Male Lobsters Research Articles

Effects of photoperiod and temperature on ovarian development and spawning of the Japanese spiny lobster Panulirus japonicus

In order to examine the effects of photoperiod and temperature on ovarian development and spawning in the Japanese spiny lobster Panulirus japonicus, spent female lobsters were cultured with male lobsters under six conditions of short (10 L) or long (14 L) photoperiod at 13, 19 or 25 °C during the months December–March. Under the long photoperiod, ovarian development progressed at all temperatures and at higher temperatures, development was accelerated. Spawning occurred in all the females kept at 25 °C and the ovaries in females at 19 °C also developed up to the point of approaching spawning at the end of the experiment. Ovarian development under the short photoperiod depended on temperature. It progressed slowly at 13 °C, whereas it was prevented or considerably delayed at 19 and 25 °C. These results suggest that both photoperiod and temperature are important factors controlling ovarian development and spawning for P. japonicus. When spent females were cultured under conditions of 10, 11.25, 12.5 and 14 L at 25 °C during the months December–March, ovarian development was suppressed at photoperiods, shorter than 14 L, whereas it progressed smoothly at 14 L and most females spawned. Hence, the critical photoperiod for ovarian development and spawning at 25 °C appears to be between 12.5 and 14 L.

Thermal acclimation and stress in the American lobster, Homarus americanus: equivalent temperature shifts elicit unique gene expression patterns for molecular chaperones and polyubiquitin

Using homologous molecular probes, we examined the influence of equivalent temperature shifts on the in vivo expression of genes coding for a constitutive heat shock protein (Hsc70), heat shock proteins (Hsps) (Hsp70 and Hsp90), and polyubiquitin, after acclimation in the American lobster, Homarus americanus. We acclimated sibling, intermolt, juvenile male lobsters to thermal regimes experienced during overwintering conditions (0.4 +/- 0.3 degrees C), and to ambient Pacific Ocean temperatures (13.6 +/- 1.2 degrees C), for 4-5 weeks. Both groups were subjected to an acute thermal stress of 13.0 degrees C, a temperature shift previously found to elicit a robust heat shock response in ambient-acclimated lobsters. Animals were examined after several durations of acute heat shock (0.25-2 hours) and after several recovery periods (2-48 hours) at the previous acclimation temperature, following a 2-hour heat shock. Significant inductions in Hsp70, Hsp90, and polyubiquitin messenger RNA (mRNA) levels were found for the ambient-acclimated group. Alternatively, for the cold-acclimated group, an acute thermal stress over an equivalent interval resulted in no induction in mRNA levels for any of the genes examined. For the ambient-acclimated group, measurements of polyubiquitin mRNA levels showed that hepatopancreas, a digestive tissue, incurred greater irreversible protein damage relative to the abdominal muscle, a tissue possessing superior stability over the thermal intervals tested.

ARE MORPHOMETRICAL APPROACHES APPROPRIATE TO ESTABLISH SIZE AT MATURITY FOR MALE AMERICAN LOBSTER, HOMARUS AMERICANUS?

Study on the size at maturity of male American lobster (Homarus americanus) has traditionally been done based on a linear relationship between chelae size vs. body size assuming that a sharp change in slope occurs at onset of maturity. We analyzed this sexual dimorphism by standard loglinear transformations and bivariate allometric plots as well as by multivariate Principal Components Analysis (PCA) in order to verify the validity of this approach for determining size at maturity. These analyses showed that onset of maturity cannot be detected efficiently by claw morphometry because this secondary sexual character gradually changes from early juvenile stages, contrary to what has been believed. Observation of the presence of spermatozoa in the vasa deferentia (gonadal maturity) showed that 50% gonadal maturity occurred at 49.8 mm of carapace length for male lobster from the southern Gulf of St. Lawrence. However, gonadal maturity does not necessarily correspond to the ability to mate (behavioral maturity) in many crustacean species. Therefore, further studies are needed to assess the behavioral maturity to determine the size at maturity for male lobsters.

