Reproductive Incompatibility Research Articles

Wolbachia and cytoplasmic incompatibility in mycophagous Drosophila and their relatives

Bacterial symbionts belonging to the genus Wolbachia are associated with postzygotic reproductive incompatibility in a number of insect species. Using polymerase chain reaction (PCR) amplification of bacterial gene sequences, strains from 10 species belonging to the closely related quinaria, testacea and tripunctata groups of Drosophila were screened for the presence of Wolbachia in their reproductive tissues. Those screened included the mycophagous species D. falleni, D. recens, D. phalerata, D. testacea, D. neotestacea, D. orientacea, D. putrida and D. tripunctata, and the nonmycophagous species D. palustris and D. quinaria. Two species, D. recens and D. orientacea, were found to be infected with Wolbachia. Subsequent tests of four additional strains of D. recens found all to be infected with the bacteria. It was established that these bacteria cause partial cytoplasmic incompatibility in D. recens by antibiotic curing followed by crosses between cured and uncured strains. Curing was confirmed by a PCR assay. Although most species of insects shown to be infected with Wolbachia are cosmopolitan and/or have undergone recent range expansion in association with human activity, D. recens and D. orientacea are endemic species with specialized ecological habits. Preliminary molecular phylogenetic analysis indicates that, among the species we examined, D. quinaria is most closely related to D. recens. To determine whether the bacteria are involved in reproductive isolation between these two species, reciprocal crosses were carried out between D. quinaria and both infected and uninfected (cured) strains of D. recens. Although these species did mate with each other, all interspecific crosses failed to yield hybrid progeny, indicating that the bacteria are not responsible for reproductive incompatibility between these species.

Monitoring Laboratory and Field Biotypes of the Walnut Aphid Parasite, Trioxys pallidus, in Population Cages Using RAPD-PCR

A discriminate analysis, based on the frequencies of occurrence of six random amplified polymorphic DNA (RAPD) fragments, distinguished individuals of a pesticide-resistant laboratory biotype (SEL) of the walnut aphid parasite, Trioxys pallidus Haliday (Hymenoptera: Aphidiidae), from individuals of a wild orchard biotype (RB). In mixed populations in the laboratory, the SEL biotype was heavily favored, irrespective of pesticide treatment, suggesting a high degree of laboratory adaptation. The resistance levels in untreated and pesticide-treated mixed (SEL + RB) populations were not different after eight generations. Analyses of RAPDpolymerase chain reaction (PCR) data suggested that the selective advantage of the SEL biotype may have been aided by a partial mating incompatibility between the biotypes. The data can be explained by either of two types of reproductive incompatibility: (1) RB females mating with SEL males produced only male offspring; or (2) the RB biotype could not successfully find mates un...

Evolution and phylogeny of Wolbachia: reproductive parasites of arthropods.

Wolbachia are cytoplasmically inherited bacteria found in reproductive tissues of many arthropod species. These bacteria are associated with reproductive alterations in their hosts, including parthenogenesis, reproductive incompatibility and feminization. A fine-scale phylogenetic analysis was done using DNA sequences from ftsZ, a rapidly evolving bacterial cell-cycle gene. ftsZ sequences were determined for 38 different Wolbachia strains from 31 different species of insects and one isopod. The following results were found: (i) there are two major division of Wolbachia (A and B) which diverged 58-67 millions years before present based upon synonymous substitution rates; (ii) a general concordance is found between the ftsZ and 16S rDNA phylogenies, indicating that these represent bacterial strain (rather than simply gene) phylogenies; however, a possible example of recombination between A and B division bacteria may have occurred in the feminizing Wolbachia present in an isopod; (iii) extensive horizontal transmission of Wolbachia has occurred between insect taxa, including different insect orders; one strain in particular (designated Adm) shows extensive recent horizontal transmission; (iv) there is an association between the Wolbachia found in a parasitic wasp (Nasonia) and its fly host (Protocalliphora), suggesting exchange of bacteria between these species; (v) parthenogenesis induction has evolved several times among the Wolbachia; and (vi) some insects harbour infections with more than one Wolbachia strain, even within individual insects.

