Optimal reproductive phenology under size‐dependent cannibalism

Intra‐cohort cannibalism is an example of a size‐mediated priority effect. If early life stages cannibalize slightly smaller individuals, then parents face a trade‐off between breeding at the best time for larval growth or development and predation risk from offspring born earlier. This game‐theoretic situation among parents may drive adaptive reproductive phenology toward earlier breeding. However, it is not straightforward to quantify how cannibalism affects seasonal egg fitness or to distinguish emergent breeding phenology from alternative adaptive drivers. Here, we devise an age‐structured game‐theoretic mathematical model to find evolutionary stable breeding phenologies. We predict how size‐dependent cannibalism acting on eggs, larvae, or both changes emergent breeding phenology and find that breeding under inter‐cohort cannibalism occurs earlier than the optimal match to environmental conditions. We show that emergent breeding phenology patterns at the level of the population are sensitive to the ontogeny of cannibalism, that is, which life stage is subject to cannibalism. This suggests that the nature of cannibalism among early life stages is a potential driver of the diversity of reproductive phenologies seen across taxa and may be a contributing factor in situations where breeding occurs earlier than expected from environmental conditions.     

Body size,temperature, and seasonal differences in size structure influence the occurrence of cannibalism in larvae of the migratory dragonfly, <Emphasis Type="Italic">Anax junius</Emphasis>

The aim of this study was to test the hypotheses that body size and seasonal differences in temperature and size structure influence cannibalism in larval dragonflies. In the first two experiments, larvae that were either similar or different in size were paired to examine the potential for intra- and intercohort cannibalism. In the third experiment, size structure of an assemblage of larvae and water temperature were manipulated to explore the seasonal dynamics of cannibalism. Cannibalism was common between individuals that differed in body size by one or more instars. Cannibalism also occurred between individuals similar in size but the rate varied across developmental stages. Results suggest that cannibalism may be most common when water temperatures are warm and late-instar larvae are present at high densities. These results highlight the importance of intra- and intercohort cannibalism as factors that can influence the population dynamics of generalist predators.     

An experimental study of population regulation in the salamander,Notophthalmus viridescens dorsalis (Urodela: Salamandridae)

Summary The roles of density-dependent larval survival and cannibalism of larvae as potential mechanisms of population regulation in the newt (Notophthalmus viridescens dorsalis) were evaluated in laboratory and field experiments. In laboratory containers, adults cannibalized larvae and large larvae cannibalized smaller larvae. In artificial ponds, larval survival did not depend on initial larval density. No cannibalism could be demonstrated in the complex environment, although the experiment was powerful enough to detect an ecologically relevant difference in survival. Adult growth was negatively correlated with the final biomass of larval newts, suggesting that the two life stages competed for resources. Larval growth rates were negatively correlated with final larval density, suggesting that larvae competed with each other. The proportion of larvae that became sexually mature at age 7 months (paedomorphs and adults that skipped the eft stage) varied inversely with larval density. Therefore, the potential regulatory mechanisms identified in this study are competition within and between life stages.     

Larval size relative to larval feeding, cannibalism of larvae, egg or adult female size and larval–adult setal patterns among 13 phytoseiid mite species

Phytoseiid mite larvae vary in size and feeding type. We compared larval size to feeding by larvae, cannibalism of larvae by adult females, egg and adult female size and the setae lengths of larvae and adults among 13 species. There was no relationship between size of larvae and either feeding by larvae or cannibalism of larvae by adult female mites. Correlations were highest between larval size as measured by idiosoma plus extended leg lengths and adult female size of idiosoma plus extended leg lengths (r²=0.746), while next highest was larval idiosoma length and adult female idiosoma length (r²=0.662) and then larval idiosoma length and egg length (r²=0.579). Based on idiosoma length, Phytoseiulus persimilis had the largest larvae (non-feeding) among species and Euseius finlandicus had the smallest larvae (obligatory feeding). However, based on idiosoma length plus extended leg length, obligatory feeding larvae (on pollen or mites) of E. finlandicus and Euseius hibisci were largest and facultative feeding larvae (on mites) of Neoseiulus californicus and obligatory feeding larvae (on mites) of Galendromus occidentalis were the smallest. Among species with non- or facultative feeding larvae, Amblyseius andersoni and Neoseiulus barkeri had larger larvae and Typhlodromus pyri and Neoseiulus fallacis had smaller larvae when leg lengths were included in larval size. Setae lengths of larvae versus adult females (after adjustment for body sizes) showed high correlation for j6 (r²=0.942) and s4 (r²=0.854), but low correlation for larval Z4 versus adult female Z4 (r²=0.084) or Z5 (r²=0.063). Overall, larval morphological traits were most closely correlated to traits of other life stages, although for setae there were some exceptions. Differences in the functions of setae j6, s4 and Z4 in the larva versus adult female are discussed.     

