Pulling or drilling, does size or species matter? An experimental study of prey handling in Octopus dierythraeus ()

The influence of both predator and prey size on the shift from a pulling to a drilling predatory response was examined in the intertidal octopus Octopus dierythraeus, using an experimental program. Additionally, selective drilling, where particular regions of the prey are targeted, was examined for a variety of bivalve and gastropod prey. O. dierythraeus always initially attempted to pull bivalves apart. Shells that were eventually drilled were always subjected to significantly more pulling attempts than those that could be pulled apart, indicating that octopus are willing to expend more energy to access the flesh quickly. There was no defined threshold where bivalve size caused an octopus to switch from a pulling to a drilling response. Instead, there was a broad size range where the octopus could adopt either handling method and it varied for each individual. Octopus may only able to pull open bivalves before the molecular ratchet or ‘catch’ mechanism that many bivalves possess is engaged. This might explain the lack of a relationship between either octopus or bivalve size and the success of pulling, as it is likely that when the bivalves were presented to individual octopus they were either setting the ‘catch’ mechanism, or had already engaged it. O. dierythraeus demonstrated selective drilling on a variety of molluscan prey, with penetration sites differing between prey species. O. dierythraeus targeted the valve periphery, which was the thinnest part of the shell, therefore minimizing handling time. O. dierythraeus always drilled gastropods, but did not target the thinnest regions of the shells, with drill site varying according to the morphology of the prey. Elongate species with pronounced aperture lips were drilled in the apical region, close to the columella on the side of the opercula whereas nonelongate species were drilled immediately above the aperture. The location of drilling sites may represent a trade-off between targeting the most effective places to inject paralyzing secretions and the mechanically simplest places to drill.     

Temperature and pCO2 jointly affect the emergence and survival of cercariae from a snail host: implications for future parasitic infections in the Humboldt Current system

Ocean warming and acidification are general consequences of rising atmospheric CO₂ concentrations. In addition to future predictions, highly productive systems such as the Humboldt Current System are characterized by important variations in both temperature and pCO₂ level, but how these physical–chemical ocean changes might influence the transmission and survival of parasites has not been assessed. This study experimentally evaluated the effects of temperature (14, 18 and 25 °C) and the combined effects of temperature (∼15 and 20 °C) and pCO₂ level (∼500 and 1400 microatmospheres (µatm) on the emergence and survival of two species of marine trematodes—Echinostomatidae gen. sp. and Philophthalmidae gen. sp.—both of which infect the intertidal snail Echinolittorina peruviana. Snails were collected from intertidal rocky pools in a year-round upwelling area of the northern Humboldt Current System (23°S). Two experiments assessed parasite emergence and survival by simulating emersion-immersion tidal cycles. To assess parasite survival, 2 h old cercariae (on average) were taken from a pool of infected snails incubated at 20–25 °C, and their mortality was recorded every 6 h until all the cercariae were dead. For both species, a trade-off between high emergence and low survival of cercariae was observed in the high temperature treatment. Species-specific responses to the combination of temperature and pCO₂ levels were also observed: the emergence of Echinostomatidae cercariae was highest at 20 °C regardless of the pCO₂ levels. By contrast, the emergence of Philophthalmidae cercariae was highest at elevated pCO₂ (15 and 20 °C), suggesting that CO₂ may react synergistically with temperature, increasing transmission success of this parasite in coastal ecosystems of the Humboldt Current System where water temperature and pH are expected to decrease. In conclusion, our results suggest that integrating temperature-pCO₂ interactions in parasite studies is essential for understanding the consequence of climate change in future marine ecosystem health.     

Potential and peril of field experimentation: the use of copper to manipulate molluscan herbivores

Barriers of copper-based anti-fouling paints have become a popular method for the experimental manipulation of certain molluscan grazers, presumably by acting as a chemical barrier to movement. Although probably similar in action, copper metal can be more versatile in its application and maintenance. Its efficacy was confirmed in field experiments which examined the colonization of artificial surfaces by the intertidal red alga Halosaccion glandiforme (Rupr.). However, even though copper has the desired indirect effect on algae (i.e., the exclusion of grazers), it can still have undesirable direct effects as well, and these “costs of manipulation” must be recognized. These results demonstrate the necessity of proper controls in field experimentation, a consideration absent in many past studies. The general use of partial manipulations as control treatments appears useless for estimating artifacts associated with the use of copper barriers in particular and for other experimental manipulations in general. More meaningful controls may rely on finding multiple ways of manipulating the variable of interest.     

