Rate Of Cannibalism Research Articles

Size matters: Antagonistic effects of body size on courtship and digging in a wolf spider with non-traditional sex roles

Body size, nuptial gift characteristics and courtship behaviour, among other traits, can reflect the quality of a potential mate and, thus, might be under sexual selection. To maximize their mating success, individuals can show behavioural plasticity in sexual context. Allocosa senex is a burrow-digging wolf spider that exhibits reversal in courtship roles and in sexual size-dimorphism expected for spiders. Males construct the mating refuge and females prefer males that build longer burrows, which are considered as nuptial gifts because they are delivered to them after mating. This study aims to determine whether male body size and female reproductive status influence burrow dimensions, courtship displays, female preferences and cannibalism rate in A. senex. For that purpose, we allowed males to construct burrows and performed sexual trials under laboratory conditions. Larger males were more courted by females, and in turn, they expressed more vibratory behaviours during courtship. However, and contrary to our expectations, smaller males constructed longer burrows. We suggest that males of A. senex exhibit size-dependent behavioural plasticity, and when they are smaller, they invest more in burrow construction to compensate their lower opportunities of courting intensively as larger males. In addition, females courted differentially according to their reproductive status, overriding male preferences for virgin females. This study opens several doors to future research regarding mutual choice in A. senex and the traits assessed by males and females during courtship, as well as about the influence of intrinsic and extrinsic factors shaping reproductive decision-making in this and other wandering spider species.

TINGKAH LAKU LOBSTER PASIR (Panulirus homarus) YANG DIPELIHARA PADA SHELTER BERBEDA

Efforts are being made to reduce the high rate of cannibalism by using shelters in their maintenance of cages. Shelters are needed as a hiding place for moulting of lobsters, as well as expanding the living area. The aims of this study was to determine the behavior of spiny lobster including the frequency of molting and the level of cannibalism. This research took place in July–October 2021, at the Vocational School, IPB University. The design used in this research was a completely randomized design (CRD) using 4 treatments and 3 replications. The treatments in this study consisted of rearing of lobster with box-hole brick shelter (A), rearing of lobster with round hole brick shelter (B), rearing of lobster with pipe shelter (C) and rearing of lobster without shelter (K). The molting frequency of lobsters reared with box-hole shelters tended to be higher (60.0%) than other treatments but not significantly different (P>0.05). The percentage of cannibalism in lobsters reared without shelters / control (47.67%) tended to be higher than lobsters reared in batako shelters.