Cannibalism and the stage-dependent transmission of a viral pathogen of the Indian meal moth, Plodia interpunctella

1. The transmission of an insect pathogen by cannibalism was studied by a series of choice and no-choice experiments.
2. Infection of Plodia interpunctella larvae with a granulosis virus occurred through cannibalism of infected larvae.
3. Depending on the larval instars of the cannibal and the victim relative to each other, preferential cannibalism of both infected and healthy larvae was observed.
4. Larvae cannibalise healthy, less vulnerable larvae preferentially, but it is argued that there is no evidence that they are avoiding infection.
5. The victim cannibalised can be explained as a balance between the reduced risk of injury and the ease of cannibalism of moribund infected individuals on the one hand and the greater food resource value of healthy individuals on the other.
6. The implications for the insect population dynamics of the transmission of the pathogen via cannibalism and the effective removal of infective particles through cannibalism by immune stages are discussed.     

Onset and development of cannibalistic behaviour in early life stages of yellowtail

The onset and development of cannibalistic behaviour were observed in early life stages of yellowtail Seriola quinqueradiata . Cannibalistic behaviour was divided into four actions, i.e aim, chase, nip and ingestion. The frequency of chase was used as an index of cannibalistic behaviour because it always appeared in every sequence of cannibalism, although a sequence of cannibalistic behaviour sometimes stopped before nip or ingestion. No cannibalistic behaviour was observed during the larval phase until day 22 after hatching (when fish were 9.6mm T.L.) either in a rearing pond or in experimental tanks. The onset of cannibalistic behaviour was observed on day 23, coinciding with metamorphosis from the larval to juvenile phase, and it developed until day 39, with a tentative decrease between day 33 and day 36. This inverted peak corresponded roughly to the development of schooling behaviour after day 33, which was determined by distance to the nearest neighbour. In the rearing pond, suffocation of a cannibal by its prey, appeared from day 23. Field observation of juvenile yellowtails aggregating around floating seaweeds showed that cannibalism occurred in three out of 10 schools, in which six cannibals were found among 194 fish. Cannibalistic behaviour in early life stages of yellowtail may occur as a final phase of inter-individual interference and may have a role for size selection of a School member.     

具有时滞和自食的非自治阶段结构竞争系统的周期解

研究了一类具有时滞和自食的非自治阶段结构竞争系统的动力学行为,其中一种群分幼年和成年两个阶段.当发生自食现象时,利用重合度理论中的延拓定理,得到该系统正周期解存在的充分条件.     

Differentiated egg size of the cannibalistic salamander <Emphasis Type="Italic">Hynobius retardatus</Emphasis>

Larvae of the salamander, Hynobius retardatus, are carnivorous, and even though there are two morphs, a typical morph and a broad-headed or “cannibal” morph, both are cannibalistic. They also sometimes eat other large prey, for example larvae of the frog, Rana pirica. In natural habitats, use of both conspecific and R. pirica larvae as food may contribute more strongly to high survival and substantially to fitness when larval densities are higher, because early-stage H. retardatus larvae sometimes experience scarcity of their typical prey. In cannibalistic oviparous amphibians, larger individuals that developed from larger eggs can more efficiently catch and consume larger prey and thus their survival may be better than that of smaller individuals developed from smaller eggs. Populations might therefore diverge in respect of egg size in response to variation in the density of conspecific and R. pirica larvae in natural ponds, with eggs being larger when larval density is higher. I examined how variance in hatchling size correlated with the incidence of cannibalism, and whether increasing larval density in natural ponds correlated with increasing egg size. Variance in initial larval body size facilitated cannibalism, and egg size increased as larval density in the ponds increased. In ponds with high larval density, where cannibalism and large prey consumption is a critical factor in offspring fitness, the production of fewer clutches with larger eggs, and thus of fewer and larger offspring, results in greater maternal fitness. Variation among the mean egg size in populations is likely to represent a shift in optimum egg size across larval density gradients.     

