Proportion Of Ovigerous Females Research Articles

Morphological maturity and allometric growth in the squat lobster Munida rugosa

Size at the onset of sexual maturity was determined in Munida rugosa based on allometric growth of chelipeds and abdomen, and on the proportion of ovigerous females. The variability of three different measurements of carapace length (CL) used previously for M. rugosa was also evaluated to minimize measurement error. Both sexes had symmetrical cheliped length and allometric cheliped growth over the size-range investigated, but males showed increased allometry beyond 22 mm CL. Females had greater positive allometry in abdomen width than males, but their size at maturity could not be precisely determined because sampled females were too large.

Sex-ratio, seasonality and long-term variation in maturation and spawning of the brown shrimp Crangon crangon (L.) in the German Bight (North Sea)

Aspects of the reproductive and maturation biology of the brown shrimp Crangon crangon (L.) were studied in various subareas of the German Bight (North Sea). The size-specific sex ratio of C. crangon was examined based on length frequency distribution data. The sex ratio for the smallest size groups at which sex was determined was typically around 0.5, indicating an even ratio between males and females. The proportion of females decreased in the 30–45 mm size range. In length classes larger than 50 mm, the proportion of females constantly increases to 100% at around 60 mm total length. We concluded that sex reversal from male to female may not occur in C. crangon. Size at sexual maturity was determined from the proportion of ovigerous females. Size at maturity (L50) was estimated as 55.4 and 62.0 mm total length for spring and winter data, respectively. The seasonal spawning cycle was studied over the period 1958–2005. Between mid February and late June and for size classes larger than 65 mm ovigerous shrimps exceeded 80% and reached up to 100% of the females in the population. This period can be seen as the core spawning season. From early August to early December the proportion of ovigerous shrimps in the female population is very low. Interannual differences in the seasonal process are obvious with a dramatic decline in C. crangon reproductive success in the late 1980s. Various options are discussed for the reasons of the decline and recovery of the reproductive performance.

Population Structure of Alpheus Armillatus (Decapoda, Alpheidae) in São Sebastião and Ilhabela, Southeastern Brazil

Abstract The study of the population structure of A. armillatus was based on monthly collections (March 2000–February 2002) from two tidal flats—Sao Francisco Beach (SF), Sao Sebastiao County, and Engenho d'Agua Beach (EA), Ilhabela County—located at the northern portion of the State of Sao Paulo coast and separated by the 6 km wide Sao Sebastiao Channel. Carapace length (CL) was measured to the nearest 0.01 mm. The proportion of ovigerous females and the embryonic development stage of eggs were recorded. The Von Bertalanffy growth equation was fit to modes of the temporal sequence of frequency distributions of CL classes (SF data). The same sampling effort yielded 547 males and 566 females at SF and 145 males and 150 females at EA. Proportions of ovigerous females were higher than 60% throughout the year in both sites. The temporal trend of percentage of late eggs indicated three annual hatching periods. Growth patterns of males and females were similar, with the former tending to grow more rapidly (K = ...

Reproductive biology of the common shrimp Crangon crangon (Decapoda: Crangonidae) in the central Irish Sea

Aspects of the reproductive biology of the common shrimp Crangon crangon (L.) were studied in Port Erin Bay, Isle of Man, Irish Sea. Size at sexual maturity was determined from the proportions of ovigerous females and of females with maturing ovaries. The size at which 50% of females are mature is estimated (±95% confidence intervals) as 12.5±0.48 mm carapace length. Based on the proportions of ovigerous females and of mature females, the main breeding season was from January to June. Mean ovarian dry weights indicated two broods (winter and summer), with females bearing winter broods (WB) having higher gonad indices than those with summer broods (SB). WB females with non-eyed eggs and with eyed eggs differed in the regression of ovarian dry weight on carapace length, indicating preparation for laying a second brood. In both broods the moult stages of berried females were related to egg stage. Moulting will occur following the release of the brood. During embryonic development, mean egg length and egg volume were larger in all stages, and the mean dry weight of individual eggs of all stages heavier, in WB than in SB; there was no difference in egg number, however. Consequently, reproductive investment, the proportion of female weight devoted to egg production, was 67% higher in WB (0.20±0.04) than in SB (0.12±0.03). There is a significant effect of egg volume on brood weight, but not on egg number. In both broods, egg number was a negatively allometric function of female body size in non-eyed eggs and an isometric function of female body size in eyed eggs. Brood mortality during incubation was higher in SB (17%) than WB (10%). Differences in the reproductive variables and investment between the two broods of C. crangon are discussed in the light of reproductive strategies and life history.