Correction to: Cannibalism by damselflies increases with rising temperature.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Gilbert Benjamin, Kirk Devin and Shea Dylan 2021Correction to: Cannibalism by damselflies increases with rising temperatureBiol. Lett.172021045120210451http://doi.org/10.1098/rsbl.2021.0451SectionSupplemental MaterialYou have accessCorrectionsCorrection to: Cannibalism by damselflies increases with rising temperature Benjamin Gilbert Benjamin Gilbert http://orcid.org/0000-0002-4947-6822 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B3 Google Scholar Find this author on PubMed Search for more papers by this author , Devin Kirk†,‡ Devin Kirk Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B3 Google Scholar Find this author on PubMed Search for more papers by this author and Dylan Shea Dylan Shea http://orcid.org/0000-0001-6524-5381 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B3 Google Scholar Find this author on PubMed Search for more papers by this author Benjamin Gilbert Benjamin Gilbert http://orcid.org/0000-0002-4947-6822 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B3 Google Scholar Find this author on PubMed Search for more papers by this author , Devin Kirk†,‡ Devin Kirk Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B3 Google Scholar Find this author on PubMed Search for more papers by this author and Dylan Shea Dylan Shea http://orcid.org/0000-0001-6524-5381 Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B3 Google Scholar Find this author on PubMed Search for more papers by this author Published:06 October 2021https://doi.org/10.1098/rsbl.2021.0451This article corrects the followingResearch ArticleCannibalism by damselflies increases with rising temperaturehttps://doi.org/10.1098/rsbl.2017.0175 Denon Start, Devin Kirk, Dylan Shea and Benjamin Gilbert volume 13issue 5Biology Letters17 May 2017Biol. Lett.13, 20170175. (Published online 17 May 2017) (doi:10.1098/rsbl.2017.0175)(1) The experimental design crossed temperature with variation in hatching time, with temperature differences created through water baths so that several hatching time treatments were replicated in each batch. The original data posted were lacking data on the water bath, lacked appropriate metadata and included additional columns and data sheets not used in the analysis of the experiment. We have posted the corrected data sheet that includes the water bath information to Dryad [1].(2) In the original paper, we stated that cannibalism rate increased significantly with temperature, variation in hatching time, and their interaction. A reanalysis of the data [2] showed that temperature was only significant through its interaction with variation in hatching time (temperature F1,6 = 0.2, p = 0.66; temperature × variation in hatching time F1,114 = 6.2, p = 0.014). Variation in hatching time was also significant as a main effect (F1,114 = 34.9, p < 0.001). Owing to concerns about interpreting models with an interaction when the main effect is not significant, we used a model comparison approach to compare a model with only variation in hatching time against the full model that included both predictors and their interaction [3]. We found support for the full model that included temperature as a main effect and in interaction with variation in hatching time (χ2 (2 d.f.) = 12.3, p = 0.002).(3) In the original paper, the error bars in figure 2b were incorrect (the lower bar was missing or truncated). The corrected figure, with confidence intervals estimated from our reanalysis, is below (figure 2b Corrected).(4) In the original paper, we reported the significant effect of activity rate on the proportion of communities that experienced cannibalism. We also reported that size differences (caused by variation in hatching time) also increased cannibalism, but did not report a statistic for the latter test. The full statistical test confirmed significant effects of activity rate on proportion cannibalized (z = 3.17, p = 0.002), and the significant effect of size differences (z = 2.1, p = 0.036). The interaction of these variables was not reported in the original paper and was not significant (z = −1.48, p = 0.14). Figure 2b Corrected: Activity rate (number of times an individual moved between 2 × 2 cm2 in 3 h, was greater at high temperature (°C). Error bars are the 95% confidence intervals generated with the emmeans package [4] in R [5].Download figureOpen in new tabDownload PowerPointFootnotes†Present address: Department of Biology, Stanford University, Stanford, USA.‡Present address: Department of Zoology, University of British Columbia, Vancouver, Canada.Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.5648351.© 2021 The Author(s)Published by the Royal Society. All rights reserved.

Optimization of In Vivo Production of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV).

Insect viruses have been used to protect crops and forests worldwide for decades. Among insect viruses, isolates of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) have proven potential for the control of Spodoptera frugiperda (J. E. Smith) (FAW)(Lepidoptera: Noctuidae), a pest of many economically essential crops across several continents. Mass production of SfMNPV depends on an in vivo system using host insect rearing. However, many factors can limit its production, including abiotic factors and host characteristics, such as the stage of development and an antagonist intraspecific interaction. Thus, to improve in vivo production, we verified the most suitable larval age to inoculate the virus and the influence of incubation temperature on viral production. Subsequently, cannibal behavior was verified in FAW larvae reared at different densities, while reproducing the conditions of the best treatments. The highest viral yield occurred when FAW larvae were inoculated at 10 and 8days old and incubated at 22°C and 25°C, respectively. Nonetheless, survival (lethal period in days) and cannibal behavior were positively influenced by larval development, which potentially increases the load of contamination and requires larval individualization for these production conditions. In contrast, 4-day-old larvae, which were inoculated and incubated at 31°C, also demonstrated high viral production, with lower rates of cannibalism and death on the same day, thereby showing potential. The information presented in this study is useful for the optimization of the in vivo production systems of SfMNPV.

