Interspecific differences in male cannibalistic behavior between two sympatric cardinalfishes (Pisces: Apogonidae)

Cannibalistic behavior of a paternal mouthbrooding cardinalfish, Apogon notatus, was examined and compared with that of a sympatric congener, Apogon doederleini. In both species, males sometimes cannibalized their own entire broods, but their postcannibalistic behavior was markedly different. Males of A. doederleini respawned within a few days of cannibalism, usually changing mates, whereas males of A. notatus took several weeks to respawn, less frequently changing mates. This difference was attributed to mate availability for males. The operational sex ratio was female biased in A. doederleini but male biased in A. notatus, suggesting that the former males have higher mate availability and thus opportunities for remating soon after cannibalism. For male apogonids that accept only one clutch at a time, an effective way to compensate for reproductive loss entailed by filial cannibalism is to remate as soon as possible after cannibalism. The higher rate of filial cannibalism by A. doederleini than by A. notatus suggests that this cannibalism is facilitated by high mate availability. In contrast to filial cannibalism, heterocannibalism was more frequent in A. notatus. High population density and gregariousness may be important factors contributing to the frequent occurrence of heterocannibalism. Received: January 6, 1999 / Accepted: May 14, 1999     

Parents benefit from eating offspring: density-dependent egg survivorship compensates for filial cannibalism

Abstract Why should animals knowingly consume their own young? It is difficult to imagine many circumstances in which eating one's own young (i.e., filial cannibalism) actually increases an individual's fitness; however, filial cannibalism commonly co‐occurs with parental care in fishes. The evolutionary significance of filial cannibalism remains unclear. The most commonly accepted explanation is that filial cannibalism is a mechanism by which caring males gain energy or nutrients that they reinvest into future reproduction, thereby increasing net reproductive success. There is mixed support for this hypothesis and, at best, it can only explain filial cannibalism in some species. A recent alternative hypothesis suggests that filial cannibalism improves the survivorship of remaining eggs by increasing oxygen availability, and thus increases current reproductive success. This theory has received little attention as of yet. We evaluated the hypothesis of oxygen‐mediated filial cannibalism in the sand goby by examining the effect of oxygen and egg density on the occurrence of filial cannibalism, evaluating the effects of partial clutch cannibalism on the survivorship of remaining eggs, and comparing potential costs and benefits of filial cannibalism related to the net number of eggs surviving. Indeed, we found that oxygen level and egg density affected the occurrence of cannibalism and that simulated partial clutch cannibalism improved survivorship of the remaining eggs. Additionally, because increased egg survivorship, stemming from partial egg removal, compensated for the cost of cannibalism (i.e., number of eggs removed) at a range of cannibalism levels, filial cannibalism potentially results in no net losses in reproductive success. However, oxygen did not affect egg survivorship. Thus, we suggest a more general hypothesis of filial cannibalism mediated by density‐dependent egg survivorship.     

Avoidance of Filial Cannibalism in the Amphipod Gammarus pulex

Adult animals that cannibalise juvenile conspecifics may gain energy but also risk filial cannibalism, that is, consumption of their own offspring. However, individuals vary in the magnitude of the costs and benefits of cannibalism depending on factors such as their current energy reserves or the probability that they have offspring in the vicinity. They may therefore also vary in the extent to which they participate in cannibalism. This study investigated whether the sex or brooding status of adult amphipods (Gammarus pulex) influenced whether they participated in cannibalism of juveniles. For females carrying embryos within their brood pouch, we also investigated two hypotheses to explain the presence or absence of cannibalistic behaviour by determining whether cannibalism was correlated with factors that might reflect energy demands (body length, brood size), or that might reflect a temporal change in cannibalistic behaviour (corresponding to stage of brood development). All reproductive classes of adults participated in some level of juvenile cannibalism, but females carrying offspring at an advanced stage of development (close to emergence from the brood pouch) consumed significantly fewer juveniles than other groups. Females thus appear to significantly reduce cannibalism of juveniles concurrent with the time when their own eggs are hatching within the brood pouch, prior to the release of their offspring. Because the experiment tested female responses to unfamiliar juveniles, this reflects a temporal change in behaviour rather than a response to phenotypic recognition cues, although additional direct recognition cannot be ruled out. Brooding females with large brood sizes or large body lengths, which might have disproportionately greater energetic demands, were not more likely to cannibalise juveniles. We also noted that juveniles that survived in trials where cannibalism occurred were significantly more likely to be found at the water surface, suggesting a possible adaptation to escape cannibalistic adults. Overall, our results provide evidence that amphipods use indirect temporal cues to avoid filial cannibalism.     