Predation risk suppresses the positive feedback between size structure and cannibalism

1.?Cannibalism can play a prominent role in the structuring and dynamics of ecological communities. Previous studies have emphasized the importance of size structure and density of cannibalistic species in shaping short- and long-term cannibalism dynamics, but our understanding of how predators influence cannibalism dynamics is limited. This is despite widespread evidence that many prey species exhibit behavioural and morphological adaptations in response to predation risk. 2.?This study examined how the presence and absence of predation risk from larval dragonflies Aeshna nigroflava affected cannibalism dynamics in its prey larval salamanders Hynobius retardatus. 3.?We found that feedback dynamics between size structure and cannibalism depended on whether dragonfly predation risk was present. In the absence of dragonfly risk cues, a positive feedback between salamander size structure and cannibalism through time occurred because most of the replicates in this treatment contained at least one salamander larvae having an enlarged gape (i.e. cannibal). In contrast, this feedback and the emergence of cannibalism were rarely observed in the presence of the dragonfly risk cues. Once salamander size divergence occurred, experimental reversals of the presence or absence of dragonfly risk cues did not alter existing cannibalism dynamics as the experiment progressed. Thus, the effects of risk on the mechanisms driving cannibalism dynamics likely operated during the early developmental period of the salamander larvae. 4.?The effects of dragonfly predation risk on behavioural aspects of cannibalistic interactions among hatchlings may prohibit the initiation of dynamics between size structure and cannibalism. Our predation trials clearly showed that encounter rates among hatchlings and biting and ingestion rates of prospective prey by prospective cannibals were significantly lower in the presence vs. absence of dragonfly predation risk even though the size asymmetry between cannibals and victims was similar in both risk treatments. These results suggest that dragonfly risk cues first suppress cannibalism among hatchlings and then prevent size variation from increasing through time. 5.?We suggest that the positive feedback dynamics between size structure and cannibalism and their modification by predation risk may also operate in other systems to shape the population dynamics of cannibalistic prey species as well as overall community dynamics.     

Cannibalistic Behavior and Functional Response in Chrysomya albiceps (Diptera: Calliphoridae)

Chrysomya albiceps is a facultative predator and cannibal species during the larval stage. Very little is known about cannibalism and prey size preference, especially in blowflies. The purpose of this investigation was to determine the influence of prey size and larval density on cannibalism by third-instar larvae of C. albiceps under laboratory conditions. Our results indicate that no cannibalism occurs by third-instar larvae on first- and second-instar larvae, but third-instar larvae do eat second-instar larvae. The functional response on second-instar larvae is consistent with Holling type II. The consequences of consuming second-, compared to first- or third-, instar larvae as well as the implications of cannibalism for the population dynamics of C. albiceps are discussed.     

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

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

Population dynamics, life stage and ecological modeling in Chrysomya albiceps (Wiedemann) (Diptera: Calliphoridae)

In this study we investigated the population dynamics of Chrysomya albiceps (Wiedemann) with laboratory experiments, employing survival analysis and stage structure mathematical models, emphasizing survival among life stages. The study also assessed the theoretical influence of density dependence and cannibalism during immature stages, on the population dynamics of the species. The survival curves were similar, indicating that populations of C. albiceps exhibit the same pattern of survival among life stages. A strong nonlinear trend was observed, suggesting density dependence, acting during the first life stages of C. albiceps. The time-series simulations produced chaotic oscillations for all life stages, and the cannibalism did not produce qualitative changes in the dynamic behavior. The bifurcation analysis shows that for low values for survival, the population reaches a stable equilibrium, but the cannibalism results in chaotic oscillations practically over all the parametric space. The implications of the patterns of dynamic behavior observed are discussed.     

Shifty salamanders: transient trophic polymorphism and cannibalism within natural populations of larval ambystomatid salamanders

Introduction

Many species of ambystomatid salamanders are dependent upon highly variable temporary wetlands for larval development. High larval densities may prompt the expression of a distinct head morphology that may facilitate cannibalism. However, few studies have characterized structural cannibalism within natural populations of larval salamanders. In this study we used two species of larval salamanders, long-toed (Ambystoma macrodactylum) and ringed salamanders (A. annulatum). Head morphometrics and stable isotopic values of carbon (δ¹³C) and nitrogen (δ¹⁵N) were used to identify the presence or absence of structural cannibalism. Weather conditions were also analyzed as a potential factor associated with the expression of cannibalistic morphology.

Results

Populations of salamander larvae did not consistently exhibit cannibalistic morphologies throughout collection periods. Larval long-toed salamanders exhibited trophic polymorphisms when relatively lower precipitation amounts were observed. Larval ringed salamanders were observed to be cannibalistic but did not exhibit polymorphisms in this study.

