Temperature-specific competition between invasive mosquitofish and an endangered cyprinodontid fish

Twoline Skiffia's Latency to Exit a Refuge and to Locate Food When Socialising With Invaders and Raising Temperatures

Aquatic ecosystems are reservoirs of biodiversity and are highly threatened. Among the main threats to biodiversity are invasive species and global warming, the later has allowed the establishment of invasive species from originally warmer climates outside their native range by reducing the barriers to their establishment and distribution. Behaviour is the immediate response that species modify to counteract changes in their environment. Latency to respond to certain stimuli is an indicator of different behavioural tendencies associated with boldness, for example, quickly leaving a shelter could lead to benefits like finding a mate or locating food faster. We investigated the latency to exit a refuge and to locate food of the native twoline skiffia (Skiffia bilineata) from central Mexico at three temperatures (18°C, 23°C and 28°C) and in the presence/absence of invasive guppies (Poecilia reticulata). Our results are the first to show native fish could benefit from associating with invaders when emerging from a refuge and locating food under higher temperatures, but they would find themselves at the extreme of their thermal tolerance. Evidence of positive outcomes from biological invasions is increasing; however, further research is needed to understand if potential benefits for natives are temporary, which may make biological invasions less detrimental during the initial stages.

A systematic review of poeciliid fish invasions in Africa

BACKGROUND

This review compiles and synthesises the existing information concerning non-native poeciliid introductions to Africa. The recent upsurge in research on invasive poeciliids has revealed their widespread occurrence in Africa.

RESULTS

Within the 87 relevant articles, 74% reported on the presence of Gambusia spp., 33% on P. reticulata, 19% on X. hellerii, 11% on X. maculatus, and 5% on other ornamental poeciliids. Overall, poeciliids have been documented as introduced to 25 different countries in Africa. With Gambusia spp. being introduced to 16 countries and P. reticulata to 19 countries. Our results are representative of the current state of research on invasive poeciliids in Africa. There was a concentration of studies in South Africa, with limited research elsewhere. Current distribution data is relatively patchy, although widespread surveys of multiple river systems in Morocco and South Africa, confirmed widespread and abundant established poeciliid populations. The ecological impacts of invasive poeciliids in Africa remain understudied but evidence indicates deleterious effects on native fish, invertebrates, and amphibians, many of which are critically endangered or endemic.

CONCLUSION

Current research is limited in reporting from certain countries and ecological impacts. An increased effort to monitor species composition in vulnerable waterbodies, especially in the many African countries where invasive poeciliids are reported, should be completed to reveal further established populations. Future research should prioritise quantifying the ecological impacts of invasive poeciliids in the field and identifying both vulnerable and resistant native ecosystems to guide future management decisions.

Impact of zinc oxide nanoparticles on the behavior and stress indicators of African catfish (Clarias gariepinus) exposed to heat stress

This study was designed to assess the role of nano-zinc oxide in mitigating the deleterious effects of heat stress in African catfish (Clarias gariepinus) by evaluating parameters such as aggressive behavior (biting frequency and chasing duration), hematological indicators, and stress-related biochemical markers. A total of 96 catfish were divided into four distinct groups (24 fish/group): The first group (CON) served as the control group, receiving a diet free of nano-zinc oxide. The second group (HS) was exposed to heat stress at 35 °C ± 1 °C. The third group (ZN) was fed a diet containing nano-zinc oxide at 30 mg/kg of the diet, and the fourth group (ZHN) was exposed to heat stress (35 °C ± 1 °C) and fed a diet containing nano-zinc oxide at 30 mg/kg of the diet. The results clarified that the aggressive behavior and cortisol levels were significantly higher (P < 0.05) in the HS group compared to the CON and ZHN groups. Additionally, the level of acetylcholinesterase (AChE) was significantly lower (P < 0.05) in the HS group compared to the CON and ZHN groups. Meanwhile, a significant (P < 0.05) decrease in red blood cells, hemoglobin, packed cell volume, white blood cells, alkaline phosphatase, and lymphocytes, was observed in fish belonging to the HS group, while the levels of alanine aminotransferase, aspartate aminotransferase, neutrophils, and monocytes showed a significant increase (P < 0.05). Supplementation with nano-zinc oxide significantly recovered most hematological and biochemical parameters. In conclusion, nano-zinc oxide contributed significantly to the regulation of the negative impacts of heat stress on fish by reducing aggressive behavior and cortisol levels. Additionally, it improved the levels of AChE and certain hematological and biochemical parameters.

