Mosquitofish Gambusia Holbrooki Research Articles

Exploring invasiveness and versatility of used microhabitats of the globally invasive Gambusia holbrooki

Non-native species can lead to severe impacts on invaded ecosystems, including the decline of ecosystem function through deleterious impacts on species diversity. The successful establishment of non-native species in new environments is the first barrier a species must overcome, ultimately depending on its ability to either cope with or adapt to local site-specific conditions. Despite the widespread distribution and ecological consequences of many freshwater invaders, site-specific and climatic preferences are often unknown. This is also the case of the Eastern mosquitofish Gambusia holbrooki, a global invader considered as a pervasive threat to endemic species. Here, we determined the ecological features and preferred site-specific conditions of G. holbrooki in Türkiye, which spans a wide range of diverse biogeographically distinct ecosystems by surveying populations from 130 localities in 2016 and 2017. Gambusia holbrooki were detected by hand-net in 48 of these sites (19 lotic, 29 lentic). It showed a preference for shallow waters with medium sized rocks, and abundances differed spatially across a latitudinal gradient and was influenced predominantly by variations in pH. The only other factors predicting its presence were low current velocities and gravel substrate, highlighting its ecological versatility in utilising a wide range of microhabitats. Bioclimatic models suggest that G. holbrooki is found in areas with a wide average annual temperature ranging from 10 to 20 °C, but with temperature not being a limiting factor to its invasion. Gambusia holbrooki shows a preference for xeric freshwater ecosystems and endorheic basins, as well as temperate coastal rivers, temperate upland rivers, temperate floodplain rivers and wetlands, and tropical and subtropical coastal rivers. These results, particularly the wide occurrence with only few limiting factors, emphasise the invasion potential of mosquitofish and should substantiate the need for localised invasive species management and conservation efforts, particularly in smaller or insular areas where mosquitofish and endemic fish species co-exist.

Chronic toxicity and liver histopathology of mosquito fish (Gambusia holbrooki) exposed to natural and modified nanoclays

Nanoclays are found in the air, water, and soil, and modified nanoclays are being developed and used in several consumer products. For example, modified nanoclays are used to remove pollutants from wastewater. Ironically, however, nanoclays are now considered emerging contaminants. Indeed, release of modified nanoclays in aquatic systems, even as remediating agents, could adversely affect associated wildlife. However, aquatic organisms have interacted with natural nanoclays for millennia, and it is unclear if modified nanoclays induce stronger effects than the nanoclays that occur naturally. The concentrations over which nanoclays occur and illicit negative effects are not well studied. This study investigated the dose response of a natural nanoclay (Na+montmorillonite) relative to two modified nanoclays (Cloisite®30B and Novaclay™) on survival, body condition, and liver pathomorphology of Gambusia holbrooki after 14 days of exposure. Although none of the nanoclays affected survival and body condition of G. holbrooki over 14 days, each nanoclay induced histopathological changes in liver tissues at very low concentrations (LOAEL: 0.01 mgL−1). The effects of nanoclays on hepatic cell circulatory (blood cell aggregation with increased number of Kupffer cells and hemosiderin deposits), regressive (hepatocyte vacuolization), and degenerative (cell death) changes of mosquito fish varied among nanoclay types. Novaclay™ at low concentrations caused circulatory changes on hepatic tissues of G. holbrooki, whereas both natural nanoclays and Cloisite®30B showed little effect on circulatory endpoints. In contrast, all of the nanoclays induced regressive and degenerative changes on liver tissues of mosquito fish across all concentrations tested. This study clearly reveals that natural and modified nanoclays have important health implications for fish and other aquatic organisms. Consequently, the widespread use of modified nanoclays in several applications and increased release of natural nanoclays through erosion or other processes needs to be evaluated in more detail especially in the context of their safety for aquatic systems.

