Predation risk shapes thermal physiology of a predaceous damselfly

Predation risk has strong effects on organismal physiology that can cascade to impact ecosystem structure and function. Physiological processes in general are sensitive to temperature. Thus, the temperature at which predators and prey interact may shape physiological response to predation risk. We measured and evaluated how temperature and predation risk affected growth rates of predaceous damselfly nymphs (Enallagma vesperum, Odonata: Coenagrionidae). First, we conducted growth trials at five temperatures crossed with two levels of predation risk (fish predator present versus absent) and measured growth rates, consumption rates, assimilation efficiencies, and production efficiencies of 107 individual damselflies. Second, we used a model to evaluate if and how component physiological responses to predation risk affected growth rates across temperatures. In the absence of mortality threat, growth rates of damselflies increased with warming until about 23.5 °C and then began to decline, a typical unimodal response to changes in temperature. Under predation risk, growth rates were lower and the shape of the thermal response was less apparent. Higher metabolic and survival costs induced by predation risk were only partially offset by changes in consumption rates and assimilation efficiencies and the magnitude of non-consumptive effects varied as a function of temperature. Furthermore, we documented that thermal physiology was mediated by predation risk, a known driver of organismal physiology that occurs in the context of species interactions. A general understanding of climatic impacts on ectothermic populations requires consideration of the community context of thermal physiology, including non-consumptive effects of predators.     

Kinship shapes affiliative social networks but not aggression in ring-tailed coatis

Animal groups typically contain individuals with varying degrees of genetic relatedness, and this variation in kinship has a major influence on patterns of aggression and affiliative behaviors. This link between kinship and social behavior underlies socioecological models which have been developed to explain how and why different types of animal societies evolve. We tested if kinship and age-sex class homophily in two groups of ring-tailed coatis (Nasua nasua) predicted the network structure of three different social behaviors: 1) association, 2) grooming, and 3) aggression. Each group was studied during two consecutive years, resulting in four group-years available for analysis (total of 65 individuals). Association patterns were heavily influenced by agonistic interactions which typically occurred during feeding competition. Grooming networks were shaped by mother-offspring bonds, female-female social relationships, and a strong social attraction to adult males. Mother-offspring pairs were more likely to associate and groom each other, but relatedness had no effect on patterns of aggressive behavior. Additionally, kinship had little to no effect on coalitionary support during agonistic interactions. Adult females commonly came to the aid of juveniles during fights with other group members, but females often supported juveniles who were not their offspring (57% of coalitionary interactions). These patterns did not conform to predictions from socioecological models.     

Predation pressure shapes brain anatomy in the wild

There is remarkable diversity in brain anatomy among vertebrates and evidence is accumulating that predatory interactions are crucially important for this diversity. To test this hypothesis, we collected female guppies (Poecilia reticulata) from 16 wild populations and related their brain anatomy to several aspects of predation pressure in this ecosystem, such as the biomass of the four major predators of guppies (one prawn and three fish species), and predator diversity (number of predatory fish species in each site). We found that populations from localities with higher prawn biomass had relatively larger telencephalon size as well as larger brains. Optic tectum size was positively associated with one of the fish predator’s biomass and with overall predator diversity. However, both olfactory bulb and hypothalamus size were negatively associated with the biomass of another of the fish predators. Hence, while fish predator occurrence is associated with variation in brain anatomy, prawn occurrence is associated with variation in brain size. Our results suggest that cognitive challenges posed by local differences in predator communities may lead to changes in prey brain anatomy in the wild.     

Activity synchrony and social cohesion: a fission-fusion model.

A social group can only be spatially coherent if its members synchronize activities such as foraging and resting. However, activity synchronization is costly to individuals if it requires them to postpone an activity that would be personally more profitable in order to do what the rest of the group is doing. Such costs will be particularly high in groups whose members belong to different age, size or sex classes since the optimal allocation of time to various activities is likely to differ between such classes. Thus, differences in the costs of activity synchronization between and within classes could cause non-homogenous groups to be less stable than homogenous groups, with the result that homogenous groups predominate in the population: that is, they could cause 'social segregation' of animals of different sex, size or age. We develop a model that predicts the degree of social segregation attributable to differences in activity synchronization between homogenous and non-homogenous groups and use this model in determining whether activity synchronization can explain intersexual social segregation in red deer (Cervus elaphus). Differences in activity synchronization between mixed-sex and unisex groups of red deer explained 35% of the observed degree of intersexual social segregation, showing that activity synchronization is an important cause of social segregation in this species.     

