The nose knows who's who: chemosensory individuality and mate recognition in mice

Individual recognition is an important component of behaviors, such as mate choice and maternal bonding that are vital for reproductive success. This article highlights recent developments in our understanding of the chemosensory cues and the neural pathways involved in individuality discrimination in rodents. There appear to be several types of chemosensory signal of individuality that are influenced by the highly polymorphic families of major histocompatibility complex (MHC) proteins or major urinary proteins (MUPs). Both have the capability of binding small molecules and may influence the individual profile of these chemosignals in biological fluids such as urine, skin secretions, or saliva. Moreover, these proteins, or peptides associated with them, can be taken up into the vomeronasal organ (VNO) where they can potentially interact directly with the vomeronasal receptors. This is particularly interesting given the expression of major histocompatibility complex Ib proteins by the V2R class of vomeronasal receptor and the highly selective responses of accessory olfactory bulb (AOB) mitral cells to strain identity. These findings are consistent with the role of the vomeronasal system in mediating individual discrimination that allows mate recognition in the context of the pregnancy block effect. This is hypothesized to involve a selective increase in the inhibitory control of mitral cells in the accessory olfactory bulb at the first level of processing of the vomeronasal stimulus.     

The effects of predator presence and shoal size on foraging in bluntnose minnows,Pimephales notatus

Synopsis Shoals of 3, 5, 7, 10, 15, and 20 bluntnose minnows,Pimephales notatus, were allowed to forage in the absence and presence of a fish predator, which was separated from the shoal by a clear plexiglass partition. A typical dilution effect was observed in that individual fish in larger shoals were approached less frequently by the predator. In the absence of a predator, foraging latency decreased significantly and the rate of foraging increased with increasing shoal size. Foraging latency for each shoal size tended to increase in the presence of a predator and foraging rate decreased, significantly for shoals of 7, 15, and 20 fish. Members of larger shoals were safer and enjoyed a greater level of food consumption, perhaps due to decreased individual vigilance for predators and social facilitation. However, foraging effort decreased when a predator was present, as more time was allocated to predator avoidance.     

The role of experience and chemical alarm signalling in predator recognition by fathead minnows, Pimephales promelas

Young-of-the-year, predator-naive fathead minnows, Pimephales promelas , from a pikesympatric population did not respond to chemical stimuli from northern pike, Esox Indus , while wild-caught fish of the same age and size did. These results suggest that chemical predator recognition is a result of previous experience and not genetic factors, Wild young-of-the-year minnows responded to pike odour with a response intensity that was similar to that of older fish, demonstrating that the ability to recognize predators is learned within the first year. The intensity of response of wild minnows which had been maintained in a predator free environment for 1 year was similar to that of recently caught minnows of the same age, suggesting that reinforcement was not required for predator recognition to be retained. Naive minnows that were exposed simultaneously to chemical stimuli from pike (a neutral stimulus) and minnow alarm substance exhibited a fright response upon subsequent exposure to the pike stimulus alone. Predator-naive minnows exposed simultaneously to chemical stimuli from pike and glass-distilled water did not exhibit a fright response to the pike stimulus alone. These results demonstrate that fathead minnows can acquire predator recognition through releaserinduced recognition learning, thus confirming a known mechanism through which alarm substance may benefit the receivers of an alarm signal.     

Responses of tadpoles to hybrid predator odours: strong maternal signatures and the potential risk/response mismatch

Previous studies have established that when a prey animal knows the identity of a particular predator, it can use this knowledge to make an ‘educated guess'' about similar novel predators. Such generalization of predator recognition may be particularly beneficial when prey are exposed to introduced and invasive species of predators or hybrids. Here, we examined generalization of predator recognition for woodfrog tadpoles exposed to novel trout predators. Tadpoles conditioned to recognize tiger trout, a hybrid derived from brown trout and brook trout, showed generalization of recognition of several unknown trout odours. Interestingly, the tadpoles showed stronger responses to odours of brown trout than brook trout. In a second experiment, we found that tadpoles trained to recognize brown trout showed stronger responses to tiger trout than those tadpoles trained to recognize brook trout. Given that tiger trout always have a brown trout mother and a brook trout father, these results suggest a strong maternal signature in trout odours. Tadpoles that were trained to recognize both brown trout and brook trout showed stronger response to novel tiger trout than those trained to recognize only brown trout or only brook trout. This is consistent with a peak shift in recognition, whereby cues that are intermediate between two known cues evoke stronger responses than either known cue. Given that our woodfrog tadpoles have no evolutionary or individual experience with trout, they have no way of knowing whether or not brook trout, brown trout or tiger trout are more dangerous. The differential intensity of responses that we observed to hybrid trout cues and each of the parental species indicates that there is a likely mismatch between risk and anti-predator response intensity. Future work needs to address the critical role of prey naivety on responses to invasive and introduced hybrid predators.     

