Defensive responses of gastropods to the predatory flatworms Freemania litoricola (Heath and McGregor) and notoplana acticola (Boone)

Three species of gastropods were tested in the laboraory and in the field for responses to contact with the polyclad flatworms Freemania litoricola (Heath and McGregor) and Notoplana acticola (Boone). The three limpets differed considerably in their responses to Freemania litoricola All specimens of Notoacmea scutum (Rathke) responded in some way to this flatworm, mostly by running. Fewer than half of the Collisella digitalis (Rathke) responded to Freemania litoricola, and these responded by mushrooming - elevating the shell several millimeters off the substratum. Collisella scabra (Gould) did not respond any differently to contact with Freemania litoricola than to contact with a control probe. Differences in the responses of these limpets to Freemania litoricola are discussed in relation to the characteristic intertidal distributions of this flatworm and the limpets. In contrast to Freemania litoricola, the polyclad Notoplana acticola typically did not elicit defensive responses. This difference is related to the diets of the two flatworms. Freemania litoricola was found to be a predator on limpets, whereas no evidence was found that Notoplana acticola eats limpets.     

Habituation,reinstatement and recovery of predatory responses in two species of teleosts, Carassius auratus and Macropodus opercularis

The tendency for predatory responses to habituate and to be reinstated through sensitization and the passing of time was studied in two species of fish (the goldfish and the paradise fish). Prey (live brine shrimp), confined in a clear plastic tube were presented for short daily exposures to individual fish. Bites directed at the stimulus tube containing the prey were the primary response measure. In both species biting decreased significantly over the 6 days of the experiment. Reinstatement of the habituated response occurred by two means: (1) reinforcement (i.e. allowing the fish to chase and consume the prey), and (2) passing of time (10 days) with no intervening stimulation (recovery). Reinstatement could not be produced by presenting a novel stimulus, nutritive stimuli, nor by a shorter recovery interval.     

Avoidance and escape responses of the gastropod mollusc Olivella biplicata (Sowerby) to predatory asteroids

The sand-dwelling gastropod Olivella biplicata (Sowerby) gives two chemically-mediated defensive responses to predatory asteroids — an avoidance and an escape response. An avoidance response is triggered by water-borne chemicals diffusing from distant starfish. When snails on the surface of the sand sense a distant predatory starfish, they avoid the predator by burying themselves in the sand. Strong avoidance responses are given to the predatory asteroids Pisaster brevispinus (Stimpson), P. ochraceus (Brandt), and Pycnopodia helianthoides (Brandt). Little or no response is given to the omnivorous asteroid Patiria miniata (Brandt) or to the predatory gastropod Polinices lewisii (Gould). An escape response is given when a snail on the surface is contacted by the starfish Pisaster brevispinus. Upon contact, the snail immediately retracts the propodium, sometimes throwing the metapodium forward at the same time; the snail then turns sharply away from the point of contact, and buries itself. Both avoidance and escape responses can be observed in the field and laboratory.     

Social hierarchy,shelter use,and avoidance of predatory toadfish (Opsanus tau) by the striped blenny (Chasmodes bosquianus)

This paper describes a three-part examination of the predatory relationship between oyster toadfish (Opsanus tau) and striped blennies (Chasmodes bosquianus). In the first laboratory study, blennies avoided the toadfish when placed in a choice situation. During the second laboratory study, dominant blennies escaped attack significantly more than did subordinates by using a protective shelter. A field study demonstrated that toadfish will attack active but tethered blennies under natural conditions. As predators, toadfish appear to use a mixed strategy. During the day, when they are relatively inactive, they may feed as ambush predators. However, we suggest that at night they move about actively, stalking benthic invertebrates and small fishes. They also feed as scavengers, consuming a variety of foods.     

