, pointing to dispersal of the weevils possibly being human‐mediated. Redundancy analysis showed that the independent effects of environment and geography could account for 93.94% and 29.70% of the explained genetic variance in TTW, and 41.90% and 55.73% of the explained genetic variance in TRW, respectively, indicating possible impacts of local climates on population genetic differentiation. Our study helps to uncover population genetic processes of these local pest species with relevance to control methods.     

Measures of spatial structure in samples of genotypes for multiallelic loci.

Various spatial autocorrelation statistics have been widely used both in theoretical population genetics and to study the spatial distribution of diploid genotypes in many plant and animal populations. However, previous simulation studies have considered only diallelic loci. In this paper, we use a large number of space-time simulations to characterize for the first time the parametric and statistical values of Moran's I-statistics for converted individual genotypes as well as for join-count statistics. A wide range of levels of dispersal and numbers of alleles and allele frequencies are modelled and the results reveal the different general effects of each of these factors on these statistics. We also examine the range of appropriate sampling designs and sizes for which predicted values can be interpolated for specific sampling schemes for any given population genetic field survey. Numbers of alleles and allele frequencies each affect some statistics but not others. The results indicate generally low standard deviations. The results also develop precise and efficient methods of estimating gene dispersal, based on the various autocorrelation measures of standing spatial patterns of genetic variation within populations. The results also extend these methods to loci with multiple alleles, typical of those studied through modern molecular methods.     

APPLICABILITY OF THE HYPERGEOMETRIC PHENOTYPIC MODEL TO HAPLOID AND DIPLOID POPULATIONS

We show that the phenotypic hypergeometric model of a quantitative trait can exactly describe both haploid and diploid populations. The condition necessary for this is equiprobability of genotypes within each phenotype. This requires equal allele frequencies across the loci, which may be the case when the population is under disruptive selection.     

Discovery of a diploid population of theHemidactylus garnotii-vietnamensis complex (Reptilia: Gekkonidae)

A diploid member of the parthenogenetic gekkonid species complexHemidactylus garnotii-vietnamensis was discovered for the first time from Thailand. This gecko, seemingly unisexual and parthenogenetic, possesses 2n=2x=38 chromosomes, showing distinct heteromorphisms. The absence of bisexual congeneric species with a combination of karyomorphs to produce this karyotype indicates the occurrence of chromosomal rearrangements after the initial estabilishment of a diploid clonal lineage of hybrid origin. Results of karyotypic comparisons of the present sample and the three known triploid species belonging to theH. garnotii-vietnamensis complex suggest that a triploid karyomorph similar to that ofH. vietnamensis has first emerged through an insemination of the diploid parthenogen's egg by the sperm from a bisexual species having 44 chromosomes (all telocentric), and that the karyomorph subsequently experienced some minor chromosomal aberrations to produce the karyomorphs ofH. vietnamensis andH. garnotii. The origin of theH. stejnegeri karyotype still remains an open question for future studies.     

Analysis of genetic variation in unisexual and bisexual lizard species of the genus Leiolepis from Southeast Asia

Using multilocus DNA fingerprinting with microsatellite probes (CAC)5, (GACA)4, (GGCA)4 and (GATA)4, intraspecific variation of the Southeast Asian lizards belonging to the genus Leiolepis (bisexual species Leiolepis reevesii and triploid parthenogenetic species Leiolepis guentherpetersi) was first examined. The L. guentherpetersi lizards were characterized by monophyletic DNA fingerprint profiles for the loci detected by the (GACA)4, (GGCA)4, and (CAC)5 probes, in terms of intrapopulation similarity index constituting S = 0.96. This was different from the individual-specific profiles of the lizards from bisexual, presumably parental species, L. reevesii (S = 0.6; P < 0.001). Genetic homogeneity of triploid L. guentherpetersi lizards at the loci examined serves as one of the arguments for the parthenogenetic nature of this species. Genetic variability of triploid parthenogenetic species L. guentherpetersi appeared to be comparable with that reported earlier for the Caucasian rock lizards of the genus Darevskia, namely, D. dahlia, D. armeniaca, and D. unisexualis (P > 0.05). The results of DNA fingerprinting analysis of the same L. guentherpetersi samples with the (GATA)4 hybridization probe were unexpected. Variability of parthenogenetic species L. guentherpetersi at the (GATA)n markers was remarkably higher than that at other DNA markers (S = 0.35; P = 3.08 x 10(-11)), being comparable to the variation of the (GATA)n DNA markers in bisexual species L. reevesii (P = 0.74). The reasons for high polymorphism of the (GATA)n-containing loci in L. guentherpetersi still remain unclear. This polymorhism is probably associated with high instability of the loci, which can be revealed by means of family analysis of parthenogenetic offspring.     

Functional rare males in diploid parthenogenetic Artemia

Functional males that are produced occasionally in some asexual taxa – called ‘rare males’ – raise considerable evolutionary interest, as they might be involved in the origin of new parthenogenetic lineages. Diploid parthenogenetic Artemia produce rare males, which may retain the ability to mate with females of related sexual lineages. Here, we (i) describe the frequency of male progeny in populations of diploid parthenogenetic Artemia, (ii) characterize rare males morphologically, (iii) assess their reproductive role, using cross‐mating experiments with sexual females of related species from Central Asia and characterize the F1 hybrid offspring viability and (iv) confirm genetically both the identity and functionality of rare males using DNA barcoding and microsatellite loci. Our result suggests that these males may have an evolutionary role through genetic exchange with related sexual species and that diploid parthenogenetic Artemia is a good model system to investigate the evolutionary transitions between sexual species and parthenogenetic strains.     

The Population Genetics of Parthenogenetic Strains of DROSOPHILA MERCATORUM. II. the Capacity for Parthenogenesis in a Natural, Bisexual Population

Drosophila mercatorum is a bisexual species, but certain strains are capable of parthenogenetic reproduction in the laboratory. We investigated the parthenogenetic capacity of the virgin daughters of females captured from a natural, bisexual population in Hawaii. An isozyme survey indicated the natural population is polymorphic at about 50% of its loci, and its individuals heterozygous at 18% of their loci. The predominant mode of parthogenesis in D. mercatorum causes homozygosity for all loci in a single generation. Despite this radical change in genetic state, 23% of the virgin female lines produced adult parthenogenetic progeny, and 16% produced parthenogenetic progeny themselves capable of parthenogenetic reproduction. The parthenogenetic rats as measured by the number of parthenogenetic progeny themselves capable of parthenogenesis divided by the number of eggs laid is arougn 10(-5) for the virgin female lines. We argue that one of the major reasons for this low rate is that very few of the impaternate zygotes have a genotype that can survive and reproduce under the genetic conditions imposed by parthenogenetic reproduction. This intense selective bottleneck can be passed in a single generation if enough unfertilized eggs are laid, and once passed is accompanied by a large (perhaps a thousandfold) increase in the rate of parthenogenesis and by modifications in many phenotypic traits such as morphology and behavior.     

Population genetic consequences of feeding habits in some forest lepidoptera

By surveying variation at allozyme loci in several phytophagous lepidopteran species (Geometridae), we have tested two hypotheses about the relationship of genetic variation to environmental heterogeneity: (1) that allozyme polymorphisms may exist because of associations between genotypes and "niches" (different host plants, in this instance), and (2) that the overall genetic variation of a species is correlated with environmental heterogeneity (or breadth of the species' overall ecological niche).—Genetic differentiation among samples of oligophagous or polyphagous species taken from different host species was observed in one of three species, at only one of seven polymorphic loci. The data thus provide no evidence for pronounced genetic substructuring, or "host race" formation in these sexually reproducing species, although host plant-genotype associations in a parthenogenetic moth give evidence of the potential for diversifying selection.—In a comparison of allozyme variation in polyphagous ("generalized") and oligophagous ("specialized") species, heterozygosity appeared to be higher in specialized species, at all polymorphic loci but one. It is possible that this unexpected result arises from a functional relation between breadth of diet and genetic variation.