Predator‐Naïve Brown Trout (Salmo trutta) Show Antipredator Behaviours to Scent from an Introduced Piscivorous Mammalian Predator Fed Conspecifics

Introduced mammalian predators may pose a high risk for native and naïve prey populations, but little is known about how native fish species may recognize and respond to scents from introduced mammalian predators. We investigated the role of diet‐released chemical cues in facilitating predator recognition, hypothesizing that native brown trout (Salmo trutta) would exhibit antipredator behaviours to faeces scents from the introduced American mink (Neovision vison) fed conspecifics, but not to non‐trout diets. In treatments‐control and replicate stream tank experiments, brown trout showed significant antipredator responses to faeces scent from mink fed conspecifics, but not to faeces scent from mink fed a non‐trout diet (chicken), or the non‐predator food control, Eurasian beaver (Castor fiber). We conclude that native and naïve brown trout show relevant antipredator behaviours to an introduced mammalian predator, presumably based on diet‐released conspecific alarm cues and thereby estimate the predation risk.     

Behavioural and life history effects of predator diet cues during ontogeny in damselfly larvae

A central issue in predator–prey interactions is how predator associated chemical cues affect the behaviour and life history of prey. In this study, we investigated how growth and behaviour during ontogeny of a damselfly larva (Coenagrion hastulatum) in high and low food environments was affected by the diet of a predator (Aeshna juncea). We reared larvae in three different predator treatments; no predator, predator feeding on conspecifics and predator feeding on heterospecifics. We found that, independent of food availability, larvae displayed the strongest anti-predator behaviours where predators consumed prey conspecifics. Interestingly, the effect of predator diet on prey activity was only present early in ontogeny, whereas late in ontogeny no difference in prey activity between treatments could be found. In contrast, the significant effect of predator diet on prey spatial distribution was unaffected by time. Larval size was affected by both food availability and predator diet. Larvae reared in the high food treatment grew larger than larvae in the low food treatment. Mean larval size was smallest in the treatment where predators consumed prey conspecifics, intermediate where predators consumed heterospecifics and largest in the treatment without predators. The difference in mean larval size between treatments is probably an effect of reduced larval feeding, due to behavioural responses to chemical cues associated with predator diet. Our study suggests that anti-predator responses can be specific for certain stages in ontogeny. This finding shows the importance of considering where in its ontogeny a study organism is before results are interpreted and generalisations are made. Furthermore, this finding accentuates the importance of long-term studies and may have implications for how results generated by short-term studies can be used.     

Searching for the Audience of the Weeping Lizard's Distress Call

The evolution and functions of avian and mammalian antipredator calls are well understood, which contrasts with a lack of progress in reptiles. Here, we present the first investigation of the functions of a distress call in a lizard. We studied Liolaemus chiliensis, which emits a short and complex high‐pitched scream when it is subdued. We determined the behavioral responses of two potential targets to these calls, conspecifics, and a snake predator. Additionally, we tested whether the chemical environment (presence of chemical scents from conspecifics) modulates the lizards' responses to calls. Both the conspecifics and the predator responded to the distress calls, which triggered a longer period of immobility in the lizards and a reduction in exploratory behavior in the snake, as compared to a white noise. In addition, the lizards in the arena with scents of conspecifics responded to distress calls and noise with more movements and escape attempts. These results suggest that distress calls may enhance the survival of L. chiliensis individuals.     

Ecology of Allis Shad Alosa alosa and Twaite Shad Alosa fallax in the Solway Firth, Scotland

