Egg Cannibalism Research Articles

Explosive breeding reduces egg and tadpole cannibalism in the wood frog, Rana sylvatica

Cannibalism of anuran eggs and hatchlings by larger tadpoles has been documented in many species that inhabit seasonally ephemeral habitats and has been hypothesized to play an important role in favouring synchronized breeding. Using the wood frog, this hypothesis was tested by determining whether offspring of non-synchronized breeders were more vulnerable to cannibalism than offspring of synchronized breeders. In a laboratory experiment, small tadpoles of similar size did not cannibalize each other. However, large tadpoles preyed heavily on the eggs and hatchlings of conspecifics, and the incidence of predation increased with cannibal size. In natural populations, over 80% of adults bred explosively during a 3-day period, and their offspring were not cannibalized because hatching was synchronized and tadpoles varied only slightly in size. About 5% of adults oviposited late in the breeding season, and the resulting embryos hatched when tadpoles of synchronized breeders averaged 0·6–1·3 g. Larger tadpoles in the ponds cannibalized the eggs and hatchlings of these late late breeders. In a field experiment conducted at a natural breeding site, eggs that were added 7 days after embryos of late breeders hatched suffered complete mortality within 19 h. Similarly, more than 50% of hatchlings were cannibalized within 15 min after they were placed in the pond. These results are consistent with the view that synchronized breeding is an adaptation that reduces cannibalism in anurans that breed in temporary ponds.

Factors Associated With and Fitness Effects of Nest-Raiding in the Three-Spined Stickleback, Gasterosteus Aculeatus, in a Natural Situation

The occurrence and consequences of nest-raiding behaviours of male three-spined sticklebacks (Gasterosteus aculeatus L., forma leiura) were studied in an enclosed section of a small stream of the Tsuya River, Gifu Prefecture Central Japan. The observations were made almost daily on 99 males which were individually marked and the 189 nests built by them during the breeding season, March to mid July 1988. About 10% of the nests were subjected to raiding which included egg cannibalism, egg stealing and sneaking fertilizations. Most raidings were done by single territorial males. The probability of nest raiding was related to the degree of cover around the nest: nests in dense vegetation were most prone to raiders. The probability of raiding was further related to the stage of the nest: nests with eggs were most liable, those with fry least liable to raiding actions. Males that performed raiding behaviour could have nests in every stage, but most likely had no eggs in their nests. The probability of being raided was thus positively related to the number of neighbouring nests without eggs. Males that raided had a significantly duller overall nuptial coloration during the egg collecting phase than non-raiders. Body size and territory size did not differ between raiders and non-raiders. Raiders may thus be less attractive to ripe females. By egg stealing they may increase the attractiveness of their otherwise empty nest to spawning. Indeed, nests of raiders produced significantly more often young than those of non-raiders, but the number of young produced in successful nests was not different between the two categories of males. Nest-raiding was detrimental to the victims of raiding actions: raided nests produced less offspring early in the breeding season.

Cannibalistic Caterpillars (Utetheisa ornatrix; Lepidoptera: Arctiidae) Fail to Differentiate between Eggs on the Basis of Kinship

Utetheisa ornatrixlarvae, in exercising egg cannibalism, do not discriminate between kin and nonkin. Under natural conditions this may not be a handicap, partly because the larvae hatch largely in synchrony and do not immediately upon emergence engage in cannibalism.

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.

Reproductive competition in queenless honey bee colonies (Apis mellifera L.)

Previously we reported that there are subfamily differences in drone production in queenless honey bee colonies, but these biases are not always explained by subfamily differences in oviposition behavior. Here we determine whether these puzzling results are best explained by either inadequate sampling of the laying worker population or reproductive conflict among workers resulting in differential treatment of eggs and larvae. Using colonies composed of workers from electrophoretically distinct subfamilies, we collected samples of adult bees engaged in the following behavior: “true” egg laying, “false” egg laying, indeterminate egg laying, egg cannibalism, or nursing (contact with larvae). We also collected samples of drone brood at four different ages: 0 to 2.5-h-old eggs, 0 to 24-h-old eggs, 3 to 8-day-old larvae, and 9 to 14-day-old larvae and pupae. Allozyme analyses revealed significant subfamily differences in the likelihood of exhibiting egg laying, egg cannibalism, and nursing behavior, as well as significant subfamily differences in drone production. There were no subfamily differences among the different types of laying workers collected from each colony, suggesting that discrepancies between subfamily biases in egg-laying behavior and drone production are not due to inadequate sampling of the laying worker population. Subfamily biases in drone brood production within a colony changed significantly with brood age. Laying workers had significantly more developed ovaries than either egg cannibals or nurses, establishing a physiological correlate for the observed behavioral genetic differences. These results suggest there is reproductive conflict among subfamilies and individuals within queenless colonies of honey bees. The implications of these results for the evolution of reproductive conflict, in both queenright and queenless contexts, are discussed.

