Intraspecific egg destruction in marsh wrens: a study of mechanisms preventing filial ovicide

Marsh wrens, Cistothorus palustris, attack the nests of other birds, including conspecifics. The tendency of wrens to attack conspecific nests raises the question: what prevents breeding individuals from destroying their own offspring? In this study the mechanisms that prevent filial ovicide (i.e. the destruction of eggs by parents) are examined. The results suggest that male filial ovicide is prevented by the presence of a female in the nest area, which presumably inhibits the male's ovicidal tendencies. In addition, incubating females aggressively exclude males from their breeding area, thereby further reducing the threat to their nest. Female filial ovicide is prevented through the inhibition of intraspecific nest-destroying behaviour in breeding females and through the ability of individual females to recognize their own nest site and nest. Differences between the intraspecific nest-destroying behaviour of male and female marsh wrens may reflect different reproductive strategies of the two sexes.     

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.     

Environmental and genetic determinants of ovicide in parasitic wasp Bracon hebetor

Superparasitism occurs when a parasitoid lays a second clutchof eggs on a host previously parasitised by herself or a conspecific.Ovicide refers to a parasitoid destroying an existing clutchof eggs on a parasitized host before laying a second clutch.We investigated environmental and genetic determinants of ovicidein the parasitic wasp Bracon hebstor. Characterization of egglayingbehavior revealed that B. hebetor commits ovicide during thehost examination phase of oviposition. The temporal costs ofovicide were found to be relatively small for females that experiencedlow rates of host encounter, whereas the costs of ovicide increasedfor females that experienced a high rate of host encounter.Individual wasps committed ovicide on conspecifically parasitizedhosts more frequently than on self-parasitized hosts. Manipulationexperiments suggested that B. hebetor females learn about theirenvironment while foraging and commit ovicide on the basis ofthe travel time between successive hosts. Significant differenceswere also found in ovicidal behavior among laboratory and fieldpopulations of B. hebetor. The implications of our results forclutch size theory and the evolution of ovicide are discussed.     

Division of labour during incubation in a woodpecker Colaptes auratus with reversed sex roles and facultative polyandry

The contribution of males to incubation has rarely been studied in altricial birds because the pursuit of extra mating opportunities is believed to conflict with incubation. Woodpeckers show reversed sex roles in parental care with males doing most of the nest construction, incubating and brooding of the young while females may be polyandrous. I investigated incubation by each sex at 71 monogamous and four polyandrous nests of the Northern Flicker Colaptes auratus , predicting that males would contribute to incubation according to their energy reserves (body condition) whereas females would contribute based on alternate reproductive opportunities. Nest attendance was 99% with males contributing a mean of 66% of the total incubation including nocturnal incubation. The length of daytime bouts averaged about 2 h and did not differ between the sexes. Consistent with predictions of investment strategies, structurally larger males and those in poorer body condition incubated less than smaller males, perhaps because they required more recess time to forage or to conserve energy. Older females contributed less incubation than young females and polyandrous females contributed less incubation at their secondary nests than monogamous females. Incubation period, nest depredation rate and hatching success were not influenced by bout length, number of bouts or relative contribution of the sexes. Hatching success was 86% at nests of both monogamous and polyandrous females because males compensated for reduced female participation. Because incubation of the sexes is compensatory and not additive, incubation pattern did not influence short-term reproductive success. I conclude that males invest in incubation according to their energy needs, and females may adjust their contributions based on alternate reproductive tactics.     

Mate availability affects female choice in a fish with paternal care: female counterstrategies against male filial cannibalism