GROWTH INCREMENT AND MOLT FREQUENCY OF THE AMERICAN LOBSTER (HOMARUS AMERICANUS) IN THE SOUTHWESTERN GULF OF ST. LAWRENCE

The growth increment and molt frequency of the American lobster (Homarus americanus) ranging in size from 46 to 154 mm of carapace length (CL) from the southwestern Gulf of St. Lawrence (sGSL) were investigated by tagging and trap studies. The main molting period for lobster in sGSL was from early July to early September. Evidence for two molting seasons was observed only for male lobsters in Malpeque Bay, Prince Edward Island, and Baie des Chaleurs (Northeastern New Brunswick), but there was little evidence of double molting (< 0.2%). Evidence of animals skipping their annual molt was observed throughout sGSL. The percentage of growth increment for lobsters of the same sex tagged in premolt was significantly less than lobsters tagged in postmolt. The lower average percentage of growth increment observed for lobsters tagged in premolt is believed to be related to tagging trauma which is likely greater for lobsters actively developing a new carapace prior to molting. Male lobsters had significantly larger molt increments than females. Comparison between Malpeque Bay and Baie des Chaleurs yielded significant differences in the growth for male and female lobsters but not for berried females. The lowest average percentage of growth increment (12%) was observed for berried females. Furthermore, no relationship was observed between the growth increment and CL.

Neuroactive steroids modulate crustacean locomotor activity

We examined the effects of neuroactive steroids known to modulate gamma-aminobutyric acid A (GABA) A receptor activity, on locomotor activity in a submerged circular open-field apparatus. Juvenile male lobsters, Homarus americanus, were treated with a single administration of an agonist, 3α-hydroxy-5α-pregnan-20-one (allopregnanolone, 3α,5α-TH PROG), an antagonist, pregnenolone sulfate (PREGS), or vehicle alone. 3α,5α-TH PROG treatment (125 and 250 μg) significantly reduced while PREGS significantly elevated locomotor activity in a dose-dependent manner similar to diazepam. PREGS increased locomotor activity at 30 and 60 μg, while diminishing such activity and altering locomotor patterns at 120 μg. These results suggest that neuroactive steroids may affect crustacean GABA receptors in a fashion similar to the GABA A type found in the vertebrates, and that they may be involved in the regulation of locomotor behavior.

Growth Increment and Molt Frequency of the American Lobster (Homarus Americanus) in the Southwestern Gulf of St. Lawrence

The growth increment and molt frequency of the American lobster (Homarus americanus) ranging in size from 46 to 154 mm of carapace length |$({\rm C}_{{\rm L}})$| from the southwestern Gulf of St. Lawrence (sGSL) were investigated by tagging and trap studies. The main molting period for lobster in sGSL was from early July to early September. Evidence for two molting seasons was observed only for male lobsters in Malpeque Bay, Prince Edward Island, and Baie des Chaleurs (Northeastern New Brunswick), but there was little evidence of double molting |$(\lt 0.2\%)$|⁠. Evidence of animals skipping their annual molt was observed throughout sGSL. The percentage of growth increment for lobsters of the same sex tagged in premolt was significantly less than lobsters tagged in postmolt. The lower average percentage of growth increment observed for lobsters tagged in premolt is believed to be related to tagging trauma which is likely greater for lobsters actively developing a new carapace prior to molting. Male lobsters had significantly larger molt increments than females. Comparison between Malpeque Bay and Baie des Chaleurs yielded significant differences in the growth for male and female lobsters but not for berried females. The lowest average percentage of growth increment (12%) was observed for berried females. Furthermore, no relationship was observed between the growth increment and |${\rm C}_{{\rm L}}$|⁠.

