The effect of turbidity on recognition and generalization of predators and non‐predators in aquatic ecosystems

Recent anthropogenic activities have caused a considerable change in the turbidity of freshwater and marine ecosystems. Concomitant with such perturbations are changes in community composition. Understanding the mechanisms through which species interactions are influenced by anthropogenic change has come to the forefront of many ecological disciplines. Here, we examine how a change in the availability of visual information influences the behavior of prey fish exposed to potential predators and non‐predators. When fathead minnows, Pimephales promelas, were conditioned to recognize predators and non‐predators in clear water, they showed a highly sophisticated ability to distinguish predators from non‐predators. However, when learning occurred under conditions of increased turbidity, the ability of the prey to learn and generalize recognition of predators and non‐predators was severely impaired. Our work highlights that changes at the community level associated with anthropogenic perturbations may be mediated through altered trophic interactions, and highlights the need to closely examine behavioral interactions to understand how species interactions change.     

Microsatellite loci for fathead minnow (Pimephales promelas)

We describe the cloning and characterization of seven microsatellite loci (six dinucleotide and one tetranucleotide) from fathead minnow (Pimephales promelas). In a sample of 48 fish from a captive population, polymorphism at these loci ranged from 4 to 11 alleles with expected heterozygosities ranging from 0.59 to 0.82. These loci will be extremely useful to researchers currently studying the ecotoxicology, behaviour and population genetics of this species.     

Maternally derived Cu tolerance in larval fathead minnows: how long does it persist?

Fathead minnow Pimephales promelas larvae were produced by either copper (Cu)-exposed or naïve females and then subjected to a 96 h survival test using Cu concentrations of 400 and 800 μg l⁻¹. Three survival challenges were conducted: the first survival test featured 0 day-old larvae while the second and third featured 8 and 15 day-old larvae, respectively. The results of this study show that maternally derived Cu tolerance was relatively short-lived as it persisted for <8 days.     

Predicting the Effects of Endocrine Disrupting Chemicals on Fish Populations

This study evaluates the applicability and sensitivity of fish population dynamics modeling in assessing the potential effects of individual chemicals on population sustainability and recovery. Fish reproductive health is an increasingly important issue for ecological risk assessment following international concern over endocrine disruption. Life-history data from natural brook trout and fathead minnow populations were combined with effects data from laboratory-based studies, mainly concerning species other than brook trout and fathead minnows, to assess the likely impact of nonylphenol (NP) and methoxychlor (MXC) on brook trout (Salvelinus fontinalis) and fathead minnow (Pimephales promelas) population size. A delay differential equation (DDE) model with a 1-day timestep was used to predict the population dynamics of the brook trout and fathead minnows. The model predicts that NP, could enhance populations by up to 17% at a concentration of 30?µg l^?1 based on the results of reduction in survival and increased fecundity from life-cycle toxicity tests, however attempting to allow for growth reduction and its effect on fecundity results in a prediction of a 28% reduction in population numbers. For fathead minnows the DDE model predicts that the same concentration of NP could cause a population reduction of 21%. The differences in these predictions are related to these two species having different life history strategies, which are considered in the parameterization of the model. Post-application concentrations of MXC may peak around 300?µg l^?1 and then decline rapidly with time. Predictions show that such applications could cause a reduction of up to 30% in brook trout populations if the application occurs at the peak of the spawning season on successive years but that the effect would be less than 1% if the spawning season is avoided. Effects on the fathead minnow population size are predicted to be smaller (<4%) even if application occurs during the spawning period. Risk based statistics generated by the population dynamics models, such as interval decline risk or quasiextinction risk and predicted time to recovery complement traditional effects parameters such as LC50 and LOEC and may ultimately prove to be more useful in risk assessment.     

Natural disturbance and life history: consequences of winterkill on fathead minnow in boreal lakes

Age, growth and reproductive characteristics of fathead minnow Pimephales promelas populations inhabiting four lakes that varied in the extent and frequency of winterkill were studied in the boreal region of western Canada. The lifespan of fathead minnows inhabiting lakes prone to winterkill was 1–2 years shorter than those in less disturbed lakes. In populations prone to winterkill, fish displayed faster growth rates and grew to a larger size‐at‐age, particularly during the first year of life. Although lower population densities in winterkill lakes probably contributed to this increased growth, adults in these populations tended to spawn earlier in the season than the smaller adults in more stable populations. Fathead minnows in lakes prone to winterkill also matured at an earlier age and allocated a greater proportion of their body mass to gonads than conspecifics in the more benign, stable lakes. These trends are consistent with predictions for organisms in variable, unpredictable environments and, because fathead minnows are tolerant to a wide range of environmental conditions, suggest that variation in life‐history traits among populations is probably a product of both selection and phenotypic plasticity.     

Differential survival of two minnow species under experimental sunfish predation: implications for re‐invasion of a species into its native range

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Effects of social structure on reproductive activity in male fathead minnows (Pimephales promelas)

The selection of alternative reproductive phenotypes is oftenthought to be the result of physiological state, with smallindividuals forced energetically to postpone the allocationof resources to reproduction. However, for male fathead minnows(Pimephales promelas), we show that seasonal reproductive activityis modulated by social status. In enclosure and pond experiments,small males advanced their reproductive condition, held nesting territories, and spawned earlier in the reproductive seasononly when large males were absent or removed from the population.Since differences in the timing of reproduction among smallmales were not size- or condition-dependent, the common explanationfor the selection of alternative reproductive phenotypes, basedon state-dependence, is insufficient. In the absence of large,socially dominant individuals, small males produced comparablenumbers of offspring as the treatment with large males, although the offspring of these uninhibited small males were smallerat the end of the growing season than the young of large males.Thus, interactions among conspecifics may account for muchof the phenotypic diversity observed within and among naturalfathead minnow populations, through their direct and indirecteffects on growth, recruitment and survival.     