Indiscriminate egg cannibalism and reproductive skew in a multiple-queen ant

Societies of ants with several egg-laying queens (polygyny) permit the study of the evolution of a stable allocation of reproduction (reproductive skew). One factor that could influence the stable skew in the polygynous ant Leptothorax acervorum is cannibalism by queens of other queens9 eggs. To test for discrimination during egg-eating, isolated queens were offered a choice between their own eggs and eggs laid by either a nestmate queen or a queen from another colony. The eggs had been made distinguishable by exposing queens to dye. In a total of 45 trials, queens preferentially ate non-nestmate eggs but did not show a significant preference for a nestmate9s over their own eggs. This suggests that mutual egg-eating within colonies does not affect the stable reproductive skew. Once established, indiscriminate egg-eating could be evolutionarily stable because queens that give up egg-eating suffer the costs of having their eggs eaten but lose the nutritional benefits.

Intraclutch egg cannibalism by hatchlings of the land snailArianta arbustorum: non-random consumption of eggs?

Under natural conditions hatchlings of the land snail Arianta arbustorum cannibalize unhatched sibling eggs as well as eggs from neighbouring batches. Three series of choice experiments were conducted to determine whether cannibalistic hatchlings of A. arbustorum from four different populations discriminate (1) between fertilized and unfertiliz,ed eggs within the same batch, (2) between eggs containing well-developed embryos and ones with less advanced embryos, and (3) between small and large fertilized eggs. Newly-hatched snails did not discriminate between fertilized and unfertilized conspecific eggs. Similarly, hatchlings cannibalized in equal proportions eggs with well-developed embryos and eggs with less advanced embryos. However, cannibalistic hatchlings ate preferentially large eggs. The results of an additional choice experiment indicated that this size preference may be due to a higher encounter probability and/or a stronger attraction by chemical cues of larger eggs, and thus is not an actual ch...

Male mating success and female mate choice in the river sculpin,Cottus nozawae (Cottidae)

Mating success of males and its correlates were investigated in a natural population of the polygynous fluvial sculpinCottus nozawae. Furthermore, the female mate preference of this species was examined experimentally under alternative conditions for mating in a stream. The mating success of individual males (the number of females with which a male mated) ranged between 0 and 8 with a mean of 2.41 in 1983 and 2.52 in 1989, in a population of which the sex ratio was about 1 : 2 in both years, skewed toward females. Mainly due to the excess of nests without egg masses and the few nests with one egg mass, the distribution of male mating success did not fit a Poisson distribution, indicating its non-randomness. Male mating success was not correlated either with the size of the nest rocks or with the male size, suggesting that these two variables are not determinants of mating success. The mate choice experiments demonstrated that females of this species more frequently chose smaller males as mates whose nests already contained eggs than large males without eggs. Additionally, an analysis of stomach contents of guarding males suggested that the parental males ate their own eggs during egg guarding (filial-cannibalism). Based on these results and on a comparison of reproductive characteristics with congeneric species, it is suggested that one of the most important determinants for female mate choice inCottus species may be whether or not parental males are filial egg cannibals.

Search behavior associated with egg cannibalism in Toxorhynchites amboinensis and Toxorhynchites rutilus rutilus (Diptera: Culicidae).