The nose knows: linking sensory cue use,settlement decisions,and post-settlement survival in a temperate reef fish

Habitat selection by animals that migrate or disperse ultimately determines the biotic and abiotic environment they will experience in subsequent life stages. Intuitively, for habitat selection to be adaptive, animals should respond positively to cues produced by habitat characteristics that will enhance their fitness in the new environment. However, there are many examples of dispersing animals where individuals are attracted to cues produced by factors that reduce their fitness after arrival. In this study, we use a temperate reef fish to examine the relative importance of habitat-associated cues in habitat selection decisions, and assess whether use of these cues is adaptive across early life stages. We used a series of laboratory- and field-based manipulative experiments to test: (1) what habitat-associated cues are likely used to locate suitable habitat; (2) whether in situ settlement patterns reflect the cue response tested in the laboratory; and (3) whether the aspects of the habitat that stimulate settlement are the same as those that maximize survival. We observed a positive response to multiple habitat-associated cues, with conspecific cues eliciting the strongest behavioral response in laboratory choice experiments, and a strong inverse density-dependent relationship at settlement. Macroalgal cues also elicited a positive response at settlement, but were associated with higher mortality after settlement, suggesting that habitat selection decisions are not always adaptive. We argue that this non-intuitive behavior may still be adaptive if it improves fitness at an earlier life stage, as habitat selection behavior is the result of tradeoffs in fitness costs across multiple stages.     

Effects of predator behavior and proximity on risk assessment by Columbian black-tailed deer

In predator-prey encounters, many factors influence risk perceptionby prey and their decision to flee. Previous studies indicatethat prey take flight at longer distances when they detect predatorsat longer distances and when the predator's behavior indicatesthe increased likelihood of attack. We examined the flight decisionsof Columbian black-tailed deer (Odocoileus hemionus columbianus)using an approaching human whose speed, directness of approach,directness of gaze, and simulated gun carrying varied. Deerfled at greater distances when approached more quickly and directly,and there was a concave-down quadratic trend in the relationshipbetween the distances at which the predator began its approachand at which the deer became alert (alert distance [AD]), indicatingthat deer have a zone of awareness beyond which there is a delayin detecting an approaching predator. Time spent assessing theapproacher (assessment time) was shorter during faster approachesand was positively related with AD. Deer fled at longer distancesand had shorter assessment times when they were already alertto the predator at the initiation of approach. Males fled atshorter distances than females when approached during the gun-holdingcondition, and males had shorter assessment times than femaleswhen the approacher averted his gaze. Such sex differences inrisk assessment might reflect male motivation during the matingseason as well as exposure to human hunting. We suggest thatrisk assessment is affected the by the predator's behavior,the state of awareness of the prey, and the distance at whichthey detect the predator.     

Effects of predator density and duration of predator occupancy on crustacean abundance and diversity in experimental pools

Keystone predators, by reducing the abundance of competitively superior prey, may have indirect positive effects on weak competitors, possibly increasing their abundance or preventing local competitive exclusion. By analogy to the Intermediate Disturbance Hypothesis, we would expect species diversity to peak at intermediate predator densities. In a replicated artificial pool experiment, we examined the relationships between density of the backswimmer Notonecta maculata (0, 1, 2, and 4 per 30 l pool) and invertebrate taxon diversity over an 11-week period of predator occupancy. Diversity reached high levels at high predator density sooner than at intermediate density. At the end of the experiment, taxon diversity was greatest at densities of 2 and 4 Notonecta per pool. While the overall predator density–diversity curve was in line with the intermediate disturbance hypothesis, the reduction in diversity from intermediate to high predator density was not statistically significant. Density of the preferred prey Daphnia magna decreased with Notonecta density, while densities of the smaller cladocerans Moina brachiata and Ceriodaphnia spp. increased. Suppression of Daphnia at high Notonecta densities may partially explain the increase in Moina and Ceriodaphnia densities. However, most of the relationship between Notonecta and the smaller cladocerans appears to be independent of Daphnia, suggesting complex interactions within the community. Our results suggest that keystone predation plays a strong role in structuring this community. Although diversity did not decrease significantly at the highest predator density as predicted, such a decrease may be more likely for pools with longer durations of predator occupancy or with higher predator densities.     

