Culaea Research Articles

Within‐group variation in the willingness to risk exposure to a predator: the influence of species and size

The costs and benefits associated with feeding in the vicinity of a predator should vary within and among species, depending on an individual's vulnerability to a predator. In this paper, we investigate how willingness to risk exposure to a predator in order to gain access to food is expressed within groups of fish. We provided groups of six individually marked brook sticklebacks (Culeainconstans) and fathead minnows (Pimephalespromelas) with the opportunity to feed in safety, or in the presence of a single predator (walleye, Stizostedionvitreum ). Sticklebacks and fathead minnows are commonly found in the same locations at the same time, but sticklebacks also possess armour and spines that provide defence against some predators. Despite this morphological variation, patterns of individual behaviour were consistent between species. While feeding close to the predator, there was a positive relation between the size of the individual and the proportion of food consumed. No relation existed on the side farthest from the predator. These data suggest that fish may risk exposure to predators to exploit size‐related differences in vulnerability to gain a competitive advantage for access to food.

Recovery of fish populations in Lake 223 from experimental acidification

The fish populations of Lake 223, a lake previously acidified to pH 5.1, were monitored during 13 years of gradual pH recovery to preacidification pH 6.7. During acidification, recruitment ceased for all fish species in this lake and two were extirpated. During pH recovery, successful recruitment resumed for all fish species that remained in the lake. One of the extirpated species, fathead minnow (Pimephales promelas), successfully colonized the lake. Lake trout (Salvelinus namaycush) abundance decreased during acidification and remained low during pH recovery due to very low recruitment. Growth curves, condition factor, and annual survival of lake trout decreased during acidification and quickly increased to preacidification values during pH recovery. During the early years of pH recovery, white sucker (Catostomus commersoni) abundance increased to almost 10 times the number at the start of the experiment but decreased during the final years due to decreased annual survival and recruitment. Pearl dace (Margariscus margarita) became abundant during acidification and their abundance decreased during pH recovery as fathead minnow abundance increased. Other fish species that were caught infrequently prior to acidification, brook stickleback (Culaea inconstans), lake chub (Couesius plumbeus), and finescale dace (Phoxinus neogaeus), were caught frequently during pH recovery.

Selection of an aquatic indicator species to monitor organic contaminants in trophically simple lotic food webs

A four-step procedure was used to identify an aquatic macroinvertebrate with which to monitor organic contaminant burdens in trophically simple lake food webs of Alberta, Canada. We identified leeches (Oligochaeta: Hirudinea) as the potential indicator assemblage (Step 1), and then documented their abundance and distribution in 16 lakes to identify a species-level bioindicator (Step 2). The latter two steps involved identifying the number and level of organic contaminants within the indicator species (Step 3) and a comparison with other taxa within the food web (Step 4). The majority of lakes within the watershed contained seven to nine leech species with individuals of Nephelopsis obscura being one of the most abundant and widely distributed species that is sufficiently large to allow for rapid collection of sufficient biomass for organic contaminant analyses. Concentrations of organic contaminants in leeches from 22 sites and in sediments (two lakes) within the watershed were low, and in the majority of cases less than analytical detection levels (i.e., 0.05 &mgr;g/kg wet weight). Nevertheless, leech tissues contained trace amounts of a fungicide (i.e., hexachlorobenzene) and four pesticides including: pp'-DDE, pp'-DDD, representing intermediate and final breakdown products of pp'-DDT, a-HCH (i.e., hexachlorocyclohexane) and g-HCH (Lindane). Concentrations of these contaminants did not differ significantly between leeches collected from lakes within a national park compared to areas outside the park that may have been more vulnerable to loadings of contaminants from industrial and agricultural sources. Lastly, we compared organic contaminant concentrations in N. obscura with Gammarus lacustris and Brook's stickleback, Culaea inconstans (Gasterosteidae). Organic contaminant concentrations in N. obscura were similar or higher than those present in G. lacustris and C. inconstans. Eight organic contaminants were found in N. obscura, whereas, C. inconstans and G. lacustris contained only three and four, respectively. The fact that N. obscura typically contained higher concentrations and greater numbers of detectable compounds suggest that it is a suitable indicator of organic contamination. While current levels of organic contaminants in the Beaver Hills watershed are low, despite the intense agriculture and industrial activities, they should be monitored to act as an early warning indicator of ecosystem degradation.

