Water Stress Affects Development Time but Not Takeoff Performance in the Butterfly Pararge aegeria

The maternal energetic environment affects both egg and offspring phenotypes in green anole lizards (Anolis carolinensis)

Animals exist in dynamic environments that may affect both their own fitness and that of their offspring. Maternal effects might allow mothers to prepare their offspring for the environment in which they will be born via several mechanisms, not all of which are well understood. Resource scarcity and forced resource allocation are two scenarios that could affect maternal investment by altering the amount and type of resources available for investment in offspring, albeit in potentially different ways. We tested the hypothesis that maternal dietary restriction and sprint training have different consequences for the offspring phenotype in an oviparous lizard (Anolis carolinensis). To do this, we collected and reared eggs from adult diet-manipulated females (low-diet [LD] or high-diet [HD]) and sprint-trained females (sprint trained [ST] or untrained [UT]) and measured both egg characteristics and hatchling morphology. ST and LD mothers laid both the fewest and heaviest eggs, and ST, UT, and LD eggs also had significantly longer incubation periods than the HD group. Hatchlings from the diet experiment (LD and HD offspring) were the heaviest overall. Furthermore, both body mass of the mother at oviposition and change in maternal body mass over the course of the experiment had significant and sometimes different effects on egg and offspring phenotypes, highlighting the importance of maternal energetic state to the allocation of maternal resources.

Conserved and convergent mechanisms underlying performance-life-history trade-offs

Phenotypic trade-offs are inevitable in nature, but the mechanisms driving them are poorly understood. Movement and oxygen are essential to all animals, and as such, the common ancestor to all living animals passed on mechanisms to acquire oxygen and contract muscle, sometimes at the expense of other activities or expression of traits. Nevertheless, convergent pathways have also evolved to deal with critical trade-offs that are necessary to survive ubiquitous environmental challenges. We discuss how whole-animal performance traits, such as locomotion, are important to fitness, yet costly, resulting in trade-offs with other aspects of the phenotype via specific conserved and convergent mechanistic pathways across all animals. Specifically, we discuss conserved pathways involved in muscle structure and signaling, insulin/insulin-like signaling, sirtuins, mitochondria and hypoxia-inducible factors, as well as convergent pathways involved in energy regulation, development, reproductive investment and energy storage. The details of these mechanisms are only known from a few model systems, and more comparative studies are needed. We make two main recommendations as a framework for future studies of animal form and function. First, studies of performance should consider the broader life-history context of the organism, and vice versa, as performance expression can require a large portion of acquired resources. Second, studies of life histories or mechanistic pathways that measure performance should do so in meaningful and standardized ways. Understanding proximate mechanisms of phenotypic trade-offs will not only better explain the phenotypes of the organisms we study, but also allow predictions about phenotypic variation at the evolutionary scale.

Sub-lethal viral exposure and growth on drought stressed host plants changes resource allocation patterns and life history costs in the Speckled Wood butterfly, Pararge aegeria

This study investigated the interactive effects of growth on drought stressed host plants and pathogen challenge with the baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) on survival and fitness-related traits using the Speckled Wood butterfly, Pararge aegeria (L.). Exposure to AcMNPV significantly reduced survival to pupation. For surviving larvae, sub-lethal infection significantly decreased daily mass acquisition rates and pupal mass. Growth on drought stressed plants increased daily mass acquisition rates resulting in heavier pupae, and increased resource allocation to adult reproduction. The interaction between host plant drought and viral exposure resulted in different resource allocation strategies, and thus different growth trajectories, between larvae. This in turn resulted in significantly different allometric relationships between larval mass (at inoculation) and both development time and investment in flight muscles. For larvae with relatively lighter masses there was a cost of resisting infection when growth occurred on drought stressed host plants, both within the larval stage (i.e. longer larval development times) and in the adult stage (i.e. lower investment in flight muscle mass). This multi-factor study highlights several potential mechanisms by which the complex interplay between low host plant nutritional quality due to drought, and pathogen exposure, may differentially influence the performance of P. aegeria individuals across multiple life stages.