Determination of The Lethal Concentration 50% (Lc50) of Cadmium Chloride in mosquito fish Gambusia holbrooki

In this study 24,48 and 96-h exposure of male mosquito fish Gambusia holbrooki to cadmium chloride (CdCl2.H20) was accomplished to determine the cadmium lethal concentration 50 (LC50) in mosquito fish G. holbrooki, The data obtained were statistically evaluated by the use of EPA computer program based on Finney’s Probit Analysis Method and a (24,48 and 96h) LC50 values for Gambusia holbrooki were found to be(37.29 , 42.733 and 50.178) mg/l respectively .

Cadmium Accumulation in Some Organs of Mosquito Fish Gambusia holbrooki

The cadmium contents in muscle, brain, gills, liver , intestine and testis from exposed and control animals were determined by atomic absorption spectroscopy. The experiments were planned in three series of a total of 95 fish employing the static test method of acute toxicity. Five fishes were placed in each concentrations of three sublethal concentrations (5, 15 and 25mg/l) for two acute periods (24 and 96h). The experiments were performed as 3 replicates, the Cd accumulation in different fish organs were determined. This showed that the effect of acute Cd on different organs Cd accumulation in the G. holbrooki was found to be time dependent fashion. Atomic absorption examination showed that the Cd-content in both testis and intestine increased significantly time dependent by 502%, 167%, 168%, 146%,490%,214% in muscle ,brain, liver, gills, intestine and testis , respectively at short-acute term treatment whereas for long- acute term treatment this increasing were 44%,82 %,170%,127%,350%,400% in muscle ,brain, liver, gills, intestine and testis respectively

Risk of invasiveness of non-native fishes in the South Caucasus biodiversity and geopolitical hotspot

Aquatic invasions are one of the major threats for freshwater ecosystems. However, in developing countries, knowledge of biological invasions, essential for the implementation of appropriate legislation, is often limited if not entirely lacking. In this regard, the identification of potentially invasive non-native species by risk screening, followed by a full risk assessment of the species ranked as higher risk, enables decision-makers to be informed about the extent of the threats posed to the recipient (risk assessment) area. In this study, 32 non-native extant and horizon fish species were screened for their risk of invasiveness under current and predicted climate conditions for the South Caucasus – a biodiversity and geopolitical hotspot that includes the countries of Armenia, Azerbaijan and Georgia. Overall, the number of very high-risk species increased from four (12.5%) under current climate conditions to 12 (37.5%) under predicted climate conditions. The highest-risk species under both conditions included the already established gibel carp Carassius gibelio and topmouth gudgeon Pseudorasbora parva, the locally translocated pikeperch Sander lucioperca and the horizon North African catfish Clarias gariepinus. Under predicted climate conditions, a very high risk of invasiveness was predicted also for the translocated three-spined stickleback Gasterosteus aculeatus and Eurasian perch Perca fluviatilis, for the already established eastern mosquitofish Gambusia holbrooki, ruffe Gymnocephalus cernua, sharpbelly Hemiculter leucisculus and Nile tilapia Orechromis niloticus, and for the horizon pumpkinseed Lepomis gibbosus and largemouth bass Micropterus salmoides. Future research on the non-native species in the South Caucasus should be conducted both country- and region-wide and should account not only for the high biodiversity, but also for the critical geopolitical situation affecting the study area.

Dramatic decline of two freshwater killifishes, main anthropogenic drivers and appropriate conservation actions

Freshwater fish biodiversity loss in the Mediterranean Basin is regarded as among the highest globally, with long-term population data sets required to discern long-term population trends of threatened species, in order to design appropriate conservation interventions. In this study, we assessed the population trends of two threatened freshwater fishes, Valencia letourneuxi and Valencia robertae, employing the most recent and largest compiled database to date (16 populations over 14 years). We applied the innovative methodology of the Living Planet Index (LPI) to assess the average rate of change over time across a set of V. letourneuxi and V. robertae populations in Greece. The LPI application revealed a dramatic decline of both species, with V. letourneuxi declining by 97.7% and V. robertae by 91.0%. Beta regression showed that water pollution, eutrophication and alien Eastern mosquitofish Gambusia holbrooki’ presence were the three best fitting predictors of the decline of V. letourneuxi and V. robertae populations. Based on the above, we outline the conservation measures urgently required to revert the near collapse of the populations of the two species. Conservation actions include the strict protection of the their lowland spring habitats, habitat improvement through changes in water management and agricultural practices, mosquitofish invasion prevention and mosquitofish impact mitigation measures, as well as translocation actions and captive breeding. Lastly, the association patterns of the proposed conservation actions with anthropogenic pressures and their expected outcomes were analysed through an alluvial diagram, providing insights on the scale of pressures mitigated by conservation actions and on their conservation benefits.

