Sex change in scallop Patinopecten yessoensis: response to population composition?

Sex structure is very labile between populations and specific for each population because it is a result of genetic, ontogenetic and biocenotic influences on the mollusks. In this study, the age frequency distribution, age-sex structure, and sex ratio were assessed in the wild populations of the Yeso scallop Patinopecten yessoensis (Jay) observed at fifteen sites in the northwestern Sea of Japan (=East Sea). The sex ratio varied between the populations from 0.83:1 to 1.52:1 (males/females), with the mean sex ratio being 1.03 ± 0.05:1. Within a population, the proportions of males and females in term of number differed between age classes. Males were more numerous than females in the younger age classes, and females prevailed over males in the older age classes. It was found that in different scallop populations the sex change occurred at different ages. In the populations that predominantly consisted of young (two- to four-year-old) individuals, males prevailed over females in the age class 2 yr.; the equal male/female proportion was found in the age class 3 yr.; and in older age classes, females prevailed over males. Another pattern was observed in the populations that consisted mainly of middle-aged (five- to six-year-old) individuals. Here, the age-sex ratio became equal at an age of 4–6 years. In the old populations (mainly 6–12-year-olds) the equal male/female proportion was observed at an age of 8–10 years. Thus, the age of sex change was not uniform for the scallop populations. It depended on the age structure of the population and, thus, was socially controlled. The greater number of females in the older age classes suggests a protandric sex change.

Quantitative comparisons and models of time-averaging in bivalve and brachiopod shell accumulations

The variation in time-averaging between different types of marine skeletal accumulations within a depositional system is not well understood. Here we provide quantitative data on the magnitude of time-averaging and the age structure of the sub-fossil record of two species with divergent physical and ecological characteristics, the brachiopodBouchardia roseaand the bivalveSemele casali.Material was collected from two sites on a mixed carbonate-siliciclastic shelf off the coast of Brazil where both species are dominant components of the local fauna.Individual shells (n= 178) were dated using amino acid racemization (aspartic acid) calibrated with 24 AMS radiocarbon dates. Shell ages range from modern to 8118 yearsb.p.for brachiopods, and modern to 4437 years for bivalves. Significant differences in the shape and central tendency of age-frequency distributions are apparent between each sample. Such differences in time-averaging magnitude confirm the assumption that taphonomic processes are subject to stochastic variation at all spatial and temporal scales. Despite these differences, each sample is temporally incomplete at centennial resolution and three of the four samples have similar right-skewed age-frequency distributions. Simulations of temporal completeness indicate that samples of both species from the shallow site are consistent with a more strongly right-skewed and less-complete age-frequency distribution than those from the deep site.We conclude that intrinsic characteristics of each species exert less control on the time-averaging signature of these samples than do extrinsic factors such as variation in rates of sedimentation and taphonomic destruction. This suggests that brachiopod-dominated and bivalve-dominated shell accumulations may be more similar in temporal resolution than previously thought, and that the temporal resolution of multi-taxic shell accumulations may depend more on site-to-site differences than on the intrinsic properties of the constituent organisms.

Validated age, growth, and mortality estimates of the ocean quahog (Arctica islandica) in the western Atlantic

Kilada, R. W., Campana S. E., and Roddick, D. 2007. Validated age, growth, and mortality estimates of the ocean quahog (Arctica islandica) in the western Atlantic. ICES Journal of Marine Science, 64: 31–38. The age structure of offshore (Sable Bank) and inshore (St Mary's Bay) populations of eastern Canadian ocean quahogs (Arctica islandica), and of a northwestern Iceland population, is investigated. Age estimates for eastern Canadian ocean quahogs were validated through analysis of bomb-produced 14C in quahog shell growth increments deposited before, during, and after the atmospheric atomic bomb testing periods of the 1950s and 1960s. Delta 14C from shells with presumed birthdates between the late 1950s and 1970s clearly reflects the sharp increase in oceanic radiocarbon attributable to nuclear testing. The results validate our age interpretations of Sable Bank quahogs to an age of 45 y, and support longevity estimates of more than 200 y for the same population. Longevity calculations for the other populations exceeded 60 y. Von Bertalanffy growth parameters were estimated for the three populations; the growth rate of all three was relatively rapid for the first 20–30 y of life, but thereafter was very slow. The instantaneous rate of natural mortality (M), calculated using the age–frequency distribution of the unexploited populations, was estimated to be 0.03 and 0.10 for the Sable Bank and St Mary's Bay populations, respectively.

