Spatial overlap and interaction between sub-adult American lobsters, Homarus americanus, and the invasive European green crab Carcinus maenas

Invasive species are considered one of the major threats to biological diversity, and they can negatively impact species of particular ecological and/or economic importance. In this study, we investigate the potential threat that the European green crab, Carcinus maenas, represents to sub-adult lobsters, Homarus americanus, in Passamaquoddy Bay, Canada, northwest Atlantic. We conducted transect surveys using SCUBA diving to evaluate spatial overlap between these species inside, and immediately adjacent to, a lobster nursery area, and ran two laboratory experiments to investigate interactions between them in conditions of limited food and shelter availability. We found marked spatial overlap between these species in nature, particularly between adult green crabs and sub-adult lobsters in the shallower parts of the nursery area. It was not uncommon to see green crabs and sub-adult lobsters less than 1-2 m from one another, and we estimated mean nearest-neighbor values as low as 0.5-1 m on certain transects and months, with a grand mean of 5.17 ± 1.62 m (SE). Monte Carlo randomization of positional data revealed that green crabs and lobsters were randomly distributed relative to one another; individuals of one species did not seem to aggregate or segregate relative to individuals of the other species. In the lab, green crabs did not negatively affect survival (one exception), growth, activity, feeding, or shelter use of sub-adult lobsters. In fact, sub-adult lobsters regularly preyed upon green crabs in the first lab experiment, where heterospecific individuals were matched for body mass. Our results suggest that green crabs do not pose a significant threat to sub-adult lobsters in Passamaquoddy Bay, and may in fact represent a food subsidy for them.     

Agonistic interactions between the invasive green crab, Carcinus maenas (Linnaeus) and juvenile American lobster, Homarus americanus (Milne Edwards)

Invasive organisms have the potential for competition with native organisms. In the Southern Gulf of St. Lawrence, juvenile American lobsters have a potential spatial overlap with adult green crabs. Crustaceans use agonistic behaviour to settle disputes, with the larger organism often winning contests for limited resources such as food and shelter. Two experiments were carried out using adult green crabs (53-76 mm carapace width) and juvenile American lobsters (28-57 mm carapace length). The first experiment used a limited food resource. We found that green crabs were the first to the food in all trials, fed in significantly more trials than lobsters and spent a significantly greater proportion of time with the food. The lobsters were only able to displace the green crabs from the food in 2 of 65 attempts. The second experiment was designed to examine shelter competition; unexpectedly some predation by green crabs on lobsters occurred, which allowed us to test hypotheses about how relative size and shelter use affect predation. Green crabs captured and consumed juvenile lobsters in 6 of 11 trials. The lobsters that survived spent significantly more time in shelter. There was no clear relationship between shelter use and size of lobster. The lobsters that were larger in relation to the green crabs suffered a higher rate of predation, which we believe was due to more conspicuous activity and less use of shelter. It appears that green crabs have the potential to negatively impact native juvenile lobster.     

An unusual cuticular tumor-like growth on the abdomen of a lobster, Homarus americanus

Tumors are rare in crustaceans, and whereas a few have been reported from the lobster Homarus americanus none have been adequately described. A lobster with an unusual, large, blue-colored tumor-like growth projecting laterally outward from the first abdominal somite was caught off Stonington, Maine, USA. The growth was rugose and covered by a relatively normal appearing cuticle with dispersed focal melanization. The underlying stroma consisted of an internal area of rescaffolded fibrous connective tissue, restructured muscle fibers, few arterioles, and an epidermal area comprised of columnar, highly vacuolated epithelial cells. No infectious pathogens or unusual inclusions were observed with microscopy and no eukaryotic pathogens were detected via molecular sequencing. Given the nature of the histology and the appearance of the growth, we identify the mass as a benign papilliform hamartoma that likely originated as a result of abnormal wound repair possibly initiated around ecdysis. This represents the first tumor-like hamartoma reported from a lobster, and the second hamartoma reported from a crustacean.     

