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Ecological invasions, where non-native species spread to new areas, grow to high densities and have large, negative impacts on ecological communities, are a major worldwide problem. Recent studies suggest that one of the key mechanisms influencing invasion dynamics is personality-dependent dispersal: the tendency for dispersers to have a different personality type than the average from a source population. We examined this possibility in the invasive mosquitofish (Gambusia affinis). We measured individual tendencies to disperse in experimental streams and several personality traits: sociability, boldness, activity and exploration tendency before and three weeks after dispersal. We found that mosquitofish display consistent behavioural tendencies over time, and significant positive correlations between all personality traits. Most notably, sociability was an important indicator of dispersal distance, with more asocial individuals dispersing further, suggesting personality-biased dispersal on an invasion front. These results could have important ecological implications, as invasion by a biased subset of individuals is likely to have different ecological impacts than invasion by a random group of colonists.

Arising from: M. Wolf, G. S. van Doorn, O. Leimar & F. J. Weissing Nature447, 581–584 (2007)10.1038/nature05835 ; Wolf et al. reply Wolf et al. 1 propose a model to explain the existence of animal personalities, consistent with behavioural differences among individuals in various contexts 2 , 3 , 4 —their explanation is counter-intuitive and cogent. However, all models have their limits, and the particular life-history requirements of this one may be unclear. Here we analyse their model and clarify its organismal scope.

Ecological invasions are a major worldwide problem exacting tremendous economic and ecological costs. Efforts to explain variability in invasion speed and impact by searching for combinations of ecological conditions and species traits associated with invasions have met with mixed success. We use a simulation model that integrates insights from life-history theory, animal personalities, network theory, and spatial ecology to derive a new mechanism for explaining variation in animal invasion success. We show that spread occurs most rapidly when (1) a species includes a mix of life-history or personality types that differ in density-dependent performance and dispersal tendencies, (2) the differences between types are of intermediate magnitude, and (3) patch connections are intermediate in number and widely spread. Within-species polymorphism in phenotype (e.g., life-history strategies or personality), a feature not included in previous models, is important for overcoming the fact that different traits are associated with success in different stages of the invasion process. Polymorphism in sociability (a personality type) increases the speed of the invasion front, since asocial individuals colonize empty patches and facilitate the local growth of social types that, in turn, induce faster dispersal by asocials at the invasion edge. The results hold implications for the prediction of invasion impacts and the classification of traits associated with invasiveness.

Dispersal is a fundamental life-history trait for many ecological processes. Recent studies suggest that dispersers, in comparison to residents, display various phenotypic specializations increasing their dispersal inclination or success. Among them, dispersers are believed to be consistently more bold, exploratory, asocial or aggressive than residents. These links between behavioural types and dispersal should vary with the cause of dispersal. However, with the exception of one study, personality-dependent dispersal has not been studied in contrasting environments. Here, we used mosquitofish (Gambusia affinis) to test whether personality-dependent dispersal varies with predation risk, a factor that should induce boldness or sociability-dependent dispersal. Corroborating previous studies, we found that dispersing mosquitofish are less social than non-dispersing fish when there was no predation risk. However, personality-dependent dispersal is negated under predation risk, dispersers having similar personality types to residents. Our results suggest that adaptive dispersal decisions could commonly depend on interactions between phenotypes and ecological contexts.

Understanding/predicting ecological invasions is an important challenge in modern ecology because of their immense economical and ecological costs. Recent studies have revealed that within-species variation in behaviour (i.e. animal personality) can shed light on the invasion process. The general hypothesis is that individuals' personality type may affect their colonization success, suggesting that some individuals might be better invaders than others. We have recently shown that, in the invasive mosquitofish (Gambusia affinis), social personality trait was an important indicator of dispersal distance, with more asocial individuals dispersing further. Here, we tested how mean personality within a population, in addition to individual personality type, affect dispersal and settlement decisions in the mosquitofish. We found that individual dispersal tendencies were influenced by the population's mean boldness and sociability score. For example, individuals from populations with more asocial individuals or with more bold individuals are more likely to disperse regardless of their own personality type. We suggest that identifying behavioural traits facilitating invasions, even at the group level, can thus have direct applications in pest management.

