Frequency Of Cannibalism Research Articles

Subadult experience influences adult mate choice in an arthropod: exposed female wolf spiders prefer males of a familiar phenotype.

Current sexual selection theory proposes several potential mechanisms driving the evolution of female mating preferences, few of which involve social interactions. Although vertebrate examples of socially influenced mating preferences do exist, the invertebrate examples are virtually nonexistent. Here I demonstrate that the mating preferences of female wolf spiders can be acquired through exposure as subadults to unrelated, sexually active adult males. I first conducted exposure trials during which subadult females of the wolf spider Schizocosa uetzi were allowed to interact with mature males of an experimentally manipulated phenotype (either black or brown forelegs). After maturation, these previously exposed females were paired with a male of either a familiar or unfamiliar manipulated phenotype for mate-choice trials. Subadult females that were exposed to directed courtship by mature males of a particular morphological phenotype were subsequently more likely to mate with a male of a familiar phenotype as adults. Furthermore, females that were exposed as subadults were more likely, as adults, to cannibalize a courting male with an unfamiliar phenotype. Unexposed females did not distinguish between phenotypes in either mate choice or cannibalism frequency. These results suggest a previously uncharacterized mechanism influencing the origin of female mating preferences and ultimately the evolution of male traits: subadult experience. This study also stresses the potential importance of learning and memory on adult mate choice in an arthropod.

Egg Laying Preference, Larval Dispersion, and Cannibalism in <I>Helicoverpa armigera</I> (Lepidoptera: Noctuidae)

Abstract We investigated ovipositional preference of Helicoverpa armigera (Lepidoptera: Noctuidae) for a range of host plants, larval performance on a range of host plants, dispersion rate of a concentrated population of fifth instar larvae, the fitness consequences of cannibalism at two levels of food availability, and the frequencies of cannibalism between larvae of different instars. Eggs laid by adult females were concentrated on some specific plants, despite the wide range of host plants of H. armigera. However, the larvae dispersed when they reached high larval density and eventually exhibited a uniform spatial distribution. Cannibalism frequently occurred under poorer nutritional conditions or greater larval rearing density. The effect of cannibalism on development and pupal weight differed between rich and poor nutritional rearing conditions. The cannibals’ fitness was decreased under suitable food conditions, whereas larvae with a low frequency of cannibalism increased their pupal weight, a poten...

Fitness consequences of sexual cannibalism in female Argiope bruennichi

The evolution of sexual cannibalism as the most extreme form of nuptial feeding is still poorly understood. Although increasing evidence suggests that female aggressiveness is related to other aspects of foraging behaviour, it is not clear whether the nutritional value of a male is sufficient to provide an adaptive significance for sexual cannibalism. A widely cited though rarely tested explanation is based on a paternal investment model, and predicts that consumption of a male results in increased female fecundity. The available evidence is either correlational or restricted to species with relatively large and potentially nutritious males, and different studies have come to different conclusions. Here we present a test of the paternal investment hypothesis using the very cannibalistic and highly size-dimorphic spider Argiope bruennichi. After a preset schedule, we had females consume none, one or two males independent of the female's cannibalistic behaviour. Consumption of male bodies did not result in any detectable fitness benefit for the female: neither the number of clutches, nor clutch size or hatching success were affected by consumption of males. The frequency of cannibalism was around 80%, independent of the female mating status. We did not observe male complicity, but cannibalism was associated with prolonged copulation. This suggests a sexually selected benefit of cannibalism for males. We conclude that the paternal investment hypothesis does not explain the existence of sexual cannibalism in A. bruennichi and probably not in other spider species with a pronounced sexual size dimorphism.

