Colette M. St. Mary

Secondary defenses can reduce predation risk by altering predator behavior, but their evolution may be constrained when defended prey are indistinguishable from undefended individuals. This is particularly relevant for soft-bodied prey, for which predator attacks are lethal regardless of defense level, such that the benefits of defense are frequency-dependent. We developed two sets of evolutionary models to investigate how secondary defense evolves in the presence vs. absence of signals that allow predators to distinguish defended from undefended prey. First, we used deterministic evolutionary game theory to examine the stability of defended and undefended strategies across attack likelihoods, defense levels, and initial frequencies of defended prey. Second, we developed stochastic, multi-generational models in which predators optimized foraging decisions according to their energetic state, allowing selection to emerge from state-dependent predator behavior. For both model sets, undefended prey were evolutionarily stable when predation pressure was low, whereas stronger predation favored defended phenotypes. However, in the absence of signals defended and undefended prey frequently coexisted, with stable mixed populations emerging when predation pressure was sufficiently high, defense levels low, and the initial proportion of defended prey was above a threshold frequency. In contrast, when signals were present, mixed equilibria were generally unstable and highly defended prey frequently displaced other phenotypes, particularly under high predation pressure. Stochastic models produced similar patterns while demonstrating that 1. prey population size influenced the likelihood of invasion by defended phenotypes, with smaller populations being more conducive to invasion; 2. qualitative patterns similar to the deterministic models emerged when selection was dependent on predators’ state-dependent behavior. Our results identify conditions under which inconspicuous, costly secondary defenses can persist even when defense provides no benefit to the individual, presenting a plausible route towards the evolution of phenomena such as aposematism.

Immune responses are crucial to not only control within‐host disease dynamics and potential negative outcomes to host health but also impose energetic trade‐offs with growth and other physiological processes. Although these trade‐offs play an important role in disease outcomes, we lack mathematical models that mechanistically describe how variations in energy investment and parental reproductive timing influence offspring survival under seasonal pathogen dynamics. Here, we determine the strategies (set of tactics—growth versus immune defence—over time) that maximize host fitness under persistent infections by implementing dynamic optimization state models. We modelled individual trajectories for 1 year and accounted for natural fluctuations in resource availability. We parameterized the model using field and experimental data from a well‐studied host–pathogen system: the coqui frog ( Eleutherodactylus coqui ) and the amphibian chytrid fungus ( Batrachochytrium dendrobatidis ). This data from field monitoring and controlled experiments enable robust parameter estimation and subsequent validation using empirical data. Our models identified critical windows that maximize individual growth while limiting mortality under increased pathogen burden. Individuals generally chose growth but shifted to defence when approaching near‐lethal infection levels. Seasonality in pathogen exposure and foraging success exacerbated growth–defence trade‐offs, leading to delayed maturity and lower survival rates when frogs hatched under unfavourable conditions. Our simulations provide a mechanistic view that explains empirical results showing that periods of highest reproductive activity align with high‐resource availability and low pathogen risk. Furthermore, our findings demonstrate that shifts in energy‐allocation modulate infections and constrain fitness traits. Our results highlight the utility of dynamic state‐variable models to examine how host fitness strategies impact early‐life growth rates and recruitment (number of offspring reaching maturity). We provide detailed instructions that allow extending the application of this model to other systems. By adjusting parameter values using empirical data, this model approach can be applied to predict fitness under current and future conservation challenges, such as extreme droughts and pathogen outbreaks, and to identify the optimal time for releasing individuals in species reintroduction programmes.

Synopsis: The organization of the living world covers a vast range of spatiotemporal scales, from molecules to the biosphere, seconds to centuries. Biologists working within specialized subdisciplines tend to focus on different ranges of scales. Therefore, developing frameworks that enable testing questions and predictions of scaling requires sufficient understanding of complex processes across biological subdisciplines and spatiotemporal scales. Frameworks that enable scaling across subdisciplines would ideally allow us to test hypotheses about the degree to which explicit integration across spatiotemporal scales is needed for predicting the outcome of biological processes. For instance, how does genomic variation within populations allow us to explain community structure? How do the dynamics of cellular metabolism translate to our understanding of whole-ecosystem metabolism? Do patterns and processes operate seamlessly across biological scales, or are there fundamental laws of biological scaling that limit our ability to make predictions from one scale to another? Similarly, can sub-organismal structures and processes be sufficiently understood in isolation of potential feedbacks from the population, community, or ecosystem levels? And can we infer the sub-organismal processes from data on the population, community, or ecosystem scale? Concerted efforts to develop more cross-disciplinary frameworks will open doors to a more fully integrated field of biology. In this paper, we discuss how we might integrate across scales, specifically by (1) identifying scales and boundaries, (2) determining analogous units and processes across scales, (3) developing frameworks to unite multiple scales, and (4) extending frameworks to new empirical systems.