The relationship of hunger to predatory behaviour in hawks (Falco sparverius and Buteo platypterus)

The relationship of hunger (as measured by food consumption) to predatory behaviour in two species of falconiform birds was investigated in the laboratory. The tendency to kill prey was correlated with hunger, and only hungry birds killed prey. I suggest that there is no predatory instinct or drive which operates independently of hunger and offer other rationales for the occasional excessive killing by some vertebrate predators. Falco sparverius exhibited a circadian rhythm of hunger and killing by some vertebrate predators. Falco sparverius exhibited a circadian rhythm of hunger and killing tendency, with a peak in the late afternoon. Buteo platypterus possibly showed a slight peak in the morning.     

Responses of the limpet, Cellana grata (Gould 1859), to hypo-osmotic stress during simulated tropical, monsoon rains

Although heat stress is often cited as the dominant physical stress on tropical shores, intertidal organisms in regions with monsoonal climates are also regularly exposed to prolonged periods of heavy rainfall. Such events are predicted to have adverse physiological effects on individuals and may result in mortality. In a series of laboratory experiments, the impact of simulated monsoonal rains was investigated on the patellid limpet, Cellana grata. Sub-lethal responses in terms of body water content, body fluid osmolality and heart rate were measured in two different size cohorts maintained on horizontal and vertical substrata. Limpets were unable to achieve any effective behavioural isolation, and exposure to either simulated rainfall or diluted seawater resulted in both large and small C. grata gaining water with subsequent dilution of mantle water and haemolymph osmolalities. With increased duration of rainfall, dilution of body fluids increased with little difference between individuals on horizontal and vertical surfaces. Body fluids generally showed proportional dilution during prolonged rain, but in some individuals there was evidence for regulation of the haemolymph relative to the mantle fluid. Overall, smaller limpets were more susceptible to prolonged rainfall than large animals in terms of swelling of soft tissues and detachment and also had higher heart rates than large limpets. Both cohorts reduced heart rates with prolonged rainfall, suggesting a degree of metabolic depression, especially on horizontal surfaces. In small limpets, no difference in heart rate was found with substratum orientation, whereas large limpets had elevated heart rates on vertical as compared to horizontal substrata, when exposed to either simulated rainfall or washed with dilute seawater. This may reflect the increased energetic costs required to maintain a relatively larger body on a vertical surface under stressful conditions. Monsoonal rainfall during emersion, and subsequent dilution of seawater, therefore, have sub-lethal physiological and possible lethal effects on intertidal limpets. This influence has been largely overlooked, but coupled with the possible synergistic effects of thermal stress, monsoon rains are likely to play an important role in community dynamics on tropical shores.     

Degradation of arsenobetaine by microorganisms associated with marine macro algae,Monostroma nitidium and Hizikia fusiforme

• 1.1. Arsenobetaine-containing growth media (ZoBell 2216E; solution of inorganic salts) were mixed with each of two marine macro algae, a green alga Monostroma nitidum and a brown alga Hizikia fusiforme, as a source of microorganisms.
• 2.2. The conversion of arsenobetaine to trimethylarsine oxide and/or dimethylarsinic acid by the microorganisms associated with the marine macro algae was confirmed in both the media.
• 3.3. A striking contrast, however, in the conversion pattern was observed between the two algae: arsenobetaine was converted to trimethylarsine oxide and trimethylarsine oxide to dimethylarsine acid successively with M. nitidum, while the reverse was observed with H. fusiforme.

     

Mycobiota associated with the ambrosia beetle Scolytodes unipunctatus (Coleoptera: Curculionidae, Scolytinae)

Ambrosia beetles (Coleoptera: Scolytinae) are associated with strictly entomochoric and mutualistic fungi. We studied the mycobiota associated with Scolytodes unipunctatus, ambrosia beetles that infest Cecropia trees in Central America. Isolates were characterized using morphology and rDNA sequences (ITS region, LSU, and SSU rDNA). Four species are described here: Raffaelea scolytodis sp. nov. (Ophiostomatales), Gondwanamyces scolytodis sp. nov., Custingophora cecropiae sp. nov., and Graphium sp. (Microascales). The genus Custingophora is emended to include Knoxdaviesia anamorphs of Gondwanamyces based on uniformity of DNA sequences and phenotype.     

