Terminal Molt Research Articles

Postlarval development of <i>Halicarcinus planatus</i> females (Crustacea, Decapoda, Hymenosomatidae) in the estuary of the Deseado River, Argentina

This study analyses morphology and morphometric growth changes of Halicarcinus planatus females until their terminal moult, and characterises new juvenile stages. Monthly samples were collected in the estuary of the Deseado River, Santa Cruz Province, Argentina. Crabs were sampled between the mid-intertidal and upper subtidal levels. Intermoult stages were analysed in sub-samples of adolescents and adults, and the presence of epizoic organisms was registered. Juveniles and adults were reared at the laboratory and examined for moult changes. All 3376 crabs caught were females, indicating a clear spatial segregation between sexes. Five juvenile stages (immature 1, 2, 3, 4 and adolescent) and a mature one were recognised on the basis of morphology and morphometry. All immature stages differed in cephalothorax width (CW) and abdomen width (AW). Positive allometry was observed in some juvenile stages and isometry in an immature stage and in mature females. Adolescents and adults encompassed a wide range of sizes, and the considerable size overlap between them suggests an anomalous growth process. Moult staging analysis indicated that adolescents have a high incidence of pre-moult stages in winter, when the terminal moult occurs. The measurements performed in laboratory-reared females indicated no abnormal increases during the moult. The terminal moult occurs within a wide size range, perhaps in association with mating.

Life Cycle of a Bioluminescent Marine Ostracode, Vargula Annecohenae (Myodocopida: Cypridinidae)

Abstract We present the first complete description of a life cycle for a marine ostracode that uses bioluminescence for courtship. The life cycle of Vargula annecohenae consists of five juvenile instars separated by molts and an adult instar following the terminal molt. Body size is tightly conserved within each instar; therefore, most individuals can be reliably identified to instar by the length-to-height regression of carapace size. Sexual dimorphism becomes apparent in the penultimate A-I instar and remains evident through adulthood. Each juvenile instar of V. annecohenae lasts between 10 and 27 days, resulting in an estimated total juvenile development time of three months. Females have multiple broods and give birth to crawl-away juveniles following a 26 ± 1.6 day incubation period. Adults live up to 188 additional days, and thus V. annecohenae has a potential life span of up to nine months. This species is one of the large number of myodocopid ostracode species that use bioluminescence for courtshi...

Feeding, nutrient flow, and functional gut morphology in the cricket Gryllus bimaculatus

The flow of nutrients through the digestive tract of Gryllus bimaculatus is regulated by the proventriculus, which effectively triturates the partially digested food coming from the crop and shoves the mushy nutrient mass into the space between the paired caeca. The many folds at the base of the caeca form a sieve, and only fine food particles (4-10 microm) and fluids in the mush are filtered under pressure (produced by proventricular peristalsis) into the caeca. Combined with the release of enzymes in the caeca and the influx of water, the caeca are rapidly inflated on day 1 after the terminal molt. The remaining, mostly undigested food is shoved into a tube formed by the peritrophic membrane, which is first formed at the anterior end of the ventriculus. A mucous membrane (peritrophic gel) covers the caecal epithelium, and seems to merge with the true peritrophic membrane at the beginning of the ventriculus. The Type I peritrophic membrane is dragged posteriorly through the entire ventriculus and ileum by the posterior movement of the food bolus, which is shoved posteriorly at a rate of 6 mm/h by proventricular pressure. The growth rate of the peritrophic membrane is about 3 mm/h. Peristalsis does not occur in the midgut or ileum; the muscles in these regions function solely to counteract the internal pressure produced by the proventriculus. The exo- and endoperitrophic space in newly molted animals is open and fluids can flow in both directions. The endoperitrophic space becomes filled on day 1, and leads to a great reduction of the exoperitrophic space. In the ileal pouch (exoperitrophic space) the peritrophic membrane separates the mass of bacteria from the waste bolus within the endoperitrophic space. Feathery bristles arising from the cuticular covering of the finger-like invaginations of the ileal wall hold most of the bacterial mass in place. The crop weight decreases from day 1 to day 3 as the weight of caeca, ventriculus, and ileum increases. After day 3, food uptake and the weight of the entire gut system decrease in female crickets, partly in response to space restrictions in the abdomen caused by rapid ovarial growth.

