Dispersal syndromes in challenging environments: A cross-species experiment.

Dispersal is a central biological process tightly integrated into life-histories, morphology, physiology and behaviour. Such associations, or syndromes, are anticipated to impact the eco-evolutionary dynamics of spatially structured populations, and cascade into ecosystem processes. As for dispersal on its own, these syndromes are likely neither fixed nor random, but conditional on the experienced environment. We experimentally studied how dispersal propensity varies with individuals' phenotype and local environmental harshness using 15 species ranging from protists to vertebrates. We reveal a general phenotypic dispersal syndrome across studied species, with dispersers being larger, more active and having a marked locomotion-oriented morphology and a strengthening of the link between dispersal and some phenotypic traits with environmental harshness. Our proof-of-concept metacommunity model further reveals cascading effects of context-dependent syndromes on the local and regional organisation of functional diversity. Our study opens new avenues to advance our understanding of the functioning of spatially structured populations, communities and ecosystems.

Does range expansion modify trait covariation? A study of a northward expanding dragonfly.

The adaptive value of correlations among phenotypic traits depends on the prevailing environmental conditions. Differences in selection pressures during species range expansions may therefore shape phenotypic integration. In this study, we assessed variation in behavioral and morphological traits, as well as their covariations, in replicated southern and northern European populations of the northward expanding dragonfly Crocothemis erythraea. Larvae from northern populations were, on average, darker in color, and therefore, better camouflaged than larvae from southern populations. However, there was no difference in activity level. Darkness and activity were positively correlated in larvae from northern populations, whereas this trait covariation was missing in southern populations. This suggests the emergence of alternative strategies in time-limited northern populations, a higher activity level that required better camouflage through darker coloration, while less active larvae benefited from an energy-saving strategy by reducing the investment in costly traits, such as body darkness. We further found that larger larvae emerged into larger adults, with a higher investment in flight morphology. Our findings imply that phenotypic integration is associated with the northward range shift, potentially differentially shaping fitness consequences, and ecological interactions in southern versus northern populations.

Genetic and environmental contributions to the impact of a range-expanding predator on aquatic ecosystems.

Global change is altering biodiversity locally and globally and subsequently affecting the dynamics of communities and ecosystems. Biodiversity can be impacted both at the interspecific (i.e., species composition of communities) and at the intraspecific (evolutionary modification of phenotypic traits through selection or plasticity) levels. Changes in intraspecific diversity have been demonstrated to generate evolutionary feedbacks acting on ecological dynamics. Quantifying the role of intraspecific trait variation, global change and their interactions on ecological dynamics is of utmost importance. Here, we used the range-expanding dragonfly Crocothemis erythraea as a model species to test the relative effects of intraspecific trait variation in larvae and thermal conditions on the dynamics of freshwater community and ecosystem functioning. Using experimental mesocosms, we manipulated intraspecific trait variation arising from genetic (G), early developmental environment (EE ) and late developmental environment (EL ) contributions in a full factorial design. We showed that intraspecific trait variation arising from genetic effects has the strongest consequences on community and ecosystem dynamics relative to trait variation driven by the thermal environment (EE and EL ). Importantly, the ecological effects of trait variation due to genetic effects were partly modulated by thermal conditions (G × EL , and to a lesser extent G × EE interactions) and varied among ecological response variables. For instance, the strongest G × EL effects were observed on primary productivity and zooplankton dynamics. Trait variation driven by plasticity related to early or late developmental environments has an overall weak effect on ecological dynamics. Intraspecific trait variation induced by genetic effects can affect ecological dynamics (evo-to-eco dynamics) more strongly than variation induced by the developmental environment. However, they likely interact to modulate the structure of communities and the functioning of ecosystems, highlighting the strong context (environmental) dependency of evo-to-eco dynamics.

Bottom-up and top-down control of dispersal across major organismal groups.

Ecology and evolution unfold in spatially structured communities, where dispersal links dynamics across scales. Because dispersal is multicausal, identifying general drivers remains challenging. In a coordinated distributed experiment spanning organisms from protozoa to vertebrates, we tested whether two fundamental determinants of local dynamics, top-down and bottom-up control, generally explain active dispersal. We show that both factors consistently increased emigration rates and use metacommunity modelling to highlight consequences on local and regional dynamics.

New records of host-parasite relationships between Coenagrion scitulum (Rambur, 1842) (Odonata) and water mite larvae (Hydrachnidia) in core and edge host populations.