Variability in the edible fraction content of 60Co, 99Tc, 110mAg, 137Cs and 241Am between individual crabs and lobsters from Sellafield (north eastern Irish Sea)

We investigated the variability in anthropogenic radionuclide content of the edible fractions of individual edible crabs ( Cancer pagurus L.) and European lobsters ( Homarus gammarus L.) caught commercially in the Sellafield offshore area. Sixteen female and 18 male crabs and 20 female and 17 male lobsters were selected from commercial catches made between 25 May and 5 June 1997. Each gender group was selected to be within the known weight range for commercially caught crustacea from the area. Four artificial radionuclides ( 60Co, 110mAg, 137Cs or 241Am) were detected by γ-spectrometry. The edible fraction content of these radionuclides between males and females for either species were not statistically significantly different. 99Tc was analysed by chemical separation and β-counting. 99Tc concentrations in female crabs tended to be higher (172±205 (16) Bq kg −1(wet); mean±standard deviation ( n samples)) than those in males (85±58 (18) Bq kg −1 (wet)), although this was not a statistically significant difference. For both male and female crabs, 99Tc concentrations tended to decrease with increasing whole live weights. For 99Tc in lobsters the picture is less clear. Female lobsters contained more activity (14800±7400 (20) Bq kg −1 (wet)) than males (7100±3900 (17) Bq kg −1 (wet)). The results were used to discuss the implications for sampling and monitoring.

The timing of chemical signaling with urine in dominance fights of male lobsters ( Homarus americanus )

Chemicals carried in the urine are a rich source of information about the identity, sex, aggressive motivation, and other attributes of an animal. In agonistic interactions, animals should be careful about disclosing such information, since it can be used by receivers to the disadvantage of the sender. By adjusting the timing of urine release, the signaler may still influence the behavior of the receiver to its own benefit. Here we investigate the urine signaling of American lobsters (Homarus americanus), necessary for the maintenance of dominance, using a catheter technique with high temporal resolution. We hypothesize that urine release in lobster fights is not continuous but restricted to moments that may elicit a reaction in the receiver beneficial to the sender. We found that eventual winners signaled more readily in the initial phase of the fight. Eventual losers did not show such initial urination. This suggests that a confident lobster may use urine signals to influence the behavior of its opponent into giving up the fight at an early stage. For both winners and losers, urine release is linked to offensive behavior and increases as the intensity of agonistic behavior increases. The coupling of urine release to offensive behaviors appears to improve both the reliability and efficacy of the chemical signal. Releasing urine under the increasing risk of inflicting injury during the fight provides a handicap that may ensure reliability of the threat signal. Furthermore, the immediate coupling of urine components to offensive behavior may help to consolidate the receiver"s memory of the signaler"s individual scent and thus facilitate future recognition of the dominant animal.

Oral bioavailability and pharmacokinetics of elimination of 9-hydroxybenzo[a]pyrene and its glucoside and sulfate conjugates after administration to male and female American lobsters, Homarus americanus.

The pharmacokinetics of [(3)H]-9-hydroxybenzo[a]pyrene (9-OH-BaP), a highly lipophilic primary metabolite of benzo(a)pyrene, were examined after intrapericardial (iv) or oral doses of 50 or 200 microg/kg to intermolt American lobsters, Homarus americanus. Combining data for all lobsters, the average terminal elimination half-life of parent 9-OH-BaP was 97.3 h after iv and 56.5 h after oral administration, considerably less than found previously for benzo(a)pyrene (720 h). The oral bioavailability of parent 9-OH-BaP, calculated from the area under the hemolymph concentration curve, was 15.9%. The low bioavailability and variable elimination rates were attributed to extensive first-pass conjugation and sequestration in the hepatopancreas. BaP-9-sulfate was the major metabolite. Hemolymph concentrations of BaP-9-sulfate increased up to one day after the dose, and then decreased, with a terminal elimination half-life of 45 h. BaP 9-beta-D-glucoside was a minor metabolite in most hemolymph and tissue samples; an exception was hemolymph from the iv high-dose group. Concentrations of 9-OH-BaP and metabolites in the edible muscle tissue were similar to those in hemolymph, and 9-OH-BaP residues at 10 to 16 days after the dose were 3 to 12 ng/g muscle. Sulfotransferase and UDP-glucosyltransferase (UGT) activities with 9-OH-BaP were found in the antennal gland, intestinal mucosa, and hepatopancreas (UGT only). Sulfatase activity with BaP-9-sulfate, found in both the hepatopancreas and the antennal gland, was thought to contribute to metabolite cycling. These studies showed that 9-OH-BaP was readily conjugated to sulfate and glucose in the lobster, and that despite their high lipophilicity, 9-OH-BaP and conjugates were excreted from the lobster hemolymph and tissues much more rapidly than benzo[a]pyrene.