Predation risk and social interference as factors influencing habitat selection in two species of stream-dwelling waterstriders

We investigated how an aggressive species of waterstrider, Aquariusremigis, and potential predators, green sunfish (Lepomis cyanellus),affected the habitat use and mating behaviors of a less aggressivecongeneric species, A. conformis. Although these species sometimesco-occur, A. remigis typically lives in small streams with fewor no fish, whereas A. conformis are typically in medium- orlarge-sized streams with large populations of potentially predatoryfish. We tested in separate experiments in seminatural streams:1) the effect of fish on behaviors of A. conformis; 2) the effectof A. remigis on A. conformis; and 3) the habitat use of A.conformis when given a choice between pools with A. remigisor fish. The first experiment showed no effect of fish on eithermating behaviors or microhabitat use of A. conformis. This isin surprising contrast to the strong effects of fish alreadydocumented in A. remigis. The second experiment showed thatthe mating activity of A. conformis was reduced when A. remigiswere present; hence, A. conformis should avoid A. remigis. Finally,when A. conformis were presented with a choice between two pools,one containing A. remigis and the other containing fish, bothsingle males and pairs of A. conformis chose the pools withfish. In contrast, the habitat use of single female A. conformiswas not affected by either fish or A. remigis. Results fromthese experiments demonstrate that closely related species exhibitcontrasting social and antipredator behaviors and that aggressivesocial behavior is an important determinant of habitat partitioning     

Predation risk causes oxidative damage in prey

While there is increasing interest in non-consumptive effects of predators on prey, physiological effects are understudied. While physiological stress responses play a crucial role in preparing escape responses, the increased metabolic rates and shunting of energy away from other body functions, including antioxidant defence, may generate costs in terms of increased oxidative stress. Here, we test whether predation risk increases oxidative damage in Enallagma cyathigerum damselfly larvae. Under predation risk, larvae showed higher lipid peroxidation, which was associated with lower levels of superoxide dismutase, a major antioxidant enzyme in insects, and higher superoxide anion concentrations, a potent reactive oxygen species. The mechanisms underlying oxidative damage are likely to be due to the shunting of energy away from antioxidant defence and to an increased metabolic rate, suggesting that the observed increased oxidative damage under predation risk may be widespread. Given the potentially severe fitness consequences of oxidative damage, this largely overlooked non-consumptive effect of predators may be contributing significantly to prey population dynamics.     

Group decision-making in fission-fusion societies

The prevalent view of group splitting during group decisions is that a beneficial consensus has not been reached because time constraints, different individual information, or inter-individual conflicts lead to fission instead of a compromise. However, societies with high fission-fusion dynamics may allow their members to avoid consensus decisions that are not in their favour without foregoing grouping benefits that arise from collective behaviour. Moreover, by forming temporary subgroups that represent individual preferences better than the group as a whole fission-fusion societies could avoid a permanent break up even in situations where conflicts among their members are to strong to reach a consensus.     

Predation risk and moonlight avoidance in nocturnal seabirds

Unlike most seabird families, the vast majority of small petrel species are nocturnal on their breeding grounds. Further, they reduce markedly their activity when the light level increases. Moonlight avoidance might be a consequence of reduction in foraging profitability, as bioluminescent prey do not come to the sea surface on bright nights. Alternatively, petrels may avoid colonies during moonlit nights because of increased predation risk. We studied predation on petrels by Brown Skuas Catharacta antarctica lönnbergi at Kerguelen, and the influence of moonlight on behaviour of both skuas and petrels, to test the 'predation risk' hypothesis. On the study area, Brown Skuas hunt at night and prey heavily upon the Blue Petrel Halobaena caerulea and the Thin-billed Prion Pachyptila belcheri . Predation risk was higher on moonlit nights, as skuas caught more prey, and particularly more Blue Petrels when the light level increased. Nightly intakes of Blue Petrel and Thin-billed Prion by skuas was related to colony attendance of non-breeders rather than that of breeders. Biometry of prey also suggested that skuas caught a higher proportion of non-breeding birds than was present at the colonies. Predation risk was thus greater in non-breeders and on moonlit nights. Colony attendance by non-breeding Blue Petrels and Thin-billed Prions was also reduced during moonlit nights. Vocal activity, which is mainly by non-breeders, was also drastically reduced when the light level increased in the species suffering the highest predation rate. Our results supported the 'predation risk' hypothesis, although the 'foraging efficiency' and the 'predation risk' hypotheses are not mutually exclusive: the former might explain the moonlight avoidance behaviour of breeding, and the latter that of non-breeding individuals.     