Nucleus–cytoplasm interactions causing reproductive incompatibility between two populations of Tetranychus quercivorus Ehara et Gotoh (Acari: Tetranychidae)

Partial reproductive incompatibility between two local populations of Tetranychus quercivorus Ehara et Gotoh derived from Sapporo (43 degrees N) and Tsukuba (36 degrees N), Japan, was found. The incompatibility was unidirectional: the Sapporo female was incompatible with the Tsukuba males, which resulted in a low egg hatchability and strongly male-biased sex ratio, whereas the reciprocal cross was compatible and produced normal progeny with a female-biased sex ratio. To determine the genetic mechanism responsible for the incompatibility, crosses were made between the two populations over five to six filial generations as well as backcrosses. The results suggested that the incompatibility could be caused by an interaction between the cytoplasm from the Sapporo population and a single nuclear gene from the Tsukuba population. Compatibility was not restored when individuals of the Sapporo population were treated with antibiotics or high temperature, indicating a possibility that the cytoplasmic factors are cytoplasmically inherited elements such as mitochondria rather than microorganisms.

Biochemical identification of interbreeding between B-type and non B-type strains of the tobacco whitefly Bemisia tabaci.

Polyacrylamide gel electrophoresis and a kinetic microplate assay were used to detect heterozygotes resulting from a cross between B-type and non B-type strains of the whitefly Bemisia tabaci. Both strains were homozygous for different esterase and acetylcholinesterase (AChE) enzymes, and heterozygotes were produced in one of two crosses between B-type females (diploid) and non B-type males (haploid). In reciprocal crosses, however, no female offspring were produced, indicating that fertilization had not occurred. Despite the identification of individuals heterozygous for the esterase and AChE markers, there was clearly a significant degree of reproductive incompatibility between the two strains. The biochemical assays provided a vital component of this study and the advantages of their use are discussed.

The transfer of Wolbachia pipientis and reproductive incompatibility between infected and uninfected strains of the flour beetle, Tribolium confusum, by microinjection

We report a protocol for transferring the cytoplasmic endosymbiont Wolbachia pipientis from infected to uninfected hosts in the flour beetle, Tribolium confusum, by microinjection of cytoplasm from infected donor eggs into uninfected host eggs. Postinjection survivorship was limited by the halocarbon oil, which was lethal to hatching larvae but necessary to stem the backflow of cytoplasm out of injected eggs. In test crosses, approximately 39% of surviving and maturing larvae exhibited the complete reproductive incompatibility typically associated with W. pipientis in this species. However, some transfected females failed to transmit the W. pipientis to their progeny and the incompatibility could be lost in the generation following transfection. Conversely, in some cases, females that did not themselves exhibit the incompatibility had some offspring that did exhibit partial incompatibilities.Key words: microinjection, Wolbachia, flour beetle, Tribolium confusum.

Genetics of reproductive isolation in the Drosophila simulans clade: complex epistasis underlying hybrid male sterility.

We have analyzed the sterility associated with introgressions of the distal one-fourth of the X chromosome from either Drosophila mauritiana or Drosophila sechellia into the genome of Drosophila simulans using a series of visible and DNA markers. Because in Drosophila hybrids, male sterility is usually complete and is often tightly linked with each of several markers used in crosses, a simple genetic basis has generally been assumed. In our low resolution mapping experiment, we were not able to reject the null hypothesis that a single gene, introgressed from either D. mauritiana or D. sechellia, is the cause of male sterility. High resolution mapping, however, reveals a much more complex picture. At least three distinct factors from D. mauritiana, or two from D. sechellia, were identified that need to be jointly present to confer full sterility. Each individual factor by itself is relatively ineffective in causing sterility, or even a partial spermatogenic defect. Moreover, there appear to be more sterility factors on comparable introgressions from D. mauritiana than from D. sechellia. On the basis of these observations, we propose a model which suggests that multilocus weak allele interactions are a very common cause of reproductive incompatibility between closely related species. We also present theoretical argument and empirical evidence against extrapolating the results of within-species analysis to interpret the genetic basis of species differences. The implications of this model on the theories of evolution of species differences and the attempt to understand the mechanisms of hybrid sterility/inviability at the molecular level are discussed.

