Cannibalistic Behavior Research Articles

Suboptimal macronutrient ratios promote cannibalism in a generalist herbivore (Trichoplusia ni)

Abstract Discretional cannibalism is a widespread phenomenon among lepidopteran herbivores. Herbivores encounter variation in dietary nutrient quality when foraging, which alters feeding behaviour, as well as population‐ and trophic‐level dynamics. For example, plant resistance traits directly influence feeding patterns in insect herbivores through reduced consumption of plant tissue and increased rates of cannibalism. However, the effects of dietary composition, in particular unbalanced macronutrient ratios, on driving cannibalism remain unknown. We examined the effects of unbalanced macronutrient ratios on cannibalism in the generalist caterpillar Trichoplusia ni using an artificial diet experiment with varied ratios of two important macronutrients: protein and carbohydrates. We quantified cannibalistic behaviour from the second instar to pupation and measured survival among cannibals and non‐cannibals to understand the long‐term and short‐term costs and benefits of cannibalism. Caterpillars in high carbohydrate, low protein treatments cannibalised 20% more than the optimum control diet treatment, whereas herbivores in high protein, low carbohydrate treatments cannibalised 33% more than herbivores reared on the optimum macronutrient diet treatment. Survival of cannibals in macronutrient‐deficient diet treatments was 10.4%, compared with 76.9% for cannibals in the optimal macronutrient diet treatment. While previous work demonstrates the importance of induced chemical defence in promoting shifts to cannibalism, our results indicate that unbalanced macronutrient ratios can also promote cannibalism in insect herbivores. We propose that understanding how unbalanced macronutrient ratios drive cannibalism yields insight into how dietary quality, including both plant resistance traits and plant nutrients, influences behavioural plasticity and mediates plant–herbivore interactions.

Cannibalistic behavior of biological control agent Oenopia conglobata (Linnaeus, 1758) (Coleoptera: Coccinellidae) under laboratory conditions

BackgroundOenopia conglobata (Linnaeus) (Coleoptera: Coccinellidae) is a generalist predator feeding on several insect pests and utilized as a biological control agent in Türkiye. However, significant cannibalism has been observed among its different life stages under low food/prey availability. This study determined adult-egg, adult-larva, larva-egg, and larva-larva cannibalism of O. conglobata under laboratory conditions.ResultsCannibalism among different life stages was observed under no supplemental diet (treatment group) or sufficient (100 Ephestia kuehniella eggs per individual) supplemental diet (control group). Fifty eggs per adult were provided to the 24 h-starved male and female adults for determining adult-egg cannibalism. Similarly, male, and female adults received 30 and 20 1st and 2nd instars, respectively to observe adult-larval cannibalism. Likewise, 10, 20, 30 and 40 eggs to 24-h starved 1st, 2nd, 3rd, and 4th instars, respectively were provided to record larval–egg cannibalism. By the same way, 12-h starved 4th instar was provided 1st instar (20 per individual) to determine larval–larval cannibalism. The experiments for males, females, and instars were conducted separately and cannibalism was assessed by prey consumption in treatment group relevant to the control group. Cannibalism significantly differed among sexes and instars (for larva-egg cannibalism). Overall, males and females consumed higher number of eggs in treatment group compared to their relevant controls. Female and male adults in treatment group exhibited 8.27- and 7.16-fold cannibalism on eggs. Likewise, females exhibited the highest cannibalism (2.84-folds) on 1st instar. The 4th instar consumed the highest number of eggs; however, the highest cannibalism rate was recorded for the 3rd instar. The 3rd instar exhibited 4.63-fold cannibalism on eggs. Nevertheless, the 4th instar exhibited 3.56-folds cannibalism on 1st instar.ConclusionsStarved O. conglobata individuals exhibited significant cannibalism among different life stages. Therefore, during mass rearing they shouldn’t be starved. Furthermore, the cannibalistic behavior should be considered during the mass release of O. conglobata.

Indian palm squirrel (Funambulus palmarum) feeds on spider egg sacs

The Indian palm squirrel, Funambulus palmarum (Linnaeus, 1766) (Rodentia: Sciuridae) is known to feed on a wide range of plant items in the wild, including nuts, seeds, fruit, and bark, and will readily consume discarded food around human habitations. The species has been observed to prey opportunistically on insects such as termites and beetles. In addition, cannibalistic behaviour has also been recorded. Here we report the first observation of F. palmarum preying on spider egg sacs.

Quid Pro Quo: A Documented Case of Cannibalism in the Red-Bellied Black Snake Pseudechis porphyriacus in Lamington (Queensland, Australia)

The red-bellied black snake (Pseudechis porphyriacus) is a member of the Elapidae family and is distributed on the east coast of Australia. The species is known to feed on a variety of ectothermic prey, including frogs and lizards. It is also known to be ophiophagous (snake-feeding), and stomach-content analyses suggest that P. porphyriacus also exhibits cannibalistic behavior, yet this extreme case of ophiophagy has rarely been documented. Here, a case of cannibalism in P. porphyriacus, which was observed in Lamington (Queensland, Australia), has been photographically documented and is described.

Supplementation of Turmeric Flour on Survival of Asian Redtail Catfish (Hemibagrus Nemurus)

Asian redtail catfish culture activities are still constrained by the low survival rate in the seeds phase, one of the causes is cannibalism behavior. Several attempts have been made to improve the survival of these fish, and several studies have shown that turmeric powder can increase survival in several species. Based on this, this study aimed to evaluate the addition of turmeric flour with the coating method on the survival rate of Asian redtail catfish (Hemibagrus nemurus) seeds. This study used a completely randomized design using four treatments and was repeated three times. The treatment used was the supplemented turmeric flour to commercial feed which had a protein of 40%., the treatments were 0.0 g kg-1 (K), 2.5 g kg-1 (TK2.5), 5.0 g kg-1 (TK5.0), and 7.5 g kg-1 feed (TK7.5). The size of the Asian redtail catfish was 2.09±0.17 cm, with a stocking density of 3 L-1, and reared in an aquarium measuring 38x25x22 cm3. The study was conducted for 30 days and fed at satiation four times a day. The parameters measured were survival, cannibalism (cannibal type, cannibal index, normal death), and growth performance (absolute weight, absolute length, specific weight growth, and specific length growth). The results showed that TK5.0 was able to increase the survival rate and decrease the cannibalism index and normal death rate. Furthermore, the supplemented turmeric flour did not have an impact on the absolute weight, absolute length, specific growth rate, and specific length.

Far-reaching benefits of the consumption of conspecific eggs by neonate larvae of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae): a case study on an artificial diet

BackgroundThe consumption of conspecific eggs by neonate larvae is a common behavior in aphidophagous coccinellids. However, it is still unknown what far-reaching benefits can be brought to the artificial diet-reared cannibals and whether the age of eggs and/or ovipositing parents can affect the cannibals’ fitness. Here, the multicolored Asian ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) was used as a research model because it exhibits much stronger cannibalism behavior than other beetles. Nine types of eggs, varying according to parental age at oviposition and egg age per se, were respectively provided as foods for H. axyridis neonate larvae until they developed to 2nd instar. After that, the larvae were fed on an artificial diet and whether egg consumption by neonate larvae had far-reaching benefits was evaluated. Those larvae that directly fed on artificial diet since hatching were served as control.ResultsCompared with the control beetles, the cannibal beetles (with few exceptions) had significantly higher 2nd instar-adult survivals (61.1–75.7% vs. 34.3%) and greatly shortened 2nd instar-adult duration (22.7–24.6 days vs. 27.8 days). At adult emergence, the female cannibal beetles (with few exceptions) had significantly higher fresh weights than the control beetles (14.5–16.3 mg vs. 11.7 mg). Among the nine types of cannibals, non-significant difference was detected in almost all the measured developmental parameters.ConclusionConsumption of conspecific eggs by neonate larvae of H. axyridis had far-reaching benefits for their subsequent development on artificial diet, and neither the egg age nor parental age at oviposition affects the cannibals’ fitness. These findings provided new insights into the combined application of conspecific eggs and artificial diets in the mass rearing of coccinellids.

Development of a chub mackerel with less-aggressive fry stage by genome editing of arginine vasotocin receptor V1a2

Genome editing is a technology that can remarkably accelerate crop and animal breeding via artificial induction of desired traits with high accuracy. This study aimed to develop a chub mackerel variety with reduced aggression using an experimental system that enables efficient egg collection and genome editing. Sexual maturation and control of spawning season and time were technologically facilitated by controlling the photoperiod and water temperature of the rearing tank. In addition, appropriate low-temperature treatment conditions for delaying cleavage, shape of the glass capillary, and injection site were examined in detail in order to develop an efficient and robust microinjection system for the study. An arginine vasotocin receptor V1a2 (V1a2) knockout (KO) strain of chub mackerel was developed in order to reduce the frequency of cannibalistic behavior at the fry stage. Video data analysis using bioimage informatics quantified the frequency of aggressive behavior, indicating a significant 46% reduction (P = 0.0229) in the frequency of cannibalistic behavior than in wild type. Furthermore, in the V1a2 KO strain, the frequency of collisions with the wall and oxygen consumption also decreased. Overall, the manageable and calm phenotype reported here can potentially contribute to the development of a stable and sustainable marine product.

Immersion Effect of Estradiol-17β on Cannibalism of Asian Redtail Catfish (<I>Hemibagrus nemurus</I>) Post Larvae

Highlight Research The dose, duration of immersion, and time interval of immersion of the estradiol-17β affect the rate of cannibalism and increase the seed survival of Asian redtail catfish in low treatment in this research. Over optimum treatment increased the incidence of cannibalism at Asian redtail catfish and decrease growth performance. Treatment of estradiol-17β, give the ability of Asian redtail catfish to live on high density The treatment of estradiol-17β, has an effect on concentration plasma of body testosterone and cortisol Abstract The cannibalistic behavior of Asian redtail catfish greatly hampers the supply of these fish seeds, invoking the need to be controlled. Estradiol is one of the hormones that has been known to reduce cannibalistic behavior on fish. This study aimed to evaluate the effect of estradiol-17β immersion on the incidence of cannibalism in the rearing of post larvae of Asian redtail catfish. Post larvae was treated with a combination of doses of estradiol hormone 0, 1, and 2 ppm and immersion time of two and four hours with immersion intervals of three and six days with a completely randomized design. Each treatment had a fish density of 10 fish L-1, with mean size individual length of 6.73 ± 0.73 mm (three days of age after hatched), with four replications. Fish were fed with tubifex up until satiation point and reared for 30 days. The results showed that the administration of the estradiol-17β through immersion with a dose of 1 ppm for two hours and interval of six days was able to reduce the level of cannibalism and increase the survivability. A further increase in dose, immersion time, and interval had the opposite effect. Estradiol-17β immersion with certain dose, duration, and interval affected the rate of cannibalism, growth rate, and survival. Estradiol-17β immersion at a dose of 1 ppm for two hours and six days interval was the best to reduce the level of cannibalism and normal mortality in post larvae of Asian redtail catfish.

Maternal cannibalistic preferences affect offspring preferences and development in Menochilus sexmaculatus Fabricius (Coleoptera: Coccinellidae): A transgenerational investigation

AbstractCannibalism has been widely reported across taxa. However, the heritability and expression of cannibalistic traits have been least explored. The variation in the expression of cannibalism is likely to exist amongst the population affecting the propensity of cannibalism. Thus, to know whether the mother has any role in the transgenerational transmission of this trait in a ladybird beetle, Menochilus sexmaculatus, we studied the interaction between maternal and offspring prey preferences and its effect on, development duration and body weight of offspring over generations. An insignificant effect of maternal dietary history on offspring prey preference was observed across generations except for the non‐cannibalistic adults who significantly preferred aphids over eggs. The long‐term detrimental effect of cannibalism was found in cannibals with increased developmental duration and decreased body weight of offspring over generations. In conclusion, the results show that maternal diet did not affect the offspring preferences in M. sexmaculatus but cannibalism had a profound generational effect on the cannibalistic propensity, development and body weight of offspring across generations shows that larval dietary history and nutritional composition of prey contribute to the expression of cannibalistic behaviour across generations.

Attack behavior leading cannibalism in tropical gar (Atractosteus tropicus) larvae under different tank colors and shelter type

Aggressivity expressed as cannibalism in fish larvae is a problem that limits the development of many species in aquaculture, therefore, understanding it and generating strategies to reduce its impact is important. This study described cannibalistic attacks behavior in Tropical gar (Atractosteus tropicus) larvae. The larvae were exposed to different tank colors and shelters (rocks and plastic vegetation), in pairs (2 larvae) and in groups (10 larvae). In addition, attacks behavior, types of attacks, and morphometric aspects related to cannibalism were described. In pairs, attacks occurred in greater numbers with white background color (8.50 ± 0.70) and fewer for yellow and purple (0.66 ± 0.57, p < 0.05). The largest number of group attacks was observed with the background colors pink, blue and yellow, and purple to a lesser extent. The presence of shelters (artificial vegetation) decreased the attacks in pairs and in groups compared to the use of rocks as refuge. A. tropicus larvae show a clear preference for artificial vegetation. It was found that morphologically, both juveniles and larvae (10 Days after hatching (DAH)) can consume prey greater than their own body depth (1.59 ± 0.22, 1.00 ± 0.12) and body width (1.74 ± 0.29, 0.94 ± 0.12). The mouth depth angle was significantly higher in larvae (10 DAH) (85.63 ± 6.41°), which decreases as age increases. A total of 452 events were recorded, four behaviors were described: interaction (214 events, 47 attacks, effectiveness of the attack (EA) 21.96%), chasing (127 events, 44 attacks, EA 34.64%), escape (62 events), and fast swimming (47 events). Three types of attacks were recorded: frontal (41.24%), lateral (29.94%), and posterior (28.81%), with three attack regions: head (31.64%), body (10.72%), and tail (57.63%). The most frequent attack was posterior tail with 70 events (39.55%). Attacker presented a S-like curvature prior to the attack (30.50%). Differences were determined in the percentage of weight (g) and total length (cm) between the attacker larvae and the attacked larvae 16.39 ± 10.86% and 15.23 ± 5.68%, respectively. In conclusion, A. tropicus larvae show cannibalism Type I, II, and two variants of Type III. It is suggested that this species is a more efficient cannibal than an interspecific predator. The relation of the greater number of attacks in the white color tanks could be related to the contrast with the bottom, thus, there is a less preference for this color. This information is essential to carry out a more efficient sorting of the larvae during their culture and reduce cannibalism in the larval stage in A. tropicus. The results of this study could be useful to understand this behavior in other species.

Effects of cannibalism on the growth and development of Spodoptera frugiperda (Lepidoptera: Noctuidae)

The migratory fall armyworm, Spodoptera frugiperda (Smith), has become an important agricultural pest worldwide. In this study, a comparative analysis of the cannibalistic behavior of S. frugiperda larvae in different instar stages was carried out. The predation function of S. frugiperda and the effects of cannibalism on the development of S. frugiperda were assessed based on the Holling functional model and two-sex life tables, respectively. The functional response results reflected that the 3rd, 4th, 5th and 6th instar larvae of S. frugiperda exhibited theoretical maximum predation values of 82.89, 83.39, 110.52 and 111.2, respectively. According to observations of the development of S. frugiperda under three treatments, S. frugiperda completed its life cycle in the control and cannibal groups but not in the only cannibal group. The larval and pupal developmental duration in the control group and the cannibal group were significantly different. S. frugiperda in the cannibal group had the shortest adult period (5.82 d) and the lightest pupal weight (0.1387 g); the survival rate in the cannibal group was lower than that in the control group. Significant differences were observed in the mean fecundity of females, with the largest number of eggs (1075.06 eggs) laid by S. frugiperda in the control group. S. frugiperda in the control group had the highest intrinsic rate of increase (r), net reproductive rate (R0 ) and finite rate of increase (λ). Overall, cannibalism is not conducive to the growth and development of S. frugiperda.

Impact of invading species on biodiversity: Diet study of the green whip snake’s (Hierophis viridiflavus, L. 1789) in Switzerland

Next-generation sequencing is increasingly used in conservation biology to resolve complex interactions between species, either diet or gut parasites studies. We applied a recent long metabarcoding method to elucidate the green whip snake’s (Hierophis viridiflavus) prey consumption based on DNA extracted from stomach contents. Illegally introduced in Canton of Vaud (Switzerland), three populations of the green whip snake have strongly developed in two regions, East (Chablais) and North. We suspect that this introduced species is threatening part of the local herpetofauna, especially the Asp viper and the Western green lizard in this region. Consequently, an extermination program has been implemented from 2016 to mitigate Hierophis viridiflavus expansion and its impact arising from its generalist diet. Stomach contents of 94 individuals removed from introduction sites were analysed by long metabarcoding. Our study revealed the consumption of 67 prey belonging to 9 species, primarily small mammals and reptiles. The recurrent presence of two parasitic nematodes was also discovered. Although cannibalistic behaviour could not be highlighted with this approach, a scavenging behaviour was suspected based on the presence of an insect used in forensic entomology (Calliphora vicina). These results confirm the opportunistic feeding behaviour of Hierophis viridiflavus and its ability to predate on threatened species. Although 86.6 % of preys were not listed on the Swiss Red List, the impact on the Asp viper population can be important (up to 20 % of consumed preys) and could partially explain its strong decline.

The feeding/fasting strategy, size heterogeneity, and stocking density impact on body performance and cannibalism rate of Persian sturgeon ( Acipenser persicus ) larvae

The aim of this study was to evaluate different aspects of larviculture of Persian sturgeon (Acipenser persicus). With this regard, the growth performance, e.g., final weight, specific growth rate (SGR), and cannibalism rate of Persian sturgeon were assessed. The study was performed using two separate strategies; size heterogeneity and feeding/fasting strategy (experiment-A), besides implementing stocking density (experiment-B). In the experiment-A, twelve circular tanks (9.6 L) were considered as following: A1 (5 large starved fish +5 small starved fish); A2 (5 large fed fish +5 small fed fish); A3 (all 10 large starved fish); A4 (all 10 large fed fish); A5 (all 10 small starved fish) and A6 (all 10 small fed fish). In experiment-B, the stocking density was doubled for all groups in the same tanks: B1 (10 large starved fish +10 small starved fish); B2 (10 large fed fish +10 small fed fish); B3 (all 20 large starved fish); B4 (all 20 large fed fish); B5 (all 20 small starved fish) and B6 (all 20 small fed fish). Data were collected at the end of the 7th and 14th days. Growth performance increased significantly in all fed treatments of experiment-B in comparison to starved treatments (P < 0.05). The highest final weight and SGR was observed in B2 (363.5 ± 130.1 mg in 14th day) and B6 (26.5 ± 1.0% day−1 in 7th day), respectively. Cannibalism rate was increased in Persian sturgeon larvae maintained at low density, in which the highest rate was observed in the starved groups (A1 [27.5%], A3 [35.0%], A5 [40.0%]). Size heterogeneity leads to disappear/die all small larvae, in both low- and high-density only in the starved group, regardless of size, died at the end of the second week. In conclusion, in Persian sturgeon, cannibalistic behavior is more affected by stocking density. To manage larviculture of this species, optimizing the stocking density to prevent the cannibalistic interaction, besides having continuous feeding is a paramount.

Determining the Effect of Different Reproduction Factors on the Yield and Hatching of Tenebrio Molitor Eggs.

Simple SummaryThis study investigated the effect of various factors on the reproduction of the yellow mealworm Tenebrio molitor. More specifically, the effect of (1) the use of a grid, (2) oviposition duration, (3) age of the beetles and (4) beetle density were examined. For these parameters, it was investigated how they influence the number of eggs laid per beetle as well as the egg hatching rate and time. All these factors had a clear impact on the number of eggs. The results of this study will help producers to optimize their breeding method in order to obtain higher yields.Whereas the production of conventional livestock can rely on years of knowledge and experience, the mealworm production industry is still in its early stages. Although the yellow mealworm Tenebrio molitor has been cultivated as feed for pets and zoo animals for quite some time, the optimization of the reproduction process has not been widely explored. For reproduction, beetles are placed in crates supplemented with a substrate to oviposit their eggs. After a specified time, the beetles are removed, and the eggs are further cultivated to develop into larvae. Factors such as oviposition duration and beetle density influence the number of produced mealworms per beetle, partly due to the cannibalistic behavior of the beetles. However, reproductive success has mostly been assessed by determining the number of offspring several weeks after oviposition. As a result, the number of eggs laid and their hatch rates are unknown. In this research, eggs are separated from the oviposition substrate, i.e., harvested. This approach allows to determine the influence of beetle density, oviposition duration, beetle age and the use of a grid during oviposition on the number of eggs produced and the egg hatching rate and timing thereof. In addition, the influence of the harvesting method on the hatching of T. molitor′s eggs was determined.