Predation risk as a cost of reproduction

Predation risk as a cost of reproduction in animals has recently received increased empirical and theoretical attention. Higher risk may be associated with all stages of reproduction. Examples of evolutionary responses to this increased risk include habitat choice, duration and timing of display and copulation, changes in brightness of breeding coloration, and changes in life history traits such as age of reproduction and reproductive effort.     

捕食风险对小型哺乳动物行为、神经和内分泌的影响

长期进化过程中,猎物形成了对捕食者先天的敏感性。捕食风险对小型哺乳动物的影响主要包括行为的改变、神经环路的激活和内分泌的变化。行为的改变包括抑制运动活动、降低非防御行为以及改变生活环境。一些研究用c-fos免疫组化的方法测定了大鼠在暴露于猫的气味后大脑被激活的区域,主要包括中间杏仁核、下丘脑腹内侧区、背内侧区、前乳头状核和导水管周围灰质（periaqueductal gray）。猎物对捕食应激的反应还表现在一些内分泌指标的改变,一些激素如皮质酮（Corticoserone,CORT）和促肾上腺皮质激素（Adrenocorticotropic hormone,ACTH）的含量会显著的增加,同时在一些雄性动物中,睾丸激素的含量会有所降低。捕食者和猎物的关系近年来已经成为很多学科研究的有用工具。     

Predation on marine picoplankton populations examined with an 'add-in' approach

NW Mediterranean surface water was spiked with picoplanktonprey (heterotrophic bacteria or cyanobacteria) or predators(bacterivorous microflagellates or ciliates) to investigatedifferential grazing pressure on picoplankton populations. Addinga particular prey type did not yield different growth patternsfor heterotrophic bacteria and cyanobacteria. but gave eithersimilar, positive, effects on both picoplankton types or similarnegative effects. Natural populations of both predator typesincreased with additions of cyanobacteria, but not heterotrophicbacteria. Ciliate additions gave marked decreases in cyanobacteria.While individual groups of grazers may preferentially consumecyanobacteria, selective grazing is probably not responsiblefor the maintenance of apparently stable populations of differentgroups of picoplankters during the summer.     

Trust transitivity in social networks

Non-centralized recommendation-based decision making is a central feature of several social and technological processes, such as market dynamics, peer-to-peer file-sharing and the web of trust of digital certification. We investigate the properties of trust propagation on networks, based on a simple metric of trust transitivity. We investigate analytically the percolation properties of trust transitivity in random networks with arbitrary in/out-degree distributions, and compare with numerical realizations. We find that the existence of a non-zero fraction of absolute trust (i.e. entirely confident trust) is a requirement for the viability of global trust propagation in large systems: The average pair-wise trust is marked by a discontinuous transition at a specific fraction of absolute trust, below which it vanishes. Furthermore, we perform an extensive analysis of the Pretty Good Privacy (PGP) web of trust, in view of the concepts introduced. We compare different scenarios of trust distribution: community- and authority-centered. We find that these scenarios lead to sharply different patterns of trust propagation, due to the segregation of authority hubs and densely-connected communities. While the authority-centered scenario is more efficient, and leads to higher average trust values, it favours weakly-connected "fringe" nodes, which are directly trusted by authorities. The community-centered scheme, on the other hand, favours nodes with intermediate in/out-degrees, in detriment of the authorities and its "fringe" peers.     

Detecting social transmission in networks

In recent years researchers have drawn attention to a need for new methods with which to identify the spread of behavioural innovations through social transmission in animal populations. Network-based analyses seek to recognise diffusions mediated by social learning by detecting a correspondence between patterns of association and the flow of information through groups. Here we introduce a new order of acquisition diffusion analysis (OADA) and develop established time of acquisition diffusion analysis (TADA) methods further. Through simulation we compare the merits of these and other approaches, demonstrating that OADA and TADA have greater power and lower Type I error rates than available alternatives, and specifying when each approach should be deployed. We illustrate the new methods by applying them to reanalyse an established dataset corresponding to the diffusion of foraging innovations in starlings, where OADA and TADA detect social transmission that hitherto had been missed. The methods are potentially widely applicable by researchers wishing to detect social learning in natural and captive populations of animals, and to facilitate this we provide code to implement OADA and TADA in the statistical package R.     