Theory predicts that individuals should adopt counterstrategies against intersexual conflict with their mating partners if the counterstrategies are effective and cost-efficient. In fishes, males with parental care often cannibalize their own offspring, which reduces the female’s fitness and creates intersexual conflicts. Males of the goby Rhinogobius flumineus cannibalize more eggs in the nest when they have access to additional females prior to spawning. Thus, it is predicted that females will strategically avoid spawning with males that have high mate availability. In the present study, we experimentally tested this prediction. When sexual pairs were placed in tanks, most females (control females; 21/22) successfully spawned inside the nest. In contrast, when a gravid female (stimulus female) that was housed in a small transparent cage was shown to the experiment pairs prior to spawning, only about half of the females (experiment females; 16/29) spawned inside the nest; the remaining females released unfertilized eggs outside of the nest. Moreover, experiment females infrequently accepted and followed males into nests, and delayed spawning more often than control females. R. flumineus females prefer males that court frequently. Indeed, experiment females that infrequently received courtship tended to spawn outside of the nest. However, infrequent courtship alone could not explain outside-nest spawning, delay in spawning, or the shorter stay of females in nests. These results imply that the presence of a stimulus female dampens female spawning with males. We suggest that R. flumineus females may strategically reject or hesitate to spawn with males that have high mate availability, and that this spawning avoidance may be a counterstrategy against male filial cannibalism.     

Prolactin and parental behavior in Adélie penguins: effects of absence from nest, incubation length, and nest failure

Adélie penguin (Pygoscelis adeliae) males and females, nesting in Antarctica, alternate attendance at the nest with absences of many days to forage at sea. We investigated the importance of tactile input from egg and chicks on prolactin levels by observing nest attendance patterns and obtaining blood samples (1) during the first nest exchange of the incubation stage, (2) from birds whose incubation period was artificially increased or decreased by about 10 days, and (3) from birds whose nests had failed. Prolactin levels in females after 8 to 11 days of absence from the breeding colony did not differ from those in incubating males and did not change after females resumed incubation. Moving eggs between nests resulted in nests in which chicks hatched after about 26, 36 (normal), or 46 days. Duration of incubation did not affect prolactin levels in the parents measured during incubation, at the pip stage, hatch stage, or early brood stage. Adults first left their chicks unguarded on about the same calendar date, regardless of chick age. However, chicks from long incubation nests averaged 8 days younger when they were left unguarded than chicks from control or short-incubation nests. In females, there was no effect of nest failure on prolactin levels. In males, prolactin levels were slightly lower after nest failure than in males tending nests. Testosterone was significantly higher in males after nest failure than in males still tending nests. Prolactin is elevated in Adélie penguins as part of the program of cyclical hormonal changes that accompany the lengthy reproductive season and is relatively independent of tactile input. Sustained prolactin secretion is probably required for the maintenance of parental behavior in offshore feeding species that must be absent from the nest for many days at a time.     

Predation risk affects trade-off between nest guarding and foraging in Seychelles warblers

The fitness costs of egg loss for Seychelles warblers (Acrocephalus sechellensis)on Cousin Island are considerable because warblers have a single-eggclutch and no time to lay a successful replacement clutch. Onthe islands of Cousin and Cousine, with equal densities of Seychellesfodies (Foudia sechellarum), nearly 75% of artificial eggs placedin artificial nests were predated by fodies after 3 days. OnAride Island with no fodies present, loss of artificial eggswas not observed. Female warblers incubate the clutch, and malewarblers guard the clutch when females are absent. Deterrenceof fodies by male warblers is efficient: loss rate of eggs fromunattended warbler nests was seven times as high as from attendednests, and the more nest guarding, the lower the egg loss andthe higher the hatching success. Egg loss is independent ofthe amount of incubation by females. There is no trade-off betweenincubating and foraging by females. Nest guarding competes withforaging by males, and this trade-off has a more pronounced effecton egg loss when food availability is low. The transfer of breeding pairsfrom Cousin to either Cousine with egg-predating fodies or toAride without fodies allowed us to experimentally investigatethe presumed trade-off between nest guarding and foraging. OnCousine, individual males spent the same amount of time nestguarding and foraging as on Cousin, and egg loss was similarand inversely related to time spent nest guarding as on Cousin.Males that guarded their clutch on Cousin did not guard theclutch on Aride but allocated significantly more time to foragingand gained better body condition. Loss of warbler eggs on Aridewas not observed. Time allocation to incubating and foragingby individual females before and after both translocations remainedthe same.     