The Relationship between Circulating Ecdysteroids and Chela Allometry in Male Tanner Crabs: Evidence for a Terminal Molt in the Genus Chionoecetes

Abstract Whether male Tanner crabs, Chionoecetes bairdi, undergo a terminal molt associated with a change in claw allometry has long been debated. We measured molting hormone levels in captured male C. bairdi to assess the potential for molting. We plotted a frequency histogram of chela height to carapace width ratios and found a bimodal distribution of crabs with a ratio of approximately 0.18 separating the two modes. Male crabs with a ratio less than 0.18 were classified as “small-clawed” (SC) while crabs with a ratio greater than 0.18 were classified as “large-clawed” (LC). Circulating molting hormones between SC and LC crabs were compared. Significantly lower ecdysteroid levels were found in LC crabs, indicating that this morphotype had negligible potential for molting. Circulating ecdysteroids were measured in SC males of different shell conditions (soft, new, old, and very old) and no significant differences were found. This research suggests that the molt to LC morphology is a terminal molt. The re...

TIMING AND SEASONALITY OF THE TERMINAL MOLT AND MATING MIGRATION IN THE SPIDER CRAB, MAJA BRACHYDACTYLA: EVIDENCE OF ALTERNATIVE MATING STRATEGIES

Timing and synchronization at individual and population levels of the processes related to the terminal molt, gonad maturation, accumulation of energy reserves and migration in the spider crab Maja brachydactyla are analyzed. Also, the intra and intersexual variability is established. Two hypotheses are tested to explain the temporal and population variability: (1) physiological hypothesis: males and females begin migration when they reach the appropriate physiological stage (the optimum level of energy reserves) and (2) mating opportunities hypothesis: the timing of the migration maximize mating opportunities and mate quality. Our results show that males carry out the terminal molt before females, the former having a peak in July and the latter in August. The onset of gonad maturity in females occurs between two and three months after they have reached morphometric maturity (starting in October), coinciding with the period prior to and during the mating migration to deep waters. In an analysis of the spermathecae of primiparous females, it was found that practically no mating activity occurred in shallow waters, whereas the first copulations took place in the migration corridor. However, probably most of the mating activity occurs in deep mating grounds. Males reached gonad maturity prior to morphometric maturity. No differences were observed in the physiological status (muscle, gonad and hepatopancreas relative mass) between migrating and nonmigrating crabs, which is a clear indication that the physiological hypothesis does not hold true for this species. A higher percentage of postmolt crabs were caught in the migration corridor than in shallow waters. The physiological condition improved over time in males and females in the specimens caught in the shallow area as well as in the migration corridor. Therefore, the crabs that start migrating first did so in poorer physiological condition. Moreover, the early migrators had a significantly lower mean size than the late migrators. Our results suggest that variability within populations and between sexes are related to the different reproductive strategies and not to a physiological limitation. Thus, the poor-quality males (with a reduced competitive ability) would migrate at the beginning of the season to maximize the mating opportunities that would not be feasible if they had to compete with the late migrators, which are larger in size and in better physiological condition. Sperm competition is not clear in M. brachydactyla, but all evidences point at last male preference for fertilization of eggs.

Morphometric and gonad maturity in the spider crab Maja brachydactyla: a comparison of methods for estimating size at maturity in species with determinate growth

Abstract Ontogenetic changes in the relative growth of males and females of the spider crab Maja brachydactyla, a species with terminal moult and determinate growth, were analysed and related to their reproductive (maturity) status. Based on the allometry of cheliped size, two morphometric groups of males separated juvenile and adult phases. Juvenile males also showed two growth phases, immature (smaller ones, without spermatophores) and adolescent (with spermatophores). Size at gonad maturity in males (estimated as CL50) was 96.2 mm carapace length (CL). Histological analysis of males showed that >60% of morphometric juveniles and 100% of morphometric adults had spermatophores in the gonad. Females begin to develop gonads 2–3 months after the terminal moult. Size at morphometric maturity was estimated comparing two methodologies: the size at 50% maturity (CL50) and the median size of adult cohorts (CLM). In all cases the CLM size at maturity was greater than that resulting from the CL50 method, and, in contrast to the CL50 method, CLM was greater for females in all cases. Therefore, CLM reflects better the real size at maturity for M. brachydactyla. Owing to spatial segregation of adults and juveniles and the availability of morphological and morphometric methods to estimate maturity status, we suggest a combination of spatial closures and direct protection of juvenile habitat as management strategies alternative to minimum landing sizes.

