Risk Of Cannibalism Research Articles

Males discriminate between substrate-borne cues of conspecific females based on age and mating status in the jumping spider, Habronattus brunneus.

Sexual selection is often studied with a focus on female mate choice, wherein females evaluate male signals to select an optimal mate. However, in some systems, males should also make careful decisions about the females they choose to court, particularly when faced with the risk of precopulatory sexual cannibalism. Here, we explore the idea that male jumping spiders (Habronattus brunneus) may mitigate this risk by responding to female cues probably associated with female aggression and/or receptivity. We tested mature male spiders' ability to discriminate between substrate-borne cues (i.e. silk and excreta) produced by conspecific females of different ages and mating statuses. We found that males spent more time exploring cues produced by mature, non-mated females compared with either immature females or mated females. Heightened interest in cues produced by females that are sexually mature but not yet mated may allow males to reduce cannibalism risk, reduce wasted courtship effort and increase their reproductive success. The use of chemical and/or tactile cues in jumping spider courtship behaviour has been vastly understudied compared with the ways they use vision; this study provides the groundwork for understanding how these sensory modalities interact.

Research note: Expert opinions of feather sucking and licking behavior in meat chicken breeder birds

Feather sucking, or feather licking, has been reported anecdotally by employees in the Australian meat chicken breeder industry, but scarcely in the scientific literature. Consequently, the causes and implications of this behavior in meat chicken breeding chickens is relatively unknown. We surveyed 17 industry experts to generate hypotheses about feather sucking behavior. We aimed to understand the frequency and when it occurs, and attempted to understand what may cause an ‘outbreak’. The recruitment of participants was intentionally biased towards Australian perspectives; only 5 of the 17 participants were international. All participants, except 1, had seen feather sucking/licking behavior (94.1%) and most participants (80%) suggested that the behavior was most frequently observed during rearing. Participants presented varying concerns about this behavior, ranging from the perspective that it was ‘normal’ and had no impact on welfare, to concerns about mating injuries due to damaged feathers, increased risk of feather pecking and cannibalism, and psychological stress indicated by expression of repetitive (seemingly) functionless behavior. ‘Feather licking’, ‘feather sucking’, ‘feather eating’, and ‘feather pecking’ were terms used interchangeably, leading to confusion by participants about the cause and implications of the target behavior. The most common factors reported as the cause were boredom (52.9%), nutritional deficiencies (47.1%), and feed restriction (41.2%) and more than 80% of respondents agreed that stress contributes to feather sucking. The outputs from this study reflect only a small, but expert, number of opinions on feather sucking/licking behaviors in the Australian meat chicken breeder industry. A systematic understanding of this behavior is needed to provide insight into causation and the implications for welfare.

How molting locusts avoid cannibalism

Abstract Group living has various benefits, but it also carries costs, such as risk of cannibalism. Molting is a vulnerable period of being cannibalized in juvenile arthropods, but how gregarious arthropods avoid this threat is poorly understood. Here, we examined how actively migrating gregarious nymphs of desert locust, Schistocerca gregaria, avoid cannibalism during molting, in the Sahara Desert of Mauritania. In the field, gregarious nymphs cyclically march and feed on grass during the day. Our field observations found that marching behavior helped separating pre-molting and cannibalistic non-molting nymphs. Cannibalistic non-molting nymphs marched away from roost plants, leaving sedentary pre-molting nymphs behind, creating cannibal-free spaces. Some non-molting nymphs reached a pre-molting state after daytime marching, thus both pre- and non-molting nymphs roosted on same plants at night. However, pre-molting nymphs moved away from conspecifics prior to molting. Starvation experiments confirmed that food-satiation decreased cannibalistic necrophagy. Physiological surveys of diel feeding and molting patterns revealed that nymphs molted at times when conspecifics were food-satiated rather than hungry. Hence, our results indicate that behavioral and physiological traits of gregarious locusts could function to spatiotemporally separate molting locusts from cannibalistic conspecifics, thus reducing molting-associated cannibalism. This is the first report of migration-dependent molting synchrony as a mechanism reducing costs of aggregation in gregarious arthropods.

