Non-reciprocal cross-incompatibility in Trichogramma deion

In non-reciprocal cross-incompatibility (NRCI), the crossing of a female of a strain A with a male of a strain B results in hybrid offspring, whereas the reciprocal cross produces few or no hybrids. Only females are of hybrid origin in Hymenoptera because they arise from fertilized eggs; males arise from unfertilized (haploid) eggs. Crosses between many strains of Trichogramma deion showed some degree of NRCI. Crosses between a T. deion culture collected in Seven Pines, California (SVP) with one from Marysville, California (MRY) showed an extreme form of NRCI in which practically no female offspring was produced when MRY females were crossed with SVP males. The reciprocal cross produced a close to normal proportion of female and male offspring. Detailed studied of this cross indicated that 1) the female offspring produced in the compatible interstrain cross were not the result of parthenogenesis but were true hybrids, 2) the incompatible interstrain cross did not produce female offspring because fertilized eggs died during development, 3) the death of these eggs could not be prevented by either antibiotic or temperature treatment, 4) cytoplasmically inherited factors causing NRCI could be discounted because backcrossed females with the genome of MRY and the cytoplasm of SVP, exhibit the NRCI relationship characteristic of their genome. Therefore the NRCI between these strains appears to be caused by a modification coded for by the nuclear genes of MRY that results in incompatibility when SVP sperm fertilizes MRY eggs. In addition the level of incompatibility in crosses between the SVP females and MRY males is temperature sensitive, the higher the rearing temperature the lower the level of compatibility.     

New haplotype and inter‐strain reproductive compatibility of Wolbachia‐uninfected alfalfa weevil,Hypera postica (Coleoptera: Curculionidae), in Japan

Hypera postica is a univoltine invasive pest of alfalfa, Medicago sativa, in North America. In Japan, H. postica was first found in 1982 from Fukuoka and Okinawa Prefectures and became a serious pest of Chinese milk vetch, Astragalus sinicus, cultivated as a honey source for humans and green manure for rice. In North America, three strains, Western, Eastern and Egyptian, have been identified and the Western strain is infected with Wolbachia, which causes complete inter‐strain reproductive incompatibility. In contrast, only Western and Egyptian strains had been reported throughout Japan and none of the Western strain examined for the Fukuoka populations in northern Kyushu was infected with Wolbachia. First, we screened populations from northern Kyushu collected since 1982 for geographical and chronological distribution of the Eastern strain. The Eastern strain has been found at low frequencies since 1985 and is still present in 2014. Second, we experimentally tested our hypothesis that inter‐strain crosses between uninfected Western‐strain males and Egyptian‐strain females should produce viable offspring. We crossbred virgin adults reared individually from field‐collected larvae and confirmed that the F₁ eggs of crosses between the Western‐strain males and the Egyptian‐strain females develop successfully into larvae.     

Wolbachia Infections and the Expression of Cytoplasmic Incompatibility in Drosophila Sechellia and D. Mauritiana

Various stocks of Drosophila mauritiana and D. sechellia were found to be infected with Wolbachia, a Rickettsia-like bacterium that is known to cause cytoplasmic incompatibility and other reproductive abnormalities in arthropods. Testing for the expression of cytoplasmic incompatibility in these two species showed partial incompatibility in D. sechellia but no expression of incompatibility in D. mauritiana. To determine whether absence of cytoplasmic incompatibility in D. mauritiana was due to either the bacterial or host genome, we transferred bacteria from D. mauritiana into an uninfected strain of D. simulans, a host species known to express high levels of incompatibility with endogenous Wolbachia. We also performed the reciprocal transfer of the natural D. simulans Riverside infection into a tetracycline-treated stock of D. mauritiana. In each case, the ability to express incompatibility was unaltered by the different host genetic background. These experiments indicate that in D. simulans and D. mauritiana expression of the cytoplasmic incompatibility phenotype is determined by the bacterial strain and that D. mauritiana harbors a neutral strain of Wolbachia.     

Multiple incompatibilities within populations of Culex pipiens L. in southern France

Strains of Culex pipiens derived from natural populations collected in southern France were crossed to determine their ability to give fertile offspring. Uni- and bi-directional incompatibilities occurred between these strains and each of them had its own crossing properties. Compatibility or incompatibility of a cross seemed to be related to the geographic distance separating the parental colonies, but not to their ecological origin (hypogeous or epigeous). Our results showed evidence for the variation in time of crossing properties of a strain.     