The effects of arsenate and arsenite on the growth and morphology of the marine unicellular algae Tetraselmis chui (Chlorophyta) and Hymenomonas carterae (Chrysophyta)

The marine phytoplanktonic algae, Tetraselmis chui Stein and Hymenomonas carterae (Braarud and Fagerland) Braarud, were grown in media containing various concentrations of arsenate or arsenite. The effects of arsenic on the algae varied with the oxidation state of the element, its concentration, and the degree of illumination. Arsenate affected mainly algal growth but also cell morphology, whereas arsenite caused only morphological changes. Studies on the incorporation of ⁷⁴As-arsenate into cells grown in artificial sea water indicated that arsenate was incorporated and later partially released by both T. chui and H. carterae. Both arsenate influx and efflux seemed to be energy-dependent phenomena, because they varied with the degree of illumination. Differences between the rates of uptake and release of arsenic suggested that arsenate undergoes chemical changes after having been transported into the algal cells.     

Relationships between environment and mountain riparian plant communities associated with two rare tertiary-relict tree species, Euptelea pleiospermum (Eupteleaceae) and Cercidiphyllum japonicum (Cercidiphyllaceae)

Euptelea pleiospermum and Cercidiphyllum japonicum are dominant relictual tree species of the riparian plant communities in the subtropical region of Shennongjia Mountains, central China. Community survey and multivariate analysis were carried out to characterize their ecological ranges and regeneration characteristics, and further to explore the factors determining their present distribution boundaries and the barriers restricting their range expansion. We recorded 303 woody species, among which there were 14 relictual, rare and/or endemic woody species. Results obtained from cluster analysis corroborated the results from non-metric multidimensional scaling (NMS) ordination, classifying the 42 plots into three well-defined associations. Correlation analysis revealed that variation in species composition among associations was partly explained by some physical (altitude, slope, soil temperature) and chemical (available K, NH₄, pH) properties. Multiple regression analyses with data of adults and seedlings with physical and chemical variables revealed contrasting patterns of the two dominant relictual species. Both taxa have a high resprouting rate that keeps the stands stable irrespective of scarcity of seedlings. However, expansion of the distribution range is difficult in such a situation. E. pleiospermum prefers riparian habitats with poor nutrients in the south-facing slope of the Shennongjia Mountains, which may indicate that this species is light-demanding at some life stages and well adapted to a nutrient-poor habitat where competition from other species is limited. The Cercidiphyllum japonicum population was more scattered and fragmented, and preferred riparian habitats on gentle slopes. Both species are favored by the mild and moist microclimate, but the current conditions in these subtropical mountain riparian habitats probably do not really provide optimal ecological conditions for the two relictual species.     

Hydrozoan and protozoan epibionts on two decapod species, Liocarcinus depurator (Linnaeus, 1758) and Pilumnus hirtellus (Linnaeus, 1761), from Scotland

Crabs of the species Liocarcinus depurator and Pilumnus hirtellus, collected on the west coast of Scotland, showed hydrozoan and protozoan epibionts. The epibionts of Liocarcinus depurator were the protozoan Ephelota plana and the hydrozoans Clytia gracilis and Leuckartiara sp. The epibionts of Pilumnus hirtellus were the protozoans E. plana and Zoothamnium sp. For Liocarcinus depurator the number of Ephelota per crab fluctuated between 0 and 47 and the greatest number of suctorians were located on the chelipeds, carapace and anterior pereiopods. The hydrozoans, for Liocarcinus depurator, showed densities of 0-20 (Clytia gracilis on the second pereiopod) and 0-507 individuals per crab (Leuckartiara sp., principally on chelipeds, carapace and the fourth right pereiopod). For Pilumnus hirtellus, Ephelota plana showed densities between 3 and 56 individuals per crab, the greatest number of suctorians being located on the same areas as on Liocarcinus depurator. There was a density of 10-69 individuals per crab of Zoothamnium sp. on Pilumnus hirtellus (located on the carapace). Ephelota plana has not been observed previously as an epibiont on crustacea, nor had Zoothamnium sp. as an epibiont on Pilumnus hirtellus. Both hydrozoans, Leukartiara and Clytia, have not been previously described as epibionts on Liocarcinus depurator. Data about the morphological characteristics and distribution of these epibionts are included.     