Reproductive biology of the crab Munida subrugosa (Decapoda: Anomura: Galatheidae) in the Beagle Channel, Argentina

Munida subrugosa was sampled monthly from November 1997 to November 1999 in the Beagle Channel by means of an epibenthic trawl. The reproductive cycle started in May, reflected by the occurrence of ovigerous females. Maximum size of oocytes, maximum value of gonadosomatic index in females (16·8 g mm carapace length [CL]−1) and males (1·6 g mm CL−1), and the proportion (∼70%) of ovigerous females with full egg-clutches occurred in June. Since the proportion of ovigerous females in October was ∼5% and the planktonic larvae reportedly hatch in September, the embryonic development lasted ∼90–120 days. Females and males attained physiological maturity at 9·9 and 8·0 mm CL respectively, and males reached morphometric maturity at 24·4 mm CL. Fecundity was correlated with female size (r=0·85) and was between 124 and 10,750 eggs per female. Average diameter of recently extruded eggs was 0·69 mm (SD±0·06 mm). At the beginning of the reproductive cycle, ovigerous females had partial broods of ∼300 eggs, which represented <5% of complete clutch.

ASPECTS OF THE GROWTH AND REPRODUCTION OF THE CORAL GALL CRAB HAPALOCARCINUS MARSUPIALIS

Abstract Growth and reproduction were studied in the coral gall crab Hapalocarcinus marsupialis from fringing reefs in the Egyptian Red Sea. The host coral was Stylophora pistillata. The galls were divided into five stages, and the later stages contained larger crabs and a higher proportion of ovigerous females. Female crabs ranged from 1.17 to 5.33 mm in carapace width. They matured at about 2.5-mm carapace width (probably in the fourth instar); maturity was indicated by an increase in abdomen size, ripening ovaries, mating, and egg laying. The largest females were probably in the seventh instar. After maturity females survived for some 10 months and were ovigerous for 80% of that time, producing eight or more broods. These were all fertilised from the original mating. Reproductive investment was high, both per brood and per year.

Population parameters of American lobster inside and outside no-take reserves in Bonavista Bay, Newfoundland

Marine no-take reserves are being used increasingly to conserve exploited populations and fisheries, but there have been few studies of whether they achieve the goals for which they were created. To determine the potential effectiveness of no-take reserves as a fisheries conservation tool for American lobster ( Homarus americanus), I quantified the consequences to population structures of two small, no-take reserves (Round Island and Duck Islands) in Bonavista Bay, Newfoundland, during 1997–1999. Although this study concerned only the first 3 years following reserve establishment, there were obvious differences in lobster population parameters inside and outside no-take reserves. At the Round Island reserve, population density was high and stable over time, and female and male size increased, as did the proportion of ovigerous females. However, at the Duck Islands reserve, population density increased dramatically between 1997 and 1998, and male size increased over time, but there was no change in female size or in the proportion of ovigerous females. Lobster density, female and male size, and the proportion of ovigerous females were greater within the Round Island reserve compared to an adjacent harvested area. At the Duck Islands, females and males were larger in size within the reserve, but I found no difference in lobster density or the proportion of females that were ovigerous between the reserve and an adjacent harvested area. Taken together, these data suggest that no-take reserves offered increased survival to lobsters (particularly at the Round Island site) and thereby may, over time, provide benefits to the local fishery.