Climatic and geographic variation as a driver of phenotypic divergence in reproductive characters and body sizes of invasive Gambusia holbrooki

Understanding the invasion success of alien species includes developing knowledge on how the biological traits of their populations respond to spatial differences in environmental conditions. For invasive fishes, while the influence of latitudinal and climatic gradients on their biological traits over large spatial scales is well established, there is less certainty in how these vary over smaller scales. Here, we tested the influence of a climatic and geographic gradient on the reproductive traits and body sizes of the invasive mosquitofish Gambusia holbrooki across five climatic regions in Turkey. The results revealed that the environmental conditions across eight sites provided two gradients: a latitudinal gradient (where northern sites were cooler with less rainfall) and a coastal–inland gradient (where changes were apparent from coastal areas and into inland areas). These gradients had marked effects on the traits of both sexes. In sites in coastal and southern areas, males had significantly larger gonopodia and females had greater fecundity than in inland and warmer areas, and with both sexes having body sizes that were smaller. The spatial differences in the male traits were suggested as being driven by differences in selection pressures at the sites that related to differences in their population abundances. The results revealed that environmental conditions across a relatively small spatial scale had some strong influences on the expression of specific biological traits of these mosquitofish populations, but with further work needed to test how these influences affect their invasion success.

Nonnative Pike Killifish Do Not Exert Predatory Pressure on Juvenile Common Snook

AbstractThe Pike Killifish Belonesox belizanus is an established nonnative fish species that was first documented in south Florida, USA, in 1957 and secondarily in Tampa Bay tidal tributaries in 1994. Decreased abundance and altered size structure in small‐bodied fish populations have been linked to Pike Killifish introductions in both of these regions. Increases in the range and abundance of Pike Killifish in Tampa Bay waters and overlap in habitat usage with juvenile Common Snook Centropomus undecimalis have led to concerns about potential predation on early juvenile (≤125 mm TL) Common Snook. We investigated predation of Pike Killifish on early juvenile Common Snook through experimental predation trials and stomach content analysis of Pike Killifish from field sampling. During predation trials, fasted, large adult (≥104 mm TL) Pike Killifish were presented with one of three prey taxa: Common Snook (N = 139), Pike Killifish conspecifics (N = 68), and Eastern Mosquitofish Gambusia holbrooki (N = 68); the fate of the prey was recorded after 48 h. Common Snook with both intact (N = 70) and clipped (N = 69) anal spines were used as prey to investigate whether this structure deterred predation by Pike Killifish. Predation trials indicated that Pike Killifish were capable of consuming early juvenile Common Snook up to 60 mm TL and that the anal spine did not deter predation by Pike Killifish. Stomach content analysis was performed on 422 wild‐caught Pike Killifish from Tampa Bay tidal tributaries where early juvenile Common Snook co‐occurred, but no Common Snook remains were found in their diets. Combined, these studies indicate that despite being able to consume relatively large early juvenile Common Snook, Pike Killifish do not exert predatory pressure on early juvenile Common Snook in the wild and therefore do not appear to be a factor contributing to population‐level effects or delayed recovery in Common Snook populations.

