Pierre Juchault

Success and failure of horizontal transfers of feminizing Wolbachia endosymbionts in woodlice

Keywords: Sex ratio distorter; natural horizontal transfer; interspecific transfer; crustacea

Wolbachia endosymbiont responsible for cytoplasmic incompatibility in a terrestrial crustacean: effects in natural and foreign hosts

Wolbachia bacteria are vertically transmitted endosymbionts that disturb the reproduction of many arthropods thereby enhancing their spread in host populations. Wolbachia are often responsible for changes of sex ratios in terrestrial isopods, a result of the feminization of genotypic males. Here we found that the Wolbachia hosted by Cylisticus convexus (wCc) caused unidirectional cytoplasmic incompatibility (CI), an effect commonly found in insects. To understand the diversity of Wolbachia-induced effects in isopods, wCc were experimentally transferred in a novel isopod host, Armadillidium vulgare. wCc conserved the ability to induce CI. However, Wolbachia were not transmitted to the eggs, so the capacity to restore the compatibility in crosses involving two transinfected individuals was lost. The feminizing Wolbachia hosted by A. vulgare was unable to rescue CI induced by wCc. These results showed that Wolbachia in isopods did not evolved broadly to induce feminization, and that CI and the feminizing effect are probably due to different mechanisms. In addition, wCc reduces the mating capacity of infected C. convexus males, suggesting that the bacteria might alter reproductive behaviour. The maintenance of wCc in host populations is discussed.

Evolution of sex-determining mechanisms in a wild population of Armadillidium vulgare Latr. (Crustacea, Isopoda): competition between two feminizing parasitic sex factors

Sex determination in A. vulgare may be under the control of two maternally transmitted parasitic sex factors (PSF) that reverse genetic males (ZZ) into functional neo-females. The first PSF is a Wolbachia-like bacterium (F) and the other (f) is probably a sequence of the F bacterial DNA unstably integrated into the host genome. In the Niort population (France), where these two PSF are mixed, the frequency of neo-females harbouring f increased over a period of 23 years, at the expense of neo-females harbouring F. As the maternal transmission to offspring is higher for F than for f, the evolution of the F/f ratio disagrees with theoretical models involving a cytoplasmic factor. We show that an autosomal masculinizing gene (M) allows a high rate of paternal transmission of f, which could explain the spread of this factor in the population.

Genetic control of the vertical transmission of a cytoplasmic sex factor in Armadillidium vulgare Latr. (Crustacea, Oniscidea)

In Armadillidium vulgare, sex determination may be under the control of a maternally transmitted endosymbiotic bacteria (F), which reverses genetic males (ZZ) into functional neo-females (ZZ + F). These neo-females generally produce highly female-biased progenies (thelygenous progenies = TF) but a few of them produce highly male-biased progenies (arrhenogenous progenies = ARF). These TF and ARF traits are selected, and the inoculation of F bacteria in different categories of females shows that these traits are genetically controlled by the host and do not depend on different bacterial strains. By pairing males from the ARF strain with genetic females (WZ), it can be seen that the ARF trait is unrelated to the effect of an autosomal masculinizing gene (M). In fact, the ARF trait appears to be under the control of a polygenic system, the genes influencing the sex ratio indirectly via their effects on the cytoplasmic factor (resistance genes).

Transfer of a parasitic sex factor to the nuclear genome of the host: A hypothesis on the evolution of sex‐determining mechanisms in the terrestrial Isopod Armadillidium vulgare Latr.

In A. vulgare sex is usually determined either by a cytoplasmic feminizing factor (F symbiotic bacteria) or by another feminizing factor (f) which behaves like a mobile element of DNA and which seems to correspond to a fragment of bacterial DNA. By inhibiting the expression of male genes carried by the Z heterochromosome, these feminizing factors induce differentiation of neo‐females [ZZ(+F) or ZZ(+f)]. Such a mechanism leads to the production of progenies whose sex ratio is highly female biased. In some populations in which F and/or f factors are present, genetic females (WZ) have disappeared and all individuals (males and females) are genetic males. However in other populations, cohabitation of ZZ(+f) neo‐females and females in all points similar to genetic females is observed. Such a situation may be unstable and is not likely to be explainable only by migrations of individuals from distinct populations.