Seasonal population dynamics and production of Microsetella norvegica, a widely distributed but little-studied marine planktonic harpacticoid copepod

Microsetella norvegica is a widely distributed marine planktonic harpacticoid copepod, which is poorly known from the biological point of view. We investigated the seasonal population dynamics and production of M. norvegica in the central part of the Inland Sea of Japan. It occurred throughout the year, whilst its reproduction was confined to the warm season between May and November. The proportion of ovigerous females, which carry a single egg sac, was low (mean: 23.1 %) in August and September, and high (53.6%) in October. Their brood size attained a maximum (mean: 15.8 eggs per sac) in July and August and declined gradually to 6.2 eggs in November. Duration time from egg laying to moulting to adulthood was temperature-dependent; it was 31.9 and 14.3 days at 20 and 27°C, respectively, under excess food conditions in the laboratory. An enormously high population abundance (7.32 X 10 4 individuals m -3 ), which accounted for 86.5% of the total copepods, and biomass (69. 6 mg C m -3 ) gave an annual maximum production rate of 4.90 mg C m -3 day -1 ) in October. Nauplii and copepodites disappeared in December, and the overwintering population was represented by adults, mainly large females. Associations of M. norvegica with marine snow aggregates, which have often been found in oligotrophic waters, were not observed in the food-rich environment of the Inland Sea of Japan.

SIZE AT SEXUAL MATURITY, REPRODUCTIVE OUTPUT, AND SEASONAL REPRODUCTION OF PHILOCHERAS TRISPINOSUS (DECAPODA) IN PORT ERIN BAY, ISLE OF MAN

ABSTRACT Aspects of the reproductive biology of the crangonid shrimp Philocheras trispinosus were studied. Size of female maturity was determined from the proportions of ovigerous females and of females with maturing ovaries. The size at which 50% of females are mature is estimated (±95% confidence intervals) as 3.69 ± 0.56-mm carapace length. Brood weight and fecundity were related isometrically with female body size. Based on dry weight, the reproductive output (mass of incubating eggs/mass of female) averaged 0.24. The main spawning season (percentage ovigerous > 50%), from March-August, was reflected by monthly values of the gonad index >9. The ovarian dry weight of females with eggs near to hatching was nearly fivefold higher than for those with newly laid eggs, and the ovarian dry weight was significantly different between each egg stage. This indicates that ovarian maturation occurs during incubation, suggesting that females were potentially consecutive breeders, capable of multiple spawning within a single reproductive season.

Body size and reproductive investment of Daphnia galeata under predation by cyprinid fishes: A mesocosm study

Demographic and life-history responses of Daphnia galeata to predation by cyprinid fish were studied in a mesocosm experiment where four levels of predation were repeated at two inorganic nutrient loads. No clear trend was observed in response to nutrient enrichment, so the competition hypothesis, as shaping the demographic profile of the studied population was discarded and only the predation effects were analysed. The changes in body size distribution and reproductive effort estimated through the proportion of ovigerous females and brood sizes were analysed and compared to predicted patterns. Both a significant decrease in body size and an increase in proportion of egg-carrying females in the population could be attributed to increasing vertebrate predation. The direct effect of selective predation resulted in a decrease in population size despite an increased reproductive effort and high food abundances. An analysis of egg size vs. ovigerous female body size revealed treatment related clusters with little or no overlap which indicates that not only the direct size-selective effects take place in natural populations but that a phenotypic response takes part. The increase in proportion of ovigerous females under predation can provide a qualitative estimation of phenotypic response if size-selectivity of predators is assumed.