The basis of this study were 132 adult Allis Shad and 150 Twaite Shad collected as bycatches from salmon stake nets in Scotland on the north side of the Solway Firth. Most (60%) of the Allis Shad were immature fish 2–3 years of age (mean length 305 mm). Mature males were younger (3–5 years) and smaller (mean length 421 mm) than females (4–6 years and 481 mm mean length). The largest Allis Shad was a female of 515 mm and 2183 g. In contrast, almost all the Twaite Shad were mature, the males younger (3–5 years) and smaller (mean length 341 mm) than the females (4–6 years and 364 mm mean length). The largest Twaite Shad was a female of 400 mm and 1213 g. The food of Allis Shad consisted mainly of small zooplankton with some fish and larger Crustacea. Fine vegetable fragments were common in the stomachs and attributed to filter feeding. The food of Twaite Shad was mainly small fish with some Crustacea. Mature Allis Shad of both sexes with large gonads (maximum female GSI: 20.63) were found throughout the spring and summer but no definite evidence of local spawning was obtained. Mature Twaite Shad of both sexes with large gonads (maximum female GSI: 23.32) were found until early July, thereafter most of the fish were spent. It appears that Twaite Shad spawn locally in June. Some hybrids between the two species were found.     

Particulate and filter feeding in threadfin shad, Dorosoma petenense, at different light intensities

Previous workers inferred from stomach analyses that threadfin shad ( Dorosoma petenense ) ate plankton by both filter and particulate feeding. These inferences were confirmed in this study by laboratory experiments in which both types of feeding were observed. Threadfin shad consumed relatively small food particles (≤ 0.39 mm) by filtration, while larger prey (7.5 mm) were eaten individually. The shad were able to filter feed on small foods (brine shrimp nauplii and phytoplankton) at all light intensities from 0 to 9 × 10¹ fL. These data indicate that under natural conditions shad can filter feed at any time of the 24 h period if food conditions are sufficient to trigger feeding. Filter feeding is probably induced by chemoreception rather than vision. The particulate feeding rate decreased as light intensity decreased, reaching a minimum between 9 × 10⁻⁴ and 9 × 10⁻⁵ fL. From these data it is inferred that particulate feeding is a visual process in this species, requiring intensities equivalent to bright moonlight or greater. Filter and particulate feeding abilities allow threadfin shad to consume most of the different types of plankton and to change their diet with seasonal changes in the composition of the plankton.     

Alarm response in larval western toads,Bufo boreas: release of larval chemicals by a natural predator and its effect on predator capture efficiency

An alarm response in larvae of the western toad, Bufo boreas, was examined in the laboratory. A natural predator, the giant water bug, Lethocerus americanus, while capturing and feeding on a tadpole, can cause sufficient damage for the release of toad alarm substance and subsequent alarm response in prey conspecifics. Larvae increased their activity and avoided the side of the tank that had a predator feeding on a conspecific tadpole in a visually isolated but interconnected container. Larvae did not increase activity or avoid the side of the tank that had a predator feeding on a heterospecific tadpole. Performance of the alarm response in conspecifics increased survivorship. The capture efficiency of predators (naiads of the dragonfly Aeshna umbrosa) hunting larvae that had been exposed to the alarm substance of conspecifics was reduced: predators required more capture attempts per successful attack compared to control tests.     

Predation Risk Perception,Food Density and Conspecific Cues Shape Foraging Decisions in a Tropical Lizard

When foraging, animals can maximize their fitness if they are able to tailor their foraging decisions to current environmental conditions. When making foraging decisions, individuals need to assess the benefits of foraging while accounting for the potential risks of being captured by a predator. However, whether and how different factors interact to shape these decisions is not yet well understood, especially in individual foragers. Here we present a standardized set of manipulative field experiments in the form of foraging assays in the tropical lizard Anolis cristatellus in Puerto Rico. We presented male lizards with foraging opportunities to test how the presence of conspecifics, predation-risk perception, the abundance of food, and interactions among these factors determines the outcome of foraging decisions. In Experiment 1, anoles foraged faster when food was scarce and other conspecifics were present near the feeding tray, while they took longer to feed when food was abundant and when no conspecifics were present. These results suggest that foraging decisions in anoles are the result of a complex process in which individuals assess predation risk by using information from conspecific individuals while taking into account food abundance. In Experiment 2, a simulated increase in predation risk (i.e., distance to the feeding tray) confirmed the relevance of risk perception by showing that the use of available perches is strongly correlated with the latency to feed. We found Puerto Rican crested anoles integrate instantaneous ecological information about food abundance, conspecific activity and predation risk, and adjust their foraging behavior accordingly.     

Seasonal differences in self-grooming in meadow voles, Microtus pennsylvanicus

We determined whether seasonal differences exist in the amount of time meadow voles, Microtus pennsylvanicus, self-groom when they encounter the scents of conspecifics. To do so, we used voles that were born and reared under long photoperiod (LP) and short photoperiod (SP). LP voles represent those found in free-living populations during the spring and summer breeding season, whereas SP voles characterize those found in free-living populations during the fall and winter nonbreeding season. Experiment 1 showed that LP male and female voles self-groomed more in response to odors of LP opposite-sex conspecifics as compared to those of other LP and SP conspecifics, suggesting that they may be self-grooming to signal sexual interest or excitement to potential mates. Experiment 2 demonstrated that SP males self-groomed more in response to scents of LP female voles and those of SP males as compared to scents of LP males and SP females, whereas SP females spent similar amounts of time self-grooming in response to scents of LP males, LP females, SP females, and SP males. These seasonal differences in self-grooming may reflect differences in the messages produced by groomers when they broadcast their odors as well as differences in the meaning of such odors to opposite-sex conspecifics. Alternatively, these data may be associated with seasonal differences in sexual motivation of the groomers when exposed to scents of particular conspecifics.     

Life history variations in populations of American shad, Alosa sapidissima (Wilson), spawning in tributaries of the St John River, New Brunswick

Shad were sampled at four locations in the St John River area, New Brunswick; St John Harbour, Kennebecasis River, Washademoak Lake and Mactaquac Dam. The effect of the St John Harbour fishery on upstream spawning populations was minimal. Mactaquac Dam began operation in 1967 and since that time the populations of shad arriving at that facility have been in a state of flux. When shad populations from Kennebecasis River and Washademoak L. were compared, the Washademoak Lake population exhibited higher relative fecundity, lower mean age at maturity and possessed a lower proportion of repeat spawners. The combinations of reproductive characteristics occurring in the populations of the St John River were the same as those occurring over the Atlantic coast range of shad. The possible environmental factors influencing the variations in reproductive characteristics are discussed.     

Orientation and navigation relative to water flow, prey, conspecifics, and predators by the nudibranch mollusc Tritonia diomedea

Progress in understanding sensory and locomotory systems in Tritonia diomedea has created the potential for the neuroethological study of animal navigation in this species. Our goal is to describe the navigational behaviors to guide further work on how the nervous system integrates information from multiple senses to produce oriented locomotion. Observation of T. diomedea in its habitat has suggested that it uses water flow to navigate relative to prey, predators, and conspecifics. We test these hypotheses in the field by comparing slug orientation in time-lapse videos to flow direction in circumstances with and without prey, predators, or conspecifics upstream. T. diomedea oriented upstream both while crawling and after turning. This trend was strongest before feeding or mating; after feeding or mating, the slugs did not orient significantly to flow. Slugs turned downstream away from an upstream predator but did not react in control situations without an upstream predator. These data support the hypothesis that T. diomedea uses a combination of odors (or some other cue transported downstream) and water flow to navigate relative to prey, predators, and conspecifics. Understanding the context-dependent choice between upstream and downstream crawling in T. diomedea provides an opportunity for further work on the sensory integration underlying navigation behavior.     

Coping with divided attention: the advantage of familiarity

The ability of an animal to perform a task successfully is limited by the amount of attention being simultaneously focused on other activities. One way in which individuals might reduce the cost of divided attention is by preferentially focusing on the most beneficial tasks. In territorial animals where aggression is lower among familiar individuals, the decision to associate preferentially with familiar conspecifics may therefore confer advantages by allowing attention to be switched from aggression to predator vigilance and feeding. Wild juvenile brown trout were used to test the prediction that familiar fishes respond more quickly than unfamiliar fishes to a simulated predator attack. Our results confirm this prediction by demonstrating that familiar trout respond 14% faster than unfamiliar individuals to a predator attack. The results also show that familiar fishes consume a greater number of food items, foraging at more than twice the rate of unfamiliar conspecifics. To the best of our knowledge, these results provide the first evidence that familiarity-biased association confers advantages through the immediate fitness benefits afforded by faster predator-evasion responses and the long-term benefits provided by increased feeding opportunities.     