Experimental study of temperature effects on the sex ratio of broods in Terrestrial Crustacea Armadillidium vulgare Latr. Possible implications in natural populations

The woodlouse Armadillidium vulgare is characterized by female heterogamety (ZW) and male homogamety (ZZ). However, in several populations, sex determination is influenced by cytoplasmic sex factors (endosymbiotic bacteria = F). At 20 °C these maternally transmitted bacteria reverse genetic males into functional neo‐females (ZZ + F) producing highly female broods.

Seasonal Reproduction in the Terrestrial Isopod Armadillidium vulgare (Latreille): Geographical Variability and Genetic Control of the Response to Photoperiod and Temperature

Summary Armadillidium vulgare females of ten geographical origins were reared under various photoperiodic regimes. Long days stimulated reproduction in all the strains, but, whatever the conditions, females originating from high latitudes began to breed later than ones from low latitudes and, under natural photoperiod of Poitiers, the lag time was increased, more or less linearly, by 2 days per degree of latitude. The ability to remain in reproduction, after a first brood, was also related to the latitudinal origin of the strain. The onset of reproduction in the Sucre strain (Bolivia) was very late in respect to the latitude of the original site; the high altitude of Sucre may explain the divergence from the common rule. Reproduction characteristics of each strain persist in the females born and reared in the laboratory for several generations. This stability makes it possible to study the genetic determination of the photoperiodic responses. One genie system probably controls induction and maintenance of...

The effect of temperature on sex ratio in the isopod Porcellionides pruinosus: Environmental sex determination or a by-product of cytoplasmic sex determination?

The sex ratios of the progenies of woodlice Porcellionides pruinosus (Crustacea, Isopoda) raised at different temperatures were studied. Females from three French populations sampled in the wild produced highly female-biased broods at 20°C and male-biased broods above 30°C. The effect of high temperature was not due to selective mortality of females. Sex determination was thus sensitive to temperature in P. pruinosus. We also found an interpopulation variability of sex ratio thermosensitivity and a weak inheritance of male-biased sex ratios at high temperatures. Samples taken from a wild population throughout the year showed that while the thermal conditions required for changes in the sex ratio occurred, there was no significant variation in the sex ratio. On the other hand, almost all the females and many males in the four populations studied harboured intracytoplasmic bacteria. These maternally inherited symbionts belong to the genus Wolbachia and are known to possess a feminizing effect. While in other arthropods Wolbachia are destroyed at high temperatures, the symbionts of P. pruinosus were detected by a PCR procedure whatever the rearing temperatures. In light of these results, we propose that the thermosensitivity of sex determination in P. pruinosus could reflect the removal of the cytoplasmic effect on sex determination rather than environmental sex determination sensu stricto. The reduction in the amount of bacteria (but not their entire elimination), or the inhibition of bacterial metabolism, may be responsible for sex ratio variations relating to temperature. The incomplete inheritance of male-biased sex ratios at high temperatures might reflect a selection of thermo-tolerant bacterial strains.

Étude Expérimentale De L'Influence Des Facteurs Externes (Température Et Photopériode) Sur Le Cycle De Reproduction Du Crustacé Oniscoide Porcellionides Pr Uinosus (Brandt) Provenant De Populations Africaine (Togo) Et Européenne (France)

In contrast to many other species of Oniscoidea, the initiation of reproduction of African (Togo) and European (France) females of Porcellionides pruinosus is independant from the photoperiod. However, there are differences between these two populations as far as female reproductive activity is concerned. With females from France, like in females of the other European Oniscoid species, the reproductive activity is stimulated by long day lengths. In African females, on the other hand, the reproductive activity is more intense under short day lenths. In both populations, the disappearance of the seasonal breeding periods, both in nature and in the laboratory, is probably related to the weakness of their reactions to photoperiodic variations.

Reproduction Saisonnière Chez Hemilepistus Reaumuri (Audouin, 1826), Isopode Terrestre Des Zones Semi-Arides

In Hemilepistus reaumuri (Audouin, 1826), a monogamous desert isopod, control of reproduction by external factors is studied in females from a Tunisian population. In the wild, females perform only one brood (in May). In contrast to isopods submitted to temperate climates (long day species), H. reaumuri is unsensitive to photoperiod. Onset of reproduction is dependent on temperature: it occurs only when temperature is higher than 15°C (between 15°C and 20°C). Moreover, at 25°C, the lag time of the onset of reproduction is shortened by 50% in comparison with the delay obtained at 20°C. Whereas an isolated female remains in sexual rest, the presence of a male (even separated from the female by a wire netting) speeds up vitellogenesis following by moult. The beginning of burrow digging is well correlated with the initiation of reproduction (second phase of vitellogenesis).