Trophic ecology of the deep-sea squid Moroteuthopsis ingens (Cephalopoda: Onychoteuthidae) from the Chatham Rise, Aotearoa New Zealand

ABSTRACT Cephalopods form important components of marine trophic systems worldwide, including those in the South Pacific. Moroteuthopsis ingens (Onychoteuthidae) is one of the most abundant deep–sea squids in the Aotearoa New Zealand region and is preyed upon by predators such as the sperm whale and orange roughy. However, despite the many publications on M. ingens’ diet, knowledge on its feeding ecology remains limited. In this study, we analysed the prey of M. ingens from the Chatham Rise (an ecologically and economically important region east of Te Waipounamu/New Zealand’s South Island) using DNA barcoding and otolith identification. Lanternfishes (Myctophidae) were the most frequently encountered prey item, but other teleost species, cephalopods and crustacean fragments were also found, indicating opportunistic and likely cannibalistic feeding behaviour. Five fish species (including a possibly undescribed species of Gymnoscopelus) and Bathyteuthis abyssicola are reported as prey items of M. ingens for the first time. Moroteuthopsis ingens appears to be a component of several dynamic food chains and likely plays an important role in the transfer of carbon throughout marine environments in the Southern Hemisphere.

In pursuit of the ultimate pollen substitute (insect larvae) for honey bee (Apis mellifera) feed

Finding a pollen substitute for honey bees that is nutritionally adequate and affordable is a scientific and practical challenge. We attempted a new rational approach and tried to exploit honey bees’ natural cannibalistic behavior. We tested processed insect larvae as a food source that is nutritionally similar to bee brood, and which can easily be produced on a large scale. In cage experiments, monitoring bee mortality, food consumption and changes in bee body parts’ weights showed that flour obtained by grinding dried yellow mealworm larvae has the potential to become an excellent component for pollen substitution. Bees from the cage group fed Tenebrio molitor patties (TG) demonstrated overall best results in comparison to sugar patties fed bee group (CG), yeast patties fed bee group (YG) and pollen patties fed bee group (PG). They did not lose weight as rapidly as the CG, did not defecate inside cages as the YG, nor show increased mortality as the PG. At the same time, TG consumed less food (mean 13.7 g/cage) than CG (16.8 g/cage), YG (20.4 g/cage) and PG (23.9 g/cage) within the period of 28 days. Bees’ gut increase in weight was lowest in the CG, followed by TG and PG and was the highest in the YG which resulted in diarrhea after 14 days. Bees from TG did not lag behind other bees in head, thorax and abdomen weight after 28 days. We demonstrated that processed yellow mealworm larvae (T. molitor) can be used as an ingredient for honey bee feed.

Fast detection of cannibalism behavior of juvenile fish based on deep learning

Special behavior detection of fish is an effective way to ensure fish welfare and improve the intelligent level of aquaculture. However, due to the influence of the breeding environment and physiological factors, fish are prone to cannibalism during the juvenile period. In order to effectively monitor the behavior of the fry, this article proposes a real-time detection scheme based on the improved You Only Look Once (YOLO)-v5 to detect the cannibalism of grouper fry in recirculating aquaculture system(RAS). The specific improvements are as follows: (1) Multi-head attention mechanism is used to obtain global information in the last block of the backbone network (2) According to the idea of BIfpn, nodes that contribute little in the feature network which combines different features the neck is deleted. At the same time, feature fusion is added for nodes whose input and output are in the same layer (3) The lightweight general upsampling operator Carafe is used to replace the original upsampling. The experimental results show that the improved YOLOv5 model achieves 97% accuracy in the detection of cannibalism behavior of juvenile fish, effectively solving the problems of small targets, severe occlusion and motion blur in the culture environment. Meanwhile, compared with the YOLOv5s model, the improved model has 12.6% and 14% improvement in detection accuracy and processing speed, respectively, and achieves the requirements of high accuracy and real-time detection. In the actual aquaculture environment, farmers can take corresponding measures according to the detection results, which can effectively improve the survival rate and economic benefits of aquaculture.