Effect of Warming on Personality of Mosquitofish (Gambusia affinis) and Medaka Fish (Oryzias latipes)

Global warming may accelerate the process of biological invasions, and invasive species that can quickly adapt to new environments will have a negative impact on native species. Animal personalities have significant implications for ecology and evolution. However, few studies have simultaneously examined the combined effects of climate warming and biological invasions on native species. In this study, we hypothesized that temperature was positively correlated with personality, and invasive species had stronger personalities than native species. Accordingly, we established control (20 °C) and warming groups (20 °C, 25 °C, and 30 °C) to rear mosquitofish and medaka fish, individuals acclimatized to rearing temperatures for 7 days, then measured their personalities (sociability, exploration, novelty, and boldness). The results showed that individuals exhibited repeatable variation along the four behavioral axes across all temperature conditions, providing evidence for the presence of personalities. Significant positive correlations were found between each pair of behaviors, indicating the presence of behavioral syndrome. Sociability and exploration were most affected by temperature, showing increasing trends in sociability, exploration, and novelty in both invasive and native species with rising temperatures. Compared to medaka fish, mosquitofish exhibited higher exploration and lower sociability at elevated temperatures, while showing little change in boldness. Our results provide evidence that increased temperatures may promote biological invasions and pose a potential threat to the survival of native species. These findings are significant for understanding the complex impacts of climate change on ecosystems and for formulating effective biodiversity preservation strategies.

Novel ecological interactions alter physiological responses of range-extending tropical and local temperate fishes under ocean warming

Global warming facilitates species range-expansions, leading to novel biological interactions between local and range-expanding species. Little is still known of how such novel interactions modify the performance of interacting species or how these interactions might be altered under climate change. Here, we used an aquarium experiment to investigate the novel ecological interactions between a poleward range-extending coral reef damselfish ("tropical-vagrant") and a local temperate species ("temperate-local") collected from a climate warming hotspot in SE Australia. We measured the effect of novel interactions (isolated vs. paired fish species) on energy expenditure (activity levels, oxidative stress, and antioxidant responses), energy gain (feeding rates), and growth rates of both fish species under present-day (23 °C) and future ocean temperatures (26 °C). Short-term growth rates were faster in both species under novel interactions (paired species), regardless of elevated temperature. Compared to isolated species, activity level, feeding rate and oxidative stress level were also higher in the paired temperate fish but not in the paired tropical fish. The tropical fish showed an increased feeding rate and long-term growth under elevated temperature, irrespective of novel interactions. We conclude that novel ecological interactions under climate change can be an important driver of physiological traits in sympatric tropical and temperate fishes and can mediate critical physiological performance of fishes under ocean warming.

The invasive twospot livebearer's biology, and its current and potential global distribution

Poeciliids are widely recognized as successful invaders, possessing traits associated with invasion success. Native to Central America and south-eastern Mexico, the twospot livebearer (Pseudoxiphophorus bimaculatus) is a species recently recognized as invasive in both Central and northern Mexico. Despite its invasive status, limited research exists on its invasion process and the potential threats it poses to native species. In this study, we conducted a comprehensive review of the current knowledge on the twospot livebearer and mapped its current and potential distribution worldwide. The twospot livebearer shares similar traits with other successful invaders within the same family. Notably, it exhibits high fecundity throughout the year and demonstrates resilience to highly polluted and oxygen-deprived water conditions. This fish serves as a host for several parasites, including generalists, and has been extensively translocated for commercial purposes. Recently, it has also been used for biocontrol within its native range. Apart from existing outside its native range, the twospot livebearer, under current climate conditions and if transported there, could readily colonize biodiversity hotspots in tropical zones worldwide, including the Caribbean Islands, the Horn of Africa, North of Madagascar Island, south-eastern Brazil, and others located in southern and eastern Asia. Given that this fish is highly plastic and our Species Distribution Model, we consider that all areas with a habitat suitability >0.2 should prevent its arrival and establishment. Our findings underscore the urgent need to recognize this species as a threat to freshwater native topminnows and prevent its introduction and spread.