Exotic crayfish in a brown water stream: effects on juvenile trout, invertebrates and algae

SUMMARY1. The impact of the introduced omnivorous signal crayfish (Pacifastacus leniusculus) on trout fry, macroinvertebrates and algae was evaluated in a brown water stream in southern Sweden usingin situenclosures. We also examined the gut content of all surviving crayfish in the enclosures. Two crayfish densities in addition to a control without crayfish were used in replicate enclosures (1.26 m2) in a 1‐month experiment. Additionally, 20 trout fry (Salmo trutta) were stocked in each enclosure to assess the effects of crayfish on trout survival and growth.2. Detritus was the most common food item in crayfish guts. Animal fragments were also frequent while algae and macrophytes were scarcer. Crayfish exuviae were found in crayfish guts, but the frequency of cannibalism was low.3. Trout survival in enclosures was positively related to water velocity but was unaffected by crayfish.4. Total invertebrate biomass and taxon richness were lower in crayfish treatments. The biomass of all predatory invertebrate taxa was reduced but only three of six non‐predatory taxa were reduced in the crayfish treatments.5. Epiphytic algal biomass (measured as chlorophylla, on plastic strips) was not related to crayfish density, whereas the biomass of epilithic algae (measured as chlorophylla) was enhanced by high water velocity and high crayfish density. The latter was possibly mediated via improved light and nutrient conditions, as active crayfish re‐suspend and/or remove detritus and senescent algal cells during periods of low water velocity.6. We conclude that the introduced signal crayfish may affect stream communities directly and indirectly. Invaded communities will have reduced macroinvertebrate taxon richness and the signal crayfish will replace vulnerable invertebrate predators such as leeches. In streams that transport large amounts of sediment or organic matter, a high density of crayfish is likely to enhance benthic algal production through physical activity rather than via trophic effects.

The Effect of Limb Loss on the Courtship and Mating Behavior of the Wolf Spider Pardosa Milvina (Araneae: Lycosidae)

Limb loss is common in the wolf spider Pardosa milvina, appearing in nearly one third of adult males but occurring less frequently among adult females and juveniles. Since males wave their first pair of legs during courtship displays, the reproductive consequences of limb loss may be significant. We measured the courtship and mating effects of the loss of one, two, or four legs among adult male P. milvina. Missing one or two legs did not significantly reduce a male's ability to mate, but missing four legs was detrimental to mating success, reduced both courtship intensity and copulation duration, and increased cannibalism frequency. Results suggest behavioral flexibility in compensating for limited leg loss and a defensive function of the anteriormost legs to thwart female cannibalism attempts.

Sexual cannibalism and sperm competition in the golden orb-web spider Nephila plumipes (Araneoidea): female and male perspectives

Mating systems are frequently shaped by conflicts over reproductive interests between males and females. Sexual cannibalism can be an especially dramatic manifestation of such conflicts. However, the resolutions of this conflict differ among sexually cannibalistic spider species. Cannibalism may be in the interest of both sexes when females consume males as a foraging decision to improve fecundity and/or males sacrifice their bodies to increase fertilization success. In other species, females exert sequential choice of partner by selectively terminating copulation through cannibalism while males fail to obtain a paternity advantage. Here, we investigate the adaptive value of cannibalism in the orb-web spider Nephila plumipes where 60% of males do not survive copulation. Virgin females in poor condition are more frequently cannibalistic and more likely to kill large males, but the frequency of cannibalism among mated females is not influenced by these factors. Instead, males that mate with mated females increase their fertilization success by being cannibalized. Cannibalized males generally mate for longer, but longer copulations correspond with increased paternity only in mated females. The amount of sperm from particular males that a female stored was not influenced by any of the measured variables. The number of sperm stored was not related to paternity, nor was there any detectable reduction in sperm number after females had reproduced. Our data suggest that the conflict between the sexes differs between virgin and mated females. Females should always cannibalize a male, but males only gain from cannibalism when mating with mated females, not when mating with virgin females. Interestingly, the frequencies of cannibalism are not different in matings with virgin or mated females. Key words: cannibalism, foraging, mating, paternity advantage. [Behav Ecol 12:547–552 (2001)]

Factors which affect the occurrence of cannibalism and the broad-headed "cannibal" morph in larvae of the salamander Hynobius retardatus

