SUMMARYRate-independent plasticity and viscoplasticity in which the boundary of the elastic domain is defined by an arbitrary number of yield surfaces intersecting in a non-smooth fashion are considered in detail. It is shown that the standard Kuhn-Tucker optimality conditions lead to the only computationally useful characterization of plastic loading. On the computational side, an unconditionally convergent return mapping algorithm is developed which places no restrictions (aside from convexity) on the functional forms of the yield condition, flow rule and hardening law. The proposed general purpose procedure is amenable to exact linearization leading to a closed-form expression of the so-called consistent (algorithmic) tangent moduli. For viscoplasticity, a closed-form algorithm is developed based on the rate-independent solution. The methodology is applied to structural elements in which the elastic domain possesses a non-smooth boundary. Numerical simulations are presented that illustrate the excellent performance of the algorithm.

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Life-history theory suggests that animals may skip reproductive events after initial maturation to maximize lifetime fitness. In iteroparous teleosts, verifying past spawning history is particularly difficult; the degree of skipped spawning at the population level therefore remains unknown. We unequivocally show frequent skipped spawning in Northeast Arctic cod (NEAC) in a massive field and laboratory effort from 2006 to 2008. This was verified by postovulatory follicles in temporarily arrested ovaries close to the putative spawning period. At the population level, "skippers" were estimated to be approximately equally abundant as spawning females in 2008, constituting ∼24% of the females 60-100 cm. These females never truly started vitellogenesis and principally remained on the feeding grounds when spawners migrated southward, avoiding any migration costs. The proximate cause of skipping seems to be insufficient energy to initiate oocyte development, indicating that skipped spawning may partly be a density-dependent response important in population regulation. Our data also indicate more skipping among smaller females and potential tradeoffs between current and future reproductive effort. We propose that skipped spawning is an integral life-history component for NEAC, likely varying annually, and it could therefore be an underlying factor causing some of the currently unexplained large NEAC recruitment variation. The same may hold for other teleosts.codfish | population dynamics | reproductive biology | total egg production | stock reproductive potential P opulation demography changes according to reproduction and mortality. In high latitude marine ectotherms, including teleosts, survival of the youngest age classes varies substantially, resulting in large fluctuations in population size (1). Historic spawning stock biomass (SSB) is used to forecast future fish recruitment, although the amount of unexplained variation indicates that SSB may not accurately reflect offspring production (2, 3). One factor that could significantly impact egg production is skipped spawning-the failure of iteroparous spawners to use each spawning opportunity after sexual maturity sensu (4). For most teleosts this phenomenon and its impact on population demography has received scant attention, but theoretical models indicate that up to 30% of the mature individuals may skip spawning and that it is an adaptive strategy optimizing lifetime fitness (5). To date, skipped spawning has been documented in more than 30 species (4, 6), including freshwater (7), marine (8), and anadromous teleosts (9). It has been documented for fish with both indeterminate and determinate fecundity and sequential hermaphrodites (6) and in species with as diverse life histories as the European horse mackerel Trachurus trachurus (10) and the orange roughy Hoplostethus atlanticus (8). Given the difficulty in conclusively establishing past spawning, reports of skipped spawning in teleosts are commonly anecdotal (4).The major process of energy transfer and oocyte gr...

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Abstract:The fecundity of European plaice (Pleuronectes platessa) in the Irish Sea between 2000 and 2004 was estimated during the spawning season for fish in the three main spawning areas (Liverpool Bay, the Cumbrian coast, and the western Irish Sea) and one small spawning group on the west coast of the Isle of Man. Fecundity was also estimated during September of 2003 and 2004. The aim of this was to assess the variability in fecundity between areas and years in the Irish Sea and also to identify when differences in fecundity become apparent in the maturation cycle. There were variations in fecundity on both the temporal and spatial scales. The greatest variation in fecundity between years occurred in the western Irish Sea, whereas there was no variation between years in the southeastern Irish Sea (Liverpool Bay). There was no difference in fecundity between areas or years during September. The maximum fecundity in plaice is determined by the total weight of the fish at the end of follicle recruitment in the ovary, and differences in the fecundity of each population are the result of different levels of down-regulation in the period between the end of follicle proliferation and spawning.