Age frequency distribution of joint ER/PR phenotypes in primary breast cancer patients: An analysis of 3,620 cases at a single Japanese institute

597 Background: Hormone receptor (HR) expression may reflect the different subtypes of breast cancer. Recent clinical trials have reported that joint Estrogen receptor (ER)/Progesterone receptor (PR) phenotypes in breast cancer have specific spectrum for treatment response. To analyze the epidemiologic character of ER/PR subtypes in Japanese patients, a retrospective data survey was conducted for 3,620 breast cancer patients treated at a single institute during 1975–2005. Methods: Patients records were obtained from cancer registration of the Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital and analyzed with SAS software. Among 3,620 operated patients, data of ER/PR subtypes were available in 2,707 cases. HRs were evaluated by ligand binding assay (LBA) or enzyme immuno assay (EIA) from 1975 to 2000 (n=1721), and by immunohistochemistry (IHC) after that (n=986). Results: Both mean and median of patient’s age increased through the operated year (p<0.0001). Therefore, all analysis related to distribution of age were adjusted by the operated year. As reported before, ER+ population showed liner trend with age by LBA/EIA (p<0.0001), while this was not observed by IHC. ER-/PR+ population was 10.6% by LBA/EIA, whereas it decreased to 2.1% by IHC. These are due to the increase of ER+ population with IHC analysis, since marginal distribution between two methods in the patients tested by both assays was significantly different for ER, but not for PR (n=181, p=0.0038 and n=175, p=0.1944). Irrespective of assay methods, peak age frequency of ER+/PR+ was between 46 and 50 years of age, whereas that of ER+/PR- was 56–60. For ER/PR phenotypes there was a significant difference of odds ratio across the age (<55 vs. ≥55, p=0.04 for IHC, p=0.0002 for LBA/EIA). Conclusion: Changes of standard assay from LBA/EIA to IHC affected the population of ER+ and lead the decrease of ER-/PR+ subtype. Japanese women’s peak age frequency of ER+/PR+ was in the premenopausal period compared to that of non-Hispanic white women in the postmenopausal age (Anderson WF, JCO 2001). Difference of most frequent age of each subtype among the races may be taken into account for the development of chemoprevention strategy with anti-estrogens. No significant financial relationships to disclose.

Age and diameter structure of a managed uneven-aged oak forest

We studied the age and diameter structure on one section (259 ha) of a 63 000-ha privately owned forest in the Ozark Highlands of Missouri. The forest has been managed using a partial cutting strategy since 1954. Because a majority of the trees predate current management practices, the existing stand structure is a function of not only the current silvicultural system and the dynamics of this ecosystem but also the initial stand conditions. To determine age structure and evaluate the relationship of diameter and age, a random sample of 600 oaks [Formula: see text]4 cm DBH were collected from ten 0.4-ha plots. Based on the test of a binomial proportion, the oak populations on 7 of the 10 plots were deemed uneven aged, two were deemed two aged, and one was even aged. DBH accounted for 40 (red oaks) to 62% (white oaks) of the variation in tree age. Although the overall diameter frequency distribution of oaks formed a reverse-J shape, the age-frequency distribution approximated a normal (bell-shaped) distribution. We show how this apparent inconsistency between diameter and age distributions can be an artifact of a minimum sampling diameter. Such a truncation of the sampled population reduces the observed frequency of trees in the younger age-classes, which in turn results in a bell-shaped rather than a reverse-J-shaped age-frequency distribution. Thus, the lack of a reverse- J-shaped age distribution should not be interpreted as a failure to sustain regeneration in an uneven-aged stand.

A Mark-Recapture Experiment on Queen Scallops, Aequ1Pecten Opercularis, on a North Irish Sea Fishing Ground

A single-season mark-recapture experiment was carried out on queen scallops, Aequipecten opercularis (L.) (Bivalvia: Pectinidae) to assess the suitability of the technique for estimating population sizes and mortality rates of exploited populations. Tag-loss and tagging-induced mortality were 7.7% and 11.9% respectively. Non-reporting was negligible.In a single fishing season (June-December 1989) 25.4% of releases were recaptured alive. Mean density of commercial-sized queens was estimated as 0.47 m−2 over the fishing ground. Instantaneous rates of total (Z), fishing (F) and-natural (M) mortality, calculated from the monthly decline of recaptures during the fishing season, were 0.;41,0.21 and 0.20 per month respectively. The calculated M is very high but includes non-yield or indirect fishing mortality. Analysis of the age-frequency distribution of queens from an adjacent, largely unexploited, area indicated an M of only 0.036 per month (0.43 y−1). There was some indication of an increase in M in older year classes, associated with senescence.The mark-recapture methodology used here is suitable for this species, but single-release experiments place too much reliance on commercial catch-statistics.