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.     

Simultaneous spawning by female stream goby Rhinogobius sp. and the association with brood cannibalism by nesting males

A laboratory experiment was conducted by varying the undersurface area of nesting substratum and the number of females in an experimental tank to elucidate the determinants of the mating pattern in the stream goby, Rhinogobius sp. cross‐band type. Males with larger nests tended to attract two or more females to their nest in a tank. Moreover, males spawned simultaneously with multiple females and entire brood cannibalism by males was rarely observed under a female‐biased sex ratio. When males spawned with a single female with low fecundity, however, entire brood cannibalism occurred at a high frequency, suggesting that a male guarding a nest with fewer eggs consumes the brood. Therefore, spawning behaviour of females that leads to a large egg mass would decrease the risk of entire brood cannibalism. In this species, simultaneous spawning by multiple females in a nest serves as a female counter‐measure against entire brood cannibalism. These results suggest that a conflict of interest between the sexes through brood cannibalism is a major determinant of simultaneous spawning.     

Parental fish change their cannibalistic behaviour in response to the cost-to-benefit ratio of parental care

Partial filial cannibalism, the act of cannibalizing some offspring, has been explained as a response to the high energetic cost of care. I tested this hypothesis by manipulating the cost-to-benefit ratio of care in the scissortail sergeant, Abudefduf sexfasciatus, a tropical damselfish with male care. Background egg mortality was lower than the incidence of cannibalism, confirming that males did not just dispose of dead eggs. Investment in the current brood affected future investment, because males forced to skip a brood cycle put more effort into courtship during the following cycle and obtained larger broods than did unmanipulated males. Any factor influencing the cost-to-benefit ratio of parental care should also affect the incidence of cannibalism. I reduced the cost of care by supplementary feeding and reduced the benefit of care by simulating a decrease in paternity certainty through simulated intrusions by non-nesting males. Supplementary feeding significantly reduced partial filial cannibalism by parental males, a result compatible with the hypothesis that eggs are consumed to cover the energetic costs of parental care. Cannibalism decreased regardless of whether males were fed with conspecific eggs or crabmeat. Cannibalism was only reduced but not fully eliminated by supplementary feeding, and residual levels of cannibalism after feeding were similar to the background rate of egg mortality. Simulated intrusions by non-nesting males led to an increase in filial cannibalism and a decrease in parental effort.     

Filial cannibalism in an assassin bug

Filial cannibalism has been described in many fish species with male parental care, and has typically been explained as a response to high energetic costs of brood defence and decreased feeding opportunities during the period of care. We investigated filial cannibalism in an insect, the assassin bug Rhinocoris tristis. In this species, males guard eggs of a number of females, cannibalizing some of their offspring within the brood. We monitored guarding males in both the field and the laboratory. Males typically ate eggs around the periphery of the brood, which were those most likely to have been parasitized by wasps. However, cannibalism persisted in the laboratory in the absence of parasites, and the number of cannibalized eggs was related to the length of care and overall brood size, suggesting that males use eggs as an alternative source of food. This conclusion was further supported by the fact that males in the field did not lose weight while guarding, despite being unable to forage efficiently while caring. Males were also observed to adopt broods, but in a laboratory experiment did not eat more eggs from adopted than from their own broods.     

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.     

Brood conspicuousness and clutch viability in male‐caring assassin bugs (Rhinocoris tristis)

