Male mating behaviour reduces the risk of sexual cannibalism in an Australian praying mantid

In cases where sexual cannibalism represents a sexual conflict, we should expect to find male traits that reduce the risk of cannibalism. In fact, a wide variety of such traits have been proposed, including elaborate courtship displays, cautious approach behaviours, and opportunistic mating whilst a female is feeding. However, there is very little direct evidence that these behaviours actually reduce the risk of sexual cannibalism for males, and the evidence that does exist comes mainly from spider studies. In this study of Pseudomantis albofimbriata praying mantids we found evidence of various male behaviours that reduced the risk of sexual cannibalism. Most males attempted to avoid detection entirely and others moved in a slow and stealthy manner. We also observed five cases of opportunistic mating, but saw no evidence of any male courtship routine. It seems that mounting from the rear of a female or slowly approaching her from the front, allows many males to go unnoticed and, therefore, substantially reduces the risk of sexual cannibalism in this mating system. Interestingly, we could not identify any female traits that males use to assess the risk of sexual cannibalism. It may be that P. albofimbriata males use alternative means to assess these risks. The presence of these behavioural strategies by males suggests a net cost of being consumed, and that sexual cannibalism is likely to be a female strategy in this system.     

Morphological controls on cannibalism in a planktonic marine phagotroph

The ingestion preferences of planktonic protozoa influence the structure and succession of microbial communities and thus biogeochemical cycling within aquatic environments. Some predatory ciliates and flagellates are reported to switch to cannibalism when no suitable non-self prey items are available for consumption. However, the importance of cannibalism as a survival strategy, and its ubiquity within the planktonic protozoa is not known. We report the first attempt to quantify cannibalism in a phagotrophic marine dinoflagellate (Oxyrrhis marina). Cannibalistic Oxyrrhis cells seldom comprised >2% of any experimental population, including those in which all non-self prey items had been grazed to extinction. Such 'prey-deplete' cultures became dominated by homogeneous populations of highly motile Oxyrrhis that were morphologically unable (too similar in size) to cannibalise. That cannibalism can only occur when 'victim' and 'cannibal' cell size-classes of sufficient difference collide, suggests that cannibalism may be of limited use as a long-term survival strategy in phagotrophic protozoa.     

Seasonal aspects of sexual cannibalism in the praying mantis (<Emphasis Type="Italic">Mantis religiosa</Emphasis>)

According to the adaptive foraging hypothesis of sexual cannibalism, females face a trade-off between mating and consuming a courting male. Because male and prey availability can change seasonally, sexual cannibalism may change with season. However, we are not aware of any work examining how sexual cannibalism in insects relates to the time of season. Here, we examined the seasonal pattern of sexual cannibalism and reproductive behaviour in the sexually cannibalistic praying mantis (Mantis religiosa). We repeatedly collected the last instars of praying mantises from the field and brought them up under natural weather and photoperiod, but standardised feeding and socioecological conditions. After the females reached sexual maturity, we allowed all of the females to mate during two mating trials. In comparison to female praying mantises maturing later in the season, early-maturing females were larger but of poorer body condition on the day of a mating trial (20 days after the adult moult). During the first round of mating trials, early-maturing virgin females cannibalised males more frequently than their late-maturing counterparts. In contrast, late-maturing females that mated in the first round of mating trials were more likely than early-maturing, nonvirgin females to be cannibalistic in the second round of mating trials. The latency time until copulation was correlated with a risk of sexual cannibalism and was longer in early-maturing females. Our study suggests that the date of the last (adult) moult plays an important role in the occurrence of sexual cannibalism.     

Distribution,abundance, and feeding of a disjunct population of lady crab in the southern Gulf of St. Lawrence,Canada

The lady crab (Ovalipes ocellatus) is one of the most common native species of swimming crab (Portunidae) of the Atlantic Coast of North America but most populations occur south of Cape Cod, Massachusetts. There is a disjunct population in Northumberland Strait (southern Gulf of St Lawrence), which was the focus of this study. Adult lady crabs were collected by trawling in water >4 m deep from May to October 1999 to 2005 to determine abundance, distribution, and diet. Lady crab occurred only in a small area (about 2,500 km²) in the central part of Northumberland Strait where bottom water temperature was >18°C during summer, and the substrate was mainly sand or sandy gravel. Male lady crab attained a maximum carapace width (CW) of 112 mm compared to 92 mm CW for females. The summer and autumn diet consisted mainly of infauna. The principal prey (each >5% of diet by weight) were: small bivalve molluscs (primarily Atlantic razor clam Siliqua costata and Macoma sp.; 43%), small rock crab (Cancer irroratus; 13%), polychaetes (11%), fish remains (9%), and small lady crab (9%). All stomachs collected during May (water temperature ≤10°C) were empty. There was little evidence of any difference in feeding intensity between 0700 h and 1900 h.     