Effects of exposure to predatory cues on territorial behaviour of male fathead minnows

We conducted a laboratory study to determine if male fathead minnows, Pimephales promelas, altered their territorial behaviour associated with reproduction in response to combinations of visual and chemical cues from northern pike, Esox lucius. We introduced the following stimuli to a territorial male: a brick (control), fathead minnow alarm pheromone, a pike fed brook stickleback, Culea inconstans, or a pike fed fathead minnow. The territorial behaviour of males did not change when the control was added. Male minnows experiencing threat from pike fed stickleback significantly reduced the frequency at which they performed three territorial behaviours, but, within 12 h, had returned to pre-exposure activity levels. Male minnows subjected to alarm pheromone alone and to pike fed fathead minnow significantly reduced their territorial behaviour, abandoned their nests, and did not return to pre-exposure levels of activity after 24 h. We suggest that because risk of predation triggers prolonged decreases in territorial defense, it may affect competition between nesting males and female mate choice. We conclude that fathead minnows can assess the severity of predatory threat and adjust their reproductive behaviour accordingly.

Characteristics and distribution of large tandem duplications in brook stickleback (Culaea inconstans) mitochondrial DNA.

Most animal mitochondrial DNAs (mtDNAs) range in size from 15 to 18 kb, but increased sizes up to approximately 40 kb are occasionally found. We investigated large size variation in mtDNA of the brook stickleback fish, Culaea inconstans, and characterized four large (2.7-5.8 kb) tandem duplications. Duplications differ in size, frequency of occurrence, and degree of associated heteroplasmy, but each includes the control region and one or more adjacent genes. Duplications are correlated with two mtDNA lineages sampled from 31 populations. L1 duplications (3.2-4.8 kb) were present in all lineage I individuals (n = 121, 19 populations); 53 fish were heteroplasmic due to variation in the copy number of a tandemly repeated 270-bp sequence within the duplicated region. In contrast, duplications, L2, L3, and L4 (2.7-5.8 kb) occurred in only 117 of 174 lineage II fish, in eight of 14 populations. Nine fish with L3 or L4 duplications were heteroplasmic, possessing some mtDNAs that lacked duplications (normal-length mtDNAs). Heteroplasmy in L2 was associated with a small variable region near the ND5 gene. Phylogenetic analysis of restriction sites in Culaea mtDNAs and haplotype-defining sequence differences present in both copies argue for multiple independent events that gave rise to three of the four duplications.

A comparison of startle response in two morphs of the brook stickleback (Culaea inconstans): Further evidence for a trade-off between defensive morphology and swimming ability

It is generally thought that predation pressure drives the evolution of long spines and robust pelvic girdles in sticklebacks (Pisces: Gasterosteidae). However, the lack of these traits in some environments with intense predation pressure suggests that there may be a limit to which apparently defensive structures benefit sticklebacks. This paper focuses on a trade-off between defensive morphology and escape response performance in a genetically based polymorphic population of brook stickleback (Culaea inconstans), in which fish have fully developed pelvic girdles and pelvic spines (‘complete’ morph) or completely lack these defensive structures (‘absent’ morph). Startle response experiments revealed that the absent morph did better in all aspects of startle performance (displacement, maximum velocity, acceleration) than the complete morph. The absent morph also bent deeper than the complete morph during the initial phase of the startle response. The pelvic girdle polymorphism in this population may be maintained because individuals with a complete pelvic girdle and spines may be able to escape more easily from predators once they are captured, whereas individuals lacking these structures may better avoid capture when they are attacked.

Integrating Phylogenetic and Experimental Analyses: The Evolution of Male and Female Nuptial Coloration in the Stickleback Fishes (Gasterosteidae)