Does Female Personality Determine Mate Choice Through Sexual Cannibalism?

Animal personalities (e.g. consistent across‐context behavioural differences between individuals) can lead to differences in mate choice. However, evidence for this link remains limited. Pre‐mating sexual cannibalism can be a behavioural syndrome (i.e. a suboptimal personality) in which adaptive female aggression towards heterospecific prey spills over on non‐adaptive aggression towards courting males, independently of the female mating or feeding status (i.e. the ‘aggressive spillover hypothesis’, ASH). On the other hand, sexual cannibalism can also be a form of mate choice by which females selectively kill or mate with males depending on the male phenotype. We introduce the hypothesis that the most aggressive females in the population will not only attack males more frequently, but will be less likely to impose sexual selection on males through sexual cannibalism. Assuming that in a field common garden experiment in which females were fed ad libitum the rate of weight gain by a female may reflect her voracity or aggressiveness, we show that in the cannibalistic burrowing wolf spider Lycosa hispanica (formerly L. tarantula), voracity towards heterospecific prey predicts a female's tendency towards sexual cannibalism. Unmated females with higher weight gains were more cannibalistic and attacked males regardless of the male phenotype. On the other hand, females that were less voracious tended to be less cannibalistic, and when they did kill a male, they were selective, killing males in poorer condition and mating with those in better condition. Our results demonstrate that females with different phenotypes (growth rates) differently imposed selection on male condition, tentatively supporting the hypothesis that female aggression levels can spill over on sexual selection through sexual cannibalism.     

The evolution of filial cannibalism and female mate choice strategies as resolutions to sexual conflict in fishes

Filial cannibalism (the consumption of one's own viable offspring) is common among fish with paternal care. In this study, I use a computer simulation to study simultaneous evolution of male filial cannibalism and female mate choice. Under certain conditions, selection on parental males favors filial cannibalism. When filial cannibalism increases a male's probability to raise the current brood successfully, filial cannibalism also benefits the female. However, when egg eating is a male investment into future reproduction, a conflict between female and male interests emerges. Here I investigate how female discrimination against filial cannibals affects evolution of filial cannibalism and how different female choice criteria perform against filial cannibalism. The introduction of discriminating females makes the fixation of filial cannibalism less likely. I introduced three different female choice criteria: (1) females who could discern a male's genotype, that is, whether the male was going to eat eggs as an investment in future reproductive events; (2) energy-choosing females that preferred to mate with males who had enough energy reserves to live through the current brood cycle without consuming eggs; and (3) females that preferred to mate with already mated males, that is, males with eggs in their nest. Genotype choice never coexisted with filial cannibals at fixation and filial cannibals were unable to invade a population with genotype-choosing females. Energy choice was successful only when males had high energy reserves and were less dependent on filial cannibalism as an alternative energy source. The egg choosers frequently coexisted with the cannibals at fixation. When the female strategies were entered simultaneously, the most frequent outcome for low mate sampling costs was that both the cannibals and the egg choice was fixed and all other strategies went extinct. These results suggest that sexual conflicts may not always evolve toward a resolution of the conflict, but sometimes the stable state retains the conflict. In the present case, this was because the egg-preference strategy had a higher fitness than the other female strategies. The outcome of this simulation is similar to empirical findings. In fish with paternal care, male filial cannibalism and female preference for mates with eggs commonly co-occur.     