Cannibalism in amphibian larvae may be suppressed among siblings in comparison to distant relatives or nonkin, even when a "cannibal" morph that can consume conspecifics shows adaptive advantages. Two experimental studies were undertaken to analyze factors which affect the frequency of cannibalism and the occurrence of the broad-headed "cannibal" morph in larvae of the salamander Hynobius retardatus. The first experiment investigated whether or not the broad-headed "cannibal" morph is only induced after performing cannibalism. Because the broad-headed "cannibal" morph was observed in larval populations that showed no cannibalism, it was concluded that the "cannibal" morph could be induced without actual cannibalism. Second, possible factors affecting the occurrence of the broad-headed "cannibal" morph were analyzed with respect to the density of larvae, level of food supply, and kinship among larvae, alone or in combination. Appearance of the broad-headed "cannibal" morph was affected by interactive effects of density×kinship: although the morph was induced significantly more often at a higher density if the conspecifics were distantly or not related, it was strongly suppressed even at high density if larval kinship was very close or among siblings. In contrast, the frequency of cannibalism was independently affected by larval density, level of food supply, and kinship among larvae: it was significantly larger at high than at low larval densities, at low than at high food supply, and in mixed-sibling groups than in pure sibships. These results suggest that the "cannibal" morphs in H. retardatus are induced even without cannibalism at a high density of conspecifics in mixed-sibling groups, but the occurrence of this morph, which continuously consumes conspecifics, is suppressed among siblings.

Cod (Gadus morhua L.) cannibalism in the Central Baltic: interannual variability and influence of recruit abundance and distribution

Baltic cod feed mainly on clupeoids and invertebrates. Other fish, including cod, form only a small part of their diet. To examine the frequency of cannibalism in the Central Baltic, stomach data were analysed for 1963–1990. During this period, cod in cod stomachs in the Gotland Basin constituted 2.8% by weight of the total food content, while the frequency of occurrence was 1.1%. Cannibalism was recorded mainly in cod >35 cm, and the size range of cod found in stomachs was 5–15 cm. Cannibalism was observed in restricted areas only and varied strongly between years. The intensity of predation on cod was significantly different between the periods 1969–1975, 1976– 1979, and 1980–1990. Until 1980, the population in the eastern part mainly inhabited near-bottom layers. Higher abundance of recruits and their wide distribution raised the level of cannibalism. Development of stagnation during the 1980s resulted in the reduction of recruitment and stock size. The distribution of the adult population changed from near-bottom to mid-water during the first half of the year. The low abundance of small cod and the differences in distribution between small and large fish appear to have been the major factors determining very low predation on cod during 1980–90. Overall, the influence of cod cannibalism on recruitment success is negligible in the Central Baltic. Stock dynamics in the area are determined by the combined effects of variable oceanographic conditions and the fishery. 2000 International Council for the Exploration of the Sea

Age‐related cannibalism and horizontal transmission of a nuclear polyhedrosis virus in larval Spodoptera frugiperda

Summary1. Experiments were carried out to investigate the incidence of cannibalism throughout the larval development of the noctuid moth Spodoptera frugiperda, and to examine the risk of infection from consuming conspecifics infected with a nuclear polyhedrosis virus (SfNPV).2. Cannibalism was observed commonly even when food was not limiting, but occurred more frequently at low food quantities and/or high rearing densities. The sex of the larvae had no effect on the incidence of cannibalistic behaviour, however the probability of cannibalism occurring was affected by larval stage. The frequency of cannibalism was significantly higher among fifth‐ and sixth‐instar larvae than among earlier instars, and larvae were more likely to consume younger conspecifics than larvae of the same stage.3. Fifth‐instar larvae offered fourth‐instar victims fed equally on healthy larvae, virus‐infected larvae (2 days post‐infection), uninfected corpses, and virus‐killed corpses (6 days post‐infection). Horizontal transmission of SfNPV was only recorded in larvae offered virus‐killed corpses, however, and total mortality in this treatment was only 32%.4. In a similar experiment, fourth‐instar larvae avoided cannibalising virus‐killed corpses. Horizontal transmission of SfNPV was recorded in fourth‐instar larvae that consumed 2‐day post‐infected larvae. The low incidence of cannibalism observed in fourth‐instar larvae, however, suggests that this is unlikely to provide an important route for the transmission of SfNPV.