Agonistic interactions between invasive green crabs, Carcinus maenas (Linnaeus), and sub-adult American lobsters, Homarus americanus (Milne Edwards)

The invasive green crab, Carcinus maenas, has recently expanded its range into the Southern Gulf of St. Lawrence, where there is potential for substantial niche overlap with juvenile American lobsters, Homarus americanus. We used two experiments to elicit, record and analyze the agonistic interactions of adult green crabs (carapace width of 63-75 mm) and sub-adult (carapace length of 55-70 mm) lobsters. The first experiment gave each animal equal access to a limited food resource. The green crabs were first to the food in significantly more trials, spent a significantly greater proportion of time with the food, and were able to successfully defend the food from attacks by the heavier lobsters. In the second experiment, we allowed the lobsters to gain possession and initiate feeding on the food before releasing the green crabs. In these trials, the lobsters spent significantly more time with the food, and were able to defend the food from the green crabs. The results of both experiments are discussed in the context of game theory. The different behaviour of the crustaceans in the two experiments is consistent with the “bourgeois” strategy in a hawk and dove game simulation. With this strategy, an animal acts like a hawk if in possession of a resource, but acts like a dove if the other animal is in possession of the resource. The fact that the green crabs were able to physically compete with, and in many cases dominate the larger, heavier lobsters supports the potential for competitive impacts of green crabs on sub-adult lobsters.     

Modelling torque generation by the mero-carpopodite joint of the american lobster and the snow crab

The torque generated by a rotating joint comprises the useful force exerted by the joint on the external environment, and both the magnitude and distribution of torque through the step cycle during walking are important variables in understanding the mechanics of walking. The mechanics of the American lobster (Homarus americanus) and snow crab (Chionoecetes opilio) during walking were modelled to examine the relative roles of flexor versus extensor apodeme-muscle complexes, investigate which legs of these decapods likely contribute the greatest to locomotion, determine scaling effects of torque generation, and assess the relative roles of various model variables on torque production. Force generated along the length of the apodeme by the muscle was modelled based on apodeme surface area, muscle stress, and muscle fibre pinnation angle. Torque was then calculated from this estimated force and the corresponding moment arm. The flexor apodeme-muscle complex is calculated to generate consistently greater forces than the extensor, and generally this results in flexor torque being larger than extensor, though the snow crab does illustrate the opposite in two of its legs. This greater torque generation in flexion suggests that, in addition to the pushing of the trailing legs, the pulling action of the leading legs may play a significant role, at least during lateral walking. Leg 4 of both species appears to generate greater torques and thus provide the greatest forces for locomotion. Torque generation as a function of body size shows a second order response due to the increase in apodeme surface area. The pinnation angle of the muscle fibre is found to be insignificant in force generation, apodeme surface area (representing muscle cross sectional area) likely plays the most influential role in total force production, and moment arm controls the distribution of this force through the step cycle. Muscle stress remain a largely unknown quantity however, and may significantly affect both magnitude and distribution through step cycle of forces, and thus torque. Despite the uncertainty associated with the muscle stress parameter, the modelled results fit well with previously published force measurements.     

Exposure to the steroid hormone 20-hydroxyecdysone modulates agonistic interactions in male Homarus americanus

In this study we present evidence that 20-hydroxyecdysone (20E) affects agonistic behavior in male American lobsters and that male and female animals differ in their response to the hormone. Thirty-minute staged fights were conducted between large males exposed either to artificial seawater (ASW) or 20E and small, anosmic opponents. The nephropores of both combatants were blocked. Fights were videotaped and quantitatively analyzed for aggressive, defensive and avoidance behaviors using an ethogram in which behaviors are ranked according to aggressiveness. Unlike female lobsters, exposing male lobsters to 20E did not increase their aggressive behavior; however, there was a marginally significant trend toward an increase in defensive behaviors with a lower aggressive content than in their ASW-exposed counterparts. The opponents of 20E-exposed animals performed significantly more aggressive behaviors than their counterparts. In fights with 20E-exposed animals, the overall aggressive intensity of the fight was increased and the animals performed a greater number of avoidance behaviors. Unlike the effects of 20E on females, where exposure to 20E caused an increase in overall agonistic arousal, males only exhibited a change in frequency of their behaviors. These findings suggest that while 20E affects both males and females in agonistic encounters, the nature of the effect is different for the two sexes.     