Abstract 1. Conspicuousness to mates can bring benefits to both males (increased mating success) and females (reduced search costs), but also brings costs (e.g. increased predation and parasitism). Assassin bugs, Rhinocoris tristis, lay egg clutches either on exposed stems or hidden under leaves. Males guard eggs against parasitoids. Guarding males are attractive to females who add subsequent clutches to the brood. This is an excellent opportunity to study the effects of conspicuousness on the fitness of males and females. 2. Using viable eggs in a multi‐clutch brood as a correlate of fitness, the present study examined whether laying eggs on stems affected (1) female fitness, through exposure to parasitism and cannibalism, and (2) male fitness, through attracting further females. 3. Stem broods were more parasitised. However, males on stems accumulated more mates and more eggs, a net benefit even accounting for parasitism. The eggs gained from being on a stem were cannibalised. By contrast, higher mortality on stems suggests that females should gain by ovipositing on leaves. To the extent that egg viability represents fitness, male and female interests may therefore differ. This suggests a potential for sexual conflict that may affect other species with male care. 4. Despite higher costs, females actually initiated more broods, and subsequently added bigger clutches to broods, on stems than under leaves. This suggests either that viable eggs do not reflect fitness, or that females laid in unfavourable locations. The key is now to address lifetime fitness, since unmeasured factors may affect offspring viability post‐hatching, and to investigate who controls the location of oviposition in R. tristis.     

Why egg-caring males of Isaza (<Emphasis Type="Italic">Gymnogobius isaza</Emphasis>, Gobiidae) refuse additional females: preliminary field observations

Like many other gobies, males of the Isaza goby, Gymnogobius isaza endemic to Lake Biwa, Japan, conduct parental care of eggs at nests, and females are likely to choose mates while visiting nests. The reproductive strategy should induce polygyny, but Isaza males never accept additional females in one breeding cycle. Sampling data of broods indicated that the egg mass areas were much smaller than the nest sizes, suggesting that nest size is not the limiting factor in obtaining further eggs from additional females. The brood size greatly decreased as the duration of care progressed. Few individuals including caring males ate eggs, and heterospecific egg predators were rarely observed. Sixty percent of egg masses at the middle stages of egg development were infected with aquatic fungi, some being covered with a fungus mat that drastically reduced survivorship. Infected egg masses contained more eggs than non-infected ones at the same stage, indicating that large egg masses are prone to be frequently destroyed by fungi. It is likely that the activity of parental males is lowered during the long care periods at low water temperature in early spring. Such lowered activity of caring males might be responsible for infections in large broods that would have needed more care. We propose the hypothesis that male rejection of additional females may be related to optimal brood size, which will be less susceptible to fungus infection and produce more hatching young than otherwise. This hypothesis will explain not only male avoidance of additional females but also some unique reproductive behaviors of this fish such as some females spawning of a portion of of the mature eggs in one nest.     

Mating affects reproductive investment into eggs,but not the timing of oogenesis in the flesh fly <Emphasis Type="Italic">Sarcophaga crassipalpis</Emphasis>

We examined the effects of mating on reproductive investment and the timing of oogenesis in the flesh fly Sarcophaga crassipalpis by exposing females to males or not. All females exposed to males were mated within a few days and we found that mating affected reproductive investment. Virgin females not exposed to males produced a large clutch of eggs (∼91), but females exposed to males and mated produced 10% more. There was no effect of mating on egg length or mass. There was also no effect of mating on the timing of oogenesis. Females in both treatments provisioned their eggs at the same rate with yolk first becoming visible in the oocytes on day three of adulthood and complete provisioning of eggs occurring by the seventh day of adulthood. We examined the biochemical basis of egg provisioning by identifying the yolk proteins and quantifying their blood titer during the oogenic period in both, females exposed to males and mated and those not exposed to males. There was no difference in the timing of the first appearance, peak titer, or disappearance of yolk proteins in the blood between the two treatments. However, consistent with our observation of greater egg production in mated females, these females contained a greater peak yolk protein titer.     

Female Mate Choice in a Paternal Brooding Blenny: The Process and Benefits of Mating with Males Tending Young Eggs

Female mate preference for males tending young offspring has been demonstrated in many fishes; however, not much is known about the choice process. Using the barred chin blenny Rhabdoblennius ellipes, a fish with male uniparental care, field experiments were conducted to investigate the female preference for males tending young eggs and then whether females choose the males with young eggs by discriminating young eggs from old eggs in the nests. Males tending young eggs (0‐ to 2‐d old) acquired new eggs nine times more frequently than those tending old eggs (3‐ to 5‐d old) regardless of other traits in males and nests. In the two egg‐switching field experiments (old to young and young to old), contrary to our expectation, male mating success was neither enhanced when given young eggs nor inhibited when given old eggs. These results suggested that females choose males with young eggs not by discriminating the developmental stage of eggs in the nests but by using other choice processes. By choosing males with young eggs, females may benefit from the dilution effects of egg predation and filial cannibalism risks and avoid male parental care failure.     