Adult neurogenesis in the central olfactory pathway in the absence of receptor neuron turnover in Libinia emarginata

Life-long neurogenesis is a characteristic feature of the olfactory pathways of a phylogenetically diverse array of animals. In both vertebrates and invertebrates, the life-long addition of olfactory interneurons in the brain occurs in parallel with the continuous proliferation of olfactory receptor neurons in the olfactory organ. It has been proposed that these two processes are related functionally, with new olfactory interneurons being added to accommodate the new olfactory receptor neurons added in the periphery. While this has not been tested directly because the two processes are not readily separable, this question can be addressed in the olfactory pathway of the crab, Libinia emarginata. Unlike most decapod crustaceans, which moult and grow throughout life, L. emarginata has a terminal, maturational moult after which animals become anecdysic (stop moulting). Because the addition of new receptor neurons in crustaceans is associated with moulting, a comparison of neurogenesis in immature and mature L. emarginata provides an opportunity to examine the interdependence of central and peripheral neurogenesis in the olfactory pathway. This study demonstrates that the continuous addition of olfactory receptor neurons in L. emarginata ceases at the terminal moult but that proliferation and differentiation of olfactory interneurons in the brain continues in mature animals. Contrary to the general assumption, therefore, continuous neurogenesis in the central olfactory pathway of this species does not occur as part of a process involving the coregulation of central and peripheral neurogenesis. These findings suggest that peripheral neurogenesis is not a requirement for continuous neurogenesis in the central olfactory pathway.

Life history of the slipper lobster Scyllarides astori Holthuis 1960, in the Galapagos islands, Ecuador

Growth of the scyllarid lobster Scyllarides astori was estimated in the Galapagos Marine Reserve by use of tag-recapture data and analysis of length–frequency distributions. Asymptotic carapace lengths (CL ∞), obtained from Powell–Wetherall plots, were 17.53 cm for males and 16.38 cm for females. A ‘forced’ Gulland–Holt plot gave growth constants ( K) of 0.153 yr − 1 for males and 0.162 yr − 1 for females. The narrow size distribution suggests that juveniles occupy a different spatial niche and that adult growth is either very slow or that there is a terminal moult. Currently mainly used for local consumption, there is pressure to allow exportation of S. astori on a large scale to continental Ecuador and abroad. However, its slow growth and low abundance point to the need for a cautious approach and the implementation of clear and enforceable regulations in order to ensure the biological and economical sustainability of the population.

Effect of Eyestalk-Ablation on Circulating Ecdysteroids in Hemolymph of Snow Crabs, Chionoecetes opilio: Physiological Evidence for a Terminal Molt

Bering Sea snow crabs (Chionoecetes opilio) are a commercially important crab harvested in the Bering Sea. Optimal management of this species requires an understanding of the biology of this crab that is currently incomplete. Fisheries managers apply a continuous growth model in their management of snow crab, which assumes that male crabs increase in size throughout their lifespan. Male snow crabs undergo a morphometric molt that leads to a disproportionate increase in chelae size and it is still debated whether this molt is associated with a terminal molt. This study was conducted to determine whether adult male C. opilio are anecdysic. Using current knowledge of the hormonal regulation of crustacean growth, snow crab physiology was manipulated to induce an increase in molting hormones (ecdysteroids). Since female snow crabs are known to undergo a terminal molt after attaining reproductive maturity, we compared ecdysteroid levels in eyestalk-ablated terminally molted females, small-clawed males and large-clawed males. Snow crabs were collected from the Bering Sea and maintained in circulating seawater at approximately 6°C. Animals were either eyestalk-ablated or left intact. Ecdysteroid levels in hemolymph were quantified using an enzyme-linked immunosorbant assay (ELISA). Circulating ecdysteroids were significantly higher in small-clawed male crabs when compared to large-clawed males or terminally molted females. Eyestalk-ablation increased circulating ecdysteroids in small-clawed males, but had no significant effect on circulating ecdysteroids in large-clawed males or in terminally molted females.

