Explaining the invasive success of the eastern mosquitofish (Gambusia holbrooki): the role of temperature

The eastern mosquitofish (Gambusia holbrooki) is one of the most widely distributed and invasive inland fish. It is known that it has not been established in northern Europe or upstream of rivers, where the temperature is too low for survival and reproduction. This thesis examines how temperature affects the competitive ability and life history traits of mosquitofish. We sampled mosquitofish along latitudinal gradients and along rivers and we found that mosquitofish in more favorable environments (i.e. low latitudes and downstream river reaches) had a higher reproductive effort and lower body condition but these patterns of variation were weak and dependent on fish age. We also carried out an experiment which showed that as the temperature rises mosquitofish increases its competitive ability for resources and its aggressive behavior towards Aphanius iberus, an endangered Iberian endemism. Our results imply that climate change will favor the invasive success of mosquitofish and will increase its impact on native fishLa gambúsia (Gambusia holbrooki) és un dels peixos continentals més àmpliament distribuït i més invasors. Se sap que no s’ha pogut establir al nord d’Europa ni a trams alts de rius, on la temperatura és massa baixa per a la supervivència i la reproducció. Aquesta tesi analitza com afecta la temperatura a la capacitat competitiva i a les característiques del cicle vital de la gambúsia. Es van mostrejar gradients latitudinals i al llarg de rius i es va trobar que la gambúsia que vivia a ambients més favorables (és a dir, latituds menors i zones baixes dels rius), presentava un major esforç reproductiu i una menor condició corporal però que aquests patrons de variació eren febles i depenien de l'edat dels peixos. També es va portar a terme un experiment en què es va demostrar que a mesura que puja la temperatura la gambúsia incrementa la seva capacitat de competència pels recursos i el comportament agressiu contra el fartet (Aphanius iberus), endemisme ibèric en perill d'extinció. Els nostres resultats impliquen que el canvi climàtic afavorirà l'èxit invasor de la gambúsia i augmentarà el seu impacte en els peixos natiu

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

Condition-specific competition is widespread in nature. Species inhabiting heterogeneous environments tend to differ in competitive abilities depending on environmental stressors. Interactions between these factors can allow coexistence of competing species, which may be particularly important between invasive and native species. Here, we examine the effects of temperature on competitive interactions between invasive mosquitofish, Gambusia holbrooki, and an endemic Iberian toothcarp, Aphanius iberus. We compare the tendency to approach heterospecifics and food capture rates between these two species, and examine differences between sexes and species in aggressive interactions, at three different temperatures (19, 24 and 29°C) in three laboratory experiments. Mosquitofish exhibit much more aggression than toothcarp. We show that mosquitofish have the capacity to competitively displace toothcarp through interference competition and this outcome is more likely at higher temperatures. We also show a reversal in the competitive hierarchy through reduced food capture rate by mosquitofish at lower temperatures and suggest that these two types of competition may act synergistically to deprive toothcarp of food at higher temperatures. Males of both species carry out more overtly aggressive acts than females, which is probably related to the marked sexual dimorphism and associated mating systems of these two species. Mosquitofish may thus impact heavily on toothcarp, and competition from mosquitofish, especially in warmer summer months, may lead to changes in abundance of the native species and displacement to non-preferred habitats. Globally increasing temperatures mean that highly invasive, warm-water mosquitofish may be able to colonize environments from which they are currently excluded through reduced physiological tolerance to low temperatures. Research into the effects of temperature on interactions between native and invasive species is thus of fundamental importance

Temperature-Specific Competition between Invasive Mosquitofish and an Endangered Cyprinodontid Fish