Tropical Drosophila pandora carry Wolbachia infections causing cytoplasmic incompatibility or male killing

Wolbachia infections have been described in several Drosophila species, but relatively few have been assessed for phenotypic effects. Cytoplasmic incompatibility (CI) is the most common phenotypic effect that has been detected, while some infections cause male killing or feminization, and many Wolbachia infections have few host effects. Here, we describe two new infections in a recently described species, Drosophila pandora, one of which causes near‐complete CI and near‐perfect maternal transmission (the “CI” strain). The other infection is a male killer (the “MK” strain), which we confirm by observing reinitiation of male production following tetracycline treatment. No incompatibility was detected in crosses between CI strain males and MK strain females, and rare MK males do not cause CI. Molecular analyses indicate that the CI and MK infections are distantly related and the CI infection is closely related to the wRi infection of Drosophila simulans. Two population surveys indicate that all individuals are infected with Wolbachia, but the MK infection is uncommon. Given patterns of incompatibility among the strains, the infection dynamics is expected to be governed by the relative fitness of the females, suggesting that the CI infection should have a higher fitness. This was evidenced by changes in infection frequencies and sex ratios in population cages initiated at different starting frequencies of the infections.     

Experimental induction and termination of non-reciprocal reproductive incompatibilities in a parahaploid mite

Two experiments were conducted to investigate the relationship between rearing temperatures, the presence or absence of Wolbachia endosymbionts, and non-reciprocal reproductive incompatibility in inbred lines of the parahaploid phytoseiid mite Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae).Heat-treated females crossed with infected males reared at room temperature produced few eggs and high proportions of shriveled eggs. No female progeny were produced. The reciprocal cross was normal. A second experiment showed that the incompatible cross from the first experiment could be made compatible if the infected line was heat-treated and those males crossed with the original heat-treated females. Furthermore, a new incompatibility was induced in a formerly compatible cross when the newly heat-treated females were crossed with males from their base colony. Heat-treatment was correlated with the loss of Wolbachia in both experiments. Wolbachia may thus affect non-reciprocal reproductive incompatibility in M. occidentalis, and may produce a unique incompatibility phenotype in this parahaploid species, including both reduced numbers of male progeny and a lack of female progeny.     

Biosystematics of phytoseiid mites (Acari: Phytoseiidae) associated with cassava

Laboratory crossing experiments indicate that populations of A. limonicus sensu lato collected from cassava (Manihot esculenta Crantz) in Brazil (Cruz das Almas) and Colombia (Palmira and Monteria) are conspecific and different from A. limonicus Garman & McGregor sensu stricto collected in Riverside, California, USA and Jaguariuna, Brazil. A. limonicus s.l. did not cross with A. tenuiscutus, A. rapax or A. limonicus s.s.. A. limonicus s.s. did not cross with A. rapax. Populations of A. aerialis, A. anonymus and A. idaeus from Colombia are conspecific with Brazilian populations of these species.     

Wolbachia Infection and Cytoplasmic Incompatibility in Drosophila Species

Forty-one stocks from 30 Drosophila species were surveyed for Wolbachia infection using PCR technology. D. sechellia and two strains of D. auraria were found to be infected and were tested for the expression of cytoplasmic incompatibility, along with D. ananassae and D. melanogaster strains, which are already known to be infected. D. ananassae and D. melanogaster show levels of incompatibility up to 25%, while D. auraria and D. sechellia exhibit levels of egg mortality ~60%. A dot-blot assay using the dnaA sequence as probe was developed to assess the infection levels in individual males that were used in incompatibility crosses. A positive correlation between bacterial density and cytoplasmic incompatibility was observed. The stocks examined can be clustered into at least two groups, depending on the levels of infection relative to the degree of cytoplasmic incompatibility exhibited. One group, containing D. simulans Hawaii, D. sechellia, and D. auraria, exhibits high levels of cytoplasmic incompatibility relative to levels of infection; all the other species and D. simulans Riverside exhibit significantly lower levels of cytoplasmic incompatibility relative to levels of infection. These data show that, in addition to bacterial density, bacterial and/or host factors also affect the expression of cytoplasmic incompatibility.     