Coexisting with the alien: Evidence for environmental control on trophic interactions between a native (Atherina boyeri) and a non-indigenous fish species (Gambusia holbrooki) in a Mediterranean coastal ecosystem

Biological invasions are a widespread problem worldwide, as invasive non-indigenous species (NIS) may affect native populations through direct (e. g., predation) or indirect (e.g., competition) trophic interactions, leading to changes in the food web structure. The trophic relationships of the invasive eastern mosquitofish Gambusia holbrooki and the native big-scale sand smelt Atherina boyeri coexisting in three Mediterranean coastal ponds characterized by different trophic statuses (from oligotrophic to hypereutrophic) were assessed in spring through isotopic niche analysis and Bayesian mixing models. The two fish relied on the distinctive trophic pathways in the different ponds, with the evidence of minimal interspecific niche overlap indicating site-specific niche divergence mechanisms. In more detail, under hypereutrophic and mesotrophic conditions, the two species occupied different trophic positions but relying on a single trophic pathway, whereas, under oligotrophic conditions, both occupied a similar trophic position but belonging to distinct trophic pathways. Furthermore, the invaders showed the widest niche breadth while the native species showed a niche compression and displacement in the ponds at a higher trophic status compared to the oligotrophic pond. We argue that this may be the result of an asymmetric competition arising between the two species because of the higher competitive ability of G. holbrooki and may have been further shaped by the trophic status of the ponds, through a conjoint effect of prey availability and habitat complexity. While the high trophic plasticity and adaptability of both species to different environmental features and resource availability may have favored their coexistence through site-specific mechanisms of niche segregation, we provide also empirical evidence of the importance of environmental control in invaded food webs, calling for greater attention to this aspect in future studies.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Behavioral Interactions between a Native and an Invasive Fish Species in a Thermally Heterogeneous Experimental Chamber

Mechanisms of the displacement of native fish by nonnative fish can include agonistic behaviors that push native fish species out of their preferred habitat, including their thermal optima. To examine these interactions, we built an experimental thermal preference chamber to evaluate: (1) the thermal preference of native, glacial relict northern redbelly dace Chrosomus eos; (2) if the thermal preference and movement changed in the presence of the invasive western mosquitofish Gambusia affinis; and (3) the direction of agonistic interactions. We hypothesized that G. affinis would express agonistic behavior toward C. eos, because G. affinis is widely recognized as an aggressive invader. Given the temperature range of the experimental chamber, i.e., 20–30 °C, C. eos selected an average of 24.3 °C as its thermal preference. After G. affinis’ introduction, the thermal preference of C. eos increased by 1.7 °C and the movement, given by distance (cm) travelled, increased by 21%. Contrary to our prediction, more agonistic interactions were observed in C. eos toward G. affinis. These results indicate that agonistic behavior of G. affinis toward native fish species may be species- and condition-specific, and may not always be the primary mechanism of native species’ displacement. Biological invasions are a global issue and altered thermal regimes are expected to continue. This study provided the novel approach using of a thermally heterogeneous thermal chamber to examine thermal preferences and aggressive interactions between a native and an invasive species. Future research should examine other life history traits that may be conveying the competitive advantage to G. affinis.

Off to new shores: Climate niche expansion in invasive mosquitofish (Gambusia spp.)

AIM

Formerly introduced for their presumed value in controlling mosquito-borne diseases, the two mosquitofish Gambusia affinis and G. holbrooki (Poeciliidae) are now among the world's most widespread invasive alien species, negatively impacting aquatic ecosystems around the world. These inconspicuous freshwater fish are, once their presence is noticed, difficult to eradicate. It is, therefore, of utmost importance to assess their geographic potential and to identify their likely ability to persist under novel climatic conditions.

LOCATION

Global.

METHODS

We build species distribution models using occurrence data from the native and introduced distribution ranges to identify putative niche shifts and further ascertain the areas climatically suitable for the establishment and possible spread of mosquitofish.