Fitness consequences of cannibalism in the fall armyworm, Spodoptera frugiperda

We investigated the consequences of cannibalism for some correlates of fitness in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae). The benefits gained by cannibals were ascertained by comparing survival, development rate, and pupal weight of larvae that had the opportunity to cannibalize with those that did not, at two levels of food availability. Larvae in the cannibalism treatments were provided with a conspecific one instar younger than themselves on five dates throughout larval development. Cannibalism was frequent; given the opportunity all larvae predated at least one younger conspecific. The frequency of cannibalism was not affected by the sex of the cannibal or by the availability of alternative food. However, cannibals suffered a significant reduction in survival at both high and low food availability. Furthermore, cannibals had a lower pupal weight in the high food treatment and a reduced development rate in the low food treatment. The only detectable fitness benefit associated with cannibalism was a positive correlation between the number of victims consumed and development rate under conditions of low food availability. On balance, cannibalism appears to be costly; alternative explanations for its occurrence in this species are discussed.

Filial Cannibalism in the Swordtail Xiphophorus Helleri (Poeciliidae)

To understand behaviour during filial cannibalism in swordtails (Xiphophorus helleri), the parturition behaviour of eight individually kept females was recorded on videotape. Three levels of female activity (low, medium and high) were quantified by measuring the duration of each. Four additional behavioural events (non-cannibalistic feeding, as well as the birth, attack and cannibalism of juveniles) were quantified by determining the frequency of each. Females gave birth most frequently at a low level of activity and at this level of activity they most often gave birth at the top of the tank. Of all the attacks by females on the young, 84.4% occurred in the light. Most attacks were recorded at the bottom of the tank and 84.0% of all cannibalism occurred at the bottom. Cannibalism was most successful at the bottom of the tank with a cannibalism:attack ratio of 1:2.2 and least successful in the middle where no cannibalism was recorded. In the light, females spent more time at the top of the tank, whereas in the dark they spent more time at the bottom. It was suggested that the rate of cannibalism might be reduced if parts of the tank were kept constantly dark and if females were restricted from reaching those areas in the tank where the frequency of cannibalism was highest, namely the top and the bottom of the tank. Experimental designs and working hypotheses for future studies are discussed.

Cannibalism and interspecific predation in two predatory ladybirds in relation to prey abundance in the field

Life tables for two predatory ladybirds,Coccinella septempunctata andHarmonia axyridis, were constructed in two years in which prey abundance differed. The prey aphid,Aphis gossypii, was abundant on its primary host from late May to late June. Females ofH. axyridis andC. septempumctata laid their eggs during the increase and peak in aphid abundance. The oviposition period ofC. septempunctata started before and was shorter than that ofH. axyridis. In both species, intraguild predation and/or cannibalism of the egg and fourth instar stages, but rarely of other developmental stages, were observed. Fourth instar larvae ofH. axyridis had to complete their development when aphids were scarce more frequently than those ofC. septempunctata. The highest frequency of intra- and interspecific predation was of fourth instarH. axyridis larvae. In terms of intraguild predation, the larvae ofH. axyridis preyed on larvae ofC. septempunctata, but the reverse was not observed. Percentage survival from egg to adult inH. axyridis was higher than inC. septempunctata in both years, and least in both species in the year of low aphid abundance. These results suggest that prey abundance influenced the frequency of cannibalism and intraguild predation, which were important in structuring this guild of ladybirds.

