Females may invest more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred partners may be fitter than offspring sired by non-preferred ones. In this study, we tested the differential maternal allocation hypothesis in the freshwater crayfish, Austropotamobius italicus, by means of a pairing experiment aimed at evaluating the effects of specific male traits (body size, chelae size and chelae asymmetry) on female primary reproductive effort. Our results showed that females laid larger but fewer eggs for relatively small-sized, large-clawed males, and smaller but more numerous eggs for relatively large-sized, small-clawed males. Chelae asymmetry had no effects on female reproductive investment. While the ultimate consequences of this pattern of female allocation remain unclear, females were nevertheless able to adjust their primary reproductive effort in relation to mate characteristics in a species where inter-male competition and sexual coercion may mask or obscure their sexual preferences. In addition, our results suggest that female allocation may differentially affect male characters, thus promoting a trade-off between the expression of different male traits.
1. In sexually reproducing organisms, the energetic costs of spermatogenesis can be considerable, and can limit the reproductive potential of the males. In species where males mate more than once during the reproductive season, the costs of sperm production are generally predicted to result in a decrease of ejaculate size and quality with successive fertilizations. 2. In this study we examined the variation in ejaculate size among successive fertilizations in a long-lived freshwater crayfish species, Austropotamobius italicus. 3. Sexually active adult males of various sizes were allowed to mate repeatedly with different females on consecutive days. Trials for a given male ended when he copulated but did not release any sperm or refused to mate. 4. Males fertilized between 0 and 4 females, and most (42.5%) fertilized a single female. The overall number of females fertilized by a given male decreased with increasing male body size. Ejaculate size decreased markedly with consecutive fertilizations in a similar fashion among both large and small males, while simultaneously increasing with female body size. The total ejaculate size over successive fertilizations decreased with increasing male size. 5. Our study indicates that either sperm production or release involves non-trivial costs in freshwater crayfish, and suggests that large/old males may face greater difficulties in gamete release than small/young ones, as shown by the lower number of females fertilized by large compared with small males, which may reflect the ongoing senescence of their reproductive performance.
Information was gathered on the distribution of white-clawed crayfish Austropotamobius pallipes complex in the watercourses of the Alessandria province (NW Italy), on the biological and ecological preferences of the species, and on the features of the biotopes in which it is found. A total of 409 sites on 361 watercourses connected to the main sub-basins of the Po River were analysed, with data gathered during the field research phase, conducted for three consecutive summers from 2002 through 2004. Thirteen percent of the sites investigated were found to currently house crayfish populations. The persistence in time of superficial water and natural morphology of the watercourse were found to be the chief requirements for the presence of crayfish. Data on land use, human density and other factors which potentially limit the survival of crayfish populations were also analysed.
Key-words:Austropotamobius pallipes complex, freshwater crayfish, bio-ecological characteristics.
STATUT DU COMPLEXE D'ESPACE D'AUSTROPOTAMOBIUS PALLIPES DANS LES COURS D'EAU DE LA PROVINCE D'ALESSANDRIA (ITALIE NORD-OCCIDENTALE)
RÉSUMÉLe projet de recherche a prévu la récolte d'informations sur la répartition du complexe d'espèce Austropotamobius pallipes dans les réseaux hydrographiques de la province d'Alessandria (Italie nord-occidental), sur les caractères bio-écologiques de l'espèce et sur les caractéristiques des milieux où elle a été trouvée. Les prospections de terrain ont été faites durant trois étés consécutifs de la période 2002-2004 et ont permis d'analyser 409 sites sur 361 cours d'eau, appartenant aux principaux sous-bassins du fleuve Pô. Des populations d'écrevisses n'ont été trouvées que dans 13 % des sites prospectés. La persistance temporelle des débits hydriques superficiels et la morphologie naturelle constituent la condition essentielle pour la présence des écrevisses. En outre, les données
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