Different circadian pacemakers control feeding and locomotor activity rhythms in European starlings

Summary In higher organisms, many physiological and behavioral functions exhibit daily variations, generated by endogenous circadian oscillators. It is not yet clear whether all the various rhythms that occur within an individual depend on one and the same pacemaker or whether different pacemakers are involved. To examine this question, the feeding and perch-hopping rhythms were measured in European starlings (Sturnus vulgaris) under light-dark cycles and continuous dim light. In dim light, the internal phase relationship between the feeding and perch-hopping rhythms changed systematically as a function of the circadian period, and the two rhythms could even dissociate and show different circadian periods in individuals with extremely long or extremely short circadian periods. Moreover, in some birds kept on lowamplitude light-dark cycles, the rhythm of feeding was synchronized 180° out of phase with the rhythm of locomotor activity. These results strongly suggest that in the European starling the feeding and locomotor activity rhythms are controlled by separate circadian pacemakers.     

Effects of dark-light step transitions on circadian locomotor activity rhythms of the hagfish,Eptatretus burgeri

Captive hagfish,Eptatretus burgeri, were subjected to step transitions from continuous dark (DD) to continuous light (LL) and their locomotor activity patterns recorded. Free-running activity rhythms occurred in both the DD and LL regimes. The timing of the transition influenced the circadian period (τ), the relationship between the period response (δτ, or τ{inLL}–τ{inDD}, change in the circadian period) and the former being represented by a cosine curve δτ became most positive and most negative when hagfish underwent a DD-LL transition shortly before the beginning of the duration of activity (α) and shortly after the end of such, respectively. The phase response (δ-phase, change in the relative timing of the activity phase) was characterized by a delay in the activity phase after the DD-LL transition, although its magnitude bore no relation to the timing of the transition.     

Antennae-whipping behavior in the American lobster, Homarus Americanus (Milne-Edwards)

Electrophysiological techniques were employed to demonstrate that an acrylic coating blocks the mechanosensory activity of the cuticular hair organs on the chelipeds of Homarus americanus (Milne-Edwards) without eliciting spurious activity in their innervation.Agonistic encounters between animals with acrylic on the dorsal surface of the claws (experimental), on the ventral surface of the claws (“plastic” control), and absent (“bare” control) were observed. Experimental animals responded to <3% of all antennae-whips, while “plastic” control animals responded to 73%, and “bare” control animals to 64%, of all antennae-whips. We conclude that antennae-whipping is a form of tactile communication, in which information probably is received through mechanosensory activity in the cuticular hair organs on the dorsal surface of the chelipeds.     

Complex circadian regulation of pineal melatonin and wheel-running in Syrian hamsters

Circadian regulation of pineal melatonin content was studied in Syrian hamsters (Mesocricetus auratus), especially melatonin peak width and the temporal correlation to wheel-running activity. Melatonin was measured by radioimmunoassay in glands removed at different circadian times with respect to activity onset (= CT 12). Pineal melatonin peak width (h; for mean 125 pg/gland) and activity duration () were both 4–5 h longer after 12 or 27 weeks than after 5 or 6 days in continuous darkness (DD). Increased peak width was associated with a delay in the morning decline (M) of melatonin to baseline, correlated with a similar delay in wheel-running offset. In contrast, the evening rise (E) in melatonin occurred at approximately the same circadian phase regardless of the length of DD. Fifteen min light pulses produced similar phase-shifts in melatonin and activity. In a phase advance shift, M advanced at once, while E advanced only after several days of adjustment. Independent timing of shifts in the E and M components of the melatonin rhythm suggest that these events are controlled separately by at least two circadian oscillators whose mutual phase relationship determines melatonin peak width. This two-oscillator control of melatonin peak width is integral to the circadian mechanism of hamster photoperiodic time measurement.Abbreviations CT circadian time - DD continuous dark - L: D light: dark cycle - PMEL pineal melatonin - PRC phase response curve - RIA radioimmunoassay; , duration (h) of the active phase of the circadian wheel-running rhythm; , free-running period     

