**This post is a part of the series on the 2020 AGA Presidential Symposium – Genes as Environment: Indirect Genetic Effects on Evolution, Agriculture, & Medicine**
About the Blog Author: The following is a brief commentary on Baud et al. (2022) – Indirect Genetic Effects: A Cross-disciplinary Perspective on Empirical Studies by co-author Sarah McPeek. Sarah is a third year PhD candidate with Dr. Butch Brodie at the University of Virginia. She studies IGE among plants and how these effects mediate interactions with pollinating and herbivorous insects. Follow Sarah’s work @sarahjmcpeek and read more science writing at sarahjmcpeek.com.
One individual’s genes can affect another individual’s phenotypic expression. We call this general phenomenon an Indirect Genetic Effect (IGE). Across disciplines, geneticists apply many variants on the theme such as ‘social genetic effects,’ ‘maternal effects,’ ‘horizontal effects,’ ‘neighbor effects,’ and more. Indeed, when my colleagues and I set out to write our perspective, we struggled at first to compile and synthesize the literature because different fields ascribe different language to these ideas. By bringing all these terms together under the concept of indirect genetic effects, we hope to foster collaboration among geneticists with different interests and approaches for studying IGE.
That said, our aim is not to replace area-specific terms with the general expression IGE. On the contrary, the diversity of language for IGE speaks to the diverse contexts where and how IGE occur. Maternal/parental effects are a subclass of IGE imposed by parents on their offspring. Neighbor effects are another subclass of IGE best applied to sessile species, such as plants in a patch. Social genetic effects and interacting phenotypes typically refer to IGE generated by some form of social interaction. Each subclass of IGE, indeed, each empirical study from natural, laboratory, agricultural, or medical settings, comes with its own list of particulars.
Rather than treating these nuances as nuisances, we believe the specifics of a given study system contextualize IGE. Further, they inform the questions we can address using different natural and experimental populations. To measure IGE, we need to understand who interacts with whom, how frequently, and how consistently. For many questions, we may also be interested in which traits of conspecifics affect traits in the focal individual, and how these effects occur mechanistically. Where we are able, we may want to examine which genes underlie these patterns. Experimenters may rarely be able to work out all these components in a single population. Thus, synthesizing pieces across wild and experimental systems will help us resolve general patterns of IGE and connect data to theory.
In our perspective, we highlight situations that bias the measurement of IGE and offer techniques to help experimenters account for the idiosyncrasies of their study population. We live in an exciting era of new tools that refine our ability to detect, quantify, and characterize IGE. Experimenters can employ remote tracking technologies in longitudinal studies of IGE in wild and captive populations. Video monitoring and computer-based video analysis allow researchers to capture detailed social interactions and intricate phenotypic measures of large samples of individuals. Advances in genetic sequencing, mapping, and editing present opportunities to explore the genes involved in IGE and the molecular mechanisms that control phenotypic effects. These advances expand the scope of questions we can ask in a wide range of empirical systems.
IGE demonstrate that no creatures exist individually. Neither do ideas, nor scientists. We hope our perspective will inspire crosstalk among fields in a common language, refined and contextualized by the tools, approaches, and goals of each researcher. The time for empiricists to tackle IGE, with all their complexities and complications, is here. We have a lot to learn from each other!