Antioxidant responses of citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), exposed to thermal stress

Relatively low or high temperatures are responsible for a variety of physiological stress responses in insects and mites. Induced thermal stress was recently associated with increased reactive oxygen species (ROS) generation, which caused oxidative damage. In this study, we examined the time-related effect of the relatively low (0, 5, 10, and 15 °C) or high (32, 35, 38, and 41 °C) temperatures on the activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidases (POX), and glutathione-S-transferase (GST), and the total antioxidant capacity (TEAC) of the citrus red mite, Panonychus citri (McGregor). The malondialdehyde (MDA) concentration, as a marker of lipid peroxidation in organisms, was also measured in the citrus red mite under thermal stress conditions. Results showed that SOD and GST activities were significantly increased and play an important role in the process of antioxidant response to thermal stress. Lipid peroxidation levels increased significantly (P < 0.001) and changed in a time-dependent manner. CAT and POX activity, as well as TEAC, did not vary significantly and play a minor role to remove the ROS generation. These results suggest that thermal stress leads to oxidative stress and antioxidant enzymes play an important role in reducing oxidative damage in the citrus red mite.     

Morphological and genetic differentiation of two loliginid squids, Uroteuthis (Photololigo) chinensis and Uroteuthis (Photololigo) edulis (Cephalopoda: Loliginidae), in Asia

The squids Uroteuthis (Photololigo) edulis and Uroteuthis (Photololigo) chinensis (family Loliginidae) are commercially important fishery species in many coastal regions of Asia. The morphologies of these two squids are very similar, and identification based on morphology has been inadequate. The occurrence of cryptic species in the family Loliginidae has been reported. The widely distributed U. (P.) chinensis and U. (P.) edulis are believed to comprise several cryptic species. In this study, the taxonomic status of the two species in East Asia was elucidated by morphological and genetic analyses. Analysis of U. (P.) chinensis from Hong Kong and Xiamen (China) and U. (P.) edulis from Yamaguchi (Japan) and Shanghai (China) was performed in order to determine the effectiveness of different morphometric variables in discriminating between the two species. Multivariate analysis of 27 morphometric indices revealed no new morphological characters for the taxonomic identification of the two taxa, which can be distinguished by the teeth shape and number on arm sucker rings, and the percentage of hectocotylized part of left arm IV of males. The morphometric differences between U. (P.) edulis individuals from the two localities is most probably due to differences in the maturity stages of the sampled individuals between the two localities. Genetic analysis based on the mitochondrial COI and 16S rRNA genes revealed a high divergence of 15.5% and 7.5% respectively, indicating that U. (P.) edulis and U. (P.) chinensis are distinct species.     

