On the evolution of trophic position.

The trophic structure of food webs is primarily determined by the variation in trophic position among species and individuals. Temporal dynamics of food web structure are central to our understanding of energy and nutrient fluxes in changing environments, but little is known about how evolutionary processes shape trophic position variation in natural populations. We propose that trophic position, whose expression depends on both environmental and genetic determinants of the diet variation in individual consumers, is a quantitative trait that can evolve via natural selection. Such evolution can occur either when trophic position is correlated with other heritable morphological and behavioural traits under selection, or when trophic position is a target of selection, which is possible if the fitness effects of prey items are heterogeneously distributed along food chains. Recognising trophic position as an evolving trait, whose expression depends on the food web context, provides an important conceptual link between behavioural foraging theory and food web dynamics, and a useful starting point for the integration of ecological and evolutionary studies of trophic position.

Non-additive effects of foundation species determine the response of aquatic ecosystems to nutrient perturbation.

Eutrophication is a persistent threat to aquatic ecosystems worldwide. Foundation species, namely those that play a central role in the structuring of communities and functioning of ecosystems, are likely important for the resilience of aquatic ecosystems in the face of disturbance. However, little is known about how interactions among such species influence ecosystem responses to nutrient perturbation. Here, using an array (N = 20) of outdoor experimental pond ecosystems (15,000 L), we manipulated the presence of two foundation species, the macrophyte Myriophyllum spicatum and the mussel Dreissena polymorpha, and quantified ecosystem responses to multiple nutrient disturbances, spread over two years. In the first year, we added five nutrient pulses, ramping up from 10 to 50 µg P/L over a 10-week period from mid-July to mid-October, and in the second year, we added a single large pulse of 50 µg P/L in mid-October. We used automated sondes to measure multiple ecosystems properties at high frequency (15-minute intervals), including phytoplankton and dissolved organic matter fluorescence, and to model whole-ecosystem metabolism. Overall, both foundation species strongly affected the ecosystem responses to nutrient perturbation, and, as expected, initially suppressed the increase in phytoplankton abundance following nutrient additions. However, when both species were present, phytoplankton biomass increased substantially relative to other treatment combinations: non-additivity was evident for multiple ecosystem metrics following the nutrient perturbations in both years but was diminished in the intervening months between our perturbations. Overall, these results demonstrate how interactions between foundation species can cause surprisingly strong deviations from the expected responses of aquatic ecosystems to perturbations such as nutrient additions.

Dietary-based developmental plasticity affects juvenile survival in an aquatic detritivore.

Developmental plasticity is ubiquitous in natural populations, but the underlying causes and fitness consequences are poorly understood. For consumers, nutritional variation of juvenile diets is probably associated with plasticity in developmental rates, but little is known about how diet quality can affect phenotypic trajectories in ways that might influence survival to maturity and lifetime reproductive output. Here, we tested how the diet quality of a freshwater detritivorous isopod (Asellus aquaticus), in terms of elemental ratios of diet (i.e. carbon : nitrogen : phosphorus; C : N : P), can affect (i) developmental rates of body size and pigmentation and (ii) variation in juvenile survival. We reared 1047 individuals, in a full-sib split-family design (29 families), on either a high- (low C : P, C : N) or low-quality (high C : P, C : N) diet, and quantified developmental trajectories of body size and pigmentation for every individual over 12 weeks. Our diet contrast caused strong divergence in the developmental rates of pigmentation but not growth, culminating in a distribution of adult pigmentation spanning the broad range of phenotypes observed both within and among natural populations. Under low-quality diet, we found highest survival at intermediate growth and pigmentation rates. By contrast, survival under high-quality diet survival increased continuously with pigmentation rate, with longest lifespans at intermediate growth rates and high pigmentation rates. Building on previous work which suggests that visual predation mediates the evolution of cryptic pigmentation in A. aquaticus, our study shows how diet quality and composition can generate substantial phenotypic variation by affecting rates of growth and pigmentation during development in the absence of predation.

Fifty years of capacity building in the search for new marine natural products.

The Convention on Biological Diversity, and the Nagoya Protocol in particular, provide a framework for the fair and equitable sharing of benefits arising from the utilization of biological resources and traditional knowledge, and ultimately aim to promote capacity-building in the developing world. However, measuring capacity-building is a challenging task due to its intangible nature. By compiling and analyzing a database of scientific peer-reviewed publications over a period of 50 y (1965 to 2015), we investigated capacity-building in global marine natural product discovery. We used publication and authorship metrics to assess how the capacity to become scientifically proficient, prolific, and independent has changed in bioprospecting countries. Our results show that marine bioprospecting is a dynamically growing field of research with continuously increasing numbers of participating countries, publications, and scientists. Yet despite longstanding efforts to promote equitability and scientific independence, not all countries have similarly increased their capacity to explore marine biodiversity within their national jurisdiction areas. Although developing countries show an increasing trend in the number of publications, a few developed countries still account for almost one-half of all publications in the field. Multiple lines of evidence suggest that economic capacity affects how well countries with species-rich marine ecosystems can scientifically explore those resources. Overall, the capacity-building data analyzed here provides a timely contribution to the ongoing international debate about access to and benefit-sharing of biological resources for countries exploring biodiversity within and outside their national jurisdiction areas.

The role of plasticity in the evolution of cryptic pigmentation in a freshwater isopod.

Cryptic pigmentation of prey is often thought to evolve in response to predator-mediated selection, but pigmentation traits can also be plastic, and change with respect to both abiotic and biotic environmental conditions. In such cases, identifying the presence of, and drivers of trait plasticity is useful for understanding the evolution of crypsis. Previous work suggests that cryptic pigmentation of freshwater isopods (Asellus aquaticus) has evolved in response to predation pressure by fish in habitats with varying macrophyte cover and coloration. However, macrophytes can potentially influence the distribution of pigmentation by altering not only habitat-specific predation susceptibility, but also dietary resources and abiotic conditions. The goals of this study were to experimentally test how two putative agents of selection, namely macrophytes and fish, affect the pigmentation of A. aquaticus, and to assess whether pigmentation is plastic, using a diet manipulation in a common garden. We performed two experiments: (a) in an outdoor mesocosm experiment, we investigated how different densities of predatory fish (0/30/60 three-spined stickleback [Gasterosteus aculeatus] per mesocosm) and macrophytes (presence/absence) affected the abundance, pigmentation and body size structure of isopod populations. (b) In a subsequent laboratory experiment, we reared isopods in a common garden experiment on two different food sources (high/low protein content) to test whether variation in pigmentation of isopods can be explained by diet-based developmental plasticity. We found that fish presence strongly reduced isopod densities, particularly in the absence of macrophytes, but had no effect on pigmentation or size structure of the populations. However, we found that isopods showed consistently higher pigmentation in the presence of macrophytes, regardless of fish presence or absence. Our laboratory experiment, in which we manipulated the protein content of the isopods' diet, revealed strong plasticity of pigmentation and weak plasticity of growth rate. The combined results of both experiments suggest that pigmentation of A. aquaticus is a developmentally plastic trait and that multiple environmental factors (e.g. macrophytes, diet and predation) might jointly influence the evolution of cryptic pigmentation of A. aquaticus in nature on relatively short time-scales.