Antipredatory displays that incorporate hidden contrasting coloration are found in a variety of different animals. These displays are seen in organisms that have drab coloration at rest, but when disturbed reveal conspicuous coloration. Examples include the bright abdomens of mountain katydids and the colorful underwings of hawk moths. Such hidden displays can function as secondary defenses, enabling evasion of a pursuant predator. To begin to understand why some species have these displays while others do not, we conducted phylogenetic comparative analyses to investigate factors associated with the evolution of hidden contrasting coloration in leaf‐footed bugs. First, we investigated whether hidden contrasting coloration was associated with body size because these displays are considered to be more effective in larger organisms. We then investigated whether hidden contrasting coloration was associated with an alternative antipredatory defense, in this case rapid autotomy. We found that leaf‐footed bugs with hidden contrasting coloration tended to autotomize more slowly, but this result was not statistically significant. We also found that the presence of a body size association was dependent upon the form of the hidden color display. Leaf‐footed bugs that reveal red/orange coloration were the same size, on average, as species without a hidden color display. However, species that reveal white patches on a black background were significantly larger than species without a hidden color display. These results highlight the diversity of forms that hidden contrasting color signal can take, upon which selection may act differently.

Sacrificing body parts is one of many behaviors that animals use to escape predation. This trait, termed autotomy, is classically associated with lizards. However, several other taxa also autotomize, and this trait has independently evolved multiple times throughout Animalia. Despite having multiple origins and being an iconic antipredatory trait, much remains unknown about the evolution of autotomy. Here, we combine morphological, behavioral, and genomic data to investigate the evolution of autotomy within leaf‐footed bugs and allies (Insecta: Hemiptera: Coreidae + Alydidae). We found that the ancestor of leaf‐footed bugs autotomized and did so slowly; rapid autotomy (<2 min) then arose multiple times. The ancestor likely used slow autotomy to reduce the cost of injury or to escape nonpredatory entrapment but could not use autotomy to escape predation. This result suggests that autotomy to escape predation is a co‐opted benefit (i.e., exaptation), revealing one way that sacrificing a limb to escape predation may arise. In addition to identifying the origins of rapid autotomy, we also show that across species variation in the rates of autotomy can be explained by body size, distance from the equator, and enlargement of the autotomizable appendage.

Understanding yeast dynamics during fermentation is important for quality control, whether monitoring fermentation consistency or identifying aberrant events, such as premature yeast flocculation (PYF). Previous models of fermentation dynamics tend to be parameter rich and require large time series, which are rare in industry. This research investigates five simpler models to 1) describe fermentation dynamics, 2) refine quality control sampling regimes to improve model fit, and 3) identify PYF fermentations. The ability of these models to describe yeast dynamics was evaluated using model fitting with time series data and Akaike Information Criterion (AIC) model selection. Data simulated from large time series was used with this model fitting approach to improve sampling schedules without increasing sampling effort. Lastly, PYF was identified in fermentations of fungal-contaminated malt using linear discriminant analysis (LDA). For large data sets, a four-parameter extension of the normal curve performed best while smaller data sets were better described by the 2-parameter gamma model. Moving sampling effort nearer the population peak improved model fits. Lastly, all models detected PYF, however the two-parameter gamma model provided a simple metric for distinguishing PYF. This research provides guidelines on appropriate model use, improving sampling regimes, and identifying PYF.

Relatively few studies have addressed fishery-induced-evolution of sequential hermaphrodites although declines in the mean size-at-maturation and/or sex change have been documented for several species. We sought to explore the evolutionary impacts of size-selective exploitation on maturation and sex change of a protogynous hermaphrodite using an individual-based model accounting for growth, survival, maturation, sex change, and reproduction. Because sex change rules are unknown for many exploited species, critical size-at-sex change (static and genetic control) and social control of sex change were evaluated to determine how life-history-traits (maturation, sex change) and population reference points change due in part to evolution. When simulating critical size-at-sex change, mean length-at-maturation increased, contrary to typical predictions for dioecious species, and mean length-at-sex change decreased (when under genetic control) from exploitation. These changes occurred slowly and resulted in lower male: female sex ratios, sperm limitation, and extirpation at high exploitation rates. Under social control of sex change, both the mean lengths-at-maturation and sex change decreased relatively rapidly from exploitation. These populations maintained high male: female sex ratios, avoided sperm limitation, and withstood higher exploitation rates than critical size-at-sex change populations. Results from these models highlight the need for a better understanding of sex change rules for exploited hermaphrodites.