Circadian rhythms in juvenile american shad, Alosa sapidissima

Swimming activity (in cm s⁻¹) of a school (55 individuals) of young-of-the-year ( total length=110 mm) American shad, Alosa sapidissima , was determined under a variety of photoperiod conditions. These included a normal (ambient), a shifted, and constant-light day. Swimming activity was measured over 4-day periods. During normal days swimming speeds followed periods of about 24 h, with fast speeds (up to 45 cm s⁻¹) and schooling occurring during the photoperiod. Under dark conditions speeds were slower (8 cm s⁻¹) with most fish swimming as individuals. During a shifted day swimming speeds and schooling corresponded to the imposed day. Under constant light (equivalent to bright moonlight) no schooling was evident, and a constant, but slow, swimming speed was observed in each 24-h period. These shad demonstrated an exogenous rhythm with respect to the imposed day length. It is hypothesized that an endogenous circadian rhythm would only be of use to a fish required to hunt or chase its prey. Shad, being plankton feeders, do not chase prey and therefore can exhibit an exogenous circadian rhythm with no detrimental feeding results.     

Marmoset (Callithrix geoffroyi) Food-Associated Calls are Functionally Referential

Signals that are functionally referential provide listeners with information about a signaler's external environment, such as the presence of a nearby predator. Just as alarm calls may signal the presence of a predator, food-associated calls may signal the presence of food. To date, however, the only conclusive evidence that conspecifics perceive information about food from food-associated calls comes from a single species, the domestic chicken. Geoffroy's marmosets, small, arboreal New World primates, often emit food-associated calls when finding or consuming food. We presented playbacks of food calls and control sounds to two groups of naturalistically housed marmosets and observed the frequency of food-related behaviors (FRBs) during the 20-min post-playback period. Relative to the control playbacks, food call playbacks elicited an increase in the frequency of two FRBs (foraging and feeding), lasting throughout the post-playback observations. Moreover, the effect of food call playbacks was robust, occurring without regard to the type of food eliciting the food calls, the rate of food calling, or whether the signaler was a member of the receiver's group. To our knowledge, this research is the first to demonstrate that the food-associated calls of a primate species, like the food-associated calls of domestic chickens, meet the perception criterion for functionally referential communication. The results are discussed in light of the affective and cognitive mechanisms that may underlie the responses of receivers to hearing food-associated calls given by marmoset conspecifics.     

Length and restriction site heteroplasmy in the mitochondrial DNA of american shad (alosa sapidissima)

Restriction endonuclease analysis was used to assess mitochondrial DNA (mtDNA) variation in American shad (Alosa sapidissima) collected from 14 rivers ranging from Florida to Quebec. Two types of heteroplasmy were observed, one involving a major length polymorphism and the other a single restriction site. Shad mtDNA occurred in two principal size classes, 18.3 and 19.8 kb. Of 244 shad examined, 30 were heteroplasmic and carried both size classes of mtDNA in varying proportions; the remainder were homoplasmic for the smaller size class of mtDNA. The large mtDNA variant occurred most frequently at the southern end of the range, and except for two individuals from Nova Scotia, was not detected among shad from rivers north of the Delaware. In contrast, ten shad heteroplasmic for a SalI restriction site originated from rivers ranging from South Carolina to Nova Scotia. DNA mapping and hybridization experiments indicated that the length polymorphism is in the D-loop-containing region and consists of a tandemly repeated 1.5-kb DNA sequence occurring in two and three copies, respectively, in the two major size classes of shad mtDNA. Continuous length variation up to approximately 40 bp occurs among copies of the repeat both within and among individuals. Restriction site data support the conclusion that both forms of heteroplasmy in shad mtDNA have originated more than once.     