Egg speckling patterns do not advertise offspring quality or influence male provisioning in great tits

Many passerine birds lay white eggs with reddish brown speckles produced by protoporphyrin pigment. However, the function of these spots is contested. Recently, the sexually selected eggshell coloration (SSEC) hypothesis proposed that eggshell color is a sexually selected signal through which a female advertises her quality (and hence the potential quality of her future young) to her male partner, thereby encouraging him to contribute more to breeding attempts. We performed a test of the SSEC hypothesis in a common passerine, the great tit Parus major. We used a double cross-fostering design to determine whether males change their provisioning behavior based on eggshell patterns they observe at the nest. We also tested the assumption that egg patterning reflects female and/or offspring quality. Because birds differ from humans in their color and pattern perception, we used digital photography and models of bird vision to quantify egg patterns objectively. Neither male provisioning nor chick growth was related to the pattern of eggs males observed during incubation. Although heavy females laid paler, less speckled eggs, these eggs did not produce chicks that grew faster. Therefore, we conclude that the SSEC hypothesis is an unlikely explanation for the evolution of egg speckling in great tits.     

Mate-sharing costs in polygynous Northern Lapwings Vanellus vanellus

In this study bigamous female Northern Lapwings Vanellus vanellus received significantly less incubation relief from their males than monogamous females. On average, monogamous males spent 34.3% of their time incubating and bigamous males 29.9%. Bigamous males divided their effort between their nests, incubating on average 9.4% on primary nests and 20.5% on secondary nests. Bigamous females compensated for the lack of male relief. Primary females incubated for 71.8% of their time, secondary females for 64.2%, while monogamous females spent 52.7% of their time incubating. As a result, there was no significant difference in total nest attentiveness among nests of different status. Primary and secondary females received equivalent incubation relief from the male. Bigamous males increased their contribution to incubation significantly as the season progressed. A bigamous male's distribution of incubation relief between his females was unrelated to female body mass, or to the degree of asynchrony between primary and secondary females in arrival and laying. Incubation time was significantly, negatively, correlated with total nest attentiveness. Monogamous females spent most time, secondary females spent an intermediate time, and primary females spent the least time on maintenance behaviour (foraging, comfort behaviour, inactivity). No significant differences were found in hatching success among females of different mating status. However, the ratio of unhatched to hatched eggs (i.e. the eggs that remained in the nest at the time of hatching) differed significantly: secondary females hatched a smaller proportion of their eggs than monogamous and primary females.     

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.     

Have your cake and eat it too: male sand gobies show more parental care in the presence of female partners

Traditionally, male parental effort and mate attraction effortare expected to be in conflict as they compete for the sameresource budget. However, the quality of care provided by themale may be of a direct benefit to females and may provide animportant mate choice cue. In a laboratory experiment, we examinedhow males modified their parental behavior with respect to matingopportunity by allowing male sand gobies to mate with a singlefemale either in a big or small nest (a constraint on futuremating potential). We then exposed half of these males to thevisual stimulus from additional females and recorded male eggfanning and nest building (two components of care), courtshipbehavior, and reproductive success through out the brood cycle.We found that males fanned longer and more frequently and didmore nest construction in the presence of females and in bignests. Males guarding large nests courted females more thandid males guarding small nests. All males consumed eggs duringthe brood cycle, but complete clutch cannibalism was most frequentwhen males were guarding small nests in the absence of females.The pattern of filial cannibalism that we observed suggeststhat males prematurely terminated care when their reproductivepotential was low, that is, when there was little nest spacefor additional mating and no mates present. We found no supportfor a trade-off between mate attraction and parental care. Indeed,taken together our results suggest that males may use parentalcare as a courtship strategy and that males who invest in mateattraction also have higher parental effort.     

中华蛸繁殖行为

为了解中华峭(Octopus sinensis)繁殖行为特征,通过肉眼观察及水下摄像对其行为进行研究.结果 表明,中华蛸在繁殖期有运动、捕食、求偶、交配、产卵和护卵行为.中华蛸运动依靠漏斗喷水的反作用力进行游泳和爬行;以突然袭击的方式捕食日本蟳(Charybdis japonica),繁殖后期不再进食;中华蛸具明显的求...     

