Proportion Of Gravid Females Research Articles

Toxicity of Creosote Water-Soluble Fractions Generated from Contaminated Sediments to the Bay Mysid

Creosote, a globally used wood preservative, is a complex mixture consisting primarily of aromatic organic compounds (ACs). Creosote-derived ACs can persist for decades in aquatic sediments. Natural and anthropogenic activities may result in dissolution and resuspension of sediment-associated ACs. These processes were mimicked by generating a water-soluble fraction (WSF) from creosote-contaminated sediment (ERS) collected from a polluted site. The epibenthic mysidMysidopsis bahiawas exposed to five sublethal concentrations of WSF for 7 days. The WSF significantly decreased dry weight gain and proportion of gravid females (EC50=15 μg/liter total identified ACs). Chemical analysis indicated that high-molecular-weight ACs (more than three aromatic rings) dominated the ERS, but were undetected in the WSF. Low-molecular-weight ACs (fewer than three aromatic rings) dominated the WSF. Compositional differences can thus result from fractionation processes and affect environmental fate and toxicity of the mixture.

Body mass changes in Trimeresurus flavoviridis (Viperidae) on Okinawa Island, Japan

AbstractBody masses of wild‐caught habu, Trimeresurus flavoviridis, were measured with known error range. Habu larger than mature female size had steeper slope in length‐mass regression than smaller individuals. Females outweighed males in most snout‐ventlength classes and in early summer. Gravid females outweighed non‐gravid ones by about 20% on the average, but the body mass ranges of the two groups overlapped. Through the body mass change in mature females, the proportion of gravid females was estimated to be about 0.5.

Effects of bait age on the number, sex, and age composition of Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) in Western Australian blowfly traps

Daily catches of the Australian sheep blowfly, Lucilia cuprina, in Western Australian blowfly traps were not significantly affected by exposing the baits in traps for up to 3 days in the field before trapping. Exposure of the baits for longer periods significantly increased the daily catch totals of both sexes. Baits with a mean exposure time before trapping of 7 days (old baits) returned significantly higher catches than baits with a zero exposure time (fresh baits): 5-fold and 3-fold increases, respectively, for males and females. Exposure of baits for only 1 day was sufficient to produce significant changes in the reproductive age composition of female catches; proportions of newly emerged females increased and proportions of gravid females decreased. Coefficients of variation for old bait/new bait catch ratios were small, 16.4% for males and 12.3% for females, which confirmed that both baits exhibited consistent levels of attractiveness on different trapping dates. Procedures are suggested for estimating population densities of L. cuprina based on trap catches using fresh and old baits.

Assessing sublethal levels of sediment contamination using the estuarine amphipod Leptocheirus plumulosus

AbstractRecent emphasis on the incorporation of sublethal end points into sediment toxicity test methods follows the realization that acute lethality tests may not provide sufficient sensitivity for predicting subtle ecological effects of sediment contamination. To this end, a partial life‐cycle test with the amphipod Leptocheirus plumulosus Shoemaker was evaluated for solid‐phase testing of contaminated estuarine sediments. Initially, juvenile and adultLeptocheirus plumulosus and the amphipod Hyalella azteca were exposed to gradients of chemical contamination prepared by diluting field‐collected contaminated sediment with texturally similar reference sediment. Ten‐day exposure results indicate juvenile Leptocheirus plumulosus is more sensitive than adult Leptocheirus plumulosus and Hyalella azteca, with significant mortality of juvenile Leptocheirus plumulosus occurring in sediment diluted to 12.5% of the adult lowest‐observed‐effect concentration (LOEC). Long‐term exposure (30 d) of juveniles to dilutions of the acute juvenile LOEC shows significant effects on growth in sediment concentrations below the lethal threshold. Effects on reproductive end points (proportion of gravid females, number of young) parallel growth effects. Evaluation of nontoxicant experimental variables indicates significant effects of temperature and feeding regime on sensitivity of juvenile Leptocheirus plumulosus to contaminated sediment.

An Approach to Modeling Crustacean Egg-Bearing Fractions as a Function of Size and Season

We present an approach to the analysis of crustacean egg production ogives with emphasis on detecting seasonal trends. The relationship between the proportion of gravid females (by size) and season is a prerequisite to the estimation of egg production potentials of populations. The basic method consists of relating, for each sample, the proportion of berried females with their size through a three-parameter logistic function where the asymptote may be less than 1. We then provide guidance for detecting seasonal trends in the estimates of the parameters for the individual samples. This is accomplished by restricting the basic model such that some parameters are considered to be either fixed for all samples or as simple functions of time or environmental variables such as temperature. Parameter estimates are obtained via maximum likelihood methods, and comparisons between alternative models are presented graphically and using likelihood ratio tests. We illustrate the approach and its application with data for a tropical shrimp, Penaeus esculentus, from northern Australia.

Age Structure and Reproductive Biology of a Natural House Fly (Diptera: Muscidae) Population

Spatial and temporal components of sex ratio and female age structure were studied in sweep net samples of Musca domestica L. Nine age groups were recognized. Collections were made on nine dates from three sites at a dairy farm. Diurnal components of sex ratio and age structure also were investigated by making sweeps at 0700, 1200, and 1700 hours at one sampling location. Insemination rates were examined with respect to gonotrophic development. Sex ratio and proportions of gravid females did not vary consistently over space or time. The proportion of males netted increased linearly with hour of the day. Insemination correlated with the onset of vitellogenesis and was 91% complete within a day. Previtellogenic females (<2.5 days old) were virgin; their relative abundance was greatest where males were most abundant and parous flies were least abundant. The effective sex ratio of males to receptive virgins was estimated to be ca. 6:1.