RESULTS

We found significant niche expansions into climatic regions outside their natural climatic conditions, emphasizing the importance of integrating climatic niches of both native and invasive ranges into projections. In particular, there was a marked shift toward tropical regions in Asia and a clear niche shift of European G. holbrooki. This ecological flexibility partly explains the massive success of the two species, and substantially increases the risk for further range expansion. We also showed that the potential for additional expansion resulting from climate change is enormous-especially in Europe.

MAIN CONCLUSIONS

Despite the successful invasion history and ongoing range expansions, many countries still lack proper preventive measures. Thus, we urge policy makers to carefully evaluate the risk both mosquitofish pose to a particular area and to initiate appropriate management strategies.

Behavioural plasticity in a native species may be related to foraging resilience in the presence of an aggressive invader

Competition between invasive and native species can result in the exploitation of resources by the invader, reducing foraging rates of natives. However, it is increasingly recognized that multiple factors can enhance the resilience of native species competing for limiting resources with invaders. Although extensively studied in terrestrial species, little research has focused on behavioural plasticity in aquatic ecosystems and how this influences native species resilience. Here, we examined the role of behavioural plasticity in interactions between a native Australian fish, Pseudomugil signifer, and a widespread invasive fish, Gambusia holbrooki. To determine whether P. signifer displays behavioural plasticity that may mitigate competition with G. holbrooki, we first quantified social behaviours (aggression, submission and affiliation) and shoal cohesion for each species in single- and mixed-species groups. Second, we compared the feeding rates of both species in these groups to ascertain if any modulation of social behaviours and cohesion related to foraging success. We found that aggressive and submissive behaviours of G. holbrooki and P. signifer showed plasticity in the presence of heterospecifics, but social affiliation, shoaling and, most importantly, foraging, remained inflexible. This variation in the degree of plasticity highlights the complexity of the behavioural response of a native species and suggests that both behavioural modulation and consistency may be related to sustaining foraging efficiency in the presence of an invader.

Linking multiple aspects of thermal performance to explore the potential for thermal resource partitioning between a native and an invasive crayfish

Ecologists require standardized, ecologically relevant information on the thermal ecology of aquatic ectotherms to address growing concerns related to changing climates, altered habitats, and introduced species. We measured multiple thermal endpoints to investigate potential for establishment of the invasive Ringed Crayfish (Faxonius neglectus) in thermally heterogeneous habitat of the narrowly distributed endemic Coldwater Crayfish (Faxonius eupunctus). For each species, we examined the relationships between thermal endpoints at the cellular and organismal levels. We then compared results between the two species to gain insight as to the generality of linkages between cellular and organismal-level endpoints, as well as the potential for thermal niche separation between the native and potential invader. At the cellular level, we found no differences in the temperature for maximum activity of electron transport system enzymes (ETS_max) between species. At the organismal level, F. neglectus preferred significantly warmer temperatures than F. eupunctus, but this difference was small (1.3 °C) and likely to have only limited biological significance. The critical thermal maximum (CTM) did not differ between species. For both species, the thermal performance curve for ETS enzyme activity served as a useful framework to link thermal endpoints and estimate the transition from optimal to stressful temperatures - organismal thermal preference and optimal temperature estimates consistently fell below ETS_max whereas CTM estimates fell above ETS_max. Taken together, the strong similarities in thermal endpoint patterns between the two species suggest habitats thermally suitable for the native F. eupunctus will also be thermally available to expanding populations of F. neglectus, thereby increasing the opportunity for negative interactions and population effects if F. neglectus invades one of the few remaining, uninvaded, critical habitats of F. eupunctus.

Non-native freshwater fauna in Portugal: A review

We present the most updated list of non-native freshwater fauna established in Portugal, including the Azores and Madeira archipelagos. This list includes 67 species at national level but corresponds to 84 species records, of which 53 are in the mainland, 23 in the Azores and 8 in Madeira archipelagos. We also discuss the progression of the cumulative number of introductions since 1800 and identify the most probable vectors of introduction, main taxonomic groups and their regions of origin. Furthermore, we review the existing knowledge about ecological and economic impacts, invasion risk and potential distribution of invaders, under present and future climatic conditions, and the applied management actions, including the production of legislation. Along the 20th century the number of successful introductions increased at an approximate rate of two new species per decade until the beginning of 1970s. Since then, this rate increased to about 14 new species per decade. These introductions were mainly a result of fisheries, as contaminants or for ornamental purposes. Fish and mollusks are the taxonomic groups with more established species, representing more than half of the total. Most species (>70%) are native from other regions of Europe and North America. Studies about ecological or socioeconomic impacts are more common for fish, crustaceans and mollusks. Impacts for most amphibians, reptiles and mammals are not thoroughly studied. A few studies on the impacts and management actions of health-threatening mosquitoes are also available. The potential distribution in the Portuguese territory was modelled for 26 species. Only a minority of these models provides projections of distributions under scenarios of future climate change. A comparison of the Portuguese and EU legislation shows large discrepancies in the invasive species lists. Using the EU list and a ranking procedure for the national context, we identify freshwater species of high national concern for which actions are urgently needed.