Male sexual cannibalism in a sand‐dwelling wolf spider with sex role reversal

Sexual cannibalism usually involves females attacking and consuming males before, during or after copulation. Sex role reversed systems may provide insight into the debate about whether it arises as mistaken identity, a spillover in female aggressiveness, foraging decisions, and/or extreme mate choice. In such systems, males may be selective and voracious to compensate for their higher reproductive costs, and thus males may be the sexually cannibalistic sex. Allocosa brasiliensis shows a reversal in sex roles and male‐biased sexual size dimorphism (the opposite of the common pattern in spiders). The present study aimed to test whether males cannibalize or mate according to female reproductive status or body characteristics. Each of 20 adult males was consecutively exposed to one virgin and one mated female, alternating the order of exposure. Males preferred to mate with virgin females in good body condition and heavier‐mated females. Males attacked 15% of virgins and 40% of mated females and cannibalized 10% and 25% of the total trials, respectively. The astonishing male cannibalistic behaviour best agrees with extreme mate choice hypotheses because attacks were more frequent on mated females of low body condition. This is the first report of male sexual cannibalism in a sex role reversed system. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 68–75.     

Challenging the Aggressive Spillover Hypothesis: Is Pre‐Copulatory Sexual Cannibalism a Part of a Behavioural Syndrome?

Pre‐copulatory cannibalism – females devouring males during courtship – may bring no benefit to either sex. The ‘aggressive spillover hypothesis’ (ASH) posits that pre‐copulatory cannibalism represents a spillover of female aggressiveness from the juvenile foraging context, when aggressiveness is advantageous, to the adult mating context, when aggressiveness may be non‐adaptive or maladaptive. The ASH suggests that individuals exhibit limited plasticity in aggressive behaviours because they are genetically canalised for indiscriminate aggressiveness towards prey and conspecifics, including males. Hence, a tendency to employ pre‐copulatory cannibalism is a part of the female aggression syndrome, an assertion generally accepted in the personality field. We here re‐evaluate the previous findings in the light of personality criteria, which we propose for ASH validation: between‐individual differences, repeatability and heritability in tendency for pre‐copulatory attacks (and pre‐copulatory cannibalism) and voracity towards prey, and their correlation. To re‐evaluate ASH and to allow for additional or alternative explanations, we ask whether pre‐copulatory cannibalism depends on female hunger, mating status, size and/or male quality. Finally, we ask whether cannibalistic females have a reduced reproductive success as predicted by the ASH. While repeatability and heritability in voracity towards prey and its correlation with the tendency to engage in pre‐copulatory cannibalism were found in certain systems, we lack any evidence for repeatability and heritability in pre‐copulatory cannibalistic attempts and for its maladaptiveness. Rather than only resorting to the ASH, foraging and mate choice hypotheses may also explain pre‐copulatory cannibalism. We suggest clarifying the use of the terms sexual cannibalism (effect) and female aggressiveness or tendency to attack and devour males (cause), and argue that male strategies to avoid cannibalism should be considered. We propose testing the ASH as the explanation for pre‐copulatory cannibalism in those cases where female tendency to devour males correlates with actual pre‐copulatory cannibalism and when all the above criteria are fulfilled. Finally, we propose future directions for studying the ASH.     

Sexual cannibalism in Nephila plumipes as a consequence of female life history strategies

The evolution of sexual cannibalism has been modelled as both an adaptive and nonadaptive female strategy. Recent evidence from several species suggests a connection between female foraging and sexual cannibalism, but the precise benefits for females have remained obscure. Here, we investigate the difference between cannibalistic and noncannibalistic female Nephila plumipes by removing the potential nutritional benefit of cannibalism. Courting and mating males that were killed by a female were immediately removed so that the female could not consume them. Nevertheless, cannibalistic females gained more mass from maturation to oviposition and produced larger first clutches than noncannibalistic females, although cannibalistic females matured at a smaller size and mass than noncannibalistic females. In juvenile instars, mass gain was generally smaller in females that moulted in a good condition but intermoult intervals were shorter. However, the time from maturity to oviposition was not shorter in females that matured in a good condition. Male behaviour did not differ according to the risk of cannibalism. We suggest that sexual cannibalism in N. plumipes is a side‐effect of an increased foraging vigour of females that matured at a smaller size and body mass. Selection pressure on males to avoid cannibalism may be weak because of limited mating opportunities.     

Does a single meal affect female reproductive output in the sexually cannibalistic praying mantid Iris oratoria?

1. One explanation of the evolution of sexual cannibalism, the female’s consumption of a male during or following courtship or copulation, is that this behaviour increases the female’s fitness. This study tests the assumption that a single meal increases female reproductive output significantly in the sexually cannibalistic praying mantid Iris oratoria L. 2. In 38 mating trials, seven of the females cannibalised the males. In order to augment the number of females that fed, an additional nine females were each fed one cricket nymph at the end of the mating trial. 3. Three measures of female reproductive output – the occurrence of oviposition, the mass of the first ootheca, and the number of eggs in the first ootheca – increased significantly with female feeding condition, which was a reflection of food consumed before the mating trial. Females that copulated later in the season tended to lay lighter oothecae. 4. The females’ consumption of a meal during the mating trial, either a conspecific male or a cricket, did not influence any measure of reproductive output significantly, although possible effects upon subsequent oothecae cannot be ruled out. 5. If, as the present study suggests, a single meal provides a negligible or delayed benefit to female reproductive output, the evolution of sexual cannibalism might lie in alternative explanations, which include possible fitness benefits to cannibalistic females in the nymphal stage or possible paternity benefits to the cannibalised males.     

Egg cannibalism in river blennies: the role of natural prey availability

The abundance of benthic macro-invertebrates, the main prey of river blennies Salaria fluviatilis , decreased drastically through the blenny reproductive season in the River Matarraña, south-east Spain. Despite this, females maintained their body condition, while the body condition of males increased. The latter coincided with the onset of egg guarding, which is carried out by males and which provided them with an opportunity to cannibalize eggs. Indeed, significantly more males than females were egg cannibals. The proportion of cannibalistic males increased as the season progressed, but the overall frequency remained low (7·4%). The number of eggs eaten was not related to the weight of macro-invertebrates ingested by males. In addition, the body condition of cannibalistic and non-cannibalistic males was similar and was not correlated with the number of eggs ingested. It is possible that non-cannibalistic males may have eaten and digested eggs prior to capture. It is concluded that even in productive rivers such as the Matarraña, males may still rely on filial cannibalism to survive until the end of the parental care period.     

Cannibalism in whitefish (Coregonus lavaretus)

Summary Cannibalism in whitefish (Coregonus lavaretus) is studied on the basis of an evolutionary model. The model predicts that individuals may be cannibalistic if they gain sufficiently in terms of fitness relative to the reduction in survival caused by this behaviour. If cannibalistic forms mainly increase survival it is predicted that cannibalism is particularly likely to be an evolutionarily optimal strategy if only a few age classes are being cannibalized and if, simultaneously, many age classes are cannibalistic. The same pattern, although less apparent, emerges on the basis of a model assuming that cannibalistic forms mainly increase fecundity.The whitefish in River Sokna spawn during late October to late November. Males dominate the spawning run numerically. Growth rate in mature stages is low, 1.0 cm·y^-1 for males and 1.3 cm·y^-1 for females. Yearly survival rate in mature stages is 0.574, and survival from egg to mature is 0.000078%. Larger whitefish on the average lay more and larger eggs than do smaller. Females were more cannibalistic than males; in total cannibalism contributed to an egg mortality of at least 8.8%. This is consistent with the derived theoretical predictions.Our theoretical and empirical analyses on whitefish are supported by the observed lack of sexual differences in the cannibalistic behaviour of brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus).     

Filial Cannibalism in the Paternal Mouthbrooding Cardinalfish Apogon lineatus: Egg Production by the Female as the Nutrition Source for the Mouthbrooding Male

We investigated about filial cannibalism by Apogon lineatus based on 25 mouthbrooding males sampled in Tokyo Bay, Japan. Eggs were found in the stomachs of all mouthbrooding males, indicating that Apogon lineatus performs partial brood cannibalism. The number of eggs in the stomachs ranged from 1015 to 9384, corresponding to 30% on average of the entire brood. This study revealed that mouthbrooding males could gain considerable energy by partial brood cannibalism during brood periods, that is, females would produce surplus eggs as the nutrition sources for starving males.     

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.     

Cannibalism as an interacting phenotype: precannibalistic aggression is influenced by social partners in the endangered Socorro Isopod (Thermosphaeroma thermophilum)

Models for the evolution of cannibalism highlight the importance of asymmetries between individuals in initiating cannibalistic attacks. Studies may include measures of body size but typically group individuals into size/age classes or compare populations. Such broad comparisons may obscure the details of interactions that ultimately determine how socially contingent characteristics evolve. We propose that understanding cannibalism is facilitated by using an interacting phenotypes perspective that includes the influences of the phenotype of a social partner on the behaviour of a focal individual and focuses on variation in individual pairwise interactions. We investigated how relative body size, a composite trait between a focal individual and its social partner, and the sex of the partners influenced precannibalistic aggression in the endangered Socorro isopod, Thermosphaeroma thermophilum. We also investigated whether differences in mating interest among males and females influenced cannibalism in mixed sex pairs. We studied these questions in three populations that differ markedly in range of body size and opportunities for interactions among individuals. We found that relative body size influences the probability of and latency to attack. We observed differences in the likelihood of and latency to attack based on both an individual's sex and the sex of its partner but found no evidence of sexual conflict. The instigation of precannibalistic aggression in these isopods is therefore a property of both an individual and its social partner. Our results suggest that interacting phenotype models would be improved by incorporating a new conditional ψ, which describes the strength of a social partner's influence on focal behaviour.     

Effect of the presence of predatory cues and hunger on cannibalistic behaviour of ladybird beetle,Menochilus sexmaculatus Fabricius (Coleoptera: Coccinellidae)

1. Cannibalism and its role in population dynamics, along with various factors influencing the rate of cannibalism, have been widely studied across taxa.
2. The effects of predatory cue concentrations and starvation on cannibalistic tendencies and other life-history traits in cannibalistic and non-cannibalistic adults of Menochilus sexmaculatus were investigated.
3. Egg cannibalism increased with increasing predatory cue concentration and was maximum in high predatory cue treatment; increased with starvation irrespective of their diet history.
4. Latency to cannibalise eggs was shorter for cannibalistic adults as compared to non-cannibalistic adults irrespective of their hunger status and concentration of conspecific cues.
5. Non-cannibalistic females have higher fecundity than cannibalistic females.
6. In conclusion, both cannibalistic and non-cannibalistic individuals respond differently to intrinsic (hunger) and extrinsic cues (predatory cue concentrations). Cannibalistic individuals cannibalise more than non-cannibalistic ones at low levels of starvation and predatory cues.
7. Our finding suggests that cannibalistic individuals are better at assessing the risk and removing future competitors, which might favour these individuals over non-cannibalistic ones in adverse conditions and increased competition.

     

Filial cannibalism by mouthbrooding males of the cardinal fish,Apogon doederleini, in relation to their physical condition

Synopsis Paternal brood cannibalism was observed in a population ofApogon doederleini in Shikoku Island, Japan. Of 361 egg masses mouthbrooded by males, 47 disappeared within a day of spawning. A stomach check with a syringe ascertained that they had been consumed by the males. The frequency of this cannibalism increased as the breeding season advanced. As males completed 4–7 breeding cycles in a breeding season and spent 80% of the time mouthbrooding without taking ordinary food, their physical condition deteriorated greatly late in the breeding season. We concluded that parental physical condition is an important factor in the occurrence of brood cannibalism.     

You eat what you are: personality‐dependent filial cannibalism in a fish with paternal care

Many animal parents invest heavily to ensure offspring survival, yet some eventually consume some or all of their very own young. This so‐called filial cannibalism is known from a wide range of taxa, but its adaptive benefit remains largely unclear. The extent to which parents cannibalize their broods varies substantially not only between species, but also between individuals, indicating that intrinsic behavioral differences, or animal personalities, might constitute a relevant proximate trigger for filial cannibalism. Using a marine fish with extensive paternal care, the common goby (Pomatoschistus microps), we investigated the influence of animal personality on filial cannibalism by assessing (1) behavioral consistency across a breeding and a nonbreeding context; (2) correlations between different breeding (egg fanning; filial cannibalism) and nonbreeding (activity) behaviors, and, in a separate experiment; (3) whether previously established personality scores affect filial cannibalism levels. We found consistent individual differences in activity across contexts. Partial filial cannibalism was independent of egg fanning but correlated strongly with activity, where active males cannibalized more eggs than less active males. This pattern was strong initially but vanished as the breeding season progressed. The incidence of whole clutch filial cannibalism increased with activity and clutch size. Our findings indicate that filial cannibalism cannot generally be adjusted independently of male personality and is thus phenotypically less plastic than typically assumed. The present work stresses the multidimensional interaction between animal personality, individual plasticity and the environment in shaping filial cannibalism.     

Adaptive filial cannibalism in the beaugregory damselfish

Cannibalism of small numbers of offspring by a parent has been proposed as an adaptive parental strategy, by providing energy to support parental care. There are few empirical studies, however, to support this hypothesis. The beaugregory damselfish, Stegastes leucostictus, is a marine teleost that does not actively ventilate its eggs by fanning them. Partial cannibalism is common in this species, but in field studies was found to be unrelated to ration level. Filial cannibalism differed from predation in the pattern of egg eating; filial cannibalism was characterised by a random pattern of egg loss from a clutch rather than an aggregated distribution. Embryos developed quicker and had higher survival rates when they were at low densities and in nest sites where oxygen levels were high, and experimental reduction of oxygen levels increased rates of filial cannibalism. Here I present a hypothesis for filial cannibalism in the beaugregory damselfish; males cannibalise egg clutches in order to reduce clutch density and improve oxygen supply to the remaining embryos. I use a model of filial cannibalism to demonstrate how oxygen mediated cannibalism may be adaptive, and discuss the evolution of filial cannibalism in the beaugregory damselfish and other teleosts.     

Effects of a low oxygen environment on parental effort and filial cannibalism in the male sand goby, Pomatoschistus minutus

In fish, brood cycling parental males sometimes eat some orall of their eggs, a behavior termed filial cannibalism. Wetested predictions of filial cannibalism models related to thecost of parental care in the male sand goby, Pomatoschistusminutus, by increasing the parental effort (fanning expenditure)through reduced levels of dissolved oxygen to 39% in an experimentalgroup, whereas a control group had fully saturated water. Malesshowed both full-clutch cannibalism and partial-clutch cannibalismin both treatments. Giving the males one to three females tospawn with, we found that small clutches were completely eatenmore often than were larger ones, whereas partial-clutch cannibalismwas not affected by clutch size. Although treatment did notaffect filial cannibalism, it did affect a male's energy statesuch that males in the low oxygen treatment lost more body fat,indicating a greater fanning effort. This shows that males inthe low oxygen treatment allocated more energy to the presentbrood, potentially at the expense of future reproductive success.Our study strongly suggests that filial cannibalism in malesand gobies represents a strategic life-history decision asan investment in future reproductive success, and is not triggeredby a proximate need for food necessary for the male's own survival.Furthermore, males in the low oxygen treatment built nests withlarger entrances, and were less likely to rebuild their nestsafter destruction. Presumably, this makes fanning easier butthe nest more vulnerable to predators, suggesting a trade-offbetween fanning and nest defense.     

The cannibalistic behaviour of two Gammarus species (Crustacea: Amphipoda)

This study examines the cannibalistic behaviour of the freshwater amphipods Gammarus duebeni celticus Stock & Pinkster, 1970 and G. pulex (L., 1758). In the first experiment, interactions were staged among all combinations of single adult males, single adult females, adults in the precopulatory mate-guarding phase and juveniles. Cannibalism by inter-moult individuals on newly moulted conspecifics occurred in all interaction categories in both species. Gammarus d. celticus , however, were significantly more cannibalistic than G. pulex. Cannibalism between and within sex and size categories (males > females > juveniles) was facilitated by the vulnerability of individuals at moult. Individuals of smaller size categories, however, did not cannibalize newly moulted conspecifics of larger size categories. Males were less cannibalistic on newly moulted females than on newly moulted males and juveniles and, when in the precopulatory condition, appeared to defend females from cannibalistic attacks. In a second experiment, stream conditions were simulated in the laboratory and replicated populations monitored for nine weeks. High levels of cannibalism, and the species and sex differences in cannibalism identified in the first experiment, were confirmed under these heterogeneous conditions. Cannibalism by males on their newly moulted female mating partners, termed 'reversed' sexual cannibalism, was further investigated. When males were deprived of foraging opportunities, cannibalism of precopulatory partners was significantly more frequent. The occurrence of 'reversed' sexual cannibalism is thus interpreted as a conflict between motivation to feed and motivation to mate.