Ovigerous Females (ovigerou + female)

Distribution by Scientific Domains

Selected Abstracts

Size at the onset of sexual maturity in the anomuran crab, Aegla uruguayana (Aeglidae)

ACTA ZOOLOGICA, Issue 4 2006
Verónica E. Viau
Abstract The size at maturity was studied in the crab Aegla uruguayana from the Areco River (31°14, S, 59°28, W), Argentina. Size at sexual maturity was determined according to three criteria: morphometric (change in the relative growth of reproductive characters), histological (first maturation of gonads) and functional (capability to mate and carry eggs). Regarding females, morphometric maturity occurred at a carapace length (CL) of 11.50 mm, considering abdomen width as a reproductive character. Gonad maturity of females could be observed at a minimum size ranging from 15 to 17 mm CL. The smallest ovigerous female observed in the field was 15.60 mm CL, although a relevant population incidence of ovigerous females (86.6%) has just been observed at values higher than 17 mm CL. As for males, the relative growth of the left chela length changed at a value of 15.40 mm CL, while morphological changes in sexual tube occurred between CL of 14 and 16 mm. Testicular maturation occurred at a CL ranging from 17 to 19 mm. The smallest size of males having spermatozoids in their vasa deferentia was 18.70 mm CL. The results obtained indicated that, in both sexes, functional maturity occurred after morphometric maturity and at a size similar to that of gonad maturity. Comparing sexes, females acquired sexual maturity (morphometric, gonad and functional maturity) at sizes statistically smaller than those of males. [source]

Long-term responses of zooplankton to invasion by a planktivorous fish in a subarctic watercourse

Summary 1.,Introduced or invading predators may have strong impacts on prey populations of the recipient community mediated by direct and indirect interactions. The long-term progression of predation effects, covering the invasion and establishment phase of alien predators, however, has rarely been documented. 2.,This paper documents the impact of an invasive, specialized planktivorous fish on its prey in a subarctic watercourse. Potential predation effects on the crustacean plankton, at the community, population and individual levels, were explored in a long-term study following the invasion by vendace (Coregonus albula). 3.,Over the 12-year period, the density and species richness of zooplankton decreased, smaller species became more abundant and Daphnia longispina, one of the largest cladocerans, was eliminated from the zooplankton community. 4.,Within the dominant cladocerans, including Daphnia spp., Bosmina longispina and Bosmina longirostris, the body size of ovigerous females and the size at first reproduction decreased after the arrival of the new predator. The clutch sizes of Daphnia spp. and B. longirostris also increased. 5.,Increased predation pressure following the vendace invasion induced many effects on the crustacean zooplankton, and we document comprehensive and strong direct and indirect long-term impacts of an introduced non-native predator on the native prey community. [source]

Aseasonality in the abundance and life history of an ecologically dominant freshwater crab in the Rift Valley, Kenya

Summary 1. Freshwater crabs appear to show at least two alternative life history patterns, which differ in the timing of seasonal reproduction. Reproduction occurs during low flow among temperate lotic species, but during high water levels among wetland species. Crab biomass is often very high and both strategies would lead to spatial and temporal pulses in density and biomass. The life history and reproductive strategy adopted by tropical lotic species is poorly known, however, despite their importance in community and ecosystem dynamics. 2. In this study, we determined annual patterns of life history, density and biomass of a lotic freshwater crab in a small headwater stream in the East African highlands where it maintains high biomass. This crab is an as yet undescribed species of Potamonautes, here referred to as the Chinga crab. 3. Crabs were sampled non-destructively for 15 months using baited traps and benthic sampling with a Surber sampler. At the end of the study, an intensive hand search was carried out. Each method was biased towards different size classes of crabs and the efficiency of both long-term methods varied according to water levels in the stream. The intensive search was more effective than benthic sampling, but failed to record the large individuals caught by baited traps. 4. Population density and biomass remained constantly high throughout the study period. Reproduction, as evidenced by the presence of ovigerous females and small free-living juveniles, also showed no seasonality. As a consequence, the population size structure (size-frequency distribution) of crabs remained constant throughout the year. 5. The Chinga crab illustrates a third life history pattern, with no clear breeding season, and this may be common among tropical species. This is probably a consequence of the non-seasonal nature of its habitat: temperature varied little throughout the year and rainfall fluctuations were relatively small. This strategy allows the species to maintain high biomass without seasonal pulses and, perhaps, to dominate community and ecosystem processes. [source]

Testing the abundant-centre hypothesis using intertidal porcelain crabs along the Chilean coast: linking abundance and life-history variation

Marcelo M. Rivadeneira
Abstract Aim, The abundant-centre hypothesis (ACH) is based on the assumption that physiological constraints limit populations at the edges of their distributional range, yet the geographical variation of physiological performance or life-history traits has rarely been examined. Here we examine the applicability of the ACH in a marine system by testing whether physiological predictions are reflected in large-scale variations of life-history traits. Location, The Chilean coast (18°,42° S), encompassing more than 2500 km along the Pacific coast of South America. Methods, Five porcelain crab species (Petrolisthes granulosus, Petrolisthes laevigatus, Petrolisthes tuberculatus, Petrolisthes violaceus and Allopetrolisthes angulosus) were sampled on intertidal boulder beaches at 13 sampling sites. For each species and site we evaluated: (1) relative abundance (density), (2) maximum size, (3) size at maturity, (4) sex ratio, (5) proportion of ovigerous females, and (6) presence of recruits. The shape of the spatial distribution of each trait was evaluated statistically against the prediction of four hypothetical models (normal, ramped-south, ramped-north and abundant-edge). Results, The relative abundance and life-history traits showed different spatial patterns among species. Relative abundance (across sites) was fitted by a normal model in only two species. No model fitted the spatial variation in body size and size at first maturity, which showed a slight but monotonic poleward increase in all species. Sex ratio showed a prominent hump-shaped pattern, with females prevailing in the centre of the ranges and males dominating towards the range boundaries; this pattern was statistically significant in three of the five studied species. The proportion of ovigerous females showed no clear latitudinal trends, and mature individuals were observed across most of the geographical range of the species. However, recruits tended to be absent towards the southern (poleward) boundaries of the distribution. Main conclusions, The ACH does not apply to all species equally. The link between abundance and life-history traits is complex and variable among the porcelain crab species studied. Overall, the observed patterns were consistent with the idea that equatorward boundaries might be controlled by physiological restrictions mainly affecting adult survival, whereas poleward boundaries might be shaped by limitations in reproductive output and larval survival. Our results underline the importance of incorporating ecological, physiological and life-history studies in future tests of the ACH. [source]