Native bluegill influence the foraging and aggressive behavior of invasive mosquitofish

Two fish species that are common invaders of aquatic ecosystems world-wide are Gambusia affinis and G. holbrooki, commonly known as mosquitofish. In North America, introduced G. affinis are thought to have contributed to the population decline of several native fish species. Sunfish (family Centrarchidae) naturally occur across much of North American, thus mosquitofish and sunfish are likely to come into contact and interact more frequently as mosquitofish spread. However, the nature of this interaction is not well known. We used a lab experiment to explore whether and how the aggressive and foraging behaviors of G. affinis might be influenced by a representative and ubiquitous native centrarchid (Lepomis macrochirus; bluegill sunfish), a species with juveniles that inhabit littoral habitats also preferred by mosquitofish. The experiment partnered an individual male or female mosquitofish (focal fish) with a juvenile bluegill, or a same- or opposite-sex conspecific, filmed these one-to-one interactions, and quantified foraging and aggressive actions for the focal mosquitofish. We found that juvenile bluegill affect foraging in male mosquitofish, resulting in lower percent of handling attempts and handling time in which the male consumed a food item. The presence of juvenile bluegill also led to a reduction in the number of aggressive acts by mosquitofish compared to aggression levels when focal mosquitofish were with conspecifics. In nature, when mosquitofish encounter juvenile bluegill in littoral habitats, our results suggest that the foraging and aggressive behaviors of mosquitofish will be modified, especially for males. This mechanism may influence the rate or geographic extent of the spread of mosquitofish into North American waterbodies.

Temperature-mediated feeding between spring-associated and riverine-associated congeners, with implications for community segregation

Freshwater fish communities segregate along water temperature gradients attributed in part to temperature-mediated physiological processes that affect species fitness. In spring complexes of southwest USA, spring complexes with narrow range of water temperatures are dominated by a community of fishes (i.e., spring-associated fishes), whereas riverine habitats with wide-range of water temperatures are dominated by a different community of fishes (i.e., riverine-associated fishes). The purpose of this study was to test a prediction of the concept that temperature-mediated species performance is a mechanism in maintaining community segregation. We predicted that a spring-associated fish (Largespring Gambusia Gambusia geiseri) would feed first and more often in a pairing with a riverine-associated fish (Western Mosquitofish G. affinis) at an average spring temperature (23 °C) and that the riverine-associated fish would feed first and more often in a pairing with the spring-associated fish at a warm riverine temperature (30 °C). Among four trails consisting of 30 pairings, at the spring complex temperature (23 °C), Largespring Gambusia had a greater number of first feeds (mean ± 1 SD, 5.0 ± 0.82) than Western Mosquitofish (2.5 ± 1.73) and had greater mean number of total feeds (1.9 ± 0.31) than Western Mosquitofish (0.81 ± 0.70). At the riverine environment temperature (30 °C), Western Mosquitofish had a greater number of first feeds (5.25 ± 1.71) than Largespring Gambusia (2.5 ± 1.73) and had greater mean number of total feeds (2.78 ± 1.05) than Largespring Gambusia (0.94 ± 0.68). Our findings suggest that temperature-mediated species performance could be maintaining segregation between the two fish communities. This study benefits our understanding of distributional patterns and improves threat assessments of stenothermal aquatic organisms.