Gastropod mollusc aliphatic alcohol oxidase: subcellular localisation and properties

The digestive gland and other tissues of several species of terrestrial gastropod mollusc contain an aliphatic alcohol oxidase activity (EC1.1.3.13). The enzyme is FAD dependent, consumes oxygen and generates hydrogen peroxide and the corresponding aldehyde. Saturated primary alcohols are favoured as substrates with octanol preferred with an apparent K_m of 3–4 μM. The activity is clearly distinguishable from previously reported molluscan aromatic alcohol oxidase (EC1.1.3.7) on the basis of FAD dependence, sensitivity to heat treatment and high salt concentration and with regard to substrate preferences. The aliphatic alcohol oxidase is membrane associated and most likely localised to the endoplasmic reticulum. Extraction of membranes with 1% Igipal solubilises the enzyme in active form. This enzyme is a further example of an oxidase apparently restricted to molluscs.     

Variation in foot size and shape in some British land snails and its functional significance

Live weight, and the length, breadth and surface area of the extended foot sole were measured in 24 species of British terrestrial snails. Allometric relationships between these variables are described, concentrating on the relationship between foot surface area and weight. Intraspecific foot area/weight relationships deviate from isometric expectation for several species; this may be attributed to density changes, foot-shape variation or the physical constraint imposed by shell aperture size.
The rate of increase of foot sole area with live weight among species is greater than expected under isometry, indicating that larger species partially compensate for the increase in foot loading (weight per unit foot area). The rate of whorl expansion of the shell is related to the deviations from the interspecific foot area/weight relationship, reinforcing the possibility that shell aperture area may limit foot size in some species. Foot ratio (foot length:foot width) is negatively related to live weight and foot loading.
The findings are discussed in relation to the known behaviour and microdistribution patterns of the species.     

Dispersal of the estuarine gastropod Pyrazus ebeninus is only weakly influenced by pneumatophore density

Studies on rocky intertidal gastropods indicate habitat complexity and body size to be major determinants of dispersal patterns. Considerations of effects of habitat complexity and body size on soft sediment gastropods are, however, less common. In neither habitat has the interaction between habitat complexity and body size been considered despite the increasing recognition in the general ecological literature that complexity effects are body-size-dependent. We tested independent and interacting effects of habitat complexity and body size on movement of the mud-whelk, Pyrazus ebeninus, by marking large (61-85 mm) and small (31-55 mm) snails in sites with low and high densities of pneumatophores and determining the distance and direction of their dispersal over periods of 1 week, 2 weeks and 1 month. Contrary to our expectation, we found no effect of pneumatophore density on the distance of snail migration over each of the temporal scales; net distance travelled by snails was determined only by body size and idiosynchratic, site-specific factors. The direction of snail movement was, by contrast, influenced on some temporal scales by both pneumatophore density and snail size. Over 1 week, site effects dominated patterns of movement and neither size of snail nor density of pneumatophore produced statistically significant effects. As the temporal scale increased, effects of size and pneumatophore density became increasingly apparent. Over the 1-month period, large snails at all sites and small snails at sites with high pneumatophore density migrated down the shore, while small snails at sites with low pneumatophore displayed non-directional movement. Thus, overall this study provides only weak support for effects of pneumatophore density on snail movement. In combination with other studies, our results suggest that, in comparison to on rocky shores where habitat complexity has strong effects on the distribution, abundance and behaviour of gastropods in soft-sediment systems habitat complexity is a less important structuring agent.     

Neutral N-glycan patterns of the gastropods Limax maximus, Cepaea hortensis, Planorbarius corneus, Arianta arbustorum and Achatina fulica

The N-glycosylation potentials of Limax maximus, Cepaea hortensis, Planorbarius corneus, Arianta arbustorum and Achatina fulica were analysed by investigation of the N-glycan structures of the skin and viscera glycoproteins by a combination of HPLC and mass-spectrometry methods. It is one of the first steps to enlarge the knowledge on the glycosylation abilities of gastropods, which may help to establish new cell culture systems, to uncover new means for pest control for some species, and to identify carbohydrate-epitopes which may be relevant for immune response. All snails analysed contained mainly oligomannosidic and small paucimannosidic structures, often terminated with 3-O-methylated mannoses. The truncated structures carried modifications by β1-2-linked xylose to the β-mannose residue, and/or an α-fucosylation, mainly α1,6-linked to the innermost N-acetylglucosaminyl residue of the core. Many of these structures were missing the terminal N-acetylglucosamine, which has been shown to be a prerequisite for processing to complex N-glycans in the Golgi. In some species (Planorbarius corneus and Achatina fulica) traces of large structures, terminated by 3-O-methylated galactoses and carrying xylose and/or fucose residues, were also detected. In Planorbarius viscera low amounts of terminal α1-2-fucosylation were determined. Combining these results, gastropods seem to be capable to produce all kinds of structures ranging from those typical in mammals through to structures similar to those found in plants, insects or nematodes. The detailed knowledge of this very complex glycosylation system of the gastropods will be a valuable tool to understand the principle rules of glycosylation in all organisms.     