Studies on the locomotor activity of the freshwater crab,Potamon fluviatile

Locomotor activity in the freshwater crab, Potamon fluviatile, was studied both in the field, by direct counts of animals along a stream section, and by means of actographs. General metabolism was evaluated through the analysis of oxygen consumption. Sex, size, and environmental factors proved to influence both the intensity and the timing of locomotion. In the laboratory, the two sexes behaved in the same way and consumed oxygen to the same extent, while the higher females' activity recorded in the field was due to their reproductive state. Younger age classes were more cryptic in the field and also less active in the laboratory, even though they had a higher weight-relative oxygen consumption. A rise in temperature, at least under the range examined in the present study, increased the crabs' activity rate, and also caused a change in their rhythmicity pattern, with a passage from diurnalism to nocturnalism. A lowering in relative humidity increased locomotion intensity, as a hygrokinetic response.     

Further observations of transport within paddle cilia

Summary Rhabdopleura has densely ciliated tentacles and cephalic shield. These cilia are of two sorts, ordinary cilia and those bearing paddle-like swellings. These swellings, about l m across, are in the ciliary membrane. The axoneme bundle within the cilium remains intact, keeping the usual spatial arrangements, except that in the swelling its overall diameter is reduced. It is suggested that the mechanism for moving the paddle-like swellings along the length of the cilium is the releasing and reattaching of the side filaments from the axoneme to the ciliary membrane. Acknowledgements. I wish to thank the Director and staff of the Plymouth Marine Biological Association for their help and facilities while collecting the material. Mr. R.F. Moss gave much skilled technical assistance. I wish also to thank Professor W.E. Knight-Jones who identified the specimens of Vermiliopsis and Dodecacera.     

Ionoregulatory and urinary responses to emersion in the mangrove crab Ucides cordatus and the intertidal crab Carcinus maenas

The mangrove crab Ucides cordatus showed a significant reduction in its output of isosmotic urine (to 60% of submerged rates) in humid, emersed conditions when in apparent water balance. A similar, but lesser, reduction was observed in the intertidal temperature species Carcinus maenas. Some of the decrease is effected by increased water withdrawal of an isosmotic fluid in the antennal gland (inulin urine to haemolymph concentration ratio=1.27) in Ucides but most is due to the reduced filtration rate which decreases from 3.41 to 2.19 ml·100 g^-1·day^-1 (in Carcinus from 7.37 to 5.88). In Carcinus, inulin urine to haemolymph concentration ratios are within the range 1.34–1.41 and show significant change on emersion. Comparisons of ion and inulin clearance ratios revealed interspecific differences in renal handling of Na⁺ and Cl^-. During emersion total Na⁺ efflux is markedly reduced in both species. Urinary Na⁺ losses are responsible for most of the efflux in Carcinus but represent only 50% of the total in Ucides. Significant Na⁺ uptake from interstitial water occurs in Ucides. REductions in ion and water loss appear to be mainly dependent on decreases in urine output (clearance rate). However, some released urine was found to accumulate in the branchial chambers in both species. Whether or not extrarenal reabsorption of ions from released urine occurs in the gill chambers in either crab species remains to be proved.Abbreviations CPM counts per minute - ECF extracellular fluid - k rate constant for inulin clearance - k ^Na rate constant for sodium efflux - J _out ^Na sodium efflux rate - Q _tot total radioactivity injected - SEM standard error of mean - SW sea water - 9-SW sea water, salinity 9 mg·ml^-1 (ppt) - 26-SW sea water, salinity 26 mg·ml^-1 (ppt) - U/B ratio of urine (U) to haemolymph (B) concentrations - V _c1 clearance rate - V _u urine output - V _a inulin space     

Egg cannibalism in Helicoverpa armigera on sorghum and pigeonpea

Egg cannibalism by Helicoverpa armigeraHübner (Lepidoptera: Noctuidae) larvae was studied in the laboratory and in the field. In laboratory experiments, first instars were exposed to increasing densities of H. armigera eggs on sorghum, Sorghum bicolor (L.) Moench, and pigeonpea, Cajanus cajan (L.) Millsp. The number of eggs eaten per larva increasedsignificantly as egg availability increased on both sorghum and pigeonpea. In small cages 21–37% of eggs were eaten on sorghum, 4–12%on pigeonpea. Plant feeding declinedsignificantly on both sorghum and pigeonpea asegg density increased. Cannibalism was greateron sorghum than on pigeonpea while plantfeeding was greater on pigeonpea than onsorghum. Only around 8% of eggs were eaten inlarger cages with sorghum. The response toincreasing egg availability in all experimentswas linear. Immunoassay with an anti-vitellinmonoclonal antibody showed that egg cannibalismoccurs on pigeonpea under field conditions.Seven percent of all larvae had egg protein intheir gut. Cannibalism may make a significantcontribution to H. armigera populationsuppression.     