Observations based on time-lapse video recordings were used to study behavior associated with egg cannibalism in fourth-instar Toxorhynchites amboinensis (Doleschall) and Tx. r. rutilus (Coquillett). Analysis indicated that, once triggered by finding of the first egg, larvae of both species engaged in a systematic search of the water surface in an attempt to find additional eggs, which were often seized and eaten. Seven behavioral elements were identified in the search repertoire, and their relationships studied by analysis of a matrix of preceding and succeeding behaviors. The pivotal behavior was "sweep-adjust," which accounted for 87.2% of the time budget in Tx. amboinensis and 73.3% in Tx. r. rutilus. Activity in sweep-adjust consisted predominantly of side-to-side sweeps of the head, held just below the surface, punctuated by small forward adjustments of position. Quantitative aspects of the sweep arcs, in terms of angular and linear velocity, were determined for the two species. Eggs encountered during search probably were detected by mechanoreception, only within a very limited, kidney-shaped zone (area approximately 9.8 mm2) centered at the anterior margin of the head. Eggs were seized with the lateral palatal brushes but without head extension as seen in strikes at subsurface prey.

The cost of parental care and egg cannibalism in the river bullhead, Cottus gobio L. (Pisces, Cottidae)

Male river bullheads guard and care for egg masses during a single brood cycle every breeding season. A study of two bullhead populations demonstrated that nesting males show a strong reduction in food intake rate and that their physical condition deteriorates during parental care. The estimated weight loss for the average guarding male was 18.8% in one population and 13.5% in the other. This could in part be responsible for the peak of male mortality observed during the second part of the breeding season. A high incidence of egg cannibalism was observed in males guarding eggs. Analysis of the developmental stage of individual egg masses demonstrated that heterocannibalism is very rare in this species and that the observed rate of egg cannibalism is mainly due to guarding males preying upon their own eggs (filial cannibalism). In both populations the frequency of filial cannibalism was negatively correlated with the male's chance of getting other food items. The probability of a male cannibalizing its own eggs was also significantly influenced by the time elapsed since the beginning of parental care. The observed limited cannibalism of progeny in the river bullhead cannot be explained as a male's strategy for obtaining energy to be used in subsequent brood cycles, as suggested for other fishes which show filial cannibalism. Rather, it can be interpreted as a behaviour aimed at avoiding the risk of dying of starvation before the eggs hatch. The observed criteria of female mate choice, i.e. a preference for males in good physical condition and for males that already have eggs in their nests, are consistent with the prediction of Rohwer's filial cannibalism theory, although other hypotheses cannot be excluded.

Ropalidia rufoplagiata: a polistine wasp society probably lacking permanent reproductive division of labour

Ropalidia rufoplagiata Cameron (Hymenoptera: Vespidae), a polistine species from penisular India, appears to be unique among all known primitively eusocial wasps. A total of 33 out of 46 identified females from an observed colony were found to oviposit on 1-17 occasions. No single predominant egg-layer could be identified during the 45-day period. Of the 17 dissected egg-layers, 12 were mated. All egg-layers showed several oviposition-related behavioural patterns including systematic, but indiscriminate, cannibalism of eggs and larvae, cleaning of empty cells, and guarding of freshly-laid eggs. There was no correlation between the egg-laying activity of the females (whether mated or not), oophagy, and their position in the dominance hierarchy. All nest-maintenance activities were performed exclusively by the egg-layers, while the non-egg-layers were mainly involved in the extranidal task offoraging. No significant morphometric differences between egg-layers and foragers could be discerned. Almost all the older individuals in the colony were egg-layers, while foragers were mainly younger animals. Such a temporal differentiation in reproductive labour suggests the absence of a permanent reproductive caste in this species.

Egg cannibalism among offspring: a particular case of parental investment in gastropods?

Egg cannibalism among offspring: a particular case of parental investment in gastropods?

Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract. Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches. First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field. In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii. In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide. Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues. Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

Egg cannibalism by milkfish (Chanos chanos Forsskal) spawners in circular floating net cages

