The Hellmann Lab at University of Dayton
The Hellmann Lab
The Ohio State University
Exploring the underlying mechanisms of phenotypic plasticity
TRANSGENERATIONAL PLASTICITY
The environment experienced by parents can influence offspring phenotypes (transgenerational plasticity or TGP). TGP has benefits beyond developmental plasticity alone, particularly when it is risky/difficult for offspring to sample their environment or when selective pressures are high early in life. We study how TGP influences offspring traits in response to environmental challenges using threespined sticklebacks (Gasterosteus aculeatus), with a focus on the role of paternal experiences on offspring development. More recently, we have also been investigating these questions on a self-fertilizing Mangrove rivulus fish (Rivulus marmoratus), which forms lineages of genetically identical individuals. We have several areas of research under this topic:
The specificity of paternal effects
Despite growing evidence for TGP in response to environmental challenges such as predation risk, the ways in which TGP primes offspring for specific environmental conditions is largely unknown. These transgenerational effects are highly specific to the stressor fathers encounter: offspring phenotypes differ depending on whether fathers are exposed to a general, non-ecologically relevant stressor (net) compared to a predator (Chen et al. 2021) and differ depending on the type of predator fathers encounter. This work suggests that there is not one conserved pathway by which the parental environment alters offspring phenotypes, but rather, TGP may be more fine-tuned, inducing tailored changes in offspring phenotypes that are adaptive for coping with specific environmental challenges. Our lab is currently working to understand how transgenerational effects vary across different environmental stressors (e.g., salinity, predation, wildfire ash) and how the adaptive significance of these effects depends on the intensity and type of environmental cues parents encounter.
Social buffering and stress transmission effects on TGP
TGP has largely focused on how parental exposure to ecological conditions shapes the phenotypes of future generations. However, the presence of conspecifics can shape TGP in critical ways (Hellmann and Sih 2025). Non-parents can alter how parents detect and respond to environmental cues in ways that spillover to affect offspring. For example, stickleback fathers whose male neighbors were predator-exposed had offspring with altered growth and behavior, despite the father never directly encountering the predator themselves (Afseth et al. 2022). We currently have an NSF grant exploring the adaptive significance of and mechanisms underlying the use of socially acquired information in the context of TGP (‘indirect’ TGP).
In addition to inducing TGP, other conspecifics may buffer stress experienced by parents and reduce the likelihood that paternal stress influences offspring. In humans and animal models, social support is one of the biggest predictors of stress resilience - the ability to withstand or recover quickly from significant stress. Maternal resilience to stress is a key predictor of offspring disease susceptibility, but we have little understanding of the link between paternal resilience to stress and offspring outcomes. We can manipulate paternal resilience to stress via social isolation (Hellmann and Rogers 2025) or via pharmacological manipulations.
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Sex-specific transgenerational plasticity
Empirical studies and theory to date have primarily focused on maternal effects; however, the biological reality is that the environment experienced by both mothers and fathers can affect future generations. Mothers and fathers may favor different phenotypes in their offspring and the optimal phenotype for sons may be different from the optimal phenotype for daughters. We have found that maternal and paternal experiences with predation risk have distinct effects on offspring, with non-additive interactions between maternal and paternal experiences on some, but not all offspring traits (Hellmann et al. 2020a). Further, there are strong phenotypic differences between sons and daughters of predator-exposed parents. These differences emerge well before reproductive maturity and have lineage-specific consequences for the F2 generation (Hellmann et al. 2020b). These results provide strong evidence that mothers and fathers convey different information and parental cues alter different developmental programs in sons and daughters. Sex-specific TGP is potentially of great evolutionary significance, as it may allow mothers and fathers to selectively alter the phenotypes of their sons and daughters with a greater degree of precision than genetic inheritance and in ways that match the distinct life-history strategies of males and females. We currently have an NSF grant investigating how the integration of maternal and paternal cues alters the adaptive significance and persistence of TGP across multiple generations.
PHENOTYPIC PLASTICITY INDUCED BY SOCIAL ENVIRONMENTS
In many species, individuals form groups or partnerships with other conspecifics in which they have to cooperate with their current partners, potentially sacrificing current or future reproductive fitness to do so. I am interested in the factors that affect individual decisions to cooperate or compete with current partners. For my dissertation, I demonstrated that both the presence and density of neighboring groups increase the conflict between dominant and subordinate group members, modify subordinate cooperation, and alter subordinate reproduction and relatedness in a cooperatively breeding fish Neolamprologus pulcher. More recently, I have conducted a series of field experiments to understand how male-male cooperation is linked to reproductive fitness in unrelated territorial and satellite male partnerships in the ocellated wrasse (Symphodus ocellatus). Territorial males increase their defense against potential new partners at nests with high spawning activity, suggesting that threats of disruptions to established partnerships might be particularly deleterious at productive nests. Further, territorial males provide more paternal care when there is less conflict between nesting and satellite males, suggesting that male investment in a nest scales with their partner’s quality. Collectively, this work demonstrates that the stability of current partnerships and the ability to leave these partnerships is integral to understanding variation in cooperation.
