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. I study how TGP influences offspring traits in response to environmental challenges, using threespined sticklebacks (Gasterosteus aculeatus). More recently, I have also been investigating these questions on a self-fertilizing Mangrove rivulus fish (Rivulus marmoratus), which forms lineages of genetically identical individuals. I 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. I have found that 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. I am currently working to understand how transgenerational effects vary across different environmental stressors (e.g., salinity, predation, toxins) and how the adaptive significance of these effects depends on the intensity and type of environmental cues parents encounter.
Social influences on ecologically-induced TGP
I am interested how the social environment shapes TGP. For example, the experiences of other individuals may induce changes in parental state that could be transmitted across generations. Stickleback fathers whose male neighbors were predator stressed had offspring with altered growth and behavior, despite the father never directly encountering the predator themselves (Afseth et al. 2022). This suggests that social learning among the parental generation can be transmitted vertically to offspring. In addition to inducing TGP, other conspecifics may buffer stress experienced by parents and reduce the likelihood that paternal stress influences offspring. We have found evidence that fathers who were isolated had offspring with reduced survival against predators, but that the presence of conspecifics did not necessarily buffer them from the effects of predation risk (Hellmann and Rogers 2025). Collectively, both results suggest that the social environment is integral to understanding plasticity in response to the ecological environment (Hellmann and Sih 2025).
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. I have found strong sex-specific patterns of TGP in sticklebacks. Maternal and paternal experience with predation risk has 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, I found 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
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.
