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. Keywords: context-dependent dispersal; dispersal strategy; distributed experiment; predation risk; resource limitatio

Evolutionary ecology of a damselfly during range expansion

Ranges of manyspecies are shifting polewards in response to contemporary global warming. Rangeshifting species experience different selective forces at the expansion frontcompared with these experienced at the core of their range and this can havelarge impacts on the evolution of phenotypic traits at the expansion front.Determining changes in phenotypic traits during range expansion is important aschanges in traits may influence the rate of further range expansion, abioticinteractions and biotic interactions at the expansion front. Inthis thesis I combined field studies, indoor common garden experiments andoutdoor mesocosm experiments to obtain a multivariate picture on the traitdifferentiation and associated changes in (a)biotic interactions during thepoleward range expansion of the damselfly Coenagrionscitulum. Phenotypicdifferentiation associated with northward range expansion Two importantaspects may induce evolution in phenotypic traits during range expansion.Firstly, populations at the expansion front are assorted by dispersal ability,whereby only the best dispersers colonize the expansion front. Secondly,population densities in newly founded populations at the expansion front arelow which may change selection regimes for life-history traits. Besides effectsof the range expansion process per se, also geographically structured thermalregimes may contribute to changes in phenotypic traits during range expansion.Geographicallystructured thermal regimes in both the larval (length of the growth season) andadult stage (adult flight period temperature) had an impact on different traitsinvestigated. Yet, importantly, these temperature regimes had only a smallcontribution to the phenotypic differentiation between core and edgepopulations. I documented in different studies changes in flight-related traitsthat indicate a better flight ability at the expansion front. I found higherinvestment in flight muscle mass, a lower wing loading and a larger relativethorax length at the range expansion front of C. scitulum. Higher flight ability at the expansion front mayevolve through natural selection whereby individuals that disperse most rapidlyat the expansion front benefit from the low densities of conspecifics at therange edge, and through spatial sorting in dispersal ability. Linked to theevolution of higher dispersal ability, adults at the expansion front had ahigher immune response (encapsulation response). Selection for a highinvestment in immune function to lower parasite load may occur through anegative effect of high parasite load on dispersal ability. Theory predictsselection for a higher population growth rate at the expansion front, which isfavoured at the low population densities in newly colonized habitats. At theexpansion front of C. scitulum Idocumented faster larval growth and development, while fecundity did not differbetween core and edge females. I documented for the first time, an increase ofactivity level in the non-dispersive larval stage at the expansion front; whileno higher activity in adults at the expansion front was detected. My resultsindicated that the higher larval activity at the expansion front evolved tomeet a higher energy demand in edge populations that is allocated to fastergrowth and higher investment in flight-related traits at the expansion front. Abiotic andbiotic interactions at the expansion frontLow foodconditions and high competition had a negative effect on growth rate of larvae;additionally low food conditions in the larval stage decreased investment inflight muscle mass hence likely dispersal ability. Furthermore, my results suggesta higher susceptibility of edge larvae to food limitation, which highlights theimportance of optimal local conditions at the expansion front for animalfitness and further range expansion. In contrast, winter survival was nothigher in edge larvae, indicating that no thermal adaptation for enhancedwinter survival at the expansion front occurred.Thehigher investment in dispersal, faster life history and higher larval activitywas expected to influence biotic interactions at the expansion front. Higherlarval activity and growth at the expansion front may increase visibility tovisual predators, hence was expected to increase predation risk by Anax imperator larvae. Furthermore,given that higher activity and growth rates typically are associated with abetter competitive ability, we predicted larvae at the expansion front to besuperior competitors relative to larvae from core populations. In contrast tothese expectations, we did not find a difference in predator-prey interactionsnor larval competitive ability between core and edge larvae. The relativelysmall changes in larval growth and activity during the range expansion of C. scitulum may be too small to have aprofound impact on the studied biotic interactions. Sexual selection for higherflight duration of males was consistent in core and edge populations. Incontrast, I detected geographical patterns in sexual selection for male bodysize and fat content, however these geographical patterns were rather shaped bydifferences in thermal regimes than by processes associated with rangeexpansion per se.My study not only adds to thegrowing number of studies that document rapid evolutionary changes in dispersaland life-history during range expansion, but also contributes to the scarcestudies investigating abiotic and biotic interactions at the expansion front.Furthermore, my study is the first to document the evolution of a higher adultimmune response and a higher activity level in the non-dispersive larval stageat the expansion front, which may give rise to eco-evolutionary dynamics. 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What factors shape female phenotypes of a poleward-moving damselfly at the edge of its range?