Overriding the oddity effect in mixed-species aggregations: group choice by armored and nonarmored prey

Because "odd" individuals often suffer disproportionately highrates of predation, solitary individuals should join groupswhose members are most similar to themselves in appearance.We examined group-choice decisions by individuals in armoredand nonarmored species and predicted that either (1) the oddityeffect would result in preference for conspecific groups forsolitary individuals of both species, or (2) individuals inthe armored species would prefer to associate with groups containingindividuals of the more vulnerable species. Armored brook sticklebacks(Culaea inconstans) and nonarmored fathead minnows (Pimephalespromelas) have the same predators and often occur together instreams. In mixed-species shoals, yellow perch (Perca flavescens)attacked minnows earlier and more often than sticklebacks. Wetested whether solitary minnows and sticklebacks preferred toassociate with conspecific or heterospecific shoals under conditionsof both low and high predation risk. When predation risk washigh, minnows preferred to associate with conspecifics overheterospecifics, as predicted by the oddity effect. In contrast,sticklebacks preferentially associated with groups of minnowsover groups of conspecifics when predation risk was high. Whenpredation risk was low, solitary individuals of both speciespreferentially associated with conspecific over heterospecificshoals. Stickleback shoal choices under low-risk conditionsmay have been influenced by interspecific competition for food.In feeding experiments, minnows were more efficient foragersthan sticklebacks, so it should benefit sticklebacks to avoidminnows unless predation risk is high. Therefore, for armoredprey, the benefits of associating with more vulnerable preyappear to override the costs of both the oddity effect and foodcompetition when predation risk is high.     

Integrating effects of stressors across levels of biological organization: examples using organophosphorus insecticide mixtures in field-level exposures

An important uncertainty often identified inecological risk assessment is the lack of ecologicalconnectivity between endpoints measured across themany levels of biological organization within anecosystem. In the present study, we address thisissue by quantitatively linking acetylcholinesterase(AChE) activity, a common biomarker of exposure toorganophosphorus (OP) insecticides, with endpoints athigher levels of biological organization in fish andinvertebrates, and to assess the utility of thisendpoint as a predictive biomarker of effects underfield conditions. In 1997, we conducted three fieldstudies in outdoor microcosms to assess binary andternary mixtures of chlorpyrifos (CLP),azinphos-methyl (AZM), and diazinon (DIA). The firststudy (14 days) used a regression design(concentration-response) to assess direct and indirectpopulation-level responses of zooplankton andphytoplankton to a binary mixture of DIA and CLP atnominal concentrations of 0.44–44.0 g/L. A secondregression study (7 days) was conducted to assesslethality (organismal response) in fathead minnows(Pimephales promelas) to a ternary mixture ofthe three OP's at nominal concentrations of 50–1750 g/L. An ANOVA study (7 days) was also conducted toassess lethality in fathead minnows. In this study,the concentrations of the components of the mixturewere determined from exposure and toxicitydistributions using a toxic equivalent (TE) approachand apportioned to achieve equipotent mixtures at80:10:10 ratios. The abundance of Cladocera declinedby close to 100% within 24 hours of application atthe four highest concentrations; consequently, AChEcould not be measured in these treatments. At the twolowest treatments, AChE activity exhibited aconcentration-dependent decline over the study period;however, AChE activity increased over the first 24hours of exposure, while abundance decreased. Infathead minnows, mortality was significantlycorrelated with brain AChE activity in both studies. The form of this relationship was remarkablyconsistent between studies, with a 50% reduction inAChE activity corresponding to 10–15% mortality anda 90% inhibition of AChE corresponding to 50%mortality. The results of these studies show thatAChE activity, a biochemical endpoint, can be used asa reliable biomarker of effect at the organismal leveland may be useful as a predictor of population-levelresponses in invertebrates.     

Use of a 15 k gene microarray to determine gene expression changes in response to acute and chronic methylmercury exposure in the fathead minnow Pimephales promelas Rafinesque

This study describes the use of a 15 000 gene microarray developed for the toxicological model species, Pimephales promelas , in investigating the impact of acute and chronic methylmercury exposures in male gonad and liver tissues. The results show significant differences in the individual genes that were differentially expressed in response to each treatment. In liver, a total of 650 genes exhibited significantly ( P < 0·05) altered expression with greater than two-fold differences from the controls in response to acute exposure and a total of 267 genes were differentially expressed in response to chronic exposure. A majority of these genes were downregulated rather than upregulated. Fewer genes were altered in gonad than in liver at both timepoints. A total of 212 genes were differentially expressed in response to acute exposure and 155 genes were altered in response to chronic exposure. Despite the differences in individual genes expressed across treatments, the functional categories that altered genes were associated with showed some similarities. Of interest in light of other studies involving the effects of methylmercury on fish, several genes associated with apoptosis were upregulated in response to both acute and chronic exposures. Induction of apoptosis has been associated with effects on reproduction seen in the previous studies. This study demonstrates the utility of microarray analysis for investigations of the physiological effects of toxicants as well as the time-course of effects that may take place. In addition, it is the first publication to demonstrate the use of this new 15 000 gene microarray for fish biology and toxicology.