Delayed oviposition: a female strategy to counter infanticide by males?

Conflicts of interest between males and females can lead toan evolutionary arms race in which adaptations of each sex coevolve.Intersexual conflict is extreme in the brood caring, semelparousspider Stegodyphus lineatus; males encountering females thathave already produced their usually single egg sac attempt toremove and discard the egg sac and then remate with the female. Femalesthat cannot defend their eggs lose valuable time and fecundityby having to replace the clutch. Selection should favor femalesthat complete their suicidal maternal care as quickly as possiblebecause of the high risk of predation. However, some femalestake up to four times longer to oviposit than others. I proposethat females minimize the risk of male infanticide by postponingoviposition. Accordingly, early-maturing females, who sufferthe highest risk of infanticide by males, should have a longerinterval between maturation and oviposition than late-maturingfemales. The date of maturation significantly predicted theinterval between maturation and oviposition and explained upto 35% of its variation in a data set from a natural population andlonger term data from a seminatural, enclosed population. Bodysize was predicted to have a weak effect on the timing of ovipositionand was consistently less important than maturation date. Theobserved facultative timing of oviposition may have evolvedas a result of intersexual conflict over mating.     

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

Abstract.

• 1 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.
• 2 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.
• 3 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.
• 4 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.
• 5 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.
• 6 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.

     

Male altruism and wing polymorphism in a parasitic wasp

Males ofTrichogramma sp., a gregarious parasitoid which attacks eggs of the yellow-legged tussock mothIvela auripes (Lepidoptera: Lymantriidae), are polymorphic for wings. In mating within host eggs, no difference in mating success was observed between winged (large) males and wingless (small) males, whereas in mating outside eggs, the former were superior to the latter. Some wingless males were observed to perform sneaking copulation on egg masses. In the 1-male brood, which is thought to be founded by 1 mother wasp, the male size tended to decrease as the number of females per brood increased. But in the 2-male brood, which is assumed to be added with 1 more smaller male produced by the second mother wasp in double parasitism, the larger male did not reduce his size, compared with the male of the 1-male brood with an equal number of females. This phenomenon can be explained reasonably by a version of the kin-selection theory: When there is only 1 male in a host egg, he transfers resources in the egg to his sister females, but, when another male appears, he decides to act to the females less altruistically.     

Paternity, parental behavior and circulating steroid hormone concentrations in nest-tending male bluegill

Like many teleost fishes, bluegill (Lepomis macrochirus) are characterized by sole male parental care of offspring. In addition, bluegill parental males experience cuckoldry by specialized parasitic male morphs. This cuckoldry has previously been shown to influence the expression of parental care behavior. To better understand some of the proximate mechanisms mediating parental behavior, we examined the relationships between circulating steroid hormones, paternity, and parental behavior during the egg and fry stages of care in parentals that spawned during the first third of the breeding season. During the egg stage of care, we found that males with higher paternity had lower levels of testosterone, but there was no relationship between paternity and either 11-ketotestosterone or cortisol. There also was no relationship between the hormones and care behavior comprising fanning of the eggs, nest rim circles, chases of brood predators, or pecking at the eggs (indicative of egg cannibalism), except for a negative relationship between cortisol and pecking behavior. During the fry stage of care, we conversely found that males with higher paternity had higher levels of testosterone and 11-ketotestosterone. There also was a negative relationship between the concentrations of these two androgens and the defensive behavior of males when exposed to a potential brood predator (a pumpkinseed, Lepomis gibbosus). We discuss these results in relation to previous work in fishes and other vertebrate taxa. Overall, our data suggest a complex relationship between circulating steroid hormone levels, paternity and parental behavior.     