Conclusions

Structural cannibalism may be transient in both species; however in long-toed salamanders this morphology is necessary for cannibalism. Ringed salamanders can be cannibalistic without morphological adaptations; however the cannibal morph may prolong the viable time period for cannibalism. Additionally, weather conditions may alter pond hydroperiod, subsequently influencing head morphology and cannibalism.

     

Egg-hatching synchrony and larval cannibalism in the dock leaf beetle Gastrophysa viridula (Coleoptera: Chrysomelidae)

Females of leaf beetles and many other herbivorous insects lay eggs in coherent batches. Hatchlings emerge more or less simultaneously and often prey on their late-hatching clutchmates. It is not certain, however, whether this synchrony of hatching is a mere by-product of cannibalism or whether an additional synchronizing factor exists. The following simple experiment was aimed at determining the causal relationship between cannibalism and simultaneous larval emergence. Egg clutches of the dock leaf beetle Gastrophysa viridula were split into two halves. These halves were either kept as coherent groups in two separate dishes or, alternatively, only one half remained whole, whereas the other one was divided into single eggs, each of which was incubated in a separate dish. Halving of a clutch into coherent groups only slightly disrupted the synchrony of emergence. The consequence of individual isolation was more dramatic. Half-clutches consisting of disconnected solitary eggs required almost twice as much time for complete emergence of all larvae, which was significantly more than cannibalism as a sole synchronizing factor might explain. Moreover, survival rates were the same in coherent half-clutches (in the presence of cannibalism) and among isolated individuals. This group effect and the small contribution of cannibalism suggest the existence of an additional synchronizing factor. Possible mechanisms underpinning this phenomenon are discussed.     

The effect of food supply and larval cannibalism on adult size and biomass of the grazing caddis-fly Melampophylax mucoreus (Limnephilidae)

Abstract. 1. Larvae of the grazing caddis‐fly Melampophylax mucoreus were reared in a laboratory experiment investigating the effect of food availability on different substrates and cannibalism on the size and biomass of emergent adults. All experiments were performed in stream‐water filled, aerated aquaria under controlled temperature and light conditions. Larvae (fourth and fifth instar) were reared in aquaria (50 larvae in each) with three substrate scenarios: (i) limestone (LS), (ii) limestone and leaf litter (LS + L), and (iii) silicate stone (SS). 2. Cannibalism among the larvae in the LS scenario led to the highest adult dry masses (male = 5.13 ± 0.25 mg, female = 7.64 ± 0.63 mg) and to the highest mortality rate (88.7%). The SS scenario displayed the most unfavourable condition for larval growth indicated by the lowest adult dry masses (males = 3.12 ± 0.15 mg, females = 4.69 ± 0.25 mg) and a high mortality rate (81.7%). The limestone supplemented with leaf litter (ii) offered the most balanced nutrients to complete larval development and enough shelter to avoid excessive encounter rates of larvae within the aquaria, indicated by the lowest mortality rate (43.6%). Adults from the LS + L scenario showed biomasses (male = 3.94 ± 0.12 mg, female = 6.48 ± 0.24 mg) intermediate between the two other scenarios. 3. The results implied that cannibalism among larvae can lead to higher adult biomasses and therefore to increased fitness, if cannibalism supplements larval feeding requirements. Larvae developing under insufficient food availability can not compensate for this by cannibalism. Additionally, leaf litter not only provided a complementary food source for developing larvae, but also provided shelter, which reduced encounter rates. 4. Increased stress induced by high larval encounter rates (resulting in enhanced cannibalism) in the LS scenario and low food availability in the SS scenario could be indicated by premature emergence times compared with the LS + L scenario.     

Larval cannibalism and worker-induced separation of larvae in <Emphasis Type="Italic">Hypoponera</Emphasis> ants: a case of conflict over caste determination?