Assessment of the predatory capacity on mosquito larvae of Jenynsia multidentata (Anablepidae) in presence of vegetation under laboratory conditions

ABSTRACT Larvivorous fish have been studied as potential biocontrol agents of mosquito larvae and pupae through their trophic interactions. The use of native fish for mosquito control may have benefits for both aquatic biodiversity and human health. Evaluating the effect of vegetation on the predatory efficacy is fundamental to determine if this species can be used as a biocontrol agent. With the aim of evaluating Jenynsia multidentata (Jenyns, 1842) as a biocontrol agent of Culex pipiens Linnaeus, 1758, we tested its predatory capacity in the presence or absence of aquatic vegetation under laboratory conditions. Two independent experiments were conducted. Larval consumption at a density of 60 larvae (6 larvae/l) was significantly reduced with the vegetation increased. On the other hand, when the larval density was 120 (12 larvae/l), the predatory capacity of J. multidentata did not vary in the presence or absence of vegetation. This result indicated that vegetation effect on consumption could be related to prey density, since at the higher density of prey the probability of predator-prey encounter might be increased. Jenynsia multidentata is a good consumer in presence of vegetation and could be used as a potential biocontrol agent of mosquito larvae in natural environments with similar characteristics to the ones tested in these experiments.

Phylogeography and Population Genetic Analyses in the Iberian Toothcarp (Aphanius iberus Valenciennes, 1846) at Different Time Scales

Secondary freshwater fish species inhabiting fluctuating and extreme environments are susceptible to changes in dispersion, effective population size, and genetic structure. The Iberian toothcarp Aphanius iberus is an endemic cyprinodontid of the Iberian Peninsula restricted to brackish water of salt marshes and coastal lagoons on the eastern Spanish Mediterranean coast. In this study, we analyzed mitochondrial cytochrome b (cyt b) DNA and microsatellite variation to evaluate ways in which the processes of extinction, dispersal, and colonization of A. iberus across its geographic distribution have affected its population genetic structure over time and space. The A. iberus network reconstruction indicated subtle levels of phylogeographic structuring. This, combined with substantial mitochondrial DNA (mtDNA) genetic diversity, suggests that Pleistocene glaciations had a lesser effect on the demographic structure of its populations than was the case for Iberian freshwater species with a similar distribution. Haplotype network, hierarchical analysis of molecular variance, and pairwise ΦST comparisons involving some Levantine samples showed a relatively high degree of mtDNA differentiation, which could be explained by historical isolation of the Villena Lagoon population. Conversely, significant genetic differentiation that follows an isolation-by-distance pattern, and a reduction in Ne though time was detected with microsatellites, suggesting extensive habitat fragmentation on the Mediterranean coast of the Iberian Peninsula over the past hundreds of years. At a smaller geographical scale (Mar Menor Lagoon), habitat fragmentation, probably due to human activity, appears to have resulted in substantially reduced migration and increased genetic drift, as shown by expanded genetic differentiation of populations.

Environmental niche separation between native and non-native benthic invertebrate species: Case study of the northern Baltic Sea

Knowledge and understanding of geographic distributions of species is crucial for many aspects in ecology, conservation, policy making and management. In order to reach such an understanding, it is important to know abiotic variables that impact and drive distributions of native and non-native species. We used an existing long-term macrobenthos database for species presence-absence information and biomass estimates at different environmental gradients in the northern Baltic Sea. Region specific abiotic variables (e.g. salinity, depth) were derived from previously constructed bathymetric and hydrodynamic models. Multidimensional ordination techniques were then applied to investigate potential niche space separation between all native and non-native invertebrates in the northern Baltic Sea. Such an approach allowed to obtain data rich and robust estimates of the current native and non-native species distributions and outline important abiotic parameters influencing the observed pattern. The results showed clear niche space separation between native and non-native species. Non-native species were situated in an environmental space characterized by reduced salinity, high temperatures, high proportion of soft seabed and decreased depth and wave exposure whereas native species displayed an opposite pattern. Different placement of native and non-native species along the studied environmental niche space is likely to be explained by the differences in their evolutionary history, human mediated activities and geological youth of the Baltic Sea. The results of this study can provide early warnings and effectively outline coastal areas in the northern Baltic Sea that are prone to further range expansion of non-native species as climate change is expected to significantly reduce salinity and increase temperature in wide coastal areas, both supporting the disappearance of native and appearance of non-native species.