Individuals at the expansion front during a climate-driven range expansion are expected to differ phenotypically from those individuals in core populations. Little information is known about the joint, potentially opposing, effects of stressful conditions at the range edge versus evolutionary changes that take place during range expansion in shaping the phenotypes at the range front. We investigated the effect of range expansion on immune function, body condition and flight-related morphology (flight muscle ratio, wing loading, and wing aspect ratio) of field-collected females of the poleward-moving damselfly Coenagrion scitulum. Individuals at the expansion front had a lower body condition, which indicated more stressful conditions at the range edge. Despite the counteracting effect of the shorter growth season, the higher flight muscle ratios at the expansion front indicated a strong selection for dispersal ability during range expansion. The current study suggests that models need to incorporate the interplay of stressful conditions and evolutionary processes at the expansion front to arrive at robust predictions of future species distributions under global warming.© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 556-568.status: publishe

Sexual selection on flight endurance, flight-related morphology and physiology in a scrambling damselfly

We have limited knowledge on the mechanistic base of sexual selection, especially in scrambling species. This asks for a functional approach that explores the link between each component of the phenotype-performance-fitness axis and that includes both morphological and physiological traits. We explored the phenotype-performance-fitness axis in the scrambling damselfly Coenagrion puella by studying the links between a set of physiological and morphological traits, flight performance (flight speed and flight endurance), and short-term mating success. As expected for scrambling competition, there was sexual selection for increased flight endurance rather than for increased flight speed. For fat content, we could demonstrate the full phenotype-performance-fitness axis, where selection for a higher fat content could be explained by the sexual selection for a higher flight endurance and the positive covariation between fat content and flight endurance. For three other traits (size, relative flight muscle mass and wing loading), however, we detected selection that could not be explained via their effect on flight performance, generating novel testable hypotheses about how the covariation between these traits and mating success is generated. This also urges caution when using morphological traits as proxies for flight speed and flight endurance in phenotypic selection studies. © 2014 Springer International Publishing Switzerland.status: publishe

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.status: publishe

Increased activity and growth rate in the non-dispersive aquatic larval stage of a damselfly at an expanding range edge

While evolutionary changes in adult traits during range expansion have been recorded in many species, similar changes in the non-dispersive larval stage have only rarely been documented. Increased activity in the non-dispersive larval stage is an important ecologically relevant trait in aquatic communities that may be expected to evolve in the edge populations (i) as a result of the combination of spatial sorting in dispersal-related adult activity and a coupling between adult and larval behaviour and (ii) to meet higher energy demands to allow higher growth rates and a higher investment in costly dispersal-related traits. We specifically address whether activity is higher in the larval non-dispersive aquatic stage at an expanding range front by comparing larvae of replicated core and edge populations of the damselfly Coenagrion scitulum in three common garden experiments where larvae were reared from the egg stage. As expected, activity in the non-dispersive larval stage was consistently higher in the edge populations. Although changes in larval activity probably have consequences for ecological interactions, the higher activity was not associated with increased predation rates by dragonfly larvae, potentially because of associated compensatory changes in other antipredator mechanisms. We documented one of the few cases of a positive coupling of activity in the larval and adult stages. Yet, contrary to larval activity, adult activity did not differ between core and edge populations. This indicates that the higher larval activity we documented is not shaped by a coupling with adult activity. Instead, our results are consistent with the hypothesis that a higher energy need in edge populations shaped the higher larval activity. Edge larvae showed a higher growth rate which is expected to evolve at the initial low population densities in newly founded edge populations. Moreover, higher growth rate showed the expected positive covariation with larval activity. Increases in activity in the non-dispersive stage in edge populations at an expansion front should be included in the ongoing debate whether evolutionary changes at invasion fronts are driven by adaptive versus non-adaptive evolution. Moreover, they may have the potential to affect ecological interactions at expanding range fronts. © 2014 John Wiley & Sons Ltd.status: publishe

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.publisher: Elsevier articletitle: Delayed effects of chlorpyrifos across metamorphosis on dispersal-related traits in a poleward moving damselfly journaltitle: Environmental Pollution articlelink: http://dx.doi.org/10.1016/j.envpol.2016.07.047 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe