Genetic polymorphism and evolution in parthenogenetic animals. V. Triploid Adoxus obscurus (Coleoptera: Chrysomelidae)

GENOTYPIC AND ENVIRONMENTAL COMPONENTS OF VARIATION IN GROWTH AND REPRODUCTION OF FISH HEMICLONES (POECILIOPSIS: POECILIIDAE)

The frozen-niche-variation model was proposed to account for the coexistence of genetically related clones in naturally occurring unisexual populations. This model is based on two assumptions: 1) ecologically different clones have multiple independent origins from sexual ancestors; and 2) the population of sexual ancestors contains genetic variability for ecologically relevant traits. To test these assumptions, we produced 14 new "hemiclones" (nonrecombining haploid genotypes) of fish (Poeciliopsis: Poeciliidae). Our ability to synthesize many new hemiclones demonstrates the feasibility of multiple independent origins of nonrecombining genotypes. A substantial proportion (10-50%) of the phenotypic variation among hemiclones in size at birth, juvenile growth rate, and fecundity had a genetic basis. Thus, we conclude that multiple origins can give rise to an assemblage of genetically distinct hemiclones, each with a unique combination of life-history traits. Additionally, a comparative analysis of two natural hemiclones revealed that the synthetic strains represent a broad field of variation from which natural hemiclones can be selected.

Wolbachia infection in the tribe Naupactini (Coleoptera, Curculionidae): association between thelytokous parthenogenesis and infection status

Several parthenogenetic species of broad-nosed weevils exist, some of them of economic importance because of their pest status. Screening of the maternally inherited Wolbachia bacterium in 29 weevils of the tribe Naupactini, using multilocus sequence typing allowed us to assess a significant correlation between asexuality and infection, and suggests an involvement of Wolbachia in the origin of this reproductive mode. The nine Wolbachia strains retrieved from the Naupactini belong to the B supergroup. Phylogenetic analysis of these strains, along with other 23 strains obtained from arthropods and nematodes, supports previous hypotheses that horizontal transfer of Wolbachia amongst species from unrelated taxa has been pervasive.

Mitochondrial DNA diversity in an apomictic Daphnia complex from the Canadian high arctic

Cyclic parthenogenesis is the ancestral mode of reproduction in the cladoceran crustacean, Daphnia pulex, but some populations have made the transition to obligate parthenogenesis and this is the only mode of reproduction known to occur in arctic populations. Melanism and polyploidy are also common in arctic populations of this species. Prior allozyme studies of arctic D. pulex revealed substantial levels of clonal diversity on a regional scale. Clonal groupings based on cluster analysis of allozyme genotypes do not conform to groupings based on the presence/absence of melanin or on ploidy level. In order to further elucidate genetic relationships among arctic D. pulex clones, mitochondrial DNA (mtDNA) variation was examined in 31 populations from two Canadian high-arctic sites. The data were also compared to a previous study of mtDNA variation in populations from a Canadian low-arctic site. Cladistic analysis of restriction site variation of the entire mitochondrial genome and nucleotide sequence variation of the mitochondrial control region was used to construct genetic relationships among mitochondrial genotypes. Three distinct mitochondrial lineages were detected. One lineage was associated with diploid, nonmelanic clones and is the same as the lineage that is found in temperate populations of D. pulex. The other two lineages (A & B) were associated with polyploid, melanic clones. Sequence divergence between the A and B lineages was 2.4%. Sequence divergence between D. pulex and either of these two lineages exceeded 3%.(ABSTRACT TRUNCATED AT 250 WORDS)

Origins and organization of genetic diversity in natural populations of Trypanosoma brucei

Experimental work has established that a sexual process can occur in African trypanosomes (Jenni, Marti, Schweizer, Betschart, Le Page, Wells, Tait, Paindavoine, Pays & Steinert, 1986; Paindavoine, Zampetti-Bosseler, Pays, Schweizer, Guyaux, Jenni & Steinert, 1986; Tait, personal communication). However, the role of the process in natural populations of trypanosomes is poorly understood. This paper considers what information can be gained from analyses of isoenzyme polymorphism. A cladistic approach is used to help determine whether trypanosome diversity could have been produced by mutation alone. When applied to three East African populations of Trypanosoma brucei it provides evidence that some diversity has arisen through a sexual process; this explains the variation observed within a locality and can account for the evolution of differences between localities. However, the extent to which genetic exchange currently operates is less clear. Analysis of genotype frequencies indicates that agreements with Hardy-Weinberg expectations can be obtained even if genetic exchange exerted no influence over genotype frequencies. Moreover, analysis of joint locus frequencies reveals disequilibrium between loci and that trypanosome populations may be lacking several genotype combinations. Thus, genetic exchange may not occur sufficiently frequently, or in such a way as to break up associations between loci. The relevance of these observations to the evolution of strain differences within T. brucei is discussed.

Genetic polymorphism and evolution in parthenogenetic animals : Part 9: Absence of variation within parthenogenetic aphid clones

The enzyme gene variability within parthenogenetic clones of Acyrtosiphon pisum has been followed by gel electrophoresis. No variation was observed within any clone. One enzyme locus was found to vary between clones. No evidence was found to support gene recombination due to the alleged endomeiosis. This hypothesis is proven to be also theoretically untenable. The low average heterozygosity in aphids is explained as a result of directional selection operating upon the parthenogenetic aphid clones, as a consequence of which the heterozygosity is lowered.

Polyploidy in insect evolution

Of all living organisms insects are the group with the highest number of existing species. It is, of course, true that a fraction of the total number of insects has been cytologically studied. Polyploid forms are rare exceptions among them. Polyploidy in insects is always associated with the parthenogenetic mode of reproduction. The cytologically verified cases are described. As for the geographic distribution of polyploid insects, they have successfully colonized vast land areas. Their distributions are, in general, northern and montane. The polyploid races are in general far more widespread than their diploid bisexual ancestors. The possible models of origin of polyploid insects are covered as well as data on their gaenetic variability. There are apparent environmental correlations in the distribution of certain forms. Most polyploid insects have life cycles extending over two (or more) years. They are also in general flightless forms. Hypotheses on the relation between heterozygosity in polyploids as well as the consequences of mutations in polyploid lineages are also presented.

Parthenogenesis

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