Food Deprivation Suppresses a Preference for the Top-Scent Mark of an Over-Mark in Meadow Voles (Microtus pennsylvanicus)

Food availability affects whether mammals communicate their interest in interacting with opposite‐sex conspecifics. This study examined the responses of voles to over‐marks, and factors that influence the formation and maintenance of a preference for the top‐scent in an over‐mark. Specifically, we investigated how food deprivation affected the amount of time male and female voles exposed to an over‐mark, later responded to the marks of the top‐ and bottom‐scent donors when subsequently presented with the two scents side by side. Males and females that were not food deprived and males that were food deprived 6 h before exposure to an over‐mark later maintained a preference for the donor of the top‐scent mark compared with the donor of the bottom‐scent mark of the over‐mark. Females that were food deprived for 6 h before or after exposure of the over‐mark and males food deprived 6 h after the exposure to the over‐mark showed no preference for the top‐scent mark donor. Re‐feeding females that were food deprived for 6 h before exposure to an over‐mark was sufficient to restore their preference for the mark of the top‐scent male over that of the bottom‐scent male. The different responses of food‐deprived male and female voles to over‐marks of opposite‐sex conspecifics may be associated with differences in their tactics for interacting with potential mates and the higher energetic costs of reproduction in female voles than in male voles.     

Female meadow voles,Microtus pennsylvanicus,do not alter their over-marking in response to female conspecifics that were food deprived

Many terrestrial mammals will deposit scent marks and over-marks, the latter being the overlapping scent marks of two conspecifics. Studies have shown that male rodents that are exposed to the overlapping scent marks of two female conspecifics later spend more time investigating the mark of the top-scent female than that of the bottom-scent female. This suggests that over-marking is a form of competition and that the top-scent female is more likely than the bottom-scent female to be chosen as a potential mate. Thus, females should over-mark the scents of neighboring females at a rate that will maximize their chances of attracting males. However, meadow voles live in areas that may contain patchy food availability and residents may differ in their nutritional status. Females in a better nutritional state may be more likely than those in poorer nutritional states to indicate their presence in an area, signal possession of a territory, and to attract mates. Thus, we tested the prediction that female meadow voles, Microtus pennsylvanicus, that were not food deprived would deposit more over-marks than female voles that were food deprived for 6 h. Food-deprived female voles and female voles that had continuous access to food deposited a similar number of scent marks and used a similar proportion of those marks as over-marks when they encountered the scent marks of female conspecifics. These findings suggest that the nutritional status of female voles does not affect their ability to signal their presence in an area marked by a female conspecific.     

Contrasting responses of bumble bees to feeding conspecifics on their familiar and unfamiliar flowers

Animals exploiting their familiar food items often avoid spatio-temporal aggregation with others by avoiding scents, less rewarding areas or visual contacts, thereby minimizing competition or interference when resources are replenished slowly in patches. When animals are searching or assessing available food sources, however, they may benefit from reducing sampling costs by following others at food sites. Therefore, animals may adjust their responses to others depending on their familiarity with foraging situations. Here, we conducted field experiments to test whether nectar-collecting bumble bees make this adjustment. We allowed free-foraging bees to choose between two inflorescences, one occupied by a conspecific bee and another unoccupied. When bees were presented with flowers of a familiar type, they avoided occupied inflorescences. In contrast, bees visited an occupied inflorescence when the flower type was unfamiliar. To our knowledge, this is the first report suggesting that animals adjust their responses to feeding conspecifics depending on their familiarity with food sources. Such behavioural flexibilities should allow foragers to both explore and exploit their environments efficiently.     