Transporting Tenebrio molitor Eggs: The Effect of Temperature, Humidity and Time on the Hatch Rate

Insect farming can be an important tool in the realization of a more sustainable future. With a growing insect industry, animal transportation between and within farms is expected to increase. For Tenebrio molitor, using eggs may be convenient as it eliminates the risk of cannibalism, food shortages and has a low risk of asphyxiation. However, there are at least three important variables during regular transport: time, temperature and relative humidity. For each one, as well as their interactions, there is a need to assess the effect on the hatch rate and establish lower and upper boundaries at which a good hatch rate of the eggs is possible. In this study, a total of 20 temperature/RH combinations were assessed (between 5–40 °C and 40–80% RH), with an exposure time ranging between 1 and 6 days for each combination. The results indicated that between 15 and 30 °C no negative effects were observed at any of the assessed RH or exposure times. Higher temperatures did result in a lower hatch rate; no eggs hatched at 40 °C, even after one day. Lower temperatures of 5 and 10 °C can be endured without pronounced adverse effects but only for a limited time (resp. 1 or 2 days). Including relative humidity in the model did improve the overall fit, but the effect is limited (compared to temperature or exposure time) with a slightly better hatch rate in dryer conditions at the extreme temperatures.

Stage and sex-dependent responses of immature predatory mites (Blattisocius dentriticus) to predation risk from cannibalistic conspecifics

Blattisocius dendriticus (Acari: Blattisociidae) is a predatory gamasid mite with the potential for the biological control of mites attacking stored products. However, its interactions with its cannibalistic conspecifics are poorly understood. In this study, we determined the effects of predation risk from cannibalistic conspecifics on the survival, development, prey consumption, and behaviour of the predator by comparing the performance of predators exposed to cues from their conspecifics with their counterparts exposed to cues of their prey and the prey food source. The results show that the survivorship of immature predators was similar across treatments. However, predators under cannibalistic risks extended the duration of their immature stages due to a prolonged protonymphal stage. Moreover, the effects of predation risk were also sex-specific, with the males responding to the risk of cannibalism, but not the females. By highlighting the non-consumptive effects of cannibalistic conspecifics on predators associated with sex and maternal age, the present study improves our understanding of the indirect effects of cannibalism and its interactions with other factors, which may affect the performance of B. dentriticus as a biological agent.

Risky business: males choose more receptive adults over safer subadults in a cannibalistic spider.

Understanding factors affecting male mate choice can be important for tracking the dynamics of sexual selection in nature. Male brown widow spiders (Latrodectus geometricus) mate with adult as well as immature (subadult) females. Mating with adults involves costly courtship with a repertoire of signaling behaviors, and typically ends with cannibalism (“self-sacrifice” initiated by male somersault). Mating with subadults involves brief courtship with behavioral repertoire reduced to one component (vibration) and no cannibalism. We examined male mate choice as a function of risks associated with different types of mates and the cues available to courting males. Previous studies showed male preference for adults based on air-borne pheromones, but it was unclear whether that preference is maintained after males reach female’s webs. We show that males prefer adults also based on silk-borne contact cues. To determine which types of cues trigger different courtship components, we swapped adults and subadults between webs. We showed that contact with adult females’ webs triggers two courtship behaviors from the repertoire, with adult female’s bodies triggering additional behaviors. However, vibrational signals occur regardless of the web origin or female developmental stage. We conclude that males recognize subadult females as potential mates, but are more likely to invest in costly courtship behaviors and mating attempts with adults. In our experiments, subadults were less likely to mate than adults. We conclude that mating with adults could be the preferred option for males because of the higher likelihood of copulation, even at the cost of a higher risk of cannibalism.