Alternative Routes for the Horizontal Transmission of a Nucleopolyhedrovirus

Two alternative routes for nucleopolyhedrovirus transmission were investigated usingMamestra brassicaelarvae: cannibalism of infected larvae and the release of virus prior to the death of the diseased host. The low frequency of cannibalism observed suggests that this is not a relevant transmission route in this species. However, larvae were shown to transfer viable virus to the environment before death through either defecation or regurgitation. Over 40% mortality was observed in larvae reared in diet containers where infected hosts had previously fed. Virus transfer to cabbages also occurred before death of the infected host, as revealed by plant bioassay. Virus was not detected in the feces or regurgitate of diseased larvae until the late stages of infection.

The influence of cannibalism and prey density on growth in the damselfly Coenagrion hastulatum

The effects of prey density and cannibalism on individual growth rate in similar sized Coenagrion hastulatum (Zygoptera) larvae were studied in a 66 day laboratory experiment. The frequency of cannibalism decreased with increasing alternative prey densities. No significant difference in damselfly growth rate was found between intermediate and high alternative prey densities, but larvae with the lowest alternative prey densities grew more slowly. This pattern is attributed to cannibalism. Cannibals should have gained extra nutrients from consuming conspecifics. In addition cannibalism might have decreased exploitation competition at intermediate prey densities. In fact, some of the largest individuals from intermediate prey densities grew as fast or faster than the smallest individuals in the high alternative prey treatments. Individuals that were cannibals early were larger at the end of the experiment than late cannibals. Also, individuals that ate several conspecifics were larger at the end the experiment. The results suggest that cannibalistic individuals from low alternative-prey-density habitats can grow and develop as fast as those from high alternative-prey-density habitats.

Effect of Prey Vulnerability on Population Size Structure of a Gape‐Limited Predator

It is becoming apparent that population size structure can significantly affect ecological interactions (Ebenman and Persson 1988). Theoretical and empirical studies, for example, show how population size structure can affect population regulation (Lomnicki 1988) and community structure (Neill 1988, Persson 1988). To understand fully how size structure affects ecological interactions, we must understand the factors that contribute to size structure of populations. Size variation within a population can arise from age differences among individuals (e.g., different year classes or asynchrony in breeding) or growth differences among individuals of the same age. Increased size variation within even-aged populations is generally considered to result from unequal food intake among individuals (Lomnicki 1988), which can be affected by the intensity of competition (Begon 1984, Maret and Collins 1994), the relative strengths of exploitative versus interference competition (Lomnicki 1988, Smith 1990), and differences among individuals in foraging behavior under risk of predation (Turner and Mittelbach 1990). We hypothesized that prey vulnerability could be another factor influencing population size structure. If, in a population of gape-limited predators, some types of prey are not equally vulnerable to all individuals, unequal food intake may occur (Smith and Petranka 1987), resulting in increased size variation among individuals. In a gape-limited predator, prey vulnerability is a function of prey size relative to predator size, and this disparity in size, not abundance of prey alone, determines whether or not prey can be caught or eaten by a predator (Smith and Petranka 1987, Dong and Polis 1992). Factors influencing relative size of predator and prey thus determine a predator's success. In instances of cannibalism, population size structure (i.e., relative distribution of small to large conspecifics) can have a major influence on the ratio of potential predators to prey within a population (Crowley et al. 1987, Wissinger 1989, Dong and Polis 1992). Understanding the factors affecting size structure can be fundamental to understanding what controls frequency of cannibals in a population.

Prey density effect on cannibalism by Toxorhynchites towadensis (Diptera: Culicidae).

The effect of prey density on cannibalism by the larvae of Toxorhynchites towadensis (Matsumura) was studied in the laboratory. Frequency of cannibalism was compared among pairs of all possible instar combinations of Tx. towadensis in the presence and absence of Aedes albopictus (Skuse). Cannibalism occurred despite the presence of prey larvae, but more frequently between different instars than the same instars. Cannibalized larvae were always younger than or the same age as their attackers. Six predatory larvae were reared in a container with 30, 60, or 120 prey throughout their development, and cannibalism and development were observed. No cannibalism was observed when prey density was 120. However, in the continuous presence of 30 prey, cannibalism occurred on 8 occasions. Cannibalism at a prey density of 60 was intermediate in frequency. Most (92%) cannibalism occurred when 1st or 2nd instars attacked the same or younger instars. The time in cohabitation of different instars was shorter with increasing prey density.