The relationships between water mite larvae parasitizing Coenagrion scitulum in core and edge populations were described. A total of 636 larvae of 7 water mite species were found on 143 C. scitulum adults (82 females and 61 males). C. scitulum was recorded for the first time as a host species for Arrenurus cuspidator, A. bruzelii, A. bicuspidator, A. tricuspidator, A. claviger and Hydryphantes octoporus. The degree of infestation by particular parasite species was typical for these species. In contrast, the parasites' preferences for host body parts were not typical, as they preferred abdominal segments 2-4, which in earlier studies had been avoided by water mite larvae. No differences were found in degree of infestation of Coenagrion scitulum individuals between core and edge populations, with the exception of Hydryphantes octoporus, which parasitized damselflies only in core populations.

Delayed effects of chlorpyrifos across metamorphosis on dispersal-related traits in a poleward moving damselfly.

How exposure to contaminants may interfere with the widespread poleward range expansions under global warming is largely unknown. Pesticide exposure may negatively affect traits shaping the speed of range expansion, including traits related to population growth rate and dispersal-related traits. Moreover, rapid evolution of growth rates during poleward range expansions may come at a cost of a reduced investment in detoxification and repair thereby increasing the vulnerability to contaminants at expanding range fronts. We tested effects of a sublethal concentration of the widespread pesticide chlorpyrifos on traits related to range expansion in replicated edge and core populations of the poleward moving damselfly Coenagrion scitulum reared at low and high food levels in a common garden experiment. Food limitation in the larval stage had strong negative effects both in the larval stage and across metamorphosis in the adult stage. Exposure to chlorpyrifos during the larval stage did not affect larval traits but caused delayed effects across metamorphosis by increasing the incidence of wing malformations during metamorphosis and by reducing a key component of the adult immune response. There was some support for an evolutionary trade-off scenario as the faster growing edge larvae suffered a higher mortality during metamorphosis. Instead, there was no clear support for the faster growing edge larvae being more vulnerable to chlorpyrifos. Our data indicate that sublethal delayed effects of pesticide exposure, partly in association with the rapid evolution of faster growth rates, may slow down range expansions.

Rapid evolution of increased vulnerability to an insecticide at the expansion front in a poleward-moving damselfly.

Many species are too slow to track their poleward-moving climate niche under global warming. Pesticide exposure may contribute to this by reducing population growth and impairing flight ability. Moreover, edge populations at the moving range front may be more vulnerable to pesticides because of the rapid evolution of traits to enhance their rate of spread that shunt energy away from detoxification and repair. We exposed replicated edge and core populations of the poleward-moving damselfly Coenagrion scitulum to the pesticide esfenvalerate at low and high densities. Exposure to esfenvalerate had strong negative effects on survival, growth rate, and development time in the larval stage and negatively affected flight-related adult traits (mass at emergence, flight muscle mass, and fat content) across metamorphosis. Pesticide effects did not differ between edge and core populations, except that at the high concentration the pesticide-induced mortality was 17% stronger in edge populations. Pesticide exposure may therefore slow down the range expansion by lowering population growth rates, especially because edge populations suffered a higher mortality, and by negatively affecting dispersal ability by impairing flight-related traits. These results emphasize the need for direct conservation efforts toward leading-edge populations for facilitating future range shifts under global warming.

Variation in innate immunity in relation to ectoparasite load, age and season: a field experiment in great tits (Parus major).

It remains largely unknown which factors affect the innate immune responses of free-living birds. Nevertheless, the degree of innate immunity may play a crucial role in an individual's survival as it procures the first defence against pathogens. We manipulated the ectoparasite load of great tit (Parus major) nests by infesting them with hen fleas (Ceratophyllus gallinae) before egg laying. We subsequently quantified natural antibody (NAb) concentration and complement activation in nestlings and adult females during breeding and post-breeding periods. NAb concentrations increased in nestlings and adult females breeding in flea-infested nest boxes during the nestling provisioning period, but not in breeding females during incubation. In contrast, parasite abundance did not affect levels of complement activity in females. NAb levels of nestlings were already fully developed at the end of the nestling stage, but complement activation was only observed post-fledging. Concentrations of NAbs and complement activation of adult females were significantly lower during the breeding season compared with post-breeding levels, but did not differ between incubation and chick rearing. Further experimental studies in species that vary in life-history strategies will allow us to unravel the mechanisms underlying the observed variation in innate immune defences.