Plasma concentrations of parathyroid hormone-related protein (PTHrP), parathyroid hormone, alkaline phosphatase, osteocalcin and albumin-adjusted calcium were measured along with nephrogenous cyclic adenosine monophosphate (NcAMP) in 10 normal women longitudinally through pregnancy. In addition, an assessment of bone resorption was made in these same subjects by the measurement in true fasting urine specimens of the calcium/creatinine ratio (Ca/Cr), hydroxyproline/creatinine ratio (HP/Cr), pyridinoline/creatinine ratio (Pyr/Cr) and deoxypyridinoline/creatine ratio (Dpyr/Cr). The PTHrP level rose through pregnancy from (mean +/- SEM) 0.8 +/- 0.2 pmol/l in the first trimester to 2.7 +/- 0.2 pmol/l 6 weeks postpartum (p < 0.0001). Serum alkaline phosphatase rose from 94 +/- 8 U/l (first trimester) to 347 +/- 25 U/l at term (p < 0.0001). A significant positive correlation was evident between PTHrP and alkaline phosphatase up to term (r = 0.44, p < 0.005). Parathyroid hormone concentrations remained unchanged during pregnancy but rose significantly postpartum from 1.8 +/- 0.2 pmol/l (first trimester) to 3.1 +/- 0.5 pmol/l (p < 0.0001). Similarly, osteocalcin, a marker of bone formative activity, remained unchanged through pregnancy but rose significantly at 6 weeks after delivery to 0.38 +/- 0.05 nmol/l from 0.19 +/- 0.03 nmol/l (first trimester) (p = 0.019). No significant change was noted in serum-adjusted calcium or NcAMP, either through pregnancy or at the postpartum assessment. Fasting urinary Ca/Cr fell through pregnancy from 0.70 +/- 0.11 (first trimester) to a nadir of 0.19 +/- 0.04 6 weeks postpartum (p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of controlling food intake during the autumn, which is the time of late vitellogenesis, on fecundity, atresia and follicle and ovary growth was examined for plaice Pleuronectes platessa. Eighteen fish were kept in individual pens and either fed on a high or low ration diet. Fish which increased in whole body condition exhibited an increase in carcass condition which means that when food intake is sufficient to maintain whole body condition some resources are used as storage. Follicle growth rate was positively correlated with change in Fulton's condition and total atresia was negatively correlated with change in Fulton's condition. Thus, the rate of vitellogenesis was dependent on the availability of an exogenous food source. Fecundity at the end of the experiment was positively correlated with mass and total length. Food intake had no effect on relative fecundity; however, fish which had a lower food intake lost mass and had a greater intensity of atresia, lowering their absolute fecundity. One fish in a very low condition at the start of the experiment skipped spawning and one fish exhibited a decrease in average follicle diameter during the experiment which is hypothesized to be a prelude to mass atresia.

Havforskningsinstituttets institusjonelle arkiv Brage IMR - Institutional repository of the Institute of Marine Research b r a g e i m rDette er forfatters siste versjon av den fagfellevurderte artikkelen, vanligvis omtalt som postprint. I Brage IMR er denne artikkelen ikke publisert med forlagets layout fordi forlaget ikke tillater dette. Du finner lenke til forlagets versjon i Brage-posten. Det anbefales at referanser til artikkelen hentes fra forlagets side. Ved lenking til artikkelen skal det lenkes til post i Brage IMR, ikke direkte til pdf-fil.This is the author's last version of the article after peer review and is not the publisher's version, usually referred to as postprint. You will find a link to the publisher's version in Brage IMR. It is recommended that you obtain the references from the publisher's site.Linking to the article should be to the Brage-record, not directly to the pdf-file. Abstract 10To examine mechanisms that affect fecundity, atresia and skipped spawning in Northeast 11Arctic cod (Gadus morhua L.), we conducted an experiment where wild-caught cod (>60 cm) 12 kept under restricted food regimes were subjected to monthly biopsies, hormonal and physical 13 measurements. The power of body weight as a fecundity proxy increased until the presumed 14 end of follicle proliferation in early November, thereafter it remained stable. Atresia occurred 15 in most females; but, for maturing females, mainly close to spawning. 18 % of the females 16 had small gonads with predominantly previtellogenic oocytes at sacrifice in January. These 17 females were past-spawners, verified by post ovulatory follicles in their gonadss. These 18 "skippers" had lower condition than maturing cod from December, smaller livers upon 19 sacrifice and lower plasma 17-β estradiol values from early November. Until November, 20 oocytes developed similarly for all females, but in November oocyte development was 21 arrested at the early cortical alveoli stage and atresia occurred in all skippers. In sum, 22 fecundity and skipped spawning seem highly influenced by energy reserves during early 23 vitellogenesis and limited to females only. Finally, skippers were identifiable long before the 24 predicted onset of spawning, which could have implications for forecasting of egg production 25 and hence stock-recruitment relationships. 26