Sexual maturity in females of deep-sea red crab Chaceon notialis (Brachyura, Geryonidae) in the southwestern Atlantic Ocean

Summary Chaceon notialis is a brachyuran crab inhabiting the continental slope (250–1,000 m) off Uruguay in the southwestern Atlantic Ocean, constituting one of the main exploited stocks of deep-sea red crab in the world. The objective of this paper was to estimate size at morphological and physiological sexual maturity in females of Chaceon notialis in Uruguayan waters. Crabs were obtained from commercial samples taken in 1997 and 1998. For each individual, carapace width (CW) was measured and morphological (abdomen width and vulval features) and physiological (ovarian maturity) reproductive indicators were examined in order to estimate the size at sexual maturity. As the existence of a terminal molt still cannot be confirmed in females of C. notialis, we tested the alternative hypotheses that females: (1) have indeterminate growth and (2) exhibit a terminal molt. Hypothesis 1 was evaluated by fitting the logistic maturity function that provides the CW50% of females with mature vulvae, whereas hypothesis 2 was evaluated through the analysis of CW frequency distributions of morphologically and physiologically mature females. In addition, 50 pairs of female spermathecae were examined to determine if insemination had occurred; the carapace hardness of the individuals concerned was also noted. Two patterns of vulval morphology in females of C. notialis were observed for the first time: immature or ttclosedtt vulvae, and mature or ttopenedtt vulvae, respectively. Estimations of size at sexual maturity differed according to the hypothesis evaluated: under the assumption that females continue growing after the pubertal molt, mean sizes at morphological and physiological maturity (CW50%) were estimated as 70.2 mm and 71.7 mm, respectively. Alternatively, if females have a terminal molt, mean (± SD) estimates were 91.5 ± 8.5 mm and 91.1 ± 8.0 mm, respectively. Both scenarios clearly suggest synchrony between vulval and ovarian maturity. The species displays a soft mating system and most mature postmolt females lacks seminal contents in their reservoirs, in spite of evidence of successful mating (abrasion marks). This suggests that, due to selective exploitation of males, sperm supply may have become a limiting resource for the reproductive output of the population. Under the terminal molt hypothesis, females at the pubertal moult will be the only individuals in the population contributing to reproduction. Taking into account these findings, we suggest that the current regulations are reassessed, including the use of the terminal molt scenario for fishery management because it provides a precautionary framework in a situation where the life history of the targeted stock is data-limited.

Uncertainties of natural mortality estimates for eastern Bering Sea snow crab, Chionoecetes opilio

Instantaneous natural mortality ( M) estimates are very uncertain for eastern Bering Sea snow crab, Chionoecetes opilio. An M of 0.3 per year has commonly been used for the mature population, whereas a sole published study concluded that M is larger than 1.06 per year for morphometrically mature males. In this study, catch-survey models were constructed using trawl survey data from 1989 to 2000 to estimate M for the eastern Bering Sea snow crab stock under different assumptions of moulting probability of morphometrically mature males, handling mortality rate of bycatch and survey catchability. Male abundance was categorized by size (80–99, 100–119 and >119 mm carapace width), shell condition (newshell and oldshell) and morphometrically mature status. Mature female abundance was grouped by shell condition. M estimates for males vary greatly, ranging from 0 to 0.97 per year, depending on model assumptions. Moulting probability of morphometrically mature males and survey catchability for large males (>99 mm) are the two most sensitive factors. Allowing morphometrically mature males to moult resulted in a significantly better data fit than a zero moulting probability assumption, and assuming a low survey catchability for large males resulted in a high estimate of M for mature males. The F statistic test indicated that the most parsimonious model for males was the scenario of a constant M of 0.35 per year without the terminal moult assumption. Because of no retained catch, very low bycatch and no moulting after maturity, M estimates for mature females were not so sensitive to model assumptions. The M for mature females was estimated as 0.52 per year for crab south of 61.2°N latitude and 0.56 per year for all crab.