Shell recruitment in the Mediterranean hermit crab Clibanarius erythropus

Gastropod shells are vital for the majority of hermit crab species, being essential for their survival, growth, protection, and reproduction. Given their importance, shells are acquired and transferred between crabs through several modalities. We conducted observations and experiments at the Asinara Island (Sardinia, Italy) to investigate the efficacy of the different behavioral tactics adopted by the hermit crab Clibanarius erythropus to acquire shells, such as: (1) locomotion and activity at different tidal phases; (2) attendance at shell-supplying sites (simulated predation sites with five different odors: live and dead gastropods, live and dead crabs, predator); and (3) interactions with conspecifics in aggregations on simulated gastropod predation sites. In each tidal phase, locomotion was slow (0.7 cm min^− 1) and, as a consequence, the probability of encountering empty shells and conspecifics was low. Simulated gastropod predation sites quickly attracted a larger number of hermit crabs than the other sites tested. Aggregations seemed to function as shell exchange markets, as previously suggested for other species: the first attendant took the experimental shell and a chain of shell exchanges among conspecifics followed. Our results show that, in C. erythropus, aggregation is the most efficient tactic for the acquisition of new shells, whereas in other species, such as Pagurus longicarpus, it is associated with exploitation ability due to the intense locomotion. The interspecific plasticity in hermit crabs' behavior is confirmed.     

Filial cannibalism in a non-brood cycling marine fish

Synopsis Direct observation and the analysis of stomach contents indicate that custodial male Cortez damselfish, Stegastes rectifraenum, regularly eat some of the eggs they fertilize and guard. The pattern of forced starvation and brood cycling by custodial males that is seen in sticklebacks and other fishes for which filial cannibalism is known in the field does not exist for this species. These results indicate that filial cannibalism is likely to be more common among fishes than previously thought, because this behavior is not restricted to species that brood cycle.     

Mate choice and cannibalism in a natural population of a stream goby,Rhinogobius sp.

Breeding ecology of the stream goby,Rhinogobius sp. LD (Large Dark), was investigated under natural conditions. Males selectively courted females of similar size to lead them to the nests, whereas females followed courting males preferentially when the relative male size was greater. Male-male competition for a female was relatively infrequent and not severe. Developmental stages of eggs and egg numbers in one nest indicated that males receive 1–3 clutches during one breeding cycle. Males guarding multiple clutches frequently ate some of the eggs, but those guarding single clutches rarely did so. Gravid females in the nest also frequently cannibalized eggs laid by a previous female, probably in order to extend the area available for egg deposition. Mate choice in this species is discussed in relation to paternal ability, limitation of available spawning area and the female-biased sex ratio.     

Possible influences of habitat characteristics on the evolution of semelparity and cannibalism in the hump earwigAnechura harmandi

The possible influences of life history and habitat characteristics on the evolution of semelparity and cannibalism in the hump earwigAnechura harmandi were studied. This species is univoltine and overwinters as an adult. Females laid single egg-batches during winter in nests under stones at a riverside in a valley. They took care of the eggs which hatched in early spring and the offspring ate their mother before dispersing. The valley was sometimes flooded in summer. Nymphs emerged as adults and dispersed to elsewhere before the rainy season arrived. They returned to the riverside after the rainy season. The flooding and/or summer heat seemed to be the selective force for the evolution of dispersal behavior and semelparity in this species. The cannibalism of the female parent by her offspring seemed to have readily evolved after the evolution of semelparity. The unfavorable environmental conditions seemed to have a large effect on the evolution of semelparity and cannibalism in this species.     

Delayed copulation as a means of female choice by the hermit crab Pagurus filholi

Male hermit crabs perform precopulatory mate-guarding behavior during their reproductive season. As females generally cannot reject guarding attempts by males, male guarding prevents females from inspecting and choosing other male mates. However, as guarding males are often replaced by other males through competition for females during the guarding phase, females may be able to select males by delaying their copulation. To examine the possibility of female choice by hermit crabs, we investigated whether female Pagurus filholi that were being guarded in the field were ready to copulate and spawn. We found that about 30% of females guarded in the field were ready to spawn, indicating that guarded females delayed copulation with their current male. Our results suggest that by delaying copulation females may exploit male–male competition to choose dominant males. However, delaying copulation reduced the spawning potential of females. Hence, there is a trade-off between waiting for the opportunity to mate with a dominant male and decreased spawning success if females exploit male–male competition.     

Adaptations to a terrestrial existence by the robber crab,Birgus latro L.