Biochemical identification of interbreeding between B-type and non B-type strains of the tobacco whiteflyBemisia 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 whiteflyBemisia 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.     

Dynamics of double and single Wolbachia infections in Drosophila simulans from New Caledonia

The bacterial symbiont Wolbachia can cause cytoplasmic incompatibility in Drosophila simulans flies: if an infected male mates with an uninfected female, or a female with a different strain of Wolbachia, there can be a dramatic reduction in the number of viable eggs produced. Here we explore the dynamics associated with double and single Wolbachia infections in New Caledonia. Doubly infected females were compatible with all males in the population, explaining the high proportion of doubly infected flies. In this study, males that carry only wHa or wNo infections showed reduced incompatibility when mated to uninfected females, compared with previous reports. These data suggest that either the DNA of these bacterial isolates have diverged from those previously collected, or the genetic background of the host has lead to a reduction in the phenotype of incompatibility. Mitochondrial sequence polymorphism at two sites within the host genome was assayed to investigate population structure related to infection types. There was no correlation between sequence polymorphism and infection type suggesting that double infections are the stable type, with singly infected and uninfected flies arising from stochastic segregation of bacterial strains. Finally, we discuss the nomenclature of Wolbachia strain designation.     

No variation for Wolbachia-induced hybrid breakdown in two populations of a spider mite

Wolbachia are cytoplasmically transmitted bacteria that infect several species of mites. In the two-spotted spider mite Tetranychus urticae Koch this symbiont can induce reproductive incompatibility. Wolbachia-induced reproductive incompatibility is observed in crosses between Wolbachia-infected (W) males and uninfected (U) females. This incompatibility is expressed in F1 broods as male-biased sex ratios, an effect called cytoplasmic incompatibility (CI). However, in the two-spotted spider mite, Wolbachia-induced reproductive incompatibility may extend to the F2: broods of virgin F1 females from U×W crosses sometimes suffer increased mortality rates. This F2 effect is called hybrid breakdown (HB). Several isofemale lines derived from mites collected from rose and cucumber plants had been previously tested for CI. Here we report on the results obtained for HB.     

Partial cytoplasmic incompatibility between two Australian populations of Drosophila melanogaster

Drosophila melanogaster (Meigen) females from stocks collected at Melbourne (latitude 37°S) show partial incompatibility when mated with males from stocks collected at Townsville (latitude 19°S) on the east coast of Australia. The reciprocal cross is compatible. Eggs have reduced hatchability in the incompatible cross. The incompatibility is maternally inherited over three generations. Compatibility can be restored by culturing Townsville flies on medium with tetracycline for one generation and by using 2-week-old Townsville males.

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Incompatibilité cytoplasmique partielle entre deux populations australiennes de Drosophila melanogaster

Résumé Les souches de D. melanogaster récoltées à Melbourne (37°S) et Townsville (19°S) sur la côte Est de l'Australie montrent une incompatibilité partielle lorsque les femelles Melbourne sont accouplées aux mâles Townsville. Une telle incompatibilité n'est décelée, ni dans les croisements intrapopulations, ni dans le croisement réciproque. Le taux d'éclosion des oeufs est réduit d'environ 30% dans le croisement incompatible, mais la viabilité des larves n'est pas modifiée. Les éléments, mâle et femelle, de ce système d'incompatibilité sont hérités maternellement pendant 3 générations de croisements en retour. La compatibilité peut être intégralement rétablie en cultivant pendant une génération la souche Townsville avec un régime contenant de la tétracycline, et partiellement rétablie en utilisant des mâles âgés de 2 semaines.