Mating behavior of female rock shrimp Rhynchocinetes typus (Decapoda: Caridea)?indication for convenience polyandry and cryptic female choice

While studies on a wide diversity of organisms have demonstrated the importance of female behavior during matings, in crustacean studies, a strong bias towards male mating behavior prevails. Reproductively mature rock shrimp (Rhynchocinetes typus) exist as several ontogenetic stages that differ in their morphological and physiological capacities. In natural populations, the majority of males are in early ontogenetic stages (termed typus), many are in intermediate stages (intermedius), and few are in the terminal molt stage (robustus). Dominant robustus males, which have already demonstrated their biological fitness by surviving to this stage, have previously been shown to have a higher potential than subordinate typus males to defend receptive females against other males, and fertilize the entire clutch of a female. While females should thus show a preference for robustus males, they nevertheless frequently receive sperm from typus males. These observations suggested that females might have mechanisms to discriminate against sperm from subordinate males. In laboratory experiments, we observed that females avoided being seized by typus males for longer time periods in the absence of robustus males than in their presence. Following seizure, females that were initially held by typus males, required more time to initiate spawning than those held by robustus males. Many typus males transferred spermatophores to females before these started to spawn while robustus males waited until females began to spawn before they transferred spermatophores. Females manipulated spermatophores received from typus males for long time periods (minutes), but not those they received from robustus males. By accepting sperm from subordinate typus males, females may avoid further harassment (convenience polyandry), but they subsequently may discriminate against these subordinate males by delaying spawning and removing their sperm. These observations suggest that female behavior influences the outcome of matings, favoring fertilization of eggs by sperm from dominant males. Convenience polyandry and cryptic female choice may be common in other crustaceans as well.

Abundance and population structure of the Atlantic horseshoe crab Limulus polyphemus in Pleasant Bay, Cape Cod

Populations of horseshoe crabs Limulus polyphemus are widely distributed from Maine to the Gulf of Mexico, are commercially harvested, and are thought to have decreased in abundance in recent decades. To provide information needed to manage exploited populations of horseshoe crabs, we conducted comprehensive field sampling in a major shallow estuary containing preferred habitat for horseshoe crabs. The data we obtained are the first to comprehensively define abundance, determine sex ratios of horseshoe crabs across an entire estuary, and estimate cohort-specific growth and mortality of juvenile and adult horseshoe crabs. We found that juveniles were more abundant and suffered greater mortality than adults. Adults were largely found on the sediment surface, but 20% were buried shallowly in sediments. The male:female sex ratio in juveniles was 1.4:1, but the adult sex ratio was 2.3:1. Juveniles grew faster than adults, and adult crabs may plausibly molt as fre- quently as once per year rather than have a terminal molt. Spawning appeared to span late March to mid-July, and juveniles hatched at semilunar intervals during Year 0 and grew to 16.6 ± 0.9 mm pro- somal width by the start of Year 1. The distinct semilunar cohorts of Year 0 coalesced into annual cohorts after Year 0. Females deposited large numbers of eggs, but only 0.001% survived to the end of Year 0, and approximately 78% of these juveniles reached adulthood.

REPRODUCTION OF THE SPECKLED SWIMMING CRAB ARENAEUS CRIBRARIUS (BRACHYURA: PORTUNIDAE) ON THE BRAZILIAN COAST NEAR 23°30′S

Abstract The reproductive biology of Arenaeus cribrarius from Ubatuba, Sao Paulo State, Brazil, was studied. Swimming crabs were sampled monthly for two years with otter trawls in two bays. A total of 941 males and 1,012 females were examined. Mating took place mainly in autumn involving postmolt females and intermolt males. At that time, gonad regression was verified in adult males, due to spermatophore transfer, and the molting of adult females. Ovigerous females or females with mature gonads were present year-round but more frequently captured during spring and summer. We found that 1% of all adult females were premolt, which indicated the occurrence of another mature instar and thus the absence of a well-defined terminal molt after puberty. Intermolt males were captured throughout the whole study period.

Growth and condition of post-moult male snow crab ( Chionoecetes opilio) in the laboratory

We monitored soft-shell and hard-shell legal-sized male snow crabs sampled periodically in the field or fed to satiation at 4.5 °C in the laboratory for changes in nutritional condition. In soft-shell crabs, feeding resulted in a significant decrease of water content in all tissues. This decrease was associated with increased lipid (digestive gland) and protein (muscle and haemolymph) contents. The weight of the muscle in the merus and the weight of the digestive gland also increased. Feeding had no impact on the nutritional condition of hard-shell crabs in the laboratory. In the wild, soft-shell crabs required a much longer period of time to recover to the hard-shell condition than was postulated from earlier studies; nutritional condition of soft-shell crabs did not improve markedly over summer and into autumn. The results of the present study are relevant to aquaculture and stock management. Landed legal-sized hard shell adolescent crabs could be held through terminal moult and grown to a marketable condition in a reasonably short period of time. Nutritional condition indices may also provide valuable information on several aspects of production and contribute to a precautionary management of the snow crab stocks.