The Life Histories of the Offshore Oedicerotids Westwoodilla Caecula and Monoculodes Packardi (Crustacea: Amphipoda) From Loch Fyne, Scotland

Results are presented of a comparative study on seasonal variations in population density, population structure and reproductive bionomics of two species of offshore benthic oedicerotid amphipod, Westwoodilla caecula (from 35 m depth) and Monoculodes packardi (from 190 m) in Loch Fyne (Scotland). Observations on live coloration and behaviour of these species in laboratory aquaria are also included. Male W. caecula were, on average, smaller than females. In M. packardi (atypically among Oedicerotidae) the reverse was true. Population densities of both species, calculated from sledge net tows (1-mm mesh), fluctuated erratically over one year (1992). Ovigerous W, caecula were recorded virtually year-round, but were commonest from midsummer to early autumn. Ovigerous M. packardi were noted in spring and early autumn. Monoculodes packardi had a semi-annual life cycle, but the pattern for W. caecula was less clear. The two generations of M. packardi grew at broadly similar rates, presumably associated with the damped seasonal fluctuations in physical environmental factors at 190 m. Female W. caecula possibly moult eight or nine times, and may produce three successive broods in a lifetime (M. packardi may only produce two). A positive correlation was found between fecundity (stage I eggs) and body length in W. caecula but, although a similar trend was apparent in the data for M. packardi, relevant data were too few for significance to be achieved. Ovoid eggs increased in volume by ×2 from stage I-IV in W. caecula, or ×1·5 from stage I–III in M. packardi. Brood sizes were much smaller in W. caecula than in M. packardi, although apparent brood mortality was higher in the latter. There was no significant relationship between the proportion of ovigerous females in the populations of either species and seasonal variation in physical environmental factors considered (temperature, salinity, daylength).

Aspects of the Life Histories of Perioculodes Longimanus, Pontocrates Arcticus and Synchelidium Maculatum (Crustacea: Amphipoda) at Millport, Scotland

Detailed catch and life history data for Perioculodes longimanus and Pontocrates arcticus, together with more limited comparable information on Synchelidium maculatum, are reported. Samples were taken year-round using a 0–5 mm mesh D-net towed over sand in the immediate sublittoral zone (-2 to -6 m Chart Datum) in Kames Bay, Great Cumbrae Island, Scotland. Estimated population densities of Perioculodes longimanus were highest in summer. The occurrence of Pontocrates arcticus was more erratic and S. maculatum occurred only in midsummer in very low numbers. The mean sizes of all population categories of Perioculodes longimanus were bigger in summer than in late autumn and winter. Female Perioculodes longimanus parasitized with the copepod Sphaeronella minuta were significantly smaller than the whole category ‘sexable females’. Adult female S. minuta (one per amphipod brood pouch infected) carried — 70–200 eggs per sac. In both Perioculodes longimanus and Pontocrates arcticus females were larger than males. In Synchelidium maculatum, by contrast, males and females were not different in size. Gravid females were present virtually year-round in Perioculodes longimanus and Pontocrates arcticus, with particularly high proportions of ovigerous females in midsummer and low proportions in midwinter. Both of these species had an annual life cycle with only one generation per year. Longevity was estimated at 15 months. The sex ratio nearly always showed substantial female dominance in all three species. Fecundity appeared to be related to body size but, due to egg losses during sample processing, data were too few for detailed analysis. The eggs of Perioculodes longimanus and Pontocrates arcticus were elliptical in shape, with winter eggs being smaller than summer eggs in Perioculodes longimanus, but larger in Pontocrates arcticus. The percentage of ovigerous females in the population was significantly correlated with a range of environmental factors tested, the highest correlation being with maximum weekly air temperature (for Perioculodes longimanus) and daylength (Pontocrates arcticus), although causative effects cannot be established since temperature/daylength factors were not independent variables

Long‐term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation

1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short‐term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa

Reproduction in the toad Colostethus trinitatus (Anura: Dendrobatidae) in a northern Venezuela seasonal environment

ABSTRACTVarious aspects of the reproductive biology of a montane population of Colostethus trinitatus were quantified during the transition from a prolonged dry season to a wet season with abnormally low rainfall. One-third to three-quarters of the females collected in the dry period (March to June) had mature ovarian follicles. The proportion of ovigerous females did not increase in July or August when the number of rainy days was greater. However, breed-ing and egg laying were only observed in the latter season. The principal environmental change that stimulated oviposition was frequent daily rain which increased humidity in the terrestrial nest sites.Pair formation, nests, and males carrying larvae are reliable criteria that indicate the breeding period of Colostethus trinitatus. The average number of mature ovules (>2 mm) was greater in the wet season (=13.1) than during the dry months (= 11.3). Female standard length and the number of yolked follicles was positively correlated. Five nests contained an average of 13.6 eggs, and males carried only slightly fewer larvae (= 11.5). One female and one individual of unknown sex were found with eggs at two different nests. Five nests were unattended.