Pushed to the edge: Environmental factors drive ecological responses of Aphanius fasciatus when in sympatry with invasive Gambusia holbrooki

Abstract Interspecific competition may be particularly exacerbated when occurring between native and invasive alien species, with environmental conditions affecting drivers of natural selection and shaping spatio‐temporal dynamics of animal communities. The effects of invaders are particularly evident in aquatic ecosystems with delicate and complex balances, such as Mediterranean coastal wetlands, characterized by unpredictable water flows and variable reserves. Understanding how native species respond to human‐induced biological invasions is of paramount importance for planning management measures aiming at conservation purposes. This study investigated whether the occurrence of a competing invader species resulted in changes in the ecological adaptations of a native species by comparing two coastal wetland fish species: the invasive eastern mosquitofish Gambusia holbrooki and the native Mediterranean killifish Aphanius fasciatus of conservation concern. The hypothesis was tested by sampling fishes at a coastal Ramsar site in central Italy, over 2 years. Generalized linear mixed models were used to examine the occurrence of killifish in relation to water parameters and the presence of its putative competitor. The aim was to determine whether salinity, temperature, and water depth influenced the presence and abundance of killifish when in sympatry with mosquitofish. Both the probability of presence and abundance of killifish increased with water salinity, but this increase was stronger when mosquitofish was present. Increasing water temperature and water depth were associated with a higher probability of presence and abundance of killifish respectively, although the effect of water depth was small. Both salinity and the presence of the invader acted synergistically in characterizing and shaping the population structure of the native species. Living in the most extreme and stressed environments, the killifish is potentially at higher risk of extinction. These results highlight the importance of considering the interplay between multiple abiotic stressors combined with comparative data between invasive and native species as increasingly critical to aid in conservation efforts.

Repeatability of lateralisation in mosquitofish Gambusia holbrooki despite evidence for turn alternation in detour tests.

Akin to handedness in humans, some animals show a preference for moving to the left or right. This is often attributed to lateralised cognitive functions and eye dominance, which, in turn, influences their behaviour. In fishes, behavioural lateralisation has been tested using detour mazes for over 20years. Studies report that certain individuals are more likely to approach predators or potential mates from one direction. These findings imply that the lateralisation behaviour of individuals is repeatable, but this is rarely confirmed through multiple testing of each individual over time. Here we quantify the repeatability of turning behaviour by female mosquitofish (Gambusia holbrooki) in a double sided T-maze. Each female was tested three times in each of six treatments: when approaching other females, males, or an empty space; and when able to swim freely or when forced to choose by being herded from behind with a net. Although there was no turning bias based on the mean population response, we detected significant repeatability of lateralisation in five of the six treatments (R = 0.251-0.625). This is noteworthy as we also found that individuals tended to alternate between left and right turns, meaning that they tend to move back and forth along one wall of the double-sided T-maze. Furthermore, we found evidence for this wall following when re-analysing data from a previous study. We discuss potential explanations for this phenomenon, and its implications for study design.

Acute Toxicity (LC50) Of Cyhalofop Butyl on Gambusia Holbrooki

Cyhalofob butyl is a synthetic herbist. This herbicide is a systemic herbicide and is used in weed control especially on celtic agriculture. In this study, the acute toxicity (LC50) of this herbist (Chillinger 200 EC 200, cyhalofob butyl) was investigated, which is currently used intensely in the fight against herbists in Thrace region, including Cyhalofob butyl. Acute toxicity (LC50 value) for this herbicide has been investigated in the common mosquito fish (Gambusia holbrooki) in Thrace Region. Lethal Dose 50 experiments were performed in 3 replicates in static test runs (water temperature 27.70 ±0.56 C, water pH 8.88± 0.37, and conductivity 718.25±21.113 µhos). The experiment results obtained for Chillinger 200 ec during the experiments were evaluated by Trimmed Spearman–Karber method. 96-hour LC50 value for the mosquito fish Gambusia holbrooki was calculated as 4.140 ppm.

Combined effects of rearing and testing temperatures on sperm traits.