Habitual fission-fusion and social organization of the Hakone troop T of Japanese macaques in Kanagawa prefecture,Japan

To analyze the socioecological factors of habitual fission-fusion of troop members, which is an underreported phenomenon in Japanese macaques, the seasonal pattern of fission-fusion within the Hakone troop T in Kanagawa Prefecture, Japan, was examined. Although almost all the study troop members were included in a large-sized group in winter, a portion of its members of ten formed small subgroups from spring to autumn. The frequencies and age-sex composition of these subgroups changed seasonally. All troop members participated, more or less, in subgroup formation. Subgroups tended to be composed of animals of the same age-sex class. Troop members did not fission along matrilineal lines. Although the study troop members repeatedly joined with and parted from subgroups, the characteristic social structure of Japanese macaque troops was maintained. Habitual fission-fusion among troop members may be one of a number of foraging strategies that facilitate efficient food gathering when the population density exceeds and /or reaches the carrying capacity of the area. The seasonal variation of pattern and composition type of each subgroup could be attributed to alternation of attractive food plant species, as well as age, rank, and sexual activity of both sexes.     

Predation risk and feeding patterns of crucian carp

As part of an experimental study of the direct and indirect effects of piscivory on prey fish, the diets of crucian carp Carassius carassius were compared across sections of a divided pond; two sections were stocked with crucian carp alone and two with crucian carp plus perch Perca fluviatilis . Analysis of crucian gut contents indicated that the composition of invertebrate prey did not differ in the presence v . absence of perch. However, crucians, particularly small individuals (<10cm) that were most vulnerable to predation, displayed a lower intake of invertebrate prey in sections with perch. Although diet composition differed between crucians caught in inshore v. offshore habitats (with habitat use being related to crucian size and the presence or absence of perch), no clear pattern existed between habitat and total food intake. Overall, the major effects of predators on the diet of crucian carp appeared to be caused by increased ecological density (resulting from confinement of small crucians inshore) and reduced activity levels, rather than simple shifts to safer habitats.     

On realizing shapes in the theory of RNA neutral networks

It is known (Reidys et al., 1997b. Bull. Math. Biol. 59(2), 339-397) that for any two secondary structures S,S' there exists an RNA sequence compatible with both, and that this result does not extend to more than two secondary structures. Indeed, a simple formula for the number of RNA sequences compatible with secondary structures S,S' plays a role in the algorithms of Flamm et al. (2001. RNA 7, 254-265) and of Abfalter et al. (2003. Proceedings of the German Conference on Bioinformatics, ) to design an RNA switch. Here we show that a natural extension of this problem is NP-complete. Unless P=NP, there is no polynomial time algorithm, which when given secondary structures S1,...,S(k), for k4, determines the least number of positions, such that after removal of all base pairs incident to these positions there exists an RNA nucleotide sequence compatible with the given secondary structures. We also consider a restricted version of this problem with a "fixed maximum" number of possible stars and show that it has a simple polynomial time solution.     

Genotypic selection shapes patterns of within-species diversity in experimental plant populations

1.  An increasing body of evidence suggests that within-species diversity plays an important role for community and ecosystem functioning, alters complex trophic interactions and affects patterns of species diversity and coexistence. Nonetheless, we lack a good understanding of how genotypic trait variation translates into shifts in the relative abundance of genotypes within populations.
2.  In this study, we show that genotypic selection strongly alters dominance relationships among genotypes over a period of 5 years. This resulted in remarkably consistent changes in the proportional representation of genotypes, and in a concomitant decline of diversity and evenness in our experimental populations.
3.  High growth rates and the production of large offspring were positively associated with genotypic performance. Vegetative abundances of genotypes translated monotonically into flowering frequencies.
4.   Synthesis . We conclude that genotypic selection markedly affects patterns of diversity and consistently alters genotypic abundance and mean trait distributions in plant populations over a relatively short period of time.