The effect of microhabitat use on the foraging and diet of the striped bark scorpion, Centruroides vittatus (Buthidae: Scorpiones) in blackbrush habitat of south Texas

Microhabitat use by predators can be influenced by prey availability, predator size and risk of cannibalism. The preferred microhabitat for a predator can be for foraging, feeding or as a refuge. In this study in south Texas, Centruroides vittatus (Say, 1821) of all size classes utilized both ground and vegetation microhabitats. There was a high proportion of scorpions with caterpillars in legumes and low proportion of scorpions with any of the prey types on the ground. The median height of scorpions with prey did vary, with scorpions on legumes with caterpillar prey the highest and scorpions on other vegetation with dangerous prey the lowest. Intermediate size scorpions used legumes at a high frequency during January–April, and large scorpions used succulents at very high frequency during September–December. Scorpions climbed higher in blackbrush and other legumes than in other vegetation types. These results suggest that scorpions are actively foraging for caterpillars in legumes, and legumes are a quality microhabitat for foraging. The low proportion of scorpions with prey on the ground suggests that C. vittatus feed on prey on vegetation even if the prey was captured on the ground. A possible advantage for the scorpion to handle and consume prey on vegetation is lower predation risk or interference while feeding. The high use of succulents by the large scorpions cannot be explained by foraging success. A possibility is that succulents are preferred refuges by all C. vittatus but smaller scorpions avoid succulents because of the risk of cannibalism by the larger scorpions.

When and how to use a “fighter brand” to combat a low-price entry

PurposeManagers have become wary of launching fighter brands. But they should not give up on a fighter brand strategy altogether: under certain conditions a fighter brand can be effective, if it is correctly positioned.Design/methodology/approachThe authors’ decision-making framework to help managers think through the specific design of a fighter brand is supported by field experience in designing and successfully launching fighter brands. 10; The framework takes managers through four steps. 10;FindingsA fighter brand can be designed to combat, and ideally eliminate, low-price competitors while protecting an organization’s premium-price offerings.Practical implicationsIdentifying must-have features “must-haves” is at the core of the fighter brand framework.Originality/valueIf a company’s strategists can identify at least one unique must-have feature for the value segment with high certainty, and remove it from the fighter brand targeted at the price segment, the risk of cannibalization is minimal.

Male courtship reduces the risk of female aggression in web-building spiders but varies in structure

AbstractMale courtship serves multiple functions in addition to inducing females to accept them as a mate. In predatory species, male courtship can function to reduce the risk of sexual cannibalism. This is particularly important in web-building spiders in which males risk being mistaken for prey when they enter the female’s predatory trap—the web—in order to commence courtship. Male spiders generate vibrations by shuddering in the female’s web. Shudder vibrations can delay female aggression, even toward prey struggling in the web. We predicted that shudder vibrations are highly conserved across species of web-building spider as males all face the same constraint of not being mistaken for prey by females. We examined how conserved shudder vibrations are across web-building spiders by testing whether female Trichonephila plumipes delay aggressive behavior toward real prey struggling in the web during playback of conspecific or heterospecific (Argiope keyserlingi) male shudder vibrations. We found that while conspecific shudder vibrations do indeed delay female predatory behavior, heterospecific male shudder vibrations do not. There is evidence of shudder or shudder-like vibrations in male courtship behavior across web-building spider families, but these vary in structure. This suggests that despite strong constraints on courtship signal design to separate predatory responses from sexual responses, there is additional selection driving the divergence of signals across distantly related spider species.

Measuring Circular Supply Chain Risk: A Bayesian Network Methodology

The world is facing economic, as well as social, crisis due to the COVID-19 pandemic. Implementing sustainable practices is one of the possible ways to address these issues. Adopting circular oriented techniques throughout the supply chain not only guarantees economic profitability, but also provides an edge to the organization in the market of fierce global competition. The concept of implementing circularity in the supply chain is novel and dynamic in nature, and it involves certain risk. In this study, a Bayesian Network methodology is adopted to analyze how the risk propagation takes place in a circular supply chain network of an automobile organization. The circular supply chain network consists of a group of manufacturers, retailers and recyclers, located in the Delhi–NCR region. Economic, environmental, social, technological, waste management, agile vulnerability, and risk of cannibalization are the major risk categories that were identified through an extensive literature review. Further, the impact of risk on the performance of the circular supply chain is analyzed by considering performance parameters such as lost sales, impact on supply chain revenue, and inventory holding cost. Risk exposure index is incorporated into the study to analyze the vulnerability of each node. The findings of the study reveal that the reverse side of the circular supply chain can be a source of risk propagation during the implementation of the circularity concept. This work is carried out under a single industry domain. In the future, risk propagation analysis can be examined in the supply chain of other sectors. The findings of the study can assist the supply chain managers and the risk experts to focus on the areas that are more vulnerable to risk.