1. Dispersers are often not a random draw from a population, dispersal propensity being conditional on individual phenotypic traits and local contexts. This non-randomness consequently results in phenotypic differences between dispersers and non-dispersers and, in the context of biological invasions, in an invasion front made of individuals with a biased phenotype. This bias of phenotypes at the front may subsequently modulate the strength of ecological effects of an invasive species on invaded communities. 2. We recently demonstrated that more asocial mosquitofish (Gambusia affinis), one of the 100 worst invasive species, disperse further, suggesting a sociability-biased invasion front. As behavioural types are related to the strength of interspecific interactions, an invasion by a biased subset of individuals should have important ecological implications for native communities. 3. Here, we tested the impact of phenotypic biases in dispersing individuals (relative to non-dispersers) on prey communities in experimental mesocosms. 4. We show that dispersers reduce prey abundance more than do non-dispersers during the first 4 weeks after introduction, and that the disperser's social types are likely drivers of these differences. These differences in prey communities disappeared after 8 weeks suggesting prey community resilience against predation in these mesocosm ecosystems. 5. Consequently, we call for the integration of non-random dispersal, dispersal syndromes and more generally intraspecific variation into studies predicting the impacts of invasions.

To meet global nutritional needs, humans need to produce an ever-increasing amount of food with dwindling natural resources. Demand for nutritious foods, particularly lean meat, fruits, and vegetables, is rapidly accelerating. To increase the intensity of production and utilize non-arable land, many growers are turning to controlled environment agriculture systems like hydroponic crop production and aquaculture (fish farming), but these are inherently inefficient in terms of water and nutrient utilization. Aquaponics is a relatively novel agricultural method that combines hydroponic and aquacultural production models to mitigate many of the costs—both realized and implicit, environmental and economic—associated with either production model on its own. Fundamental research is needed to determine optimal system designs, water quality conditions, and potential food safety considerations specific to aquaponics. Here we demonstrate the operation of replicated, greenhouse-scale aquaponic systems with a novel design growing tilapia (Oreochromis spp.) and lettuce (Lactuca sativa L.) in continuous production. Nitrification efficiency in these systems was greater than in previous studies, and water quality conditions suggested a relationship between the system design, dissolved carbon/nitrogen ratio, nitrogen use efficiency, and environmental impact through emission of N oxides. Food safety risk was evaluated in these aquaponic systems through culture-based screening of production water for E. coli, Salmonella spp., and Listeria spp. None of these indicator organisms were detected, in accordance with most of the aquaponic food safety research to date. However, taxa containing less-common zoonotic and opportunistic human pathogens were observed, including Aeromonas hydrophila, Klebsiella pneumoniae, Pseudomonas aeruginosa, Serratia marcescens, Citrobacter freundii, and Providencia spp. Pathogenicity of the observed strains was not determined, but the persistent presence of these taxa suggests that aquaponics presents a unique environment in terms of potential food safety hazards. With increasing regulation of food production environments in the United States, European Union, and United Kingdom, understanding the hazards in aquaponics will be necessary to ensure fair and effective water quality standard enforcement. Our results provide baseline physicochemical and microbial water quality data for a novel aquaponic system design with the potential to improve efficiency and food safety risk. This information will help to inform future research and commercial system designs and the development and enforcement of regulatory microbial water quality standards.

