Cristina Coccia

Biological traits of European pond macroinvertebrates

Whilst biological traits of river macroinvertebrates show unimodal responses to geographic changes in habitat conditions in Europe, we still do not know whether spatial turnover of species result in distinct combinations of biological traits for pond macroinvertebrates. Here, we used data on the occurrence of 204 macroinvertebrate taxa in 120 ponds from four biogeographic regions of Europe, to compare their biological traits. The Mediterranean, Atlantic, Alpine, and Continental regions have specific climate, vegetation and geology. Only two taxa were exclusively found in the Alpine and Continental regions, while 28 and 34 taxa were exclusively recorded in the Atlantic and Mediterranean regions, respectively. Invertebrates in the Mediterranean region allocated much energy to reproduction and resistance forms. Most Mediterranean invertebrate species had narrow thermal ranges. In Continental areas, invertebrates allocated lesser energy to reproduction and dispersal, and organisms were short lived with high diversity of feeding groups. These characteristics suggest higher resilience. The main difference between ponds in the Alpine and Atlantic regions was their elevation. Alpine conditions necessitate specific adaptations related to rapid temperature fluctuations, and low nutrient concentrations. Even if our samples did not cover the full range of pond conditions across Europe, our analyses suggest that changes in community composition have important impacts on pond ecosystem functions. Consistent information on a larger set of ponds across Europe would be much needed, but their low accessibility (unpublished data and/or not disclosed by authors) remains problematic. There is still, therefore, a pressing need for the incorporation of high quality data sets into a standardized database so that they can be further analyzed in an integrated European-wide manner.

How far could the alien boatman Trichocorixa verticalis verticalis spread? Worldwide estimation of its current and future potential distribution.

Invasions of alien species are considered among the least reversible human impacts, with diversified effects on aquatic ecosystems. Since prevention is the most cost-effective way to avoid biodiversity loss and ecosystem problems, one challenge in ecological research is to understand the limits of the fundamental niche of the species in order to estimate how far invasive species could spread. Trichocorixa verticalis verticalis (Tvv) is a corixid (Hemiptera) originally distributed in North America, but cited as an alien species in three continents. Its impact on native communities is under study, but it is already the dominant species in several saline wetlands and represents a rare example of an aquatic alien insect. This study aims: i) to estimate areas with suitable environmental conditions for Tvv at a global scale, thus identifying potential new zones of invasion; and ii) to test possible changes in this global potential distribution under a climate change scenario. Potential distributions were estimated by applying a multidimensional envelope procedure based on both climatic data, obtained from observed occurrences, and thermal physiological data. Our results suggest Tvv may expand well beyond its current range and find inhabitable conditions in temperate areas along a wide range of latitudes, with an emphasis on coastal areas of Europe, Northern Africa, Argentina, Uruguay, Australia, New Zealand, Myanmar, India, the western boundary between USA and Canada, and areas of the Arabian Peninsula. When considering a future climatic scenario, the suitability area of Tvv showed only limited changes compared with the current potential distribution. These results allow detection of potential contact zones among currently colonized areas and potential areas of invasion. We also identified zones with a high level of suitability that overlap with areas recognized as global hotspots of biodiversity. Finally, we present hypotheses about possible means of spread, focusing on different geographical scales.

Parasitism by water mites in native and exotic Corixidae: are mites limiting the invasion of the water boatman Trichocorixa verticalis (Fieber, 1851)?

Abstract The water boatman Trichocorixa verticalis verticalis (Fieber 1851) is originally from North America and has been introduced into the southern Iberian Peninsula, where it has become the dominant Corixidae species in saline wetlands. The reasons for its success in saline habitats, and low abundance in low salinity habitats, are poorly known. Here we explore the potential role of water mites, which are typical parasites of hemipterans, in the invasion dynamics of T. v. verticalis. We compared infection levels between T. v. verticalis and the natives Sigara lateralis (Leach, 1817) and S. scripta (Rambur, 1840). No mites were found in saline wetlands where T. v. verticalis is highly dominant. Larvae of two mite species were identified infecting corixids in habitats of lower salinity: Hydrachna skorikowi and Eylais infundibulifera. Total parasite prevalence and prevalence of E. infundibulifera were significantly higher in T. v. verticalis compared with S. lateralis and S. scripta. Mean abundance of total infection and of E. infundibulifera and H. skorikowi were also higher in T. v. verticalis. When infected with H. skorikowi, native species harbored only one or two parasite individuals, while the smaller T. v. verticalis carried up to seven mites. When infected with E. infundibulifera, native species harboured only one parasite individual, while T. v. verticalis carried up to 6. Mite size didn’t differ among host species, suggesting that all are suitable for engorgement. Both mite species showed a negative correlation between prevalence and salinity. T. v. verticalis susceptibility to parasitic mites may explain its low abundance in low salinity habitats, and may contribute to the conservation of native corixids. The success of T. v. verticalis in saline wetlands may be partly explained by the absence of parasitic mites, which are less halotolerant.