Temperature experienced during early development can affect a range of adult life-history traits. Animals often show seemingly adaptive developmental plasticity-with animals reared at certain temperatures performing better as adults at those temperatures. The extent to which this type of adaptive response occurs in gonadal tissue that affects sperm traits is, however, poorly studied. We initially reared male mosquito fish (Gambusia holbrooki) at either 18°C or 30°C, and then measured their sperm reserves as adults. We also looked at the velocity of their sperm, at both the matched and mismatched temperatures. Although males reared at 30°C were larger than those initially reared at 18°C, there was no detectable effect of rearing temperature on absolute sperm number. Sperm swam faster at 30°C than 18°C regardless of the male's rearing temperature. Therefore, we found no evidence of adaptive developmental plasticity. Rearing temperature did, however, significantly influence the relationship between male body size and sperm velocity. Larger males had faster sperm when reared at the warmer temperature and slower sperm when reared at the cooler temperature. This suggests that rearing temperature could alter the relationship between pre-copulatory sexual selection and post-copulatory sexual selection as male size affects mating success. Finally, there was a positive correlation between velocities at the two test temperatures, suggesting that temperature experienced during sperm competition is unlikely to affect a male's relative fertilization success.

Sex-specific responses to competitive environment in the mosquitofish Gambusia holbrooki

The competitive environment that animals experience during development constitutes an important source of selection that can influence the development, expression and evolution of traits. Here, we examine how the sex of focal and “competitor” individuals interact to affect development in the Eastern mosquitofish Gambusia holbrooki. We raised individuals of both sexes either alone or in the presence of a male or female conspecific (hereafter “competitor”), and measured their juvenile growth rate, time to maturity and size at maturity. For males, we also measured their gonopodium length, sperm quantity, and sperm velocity. We found that responses to the competitive environment were dependent on the sex of the focal individual, the sex of their “competitor” and sometimes an interaction between the two. When there was another fish present, regardless of its sex, males had slower growth rates and took longer to mature, but eventually matured at the same size. Females also showed slower growth rates in the presence of a competitor, but in contrast to males, reached maturity sooner and at a smaller size than when there was no competitor present. Presence of a competitor influenced male sexual traits, however there was little evidence that these effects were mediated by the sex of the other fish. Males reared with another fish had longer gonopodia for their body size, as well as fewer and faster sperm. Our results suggest that effects of the competitive environment are different for males and females, potentially due to sex differences in adult life history strategies. Further, for males, both life history traits and sexual traits were influenced by the competitive environment. For life history traits this effect appears to result from decreased resources and/or increased energy expenditure, but for sexual traits, effects appear to be mediated, in part, by the social environment.

Basal resource quality and energy sources in three habitats of a lowland river ecosystem

AbstractUnderstanding energy flow through ecosystems and among sub‐habitats is critical for understanding patterns of biodiversity and ecosystem function. It can also be of considerable applied interest in situations where managing for connectivity among habitats is important for restoring degraded ecosystems. Here, we describe patterns of basal resource quality and identify primary basal energy sources in three habitats—river channels, anabranches and wetlands—of a lowland river floodplain in the Murray River catchment, Australia during a period of disconnected surface flow. We used a combination of stable isotope and fatty acid analyses to determine which basal resources were assimilated by the backswimmer Anisops thienemanni and the Eastern mosquitofish Gambusia holbrooki and assessed food quality across the three habitats. Seston was a primary basal resource for both animals in all three habitats, but was of higher quality within floodplain habitats than in the river channel. Although floodplain seston contained higher concentrations of essential fatty acids, fatty acid profiles of animals from different habitats remained similar. Our research suggests that inundation of floodplains and subsequent reconnection to the river could be valuable to afford riverine animals the opportunity to access high quality resources, but highlights a need to quantitatively assess the transfer of essential fatty acids between trophic levels to determine how much riverine animals are in fact limited by poorer quality food resources. We demonstrate the importance of estimating the quality of organic matter fluxes into food webs, and the potential role of targeted environmental flows to re‐establish high quality energy pathways in riverine ecosystems.