1. Despite a central line of research aimed at quantifying relationships between mating success and sexually dimorphic traits (e.g., ornaments), individual variation in sexually selected traits often explains only a modest portion of the variation in mating success. 2. Another line of research suggests that a significant portion of the variation in mating success observed in animal populations could be explained by correlational selection, where the fitness advantage of a given trait depends on other components of an individual's phenotype and/or its environment. We tested the hypothesis that interactions between multiple traits within an individual (phenotype dependence) or between an individual's phenotype and its social environment (context dependence) can select for individual differences in behaviour (i.e., personality) and social plasticity. 3. To quantify the importance of phenotype- and context-dependent selection on mating success, we repeatedly measured the behaviour, social environment and mating success of about 300 male stream water striders, Aquarius remigis. Rather than explaining individual differences in long-term mating success, we instead quantified how the combination of a male's phenotype interacted with the immediate social context to explain variation in hour-by-hour mating decisions. We suggest that this analysis captures more of the mechanisms leading to differences in mating success. 4. Males differed consistently in activity, aggressiveness and social plasticity. The mating advantage of these behavioural traits depended on male morphology and varied with the number of rival males in the pool, suggesting mechanisms selecting for consistent differences in behaviour and social plasticity. Accounting for phenotype and context dependence improved the amount of variation in male mating success we explained statistically by 30-274%. 5. Our analysis of the determinants of male mating success provides important insights into the evolutionary forces that shape phenotypic variation. In particular, our results suggest that sexual selection is likely to favour individual differences in behaviour, social plasticity (i.e., individuals adjusting their behaviour), niche preference (i.e., individuals dispersing to particular social conditions) or social niche construction (i.e., individuals modifying the social environment). The true effect of sexual traits can only be understood in interaction with the individual's phenotype and environment.

Male expected reproductive success can be enhanced by increased mating success (mate number) or, when females can mate multiply, by increased mating exclusivity (i.e., reduced partner promiscuity). A positive or negative covariance between these two mating outcomes could substantially increase or decrease overall variation in male expected reproductive success, yet the relationship between these mating outcomes is relatively understudied. We examined this relationship and the influence of male personality traits, female personality traits, and the social environment on mating outcomes in stream water striders, Aquarius remigis, at two experimental sex ratios: equal and 2:1 male-biased. To our knowledge, this study is the first to quantify this full set of effects. We found that mating frequency (mating success) and mating exclusivity were positively correlated in the male-biased treatment, but were not related at equal sex ratios. At both sex ratios, males that were more active and aggressive had both higher mating frequency and higher mating exclusivity. A male’s effective mating (the product of mating frequency and mating exclusivity) was also higher if on average he mated with females that tended to hide in refuges (and were presumably less available for future matings). Finally, males that were more often in pools with extremely aggressive (“hyperaggressive”) males actually had increased mating exclusivity, potentially because hyperaggression reduced average female promiscuity. This study highlights the importance of considering mating outcomes beyond mating success and examining the simultaneous contribution of male behaviours, female behaviours and social factors to mating dynamics.

A key challenge in invasion biology is identifying characteristics that allow some species to be repeatedly successful at invading novel environments. Invasions can often be disproportionately driven by a single sex, with differences in behavioural mechanisms between the sexes potentially underlying sex-biased invasiveness. Here, we took an animal personality approach to study the behaviour of two repeatedly successful congeneric invasive species, the western mosquitofish, Gambusia affinis, and the eastern mosquitofish, Gambusia holbrooki. In each species, we investigated whether males and females shared common personality traits (i.e. behavioural types and behavioural syndromes), with the aim of identifying possible behavioural mechanisms that could help explain why mosquitofish invasions are often characterised by sex-biased founder populations. We found sex-dependent personality, although sex differences varied between species. Male G. affinis were bolder and less social than female G. affinis, whereas we found no behavioural type differences between the sexes in G. holbrooki. We also found a consistent correlation between boldness and exploration in both sexes within G. affinis, but this correlation was weak in G. holbrooki. Finally, exploration was also correlated with sociability in male G. affinis, but not in females. Our results suggest that behavioural tendencies may diverge, both among species and between the sexes, because of adaptation experienced during different invasion pathways. Broadly, identifying the behavioural mechanisms that predict an individual’s ‘invasiveness’ may be difficult to tease apart between species because each invasion is characterised by different abiotic and biotic interactions that likely require different suites of behaviours. Future studies are needed to elucidate whether, in fact, personality variation between the sexes can mediate the occurrence of sex-biased invasions.