Consequences of complex signaling: predator detection of multimodal cues

Animals often evolve complex signals to enhance their detectabilityby intended receivers. But signals that are more detectableby intended receivers may also be more likely to be interceptedby others, including predators. Courtship signaling in maleSchizocosa ocreata wolf spiders (Lycosidae) includes morphologicaltraits (prominent foreleg tufts) and active behaviors that togetherproduce a complex signal with simultaneous broadcast of visualand seismic components. Females respond more readily to maleswith large tufts and are more likely to respond when multiplemodalities (visual and seismic) are present in a complex signal.These spiders cooccur with active predators that may interceptthese conspicuous courtship signals and use them as huntingcues. We used video/seismic playback to experimentally isolateand manipulate aspects of the complex signal produced by maleS. ocreata. We found that increasing the size of a visual signal(male tufts) and increasing the complexity of the courtshipsignal by adding a second modality (visual plus seismic versusvisual alone) increased the speed with which a common predator,the jumping spider Phidippus clarus (Salticidae), respondedto playbacks of courting male S. ocreata. These results indicatethat the benefits of increased signaling efficacy of large visualsignaling ornaments and complex, multimodal signaling may becountered by increased predation risks.     

Swimming behaviour of Daphnia clones: differentiation through predator infochemicals

We studied variation in small-scale swimming behavior (SSB)in four clones of Daphnia galeata (water flea) in response topredator infochemicals. The aim of this study was 3-fold. First,we tested for differences in SSB in Daphnia; second, we examinedthe potential of differences in SSB to explain survival probabilityunder predation; and third we tested the effect of differencesin SSB on survival under predation. Four treatments were applied:one kairomone-free control, one Chaoborus- (phantom midge) andone Perca (perch)-conditioned treatment, and a mixed treatmentcontaining both infochemicals. All of the three tested behavioralparameters (swimming speed, trajectory length and vertical distribution)were affected by the presence of the Chaoborus infochemical,and swimming speed and vertical distribution were also affectedby the presence of Perca infochemical. The effect of the treatmentwas interfered with by a clone effect: genetic differences werepronounced in all traits. These results illustrate that clonescan be responsive in only a subset of traits. The general theorythat clones are either responsive or non-responsive is not validfor SSB. The outcome of the predation trial confirms that adecrease in activity is a main factor in lowering Daphnia vulnerabilityto Chaoborus predation.     

The effect of predator and prey density on the induced defence of a ciliate

1. The level of antipredator defence should be proportional to the actual attack probability to minimize the cost of defence and maximize the net benefit.
2. The hypothesis that the induced antipredator morphology of Euplotes octocarinatus is a graded response to the actual risk of predation by Stylonychia mytilus was tested by manipulating the density of both prey and predator populations.
3. The magnitude of the response was graded according to both predator and prey density. A dense prey population may be protective since a prey is more exposed to a predator's attack as a solitary individual.
4. The results suggest that Euplotes is able to 'estimate' the real risk of predation and respond appropriately, without mobilizing more resources than needed.
5. Separation of the prey and predator with a nylon net revealed that the response was not induced by a water-transmitted factor but that direct cell-to-cell contacts were important. This finding departs from those of other studies.     

The effect of hunger, shoal size and the presence of a predator on shoal cohesiveness in bluntnose minnows, Pimephales notatus Rafinesque

Shoals of fish vary in their degree of cohesiveness as certain conditions such as hunger, predation risk and shoal size vary: this study relates this variation to the benefits of shoaling. Shoals of bluntnose minnows, Pimephales notatus Rafinesque, consisting of different numbers of individuals were starved for 5, 24 or 72 h and allowed to forage in the presence or absence of a predator. Cohesiveness was measured as the dispersion offish within the shoal (the radius of the longest axis of the shoal corrected for the number of fish in the shoal), straggle frequency (the number of movements by individuals of at least 5 body lengths away from the shoal) and aggressive interactions between shoal members. Cohesiveness increased as shoal size and the benefits per individual increased. Cohesiveness also increased in the presence of a predator, as did the importance of shoaling as a means of reducing predation risk. Cohesivenes decreased as hunger level increased, possibly as a result of increased competition for food among shoal members.     

Climate and density shape population dynamics of a marine top predator

Long-term studies have documented that climate fluctuations affect the dynamics of populations, but the relative influence of stochastic and density-dependent processes is still poorly understood and debated. Most studies have been conducted on terrestrial systems, and lacking are studies on marine systems explicitly integrating the fact that most populations live in seasonal environments and respond to regular or systematic environmental changes. We separated winter from summer mortality in a seabird population, the blue petrel Halobaena caerulea, in the southern Indian Ocean where the El Niño/Southern Oscillation effects occur with a 3-4-year lag. Seventy per cent of the mortality occurred in winter and was linked to climatic factors, being lower during anomalous warm events. The strength of density dependence was affected by climate, with population crashes occurring when poor conditions occurred at high densities. We found that an exceptionally long-lasting warming caused a ca. 40% decline of the population, suggesting that chronic climate change will strongly affect this top predator. These findings demonstrate that populations in marine systems are particularly susceptible to climate variation through complex interactions between seasonal mortality and density-dependent effects.     