Assimilation and oxygen uptake associated with two different feeding habits of Munida gregaria (=M. subrugosa) (Crustacea, Decapoda)

Munida gregaria is the most abundant galatheid crab species in the Beagle Channel (55 °S 68 °W) off Tierra del Fuego, Argentina. This species has two different and simultaneous feeding habits: predator and deposit feeder. The objectives of this work were to determine whether either of the two different feeding habits imply differences in assimilation and oxygen consumption. Subsamples of 40 and 20 crabs of each sex were randomly selected, transported to the laboratory, and used in assimilation and oxygen consumption experiments, respectively. Animals were placed in individual chambers at 8 ± 1 °C. The assimilation experiment was conducted using four types of diet: isopods (CRU), algae (ALG), pulverized fish food (PFF), and particulate organic matter (POM). The crabs' routine metabolism and postprandial oxygen consumption - or specific dynamic action SDA - were measured using Clark-type polarographic electrodes. Two kinds of food were offered: CRU and PFF to simulate both feeding habits. Assimilation in M. gregaria for both feeding habits presented values > 90% for dry mass and energetic content. Consumption rate varied between 15 and 50 mg_ingested g_DM^− 1, and was significantly higher for CRU and PFF diets. Females showed significantly higher consumption rates than males for all diets. On average, the routine metabolism of M. gregaria was 15 ± 5 μlO₂ h^− 1 g^− 1. Deposit feeding may confer energetic advantages to female M. gregaria, especially because this diet has a low energetic cost of assimilation. Deposits of high-energy content showed the highest consumption rates among four the experimental diets. In terms of mass and energy, the deposit diet also showed the highest assimilation efficiency. The postprandial oxygen consumption was lower in females and in the deposit feeding experiment. We suggest that females may prefer the deposit feeding habit to maximize their ingested energy, allowing them to devote more energy to reproduction. This is attained by a high consumption rate and by minimizing the energy used in assimilation.     

Respiratory and osmoregulatory responses of the hermit crab, Clibanarius vittatus (Bosc), to salinity changes

Intertidal hermit crabs were stepwise acclimated to 10, 20, and 30‰ salinity (S) and 21 ± 1 °C. Hemolymph osmolality, sodium, chloride, and magnesium were isosmotic (isoionic) to ambient sea water at 30‰ and hyperosmotic (hyperionic) at 20 and 10‰ S, while hemolymph potassium was significantly hyperionic in all acclimation salinities. Total body water did not differ significantly at any acclimation salinity. Oxygen uptake rates were higher in summer-than winter-adapted crabs. No salinity effect on oxygen consumption occurred in winter-adapted individuals. Summer-adapted, 30‰ acclimated crabs had a significantly lower oxygen consumption rate than those acclimated 10 and 20‰ S. Crabs exposed to 30 10 30‰ and 10 30 10‰ semidiurnal (12 h) and diurnal (24.8 h) fluctuating salinity regimes showed variable osmoregulatory and respiratory responses. Hemolymph osmolality followed the osmolality of the fluctuating ambient sea water in all cases, but was regulated hyperosmotically. Hemolymph sodium, chloride, and magnesium concentrations were similar to hemolymph osmolality changes. Sodium levels fluctuated the least. Hemolymph potassium was regulated hyperionically during all fluctuation patters, but corresponded to sea water potassium only under diurnal conditions. The osmoregulatory ability of Clibanarius vittatus (Bosc) resembles that reported for several euryhaline brachyuran species. The time course of normalized oxygen consumption rate changed inversely with salinity under semidiurnal and diurnal 10 30 10‰ S fluctuations. Patterns of 30 10 30‰ S cycles had no effect on oxygen consumption rate time course changes. The average hourly oxygen consumption rates during both semidiurnal fluctuations were significantly lower than respective control rates, but no statistical difference was observed under diurnal conditions.     

Infection experiments reveal broad host ranges of Eurychasma dicksonii (Oomycota) and Chytridium polysiphoniae (Chytridiomycota), two eukaryotic parasites in marine brown algae (Phaeophyceae)

Unialgal cultures of the brown alga Pylaiella littoralis (L.) Kjellman infected by either Eurychasma dicksonii (Wright) Magnus (Oomycota) or Chytridium polysiphoniae (Cohn) H. E. Petersen (Chytridiomycota) were used to elaborate the host ranges of these pathogens. Infection experiments with 48 host species covering 13 orders of the Phaeophyceae showed that 45 species were susceptible to attack by Eurychasma and 23 to Chytridium. The two pathogens showed host-specific differences in generation times: while in Pylaiella the shortest cycles were 16 days for Eurychasma and 6 days for Chytridium, one and five days more, respectively, were required in Acinetospora. Heavy parasite attack on the microscopic stages of host species with heteromorphic life histories, like kelps (Laminariales), is documented and discussed as a potential regulatory factor for the population dynamics of macroalgae.     