Swimming in the sea hare Aplysia brasiliana: Cost of transport, parapodial morphometry, and swimming behavior

The energetics and behavior of the parapodial-swimming Aplysia brasiliana were investigated in order to compare net cost of transport (COT_net) between swimming and crawling, and to compare transport costs with other swimmers. Oxygen consumption (V_O2) increased with increasing animal mass for resting, crawling, and swimming animals. Slopes of the regressions of log V_O2 on log mass were 0.90, 0.91, and 0.89 for resting, crawling, and swimming, respectively. The regression for resting V_O2 on mass was significantly lower than regressions of crawling and swimming on mass, which fell into a statistically homogenous subgroup. During 4-h swimming bouts, parapodial beat frequency dropped by less than 10% of starting values after 2 h and then stabilized for the remainder of the trial, whereas velocity steadily decreased to about 70% of starting values over the 4-h period. Initial beat frequency (at the start of a swimming bout) was negatively related to body mass, varying from 1.1 beat s^− 1 for a 34 g individual to 0.7 beats s^− 1 for a 500 g individual. Final beat frequency (at the end of a swimming bout) was also negatively related to body mass, but had a significantly lower intercept than initial beat frequency. Neither initial swimming velocity nor final swimming velocity was related to mass, but final velocity was significantly lower than initial velocity. A 250 g A. brasiliana swam at 345 m h^− 1 and crawled at 7 m h^− 1. Swimming COT_net (0.1 ml O₂ kg^− 1 m^− 1) for a 250 g A. brasiliana was 50 times less than crawling COT_net (5.3 ml O₂ kg^− 1 m^− 1). While the crawling COT_net for A. brasiliana fell within the range of other marine gastropods, swimming COT_net was less than that of swimming crustaceans, and much less than another gastropod, Melibe leonina, that uses lateral bending to swim.     

Consumption rates and prey preference of the invasive gastropod Rapana venosa in the Northern Adriatic Sea

The alien Asian gastropod Rapana venosa (Valenciennes 1846) was first recorded in 1973 along the Italian coast of the Northern Adriatic Sea. Recently, this predator of bivalves has been spreading all around the world oceans, probably helped by ship traffic and aquaculture trade. A caging experiment in natural environment was performed during the summer of 2002 in Cesenatico (Emilia-Romagna, Italy) in order to estimate consumption rates and prey preference of R. venosa. The prey items chosen were the Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819), the introduced carpet clam Tapes philippinarum (Adams and Reeve 1850), both supporting the local fisheries, and the Indo-Pacific invasive clam Anadara (Scapharca) inaequivalvis (Bruguière 1789). Results showed an average consumption of about 1 bivalve prey per day (or 1.2 g wet weight per day). Predation was species and size selective towards small specimens of A. inaequivalvis; consumption of the two commercial species was lower. These results might reduce the concern about the economical impact on the local bivalve fishery due to the presence of the predatory gastropod. On the other hand, selective predation might probably alter local community structure, influencing competition amongst filter feeder/suspension feeder bivalve species and causing long-term ecological impact. The large availability of food resource and the habitat characteristics of the Emilia-Romagna littoral makes this area an important breeding ground for R. venosa in the Mediterranean Sea, thus worthy of consideration in order to understand the bioinvasion ecology of this species and to control its likely further dispersal.     

Intrasexual copulation and mate discrimination in a population of Nodilittorina radiata (Gastropoda: Littorinidae)

Intrasexual copulation and mate discrimination by Nodilittorina radiata (Gastropoda: Littorinidae) were studied on a concrete breakwater at Hakodate Bay, southern Hokkaido, Japan. Intrasexual (male–male) copulations were observed in 4.7–21.1% of copulating pairs on the shore. As females were relatively larger than males and males copulated with females larger than themselves, we hypothesized that males choose potential mates larger than themselves. However, two male mates showed no significant size preference in intrasexual copulations, suggesting that males do not choose relatively larger individuals as mates. In a laboratory mate-choice experiment, male N. radiata preferred to mate with females, indicating precopulatory sex identification. They copulated with males, however, at the frequency of 37%, perhaps because of sex misidentification.