Condition-specific competition is widespread in nature. Species inhabiting heterogeneous environments tend to differ in competitive abilities depending on environmental stressors. Interactions between these factors can allow coexistence of competing species, which may be particularly important between invasive and native species. Here, we examine the effects of temperature on competitiveinteractions between invasive mosquitofish, Gambusia holbrooki, and an endemic Iberian toothcarp, Aphanius iberus. We compare the tendency to approach heterospecifics and food capture rates between these two species, and examine differences between sexes and species in aggressive interactions, at three different temperatures (19, 24 and 29uC) in three laboratory experiments. Mosquitofish exhibit much more aggression than toothcarp. We show that mosquitofish have the capacity to competitively displace toothcarp through interference competition and this outcome is more likely at higher temperatures. We also show a reversal in the competitive hierarchy through reduced food capture rate by mosquitofish at lower temperatures and suggest that these two types of competition may act synergistically to deprive toothcarp of food at higher temperatures. Males of both species carry out more overtly aggressive acts than females, which is probably related to the marked sexual dimorphism and associated mating systems of these two species. Mosquitofish may thus impact heavily on toothcarp, and competition from mosquitofish, especially in warmer summer months, may lead to changes in abundance of the native species and displacement to non-preferred habitats. Globally increasing temperatures mean that highly invasive, warm-water mosquitofish may be able to colonize environments from which they are currently excluded through reduced physiological tolerance to low temperatures. Research into the effects of temperature on interactions between native and invasive species is thus of fundamental importanc

Fish passage assessment at the most downstream barrier of the Ebro River (NE Iberian Peninsula)

Fish passage at artificial barriers is necessary for the conservation of healthy fish stocks. The first barrier that migratory fish encounter when ascending the Ebro River is the Xerta Weir, where a pool-type fishway was constructed in 2008. From 2007 to 2010, boat electrofishing surveys were conducted in the Ebro River downstream of the Xerta Weir to assess the potential pool of species that could use the fishway. Nine native and 12 exotic species were captured, the latter comprising 62 % of the relative abundance and 70 % of the biomass. A combination of video recording, electrofishing and trapping was used to assess the effectiveness of the fishway in facilitating the passage of fish. Eight species were detected using the fishway, of which five were native (Liza ramada, Anguilla anguilla, Barbus graellsii, Gobio lozanoi and Salaria fluviatilis) and three exotic (Alburnus alburnus, Cyprinus carpio and Rutilus rutilus). Only L. ramada used the fishway in substantial numbers. The rate of fish passage was the highest from June to August and decreased afterwards. The effectiveness of the fishway might be lowered by areas of turbulence within the fishway and by distraction flows from a nearby hydropower station.El paso de peces a través de barreras artificiales es necesario para la conservación en buen estado de las poblaciones de peces. La primera barrera que los peces migratorios encuentran ascendiendo el Río Ebro es el Azud de Xerta, donde en 2008 se construyó una escala de peces del tipo de estanques sucesivos. Para determinar el conjunto de especies que potencialmente podrían usar la escala se llevaron a cabo muestreos mediante pesca eléctrica desde embarcación aguas abajo del azud. Nueve especies nativas y 12 exóticas fueron capturadas, representando estas últimas el 62 % de la abundancia relativa y el 70 % de la biomasa. Se usó una combinación de grabaciones de video, pesca eléctrica y trampeo para evaluar la efectividad de la escala de peces. Ocho especies fueron detectadas en la escala, de las cuales cinco eran nativas (Liza ramada, Anguilla anguilla, Barbus graellsii, Gobio lozanoi y Salaria fluviatilis) y tres exóticas (Alburnus alburnus, Cyprinus carpio y Rutilus rutilus). Sólo L. ramada usó la escala en un número destacado. La tasa de paso de peces fue más alta de Junio a Agosto y descendió posteriormente. La efectividad de la escala puede estar limitada por areas de turbulencia dentro de la escala y caudales de distracción desde una central hidroeléctrica cercana

Fish passage assessment at the most downstream barrier of the Ebro River (NE Iberian Peninsula)