A comparison of claw morphology and dominance between wild and cultivated male European lobster.

Claw size and dominance in cultivated versus wild European lobsters Homarus gammarus were compared. Normally, lobsters develop a short, high and wide crusher and a slender scissor claw. In culture, both claws often develop into scissor claws. With growth, cultivated males developed one significantly elongated scissor claw (major claw), and one normal scissor claw, compared to wild males (minor claw). The differences increased with size. The wild males had higher claw index than cultured ones, due to the crusher claw. Wild lobsters with higher claw index were dominant. Cultivated males with claw indices at least 200 mm2 higher than the opponent, won. Only scissor claws were broken in the encounters. Even if cultivated lobsters in time develop claws equal to wild lobsters, they might still be less robust. In the light of these findings, we suggest that lobsters cultivated for restocking purposes should be given access to an appropriate substrate allowing them to develop one claw into a crusher during the early benthic stage.

On the survivorship and historical growth of the South African Cape rock lobster

Natural survivorship parameters for male and female Cape rock lobsters Jasus lalandii are estimated using size-structure information from pristine sections of the population, such as animals in sanctuaries. It is assumed that these pristine subpopulations are at steady states, i.e. that annual juvenile settlement is constant, and that migration into and from these populations is negligible. The natural survivorship parameters are calculated in terms of parameters for somatic growth rate, which are obtained by fitting the Ford-Walford growth model to male and female tag data. The results indicate that female natural survivorship is consistently higher than that of males, and that the somatic growth rate of J. lalandii was considerably higher at the beginning of the century than during the past 25 years.

QUANTITATIVE ANALYSIS OF THE SEASONALITY OF MALE REPRODUCTION IN THE SPINY LOBSTER PANULIRUS JAPONICUS (DECAPODA: PALINURIDAE)

ABSTRACT The gonadosomatic index (GSI), ratio of area of the lumen to that of the seminiferous tubules, and sperm density were analyzed against body size and season in male spiny lobsters, Panulirus japonicus, sampled off Oshima Island, Tokyo, Japan. For functionally mature individuals (≥54 mm carapace length), regressions of GSI and area of the lumen against body size were significant only before the spawning season. GSI showed no clear seasonal changes. Germinal cells at all stages of spermatogenesis were found in the testis, and sperm were present in the vas deferens throughout the year. However, seasonal changes in the 3 reproductive indices indicate that P. japonicus has a distinct seasonal pattern for spermatogenesis and storage of sperm. The ratio of the area of the lumen to that of the seminiferous tubules was highest before the spawning season. Sperm density during and 1 month after the spawning season (from June to September), however, was significantly lower than in other months.

The Accumulation, retention and distribution of 95mTc in crab (Cancer pagurus L.) and lobster (Homarus gammarus L.). a comparative study

The accumulation, retention and distribution of 95mTc has been compared in lobsters and edible crabs kept under identical experimental conditions. The steady-state concentration factor ( C ss ) for the uptake of 95mTc from seawater was significantly greater for female crabs ( C ss =17·9) than for males ( C ss =14·4), whereas in lobsters there was no such sex difference and the C ss of 1161 was much greater than in crabs. The uptake of technetium from food (as indicated by whole body counts) was only moderately greater in lobsters than crabs. Retention of 95mTc was similar for crabs and lobsters of both sexes but the clearance rate was greater after the nuclide had been taken up from seawater ( t b1/2 =51 days) than from food ( t b1/2 =108 days). In all crabs and most male lobsters 95mTc was predominantly in the hepatopancreas while in a few male and all female lobsters it was mainly in muscle. Lobster ovaries consistently contained more activity than testes but this difference was not seen in crabs. In hepatopancreas cells of both species 95mTc occurred mainly in the cytosol and some initial steps were taken to determine the relationship between technetium and cytosol proteins. The results for crab and lobster are compared with those from previous studies on these and other crustacean species. The possible basis for the much higher concentrations of technetium in lobsters than crabs is discussed and further research suggested.