Predation on exotic zebra mussels by native fishes: effects on predator and prey

SUMMARY 1. Exotic zebra mussels, Dreissena polymorpha, occur in southern U.S. waterways in high densities, but little is known about the interaction between native fish predators and zebra mussels. Previous studies have suggested that exotic zebra mussels are low profitability prey items and native vertebrate predators are unlikely to reduce zebra mussel densities. We tested these hypotheses by observing prey use of fishes, determining energy content of primary prey species of fishes, and conducting predator exclusion experiments in Lake Dardanelle, Arkansas. 2. Zebra mussels were the primary prey eaten by 52.9% of blue catfish, Ictalurus furcatus; 48.2% of freshwater drum, Aplodinotus grunniens; and 100% of adult redear sunfish, Lepomis microlophus. Blue catfish showed distinct seasonal prey shifts, feeding on zebra mussels in summer and shad, Dorosoma spp., during winter. Energy content (joules g⁻¹) of blue catfish prey (threadfin shad, Dorosoma petenense; gizzard shad, D. cepedianum; zebra mussels; and asiatic clams, Corbicula fluminea) showed a significant species by season interaction, but shad were always significantly greater in energy content than bivalves examined as either ash-free dry mass or whole organism dry mass. Fish predators significantly reduced densities of large zebra mussels (>5 mm length) colonising clay tiles in the summers of 1997 and 1998, but predation effects on small zebra mussels (≤5 mm length) were less clear. 3. Freshwater drum and redear sunfish process bivalve prey by crushing shells and obtain low amounts of higher-energy food (only the flesh), whereas blue catfish lack a shell-crushing apparatus and ingest large amounts of low-energy food per unit time (bivalves with their shells). Blue catfish appeared to select the abundant zebra mussel over the more energetically rich shad during summer, then shifted to shad during winter when shad experienced temperature-dependent stress and mortality. Native fish predators can suppress adult zebra mussel colonisation, but are ultimately unlikely to limit population density because of zebra mussel reproductive potential.     

Antipredator behaviour mediated by chemical cues: the role of conspecific alarm signalling and predator labelling in the avoidance response of a marine gastropod

Gastropods represent a challenge in the understanding of alarm signalling. We studied predator avoidance (climbing behaviour) of the marine snail Tegula funebralis in laboratory experiments. Snails were exposed to crude extract of conspecifics, and to water conditioned by actively feeding or non-feeding predatory crabs. Crabs had previously been maintained on different diets, and were accordingly labelled by chemical cues of various origins. Tegula -extract alone released climbing behaviour in May, but not in June. However, during both these months, snails responded to chemical cues from crabs that were actively feeding on Tegula . Crabs labelled by Tegula -diet, and actively feeding on Tegula , also caused more climbing responses compared to crabs labelled by other diets. Chemical cues derived from crabs actively feeding on another snail species, or from non-feeding crabs, did not induce snail climbing no matter the previous feeding history of the predators. When snails received Tegula -extract combined with water conditioned with a non-feeding, Tegula -labelled crab, no climbing occurred. However, when the non-feeding, Tegula -labelled crab was present in the solution of Tegula -extract, moderate climbing responses were obtained. The results imply that climbing responses of T. funebralis are in general caused by the action of a two-component system. This system seems to be a mixture of chemical cues leaking from the tissue of conspecifics when being eaten, and latent conspecific chemicals that are modified in crabs and presumably released with the urine of chemically labelled predators. The modified chemical labels appear to be fully released by crabs when feeding, and moderately released when detecting food. The responses obtained in May with crude extract alone may result from a seasonal change in alarm signalling properties, or a change in behavioural responsiveness of snails exposed to a variable predator regime.     

Piscivore enhancement effects on food webs depend on planktivore body size and species composition in replicated whole lake experiments

Recent syntheses of trophic cascade and biomanipulation research have suggested that the effects of piscivores on planktivorous fish populations are reduced, when planktivores are capable of outgrowing predator gape limitation and in systems with complex food web interactions. These hypotheses, however, have not been tested in long-term, whole-lake, experiments where processes such as fish recruitment and compensatory food web responses may be important. We conducted a replicated whole-lake experiment to test for the effects of supplemental piscivore introductions on food webs of eutrophic lakes dominated by deep-bodied planktivores. Responses to piscivore enhancement were compared between lakes differing in food web structure due to the presence of omnivorous gizzard shad (Dorosoma cepedianum). A significant decrease in the relative abundance of juvenile planktivorous fish, and an increase in total benthic macroinvertebrate density was observed in lakes containing mainly bluegills (Lepomus machrochirus). In contrast, lakes containing gizzard shad exhibited no significant responses to piscivore manipulation. Our results support the hypothesis that food webs in lakes dominated by deep-bodied planktivorous fish species respond weakly to piscivore enhancement. In addition, our findings support the hypothesis that cascading trophic interactions are weaker in lake ecosystems with more complex food web interactions such as those containing gizzard shad.