Both male and female gasterosteid fishes display nuptial coloration. Male nuptial col- oration originated in the ancestor of the Pungitius + Culaea + Gasterosteus clade. Patterns of origin and diversification of characters involved in male-male, male-female, and parental interactions indicate that the evolution of male color was influenced by intersexual selection, natural selection during parental care, and intrasexual selection, in decreasing order of importance. This macro- evolutionary hypothesis was corroborated by examining changes in male color across the breeding cycle for two stickleback species, Gasterosteus aculeatus and Culaea inconstans. Female nuptial col- oration may have originated before the male signal. The phylogenetic diversification of the male and female signals are decoupled, suggesting that they have been subject to different selection pressures throughout their evolutionary histories. Macroevolutionary patterns and experimental studies indicate that color signal evolution has been more complex in this group of fishes than was previously thought. (Comparative biology; phylogeny; sexual selection; nuptial coloration; stickleback fishes.) The power of macroevolutionary pat- terns lies in their ability to falsify hypoth- eses of character evolution. For example, a proposal that the evolution of character X was influenced by character Y is falsified if X evolved before Y. Failure to falsify a hypothesis of character evolution based upon macroevolutionary patterns pro- vides, however, only weak support for the hypothesis. This statement holds whether you are investigating unique events or sta- tistically analyzing correlated patterns of character origin in different lineages be- cause neither macroevolutionary patterns nor statistical analyses are tests of mech- anisms. The only way to unambiguously demonstrate that mechanism X has had an effect upon the evolution of character Y is to perform the appropriate experiment. The comparative phylogenetic approach is thus a powerful tool for experimental ethologists because it allows construction of a set of predictions based upon macro- evolutionary patterns that can serve as the focus for experimental investigation (Brooks and McLennan, 1991; McLennan, 1991). In this paper, I explore the feasibility of using the comparative approach to study the evolution of nuptial coloration in stick- leback fishes. A comparative study is more aptly described as a feedback loop than as a linear process. The loop begins with the reconstruction of the phylogenetic tree for the study group and proceeds with the op- timization of specific characters onto the tree, delineation of the relationship be- tween the origin and the diversification of the characters, construction of a hypothesis about the forces that have shaped the ob- served patterns, use of the hypothesis to make a series of predictions that can be tested experimentally, and experimental investigation of the predictions. During the course of the experimental analysis, it is not unusual to discover information that may either reinforce or change the original phylogenetic hypothesis. Such feedback highlights one of the certainties of biology: the situation is usually more complex than originally thought. A comparative study is thus an ongoing process whose successive sweeps we hope resemble the ever short- ening strokes of a pendulum moving clos- er and closer to the central attractor rep- resenting truth.

Geographic Variation in Mitochondrial DNA and Biogeography of Culaea inconstans (Gasterosteidae)

Mitochondrial DNA was characterized for length and restriction site polymorphism among 32 populations of Culaea inconstans (Gasterosteidae). Phylogenetic and geographic patterns of divergence in Culaea mtDNA were examined by maximum-parsimony analysis of 96 restriction sites. Gasterosteus aculeatus and Pungitius pungitius were used as outgroups. Mitochondrial genome size in Culaea, estimated from restriction digests, was variable but always larger than in other sticklebacks. Size heteroplasmy was often observed. Three types of size variation in mtDNA were observed. Tandem, direct duplications of 2.7-5.6 kb were centered around the control region, and duplications were seen in many individuals throughout the species range. Culaea mtDNAs grouped into two, highly divergent and geographically disjunct lineages. Populations from lineage II contained additional, small-size variation (100-300 bp) and a 1000-bp insertion. The disjunct distributions of the two lineages indicate that the present species distribution was influenced by postglacial dispersal from separate refugia in the Mississippi and Ohio river basins. Interpopulational relationships are insufficiently resolved to test the hypothesis of a Missouri River refugium during the Pleistocene. Relationships among populations from southern Michigan are concordant geographically with temporal availability of previously glaciated habitat. A disjunct Culaea population in New Mexico shares identical mtDNA restriction profiles with Michigan populations and likely represents an accidental

Interaction between Young-of-Year Fathead Minnows and Brook Sticklebacks: Effects on Growth and Diet Selection

The hypothesis that brook sticklebacks Culaea inconstans and fathead minnows Pimephales promelas are competitors was tested in field enclosures containing young-of-the-year individuals from both species. Growth was monitored for 6 weeks, then final weights and gut contents were examined. Fathead minnows were relatively unaffected by brook sticklebacks. Neither dietary composition nor growth was affected in enclosures containing only fathead minnows or a combination of fathead minnows and brook sticklebacks at similar density. The presence of fathead minnows did, however, stimulate growth of brook sticklebacks; this was possibly related to the relatively higher mortality of fathead minnows within the jointly occupied enclosures and the resulting reduced absolute density of fish. The diet of brook sticklebacks also became more diverse in the presence of fathead minnows. In enclosures containing only sticklebacks, the fish consumed primarily copepods. These data demonstrate that growth of brook sticklebacks may be sensitive to both intra- and interspecific competition. This apparent sensitivity of growth to the presence of fathead minnows may account for the observed spatial distribution and migratory habits of brook sticklebacks.