Properties of Drosophila simulans strains experimentally infected by different clones of the bacterium Wolbachia

Maternally inherited bacteria of the genus Wolbachia are responsible for reproductive incompatibilities between strains of Drosophila simulans. Such incompatibilities are known in several types of crosses, including both directions of crossing between two types of infected strains, 'R' and 'S'. To determine whether the bidirectional incompatibility between R and S flies is due only to differences between their bacteria, flies from an uninfected strain have been experimentally infected with bacteria associated with each type. The incompatibility properties of experimental strains are close to those of original strains harbouring the same bacteria and therefore independent of nuclear background. Backcross experiments, however, show that the infection level of a strain depends on the nature of paternal ancestors. This is not explained by nuclear effects but is possibly the result of an interaction between the infection levels of both parents, in which the infection level of S strains is an equilibrium between a tendency for females to produce weakly infected offspring and selection of more infected eggs by sperm from infected males.

The Effect of Population Subdivision on the Rate of Spread of Parasite-Mediated Cytoplasmic Incompatibility

Over 20 species of arthropods are known to harbor an endosymbiotic bacterium, Wolbachia associated with partial reproductive incompatibility. The micro-organism spreads through a random mating population with positive frequency dependence. Many insect populations, however, are subdivided to some degree. In this paper we model the effect of population subdivision on the rate of spread of Wolbachia and show that it slows the rate of spread of the micro-organism but by itself cannot cause a stable polymorphism. The effects of the micro-organism on host fitness, partial incompatibility, and environmental curing are also investigated, both for panmictic and subdivided populations. In all cases, population subdivision slows the rate of spread relative to a panmictic population, but does not produce a stable polymorphism of infection.

Patterns of Diversification and Evolution in Phyllanthus Odontadenius (Euphorbiaceae)

Experimental crossings within Phyllanthus subsect. Odontadenii reveal different levels of reproductive incompa tibility between taxa of varying morphological distinction. Some of the reproductive barriers may be circumvented using in vitro culture. Cytological and morphological studies of the progeny of experimental crosses has yielded information about the processes of differentiation of taxa within subsection Odontadenii, as well as within the Phyllanthus urinaria complex. The results of this study support the recognition of taxa earlier propose two complexes, and furthermore document the existence of a tetraploid taxon (Phyllanthus magnificens) with a base chromosome number of x = 10

Cytoplasmic incompatibility and bacterial density in Nasonia vitripennis.

Cytoplasmically (maternally) inherited bacteria that cause reproductive incompatibility between strains are widespread among insects. In the parasitoid wasp Nasonia, incompatibility results in improper condensation and fragmentation of the paternal chromosomes in fertilized eggs. Some form of genome imprinting may be involved. Because of haplodiploidy, incompatibility results in conversion of (diploid) female eggs into (haploid) males. Experiments show that bacterial density is correlated with compatibility differences between male and female Nasonia. Males from strains with high bacterial numbers are incompatible with females from strains with lower numbers. Temporal changes in compatibility of females after tetracycline treatment are generally correlated with decreases in bacterial levels in eggs. However, complete loss of bacteria in mature eggs precedes conversion of eggs to the "asymbiont" compatibility type by 3-4 days. This result is consistent with a critical "imprinting" period during egg maturation, when cytoplasmic bacteria determine compatibility. Consequent inheritance of reduced bacterial numbers in F1 progeny has different effects on compatibility type of subsequent male vs. female progeny. In some cases, partial incompatibility occurs which results in reduced offspring numbers, apparently due to incomplete paternal chromosome elimination resulting in aneuploidy.

Cytoplasmically inherited parasites and reproductive success in Tribolium flour beetles

Abstract. Numerous insect species harbour cytoplasmic microorganisms, Wolbachia pipientis , that mediate reproductive incompatibility. Males infected with this parasite are reproductively incompatible with uninfected females. All other crosses are fertile; however, the microorganism seems to have a measurable negative effect on fitness. This study determines whether the presence of the microorganism causes deviations from non-random fertilization. Such deviations may benefit either the parasite or the host. Fertilization was found to be non-random in a way that benefits the parasite. This finding is consistent with the hypothesis that parasites manipulate host behaviour to enhance their rate of spread through a population.