Risk screening of the potential invasiveness of non-native freshwater fishes in the River Ob basin (West Siberian Plain, Russia)

To inform regional managers of potentially invasive non-native (NN) freshwater fishes in the principal hydrosystem that drains the West Siberian Plain, the River Ob basin, 31 extant and potential future NN fish species were screened using the Aquatic Species Invasiveness Screening Kit (AS-ISK) with respect to current and projected future climate conditions. Calibration of the AS-ISK scores, using receiver operating characteristic curve analysis, identified ‘basic risk assessment’ and ‘climate change assessment’ threshold scores of 27.5 and 34.75, respectively, with which to distinguish species that pose a high risk of being invasive in the Ob basin and those that pose a low-to-medium risk. Of the species screened, 12 ranked as high risk (black bullhead Ameiurus melas, brown bullhead Ameiurus nebulosus, grass carp Ctenopharyngodon idella, common carp Cyprinus carpio, eastern mosquitofish Gambusia holbrooki, silver carp Hypophthalmichthys molitrix, oriental weatherfish Misgurnus anguillicaudatus, rainbow trout Oncorhynchus mykiss, Chinese (Amur) sleeper Perccottus glenii, topmouth gudgeon Pseudorasbora parva, brown trout Salmo trutta, pikeperch Sander lucioperca and rudd Scardinius erythrophthalmus). The remaining species ranked as medium or low risk. Although the risk scores increased in 68% of species under climate change conditions, this affected the risk rankings of only two species: Salmo trutta decreased in rank from high to medium and Sander lucioperca increased in rank from medium to high. The outcomes of the present study, which identified 12 species for which full risk assessments are recommended, serves to inform the development of NN species policy and management in Russia.

The occurrence, distribution and biology of invasive fish species in fresh and brackish water bodies of NE Morocco

Monitoring the presence and expansion of alien species and upgrading their biological and ecological knowledge seems crucial to mitigate their possible impact on native communities. Within inland superficial waters, alien fish represent an important threat to the biodiversity and studies on their impact on native communities have increased around the world in the last years. However, little is known about their occurrence, biology and influences in North Africa in general, and more specifically in Morocco. In the present work we aimed to: 1) investigate the presence of any native Aphanius species, especially the Mediterranean killifish Aphanius fasciatus recorded from the lower basin of the Moulouya River (NE Morocco); 2) monitor the presence and expansion of two invasive species, the eastern mosquitofish Gambusia holbrooki and the mummichog Fundulus heteroclitus; and 3) contribute to the understanding of the ecological and abiotic affinities that govern the distribution of these alien fishes in North Africa. To achieve these goals, several field sampling campaigns were carried out between 2014 and 2018 across eastern Morocco, comprising the administrative Oriental Region and the Moulouya River Basin and covering an area of 119,268 km2. No native Aphanius species were found. The eastern mosquitofish has invaded the freshwater hydrosystems of the northern part of Morocco, including the study area, while the mummichog is currently limited to the brackish and salty wetlands of Lower Moulouya. Our results show that the known ranges of these two alien species have expanded. Data published through GBIF (Doi:10.15470/2qed9o)

Differences in oxidative status explain variation in thermal acclimation capacity between individual mosquitofish (Gambusia holbrooki)

Abstract Evolutionary theory predicts that the capacity to acclimate should be favoured in variable environments. However, perfect compensation for thermal variation is rare and the capacity for thermal acclimation can vary considerably between individuals within natural populations. This variation may be explained by costs associated with acclimation, but it is not clear what these costs are. We tested the hypothesis that oxidative stress is a cost of acclimation that could explain the variation between individuals in acclimation capacity. We acclimated individual mosquitofish Gambusia holbrooki (n = 416) to 18 and 28°C sequentially, and determined swimming performance at each temperature to evaluate their acclimation capacity. Fish were then acclimated to either cold (18°C) or warm (28°C) conditions, and we increased antioxidant capacities of a subset of fish experimentally by administering N‐acetyl cysteine (NAC). We measured H2O2 production, catalase antioxidant activities and oxidative damage to proteins and membranes. We show that there is significant variation in acclimation capacity between individuals, and that there is a trade‐off between acclimation capacity and swimming performance in warm conditions. Mean swimming performance across both acclimation temperatures increased with increasing acclimation capacity, but the increase was small biologically. Hence, greater thermal plasticity (high acclimation capacity) resulted in only minor performance benefits across acclimation conditions. We verified this rather surprising result in replicate populations grown in outdoor mesocosms. Reactive oxygen species production, antioxidant activities and oxidative damage were higher in cold‐acclimated fish, and particularly in those fish with low capacity for acclimation. However, experimentally increasing antioxidant capacities with NAC alleviated these changes to oxidative status, suggesting a causal relationship. Hence, oxidative stress may be a cost that constrains the capacity for acclimation. Together, the performance trade‐off and oxidative cost indicate that phenotypic plasticity is not always advantageous in variable environments, and instead bet‐hedging may be a more beneficial strategy, particularly in short‐lived species. A free Plain Language Summary can be found within the Supporting Information of this article.