Increased male mating success in the presence of prey and rivals in a sexually cannibalistic mantis

Abstract Precopulatory sexual cannibalism—or cannibalism without mating—is expected to promote the evolution of male strategies that enhance mating success and reduce the risk of cannibalism, such as preferentially approaching feeding females. Sexual selection on male competitiveness has the potential to alter male mating decisions in the face of cannibalism risk, but such effects are poorly understood. We investigated the effect of prey availability and male–male competition on mating incidence in the highly cannibalistic Springbok mantis, Miomantis caffra. We found that matings were initiated more rapidly and more often in the presence of prey, suggesting that females distracted with foraging may be less of a threat. Competition between males also hastened the onset of copulation and led to higher mating success, with very large effects occurring in the presence of both prey and competitors, indicating that intrasexual competition may intensify attraction to foraging females. Taken together, our results suggest that precopulatory cannibalism has selected for male preference for foraging females and that males adjust their mating strategy to both the risk of competition and the threat of cannibalism.

Plant defense responses triggered by phytoseiid predatory mites (Mesostigmata: Phytoseiidae) are species-specific, depend on plant genotype and may not be related to direct plant feeding

Zoophytophagous arthropods can elicit plant defense responses affecting potential prey beyond predation. Phytophagy prevails as the main trigger for these responses, as in the case of Euseius stipulatus (Athias-Henriot) (Mesostigmata: Phytoseiidae), a predator occurring in citrus. Because other triggers cannot be excluded, our aim was to examine whether other phytoseiids co-occurring with E. stipulatus but not engaged in plant feeding [Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot] could induce similar responses (in terms of herbivore induced plant volatiles, HIPVs, and main defensive pathways), and how these affected the behavior of conspecifics and the shared prey, Tetranychus urticae Koch (Prostigmata: Tetranychidae). N. californicus triggered plant genotype-specific defense responses, including the production of different HIPVs compared to clean plants. However, we could not observe these effects for P. persimilis. T. urticae avoided better protected plants, because of stronger direct or indirect defense. As plants with weaker direct defense levels should offer higher prey densities, and those harboring conspecific predators represent higher risk of cannibalism, predators were expected to behave similarly. However, they did not. Our results demonstrate that plant defense triggered by phytoseiids is species-specific, depend on plant genotype and can be triggered by non-feeding activities. As N. californicus is a highly efficient predator used worldwide, further studies with this species are needed. Likewise, cineol, one of the volatiles identified in the blends triggered by this phytoseiid, could be used to manipulate the prey. These studies could pave the way for a more efficient use of phytoseiids in agroecosystems.

Variation in size and shape of toxin glands among cane toads from native-range and invasive populations

If optimal investment in anti-predator defences depends on predation risk, invading new regions (and thus, encountering different predators) may favour shifts in that investment. Cane toads offer an ideal system to test this prediction: expensive anti-predator toxins are stored mainly in parotoid glands whose dimensions are easy to measure, and toad invasions have changed the suites of predators they encounter. Although plasticity may influence parotoid morphology, comparisons between parents and progeny revealed that gland dimensions were highly heritable. That heritability supports the plausibility of an evolved basis to variation in gland dimensions. Measurements of 3779 adult toads show that females have larger glands than males, invasive populations have larger glands than in the native-range, and that parotoid sexual size dimorphism varies strongly among invaded areas. Geographic variation in parotoid morphology may be driven by predation risk to both adult toads and offspring (provisioned with toxins by their mother), with toxins allocated to eggs exacerbating the risk of cannibalism but reducing the risk of interspecific predation. Investment into chemical defences has evolved rapidly during the cane toad’s international diaspora, consistent with the hypothesis that organisms flexibly adjust resource allocation to anti-predator tactics in response to novel challenges.