Relatedness modulates density‐dependent cannibalism rates in Drosophila

Abstract Cannibalism is taxonomically widespread and can have large impacts on individual fitness and population‐level processes. As such, identifying how cannibalism rates vary in response to ecological cues is important for predicting species evolution and population dynamics. In this study, we aimed to identify several eco‐evolutionary factors that affect cannibalism rate and measure how they interacted with one another. To do this, we conducted two experiments using complimentary methods to measure how cannibalism rates varied among larval Drosophila melanogaster and Drosophila simulans in response to changes in conspecific relatedness, social familiarity and density. We found that larvae were more likely to cannibalise non‐related larval victims in both species, and that this effect increased at high densities in D. simulans. We found no evidence that Drosophila larvae use social familiarity to assess relatedness. Finally, in D. melanogaster, cannibalistic larvae prefer to cannibalise larvae that are being attacked by a greater number of conspecifics, implying that cues linked to conspecific abundance encourage cooperative cannibalism. By showing that cannibalism frequency in Drosophila spp. is sensitive to relatedness and several other factors, we reveal the complex relationship between cannibalism frequency and species ecology. Also, by showing that the effect of relatedness on cannibalism frequency is density dependent, we advance the current understanding of how ecological variables interact to affect kin selection. A free Plain Language Summary can be found within the Supporting Information of this article.

Effect of adult density on egg production, egg hatching success, adult mortality, nauplii cannibalism and population growth of the tropical calanoid copepod Acartia tropica

Present study evaluated the impacts of adult density on key biological parameters of a tropical estuarine calanoid copepod A. tropica. Egg production, egg hatching success (EHS), adult mortality (%), nauplii cannibalism (% hour−1), population growth and intrinsic rate of population increase in response to five different adult densities viz. 125, 250, 500, 1000 and 2000 adults/L were assessed. The highest individual egg production (IEP, eggs/female/day) was recorded at 125 adults/L treatment while relative egg production (REP, eggs/L/day) was highest at 1000 adults/L. EHS (24 h and 48 h) showed significant difference (p < 0.05) among the treatments with highest EHS recorded at 125 adults/L treatment and lowest EHS recorded at 2000 adults/L treatment. Moreover, the adult mortality and nauplii cannibalism were negatively correlated to adult density with significantly highest cumulative adult mortality (65 ± 3) and nauplii cannibalism (4.49 ± 0.27) recorded at 2000 adults/L. The highest population count after 8 days culture was recorded at 2000 adults/L treatment. However the lowest intrinsic rate of whole, live and adult population increase after 8 days culture was recorded at 2000 adults/L treatment. It is also observed that the population with an initial adult density of 2000/L decreases to a new stable equilibrium of 1000 adults/L after 8 days culture. Our results suggest to maintain A. tropica at a density of 1000 adults/L in batch culture with daily harvest of eggs and nauplii to maximise its productivity as live feed in aquaculture hatcheries.

Habitat ephemerality affects the evolution of contrasting growth strategies and cannibalism in anuran larvae.

Ephemeral streams are challenging environments for tadpoles; thus, adaptive features that increase the survival of these larvae should be favored by natural selection. In this study, we compared the adaptive growth strategies of Bombina orientalis (the oriental fire-bellied toad) tadpoles from ephemeral streams with those of such tadpoles from non-ephemeral streams. Using a common garden experiment, we tested the interactive effects of location (ephemeral vs. non-ephemeral), food availability, and growing density on larval period, weight at metamorphosis, and cannibalism. We found that tadpoles from ephemeral streams underwent a shorter larval period compared with those from non-ephemeral streams but that this difference was contingent on food availability. The observed faster growth is likely to be an adaptive response because tadpoles in ephemeral streams experience more biotic/abiotic stressors, such as desiccation risk and limited resources, compared with those in non-ephemeral streams, with their earlier metamorphosis potentially resulting in survival benefits. As a trade-off for their faster growth, tadpoles from ephemeral streams generally had a lower body weight at metamorphosis compared with those from non-ephemeral streams. We also found lower cannibalism rates among tadpoles from ephemeral streams, which can be attributed to the indirect fitness costs of cannibalizing their kin. Our study demonstrates how ephemeral habitats have affected the evolutionary change in cannibalistic behaviors in anurans and provides additional evidence that natural selection has mediated the evolution of growth strategies of tadpoles in ephemeral streams.

