The growth and reproductive biology of the invasive goldfi sh Carassius auratus auratus were studied in Lake Trasimeno, central Italy. The results of the research revealed that the population is made up of eight age-classes. The sex ratio proved to be extremely unbalanced (1 : 19 in favour of females). Growth can be deemed rapid, the von Bertalanffy growth in length function being TL = 43.019{1- e(-0.272(t+0.162) )} for the total sample and Ф’ = 2.702. No sexual dimorphism in growth was observed. Back-calculation analysis suggested the existence of an inverse Lee phenomenon among 1 year-old specimens. The reproductive period covers a broad time-span, from March to June. In females, sexual maturity is reached after the second winter of life (2+ age-class); however, a small percentage (7.55%) of females is able to reproduce at the age of 1 year. Most of the males attained sexual maturity in the fi rst year (60.61%). The reproductive investment of the females is high; the relationship between SL and the number of eggs was Ne = 0.0041 SL4.368. Fecundity varied from 286 to 219104 eggs, with an average relative fecundity of 103 ± 5 eggs g-1; the mean diameter of the eggs was 1.27 ± 0.01 mm. The reproductive investment of the females was not homogeneous across the ageclasses; in addition to absolute fecundity, relative fecundity and egg diameter were seen to increase with the size of the specimens.
The effects of body size on mating success and duration of copulation were investigated in Pyrrhocoris apterus. Under laboratory conditions relative mating success of small and large males was investigated in groups of 2 males (majority sex) : 1 female (minority sex). Large males were recorded significantly more often in copulation than small males when the female was large but not when the female was small. This was also the case when the group size was 24 males : 12 females or population density decreased by increasing the area of the experimental arena. In groups of 2females : 1 male, large females were recorded in copulation significantly more often than small females when the male was large but not when the male was small. Proportion of individuals of the minority sex that copulated was similar for males and females, regardless of body size. The average duration of copulation was similar for small and large males, but shorter for small than large females. The difference in the duration of copulation of small and large females was greater when it was with small rather than large males. The prolonged guarding of large females by small males may be explained by a trade-off between increasing the probability of inseminating an uneasily accessible high quality partner and copulating with more females.
The suitability of Liriomyza sativae Blanchard, L. trifolii (Burgess) and L. bryoniae (Kaltenbach) as hosts of the solitary larval-pupal parasitoid Dacnusa sibirica Telenga was studied. This parasitoid is used as a biological control agent against L. trifolii and L. bryoniae. The parasitoid laid eggs in L. sativae, but no adult parasitoids emerged from the puparia. In contrast, D. sibirica adults emerged from the puparia of L. trifolii and L. bryoniae, and there was no significant difference in emergence rate, female developmental time, or sex ratio when parasitizing these two host species. The parasitoid adults that emerged from the L. bryoniae puparia were significantly larger than those from L. trifolii puparia. In conclusion, D. sibirica, a useful biological control agent of L. trifolii and L. bryoniae, cannot control L. sativae.
Deviation from an equal sex ratio has been observed in several avian species and there is now descriptive as well as experimental evidence that females are able to modify the sex of their offspring within a brood. Less attention has been paid to consequences of sex ratio manipulation and sex specific differences e.g. in competitive disparities of male and female siblings and parent tactics to compensate for such competitive differences. In this study we examine differences in chick development in relation to sex and hatching order in the socially monogamous bearded tit Panurus biarmicus. Our results revealed that significantly more female than male nestlings were the biggest in the brood. Allometric measurements seem to be a good predictor of age (hatching order). This consequently means that female nestlings frequently hatch earlier and have a higher initial body mass. In contrast male nestlings seem to develop much faster than female nestlings. By modifying the hatching order in favour of female nestlings, mothers seem to promote daughters to compensate for their slower growth.
Parasitoid females may adjust offspring sex allocation according to the number and quality of hosts available. Because in solitary species only one offspring survives per host, already parasitized hosts are of low quality and generally rejected. Superparasitism (i.e., sequential oviposition by the same or different females) results in aggressive interactions and competition for nutritional resources among larvae. We examined variations in the offspring sex ratio of Dendrocerus carpenteri (Curtis) (Hymenoptera: Megaspilidae), a solitary ectoparasitoid developing as a hyperparasitoid on the prepupae and pupae of primary aphid parasitoids inside mummified aphids. Mated females produced a female-biased sex ratio of 0.433 (proportion of sons) when caged singly and provided with 12 mummies for 2 h; they parasitized an average of four mummies/h and rarely superparasitized. Superparasitism increased when two females were caged together and provided with 12 mummies, from 1.18 to 1.24 and 1.38 eggs/host parasitized in 1, 2 and 3 h, respectively. The offspring sex ratio became increasingly more female-biased with increase in superparasitism; however, sex ratio variations were not correlated with cohort size. One mated and one unmated female provided with 12 mummies and caged together for 1 h produced a mean cohort sex ratio of 0.645, which differed from the one predicted (0.717) by an algebraic model incorporating the assumptions that both females contribute equal numbers of offspring and that the mated female does not change her offspring-sex allocation strategy. The observed shift in the cohort sex ratio to an increased female-bias indicates that mated females of D. carpenteri change their behaviour when encountering parasitized mummies or a conspecific competitor in the same patch. By depositing fertilized rather than unfertilized eggs, a female can increase the proportion of her daughters among parasitoids competing for a diminishing host supply., Manfred Mackauer, Andrew Chow., and Obsahuje bibliografii
In species with last sperm precedence, post-mating guarding behaviour by males is effective for avoiding sperm displacement by additional males. However, for males to guard their mates under all circumstances may be undesirable, particularly when the population density of conspecific rival males is low. To better understand the effects of rival density on mate guarding behaviour, we compared post-copulatory behaviour in males artificially subjected to different male densities using Aquarius paludum. Our results indicate that males of A. paludum modulate their post-copulatory behaviour based on previously experienced rival densities. and Atsuo Matsueda, Kenji Fujisaki.
