Biology subjects

MacDonald, A. A. M.

Publications and source records attributed to MacDonald, A. A. M..

3 recordsLinked to original sources

bioRxiv2026

Epistasis and an oligogenic architecture underlie the strength of a plant-herbivore interaction

1. Interaction strength between consumers and resources is a fundamental driver of eco-evolutionary dynamics, and its genetic architecture is key to predicting the pace of such dynamics. Our understanding of this architecture is limited for three reasons: (i) defense phenotypes do not necessarily translate to interaction strength; (ii) interaction strength is difficult to measure in ways tied to consumer-resource theory; and (iii) association studies typically prioritize detecting large-effect loci rather than characterizing whether interactions are polygenic (many small-effect genes) or oligogenic (few large-effect genes). 2. We address these gaps by examining how genomic variation in the plant Arabidopsis thaliana influences interactions with the aphid herbivore Lipaphis pseudobrassicae in a greenhouse experiment. We grew 390 accessions spanning the species' natural range and measured aphid per-capita population growth as our interaction-strength metric. To test whether a previously identified plant defense gene (AOP2) acts additively or epistatically with other defense loci, we integrated our estimates of aphid population growth with public data on defense chemistry and gene expression. To determine whether the genetic architecture of interaction strength was polygenic or oligogenic, we used a Bayesian sparse linear mixed model that partitions these two components. 3. AOP2 showed epistasis with two other defense genes (MAM1 and GS-OH), indirectly modifying aphid population growth via the production of a specific defense compound (glucosinolate 2-hydroxy-3-butenyl). More broadly, interaction strength showed an oligogenic architecture: top single nucleotide polymorphisms (SNPs) occurred at low minor allele frequencies (< 3%) and grouped into six linkage disequilibrium blocks, including candidate genes outside canonical plant defense pathways. These six blocks explained 47% of the genetic variance in interaction strength, with only 3% additional variance attributable to polygenic effects. 4. Taken together, these results show that plant genomic variation modifies herbivore interaction strength through epistasis among defense genes and rare alleles at few loci. This oligogenic architecture imposes multiple constraints on the potential for rapid evolution, highlighting the need to integrate genomic effects into eco-evolutionary models.

ecology↗

bioRxiv2020

Climate influences the response of community functional traits to local conditions

Functional traits determine an organisms performance in a given environment and as such determine which organisms will be found where. Species respond to local conditions, but also to larger scale gradients, such as climate. Trait ecology links these responses of species to community composition and species distributions. Yet, we often do not know which environmental gradients are most important in determining community trait composition at either local or biogeographical scales, or their interaction. Here we quantify the relative contribution of local and climatic conditions to the structure and composition of functional traits found within bromeliad invertebrate communities. We conclude that climate explains more variation in invertebrate trait composition within bromeliads than does local conditions. Importantly, climate mediated the response of traits to local conditions; for example, invertebrates with benthic life-history traits increased with bromeliad water volume only under certain precipitation regimes. Our ability to detect this and other patterns hinged on the compilation of multiple fine-grained datasets, allowing us to contrast the effect of climate vs. local conditions. We suggest that, in addition to sampling communities at local scales, we need to aggregate studies that span large ranges in climate variation in order to fully understand trait filtering at local, regional and global scales.

ecology↗

bioRxiv2016

Predator phylogenetic diversity decreases predation rate via antagonistic interactions

BackgroundPredator assemblages can differ substantially in their top-down effects on community composition and ecosystem function, but few studies have sought to explain this variation in terms of the phylogenetic distance between predators. The effect of a local predator assemblage will depend on three things - which predators tend to co-occur, how similar their prey preferences are, and how they interact with each other and the whole community. Phylogenetic distance between predators may correlate with each of these processes, either because related predators are more likely to share the same traits, and therefore have similar habitat and prey preferences, or because predators are more likely to compete, and therefore diverge in habitat and prey preferences. Therefore, the phylogenetic structure of predator assemblages could provide a unifying framework for predicting how predators will impact their prey - and therefore any ecosystem functions mediated by their prey.\n\nMethodsWe examined the effects of predators on macroinvertebrate food webs found in bromeliads, combining field observations, laboratory feeding trials and a manipulative experiment. We determined whether the phylogenetic distance between predators could explain: the co-observed occurrence of predator species among bromeliads, overlap in prey preferences under no-choice conditions, and effects of predator composition on prey survival, prey composition and ecosystem processes.\n\nResultsWe found that phylogenetic distance does not predict either the co-occurrence of predator species nor the overlap in their prey preferences. However, our manipulative experiment showed that prey mortality decreased as the phylogenetic distance between predator species increased, reflecting antagonistic interactions among more distant predators. These effects of phylogenetic distance on prey mortality did not translate into effects on ecosystem function, as measured by rates of detrital decomposition and nitrogen cycling.\n\nDiscussionWe conclude that the effects of predator phylogenetic diversity on the bromeliad food web are primarily determined by antagonistic predator-predator interac-tions, rather than habitat distribution or diet overlap. This study illustrates the potential of a phylogenetic community approach to understanding food webs dynamics.

ecology↗