Density-Dependent Cannibalism in Dragonfly Nymphs (Odonata: Anisoptera) Overwintering in Temperate Freshwater Ponds.

Density-dependent mortality by predation and cannibalism has been observed in aquatic insects such as dragonflies in response to shrinking habitat caused by summer drought. Winter conditions might also reduce the amount of livable habitat in temperate ponds and could augment rates of cannibalism. We hypothesized that cannibalism in dragonfly nymphs would increase in winter due to a seasonal decrease in available habitat caused by stratified lower oxygen levels leading to increased nymph density around pond edges. To determine whether cannibalism in nymphs is density-dependent and size-dependent (i.e., with smaller nymphs consumed) we experimentally manipulated nymph density in aquaria. To evaluate whether these patterns are observed in nature during the winter, we conducted field surveys for nymphs in two ponds across the fall and winter seasons. When nymphs were housed at different densities for 24 h, cannibalism was density-dependent, and only smaller nymphs were preyed upon. Our field surveys found that fewer nymphs were caught in the late winter sampling period (mixed-effects model, P < 0.001), and that these were larger than nymphs caught in the fall, although both patterns were restricted to the deeper pond (P < 0.05). Our results were consistent with the process we hypothesized, and the observed reduction in dissolved oxygen at the bottom of the deeper pond. The lack of significant changes to the relative abundance and size of nymphs in the shallower pond reveals that differences in pond characteristics can influence the degree to which winter conditions induce density-dependent cannibalism among dragonfly nymphs.

Effects of food, kinship, and density on the longevity of spiderlings

Cannibalism is a behavioral characteristic found in a wide variety of animal groups. Although the rates of cannibalism can vary from one group to another, studies indicate that the main factors contributing to an increase in the frequency of such behavior are the availability of food, population density, the behavior and availability of victims, and environmental stress. We carried out different laboratory experiments to assess whether different factors such as the presence or absence of food among siblings and non-siblings, and at different densities among conspecific and heterospecific individuals, affect longevity of recently emerged Brazilian brown recluse (Loxosceles intermedia Mello-Leitão, 1934) and Chilean recluse (Loxosceles laeta (Nicolet, 1849)) spiderlings during periods of starvation. The results revealed that the survivorship of L. laeta during starvation was significantly higher than that of L. intermedia and that the addition of conspecific individuals increased survival rates by 1.5- and 1.6-fold, respectively. The tolerance of conspecifics differed between the two species, and generally, cannibalism was not observed, probably due to the risk of predation and limited consumption by weakened spiders, which coincided with the continued availability of endogenous vitelline reserves, thus indicating that the use of these spiderlings as a food resource may act to regulate starvation in more resistant spiders. The greater longevity and conspecific tolerance of L. laeta may be important factors contributing to the establishment of large populations of this spider in restricted areas, whereas for L. intermedia, hunger probably functions as a trigger for dispersal.

Family-specific chemical profiles provide potential kin recognition cues in the sexually cannibalistic spider Argiope bruennichi.

Kin recognition, the ability to detect relatives, is important for cooperation, altruism and also inbreeding avoidance. A large body of research on kin recognition mechanisms exists for vertebrates and insects, while little is known for other arthropod taxa. In spiders, nepotism has been reported in social and solitary species. However, there are very few examples of kin discrimination in a mating context, one coming from the orb-weaver Argiope bruennichi. Owing to effective mating plugs and high rates of sexual cannibalism, both sexes of A. bruennichi are limited to a maximum of two copulations. Males surviving their first copulation can either re-mate with the current female (monopolizing paternity) or leave and search for another. Mating experiments have shown that males readily mate with sisters but are more likely to leave after one short copulation as compared with unrelated females, allowing them to search for another mate. Here, we ask whether the observed behaviour is based on chemical cues. We detected family-specific cuticular profiles that qualify as kin recognition cues. Moreover, correlations in the relative amounts of some of the detected substances between sexes within families indicate that kin recognition is likely based on subsets of cuticular substances, rather than entire profiles.

Cannibalism and Necrophagy Promote a Resource Loop and Benefit Larval Development in Insects of Temporary Waters.

Simple SummaryThe consumption of conspecific individuals by cannibalism (i.e., the killing and eating of conspecific individuals) and necrophagy (i.e., feeding on dead individuals of the same species) has been documented in several insect species. Selective advantages have been proposed to explain the persistence of these behaviors in natural populations. In this paper, we tested the hypothesis that cannibalism and necrophagy lead to a significant resource loop within an insect cohort, allowing individual survival and development. With this aim, we performed laboratory and semi-field experiments using the tiger mosquito Aedes albopictus. Larval stages of this species develop in small aquatic habitats, such as tree holes and artificial containers. These latter are highly ephemeral habitats, where resources are often scarce and of poor quality (mainly leaf litter, wood, and vegetal detritus). We first estimated the relative rate of cannibalism and necrophagy. Then, we analyzed the effects of cannibalism and necrophagy on larval survival and adult yield. Consistent with our hypothesis, we found that conspecifics consumed about 50% of the initial cohort. Furthermore, conspecific consumption significantly increased the rate of adult emergence and larval survival, which supports that cannibalism and necrophagy can positively affect insect populations in temporary waters.Temporary aquatic habitats are contingent on the allochthonous inputs of plant and animal detritus, whose quality and availability can significantly affect the species developing in these habitats. Although animal detritus (i.e., invertebrate carcasses) is a high-quality food, it is an unpredictable and variable resource. On the contrary, conspecific individuals (dead or alive) are a nutritionally high-quality food source that is always available. In this context, conspecifics consumption, by cannibalism or necrophagy, can be a good strategy to overcome nutrient limitation and allow individual maintenance and development. Here, we tested this hypothesis by using the tiger mosquito Aedes albopictus. By carrying out laboratory and semi-field experiments, we first estimated the relative rate of cannibalism and necrophagy, under different larval densities. Then, we analyzed the effects of cannibalism and necrophagy on larval survival and adult yield. Consistent with our hypothesis, we found that cannibalism and necrophagy occurred under all experimental conditions, and that conspecific consumption had positive effects on individual development, as it significantly increased the rate of adult emergence and larval survival. Interestingly, about 50% of the initial cohort was consumed by conspecifics, suggesting that cannibalism and necrophagy can drive an important resources loop in temporary aquatic habitats.

Every-other-day clutch-initiation synchrony as an adaptive response to egg cannibalism in Glaucous-winged Gulls (Larus glaucescens)

Sea surface temperatures (SST) in the Pacific Northwest of North America rose 1 °C during the last half of the twentieth century. Cannibalism, a behavior observed in diverse taxa, is often associated with low food supplies, which for marine animals can be precipitated by high SSTs. In an 8 year study, we found that in years of higher sea surface temperatures, Glaucous-winged Gulls (Larus glaucescens) breeding in a colony in Washington State, Salish Sea, USA, tended to exhibit higher rates of egg cannibalism by males, higher levels of every-other-day clutch-initiation synchrony by females, and longer egg-laying seasons than in years of lower SST. Clutch-initiation synchrony increased the odds that an egg survived cannibalism and may serve as an adaptive response to egg cannibalism. Short-term climate and resource fluctuations associated with El Niño Southern Oscillation (ENSO) events may select for behavioral plasticity in marine organisms, allowing long-lived individuals such as marine birds to switch between alternative life history tactics. The implications for long-term SST warming, however, remain unknown.