Trade‐offs affect the adaptive value of plasticity: stronger cannibal‐induced defenses incur greater costs in toad larvae

AbstractAdaptive developmental plasticity allows individuals to match their phenotype with their environment, increasing fitness where threats are inconsistently present. However, despite clear advantages of plasticity, adaptive traits are not ubiquitously nor infinitely plastic. Trade‐offs between benefits and costs or limits are therefore theoretically necessary to constrain the evolution of plastic responses. Systems in which extreme risk can be reliably detected are ideal for investigating trade‐offs, as even costly responses may be adaptive where risk is severe. Cane toads (Rhinella marina) are abundant in Australia and produce large clutches (frequently >10,000 eggs), but asynchronous breeding and rapid development result in variable larval densities within breeding pools. In the field, we found that cannibalism by older cohorts often reduces the survival of conspecific eggs and newly hatched pre‐feeding larvae (“hatchlings”) by >99%, as feeding larvae (“tadpoles”) use chemical cues from the relatively immobile hatchlings to locate and consume them. After hatchlings become free‐swimming, however, they cannot be cannibalized. Hatchlings can reduce this period of vulnerability by accelerating development when they detect cannibal cues. However, this developmental acceleration decreases initial tadpole mass, reduces subsequent survival, growth, and development, affects behavior, and compromises feeding structures. Reaction norms differ among clutches, and greater developmental acceleration is followed by greater impairment of larval function in plastic clutches, whereas nonresponsive clutches are unaffected by cue exposure. More plastic clutches ultimately exhibit both poorer performance and greater variation among siblings in exposed and (to a lesser degree) control treatments. Variation among clutches in tadpole viability is driven by differences in plasticity rather than phenotype; fitness reductions are linked to developmental acceleration, not rapid development per se. Clutches with intrinsically slow pre‐feeding developmental rates exhibit stronger acceleration (i.e., steeper reaction norms), but clutches with intrinsically rapid development reach invulnerable stages more quickly than those that accelerate development. As a result, high cannibalism risk may favor canalized rapid development rather than facultative developmental acceleration. Cannibalism plays an important role in the recruitment of this invasive species, and hatchling defenses against this threat demonstrate how the limits and costs associated with an inducible defense can favor canalized defenses over phenotypic plasticity.

Oviposition preference and adult performance of the whitefly predator Serangium japonicum (Coleoptera: Coccinellidae): effect of leaf microstructure associated with ladybeetle attachment ability

The leaf surface microstructure can greatly influence predator feeding behavior. However, its effects on predator oviposition preference, which is crucial for arthropod fitness at the population level, are largely unknown. This study aimed to test leaf discs and plants of five common host plant species of Bemisia tabaci, including Chinese kale, cotton, cucumber, eggplant, and sweetpotato, to determine the oviposition preference and offspring and adult performance of the whitefly predator Serangium japonicum. Cannibalism risk, attachment force, microstructure of the abaxial leaf surface (ALS), and ladybeetle tarsal morphology were examined. Ladybeetle's oviposition preference had no correlation with offspring performance but positively correlated with fecundity. Further, oviposition preference to leaf discs and fecundity positively correlated with attachment force. The cannibalism risk was not significantly different between plant species. The ALS of Chinese kale and eggplant supported the smallest and the largest attachment forces, respectively. The first one had epicuticular wax crystals, whereas the latter had stellate trichomes. The ALS of cotton and sweetpotato did not bear wax crystals or long trichomes. Cucumber leaves were covered with tapered trichomes. Tenant setae on the distal second tarsomere and a pair of curved, tapered claws on the distal fourth tarsomere were the attachment structures of S. japonicum, which interacted with the plant surface structures and generated the attachment force. Plant morphological traits, associated with ladybeetle attachment force and adult performance might be key factors in ladybeetle oviposition preference, and are expected to occur in other host plant herbivore-predator systems.