Night shift: expansion of temporal niche use following reductions in predator density

Predation shapes many fundamental aspects of ecology. Uncertainty remains, however, about whether predators can influence patterns of temporal niche construction at ecologically relevant timescales. Partitioning of time is an important mechanism by which prey avoid interactions with predators. However, the traits that control a prey organism's capacity to operate during a particular portion of the diel cycle are diverse and complex. Thus, diel prey niches are often assumed to be relatively unlikely to respond to changes in predation risk at short timescales. Here we present evidence to the contrary. We report results that suggest that the anthropogenic depletion of daytime active predators (species that are either diurnal or cathemeral) in a coral reef ecosystem is associated with rapid temporal niche expansions in a multi-species assemblage of nocturnal prey fishes. Diurnal comparisons of nocturnal prey fish abundance in predator rich and predator depleted reefs at two atolls revealed that nocturnal fish were approximately six (biomass) and eight (density) times more common during the day on predator depleted reefs. Amongst these, the prey species that likely were the most specialized for nocturnal living, and thus the most vulnerable to predation (i.e. those with greatest eye size to body length ratio), showed the strongest diurnal increases at sites where daytime active predators were rare. While we were unable to determine whether these observed increases in diurnal abundance by nocturnal prey were the result of a numerical or behavioral response, either effect could be ecologically significant. These results raise the possibility that predation may play an important role in regulating the partitioning of time by prey and that anthropogenic depletions of predators may be capable of causing rapid changes to key properties of temporal community architecture.     

Sustainability and optimal control of an exploited prey predator system through provision of alternative food to predator

In the present paper, we develop a simple two species prey-predator model in which the predator is partially coupled with alternative prey. The aim is to study the consequences of providing additional food to the predator as well as the effects of harvesting efforts applied to both the species. It is observed that the provision of alternative food to predator is not always beneficial to the system. A complete picture of the long run dynamics of the system is discussed based on the effort pair as control parameters. Optimal augmentations of prey and predator biomass at final time have been investigated by optimal control theory. Also the short and large time effects of the application of optimal control have been discussed. Finally, some numerical illustrations are given to verify our analytical results with the help of different sets of parameters.     

High resolution analysis of swim path patterns of intact and olfaction-deprived minnows (Phoxinus phoxinus) stimulated with food and potential predator odour

The effects of different regimes of chemo-stimulation on the swim path in minnows ( Phoxinus phoxinus ) before and after olfactory deprivation were recorded by aid of a sensitive video-based motion analysis system (DOTFINDER 6cp, JVP). Time series of x-y co-ordinates were taken at 2·5 Hz from colour-marked individuals. From these co-ordinates, nine swim path parameters representing velocities, angles and inter-individual distances were calculated. Each experiment consisted of the application of a water control followed by stimulation with food extract, or body mucus dilutions of rainbow trout ( Oncorhynchus mykiss ) a potential predator. These procedures were replicated with the same individuals before and after removal of their olfactory epithelium. Compared to the controls, only food stimulation of intact fish resulted in significant changes of single parameters. Food-stimulated intact fish swam faster, less steadily, used more of the area and kept wider inter-individual distances than controls. No significant changes of single swim path parameters occurred between controls and experimentals in all other treatments. Cluster-analysis however, provided a fair separation of controls (stimulus=water) and experimental (stimulated by food or predator odour) individuals in intact fish, but failed to separate controls and experimentals in olfaction-deprived fish. Distance travelled, median velocity and total acea use were the most discriminating parameters.     

Effects of pond size and consequent predator density on two species of tadpoles

Experimental ponds were used as a model system of habitat patches to study the effect of habitat size on the relative growth performance of tadpoles of Bufo americanus and Pseudacris triseriata, and on colonization by predatory insects. Three pond depths and surface areas were habitat size treatments in a replicated, factorial experiment. Tadpoles of both species were astablished together at a single density and ponds were left open to natural colonization by aquatic insects. Pond area had a significant effect on the multivariate response of P. triseriata larval period, survival, and metamorphic mass. P. triseriata survived better relative to B. americanus in larger ponds. However, increasing pond area led to greater incidence of predacious beetle larvae (Dytiscus, Coleoptera: Dytiscidae). Dytiscus larvae had a significant negative effect on the survival of P. triseriata and led to reduced P. triseriata survival relative to B. americanus in colonized ponds. The results suggest that habitat size can influence community structure by altering the distribution of predation among habitat patches.