Zooplankton Dynamics of Lake Escondido (Rio Negro, Argentina), with Special Reference to a Population of Boeckella gracilipes (Copepoda, Calanoida)

AbstractThe zooplancton dynamics and the populations of Boeckella gracilipes Daday of Lake Escondido (Rio Negro, Argentina) were studied from March 1987 to March 1988. Rotifers and Cladocerans showed high densities during spring and summer, while copepods were densest in autumn. The vertical distribution study showed that rotifers prefer upper levels of the water column, while cladocerans and copepods prefer lower levels, especially during thermal stratification.Boeckella gracilipes had a sex ratio biassed toward female, though changes in the sex ratio were observed. The clutch size was high in winter when the proportion of ovigerous females was low. The instantaneous birth rates were low during winter and high in summer. This result is related to the thermal cycle of the lake, by the influence of temperature on egg development time. The mortality rates showed a similar pattern, and maximum values were registered in spring and summer.

Reduced fecundity of Psoroptes ovis (Hering) (Acari: Psoroptidae) on calves treated with ivermectin

AbstractIvermectin injected subcutaneously into calves at the rate of 200 μ/kg body weight completely eliminated females of Psoroptes ovis (Her.) in 22 days. Injection of ivermectin also adversely affected the number and hatch of eggs and the proportion of adult males forming attachment pairs. The reduced number of eggs recovered in skin scrapings was apparently the result of a significantly lower fecundity among females that temporarily survived on treated calves. Females that were exposed to ivermectin for only three days did not recover their full reproductive potential even though they were transferred to calves not injected with ivermectin. The proportion of ovigerous females among survivors was not significantly affected five days after injection. Since the number of eggs recovered in skin scrapings was substantially reduced after only three days, the effect of ivermectin on female fecundity was not primarily gonadal. Reduction in the number of P. ovis eggs three days after treatment probably occurred because of a combination of mortality of adult females and reduced oviposition by ovigerous females surviving in the population.

Short-term temporal variation in population structure of two harpacticoid copepods, Zausodes arenicolus and Paradactylopodia brevicornis

Aspects of the population biology of two harpacticoid copepod species [Zausodes arenicolus Wilson and Paradactylopodia brevicornis (Claus)] living in Tampa Bay, Florida, USA, were studied on time scales of hours to days during November 1983. Fluctuations in population agestructure, adult sex-ratio, and proportion of ovigerous females were determined for these two species in a control plot and in an experimental plot defaunated by raking. For both species, immigrants into the defaunated plot differed significantly from conspecifics in the control plot in all characteristics examined. The disturbed plot contained a larger proportion of young juveniles of both species compared to the unmanipulated site after 4 h but not after 8 h. In Z. arenicolus, adult males returned to the experimental plot more quickly than adult females. For both species, rapid and significant changes in population age-structure, adult sex-ratio, and the proportion of adult females with eggs occurred within the control plot. It is suggested that this variation was too large and occurred too rapidly to be accounted for solely by in situ processes in the absence of large-scale immigration and/or emigration of individuals. Potential implications of these results for population studies of harpacticoid copepods and other benthic invertebrates are discussed.

Population ecology of carabid cave beetles.