Summary Egg cannibalism by milkfish spawners in a circular floating net cage was investiated. The cage was lined with a fine mesh hapa net to retain spawned eggs and to prevent the entry of kh eg predators. Water samples were collected from the surface (0 m), middle (1.5 m), and bottom (3.0 m) of a 10 m diameter by 3 m deep floating net cage at the time of initial detection of spawning (0 min) and at 30, 60, 120 and 240 min thereafter. The mean number of spawned eggs at the surface significantly decreased (P<0.05) 60 min after spawning and very few eggs were recovered 240 min later. There was no significant difference (P>0.05) in the mean number of spawned eggs collected from the middle and bottom of the net cage at various times after spawning. Eggs were found in the digestive tract of all milkfish sampled (n=6) at about 5 h after spawning, indicating that carive milkfish eat their own eggs. It is recommended that spontaneously spawned milkfish eggs shoud be collected immediately after spawning to avoid loss by egg cannibalism. Zusammenfassung Ei-Kannibalismus bei Milchfisch (Chanos chanos Forsskal) Laichern in runden Netzkäligen Es wurde Kannibalismus bei laichenden Milchfischen auf ihre eigenen Eier untersucht. Die Käfige waren mit feinmaschigem Netz ausgekleidet urn die abgelaichten Eier zurückzuhalten und um andere Rauber von außen abzuhalten. Wasserproben wurden von der Oberfläche (0 m), der Käfigmitte (1,5 m Tiefe) und vom Boden des schwimmenden Netzkäfigs (10 m Durchmesser) entnommen. Die Probennahme erfolgre unmittelbar nach dern Beginn des Laichaktes (0 min) und 30, 60, 120 und 240 Minuten danach. Die mittlere Zahl der abgelaichten Eier nahm innerhalb von 60 min signifikant ab (P<0,05) und nur noch wenige Eier wurden nach 240 min gefangen. Es gab zu keiner Zeit einen signifikanten Unterschied zwischen den Zahlen aus den Proben der Käfigmitte oder des Käfigbodens. Es wurden in den Verdauungstrakten aller untersuchter Laichfische Eier der eigenen Art gefunden, was auf das kannibalistische Verhalten hinweist. Es wird empfohlen die Eier unmittelbar nach dem Ablaichen abzufischen, um Verluste durch Kannibalismus weitgehend zu vermeiden.

Egg cannibalism by sticklebacks: spite or selfishness?

Although it is generally agreed that humans can be spiteful, there are few if any, unambiguous examples of spite by non-human animals. Data are presented suggesting that female threespine sticklebacks show spiteful behaviour. In the field, they seek out conspecific eggs to attack while largely ignoring those of a closely-related sympatric species, the blackspotted stickleback. This occurs despite the fact that the latter's nests are more abundant and less well protected. In the laboratory, female threespine sticklebacks attack the eggs of conspecifics more than those of blackspotted sticklebacks, those of sympatric conspecific females more than those of allopatric females, and older eggs more than younger ones. Because there was no evidence of greater energetic or nutritional advantages from eating conspecific rather than heterospecific eggs, or older eggs rather than younger ones, threespine sticklebacks may be spiteful. Alternative proximate and evolutionary hypotheses to explain this discriminant egg-eating are discussed.

Hatchery production of Florida red tilapia seed in brackishwater tanks under natural-mouthbrooding and clutch-removal methods

Hatchery production of Florida red tilapia seed (eggs, sacfry and fry) in brackishwater (12 ppt) tanks was studied on Lee Stocking Island (Exuma Cays, Bahamas) under two methods of broodstock management. Six above-ground tanks (34.2 m 2) were each stocked with 240 year-class 1 breeders (avg. wt. = 143 g) at a ratio of 3 females to 1 male. Seed production was monitored either under the natural-mouthbrooding method by collecting free-swimming (i.e., post-yolksac stage) fry from tanks every 8–16 days, or under the clutch-removal method by removing free-swimming fry from tanks, and eggs and sacfry from the mouths of brooding females every 15–16 days, and assessing the numbers of each. Seed production over a 3-month period under the natural-mouthbrooding method (3.3 seed m −2 day −1) was significantly lower ( P < 0.001) than that obtained under the clutch-removal method (91.7 seed m −2 day −1) which is among the highest reported for tilapia hatcheries. Poor seed production under the natural-mouthbrooding method was attributable to cannibalism of eggs and fry by adults. Hatching success of eggs in upwelling incubators averaged 64.8% with effects of densities of 462, 923, 1385 and 1846/1 not differing significantly ( P > 0.05). Fry obtained from artificial incubation were significantly ( P < 0.05) larger (9.9 mg vs. 7.5 mg) and more viable than those obtained through natural mouthbrooding as evidenced by higher survival (73.9% vs. 49.7%) during a 29-day sex-reversal period. The results suggest that the clutch-removal method, while more labor intensive, yields markedly higher numbers of viable fry for growout.