Fish passage at artificial barriers is necessary for the conservation of healthy fish stocks. The first barrier that migratory fish encounter when ascending the Ebro River is the Xerta Weir, where a pool-type fishway was constructed in 2008. From 2007 to 2010, boat electrofishing surveys were conducted in the Ebro River downstream of the Xerta Weir to assess the potential pool of species that could use the fishway. Nine native and 12 exotic species were captured, the latter comprising 62 % of the relative abundance and 70 % of the biomass. A combination of video recording, electrofishing and trapping was used to assess the effectiveness of the fishway in facilitating the passage of fish. Eight species were detected using the fishway, of which five were native (Liza ramada, Anguilla anguilla, Barbus graellsii, Gobio lozanoi and Salaria fluviatilis) and three exotic (Alburnus alburnus, Cyprinus carpio and Rutilus rutilus). Only L. ramada used the fishway in substantial numbers. The rate of fish passage was the highest from June to August and decreased afterwards. The effectiveness of the fishway might be lowered by areas of turbulence within the fishway and by distraction flows from a nearby hydropower stationEl paso de peces a través de barreras artificiales es necesario para la conservación en buen estado de las poblaciones de peces. La primera barrera que los peces migratorios encuentran ascendiendo el Río Ebro es el Azud de Xerta, donde en 2008 se construyó una escala de peces del tipo de estanques sucesivos. Para determinar el conjunto de especies que potencialmente podrían usar la escala se llevaron a cabo muestreos mediante pesca eléctrica desde embarcación aguas abajo del azud. Nueve especies nativas y 12 exóticas fueron capturadas, representando estas últimas el 62 % de la abundancia relativa y el 70 % de la biomasa. Se usó una combinación de grabaciones de video, pesca eléctrica y trampeo para evaluar la efectividad de la escala de peces. Ocho especies fueron detectadas en la escala, de las cuales cinco eran nativas (Liza ramada, Anguilla anguilla, Barbus graellsii, Gobio lozanoi y Salaria fluviatilis) y tres exóticas (Alburnus alburnus, Cyprinus carpio y Rutilus rutilus). Sólo L. ramada usó la escala en un número destacado. La tasa de paso de peces fue más alta de Junio a Agosto y descendió posteriormente. La efectividad de la escala puede estar limitada por áreas de turbulencia dentro de la escala y caudales de distracción desde una central hidroeléctrica cercan

Quantifying seasonality along a latitudinal gradient : from stream temperature to growth of invasive mosquitofish

Most ecosystems undergo substantial variation over the seasons, ranging from changes in abiotic features, such as temperature, light and precipitation, to changes in species abundance and composition. How seasonality varies along latitudinal gradients is not well known in freshwater ecosystems, despite being very important in predicting the effects of climate change and in helping to advance ecological understanding. Stream temperature is often well correlated with air temperature and influences many ecosystem features such as growth and metabolism of most aquatic organisms. We evaluated the degree of seasonality in ten river mouths along a latitudinal gradient for a set of variables, ranging from air and water temperatures, to physical and chemical properties of water and growth of an invasive fish species (eastern mosquitofish, Gambusia holbrooki). Our results show that although most of the variation in air temperature was explained by latitude and season, this was not the case for water features, including temperature, in lowland Mediterranean streams, which depended less on season and much more on local factors. Similarly, although there was evidence of latitude-dependent seasonality in fish growth, the relationship was nonlinear and weak and the significant latitudinal differences in growth rates observed during winter were compensated later in the year and did not result in overall differences in size and growth. Our results suggest that although latitudinal differences in air temperature cascade through properties of freshwater ecosystems, local factors and complex interactions often override the water temperature variation with latitude and might therefore hinder projections of species distribution models and effects of climate change

Generalized linear models for selected response variables (i.e. orientations, nips, chases) of <i>Gambusia holbrooki</i> and <i>Aphanius iberus</i> using temperature and sex as predictors.

<p>Values are χ ².</p><p>“**”indicates <i>P</i><0.01;</p><p>“***”indicates <i>P</i><0.001; d.f. are 2 for temperature, 1 for sex, and 2 for their interaction.</p

Effects of temperature on the number of prey items captured by <i>Gambusia holbrooki</i> and <i>Aphanius iberus</i>.

<p>Means and SE (error bar) are shown. Note that the totals for both species for 19 and 24°C do not equal 100%. This reflects the prey that remained uneaten.</p

Aggressive acts (orientations, nips and chases) performed by <i>Gambusia holbrooki</i> towards <i>Aphanius iberus</i> and vice versa under the different temperature treatments and species combinations.

<p>Means and SE (error bar) are shown. Note the different scales on the <i>y</i>-axis for each species.</p

Mean time to a) cross the center line and b) approach a heterospecific for <i>G. holbrooki</i> and <i>A. iberus</i> as a function of temperature.

<p>Means and SE (error bar) are shown.</p