Thermal modulation of anthropogenic estrogen exposure on a freshwater fish at two life stages

Human-mediated environmental change can induce changes in the expression of complex behaviors within individuals and alter the outcomes of interactions between individuals. Although the independent effects of numerous stressors on aquatic biota are well documented (e.g., exposure to environmental contaminants), fewer studies have examined how natural variation in the ambient environment modulates these effects. In this study, we exposed reproductively mature and larval fathead minnows (Pimephales promelas) to three environmentally relevant concentrations (14, 22, and 65ng/L) of a common environmental estrogen, estrone (E1), at four water temperatures (15, 18, 21, and 24°C) reflecting natural spring and summer variation. We then conducted a series of behavioral experiments to assess the independent and interactive effects of temperature and estrogen exposure on intra- and interspecific interactions in three contexts with important fitness consequences; reproduction, foraging, and predator evasion. Our data demonstrated significant independent effects of temperature and/or estrogen exposure on the physiology, survival, and behavior of larval and adult fish. We also found evidence suggesting that thermal regime can modulate the effects of exposure on larval survival and predator-prey interactions, even within a relatively narrow range of seasonally fluctuating temperatures. These findings improve our understanding of the outcomes of interactions between anthropogenic stressors and natural abiotic environmental factors, and suggest that such interactions can have ecological and evolutionary implications for freshwater populations and communities.

Predator-induced phenotypic plasticity of shape and behavior: parallel and unique patterns across sexes and species

Phenotypic plasticity is often an adaptation of organisms to cope with temporally or spatially heterogenous landscapes. Like other adaptations, one would predict that different species, populations, or sexes might thus show some degree of parallel evolution of plasticity, in the form of parallel reaction norms, when exposed to analogous environmental gradients. Indeed, one might even expect parallelism of plasticity to repeatedly evolve in multiple traits responding to the same gradient, resulting in integrated parallelism of plasticity. In this study, we experimentally tested for parallel patterns of predator-mediated plasticity of size, shape, and behavior of 2 species and sexes of mosquitofish. Examination of behavioral trials indicated that the 2 species showed unique patterns of behavioral plasticity, whereas the 2 sexes in each species showed parallel responses. Fish shape showed parallel patterns of plasticity for both sexes and species, albeit males showed evidence of unique plasticity related to reproductive anatomy. Moreover, patterns of shape plasticity due to predator exposure were broadly parallel to what has been depicted for predator-mediated population divergence in other studies (slender bodies, expanded caudal regions, ventrally located eyes, and reduced male gonopodia). We did not find evidence of phenotypic plasticity in fish size for either species or sex. Hence, our findings support broadly integrated parallelism of plasticity for sexes within species and less integrated parallelism for species. We interpret these findings with respect to their potential broader implications for the interacting roles of adaptation and constraint in the evolutionary origins of parallelism of plasticity in general.

Genomic survey provides insights into the evolutionary changes that occurred during European expansion of the invasive mosquitofish (Gambusia holbrooki)

Biological invasions rank among the main global threats for biodiversity. The Eastern mosquitofish (Gambusia holbrooki) is considered one of the 100 world worst invasive species due to its high adaptation capability to new environments. Using the restriction-site-associated DNA tags (RADtags), introduced European locations were compared against native US mosquitofish populations to analyse genomic changes that occurred during invasive process of European locations. After filtering, 7724 RADtags containing only one SNP were retained for population studies. Comparative genomics indicated that 186 of these RADtags matched sequences in the transcriptome of Xyphophorus maculatus, the most closely related genome available. Genomic analyses showed that invasive populations show high reductions in diversity. Further, analyses of population structuring based on these data are concordant with previous analyses based on microsatellites. It is concluded that during the invasion process genetic drift was the main evolutionary force affecting patterns of diversity and population structure. While recognizing that positive selection could be masked by the strong drift during founder events, adaptive processes were evidenced in a reduced number of RADtags (<2%), with only one of these in a putative coding region. Surprisingly, balancing selection was detected in several coding RADtags, suggesting that the preservation of polymorphism in specific genes could be more important than the average population diversity for the population maintenance at any location, particularly for the survival of introduced populations.