What traits underpin the successful establishment and spread of the invasive water bug Trichocorixa verticalis verticalis

The introduction of exotic species has a major impact on a wide range of ecosystems, especially in aquatic ecosystems. Trichocorixa v. verticalis (Fieber, 1851), an euryhaline aquatic hemipteran native North America, has occurred as an exotic species in the Iberian Peninsula since at least 1997. In this study, we compared several physiological and biological traits (salinity tolerance of the different developmental stages, thermal tolerance, fecundity, and dispersal ability) in the alien species and three native, syntopic corixidae species (Sigara lateralis, Sigara scripta, and Sigara selecta), to determine which traits may explain its invasion success. Trichocorixa verticalis was the species most resistant to high conductivity at the egg stage, while S. selecta showed the highest halotolerance as adults. The invader had the highest upper thermal limit and a much higher fecundity than Sigara species. Wing morphometry suggested that T. verticalis may be a stronger flier than the native species. Our findings provide an example of how functional and ecological niche interactions among alien and native species can help predict impacts of invasion on aquatic communities.

Can differential predation of native and alien corixids explain the success of Trichocorixa verticalis verticalis (Hemiptera, Corixidae) in the Iberian Peninsula?

Invasive species represent an increasing fraction of aquatic biota. However, studies on the role and consequences of facilitative interactions among aliens remain scarce. Here, we investigated whether the spread of the alien water boatman Trichocorixa verticalis verticalis in the Iberian Peninsula is related to reduced mortality from predation compared with native Corixidae, especially since Trichocorixa co-occurs with the invasive fishes Gambusia holbrooki and Fundulus heteroclitus. All three invaders have a common native range in North America and are widespread in and around Doñana in SW Spain. Using laboratory experiments, we compared the predation rates by the two exotic fish and native Odonata larvae on Trichocorixa and the native Sigara lateralis. We found no evidence to suggest that Trichocorixa suffers lower predation rates. However, when both corixids were mixed together, predation of Trichocorixa by Odonata larvae was higher. Odonata larvae were size-limited predators and the proportion of corixids ingested was positively correlated with mask length. Since Trichocorixa is smaller than its native competitors, this may explain their higher susceptibility to predation by Odonata. This may be one of various factors explaining why Trichocorixa is particularly dominant in saline habitats where Odonata are rare, while it is still scarce in fresh waters.

Biological invasion modifies the co-occurrence patterns of insects along a stress gradient

Summary 1. Biological invasions have become one of the most important drivers of biodiversity loss and ecosystem change worldwide. However, it is still unclear how invasions may interact with local abiotic stressors, which are expected to increase as global change intensifies. Furthermore, we know little about the response to biological invasions of insects, despite their disproportionate contribution to global animal biodiversity. 2. The aim of the present work is to investigate the impact of an invasive aquatic insect on the co-occurrence patterns of native species of insects along a salinity gradient, and determine which assembly rules are driving these patterns. 3. First, we characterised the habitat specialisation and functional niches of each species from physiological and biological traits, respectively, and their degree of overlap. Second, we used field data to compare the co-occurrence patterns of native and invasive species in invaded and non-invaded areas of southern Iberia and northern Morocco. Finally, we tested if habitat filtering or niche differentiation assembly rules mediate their co-occurrence. 4. In non-invaded areas habitat filtering drives habitat segregation of species along the salinity gradient, with a lower contribution of niche differentiation. The presence of the invasive insect modifies the distribution and co-occurrence patterns of native species. In invaded areas, niche differentiation seems to be the main mechanism to avoid competition among the invasive and native species, enabling coexistence and resource partitioning. 5. The combined study of functional niche similarity and abiotic stressor tolerance of invasive and native species can improve our understanding of the effects of invasive species along abiotic stress gradients. This approach may increase our capacity to predict the outcomes of biological invasion in a global change context. This article is protected by copyright. All rights reserved.

Niche partitioning between invasive and native corixids (Hemiptera, Corixidae) in south-west Spain

Trichocorixa verticalis verticalis, a North American water boatman, is the only alien corixid in European fresh waters. It has rapidly spread, becoming the dominant corixid in and around the Doñana protected area in SW Spain. Its high abundance and similar morphology to native corixids suggest that T. verticalis may impact them through competition for food. Here we used stable isotopes of nitrogen (N) and carbon (C) and Bayesian analytical tools to investigate niche partitioning between T. verticalis and the native water boatman Sigara lateralis and Sigara scripta through a combination of experimental and field data. Species sampled from permanent ponds and laboratory aquaria could be separated based on their isotopic values (δ15N and δ13C). S. lateralis consistently showed higher δ15N values than T. verticalis, suggesting that the invasive species may be feeding at a lower trophic position and relying more on herbivory than its native competitors. This was particularly true for the T. verticalis nymph stage, which showed lower δ15N values compared to adults, indicating ontogenetic dietary shifts. In contrast, native corixids and the invasive species showed similar isotopic compositions in temporary habitats at different stages in the flooding-desiccation cycle, suggesting some degree of niche overlap and a slight reduction in trophic level for S. lateralis when inhabiting ephemeral systems. The combination of experimental and field data can help elucidate trophic interactions during a biological invasion. Stable isotopes provided insights into the trophic ecology of this invasive species and into the mechanisms facilitating co-existence with native species.

Life cycle of T. verticalis; field-data approximation

Datasets as supporting information to the article “The life cycle of the alien boatman Trichocorixa verticalis (Hemiptera, Corixidae) in saline wetlands of south-west Spain.” to be considered in Hydrobiologia. Primary contact for data associated with this article: Vanessa Cespedes vanessa.cespedes@ebd.csic.es.