Comparative Analysis of Escape Behavior in Male, and Gravid and Non-Gravid, Female Lobsters.

Few studies exist in which the parameters of a single behavior have been quantitatively compared for male and female lobsters. Here, we have examined the effects of sex and gravidity on the parameters of the escape behavior of the American lobster, Homarus americanus, elicited by a visual threat. Both non-gravid females and male lobsters readily tailflipped in response to the stimulus, but gravid females failed, with one exception, to initiate a swim, even when stimulus strength was increased. Although the total distance swum by males and non-gravid females was not statistically different, males covered more ground in the initial power swim and during the subsequent swims than did non-gravid females. Males swam for a longer time, performing more tailflips, than females. Relative to their length and weight, males swam a greater distance at each stroke during the initial power swim and the subsequent swims, although, females might have compensated by swimming at a higher frequency. There were no significant differences in swimming velocity or acceleration, nor in the calculated force or work performed by the two sex classes (male and non-gravid females). Therefore, apart from egg-bearing, which severely inhibits the escape response, it remains to be seen whether the subtle physiological and anatomical sexual dimorphism that produces longer and more swim strokes in males but higher frequency tailflips in females results in the same chances of survival for the sexes.

A Comparative Study of the Uptake, Clearance and Metabolism of Technetium in Lobster (Homarus Gammarus) and Edible Crab (Cancer Paguras)

Lobsters and edible crabs have been exposed to 95 Tc m in their sea water or in their food, and the uptake, retention and distribution of the isotope in their bodies examined. The steady-state concentration factor C 85 for uptake of 95 Tc m from sea water was significantly greater for female crabs (C 95 =17.9) than for males (C 95 =14.4). There was no such sex difference in lobsters and they took up 95 Tc m to much higher levels with a C 95 of 1160. Retention of the isotope was similar for crabs and lobsters and for animals of both sexes. However the route of uptake was important with more rapid clearance after uptake from sea water (t hi = 51 days) than after uptake from food (t hi = 108 days). Technetium was found predominantly in the hepatopancreas of all crabs and most male lobsters. In a few male lobsters and all females it was mainly in muscle. Lobster ovaries consistently contained more activity than testes but this difference was not seen in crabs. At the subcellular level 95 Tc m in hepatopancreas cells of both lobster and crab occurred mainly in the cytosol. Results of initial studies into the relationships between technetium and cytosol proteins are given and the possible basis for the much greater accumulation of the element by lobsters than crabs discussed.

Olfactory Recognition of Urine Signals in Dominance Fights Between Male Lobster, Homarus Americanus

Abstract The maintenance of dominance hierarchies in the American lobster (Homarus americanus) is based on recognition of the dominant animal by the loser of a recent fight. It is hypothesized that chemical signals are the basis of this recognition. Adult male lobsters were paired for initial boxing matches between unfamiliar animals. The same pairs were re-matched for 3 more consecutive fights. In the first experiment, treatment animals had their primary olfactory receptor cells of the lateral and medial antennules lesioned before fights 2-4 and control animals received sham lesions. The durations of fights 2-4 for control pairs were significantly shorter than the durations of fights between lesioned animals. In the second experiment, male pairs were again allowed to establish a dominance relationship in a first fight. During second fights, urine release by both animals was prevented by the use of catheters in treatment animals while control pairs wore sham catheters. Again, durations of the second fights of control animals were significantly shorter than those of treatment animals. Together, these experiments indicate that urine-carried chemical signals, perceived by the antennules, reduce the duration and aggression of male dominance fights on subsequent days because the loser of the first fight backs off almost immediately when he smells the urine of the known dominant.