Pharmacological effects of vinorelbine on body temperature and locomotor activity circadian rhythms in mice

The effects of vinorelbine (VRL) on the circadian rhythms in body temperature and locomotor activity were investigated in unrestrained B6D2F₁ mice implanted with radio-telemetry transmitters. A single intravenous VRL dose (24 or 12 mg/kg) was given at 7 h after light onset (HALO), a time of high VRL toxicity, and resulted in transient suppression of temperature and activity circadian rhythms in mice kept in light-dark (LD) 12h:12h. Such suppression was dose-dependent. It occurred within 1-5 d after VRL dosing. Recovery of both rhythms was partially complete within 5 d following the high dose and within 2 or 3 d after the low dose and was not influenced by suppression of photoperiodic synchronization by housing in continuous darkness. Moreover, VRL induced a dose-dependent relative decrease in amplitude and phase shift of the temperature circadian rhythm. The mesor and amplitude of the activity rhythm were markedly reduced following the VRL administration. The relevance of VRL dosing time was studied in mice housed in LD 12h:12h. Vinorelbine was injected weekly (20 mg/kg/injection) for 3 wk at 6 or 18 HALO. Vinorelbine treatment ablated the rest-activity and temperature rhythms 3-6 d after each dose, with fewer alterations after VRL dosing at 18 HALO compared to 6 HALO, especially for the body temperature rhythm. There was at least partial recovery 1 wk after dosing, suggesting the weekly schedule of drug treatment is acceptable for therapeutic purposes. Our findings demonstrate that VRL can transiently, yet profoundly, alter circadian clock function. Vinorelbine-induced circadian dysfunction may contribute to the toxicokinetics of this and possibly other anticancer drugs.     

RNA interference of timeless gene does not disrupt circadian locomotor rhythms in the cricket Gryllus bimaculatus

Molecular studies revealed that autoregulatory negative feedback loops consisting of so-called “clock genes” constitute the circadian clock in Drosophila. However, this hypothesis is not fully supported in other insects and is thus to be examined. In the cricket Gryllus bimaculatus, we have previously shown that period (per) plays an essential role in the rhythm generation. In the present study, we cloned cDNA of the clock gene timeless (tim) and investigated its role in the cricket circadian oscillatory mechanism using RNA interference. Molecular structure of the cricket tim has rather high similarity to those of other insect species. Real-time RT-PCR analysis revealed that tim mRNA showed rhythmic expression in both LD and DD similar to that of per, peaking during the (subjective) night. When injected with tim double-stranded RNA (dstim), tim mRNA levels were significantly reduced and its circadian expression rhythm was eliminated. After the dstim treatment, however, adult crickets showed a clear locomotor rhythm in DD, with a free-running period significantly shorter than that of control crickets injected with Discosoma sp. Red2 (DsRed2) dsRNA. These results suggest that in the cricket, tim plays some role in fine-tuning of the free-running period but may not be essential for oscillation of the circadian clock.     

RAP, an integrated program for monitoring bioluminescence and analyzing circadian rhythms in real time

To process the large number of circadian rhythmic bioluminescence data that we generated with specially developed, high-throughput monitoring apparatuses, we developed an integrated rhythm-analyzing program (RAP) with a user-friendly graphical interface. RAP does all of the following in real time: (i) displays the bioluminescence time course, (ii) records time-series data, (iii) analyzes the data, (iv) displays the analyzed results, (v) statistically evaluates the analyzed results, and (vi) provides printouts. Because RAP can import files, it can analyze not only bioluminescence data but also other data such as those obtained by DNA array experiments and by Northern and Western blot analyses. The program is a powerful tool for large-scale investigations of biological rhythmic phenomena in general.     

