Research

Theme 1: Aging and life history evolution

   

For decades, evolutionary biologists have sought to understand why organisms age and what ecological and evolutionary processes maintain variation in aging among individuals and populations. In contrast, molecular biologists investigate the physiological, molecular, and developmental mechanisms that underlie the aging process. Drawing on diverse natural systems (e.g., butterflies, anurans, and teleost fish), my research integrates these ultimate and proximate perspectives to understand (1) how interactions between organisms and environmental factors - including diet, stressors, and social cues - shape developmental processes that influence aging and life history traits, and (2) how these processes contribute to the evolution of aging. 

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Representative publications:

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Shephard et al (2026) Cryptic genetic variation revealed by diet uncovers a trade-off between growth and telomere length. Evolution.

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Shephard et al. (2023) Metabolic stress as a driver of life history plasticity: flight promotes longevity and antioxidant production in monarch butterflies. Proceedings of the Royal Society B. ​ 

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Theme 2: Organismal and population responses to stressful, changing, or novel environments

   

Individuals and populations are continually exposed to stressful, rapidly changing, or novel environments - from shifts in diet, to predation risk, and anthropogenic pollutants. Why do some organisms persist and others perish in the face of these environmental challenges? My research addresses this question by investigating (1) the mechanisms by which environmental stressors influence phenotypic development both within and across generations, and (2) how these developmental responses influence organismal performance, population persistence, and evolutionary change. 

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Current and past projects related to this theme include:

 

2A. Intergenerational effects of stress

Using three-spine stickleback (Gasterosteus aculeatus), I study how paternal stress exposure affects offspring development and somatic integrity, and the role of non-genetic inheritance mechanisms - particularly sperm-borne small non-coding RNAs - in mediating these intergenerational effects. 

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2B. Carry-over effects of early life environments

Using North American spadefoot toads (Spea), I study how early life nutritional environments shape adult somatic integrity, behavior, and physiology, and the developmental mechanisms underlying these carry-over effects. 

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Representative publications:

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Shephard and Ledón-Rettig (2025) A novel carnivorous diet reduces brain telomere length. Biology Letters.

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Shephard et al. (2024) Corticosterone contributes to diet-induced reprogramming of post-metamorphic behavior in spadefoot toads. Integrative Organismal Biology. 

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​2C. Mechanisms and costs of resistance to anthropogenic pollutants

Using butterflies, I have studied physiological mechanisms contributing to resistance to anthropogenic stressors - including heavy metal pollution, changes in macronutrient availability, and road salt - and the fitness costs and life history trade-offs associated with resistance. 

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Representative publications:

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Shephard et al. (2023) Anthropogenic sodium influences butterfly responses to nitrogen-enriched resources: implications for the nitrogen limitation hypothesis. Oecologia.

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Shephard et al. (2021) Evaluating costs of heavy metal tolerance in a widely distributed, invasive butterfly. Evolutionary Applications. 

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Theme 3: Mechanisms of phenotypic plasticity and their evolutionary causes and consequences

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Phenotypic plasticity provides a means by which organisms and populations can respond rapidly to environmental change. Yet, fundamental questions remain about the developmental mechanisms that generate plastic phenotypes, the ecological and evolutionary processes that maintain variation in plasticity, and the consequences of plasticity for evolutionary change. My research addresses these questions by integrating developmental, molecular, and physiological approaches to understand how plastic phenotypes are produced, why variation in plasticity is maintained, and the ecological and evolutionary consequences of phenotypic plasticity. 

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Current and past projects related to this theme include:

 

3A. Developmental mechanisms of phenotypic plasticity

Using transcriptomic and physiological approaches, I study the developmental mechanisms that generate plastic phenotypes, including: (1) developmental plasticity induced by early-life nutrition in anurans, and (2) sex-specific intergenerational plasticity induced by paternal experience in teleost fishes. 

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Representative publications:

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Shephard et al. (In Review) Unraveling the transcriptional basis of carry-over effects: sustained versus latent brain gene expression responses to early life diet.

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Shephard et al. (In Review) Males and females integrate paternal predation cues through distinct early-life gene expression trajectories. 

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3B. Costs of plasticity

Although evolutionary theory predicts that variation in plasticity is maintained by fitness costs, these costs have proven difficult to detect empirically. Using nematodes, I have studied the reproductive costs associated with maintaining developmental mechanisms that confer resistance to environmental stress.