The Reproductive Incompatibility System in Drosophila simulans: Dapi-Staining Analysis of the Wolbachia Symbionts in Sperm Cysts

Any hitherto available technique used to detect the presence of Wolbachia, a rickettsia-like endosymbiont of Drosophila simulans, i.e., crossing with tester strains, electron microscope observations, DAPI-staining of embryo, or amplification of specific sequences by PCR are notably time-consuming techniques. Staining sperm cysts with the fluorochrome DAPI is here shown to be a fast and reliable technique to detect the symbiont and evaluate the level of infection of individual males. Wolbachia cells are abundant in sperm cysts and make up a mass which is eliminated in the waste bag during spermatogenesis. Such a mass was absent in all those strains known to be aposymbiotic. In infected strains, tetracycline treatment led to the disappearance of the symbionts within sperm cysts. In aging males, a decrease in the proportion of infected cysts were observed. There was however no apparent change in the number of symbionts in the cysts which remained infected. The reduction of reproductive incompatibility, which is observed in older males, may be explained by this process, i.e., a decrease in the frequency of infected cysts.

Reproductive Efficiency in Reciprocal Crosses of Arachis duranensis and A. stenosperma with A. hypogaea cv. NC 61

Abstract The wild species germplasm resources of Arachis are potentially valuable for improving disease and insect resistance in A. hypogaea L. Improving cultivars through interspecific hybridization is restricted because of reproductive barriers and/or genetic incompatibility with many Arachis spp. A description of reproductive efficiency in reciprocal crosses between wild and cultivated Arachis species is needed to clarify potentials for germplasm utilization. This study documents reproductive efficiency using the diploid species A. duranensis (K 7988) and A. stenosperma (HLK 410) in reciprocal crosses with A. hypogaea cv. NC 6. A significant parental effect was observed among crosses and NC 6 was more successful when used as the female parent. Differences in total reproductive efficiency were not observed between the two wild diploid species. However, when A. duranensis was used as a female parent embryos aborted at a high frequency. In contrast, the reduced efficiency observed with A. stenosperma was due to lower fertilization. As attempts are made to utilize the genetic resources of Arachis, different approaches will be needed to overcome reproductive barriers which restrict introgression of potentially desirable traits.

Wing melanin pattern mediates species recognition in Pieris occidentalis

The western white butterfly, Pieris occidentalis Reakirt, and the checkered white butterfly, P. protodice Bosiduval & LeConte, are morphologically similar, closely related species that do not hybridize in nature despite little or no post-mating reproductive incompatibility. Field studies of interspecific mate choice indicate that female P. occidentalis significantly discriminate against courting P. protodice males relative to conspecific males. Artificially increasing wing melanization in male P. protodice so that they resemble males of P. occidentalis significantly increases their interspecific mating success. Female P. occidentalis appear to use the same male character, dorsal forewing melanin pattern, to discriminate between potential conspecific mates and between conspecific and heterospecific males.

Cytoplasmically inherited reproductive incompatibility in Tribolium flour beetles: the rate of spread and effect on population size.

This paper reports on the effects of a cytoplasmically inherited reproductive incompatibility in different genetic strains of the flour beetle, Tribolium confusum. We measured the rate of spread and the effect of host population size using different initial frequencies of infection with a cytoplasmic factor that mediates reproductive incompatibility. There were two experiments, in one the infected and uninfected lines were from the same genetic strain, b-Yugoslavia. In the other, the infected line was from the "high cannibalism" bIV strain and the uninfected line from the "low cannibalism" bI strain. We estimate that the fitness ratio of infected to uninfected in b-Yugoslavia is 0.63 and the observed rate of spread for this strain corresponds to a model of cytoplasmic inheritance that takes into account the productivity differences between the infected and cured lines. In the bI-bIV experiment, because the uninfected and infected lines are from different genetic strains, we cannot partition the effects of the cytoplasmic factor from other factors. The rate of spread in the bI-bIV experiment is faster in males and slower in females than predicted from a model of cytoplasmic inheritance. In both experiments, productivity varies with initial infection frequency; however, the relationship is not explained by a simple model that predicts lower population size at intermediate infection frequencies.