Nutritional implications for sexual cannibalism in a sexually dimorphic orb web spider

Models predicting mechanisms driving sexual cannibalism in spiders with sexual size dimorphism (SSD) often assume that spiders use post‐copulatory food to channel nutrients into eggs and fecundity is altered through changes in clutch size or egg mass. I tested these assumptions using an orb web spider with extreme SSD, Argiope keyserlingi. I fed mated female spiders prey of either high protein‐low energy or low protein‐high energy composition. I measured egg energy density; a measure of the relative volumes of yolk and albumen. I predicted that if A. keyserlingi increase their egg energy density upon feeding on prey of a specific nutrient composition, they could enhance their fecundity by investing in more energy dense eggs. However, if the egg energy densities are dissimilar to their post‐copulatory prey they must be drawing energy from their somatic reserves to invest in eggs. In a further experiment I allowed female spiders to mate with and cannibalize males to determine if cannibalism induces similar effects on egg energy density. Male spider protein energy ratio was measured and found to resemble the high protein‐low energy prey. I found disagreement between the composition of post‐copulatory food and eggs in both experiments. Additionally, spiders fed high protein‐low energy prey lost weight indicating that they draw on their energy reserves to invest in eggs. I thus concluded that spiders that feed on high protein‐low energy prey or on males increase their egg energy density and, possibly, fecundity. However, the nutrient content of the prey or males cannot provide for investment in eggs. The energy invested in eggs is drawn from somatic reserves, probably induced by an as yet undescribed physiological trigger.     

Host discrimination modulates brood guarding behaviour and the adaptive superparasitism in the parasitoid wasp Trissolcus semistriatus (Hymenoptera: Scelionidae)

Because hosts utilized by parasitoids are vulnerable to further oviposition by conspecifics, host guarding benefits female wasps. The present study aims to test whether female adults regulate brood guarding behaviour by host discrimination in a solitary parasitoid Trissolcus semistriatus by presenting an intact or parasitized host egg mass to a female adult. Virgin females without oviposition experience have host discrimination ability, which enables them to adjust the number of eggs laid in the hosts. Mating experience increases superparasitism by female adults, whereas mated females achieve a higher discrimination ability as a result of oviposition experience and show a lower superparasitism rate. As expected, females exhibit brood guard after parasitizing an intact host egg mass, whereas those females visiting a previously parasitized host egg mass, do not. Because the survival of eggs in superparasitized hosts is relatively low, regulating brood guarding behaviour by host discrimination is adaptive for female wasps.     

Within-nest spawning-site preferences of female bluefin damselfish: the effect of early-stage eggs

In some fish species with exclusive paternal care females prefer to deposit their eggs in nests containing early-stage eggs and avoid those containing only late-stage eggs. Such female preference may also be shown when it comes to deciding where to lay within a given nest; that is, females may prefer to lay contiguously to younger rather than to older eggs. To understand if females benefit from such preferences by obtaining higher offspring survival, we conducted field studies with the bluefin damselfish, Abudefduf luridus. We investigated (1) female between-nest and within-nest spawning-site preferences relative to brood characters and (2) egg-hatching success related to male filial cannibalism. We found evidence that males entirely ate some of their clutches, especially the eggs received near the end of the breeding season. These were also more susceptible to being eaten when laid in nests containing only eggs in a late stage of development. Theoretically, these patterns of clutch loss should result in adaptive female preference for nests containing early-stage eggs, but we found no evidence for such a preference in female A. luridus. However, once females had chosen a nest they strongly preferred to lay contiguously to early-stage eggs than to late-stage eggs. Moreover, females benefited from this decision by obtaining higher survival rates for their clutches. We conclude that within-nest spawning-site preference of the female for early-stage eggs may have evolved as an adaptive response to a dilution effect on the risk of egg loss.     

