Defining fitness in evolutionary ecology

Demystifying Fundamental Theories in Ecology

AbstractAs scientists, our collective goal is to make scientific progress in the pursuit of an absolute truth about the nature of the universe, through a feedback loop of observation, theory, and experimentation. What if a major limit to progress is not the science itself but rather in how broadly scientific ideas can be understood? In this introduction to a special feature, we highlight four articles, each tasked with demystifying a key theory in ecology for a general audience, with a special focus on aspects of each theory that have been misunderstood, misapplied, or underappreciated in some important way. These four theories are metabolic theory, competition theory based on consumer-resource models, mechanisms of coexistence in fluctuating environments, and metapopulation dynamics. We point out key ways in which each article applied best practices of accessible communication as well as challenges that might arise (and potential solutions for journals and authors) when attempting to publish articles with a deeper emphasis on explanation of fundamentals than a traditional article might provide.

Increasing Aridity May Threaten the Maintenance of a Plant Defence Polymorphism

It is unclear how environmental change influences standing genetic variation in wild populations. Here, we characterised environmental conditions that protect versus erode polymorphic chemical defences in Boechera stricta (Brassicaceae), a short-lived perennial wildflower. By manipulating drought and herbivory in a 4-year field experiment, we measured the effects of driver variation on vital rates of genotypes varying in defence chemistry and then assessed interacting driver effects on total fitness (estimated as each genotype's lineage growth rate, λ) using demographic models. Drought and herbivory interacted to shape vital rates, but contrasting defence genotypes had equivalent total fitness in many environments. Defence polymorphism thus may persist under a range of conditions; however, ambient field conditions fall close to the boundary of putatively polymorphic environment space, and increasing aridity may drive populations to monomorphism. Consequently, elevated intensity and/or frequency of drought under climate change may erode genetic variation for defence chemistry in B. stricta.

Kin discrimination causes plastic responses in floral and clonal allocation

The composition of a plant's neighbourhood shapes its competitive interactions. Neighbours may be related individuals due to limited seed dispersal or clonal growth, so that the ability to recognize and respond to the presence of kin is beneficial. Here, we ask whether plants plastically adjust their floral and clonal allocation in response to their neighbour's identity. In a species that reproduces both sexually and clonally, we test the following predictions in response to neighbouring kin: (i) a reduction in floral display will occur to minimize costly floral structures and pollinator competition, as well as to mitigate inbreeding; and (ii) a decrease in clonality will occur to minimize resource competition and overcrowding among kin. We grew focal individuals of Mimulus guttatus (syn. Erythranthe guttata) surrounded by neighbours of varying relatedness (non-kin, outcross siblings or self siblings) and measured a suite of vegetative, floral and clonal traits. Consistent with our predictions, focal plants reduced floral and clonal allocation in the presence of kin. Moreover, focal plants increased their floral and clonal allocation when surrounded by non-kin neighbours that were high-performing. Together, we demonstrate a clear and predictable response to kin, which has general implications for the structure and function of plant neighbourhoods.

Nonlinear transcriptomic responses to compounded environmental changes across temperature and resources in a pest beetle, Callosobruchus maculatus (Coleoptera: Chrysomelidae)

Many species are experiencing drastic and multidimensional changes to their environment due to anthropogenic events. These multidimensional changes may act nonadditively on physiological and life history responses, and thus may not be predicted by responses to single dimensional environmental changes. Therefore, work is needed to understand species' responses to multiple aspects of change. We used whole-transcriptomic RNA-Sequencing and life history assays to uncover responses to singly-applied shifts in resource or temperature environmental dimensions, in comparison to combined, multidimensional change, in the crop pest seed beetle, Callosobruchus maculatus. We found that multidimensional change caused larger fecundity, developmental period and offspring viability life history changes than predicted by additive effects of 1-dimensional changes. In addition, there was little overlap between genes differentially expressed under multidimensional treatment versus under altered resource or temperature conditions alone. Moreover, 115 genes exhibited significant resource × temperature interaction effects on expression, including those involved in energy metabolism, detoxification, and enhanced formation of cuticle structural components. We conclude that single dimensional changes alone cannot determine life history and transcriptomic responses to multidimensional environmental change. These results highlight the importance of studying multidimensional environmental change for understanding the molecular and phenotypic responses that may allow organisms including insects to rapidly adapt simultaneously to multiple aspects of environmental change.