Habitat scale, female cannibalism, and male reproductive success in three-spined sticklebacks (Gasterosteus aculeatus)

We studied the effects of habitat scale (pool size) on the risk of egg cannibalism and the breeding behavior of three-spined sticklebacks (Gasterosteus aculeatus). Laboratory experiments showed that in pools with similar population density, a larger fraction of males nested in pools of 4.8-m2 surface area than in 15-m2 pools. Breeding males in the 4.8-m2 pools also had bigger territories, obtained more eggs, and were more aggressive toward intruders than those in the 15-m2 pools. The numbers of raids attempted on nests were similar in the two pool sizes. However, raiding-shoal sizes were larger, and hence individuals in these larger shoals were more succesful at overwhelming male territorial defenses in the 15-m2 pools than in the 4.8-m2 pools. At the field site, a salt marsh containing hundreds of tide pools of different sizes, sticklebacks settled at similar densities in small (<30 m2 surface area) and large (>355 m2) pools. This resulted in significantly more fish being present in large pools than in small pools, a concomitant increase in the amount of nest raiding, and a decrease in individual male reproductive success in large compared to small pools. A photogrammetry analysis of the salt-marsh pools suggests that the majority of fish breeding at the site will be subjected to a high risk of cannibalism because most fish nest in large pools. We conclude that spatial scale has a major influence on this species' breeding behavior and reproductive success.

Chemical basis of egg cannibalism in a caterpillar (Utetheisa ornatrix)

Larvae of the mothUtetheisa ornatrix are shown to cannibalize eggs in the laboratory. They proved most cannibalistic if they were systemically deficient in pyrrolizidine alkaloid (PA), the defensive agent that protectsUtetheisa at all stages of development against predation, and whichUtetheisa acquire as larvae from their food plant. In exercising cannibalistic choice,Utetheisa larvae feed preferentially on eggs that are PA-Iaden rather than PA-free. Egg cannibalism can therefore provideUtetheisa with a supplemental means of PA procurement. Moreover, presence of PA in the egg, while providing the egg with defense against predation, can increase its vulnerability to cannibalism. Although evidence is presented thatUtetheisa larvae cannibalize eggs in nature, it is argued that such feeding may occur only opportunistically in the wild, rather than as a matter of course.

Why do ladybirds (Coleoptera: Coccinellidae) cannibalize?

Cannibalism of eggs by larvae ofAdalia bipunctata, an aphidophagous species of ladybirds, is important for survival when aphids are scarce. Ladybirds survive longer by eating eggs of their own species rather than aphids. Since it costs less, in terms of larval growth, to eat eggs rather than aphids, cannibalism has a strong advantage under conditions of prey scarcity.

Queen behaviour, reproduction and egg cannibalism in multiple-queen colonies of the ant Leptothorax acervorum

This investigation deals with the social structure of multiple-queen colonies of the facultatively polygynous ant Leptothorax acervorum. Five colonies, from Norfolk, U.K., and containing, respectively, 11, 7, 8, 5 and 13 individually marked queens, were observed in laboratory nests for 200 h overall. Thirtyone queens were mated egg-layers, five were mated non-layers, two were virgin layers and six were virgin non-layers. Laying queens had significantly unequal egg productivities within two of the five colonies. Fecundity was positively correlated with queen size, feeding rate and brood handling rate in one colony each, and was unrelated to these in all remaining colonies. There was no association between fecundity and the rates of grooming and receiving grooming in any colony. Queens in all colonies ate eggs and in three colonies the majority of eggs laid were eaten. The majority of cannibalized eggs appearch to be health, reproductive eggs, and queens ate such eggs laid by both other queens and workers. Fecundity and egg-eating rate were positively associated in only one colony. Queens did not defend their eggs, and between-queen aggression and territoriality were almost totally absent. Workers reproduced at a low level in four colonies, but did not eat undamaged eggs. Aggression among workers was relatively common, and there were also three cases of prolonged aggression by workers towards individual queens. These findings suggest that L. acervrum's social system involves reproductive conflicts between queens, between workers and between workers and queens, but the lack of overt aggression apart from egg cannibalism also suggests that such conflicts may take complex, subtle forms.