What is in a definition? Reflections on a framework for understanding reproductive isolation: a commentary on Westram et al., 2022

Abstract

Westram et al. (2022) analyse the concept of reproductive isolation (RI). Through an online survey they asked researchers: "In a sentence or two, what is reproductive isolation?" They identified three perspectives on RI: organismic, genetic and one that combines the other two. This provides an important motivation for formulating a general definition of RI. In this commentary, I discuss their approach to defining RI, and highlight certain features of it that are relevant for assessing its impact on speciation research.

Reproductive isolation, speciation, and the value of disagreement: A reply to the commentaries on ‘What is reproductive isolation?’

“…Scientific terms and concepts need a clear definition (Butlin, 2022; Rosales, 2022). However, it is difficult to find a clear definition for terms that have long been in use, with vague or varying meanings (Harrison, 2012).…”

“…Our article ‘What is reproductive isolation?’ (Westram et al, 2022a,b) is no exception: noticing that the term ‘Reproductive isolation’ (RI) is frequently used in the literature, yet almost never clearly defined, we tried to come up with a definition—but we quickly ran into numerous complexities that kept us from finding a simple answer. The complexity of the issue is reflected by the commentaries to our article, which highlight the diversity of views among speciation researchers with different interests, different empirical research experiences and different favourite species concepts [a diversity also highlighted by Rosales (2022)]. Some of the commentaries discuss the conceptual (Moyle et al, 2022) and practical (Stuckert & Matute, 2022) limitations of definitions of RI based on gene flow, whereas Planidin et al (2022) extend the concept to aspects not explicitly covered by us.…”

“…In this response, we elaborate on why we think a definition based on gene flow is appropriate if we want to ‘make explicit and further elaborate’ (Rosales, 2022) the already existing concept of RI. In addition, we consider other important axes along which speciation could be quantified that were highlighted by the commentaries and discuss how they relate to RI.…”

“…Some of the commentaries discuss the conceptual (Moyle et al, 2022) and practical (Stuckert & Matute, 2022) limitations of definitions of RI based on gene flow, whereas Planidin et al (2022) extend the concept to aspects not explicitly covered by us. Rosales (2022) discusses how scientific definitions are developed and what they mean for the community and analyses our work in this context.…”

“…Thus, we aimed to distil the key components of this blurred meaning into something specific and logically consistent. Rosales (2022) discusses this approach and describes it as 'making explicit and further elaborating the conceptual net'. This was a main aim of our article.…”