Oviposition behavior of the mirid Macrolophus pygmaeus under risk of intraguild predation and cannibalism

Zoophytophagous mirid species, that feed and develop either on prey or plant resources, are often found simultaneously on the same host. Hence, these species can engage in both intraguild predation and cannibalism, which can pose a threat to mirid eggs. Ovipositing females may respond to such risks of predation on their eggs by reducing the number of eggs laid or selecting safer oviposition sites. We tested the oviposition behavior of Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) females under the risk of cannibalism by M. pygmaeus males and intraguild predation by Nesidiocoris tenuis (Reuter) males (Hemiptera: Miridae) under laboratory conditions. Intraguild predators and cannibals were introduced during or after the oviposition period. The number of eggs laid (using counts of newly hatched nymphs) and their proportion on each part of a tomato plant were both measured. The results reveal that only cannibalism by M. pygmaeus males after the period of oviposition significantly decreased the number of hatched eggs. Cannibalism thus represents a greater risk to mirid eggs than intraguild predation. The M. pygmaeus female responded to the presence of potential intraguild predators (or competitors) by decreasing the number of eggs laid in the upper leaves. The results suggest that M. pygmaeus females avoid competition by N. tenuis, by laying fewer eggs on upper leaves. Cannibalism could regulate zoophytophagous predator populations under prey scarcity conditions and minimize the risk of crop damage associated with those biological control agents.

Synchronized hatching as a possible strategy to avoid sibling cannibalism in stink bugs

In some animals, timing of egg hatching is adjusted in response to cues from clutch mates to synchronize hatching within a clutch and this typically facilitates mass migration of hatchlings from their natal clutch. A recent study in eight species of Pentatomidae revealed that four species show synchronized hatching due to responses to earlier-hatched siblings, by comparing temporal hatching patterns between intact clutches and eggs individually detached from clutches. However, hatchlings of Pentatomidae do not migrate from their natal clutch immediately. In the present study, using the same eight species, we explored the evolutionary reason for the synchronized hatching in Pentatomidae. In all of the species examined except one non-synchronized species, Eurydema rugosum, hatchlings showed egg feeding behavior with greatly different time of onset. The highly synchronized species, Halyomorpha halys and Nezara viridula, had the time of onset of egg feeding earlier than in the other species. In these two species, based on the hatching patterns of eggs individually detached from their clutches, we concluded that eggs can be cannibalized by their earlier-hatched siblings unless they hatch in response to siblings. On the other hand, this was not the case in the moderately synchronized species, Piezodorus hybneri and Plautia stali. In the other three non-synchronized species, Aelia fieberi, Dolycoris baccarum, and Palomena angulosa, eggs seemed not to incur a risk of cannibalism. In intact H. halys clutches, almost no eggs were cannibalized by siblings. In conclusion, synchronized hatching serves as a possible strategy to avoid sibling cannibalism in Pentatomidae, although it can also have some other functions. Eggs should often be able to control when to hatch in response to environmental factors affecting survival of eggs or hatchlings. Species of various taxa show responses to siblings in the same clutch to achieve synchronized hatching among the siblings. It is typically recognized that such synchronized hatching is required so that hatchlings leave their natal clutch together, which serves, for example, to reduce the risk of being preyed on by predators. Here, we present evidence supporting that synchronized hatching observed in some stink bugs helps eggs to avoid being cannibalized by their earlier-hatched siblings. We also show that other stink bugs with no synchronized hatching have no or little risk of sibling egg cannibalism. This study deepens our knowledge that the synchronized hatching can function in various social contexts with siblings.

Extra molting, cannibalism and pupal diapause under unfavorable growth conditions in Atrophaneura alcinous (Lepidoptera: Papilionidae)

AbstractAtrophaneura alcinous adopt multiple strategies such as extra molting, cannibalism and pupal diapause under unfavorable growth conditions. The conditions under which these strategies are adopted have been separately verified, but their relationship has often been overlooked. We examined which strategy A. alcinous adopted and the relative advantages of strategies using four experimental groups under different food quantity and individual density conditions. Our results indicated that A. alcinous often extra‐molted, prolonged the larval period, and larval and pupal weights were lighter under food shortage. Cannibalism and disease often occurred under the high density and food shortage condition. We also showed that individuals cannibalized during the prepupal or pupal period were less likely to extra molt before they were killed. Extra molting tended to occur more frequently in females than in males under a shortage of food. In addition, we showed that, when food was insufficient, A. alcinous might initiate pupal diapause under low densities, but not under high densities. These results suggest that A. alcinous prolongs the larval period by engaging in extra molting during times of unfavorable food conditions. This strategy might decrease the risk of cannibalization because surrounding larvae who could potentially cannibalize others pupate before larvae who prolong the larval period pupate. Our results also suggest that diapausing pupae under a shortage of food can only survive when there are few surrounding conspecifics, due to a lower cannibalization risk. In conclusion, there is a complex interaction between extra molting, cannibalism and pupal diapause strategies.