     

Wolbachia infection and incompatibility dynamics in experimental selection lines

High and low levels of Wolbachia-induced cytoplasmic incompatibility (CI) were selected for in the parasitic wasp Nasonia vitripennis, in the single-infected strain Ti277. After nine generations of selection, males from lines selected for high incompatibility level (HI lines) were significantly more incompatible with uninfected females (AsymC) than the maternal strain. The reverse response, a full compatibility with AsymC, was observed in eight out of 12 lines selected for low incompatibility (LO lines), correlated with loss of Wolbachia infection. Bacterial density estimates in the eggs of some HI lines increased significantly. The procedure for line maintenance resulted in introgression of AsymC nuclear genome into the Ti277 background. Significant changes of CI level and bacterial density due to the introgression were also observed in the control lines, possibly reflecting an effect of host genotype on bacterial density and CI. After selection had been relaxed for six generations, bacterial density in the five high-infected HI lines declined back to a level comparable to the other lines. The data are consistent with the ‘bacterial dosage’ model, but with an upper threshold of bacterial infection above which there is no correlation between infection level and CI level. We further investigate the maternal transmission of bacterial density by a mother–daughter regression on bacterial density. The pattern observed is consistent with a density dependent regulation of bacterial numbers around an ‘equilibrium’ density, independent of any effects of CI. The equilibrium value is likely to be determined by both bacterial strain and host genotype.     

Wolbachia-induced 'hybrid breakdown' in the two-spotted spider mite Tetranychus urticae Koch

The most common post-zygotic isolation mechanism between populations of the phytophagous mite Tetranychus urticae is 'hybrid breakdown', i.e. when individuals from two different populations are crossed, F1 hybrid females are produced, but F2 recombinant male offspring suffer increased mortality. Two-spotted spider mites collected from two populations, one on rose and the other on cucumber plants, were infected with Wolbachia bacteria. These bacteria may induce cytoplasmic incompatibility in their hosts: uninfected (U) females become reproductively incompatible with infected (W) males. We report on the effect of Wolbachia infections in intra- and interstrain crosses on (i) F1 mortality and sex ratios (a test for cytoplasmic incompatibility), and (ii) the number of haploid offspring and mortality in clutches of F1 virgins (a test for hybrid breakdown). U x W crosses within the rose strain exhibited partial cvtoplasmic incompatibility. More interestingly, F2 males suffered increased mortality, a result identical to the hybrid breakdown phenomenon. The experiments were repeated using females from the cucumber strain. In interstrain U x W and U x U crosses, hybrid breakdown was much stronger in the former (80 versus 26%). This is the first report of a Wolbachia infection causing a hybrid breakdown phenotype. Our results show that Wolbhachia infections can contribute to reproductive incompatibility between populations of T. urticae.     

Movement of Drosophila melanogaster transposable elements other than P elements in a P-M hybrid dysgenic cross

Summary The Drosophila melanogaster mobile DNA sequences P factors and P elements transpose at elevated rates when P strain males are mated to M strain females in a hybrid dysgenic cross (Engels 1983). Isofemale lines derived from such a cross were analysed by in situ hybridisation using cloned copies of the transposable elements copia, 412 and F. It was found that lines derived from dysgenic crosses showed a statistically significant number of new sites for these elements when compared to a non-dysgenic control cross. This result suggests a functional coupling of copia, 412 and F transposition and some component present in the P-M dysgenic system.     

Genetic Differentiation in Tetranychus Urticae (Acari: Tetranychidae): polymorphism,host races or sibling species?

Based on allozyme electrophoresis at the Pgm locus and nuclear ribosomal DNA (ITS2) sequences, we studied the genetic variation of the two-spotted spider mite Tetranychus urticae Koch collected on rose bay, Nerium oleander L. (Apocynaceae), from several localities around the Mediterranean basin. In addition, we compared these results with those of Navajas et al. (1998) and Tsagkarakou (1997) who collected from several other host plants from the Mediterranean. In the western part of this area (Spain, France, Tunisia), we found the individuals collected from rose bay to be clearly genetically differentiated from other samples. No evidence of such host-associated differentiation was detected in the eastern Mediterranean (Italy and Greece). The genetic differentiation of mites collected on rose bay was investigated further by studying the reproductive incompatibilities between populations in Greece and in France and a laboratory strain reared on bean, Phaseolus vulgaris, in France. Reciprocal crosses performed between these strains revealed variable levels of incompatibility, spanning from partial to complete reproductive isolation. In all cases incompatibility was asymmetric. We designed a test based on double-mating to establish the fertilization status of females in fully incompatible crosses. These crosses showed that the females had been inseminated, which suggests that the barrier to reproduction is not of a prezygotic behavioral nature. The data raises the question of the relative role of ecological factors (host plant) and geographical distance, in the ongoing differentiation process potentially leading to speciation.     