Evidence that ecdysteroids and methyl farnesoate control allometric growth and differentiation in a crustacean

Allometric, or disproportionate, growth of body parts is a basic problem in morphogenesis. Male spider crabs, Libinia emarginata, have several forms or morphotypes. During the terminal molt, the propodus enlarges disproportionately, exceeding the carapace length by as much as 35%. Even though shorter clawed males are reproductive, the large-clawed males become primary reproductives. We stimulated penultimate stage males to molt by eyestalk ablation, which removes molt inhibiting hormone (MIH) and mandibular organ inhibiting hormone (MIOH), and measured ecdysones by radioimmunoassay and methyl farnesoate (MF) in hemolymph by high-performance liquid chromatography (HPLC) using an internal standard. Eyestalk ablation accelerated molting and increased ecdysteroids to peak at 150 ng/ml before the molt. In control animals the ecdysteroids peaked at 90 ng/ml 3 days before the molt, with MF remaining less than 0.5 ng/ml. These became large males with large allometric claws. In contrast, the ablated ones, with increased MF (1 to 1.5 ng/ml), increased carapace size, but retained shorter non-allometric claws, with length shorter than the carapace. The results are consistent with experiments that we have performed with MF administration (Abdu et al., Biol. Bull., Woods Hole, MA 195 (1998) 112; Laufer et al., Gen. Comp. Endocrinol. 111 (1998) 113; Laufer et al., in: IV Symp. Aquaculture in Central America: Focusing on Shrimp and Tilapia, (1997a), p. 161; Laufer et al., Invert. Reprod. Dev. 31 (1997b) 63) which led to the interpretation that ecdysteroids and low MF concentrations promote allometric growth, while ecdysones with relatively higher concentrations of MF inhibited allometric growth. These results indicate and support the conclusion that MF and ecdysteroids determine the control of morphogenesis in allometric growth of Crustacea.

Reproductive biology of spider crab females (Maja brachydactyla) off the coast of Asturias (north-west Spain)

The first results of the females reproductive cycle of Maja brachydactyla (Braquiura: Majidae) off the coast of Asturias (north-west Spain) are presented. Mean size of mature females was 133·4 mm (N=1022) in 1997 and 125·0 mm (N=942) in 1998. Only one cohort is exploited each fishing season. This cohort passed through the terminal moult the year before and recruited in to the fishery beginning in June. The breeding cycle off the coast of Asturias begins in December and ends in November the following year. Results from this study indicate that females produce 3–4 broods per year in these waters, which is the highest reported number for M. brachydactyla. The results are discussed in terms of their importance for management of the fishery.

Role of ecdysteroids and methyl farnesoate in morphogenesis and terminal moult in polymorphic males of the spider crab Libinia emarginata

Here we examine morphogenesis and terminal anecdysis in male morphotypes of the spider crab Libinia emarginata through eyestalk removal (ablation). Methyl farnesoate (MF), an unepoxidated form of juvenile hormone (JH III) and hydroxyecdysone, a moulting hormone, were measured in attempt to understand these processes and to determine the physiological characteristics of each morphotype, to be able to induce maturation by hormonal treatment and improve crustacean culture. Following arrival at the laboratory, ablated small-claw unabraded small-carapace males (SUM) moulted within 30 days to a juvenile and control SUM moulted within 75 days to a mature morphotype with large claws. Following eyestalk removal small-carapace abraded males (SAM), large-carapace unabraded large-claw (LUL) and large-carapace abraded large-claw (LAL) males never moulted even after 60 days, while the other ablated morphs moulted in 25–35 days. Significant increase of MF levels was observed in SUM, SAM and LUL de-stalked animals compared to intact control group, while no differences were observed in LAL individuals. In fact, LAL crabs presented the highest level of MF up to 2.23 ng/ml. Ten days prior to moulting MF increased 4-fold, and the ecdysteroids increased 15-fold in the haemolymph of ablated SUM and 25% in their testes. Ecdysteroid levels in the haemolymph of the SAM, LUL and LAL morphotypes remained low (around 5 ng/ml), and none of these animals moulted. The results strongly suggest that: (1) SUM are able to moult, and represent the juvenile stage, (2) SAM, LUL and LAL are terminally moulted and may represent the reproductive population, (3) circulating ecdysteroids induce moulting in juveniles, (4) high levels of ecdysteroids in the testes of SAM, LUL and LAL suggest a gonadal function, and (5) circulating MF controls morphogenesis of juveniles (SUM) and seems to stimulate gonads in adults.