Influence of Temperature on Intra- and Interspecific Resource Utilization within a Community of Lepidopteran Maize Stemborers

Competition or facilitation characterises intra- and interspecific interactions within communities of species that utilize the same resources. Temperature is an important factor influencing those interactions and eventual outcomes. The noctuid stemborers, Busseola fusca and Sesamia calamistis and the crambid Chilo partellus attack maize in sub-Saharan Africa. They often occur as a community of interacting species in the same field and plant at all elevations. The influence of temperature on the intra- and interspecific interactions among larvae of these species, was studied using potted maize plants exposed to varying temperatures in a greenhouse and artificial stems kept at different constant temperatures (15°C, 20°C, 25°C and 30°C) in an incubator. The experiments involved single- and multi-species infestation treatments. Survival and relative growth rates of each species were assessed. Both intra- and interspecific competitions were observed among all three species. Interspecific competition was stronger between the noctuids and the crambid than between the two noctuids. Temperature affected both survival and relative growth rates of the three species. Particularly at high temperatures, C. partellus was superior in interspecific interactions shown by higher larval survival and relative growth rates. In contrast, low temperatures favoured survival of B. fusca and S. calamistis but affected the relative growth rates of all three species. Survival and relative growth rates of B. fusca and S. calamistis in interspecific interactions did not differ significantly across temperatures. Temperature increase caused by future climate change is likely to confer an advantage on C. partellus over the noctuids in the utilization of resources (crops).

Climate change simulations predict altered biotic response in a thermally heterogeneous stream system

Climate change is predicted to increase water temperatures in many lotic systems, but little is known about how changes in air temperature affect lotic systems heavily influenced by groundwater. Our objectives were to document spatial variation in temperature for spring-fed Ozark streams in Southern Missouri USA, create a spatially explicit model of mean daily water temperature, and use downscaled climate models to predict the number of days meeting suitable stream temperature for three aquatic species of concern to conservation and management. Longitudinal temperature transects and stationary temperature loggers were used in the Current and Jacks Fork Rivers during 2012 to determine spatial and temporal variability of water temperature. Groundwater spring influence affected river water temperatures in both winter and summer, but springs that contributed less than 5% of the main stem discharge did not affect river temperatures beyond a few hundred meters downstream. A multiple regression model using variables related to season, mean daily air temperature, and a spatial influence factor (metric to account for groundwater influence) was a strong predictor of mean daily water temperature (r2 = 0.98; RMSE = 0.82). Data from two downscaled climate simulations under the A2 emissions scenario were used to predict daily water temperatures for time steps of 1995, 2040, 2060, and 2080. By 2080, peak numbers of optimal growth temperature days for smallmouth bass are expected to shift to areas with more spring influence, largemouth bass are expected to experience more optimal growth days (21-317% increase) regardless of spring influence, and Ozark hellbenders may experience a reduction in the number of optimal growth days in areas with the highest spring influence. Our results provide a framework for assessing fine-scale (10 s m) thermal heterogeneity and predict shifts in thermal conditions at the watershed and reach scale.

Gene flow and maintenance of genetic diversity in invasive mosquitofish (Gambusia holbrooki)

Genetic analyses contribute to studies of biological invasions by mapping the origin and dispersal patterns of invasive species occupying new territories. Using microsatellite loci, we assessed the genetic diversity and spatial population structure of mosquitofish (Gambusia holbrooki) that had invaded Spanish watersheds, along with the American locations close to the suspected potential source populations. Mosquitofish populations from the Spanish streams that were studied had similar levels of genetic diversity to the American samples; therefore, these populations did not appear to have undergone substantial losses of genetic diversity during the invasion process. Population structure analyses indicated that the Spanish populations fell into four main clusters, which were primarily associated with hydrography. Dispersal patterns indicated that local populations were highly connected upstream and downstream through active dispersal, with an average of 21.5% fish from other locations in each population. After initially introducing fish to one location in a given basin, such dispersal potential might contribute to the spread and colonization of suitable habitats throughout the entire river basin. The two-dimension isolation-by-distance pattern here obtained, indicated that the human-mediated translocation of mosquitofish among the three study basins is a regular occurrence. Overall, both phenomena, high natural dispersal and human translocation, favor gene flow among river basins and the retention of high genetic diversity, which might help retain the invasive potential of mosquitofish populations.