Cultural transmission of predator recognition in fishes: intraspecific and interspecific learning

Individuals that live in groups may have the opportunity to learn to recognize unfamiliar predators by observing the fright responses of experienced individuals in the group. In intraspecific trials, naive fathead minnows, Pimephales promelas, gave fright responses to chemical stimuli from predatory northern pike, Esox lucius, when paired with pike-experienced conspecifics but not when paired with pike-naive conspecifics. These pike-conditioned minnows retained the fright responses to pike odour when tested alone, indicating that learning had occurred, and transmitted their fright responses to pike-naive minnows in subsequent trials. Brook stickleback, Culaea inconstans, are found in mixed-species aggregations with fathead minnows and are also vulnerable to predation by northern pike. In a series of interspecific tests, pike-naive brook stickleback gave fright responses to chemical stimuli from northern pike when paired with pike-experienced minnows but not when paired with pike-naive minnows. Pike-conditioned stickleback also retained the fright responses when tested alone and subsequently also transmitted the fright responses to pike-naive minnows. Individuals may benefit from observations of the fright responses of conspecifics or heterospecifics by (1) being alerted to the immediate presence of unfamiliar predators and (2) learning to recognize unfamiliar predators as a potential threat.

The interaction between antipredator behaviour and antipredator morphology: experiments with fathead minnows and brook sticklebacks

Prey species have two fundamental strategies for reducing their probability of being killed by a predator: behavioural modification and morphological defenses. It is hypothesized that prey species which possess morphological defenses should exhibit less behavioural modification in response to predation risk than species lacking such defenses. Experiments were conducted to examine behavioural modification by armoured (brook sticklebacks, Culea inconstans) and unarmoured (fathead minnows, Pimephales promelas) prey species foraging in the presence of a predator (yellow perch, Perca flavescens). Two experiments measured habitat avoidance and reactive distance to an approaching predator. The results of these experiments were consistent with the hypothesis. Compared with fathead minnows, brook sticklebacks exhibited relatively little behavioural modification in response to the presence of a predator, both in terms of avoiding dangerous areas and in their reactive distance to an approaching predator. Sticklebacks, however, graded their reactive distance to an approaching predator in relation to both their body size and group size. These data suggest that the morphology of brook sticklebacks and their behavioural sensitivity to predation risk may allow them to efficiently exploit habitats that contain predators.

Correlation between the Level of Infection with Bunodera inconstans and Neoechinorhynchus rutili and Behavioral Intensity in Female Brook Sticklebacks

We investigated the influence of 2 intestinal helminths, Bunodera inconstans and Neoechinorhynchus rutili, on the development of female behavioral and morphological characters in brook sticklebacks. The number of N. rutili per female is positively correlated with standard length. Both the number of B. inconstans per female and the number of N. rutili per female are negatively correlated with the intensity of a female's aggressive response to an intruding female and are positively correlated with the intensity and duration of female courtship. The results of this study indicate that infection with N. rutili and B. inconstans may influence a female brook stickleback's ability either to compete for a mate or to sample from a large subset of territorial males.

Fathead minnows avoid conspedfic and heterospedfic alarm pheromones in the faeces of northern pike

Groups of fathead minnows Pimephales promelas were tested to determine if they avoided areas of a test tank labelled with the faeces of a predator (northern pike, Esox lucius) which had recently been fed minnows, brook sticklebacks Culaea inconstans, or swordtails Xiphophorus helleri. Minnows exhibited a fright reaction upon presentation of sponges labelled with faeces, when the pike had consumed minnows or sticklebacks, but not swordtails (which lack alarm pheromones). The fright reaction was characterized by increased shoal cohesiveness and increased dashing and freezing behaviour. Minnows avoided the area of the tank containing the faeces from pike on diets of minnows or sticklebacks, but not from pike fed a diet of swordtails. These data demonstrate that: (1) minnows actively avoid the faeces of pike fed minnows or brook sticklebacks, and (2) minnows exhibit a fright reaction to the faeces of a pike fed brook sticklebacks.