Functional responses associated with pallial organ variations in the Pacific oyster Crassostrea gigas (Thunberg, 1793)

The plasticity and function of the pallial organs were studied in the Pacific oyster Crassostrea gigas from three sites of Bourgneuf Bay (French Atlantic coast, 46-47°N, 1-2°W) characterized by different turbidity conditions. Labial palp area was closely and positively related to the turbidity gradient. No clear pattern was established between the gill area and the gradient of suspended particulate matter (SPM). The functional responses induced by these morphological variations were investigated in the laboratory by means of ecophysiological experiments and endoscopic observations. Oysters with different pallial organ areas were supplied with mixed suspensions of heat-killed Tetraselmis suecica and living Skeletonema costatum added to different concentrations of kaolinite to simulate low (SPM = 8.5 ± 0.4 mg l^− 1) and high (SPM = 48.3 ± 1.4 mg l^− 1) turbidity conditions. At each SPM concentration, heat-killed T. suecica were preferentially rejected in pseudofaeces compared to S. costatum, indicating a preingestive particle selection. At low seston load, clearance rate (CR) was closely and positively related to gill area and particle selection occurred only on the gills, between the ventral grooves and dorsal tracts. At higher seston load, palps exhibited a particle-sorting capacity dependent on gill area. Indeed, with small gills, an increase in selection efficiency (SE) and CR was positively related to palp area. On the other hand, large gills processed the particles without an effect of palps but with a decrease in CR. The functional responses associated with pallial organ variations clearly showed that the preingestive particle processing in oysters is an integrated mechanism dependant on the gill and labial palp areas.     

Different responses to selection in two stocks of the bay scallop, Argopecten irradians irradians Lamarck (1819)

Two different stocks (A and B) of the bay scallop Argopecten irradians irradians (Lamarck, 1819) were used to test mass selection on growth. Stock A was a descending stock from the initial introduction from U.S.A. in 1982, which had been cultured in China for about 20 years. Stock B was the third generation from a recent introduction from U.S.A. in 1999. Truncation selection was conducted by selecting the largest 11% scallops in shell length from Stock A and the largest 12.7% scallops from Stock B as parents for the respective selected groups. Before the removal of parents for truncation selection, equal numbers of scallops were randomly chosen from Stock A and B to serve as parents for the control groups. Offspring from the four groups were reared under the same hatchery, nursery, and grow-out conditions. Values of response to selection and realized heritability at larvae, spat and grow-out stages for Stock B were all significantly (P<0.001) higher than its counterpart for Stock A. For Stock A, no significant response to selection was observed (P>0.05) at any stage, and the realized heritability for shell length was 0.015±0.024 for larvae, 0.040±0.027 for spat, and 0.080±0.009 for grow-out, respectively. For Stock B, however, significant (P<0.05) response to selection was observed, and the realized heritability for shell length was 0.511±0.010 for larvae, 0.341±0.022 for spat, and 0.338±0.015 for grow-out. On average, responses to selection at the three stages for Stock B was 30×, 7.1×, and 3× higher than its counterpart for Stock A, respectively. Accordingly, realized heritability at above stages for Stock B was 33×, 7.5×, and 3.2× higher than its counterpart for Stock A, respectively. Differences in response to selection and realized heritability between the two stocks are presumably due to differences in genetic variability. As the 20th generation from the initial introduction consisted of only 26 scallops, Stock A is known to be highly inbred, while inbreeding in Stock B is negligible.