Multivariate models of animal sex: breaking binaries leads to a better understanding of ecology and evolution

Abstract

Sex is often used to describe a suite of phenotypic and genotypic traits of an organism related to reproduction. However, not all of these traits - gamete type, chromosomal inheritance, physiology, morphology, behavior, etc. - are necessarily linked, and the rhetorical collapse of variation into a single term elides much of the complexity inherent in reproductive phenotypes. We argue that consideration of sex as a constructed category operating at multiple biological levels opens up new avenues for inquiry in our study of biological variation. We apply this framework to three case studies that illustrate the diversity of sex variation, from decoupling sexual phenotypes to the evolutionary and ecological consequences of intrasexual polymorphisms. We argue that instead of assuming binary or bimodal sex in these systems, some may be better categorized as multimodal. Finally, we conduct a meta-analysis of terms used to describe diversity in sexual phenotypes in the scientific literature to highlight how a more inclusive and expansive framework for multimodal sex can clarify, rather than cloud, studies of sexual diversity within and across species. We argue that such an expanded understanding of sex better equips us to understand evolutionary processes on their own terms, and that as biologists it is incumbent upon us to push back against misunderstandings of the biology of sexual phenotypes that enact harm on marginalized communities.

Increasing LGBTQ+ inclusion & competency in wildlife sciences: intersections of sociocultural, structural, and historic barriers to inclusion

“…As wildlife ecologists, we should clearly state how sex of an animal is measured (chromosomal, gonadal, phenotypic, genetic, gametic, etc. ) and avoid contributing to the notion that biological sex and gender are entirely binary (Alexander et al 2021, McLaughlin et al 2023. Although chromosomal, genetic, and gametic sex assignment may appear similar, they are not.…”

“…When scientists, researchers, and other professionals become too siloed and/or fall behind on current research findings, they run the risk of perpetuating damaging biases that further marginalize LGBTQ+ people. We caution researchers against relying on biological determinism as the primary argument for LGBTQ+ inclusion-human rights should not be based on chromosomes or genetics, but rather on morality and inherent human value (Alexander et al 2021(Alexander et al , 2023McLaughlin et al 2023).…”

“…For example, sex determination is a key component of wildlife studies, used across most subfields. However, the methodology scientists use to determine sex is often not discussed (McLaughlin et al 2023). As wildlife ecologists, we should clearly state how sex of an animal is measured (chromosomal, gonadal, phenotypic, genetic, gametic, etc.)…”

“…Assigning sex can be based on chromosome type (e.g., XY or XX chromosomes), identification of the presence of a sex determining gene (e.g., sry ), or based on gamete production (spermatogenesis or oogenesis). Furthermore, authors of wildlife studies often conflate gender and sex when discussing assigned sex (McLaughlin et al 2023), creating further confusion or allowing for misinterpretation with lay audiences.…”

Gendered conflict in the human family

“…Subdisciplinary boundaries are of course fuzzy (Sear et al, 2007), and this is not the place to review the history and differing assumptions of evolutionary psychology, behavioural ecology and approaches to cultural evolution (see Laland & Brown, 2011;Smith et al, 2001). Our point here is only to emphasize that a variety of beliefs about the meanings and implications of sex and gender are compatible with an evolutionary perspective, including extensions beyond the sex/gender binary (DuBois & Shattuck-Heidorn, 2021;McLaughlin et al, 2023). Moreover, evolutionary scholarship that is informed by, and contributes to, feminist thought is fully realizable, especially when socioecological contingencies are fully explored.…”