Characterization of Wolbachia postica, the cause of reproductive incompatibility among alfalfa weevil strains

Wolbachia postica, which causes reproductive incompatibility between male western alfalfa weevils and female eastern or Egyptian weevils, was isolated by Renografin density gradients. Hybridization of DNA from this isolated microorganism with a mycoplasma-specific gene probe confirmed it is not a mycoplasma but a wolbachia. Polyclonal antibodies produced against inactivated Wolbachia postica showed high sensitivity in fluorescent light microscopy and immunoelectron microscopy. This antibody was specific for Wolbachia-infected adult weevil by immunoblots which were reliable and reproducible, and more sensitive than the Giemsa stain procedure. A 135-kDa protein detected in all weevils infected with wolbachiae appeared to be a good marker for the microorganism. This technique facilitates the detection of wolbachiae-infected male weevils. Dissection of the ovary was not required to analyze the female weevils.

Hormonal evaluation of female infertility and reproductive disorders.

Performance of the male and female reproductive systems reflects the orderly operation of the hypothalamic-pituitary-gonadal axis. Aberrant operation of this axis can result in many different reproductive disorders, including various forms of infertility. Proper evaluation of these disorders involves a multifaceted diagnostic approach, which includes a critical contribution from the clinical laboratory. This adjunctive testing, involving the measurements of peptide and sex-steroid hormone concentrations, allows the clinician to biochemically "dissect" the hypothalamic-pituitary-gonadal axis and ascertain the presence as well as location of the specific defect. In practice, the specific tests utilized during the evaluation of a patient depend upon the underlying disorder. Typically, in evaluating the reproductive disorders discussed in this review, a primary battery of tests is obtained that reflects the initial clinical presentation and physical examination. The results of these initial studies then dictate any secondary testing required to complete the evaluation. Such an approach, in use at our institution, is provided in Table 5. Although this discussion has concentrated on the laboratory assessment of the female reproductive system, it is important to remember the special case of infertility, where couples, in general, are evaluated together by the clinician. The cause of infertility can reside with the female, the male, or, in the cases of immunological "incompatibilities," a combination of the male and the female. As such, rigorous schemes for evaluating male reproductive disorders (1, 3, 89-94) and immunological incompatibilities (95-98) have been developed, and the information derived from such testing represents a critical contribution to establishing the etiology of a couple's infertility. Although the laboratory assessment of peptide and sex-steroid hormone concentrations clearly plays a pivotal role in the evaluation of reproductive disorders, these diagnostic tools probably will continue to change and improve in the years to come. Such changes will probably occur as the finer details of the operation of the hypothalamic-pituitary-gonadal axis become known. With this improved knowledge, we should have the capacity to design assays that will allow more clinically refined and biochemically precise means of diagnosing and treating specific reproductive disorders.

Environmental factors affecting reproductive incompatibility in flour beetles, genus Tribolium

This paper reports the effect of high temperatures on the reproductive compatibility of geographic strains of flour beetles, Tribolium confusum. Some geographic strains are reproductively incompatible with other strains owing to a maternally inherited microorganism: Males infected with the microorganism are reproductively incompatible with uninfected females. All other crosses are fertile. Previous reports indicated that infected strains can be cured of the microorganism by culturing the beetles on medium containing tetracycline and that cured males become reproductively compatible. This study reports that raising larvae at high temperatures (37°C) promotes curing. The proportion of individuals cured is a function of sex and the period of exposure to high temperature.

Nuclear‐nuclear and nuclear‐cytoplasmic interactions contribute to the reproductive incompatibility between two strains of the twospotted spider mite

Des hybrides entre deux races de Tetranychus urticae, une portant la mutation marquee yeux blancs, ont donne des mâles viables avec une proportion d'yeux blancs, 1 type sauvage, avec une grande proportion d'œufs non viables. La proportion est la meme dans le cas des deux croisements reciproques. Les interactions nucleo-nucleaires et nucleocytoplasmiques contribuent a la sterilite partielle des hybrides observee