Shelter‐related aggression between adult male conspecific intruders and resident maternal American lobsters (Homarus Americanus) with eggs at different stages of embryogenesis

It has recently been shown that maternal (ovigerous/hatching) American lobsters (Homarus americanus) reliably out‐compete non‐maternal females for shelters. It is also known that nonmaternal females are subordinate to male conspecifics. To complement those studies, this maternal status effect on aggression was evaluated using intruding conspecific males. Resident maternal females were used whose eggs were at mid‐embryogenesis, late‐embryogenesis/hatch‐ing, or were 3–4 weeks post‐hatching (non‐maternal). The males reliably evicted resident females at all three stages. This male shelter competition advantage over maternal females is most likely produced by a combination of the necessity of the possession of a shelter by males for mating purposes, and the low shelter fidelity of ovigerous females due to their continual migratory behavior during the 9–12 month period of embryogenesis.

Predicting the winning or losing of symmetrical contests in the American lobster Homarus americanus (Milne-Edwards)

The ability to predict the outcome of symmetrical contests between male lobsters ( Homarus americanus) on the basis of 21 variables was investigated using a stepwise discriminant analysis. Measured variables included wet weight, carapace length, claw length, width and thickness, claw volume, claw contraction force, handedness, antenna length, color, plasma protein level, plasma calcium level, exoskeleton calcium concentration and motor activity. Plasma protein level, exoskeleton calcium concentration and claw dimensions were found to be important in the above ascending order for discrimination with an average squared canonical correlation of 0.55–0.65. The discussion focuses on the variables differentiating winners from losers and whether these variables could also aid competing lobsters when assessing the relative fighting ability of their rivals.

Age structure of Panulirus ornatus in two habitats in Torres Strait, Australia

The lobster population in Torres Strait, Australia, is made up of juvenile and sub-adult lobsters up to two years old (1+ and 2+), with some 3-year-old (3+) male lobsters. These lobsters live either on shallow reefs or in the deeper areas between reefs. Intensive surveys of lobsters in these two habitats showed that 1+ lobsters live only in the deep habitat, 2+ lobsters live in the deep habitat and on shallow reefs, and 3+ male lobsters live mainly on shallow reefs. In the deep habitat, lobsters were found mainly in areas that had rock and rubble substratum. There may be little movement of lobsters onto or off the shallow reefs during the winter months and 1+ lobsters probably recruit onto the shallow reefs so

Pharmacokinetics of 2-naphthol following intrapericardial administration, and formation of 2-naphthyl- beta --glucoside and 2-naphthyl sulphate D in the American lobster, Homarus americanus

1. Following a 0 25-mg kg intrapericardial dose of the phenolic compound, 2- naphthol, to the American lobster, Homarus americanus, a two-compartment model best described the disposition of parent \\ [C]-2-naphthol in the haemolymph. Male and female lobsters had similar alpha -phase half lives of 26 19 min (mean SD, n 4) and 29 15 min respectively. The beta -phase half lives were significantly longer in males,63 9 30 9 h, thanin females, 30 6 6 8 h (p 0 05). The total body clearance for females was 26 4 6 5 ml h kg and was higher than that of males, 11 1 5 9 ml h kg (p 0 05). 2. 2-Naphthol was converted to 2-naphthyl- beta -D-glucoside (major metabolite) and 2- naphthyl sulphate (minor metabolite) such that at 24 h 39-60 6% of the radioactivity in haemolymph was 2-naphthyl- beta -D-glucoside, 38 6-58 9% 2-naphthol and 0 5-4% 2- naphthyl sulphate. 3. The2-naphthol-derivedradioactivity was 99%boundtohaemolymphproteinsat 1 min and 90% bound at 1 day after the dose, indicating that both 2-naphthol and 2- naphthyl- beta -D-glucoside were highly protein bound. 4. 2-Naphthyl- beta -D-glucoside was slowly eliminated from haemolymph in both males and females, with elimination half lives of 34-78 h. 2-Naphthyl- beta -D-glucoside was the major metabolite in urine samples collected at 5 days after the dose. Hepatopancreas and antennal gland contained glucosidase activities, and the long half life of 2-naphthyl- beta -Dglucoside could be explained by conjugation-deconjugation cycling. 5. 2-Naphthyl sulphate was eliminated from haemolymph with a half-life 10 h and was excreted in urine.