Egg Discrimination and Sex-Specific Pecking Behaviour in Parasitic Cowbirds

We studied egg‐pecking behaviour in males and females of three cowbird species: the shiny cowbird (Molothrus bonariensis), a host generalist brood parasite, the screaming cowbird (M. rufoaxillaris), a host specialist brood parasite, and the bay‐winged cowbird (Agelaioides badius), a non‐parasitic species. We conducted three experiments in which we offered each bird an artificial nest with two plaster eggs and recorded whether egg pecking occurred and the number of pecks on each egg. In expt 1, we tested if there were species and sex differences in egg‐pecking behaviour by offering the birds two spotted eggs of similar pattern. Shiny and screaming cowbirds responded in 40.3% and 44% of the trials, respectively, with females and males presenting similar levels of response. In contrast, bay‐winged cowbirds did not show any response. In expt 2, we tested if shiny cowbirds responded differentially when they faced a choice between one host and one shiny cowbird egg, while in expt 3, we tested if screaming cowbirds responded differentially when they faced a choice between one shiny and one screaming cowbird egg. Shiny cowbirds pecked preferentially host eggs while screaming cowbirds pecked more frequently shiny cowbird eggs. Our results show that egg‐pecking behaviour is present in both sexes of parasitic cowbirds, but not in non‐parasitic birds, and that parasitic cowbirds can discriminate between eggs of their own species and the eggs of their hosts or other brood parasites.     

A Test for Male Parental Care in a Fundulid, the Bluefin Killifish, Lucania goodei

Under field conditions, breeding male bluefin killifish, Lucania goodei, have been observed aggressively defending territories from other breeding males, non-breeding females, and minnows (mainly Notropis harperi). We performed an aquarium experiment to test whether male aggression serves to protect newly deposited eggs from predation. We allowed a male and a female to spawn in a yarn mop, removed the female, and exposed the eggs to one of four treatments (spawning male present, two minnows present, spawning mal+two minnows present, no adult fish present). Mops were censused daily for seven days. Egg predation rates were highest in the male+minnows and male only treatments. Egg predation rates in the male+minnows treatment did not differ from the predicted predation rate (sum of male only and minnows only treatments). Hence, there is no evidence for male parental care in L. goodei. In addition, we compared the egg predation rates (filial cannibalism) between males of 3 different color morphs and found no evidence for differential egg cannibalism.     

Eggshell characteristics and yolk composition in the common cuckoo Cuculus canorus: are they adapted to brood parasitism?

The developmental rate of cuckoo embryos and their hatching size is greater than that of host species, which may require more nutrient resources in the egg and more intensive gas exchange during development. In the present study, we compared various egg characteristics of a brood parasite, the common cuckoo Cuculus canorus, and its frequent host, the great reed warbler Acrocephalus arundinaceus. As maternally‐derived testosterone is known to enhance growth rate of embryos and hatchlings, cuckoo eggs are expected to contain higher concentration of testosterone than host eggs. In addition, we expected higher concentration of antioxidants in cuckoo eggs to protect embryos from oxidative stress associated with accelerated growth. Our results showed that cuckoo eggs had thicker shells and higher pore density than great reed warbler eggs. Yolk was significantly heavier in cuckoo eggs and contained higher concentrations of carotenoids and vitamin E, however, yolk androgen and immunoglobulin concentrations were lower in cuckoo eggs as compared to great reed warbler eggs. We also examined whether eggshell colour was associated to egg quality, and detected a positive association between blue‐green chroma and yolk antioxidant concentration in both species, suggesting that eggshell colour reflects the antioxidant investment of the female into the eggs. Our results suggest that cuckoo females increase the size, growth rate and competitive ability of their young by providing them with more nutrients and more dietary antioxidants for embryonic development, and not through elevated yolk testosterone or antibody levels. In addition, increased porosity of cuckoo eggshells may allow embryos to develop more rapidly because of a greater capacity of gas exchange.     

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.