Cannibalism and the Resulting Dimorphism in Larvae of a Salamander Hynobius retardatus, Inhabited in Hokkaido, Japan

Abstract A cannibalism in the larvae of a salamander (Hynobius retardatus) and a resultant dimorphism were firstly described in laboratory-raised population. The cannibalistic larva develops to a “broad-headed” morph which has a wider head and grows faster compared with a non-cannibalistic “typical” morph. Laboratory experiments were conducted to examine a possible relationship between the dimorphism and cannibalism. Level of food supply and kinship of larvae affected the frequency of cannibalism. Low level of the food supply resulted in higher incidence of the cannibalism. The frequency of cannibalism in siblings was significantly lower than in the mixed-sibling groups. Possible biological significance of the cannibalism in this species was discussed.

Araneophagic jumping spiders discriminate between the draglines of familiar and unfamiliar conspecifics

Three species of jumping spiders – Portia fimbriata, P. labiata and P. schultzi – were tested for ability to distinguish between draglines of familiar versus unfamiliar potential rivals of the same species and sex, where the familiar rival was an individual that had been victorious in an earlier agonistic interaction. In choice tests, P. labiata females spent more time on the side of the cage covered by draglines of the unfamiliar conspecific female. However, there was no evidence of discrimination by females of the other two species or by P. labiata males. Frequency of cannibalism is suggested as the ultimate cause of variation in reaction to familiar versus unfamiliar draglines, as P. labiata females are known from other studies to be especially cannibalistic.

Individual responses to population size structure: the role of size variation in controlling expression of a trophic polyphenism.

We investigated how size structure affects development of alternative larval phenotypes in Arizona tiger salamanders, Ambystoma tigrinum nebulosum, by testing the hypothesis that population size structure per se is a significant component of an individual's environment. Larvae of this subspecies exhibit one of two feeding phenotypes; typical larvae eat zooplankton and macroinvertebrates and cannibalistic larvae feed primarily on conspecifics. Previous laboratory experiments showed that larval density positively affected expression of the cannibalistic phenotype. In this study we tested the hypothesis that size variation among larvae also serves as a cue triggering development of the cannibalistic phenotype. We report laboratory experiments and field observations showing that both an individual larva's position in a size distribution and the amount of size vaiation among larvae serve as cues stimulating development of cannibalistic larvae. Larval density and population size structure provide a larva with an indication of the abundance and vulnerability of potential conspecific prey. Size variation among larvae, in turn, appears to be influenced by larval density. Thus, a complex relationship exists between larval density, population size structure, and the frequency of cannibals within a habitat.

Inter-population differences in propensity for egg cannibalism in hatchlings of the land snail Arianta arbustorum

Abstract. Under natural conditions hatchlings of the land snail Arianta arbustorum cannibalize unhatched sibling eggs. Newly hatched A. arbustorum from different populations (from a lowland forest, a subalpine forest and an alpine pasture in Switzerland) differed significantly in the frequency of cannibalistic attacks on conspecific eggs. The percentage of cannibalistic hatchlings ranged from 50·0% in a subalpine forest to 87·8% in a lowland forest. Two populations were consistent in the proportion of cannibalistic hatchlings over 3 years, while in a third population the proportion of cannibalistic hatchlings varied between years. Hatchlings from populations with a high frequency of cannibals also began to eat eggs at an earlier age. In two populations, the proportion of cannibalistic hatchlings per batch increased over the course of the season, while in a third population the proportion of cannibals per batch was constantly high. Propensity for egg cannibalism was not correlated with absolute egg size, suggesting that the amount of energy and nutrients received during embryonic development did not affect cannibalistic behaviour during the hatchling stage. Differences in the investment in single eggs could explain the inter-population variation in propensity for egg cannibalism in A. arbustorum.