What makes a nest-building male successful? Male behavior and female care in penduline tits

Why do females increase parental effort when caring for theoffspring of attractive males? First, attractive males may bepoor fathers so that their females are compelled to increasetheir own contribution in order to fledge some young (the partner-compensationhypothesis). Second, females mated to attractive males may bewilling to increase their parental effort to reap high indirectbenefits for their offspring, and in turn males can decreasetheir own contribution (the differential allocation hypothesis[DAH]). We investigated these hypotheses in the penduline titRemiz pendulinus, a small passerine bird that has sequentialpolygamy by both sexes and strict uniparental care either bythe male or the female. We focused on two sexually selectedmale traits: nest size and nest-building behavior. We show thatmale care is unrelated to nest-building behavior, whereas femalesare more likely to care for the offspring of those males thatspend more time nest building. Females also more likely carefor the offspring of males that build large nests. Consequently,the reproductive success of males increases with nest size andnest-building behavior. Our results are consistent with theDAH and suggest that nest-building behavior and nest size areunder postmating sexual selection in penduline tits.     

Nonindependent mating in a coral reef damselfish: evidence of mate choice copying in the wild

Theoretical and experimental studies have shown that mate choicecopying is a viable mating strategy under certain conditions.Copying experiments in fish have been conducted primarily inthe laboratory, except for one study conducted in the fieldunder artificial conditions. We investigated whether in a wildpopulation of the coral reef whitebelly damselfish (Amblyglyphidodonleucogaster) females copy the choice of other females. Femalespreferentially spawn with males that have recently mated. Todetermine if the presence of new eggs in the nest was the reasonfemales chose mates or whether females were mate choice copying,we conducted egg-switching experiments. Eggs from males thatrecently mated were donated to males that had no eggs. If femalesare mate choice copying, then donor males with no eggs in thenest should continue to receive additional eggs. If femalesare using the presence of new eggs as the criterion for matechoice, then foster males with new eggs should receive additionaleggs. We found that donor males received new eggs significantlymore often than expected. More females mated with donor malesthan foster males. Furthermore, females preferentially choseto mate with males whom they had seen mating with another female.Females appear to remember the mate choice of other femalesand choose to mate with those same males even after 1 day. Theseresults suggest that females may be copying the mating decisionof other females rather than choosing males based on the presenceof new eggs in the nest.     

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.     

Accepting unrelated broods helps replacement male yellow-headed blackbirds attract mates

Replacement male yellow-headed blackbirds (Xanthocephalus xanthocephalus)did not destroy broods sired by the previous territorial maleand they showed no aggression toward females with unrelatedbroods. To test whether their tolerance of unrelated young wasmisdirected normal parental care, we removed males from experimentalterritories after primary nests were completed but before secondarynests were initiated. Replacement males fed young that theypresumably had sired in secondary nests and ignored foster youngin primary nests, whereas control males fed young in their primarynests. To identify potential benefits of accepting unrelatedyoung, we analyzed patterns of within-season breeding dispersaland of female settlement on territories following nest lossesto predators. Although some female yellowheads do renest onthe same territory following nest failures, the number of nestsinitiated on territories after a predation event was significantlylower than the number initiated on territories without predationover the same period of time. This implies that late-settlingfemales use the number of active or failed nests and/or thenumber of females on a territory when choosing where to breed.If replacement males that accepted unrelated offspring attractmore new females in the remainder of the current breeding seasonthan infanticidal males, then tolerance of unrelated young byreplacement males may be adaptive in some polygynous birds.     

Parasitic spawning in sand gobies: an experimental assessment of nest-opening size, sneaker male cues, paternity, and filial cannibalism

Sneaking is common in nest-building fish with paternal care,but the role of nest-opening size in protecting against entryby sneaker males has never been tested before. Using the sandgoby (Pomatoschistus minutus), a fish with exclusive paternalcare, experimental manipulations of nest openings provided nosupport for the hypothesis that nest openings serve as physicalor visual defense or that sneaker males prefer to parasitizenests with wide openings. Female mating preference was alsonot influenced by nest-opening size. However, female courtshipbehavior and visibility were important cues for sneaker males.Most sneak entries occurred when the nest holder was occupiedwith courtship, chasing another sneaker male or nest building.In half the cases of observed sneak entry, the sneaker malefertilized eggs, also when sneaking only occurred before spawning.Sneak entry and its duration were good estimates of stolen paternity,but neither sneak entries nor degree of fertilizations werecorrelated with filial cannibalistic behavior. Testes size didnot explain parasitic spawning success in replicates with geneticallydetermined sneaking. However, all sneaker males without breedingcoloration had huge testes and small sperm duct glands, whereasnest-holding males had small testes and large sperm duct glands,and sneaker males with breeding coloration were intermediate.     