For the last few decades, many studies have analysed the important influence of environmental conditions on the breeding biology of ungulates. However, with reference to Mediterranean wild boar populations, there are hardly any studies. In this paper, we will research the effect of rainfall over eight years on some reproductive variables in a wild boar population located in a Mediterranean ecosystem. Our results indicated that the percentage of pregnant females was higher in rainy years than in dry ones and females over 2 years of age significantly increased their litter size in these rainy years. In addition, dry summers and autumns determined an early rut period and a high concentration of births. However, rainfall did not influence the foetal sex ratio, although we did observe that the sex of the heaviest piglet within each litter was predominantly male, this circumstance being more significant in dry years than in rainy ones. We believe that these results could be showing the wild boar’s survival strategy in the changeable environmental conditions of Mediterranean ecosystems.
Bethylid wasps are a medium sized family of parasitic Hymenoptera, with biological control potential, which have recently proved excellent model systems for testing evolutionary and life history theory. We report observations on a species of Laelius from The Netherlands. The species is morphologically indistinguishable from Laelius pedatus, previously reported only from the New World. Reciprocal crosses between the Dutch wasps and L. pedatus from Madison, Wisconsin, USA confirmed that the Dutch population belongs to L. pedatus. We compared the life history of the Dutch wasps with those from Madison by rearing them on Trogoderma glabrum, but found no significant differences. The Dutch wasps successfully parasitize Trogoderma angustum, an invasive museum and domestic pest found in situ, but suffer high developmental mortality on T. glabrum. Wasp egg size was positively correlated with the size of ovipositing female, which was also negatively correlated with the developmental mortality of offspring. Larger wasps also carried more mature eggs. Time taken to lay the clutch increased with the size of the eventual clutch laid and was longer in unmated than mated females. When some wasps died before completing development, surviving members of the brood grew to a larger size and took longer to complete development. The number of males per brood increased with previous oviposition experience, an indication of sperm depletion through life. We discuss the implications of these trends for parasitoid life history theory.
The body length variation, sex ratio, ovarian development and natural enemies (parasitoids and entomopathogenic fungi) of Coccinella septempunctata were studied during two dormancy seasons in three hibernation sites in the Karkonosze mountains: the top of Mt. Śnieżka (1,600 m a.s.l.), the top of Mt. Szrenica (1,360 m a.s.l.) and Karpacz, the village at the foot of Mt. Śnieżka (800 m a.s.l.). The proportion of females and mean body length increased with the altitude of the hibernaculum. Post-diapause maturation of ovaries occurred earlier in spring in females from Karpacz than from the mountain tops. The rate of parasitization of C. septempunctata by its most common parasitoid, the braconid Dinocampus coccinellae, in both seasons exceeded 70% at Karpacz and was 14-28% in the mountain top hibernacula. In contrast, the incidence of fungal infection (mainly by Paecilomyces farinosus and Beauveria bassiana) was higher in beetles overwintering on the two mountain tops.
The univoltine leaf miner Chromatomyia fuscula Zetterstedt is a Scandinavian cereal pest. We wanted to compare the phenology of C. fuscula in southern Norway with that of its most important natural enemies: 15 parasitoids of the families Eulophidae and Pteromalidae (Hymenoptera: Chalcidoidea). The use of two Malaise traps in an organically-grown spring barley field and its boundary through 6 seasons (1992-1997) also allowed us to compare these two habitats and to observe the effect of harvesting on the parasitoid activity without interference from pesticides. C. fuscula overwinters as an adult and oviposits in May/June. Few specimens of the next generation, emerging in the crop, were caught in the boundary traps, suggesting the fly hibernates elsewhere. In contrast, the F1 generation of the parasitoids was caught in considerable amounts both in the crop and boundary. The abundance of parasitoids was highest in July/August; in the crop it usually started decreasing well before harvesting; in the boundary it peaked two weeks or more after harvesting. The results suggest that many parasitoids (especially females) move from the crop to the boundary (or beyond) before harvesting. In both habitats parasitoid species richness usually increased until harvesting, and thereafter decreased. The pooled parasitoid female proportion was 0.36; in crop and boundary it was 0.30 and 0.66, respectively, and the majority of species had a higher proportion of females in the boundary than in the crop. The phenology of two of the most common parasitoids is presented: The pupal parasitoid Cyrtogaster vulgaris Walker (Pteromalidae) had a high activity in the boundary, also very early (females only) and late (both sexes) in the season. The larval parasitoid Diglyphus begini (Ashmead) (Eulophidae) was less active early and late in the season, and had a much smaller boundary activity than C. vulgaris. Both sexes were present throughout the season. The annual sex ratio of D. begini was density dependent, being highly male biased in the two years with highest catches. In C. vulgaris neither density nor habitat explained the sex ratio. D. begini probably overwinters inside the mine as a preadult, having one generation on C. fuscula in the crop and another one in an alternate host away from the habitats sampled here. C. vulgaris overwinters as fertilized females in the border habitat.