Female control of a novel form of cannibalism during copulation in a South American widow spider

Sexual cannibalism is an extreme form of sexual conflict that may have broad evolutionary effects on mating behaviour. Latrodectus spiders (∼30 “widow” species) could enable comparative tests of the evolution of sexual cannibalism, but most species are poorly-studied. Here we describe the mating and remating behaviour of a species endemic to South America, L. mirabilis, with a focus on the occurrence and consequences of sexual cannibalism. Mating and cannibalistic behaviours were novel relative to other Latrodectus species. Cannibalism started during copulation when females grasped the male’s legs with their chelicerae, and continued as females pulled the male’s abdomen onto their chelicerae, without interrupting copulation. Cannibalism was initiated by females, and not facilitated by males as was observed in other Latrodectus species. Females frequently remated however, so cannibalized males might lose paternity to future rivals. We report high rates of cannibalism, with 70 % of males killed by females during their first mating, and 85 % killed by previously-mated females. We discuss our novel findings in the context of previous observations in other Latrodectus species, proposing that foundational studies in a wider range of species are necessary to support comparative tests about the evolution of sexual cannibalism within this model taxon.

Cannibalism as a potential factor affecting recruitment of the invasive Asian shore crab Hemigrapsus sanguineus

Cannibalism affects the population dynamics of many marine species, but its potential for influencing population sizes of non-native species is not well understood. A series of laboratory experiments was conducted in 2016 to examine the frequency of cannibalism in the Asian shore crab (Hemigrapsus sanguineus) and the factors influencing its rates of occurrence. Predators and prey varied in size from planktonic megalopae (the last larval stage) and the first benthic crab stage to small juveniles (3–6 mm carapace width, CW), large juveniles (7–10 mm CW), and adult crabs (12–15 mm CW). Individual crabs were paired with groups of smaller prey in glass culture dishes with sand and rocks as potential shelter for the prey, both with and without an alternative food source (commercial crab pellets). Adult and large juvenile crabs consumed megalopae, first-stage crabs and small juveniles, regardless of the presence of food. Megalopae were cannibalized the most heavily, and the size difference between predator and prey was an important factor determining cannibalism rates. Cannibalism of settling megalopae and newly settled juveniles by larger conspecifics could affect recruitment to benthic populations of this non-native crab species.

Assessment of growth characteristics, the survival rate and body composition of Asian sea bass Lates calcarifer (Bloch, 1790) under different feeding rates in closed aquaculture system.

One of the essential factors to be addressed in the development of aquaculture is the feeding regime. This study was investigated to assess the effects of feeding rate on growth performance, feed utilization, chemical body composition survival rate, cannibalism and morphological indices of Asian Seabass, Lates calcarifer. Intended for the trial, one hundred forty sea bass individuals with an average weight 5.47 ± 0.11 g were randomly distributed in 4 concrete tanks (914 cm × 183 cm 122 cm) each; length × width × depth) and volume 18,399 L, for total 68 days. The fishes were fed with a pelleted diet containing 46% crude protein for different feeding groups designated as (T1, T2, T3 and T4). The feed was supplied with a rate of (T1) 3%, (T2) 4%, (T3) 6%, and (T4) 9% of fish biomass per day and feeding frequency were maintained three times per day to all the groups. At the end of the trial water physicochemical parameters was in acceptable range for Asian sea bass growth. The average daily weight gain (g), weight gain (g) and specific growth rate (%) was significantly higher (p < 0.05) in T3 and T4 as compared to T1 and T2 group. The poorest feed conversion ratio was recorded in T1 group with 3% biomass per day. The cannibalism rate was significantly (p < 0.05) higher in T1 (3%) compared to T3 and T4 treatment. The morphological indices, condition factors (CF), viscerosomatic index and hepatosomatic index (HSI) was significantly higher in T4 group as compared to other treatments. The protein, moisture and ash contents of the whole biomass of the Asian sea bass were not significantly influenced by feeding rate. The fat levels in the fish bodies increased significantly (p < 0.05) with increasing feeding ratio. The phenomenal regression indicates that 6.5% feeding rate per day is optimum for best growth performance, survival and minimum cannibalism rate for Asian sea bass in captivity. The outcome of the finding will help in promotion for not only the coastal aquaculture in Pakistan abut also elsewhere.

Genetic component of cannibalism in Asian seabass Lates Calcarifer

Cannibalism in the early phase of growth development has been a major concern for marine finfish, including Asian seabass Lates calcarifer, as it is one of the key factors determining economic return of commercial hatcheries. This study thus explored genetic variation in cannibalism through estimation of heritability for cannibalism rates recorded at four different time intervals (from stocking to 10d, 11–20d, 21–30d and 0−30d). The study included a total of 18,841 fish produced from 64 full- and half-sib families (41 sires and 56 dams). Threshold mixed model analysis showed that there were significant differences in cannibalism rates (p < 0.001) among families; the cannibalistic rate ranged from 12.97 to 55.62 %. The heritability (h2) for cannibalism was low to moderate (0.11 ± 0.01 to 0.28 ± 0.06) across the three statistical models used. The common full sib effect (c2) estimated for cannibalism rates accounted for only 3–9% of the total phenotypic variation. Genetic correlations for the cannibalistic rates between successive measurement intervals were moderate to high and positive (0.55 to 0.97). Cannibalism displayed a negative (i.e., favourable) genetic association with body weight, although all the estimates had high standard errors. The new set of genetic parameters obtained from this study suggests that family selection for reduced cannibalism rate and improved survival rate during the fingerling phase could be effective for this population of Asian seabass L. calcarifer.

Capturing, induced spawning, and first feeding of wild-caught Pseudopimelodus mangurus, an endangered catfish species

This study aimed to describe a procedure for sampling, reproduction, and first feeding of the Neotropical catfish Pseudopimelodus mangurus, an endangered fish species. Wild adult P. mangurus specimens were collected in the Mogi Guassu River and subsequently induced to spawn in laboratory conditions. After hand-stripping, the females, the average weight of the oocytes was 143 ± 1.6 g, with a fecundity of 718 ± 49.8 oocytes g-1. The diameter of the oocytes non-hydrated was 1,226.3 ± 47.7 μm to 1,761.2 ± 26.4 μm after hydration. The fertilization rates were 98.00 ± 0.63%, and the hatching rate was 68.94 ± 11.83%. The first feeding was made three days post-hatching with six different treatments, in which the best results arose with sequential feeding with Artemia nauplii, Astyanax altiparanae and Prochilodus lineatus larvae. This condition resulted in a final length of 2,012.7 ± 44.8 μm by the 10th day of the experiment, higher survival (65 ± 0.9%) and lower cannibalism rate (14 ± 0.3%). The data obtained in this study is important for the establishment of reproductive biotechniques, mass production of P. mangurus, and future establishment of ex-situ GenBank.

Improving pikeperch larviculture by combining environmental, feeding and populational factors

Pikeperch (Sander lucioperca) has a high potential for inland aquaculture diversification in Europe. Bottlenecks (i.e. low survival, cannibalism and deformity rates) hamper further expansion of pikeperch culture, because of the weak production performances at the nursery level. To improve the production of pikeperch juveniles under recirculation system we used a pilot scale larval rearing system (700 L tanks) and multifactorial designs. Three successive larval rearing trials (duration: 35-49 days) were conducted to identify the best combination of environmental, feeding and population factors. Considering the main significant effects observed on survival, growth, swim bladder inflation rates and biomass gain, a favourable combination of twelve factor (F) modalities was proposed (F1- initial density: 100 larvae.L-1, F2- no sorting of fish jumper, F3- no sibling population, F4- eggs from large females, F5- discontinuous feeding, F6- no co-feeding, F7- light intensity: 50 lx, F8- beginning of the weaning at 16 dph (days post-hatching), F9- weaning duration: 9 days, F10- water renewal rate of 100 % per hour, F11- tank cleaning during morning and F12- tank bottom-up water current). A final validation step was realized over a last trial (seven replicates, duration: 49 days), and validated with the best productive results obtained over the global experimental period (2015-2018). These results were: a final body weight of 815.64 ± 95.34 mg, a survival rate of 16.9 ± 1.7 %, a specific growth rate of 15.1 ± 5.9 %.d-1, a final fish biomass of 9.55 ± 0.23 kg, a swim bladder inflation rate of 92.6 ± 3.2 % and a food conversion rate of 0.65 ± 0.02 (dry food). The final stocking density was 13.6 kg.m-3 of rearing volume. Authors were able to validate and provide a reliable basic protocol for pikeperch larval rearing using recirculating units.

Impacts of female body size on cannibalism and juvenile abundance in a dominant arctic spider.

Body size influences an individual's physiology and the nature of its intra- and interspecific interactions. Changes in this key functional trait can therefore have important implications for populations as well. For example, among invertebrates, there is typically a positive correlation between female body size and reproductive output. Increasing body size can consequently trigger changes in population density, population structure (e.g. adult to juvenile ratio) and the strength of intraspecific competition. Body size changes have been documented in several species in the Arctic, a region that is warming rapidly. In particular, wolf spiders, one of the most abundant arctic invertebrate predators, are becoming larger and therefore more fecund. Whether these changes are affecting their populations and role within food webs is currently unclear. We investigated the population structure and feeding ecology of the dominant wolf spider species Pardosa lapponica at two tundra sites where adult spiders naturally differ in mean body size. Additionally, we performed a mesocosm experiment to investigate how variation in wolf spider density, which is likely to change as a function of body size, influences feeding ecology and its sensitivity to warming. We found that juvenile abundance is negatively associated with female size and that wolf spiders occupied higher trophic positions where adult females were larger. Because female body size is positively related to fecundity in P. lapponica, the unexpected finding of fewer juveniles with larger females suggests an increase in density-dependent cannibalism as a result of increased intraspecific competition for resources. Higher rates of density-dependent cannibalism are further supported by the results from our mesocosm experiment, in which individuals occupied higher trophic positions in plots with higher wolf spider densities. We observed no changes in wolf spider feeding ecology in association with short-term experimental warming. Our results suggest that body size variation in wolf spiders is associated with variation in intraspecific competition, feeding ecology and population structure. Given the widespread distribution of wolf spiders in arctic ecosystems, body size shifts in these predators as a result of climate change could have implications for lower trophic levels and for ecosystem functioning.

Behavioural correlations and aggression in praying mantids

Distinct behaviours can co-vary within individuals. As such, the magnitude of certain behaviours may be partly predicted by other behaviours, rather than the environment. This can constrain behaviours, potentially reducing behavioural variability. Pre-copulatory sexual cannibalism, the consumption of potential mates before copulation, can lead to females remaining unmated, particularly if males are rare. One possible explanation for the persistence of pre-copulatory cannibalism is that sexual cannibalism is correlated with high levels of aggression towards prey. Here, we test this in two species of praying mantis: the highly cannibalistic Miomantis caffra and the less cannibalistic Orthodera novaezealandiae. If cannibalism in M. caffra is linked to aggression towards prey, we predicted that (1) M. caffra would be more aggressive towards prey than O. novaezealandiae, (2) female M. caffra would be more aggressive than males, (3) aggression towards prey would be correlated across juvenile and adult instars for M. caffra but not O. novaezealandiae, and (4) aggression towards prey would be associated with a propensity for sexual cannibalism among individual M. caffra. We found evidence supporting predictions one and two, but not predictions three and four. Surprisingly, aggression was shown to be repeatable and correlated across instars for O. novaezealandiae but not M. caffra. Our results suggest sexual cannibalism is not a product of behavioural co-variation, even in clades where sexual cannibalism is common. This suggests that sexual cannibalism evolves due to the direct benefits it brings to females, rather than being a by-product of high aggression towards heterospecific prey.Significance statementIn some animals, different behaviours co-vary within individuals. This may lead to the emergence of costly behaviours and reduce behavioural plasticity. It is theorized that pre-copulatory cannibalism is a costly behavioural by-product of selection for high levels of aggression towards prey. However, there are very few studies that explicitly test this. Here, we provide a behavioural comparison between two species of praying mantis that vary in their propensity to cannibalize and tested whether general aggression is linked cannibalism. We found that aggression towards prey in adults can be linked to juvenile aggression but not a propensity for cannibalism. Although cannibalism rates were higher in the species that was more aggressive towards prey, aggression towards prey was not linked to cannibalism within individuals. This suggests that pre-copulatory cannibalism is not a behavioural by-product but a result of direct selection.