Experimental manipulation of female tail length did not cause differential allocation by males in the barn swallow

The evolution and maintenance of female ornamentation has attracted increasing attention, because the previous explanation, that is a non‐functional copy of functional male ornamentation, seems insufficient to explain female ornamentation. A post‐mating sexual selection, differential allocation, may be more common than pre‐mating sexual selection, but few studies have investigated differential allocation by males. Here, we studied differential allocation of incubation investment by male barn swallows Hirundo rustica, a model species for the study of sexual selection, because our previous correlative study demonstrated a positive relationship between female tail length and male incubation investment. We manipulated the length of the outermost tail feathers in females after clutch completion and examined whether males adjust incubation investment according to female ornamentation. Because extra‐pair paternity is virtually absent in the study population, we were able to study differential allocation based on the tradeoff between current and future reproductive investments, rather than the tradeoff between current paternal investment and additional mating effort. The experimental treatment had no significant effect on male nest attentiveness, whereas female tail length before manipulation predicted male nest attentiveness. The observed pattern is consistent with differential access; that is, well‐ornamented individuals have greater access to mates with high reproductive (parental) ability, rather than differential allocation during incubation. Alternatively, males can directly assess eggs in their nests, and thus, as seen in other species, males might adjust their incubation investment based on the egg characteristics of long‐tailed females.     

Does paternity or paternal investment determine the level of paternal care and does female choice explain egg stealing in the fifteen-spined stickleback?

An earlier field study on the fifteen-spined stickleback (Spinachia spinachia) showed that frequent male—male interactionsresult in high frequencies of sneaking and egg stealing. Moreover,sneaking behavior was performed not only by males adoptingalternative mating strategies, but also by males with theirown nests. The advantage of sneaking is easily understood, but it is more difficult to explain the evolutionary benefitof stealing eggs from other males. I investigated whether malessuffering from sneaking adjust their paternal effort in relationto their degree of paternity. I also examined whether femalesprefer males that have more eggs in their nests, as this couldexplain egg stealing. There was no relationship between thedegree of paternity and fanning activity, hatching success,or nest defense. However, the older the eggs become, the morethe males increase their attack rate toward potential egg predators(goldsinny wrasse and shore crabs). Thus, males adjusted theirlevel of defense to the amount of energy and time already investedin the clutch. Females did not prefer males with more eggs intheir nests. On the contrary, females preferred males withreduced clutches over males with enlarged clutches. Therefore,female choice is unlikely to be a driving force behind eggstealing in this species.     

Effects of northern pike on patterns of nest use and resproductive behavior of male fathead minnows in a boreal lake

We conducted a two-part study to assets predator avoidance byreproductive male fathead minnows (Pimephales promelos) subjectedto predation threat from northern pike (Esox lucius). First,we determined if patterns of nest use by egg-guarding male minnowsin a boreal lake were related to pike densities. We samplednorthern pike and identified four areas of "high pike-density"and three areas of "low pike-density." We censused natural nestsand placed nest boards in these areas. We found eggs on naturalnests more frequently in areas with low densities of pike thanin areas with high densities of pike. However, we could notfully explain the distribution of nests by predation risk. Second,we evaluated the behavioral response of egg-guarding males toa control stimulus (a piece of wood) or a live pike in a wirecage. We used time to return to the nest after a stimulus asa measure of risk taking. Males took different amounts of riskbased on predation threat; males in the predator treatment tooklonger to return to their nests than control males. Risk takingwas not related to the number or age of the eggs but to distanceto nearest egg-guarding neighbor; males with close neighborsreturned sooner than more isolated males. Males in the predatortreatment had lower total activity and egg rubbing than controlmales after they returned to their nests. We conclude that malefathead minnows altered their reproductive behavior in waysthat reduced predation risk, but the cost of predator avoidancemight include egg predation, lost mating opportunities, or usurpationof nests