The population ecology of three species of obligate cave dwelling (i.e., troglobitic) carabid beetles, Neaphaenops tellkampfi, Pseudanophthalmus menetriesi and P. pubescens, was studied in five cave habitats in west central Kentucky. Population size, timing of teneral occurrence, sex ratio, proportion of ovigerous females and clutch size were monitored in 12 populations. The data indicate that cave carabid beetles undergo density fluctuations at the local population (subpopulation) level which are intermediate in severity to those observed in surface dwelling carabid species. However, composite populations of N. tellkampfi show overall density fluctuations which are not statistically different in severity from those of more stable surface carabid species. It appears that spatial heterogeneity has a damping effect on density fluctuations in N. tellkampfi over the geographic area studied. A similar explanation has been offered for the more stable surface carabid species.The predictable nature of the cave environment and the reduced number of selection pressures in cave habitats has permitted us to consider evolutionary patterns in these cave carabid species as they relate to differences in ecology. Two major adaptive pathways can be inferred from the population data of this study. Pseudanophthalmus menetriesi and P. pubescens appear to have undergone divergent evolution for habitat specialization in mesic and riparian habitats respectively. Significant life history differences between these two species appear to be related to the characteristics of mesic vs. riparian habitats. Neaphaenops tellkampfi is specialized to prey on cave cricket (Hadenoecus subterraneus) eggs and nymphs, resources which are highly seasonal and become rare in the fall. As a result N. tellkampfi has retained some generalist traits in feeding and in habitat utilization. Its life history characteristics are more variable than those of the Pseudanophthalmus spp. and appear to allow N. tellkampfi to exploit two distinct subniches in the depauperate cave environment.

Population Dynamics of Daphnia galeata mendotae as Modified by Chronic Cadmium Stress

Forty populations of Daphnia galeata mendotae were maintained for 22 wk (or until they became extinct) in a medium consisting of filtered Lake Michigan water to which Chlamydomonas reinhardi and different concentrations of a mixture of labelled (109Cd) plus stable CdCl2 were added 24 h before use. The medium was changed daily Monday through Fridays. Weekly determinations were made of total numbers, average individual dry weight, mean brood size, egg–female ratio, aborted eggs and embryos, and average whole-body 109Cd content. Chronic cadmium stress reduced the populations' average numbers and biomass, while it increased the populations' turnover rates, temporal variability, probability of extinction, and proportion of ovigerous females. For individuals there was increased prenatal mortality, reduced life expectancy, increased average weight, and increased brood size. Due to compensatory increases in the proportion of ovigerous females and mean brood size, the cadmium sensitivity of population attributes was considerably less than that of the most sensitive individual attribute, prenatal mortality. A linear relationship between population carrying capacity (relative mean numbers) and added cadmium concentration indicated that the effective concentration for a 50% reduction of carrying capacity (EC50) is 7.7 μg Cd/L and that for a 1% reduction (EC1) is 0.15 μg Cd/L. An increase of 0.15 μg Cd/L in Lake Michigan itself, barring synergistic interaction with other factors in the lake, would probably not have a detectable effect on the population dynamics of D. galeata mendotae. Key words: zooplankton dynamics, stress ecology, Daphnia galeata mendotae, cadmium, heavy metals, toxic substances, Laurentian Great Lakes

The effect of heated effluent on egg production in the estuarine prawn Upogebia Africana (Ortmann)

Egg production of a population of Upogebia africana (Ortmann) in a pond containing water heated by a thermal power station at Knysna, South Africa was compared with that of the population in the adjacent estuary and in two other estuaries. The breeding cycle, proportions of ovigerous females, incubation time for eggs at different temperatures, number of eggs produced, sex ratios, and size-frequency of males and females were all investigated. The number of eggs produced/100 prawns was found to be nearly twice as high in the population exposed to heated effluent as compared with the population in the adjacent estuary. The increase was due to a combination of a change in sex ratio resulting in more females in the population and a greater proportion of larger females in the pond. Since the number of eggs produced/female is positively related to the size of the prawn, large females in warmer water produced more eggs than smaller females in the adjacent estuary. Exposure to heated effluent did not alter the initiation or duration of the breeding season, nor cause precocious maturity; nor did it alter the number of eggs carried per female at various sizes.