Male mate choice based upon female nuptial coloration in the brook stickleback, Culaea inconstans(Kirtland)

Female brook sticklebacks develop distinct nuptial coloration following ovulation. When given a choice between a gravid, uncoloured, inter-spawning interval female and a gravid, nuptially coloured female, male brook sticklebacks from two Ontario populations (1) approached the nuptially coloured female first, (2) directed their first courtship pummel towards her, and (3) spent significantly more time with her than with the inter-spawning interval female. Males from Tooley Creek spent more of their time near the nuptially coloured female engaged in courtship behaviour and more of their time near the inter-spawning interval female engaged in aggressive behaviour. Males from Algonquin Park showed no difference in the intensity of courtship or aggression directed towards the two females. These results corroborate the hypothesis that female nuptial coloration plays a role in signalling courtship readiness in at least some gasterosteids. The hypothesis that males should become more discriminating in their choice of spawning partners as they increase their parental investment was tested by comparing male mate choice based upon female colour for males with no eggs, one clutch and two clutches. The results corroborated the hypothesis: compared to when they were eggless, males with two clutches (1) spent less time with the inter-spawning interval female, (2) spent more time with the nuptially coloured female, (3) spent a greater proportion of the time near the nuptially coloured female engaged in courtship behaviour, and (4) displayed a trend towards increasing levels of aggression directed towards the inter-spawning interval female with increasing parental investment.

Evidence for a trade-off between defensive morphology and startle-response performance in the brook stickleback (Culaea inconstans)

It is generally believed that predation pressure may drive the evolution of long spines, a robust pelvic girdle, and a deep body in sticklebacks (Pisces: Gasterosteidae). However, the lack of such traits in environments under intense predation pressure suggests that there may be a limit to which these apparently defensive structures benefit sticklebacks. In some environments, well-developed defensive structures may not increase stickleback survival, but may actually reduce fitness if there is a cost associated with them. This paper focuses on a trade-off between defensive morphology and escape-response performance in the brook stickleback (Culaea inconstans). Our study of four populations of brook stickleback reveals that the population with the largest pelvic girdles and deepest bodies has a poorly developed escape response (i.e., small displacement, low maximum velocity, and low acceleration), while the population with the smallest pelvic girdles and shallowest bodies has a highly developed escape response. The two populations with intermediate defensive structures are intermediate in escape-response performance. Consideration of predation regimes in different environments may help us understand selection pressures that favor heavily versus poorly armored stickleback morphs.

Predator Community Composition and Patterns of Variation in Life History and Morphology Among Hyalella (Amphipoda) Populations in Southeast Michigan

-The amphipod, Hyalella azteca, is found in an ecologically diverse array of permanent freshwater habitats, including lakes with predatory fish and fishless ponds and marshes. To determine the extent to which Hyalella populations vary among habitats and the degree of covariation between predator community composition and Hyalella traits, I examined morphological and life history traits of adult individuals collected from nine diverse habitats in SE Michigan. Two distinct Hyalella morphotypes were apparent in the samples. A small-bodied morphotype had smaller adult body size, smaller size at first reproduction, and smaller eggs than a second, large-bodied morphotype. For morphological traits other than size, differences between morphotypes were less clear, with small but significant differences found in one sex only in antennal segment number and dorsal spine length and no differences between morphotypes in gnathopod width. Morphotype was consistently associated with habitat type. In general, fishless habitats and habitats in which sticklebacks (Culaea inconstans) are dominant fish predators contained only individuals of the largebodied morphotype, whereas habitats with well-developed centrarchid fish communities contained only individuals of the small-bodied morphotype. I suggest that the regime of sizebiased predation experienced by Hyalella in each habitat may be the primary determinant of the pattern of association between Hyalella morphotype and habitat type. Morphotypes co-occur in a single habitat, probably because the unusual character of this water body provides extensive regions that are suitable for each morphotype.