Size-mediated priority and temperature effects on intra-cohort competition and cannibalism in a damselfly.

A shift in the relative arrival of offspring, for example a shift in hatching time, can affect competition at the intraspecific level through size-mediated priority effects, where the larger individuals gain more resources. These priority effects are likely to be affected by climate warming and the rate of intraspecific predation, that is cannibalism. In a laboratory experiment, we examined size-mediated priority effects in larvae of the univoltine damselfly, Lestes sponsa, at two different temperatures (21 and 23°C). We created three size groups of larvae by manipulating hatching time: early hatched with a large size (extra-advanced), intermediate hatched with an intermediate size (advanced) and late hatched with a small size (non-advanced). Thereafter, we reared the larvae from these groups in non-mixed and mixed groups of 12 larvae. We found strong priority and temperature effects. First, extra-advanced larvae most often had higher survival, growth and development rates than non-advanced larvae in mixed groups, compared to groups that consisted of only extra-advanced larvae. Second, temperature increased growth and development rates and cannibalism. However, the strength of priority effects did not differ between the two experimental temperatures, because there was no statistical interaction between temperature and treatments. That is, the mixed and non-mixed groups of non-advanced, advanced and extra-advanced larvae showed the same relative change in life-history traits across the two temperatures. Non-advanced and advanced larvae had similar or higher growth rate and mass in mixed groups compared to non-mixed groups, suggesting that predation from advanced larvae in the mixed group released resources for the non-advanced and advanced larvae that survived despite cannibalism risk. Thus, a thinning effect occurred due to cannibalism caused by priority effects. The results suggest that a shift in the relative arrival of offspring can cause temperature-dependent priority effects, mediated through cannibalism, growth and development, which may change the size distribution and abundance of emerging aquatic insects.

Bringing down the house: male widow spiders reduce the webs of aggressive females more

Theory suggests that males should adjust courtship in response to a variety of factors, including female quality, the risk of male-male competition, and often in spiders, the risk of sexual cannibalism. Male black widow spiders demonstrate a behavior during courtship whereby they tear down and bundle a female’s web in addition to providing other vibratory and contact sexual signals. This web reduction has been hypothesized to play a role in all three factors (sexual signaling, competition reduction, and cannibalism reduction), but rarely are these tested together. Here, we test these hypotheses by conducting mating trials using the western black widow (Latrodectus hesperus) and measuring both male and female quality and behavior. Our results indicate that amount of web reduction is best predicted by female aggression, and not aspects of either male or female quality (e.g., body mass), or by the potential for the web to attract other males (e.g., web mass). Yet, actual mating success was best predicted by the proportion of web reduced. Furthermore, there was no consistent among-individual variation in either reduction behavior or male success, indicating that all variation in both measures was due to plasticity and/or other unaccounted-for male or female traits. Collectively, we conclude that the primary function of web reduction behavior is to reduce female aggression and thus the risk of sexual cannibalism, and that any other functions such as signaling and reducing male-male competition have relatively lower importance. Male widow spiders must account for female aggression, quality, and male-male competition when courting females. During courtship, males will reduce a female’s web by tearing it down and bundling the silk, which may aid in all three of these issues. Our results demonstrate that males reduce the webs of aggressive females more, and less so to potentially reduce competition from other males or in response to female quality. Ultimate mating success was dictated by how much a male reduced the web of a given female. Finally, males showed no among-individual variation in reduction behavior, indicating that the extensive variation in this behavior is due solely to plasticity in response to the female.