An investigation into the association between cannibalism and serial killers

The aim of the current study was to compare and contrast non-cannibalistic and cannibalistic serial killers. Using case study data, the present study assessed common patterns among the life histories of cannibalistic serial killers compared to those of a control sample of serial killers that did not commit cannibalism. These include but are not limited to childhood experiences, socio-economic status, biological abnormalities and life events. Results indicated that factors that may differentiate cannibals from non-cannibals likely result from childhood influences, rather than influences at the time of the kill. Findings may be used to identify potential warning signs or triggers for cannibalistic behaviour.

Resource competition explains rare cannibalism in the wild in livebearing fishes.

Cannibalism, the act of preying on and consuming a conspecific, is taxonomically widespread, and putatively important in the wild, particularly in teleost fishes. Nonetheless, most studies of cannibalism in fishes have been performed in the laboratory. Here, we test four predictions for the evolution of cannibalism by conducting one of the largest assessments of cannibalism in the wild to date coupled with a mesocosm experiment. Focusing on mosquitofishes and guppies, we examined 17 species (11,946 individuals) across 189 populations in the wild, spanning both native and invasive ranges and including disparate types of habitats. We found cannibalism to be quite rare in the wild: most populations and species showed no evidence of cannibalism, and the prevalence of cannibalism was typically less than 5% within populations when it occurred. Most victims were juveniles (94%; only half of these appeared to have been newborn offspring), with the remaining 6% of victims being adult males. Females exhibited more cannibalism than males, but this was only partially explained by their larger body size, suggesting greater energetic requirements of reproduction likely play a role as well. We found no evidence that dispersal‐limited environments had a lower prevalence of cannibalism, but prevalence was greater in populations with higher conspecific densities, suggesting that more intense resource competition drives cannibalistic behavior. Supporting this conclusion, our mesocosm experiment revealed that cannibalism prevalence increased with higher conspecific density and lower resource levels but was not associated with juvenile density or strongly influenced by predation risk. We suggest that cannibalism in livebearing fishes is rare in the wild because preying on conspecifics is energetically costly and only becomes worth the effort when competition for other food is intense. Due to the artificially reduced cost of capturing conspecifics within confined spaces, cannibalism in captive settings can be much more frequent.

Egg cannibalism as a foraging tactic by less fit Glaucous-winged Gulls (Larus glaucescens)

Cannibalism, the killing and eating of conspecifics of any life stage, leads to a variety of behavioral and ecological consequences and is influenced by a range of environmental circumstances among numerous taxa. In birds, cannibalism is particularly well known among gulls. Although multiple studies have linked cannibalism to egg and chick failure in gull populations, gull cannibal behavior is poorly understood. During the 2014 and 2015 breeding seasons, we observed the behavior of Glaucous-winged Gulls (Larus glaucescens) that used conspecific egg predation, a form of cannibalism, as a feeding tactic on Protection Island, Washington, USA. Most egg stealing by egg cannibals occurred during colony disturbances, especially by Bald Eagles (Haliaeetus leucocephalus), but egg stealing often occurred without concurrent disturbances. Among other findings, our data showed that egg cannibals were always males, the number of eggs stolen each day correlated with the daily number of eggs laid, egg cannibals ate fewer fish than non-cannibals, and the reproductive success of egg cannibals was lower than that of non-cannibals. This study provides the most comprehensive evaluation to date of how larid cannibals find, capture, and eat conspecific eggs, and it includes the first assessment of reproductive success of egg cannibals in comparison with non-cannibals.