Changes in muscle of postmoult snow crabs Chionoecetes opilio (O. Fabricius) fed different rations

Somatic growth, muscle cell condition and metabolism, and gonadal production have been studied in male snow crabs Chionoecetes opilio fed 0, 0.4 and 2 g·animal−1·day−1 and sampled 5, 25, and 60 days after the terminal moult. Twenty-five days after moulting, muscle growth rate was low in crabs fed a high ration and negative in the other groups, and no gonadal production took place. This suggests that the energy was utilised in priority to sustain a high maintenance metabolism. Between 25 and 60 days post-moult, maintenance costs were apparently lower and more energy was directed, in decreasing order of priority, towards gonadal production, which was independent of food ration, muscle growth and reserve build-up in the digestive gland, the two latter being directly related to food ration. Starvation caused the death of merus muscle cells, as indicated by the significant decrease in DNA content, but after 60 days the size of the remaining cells (protein:DNA ratio) had increased as much as that of crabs fed a high ration. It may be a better strategy to maintain fewer cells, by using material and energy obtained from the sacrificed ones, than to keep all cells in a deficient state. Crabs fed a high ration filled the new larger exoskeleton through hypertrophy and hyperplasia. After 25 days of undernutrition, the reduced number of muscle cells relatively to the merus volume was counterbalanced by an enhanced activity of phosphofructokinase (PFK), citrate synthase (CS) and cytochrome C oxidase (CCO) per g of muscle dry weight. An inverse relationship between food ration and enzyme activity per g dry weight further attenuated the effect of food ration on the enzyme total activity in the whole merus muscle. After 60 days of starvation, the still high enzyme activity per g dry weight could no longer compensate for the continuing loss of cells and, at that time, the enzyme total activity was directly related to food ration. Our results suggest that the feeding status of wild crabs may affect their locomotor ability through effects on muscle capabilities.

Sources of seasonal variability in mesozooplankton aspartate transcarbamylase activity in coastal waters off Plymouth, UK

Some investigators have proposed aspartate transcarbamylase (ATCase) activity as an overall index of mesozooplankton productivity. However, seasonal changes in mesozooplankton species composition have never been investigated as a possible source of variation in ATCase activity. In this study, we investigate mesozooplankton composition in terms of (i) developmental stages, (ii) species and developmental stages body mass and (iii) species composition, and their relationship to ATCase activity. In controlled laboratory conditions, ATCase activity variability was closely related to changes in somatic growth rate of the copepod Calanus helgolandicus, but was not related to changes in nucleic acid concentrations. It can be argued, however, that the activity of this enzyme is partially involved in copepod somatic productivity, and should be a good index of embryogenesis. In addition, changes in ATCase activity were not significantly influenced by variability in mesozooplankton biomass, when investigated both on inter- and intraspecific levels. Finally, when a complete seasonal cycle was investigated at a fixed station off Plymouth (English Channel), ATCase activity was not correlated with the abundance of any mesozooplankton species apart from copepodites and adult C.helgolandicus. Furthermore, ATCase activity measured both on mesozooplankton and female C.helgolandicus was significantly correlated (R2 = 0.72, n = 33, P < 0.001) throughout the year, apart from April. At that particular time of the year, ATCase activity was in phase with the peak of abundance of copepod eggs and nauplii. It is suggested that mesozooplankton peaks of ATCase activity reflect two periods in the life history of the copepod: embryogenesis and terminal moult. We propose further experiments to test this hypothesis and to promote the development of molecular biomarkers in order to characterize specific zooplankton metabolic processes.