Summary The activity of carbonic anhydrase (CA), which catalyses the equilibrium CO₂H⁺+HCO ₃ ^- , was investigated in various tissues implicated in the excretion of CO₂ by Birgus latro. Carbonic anhydrase was detected in the water-soluble fraction of gill tissue but also occurred in association with lipids (membrane bound). This is consistent with a CO₂ excretory role and an ion regulation function for the gills. In the lungs (branchial chamber lining) CA activity was found in the membrane bound fraction but was not detected in the soluble fraction, suggesting that the lung CA is not important for ion regulation. The specific CA activity of gill tissue homogenate (A=1.8±0.7·mg^-1) was higher than that measured for lung homogenates (A=0.4±0.2·mg^-1), but when the whole organ was considered the total CA activity in the lungs was not significantly different from total CA activity in the gills. In comparison to aquatic and amphibious crustaceans the specific activity of carbonic anhydrase in the lungs was high (25% cf. gill activity). This CA activity in the lungs could be correlated with significant CO₂ excretion by the lungs. CA may be retained in the branchial tissue as an adjunct to ion reabsorption by the gills.     

A trematode infection with no effect on reproductive success of a sand-bubbler crab

The infection effects of the parasitic digenean trematode on the body weight and reproductive success of the sand-bubbler crab were examined. Gynaecotyla squatarolae (Trematoda: Microphallidae) infects the body cavity of Scopimera globosa (Decapoda: Scopimeridae) and uses the crab as its second intermediate host. The parasites infected all reproductive crabs examined to varying degrees. Larger crabs of both sexes had more parasites than smaller ones, probably because body size reflects age, and older crabs had a longer period of exposure to infection. Males had more parasites than females, probably because of sexual difference in acting time on the surface. Ovigerous females stay in closed burrows and do not act on the surface during incubation, and so have less chance of infection than males. The quantity of infecting parasites did not explain variations in either body weight or reproductive success of individual crabs in a field experiment. The life history of this parasite, relative body size of the crabs, and cost and the possible benefit of manipulation for the parasite may explain these results.     

The invasive green crab and Japanese shore crab: behavioral interactions with a native crab species,the blue crab

Blue crabs, Callinectes sapidus (Rathbun), are an ecologically and commercially important species along the East coast of North America. Over the past century and a half, blue crabs have been exposed to an expanding set of exotic species, a few of which are potential competitors. To test for interactions with invasive crabs, juvenile C. sapidus males were placed in competition experiments for a food item with two common non-indigenous crabs, the green crab Carcinus maenas (L.) and the Japanese shore crab, Hemigrapsus sanguineus (De Haan). Agonistic interactions were evaluated when they occurred. In addition, each species’ potential to resist predators was examined by testing carapace strength. Results showed that C. maenas was a superior competitor to both C. sapidus and H. sanguineus for obtaining food, while the latter two species were evenly matched against each other. Regarding agonism, C. sapidus, was the “loser” a disproportionate number of times. C. sapidus carapaces also had a significantly lower breaking strength. These experiments suggest that both as a competitor, and as potential prey, juvenile blue crabs have some disadvantages compared with these common sympatric exotic crab species, and in areas where these exotics are common, juvenile native blue crabs may be forced to expend more energy in conflict that could be spent foraging, and may be forced away from prime food items toward less optimum prey.     

Adult cannibalism in an oligophagous herbivore,the Colorado potato beetle

Cannibalism, or intraspecific predation, can play a major role in changing individual fitness and population processes. In insects, cannibalism frequently occurs across life stages, with cannibals consuming a smaller or more vulnerable stage. Predation of adult insects on one another is considered to be uncommon. We investigated adult cannibalism in the Colorado potato beetle, Leptinotarsa decemlineata (Say), which is an oligophagous herbivore specializing on plants in family Solanaceae, and an important agricultural pest. Under laboratory conditions, starvation and crowding encouraged teneral adults to feed upon each other, which reduced their weight loss during the period of starvation. However, pupae were attacked and consumed before adults. Injured beetles had a higher probability of being cannibalized than intact beetles. Males were more frequently attacked than females, but that appeared to be a function of their smaller size rather than other gender‐specific traits. Cannibalizing eggs at a larval stage did not affect beetle propensity to cannibalize adults at an adult stage. When given a choice between conspecific adults and mealworms, the beetles preferred to eat conspecifics. Cannibalistic behavior, including adult cannibalism, could be important for population persistence in this species.     

Differential cannibalism and population dynamics in a host-parasitoid system

The effects of host cannibalism on a host-parasitoid system were explored through experiment and modelling. In individual encounters between parasitized and unparasitized Plodia interpunctella larvae, parasitized larvae were more likely to be cannibalized. Inclusion of this differential cannibalism into a simple Lotka-Volterra-type model of host-parasitoid population dynamics generates alternative stable states-including stable coexistence and extinction of the parasitoid — which depend on starting conditions. Possible mechanisms for differential cannibalism, and its implications for studies of host-parasitoid populations and biological control programmes are discussed.