Predator–prey interactions and metabolic rates are altered in stable and unstable groups in a social fish

Understanding the determinants and consequences of predation effort, success and prey responses is important since these factors affect the fitness of predators and prey. When predators are also invasive species, the impacts on prey can be particularly far‐reaching with ultimate ecosystem‐level consequences. However, predators are typically viewed as behaviourally fixed within this interaction and it is unclear how variation in predator social dynamics affects predator–prey interactions. Using the invasive eastern mosquitofish Gambusia holbrooki and a native glass shrimp Paratya australiensis in Australia, we investigated how varying levels of social conflict within predator groups influences predator–prey interactions. By experimentally manipulating group stability of G. holbrooki, we show that rates of social conflict were lower in groups with large size differences, but that routine metabolic rates were higher in groups with large size differences. Predation effort and success did not vary depending on group stability, but in stable groups predation effort by aggressive dominants was greater than subordinates. The anti‐predator responses of prey to the stability of predator groups were mixed. While more prey utilized shelters when exposed to stable compared to unstable groups of predators, a greater proportion were sedentary when predator groups were unstable. Overall, this study demonstrates predator group stability is modulated by differences in body size and can influence prey responses. Further, it reveals a hidden metabolic cost of living in stable groups despite reduced overt social conflict. For invasive species management, it is therefore important to consider the behavioural and physiological plasticity of the invasive predators, whose complex social interactions and metabolic demands can modulate patterns of predator–prey interactions.

An experimental test of the role of male mating history on paternal effects in the livebearer fish Gambusia holbrooki.

Studies often show that paternal age affects offspring fitness. However, such effects could be due either to age, or to a male's previous mating effort (which is necessarily confounded with age). We experimentally tested whether differences in the mating history of old males affect offspring performance in the mosquitofish Gambusia holbrooki. Upon maturation, males were housed for a duration of the natural field-breeding season (23 weeks) either with mating access to females (lifetime-mating), or with visual but no physical access to females (no-mating). We then paired these males with a female to test whether male mating history had a significant effect on their mate's breeding success or offspring performance. The daughters, but not the sons, of 'no-mating' treatment males matured significantly sooner, and at a significantly smaller size, than those of 'lifetime-mating' treatment males. There was, however, no effect of male mating history on their daughters' initial fecundity, or on proxy measures of their sons' reproductive success. These results, when combined with earlier studies showing effects of male mating history on sperm quality, growth and immunity, suggest that variation in paternal effects currently attributed to male age could partly arise because older males have usually mated more often than younger males.

Impacts of the alien mosquitofish on the abundance and condition of two Mediterranean native fish

The rapid decline of the Greek native Valencia letourneuxi, and its recently described sister species Valencia robertae, has been often attributed to habitat degradation, as well as aggression from or resource competition with the alien mosquitofish Gambusia holbrooki. The mosquitofish is extremely wide-spread in Mediterranean freshwater ecosystems, however, documentation on its presumed negative impacts on native freshwater fishes is limited. In this study, we compared abundance, condition and gonad weight of Valencia spp. in no co-occurrence versus co-occurrence to the mosquitofish, using data collected from eight aquatic systems of Greece, over a five year period (2005 to 2009). Our results show that Valencia abundance is significantly lower in co-occurrence to the Eastern mosquitofish. Furthermore, female Valencia spp. individuals in co-occurrence to the mosquitofish were smaller in length and had poorer somatic condition compared to females in habitats not invaded by the mosquitofish. The mechanisms responsible for these effects of the alien mosquitofish as well as the conservation implications for native Valencia populations are discussed.