Acquired Recognition of Chemical Stimuli from Pike, Esox lucius, by Brook Sticklebacks, Culaea inconstans (Osteichthyes, Gasterosteidae)

AbstractIn this study we test whether brook sticklebacks (Culaea inconstans) can acquire predator recognition through releaser‐induced recognition learning, i.e. simultaneous exposure to aversive ('releasing') stimuli and neutral stimuli causing learned aversion to the neutral stimuli. We exposed wild‐caught pike‐naive brook sticklebacks (collected from a creek containing fathead minnows, Pimephales promelas, but not pike, Esox lucius) to chemical stimuli from pike that were mixed with brook stickleback skin extract, fathead minnow skin extract, or a control of distilled water. In subsequent tests 2 d later, when only pike stimuli were presented, sticklebacks conditioned with stickleback skin extract and fathead minnow skin extract exhibited antipredator behaviour (i.e. increased schooling and movement toward the substrate), while those conditioned with distilled water did not. Sticklebacks conditioned with stickleback skin extract responded to pike with a more intense response, in terms of movement toward the substrate, than those conditioned with fathead minnow skin extract, suggesting that conspecific skin extract may be a stronger stimulus than heterospecific skin extract for learning recognition of predators. To our knowledge this is the first study to demonstrate that an acanthopterygian fish can acquire predator recognition through the pairing of conspecific alarm pheromone with the cue of a predator. Furthermore, our results are the first to demonstrate that fish can acquire predator recognition through the pairing of a heterospecific alarm pheromone with the cue of a predator. These results suggest that brook sticklebacks will benefit by being in close proximity to fathead minnows. Acquired predator recognition has long‐term consequences in mediating predator‐prey interactions.

The role of experience in risk assessment: Avoidance of areas chemically labelled with fathead minnow alarm pheromone by conspecifics and heterospecifics

:In two field experiments, we investigated risk avoidance behaviour by individual fathead minnows (Pimephales promelas Rafinesque) and brook stickleback (Culaea inconstans Kirtland) in response to release of fathead minnow alarm pheromone. There was an initial decrease in the number of fish caught in areas labelled with alarm pheromone (risky areas) relative to areas labelled with distilled water (safe areas), after the source of the pheromone was removed. Numbers of minnows or stickleback caught in risky and safe areas were no longer different 4 hours after the pheromone source was removed. For minnows, there was no significant difference in the immigration rates of individuals into risky and safe areas from neighbouring locations. For minnows, and probably stickleback, new individuals, naive to the association of an area with alarm pheromone, immigrated into risky areas before the return of experienced fish. Fish present at the time of pheromone release did not return for 7 or 8 hours after the source of the pheromone was gone. This raises the possibility that the chief beneficiaries of chemical alarm signals may be only those individuals present at the time of pheromone release.

The effects of an abandoned roast yard on the fish and macroinvertebrate communities of surrounding beaver ponds

Recently formed beaver-ponds surrounding an abandoned copper-nickel ore roast yard near Sudbury, Ontario, Canada, were influenced by highly acidic and heavy-metal contaminated effluent. Fish, including Culaea inconstans, Phoxinus neogaeus, Phoxinus eos, and Pimephales promelas, were found in the ponds upstream of the roast yard only. Macroinvertebrate taxon richness and diversity were greater in the upstream ponds than in the downstream ponds. Acid intolerant taxa, including Mollusca and Hyalella azteca, were found upstream only; acid tolerant taxa, including Enallagma and Ischnura (Odonata: Coenagrionidae) were found in the downstream ponds. One taxon, a species of Chironomus, was especially tolerant of both acid and metal stresses, and was the only invertebrate taxon found in the pond located directly on the roast yard itself. We conclude that long-abandoned mining and refining sites can continue to have a marked effect on aquatic communities.

Risk-sensitive habitat use by brook stickleback (Culaea inconstans) in areas associated with minnow alarm pheromone

Brook stickleback (Culaea inconstans) share habitat and predators with cyprinid species, and they exploit the alarm pheromone of fathead minnows (Pimephales promelas) to avoid areas of high predation risk. In this field experiment, we measured the retention and duration of area avoidance by brook stickleback from areas marked with alarm pheromone of fathead minnows. Area avoidance was greatest during the first 2 hr after the source of the alarm pheromone was removed (P<0.05), but after 4 hr, area use was not significantly different from premarking levels. This study shows that brook stickleback: (1) use the alarm pheromone of fathead minnows to avoid high risk areas, (2) continue to avoid locations associated with predation risk after the source of the pheromone has gone, and (3) avoid risky areas temporarily, and resume use of risky areas after 2-4 hr. This behavioral response by stickleback to minnow alarm pheromone could serve to minimize risk of predation.