Exogenous corticosteroid and shifts of circadian rhythms in hamsters

We tested the hypothesis that glucocorticoid stimulation mediates the effect of exercise on circadian clock resetting in hamsters. We injected animals with 1 and 5 mg dexamethasone—a potent glucocorticoid agonist—at zeitgeber time (ZT) 4 and ZT6, circadian phases at which vigorous exercise induces maximal phase advances of about 3h. Neither dose of dexamethasone induced phase shifts that were significantly larger than those induced by injections of saline vehicle at either of the phases tested. Some animals, however, showed quite large and consistent phase shifts to repeated injections whether with saline or dexamethasone, such that there was a statistically significant correlation between individuals' responses to the two treatments. The data indicate no role for increased glucocorticoid activity in mediating the effects of exercise on circadian phase shifting, but suggest a modest role for nonspecific stimulation, independent of exercise, in inducing phase shifts at ZT4-ZT6. (Chronobiology International, 18(2), 203-213, 2001)     

Development of the circadian clock in the German cockroach, Blattella germanica

The cell distribution and immunoreactivity (ir) against period (PER), pigment dispersing factor (PDF) and corazonin (CRZ), were compared between adults and nymphs in the central nervous system of the German cockroach. Although PER-ir cells in the optic lobes (OL) were expressed in the nymphs from the first instar, the links between major clock cells became more elaborated after second/third instar. A circadian rhythm of locomotion was initiated at the fourth/fifth instar. The results suggest that the clock was running from hatching, but the control network needed more time to develop. In addition, the putative downstream regulators, PDF-ir and CRZ-ir, are co-localized in various regions of the brain, indicating potential output routes of the circadian clock. CRZ-ir cells with typical morphology of neurosecretory cells in the dorsolateral protocerebrum send out three neural fibers to reach the ipsilateral corpora cardiaca (CC), the antennal lobe and two hemispheres of the protocerebrum. Based on co-localization with some PER-ir/PDF-ir cells, the CRZ-ir cells have the potential to serve as a bridge between circadian neural signals and endocrine regulation. Based on PDF's role in the regulation of locomotion, our results support the finding that the locomotor circadian rhythm is possibly controlled by a hormonal route.     

Activation of carbonic anhydrase in branchial cavity tissues of lobsters (Homarus gammarus) by dilute seawater exposure

Activities of carbonic anhydrase (CA) and its distribution in the branchial cavity tissues were studied in European lobsters (Homarus gammarus) from ambient seawater (SW; salinity=38 ppt, 1126 mosmol/l) and acclimated to dilute seawater (DSW; salinity=20 ppt, 548 mosmol/l). Acetazolamide inhibited dose dependently the activity of CA in homogenates of epipodites, where the inhibition constant (IC₅₀=0.12 μM) did not differ significantly from that of membrane vesicles and cytosolic fraction. In DSW-acclimated lobsters, almost 70% of total CA in tissues of the branchial cavity was found in epipodites (E) and the rest was equally distributed between branchiostegites (B) and gills (G). Upon acclimation to dilute seawater, CA activity in membrane fractions of E and B was increased 6-fold and in homogenates, respectively 5- and 13-fold compared to SW-acclimated lobsters. Exposure to DSW enhanced cytosolic CA in E (8-fold) and B (7-fold) over SW-acclimated animals. Slight activation of CA in homogenates and in partially purified membranes of G was not confirmed as a statistically significant difference between SW and DSW groups. In DSW, cytosol specific activity of CA was increased compare to the SW cytosol. These results indicate the importance of E and B in CA induction when lobsters are acclimated to DSW. In subcellular fractions from DSW-acclimated lobsters, the main proportion of 75.8% (E), 61.0% (B) of total CA activity in each of these tissues remained in cytosol portion. Partially purified membranes contained 6.8% (E) and 16.2% (B) and the remainder of 15% (E) and 27% (B) was found in mitochondrial and nuclear fractions. In gills, 49.2% and 9.0 % of total gill CA activity was found respectively in cytosol and partially purified vesicles and the rest in mitochondrial and nuclear fractions.     

Presence of circadian rhythms in the locomotor activity of a cave-dwelling millipede Glyphiulus cavernicolus sulu (Cambalidae, Spirostreptida)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757-765, 2000)