Jean-Pierre Mocquard

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.

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...

[Morphometry, Sexual Dimorphism and Size At Maturity of the White-Clawed Crayfish Austropotamobius Pallipes Pallipes (Lereboullet) From a Wild French Population At Deux-Sèvres (Decapoda, Astacidea), Morphometry, Sexual Dimorphism and Size At Maturity of the White-Clawed Crayfish Austropotamobius Pallipes Pallipes (Lereboullet) From a Wild French Population At Deux-Sèvres (Decapoda, Astacidea)]

This paper describes patterns of sex and size dimorphism and allometric growth in a French population of the native crayfish species, Austropotamobius pallipes pallipes. The threatened status of this species shows the necessity to establish a suitable management to protect it. An efficient management requires an increase in our knowledge about existing populations. By using allometric relationships, we characterized the size at the onset of sexual maturity in both sexes and evaluated sexual dimorphism in this population. The size at the onset of sexual maturity appeared to be different in both sexes (20.1 mm POL in males and 18.17 mm POL in females). The sexual dimorphism, shown by the variables of claw length and abdominal width, was not closely related to the puberal moult. The growth rates of this population were very different from those shown by other European populations. Discriminant analysis was performed on the data, but it did not separate the juveniles of both sexes. This study provides fundamental results concerning the relative growth of A. pallipes which could be used to compare several French populations in the future.

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.

Size At Sexual Maturity and Morphometric Variability in Three Populations of a Ustropotamobi Us Pallipes Pallipes (Lereboullet, 1858) According To a Restocking Strategy

Size at sexual maturity was determined by the allometric equation in three populations of Austropotamobius pallipes pallipes from the Poitou-Charentes region, France. Seven morphological characters were measured and POL (post orbital length) was used as a reference parameter. The puberal moult was identified by changes in the relative growth of CW (claw width) and CL (claw length) in both sexes. Males have shown variation of the relative growth of CW and CL at 19.15 mm of POL for the Gatineau (Gat) stream, 20.1 mm of POL for the Magnerolle (Mag) and 20.3 mm for the Fontaine Saint-Pierre (Fsp) populations, respectively. Sexual maturity of females occurred at 16.17 mm POL for the Fsp, 18.2 mm for the Mag and for the Gat. Geographic variation in A. pallipes was investigated using multivariate analysis of five morphometric characters on mature specimens. By canonical discriminant analysis, the Mag population was distinct from the other two populations. Results are discussed with regard to restocking strategy.

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).

Effet De L'Inoculation D'Une Bacterie Endocellulaire Feminisante Sur La Croissance Et La Reproduction Des Femelles Du Crustacé Oniscoïde Armadillidium Vulgare (Latr.). Consequences Possibles Sur L'Evolution Des Populations

In the populations of Armadillidium vulgare the three different types of functional females can be distinguished: ZW genetic females and two types of neo-females (i.e., feminized males). Sexual reversal of males is caused by the feminizing action of either intracytoplasmic symbiotic bacteria (F) or a less stable f factor. The inoculation of crushed ovaries of symbiotic females (ZZ F neo-) in non-symbiotic females (ZW 9 and ZZ f neo-) does not alter the onset of reproduction. Growth, however, and consequently fertility, is considerably slowed down by the introduction of these feminizing bacteria. There is no such noticeable pathogenic effect in ZZ f neo-females. These results are analyzed according to the various possible origins of the microorganism and of the different types of females. This phenomenon might have a certain impact on the evolution of populations.

Individual variation in the seasonal reproduction of the terrestrial isopod Armadillidium vulgare Latr. (Crustacea, Oniscidea)

Abstract Under particular conditions of photoperiod and temperature, Armadillidium vulgare females, originating from a single population, might exhibit individual differences in the onset of reproduction and duration of the breeding period. In a population issued from a strain from middle latitudes, some females underwent only one parturial moult (northern tendency) and others three parturial moults (southern tendency). Females with an atypical northern phenology are the most numerous and tend to be found near the Danish population. In the latter, there is an asymmetrical response to laboratory selection (favourable to females with a longer breeding period). The asymmetrical variation in atypical individuals acts as a safety device against the unpredictability of the environment. The adaptation of this species, originally from the Mediterranean periphery, to a northern environment has led to a reduction in its capacity to breed over long periods of time. Populations from middle latitudes can undergo one or several parturial moults which enables the species to successfully colonize even far-away countries. These intrapopulation differences have an essential role and explain why Armadillidium vulgare is one of the most widely distributed species among Oniscidea.