Reproductive altruism and cooperative brood care are key characteristics of eusocial insects and reasons for their ecological success. Yet, Hymenopteran societies are also the stage for a multitude of intracolonial conflicts. Recently, a conflict between adult and larval colony members over caste fate was described and evidence for overt conflict was uncovered in several bee species. In theory, diploid larvae of many Hymenopteran species should experience strong fitness benefits, if they would be able to change their developmental pathway towards the queen caste. However, larval self-determination potential is low in most advanced eusocial Hymenopterans, because workers often control larval food intake and queenworker caste dimorphisms are generally high. In the ant genus Hypoponera, larvae actively feed on food provided by workers and here we show extremely low queenworker size differences in these ants: the lowest in H. opacior, where fertile wingless (intermorphic) queens weigh on average only 13% more than workers. Thus, slightly better nutrition during development might change the fate of a Hypoponera larva from a completely sterile worker to a fertile queen. One possibility to obtain extra food for Hypoponera larvae with their well-developed mandibles would be to cannibalise adjacent larvae. Indeed, we observed frequently larval cannibalism in ant nests. Yet, adult workers apparently try to prohibit larval cannibalism by carefully separating larvae in the nest. Larvae, which were experimentally brought into close contact, were rapidly set apart. Workers further sorted larvae according to size and responded swiftly to decreasing food levels, by increasing inter-larval distance. Still, an experimental manipulation of the larval cannibalism rate in H. schauinslandi failed to provide conclusive evidence for the link between larval cannibalism and caste development. Hence, further experiments are needed to determine whether the widespread larval cannibalism in Hypoponera and the untypical brood distribution can be explained by an overt caste conflict. Received 18 December 2006; revised 2 August and 20 September 2007; accepted 21 September 2007.     

The effects of nurse eggs and sibling interactions on the larval development of the poecilogonous annelid Boccardia proboscidea (Spionidae)

In poecilogony, different types of larvae are produced within the same species. Previous studies have suggested maternal control of the production of larval types; however, it is not clear which factors or mechanisms generate contrasting developmental patterns among siblings. The spionid polychaete Boccardia proboscidea produces within the same capsule adelphophagic larvae that eat nurse eggs and siblings and complete all or most of their development inside the capsule (Type A larvae), and larvae with little growth until they hatch as planktotrophic larvae (Type B larvae). In this study, we manipulated capsule content to explore the factors determining larval type in B. proboscidea and the role of extra‐embryonic maternal nutrition and sib–sib interaction in the developmental fate of offspring. When early larval stages were grown individually in vitro, with nurse eggs as the only food source, some of them remained small, while others continue developing into larger pre‐competent larvae by feeding on nurse eggs. This suggests that larval types in B. proboscidea are determined very early in development and are not solely the product of sib–sib interaction inside the capsule. However, our data also suggest that hatching size variability within larval types of a clutch depends on nurse egg availability. Type B larvae grew normally to metamorphosis when phytoplankton was available, but suffered high rates of cannibalism by Type A larvae. These results are consistent with the hypothesis that individual larval fates are determined very early in development and that once their fate is determined, hatching size and intracapsular survival are affected by maternal food provisioning and sibling interaction.     

Cannibalizing Harmonia axyridis (Coleoptera: Coccinellidae) larvae use endogenous cues to avoid eating relatives

Cannibalism is widespread among many different organisms, and can have both negative and positive fitness consequences. Avoiding eating relatives can minimize negative fitness consequences of cannibalism. Such avoidance requires kin discrimination, but evidence for this ability among cannibals is limited with little data that address the cues used in such discrimination. We examined whether larvae of the ladybird beetle Harmonia axyridis avoid eating their relatives. We further manipulated environmental factors to create individuals that had similar or dissimilar rearing environments to begin to test for endogenous versus exogenous recognition cues. In our experiments, third-instar larvae were much less likely to cannibalize if they were interacting with a relative. Larvae that did cannibalize kin required more encounters, and significantly delayed cannibalism, compared to larvae cannibalizing unrelated individuals. Acquired cues were less important. Even though the different rearing environment resulted in significantly different phenotypic effects, similarity or dissimilarity of rearing environment had no effect on cannibalism, and there was no interaction between environments and relatedness in cannibalism. We suggest that H. axyridis has a well-developed kin discrimination system, and that kin recognition in this ladybird beetle is based on endogenous rather than exogenous cues. We also argue that these cues reflect either direct or indirect genetic effects on larval phenotypes.     

Cannibalism in discrete-time predator-prey systems

In this study, we propose and investigate a two-stage population model with cannibalism. It is shown that cannibalism can destabilize and lower the magnitude of the interior steady state. However, it is proved that cannibalism has no effect on the persistence of the population. Based on this model, we study two systems of predator-prey interactions where the prey population is cannibalistic. A sufficient condition based on the nontrivial boundary steady state for which both populations can coexist is derived. It is found via numerical simulations that introduction of the predator population may either stabilize or destabilize the prey dynamics, depending on cannibalism coefficients and other vital parameters.