Male mating performance and cytoplasmic incompatibility in a wPip Wolbachia trans‐infected line of Aedes albopictus (Stegomyia albopicta)

Wolbachia pipientis Hertig (Rickettsiales: Rickettsiaceae) is a maternally inherited endosymbiont of a large number of insects and other arthropods that induces various effects on host reproductive biology. Among these, cytoplasmic incompatibility (CI) is a form of sterility induced in eggs produced by mating between infected males and females uninfected or infected by an incompatible Wolbachia strain. This phenomenon has been proposed as a potential way to produce functionally sterile males to be used in genetic control programmes. In this paper, we report on experiments carried out to evaluate the mating performances of males of an Aedes albopictus (Stegomyia albopicta) (Diptera: Culicidae) line (ARwP), harbouring a new Wolbachia infection [the wPip strain from Culex pipiens Linnaeus (Diptera: Culicidae)], in comparison with naturally infected males (SR line). ARwP males did not differ from SR males with regard to insemination capacity. Mating competitiveness did not differ significantly between lines in either laboratory or greenhouse conditions. Moreover, crosses with SR females were characterized by a 100% CI regardless of ARwP male age. All of these findings suggest that ARwP males may represent a very efficient tool for control programmes against Ae. albopictus based on the release of functionally sterile males.     

Molecular evidence for single Wolbachia infections among geographic strains of the flour beetle Tribolium confusum.

Infections with the rickettsial microorganism Wolbachia are cytoplasmically inherited and occur in a wide range of insect species and several other arthropods. Wolbachia infection often results in unidirectional cytoplasmic incompatibility (CI): crosses between infected males and uninfected females are incompatible and show a reduction of progeny or complete inviability. Unidirectional CI can also occur when males harbouring two incompatible Wolbachia strains are crossed with females infected with only one of the two strains. In the flour beetle Tribolium confusum, Wolbachia infections are of particular interest because of the severity of incompatibility. Typically, no progeny results from the incompatible cross, whereas only partial incompatibility is observed in most other hosts. Werren et al. (1995a) reported that Wolbachia infections in T. confusum consist of two bacterial strains belonging to distinct phylogenic groups, based on PCR amplification and sequence analysis of the bacterial cell division gene ftsZ. However, Fialho & Stevens (1996) showed that eight strains of T. confusum were infected with a single and common incompatibility type. Here we report analysis of the ftsZ gene by specific PCR amplification. Diagnostic restriction enzyme assays revealed no evidence of double infections in 11 geographic strains of T. confusum, including the strain examined by Werren et al. (1995a). Further, sequence analysis of the Wolbachia ftsZ gene and an internal transcribed spacer (ITS) region in two of these strains displayed no nucleotide variation or evidence of polymorphisms. Results suggest that T. confusum is infected with B-group Wolbachia only.     

Intraspecific unilateral incompatibility in Vicia faba L.

Summary Unilateral incompatibility was discovered when crossing was attempted between different self-compatible types and subspecies of V. faba. Crossing in the direction female less self-fertile x male more self-fertile failed, whereas the reciprocal-crossing succeeded. Unilateral incompatibility developed with the evolution of less fertile and large seeded field bean types. How a cross fertilized (and self-incompatible) system may develop from a self fertilized one is discussed.The unilateral incompatibility in V. faba and other plant species is compared. The two-power competition hypothesis can explain all kinds of unilateral incompatibility reported so far in the literature. Breeding field beans for improved self-fertility is discussed.     

Lethal stage of female embryos in crosses between two local populations of the spider mite,Tetranychus quercivorus Ehara et Gotoh (Acari: Tetranychidae)

Unidirectional incompatibility has been known in the spider mite, Tetranychus quercivorus Ehara et Gotoh. In a cross between females from Tsukuba (36°N) and males from Sapporo (43°N), most eggs obtained hatched and reached adulthood with a female-biased sex ratio, whereas in the reciprocal cross, almost all fertilized eggs died and an extremely male-biased sex ration occurred. Embryonic development was examined to determine the lethal stage of hybrid eggs obtained from the incompatible cross (Sapporo X Tsukuba ). Development of normal embryos was divided into 18 stages, which were described and illustrated. In the incompatible cross, most embryos attained the eye-spot stage without showing any abnormality, but the majority of them stopped their growth then and died at this stage.