Introduction
It is incumbent on any scientist, no matter the field of inquiry, to adhere to (or at least specify) definitions. (Patten 2015)
Intra-specific diversity (ISD) represents the “evolutionary potential within a species” (Haig et al. 2006) and understanding and preserving this diveristy is an important conservation goal (Ford 2004). However, units of ISD do not have taxonomic standards, are not universally recognized, and thus are more contested than species (Ginsburg 1937; Hubbs 1943; Haig et al. 2006; Patten 2015). Intra-specific diversity can be challenging to understand, given the variable roles of phenotype, genotype, and phenotypic plasticity (interactions of the genotype with the environment): VariabilityPhenotype = VariabilityGenotype + VariabilityEnvironment + VariabilityGenotype X Environment (DeWitt and Scheiner 2004). Some researchers use holistic assessments of phenotypic expression relative to genotype and particular environments. However, an easier, and therefore more common strategy among researchers is to focus on components of this relationship. Given these challenges, it is perhaps not surprising that the terminology for describing ISD is often used ambiguously. The ambiguous use of terminology to describe ISD ironically creates another impediment to understanding and thus preserving this diversity.
The scientific literature includes a plethora of terms to denote ISD. These include morphotypes (Lessios and Weinberg 1994; Chavarie et al. 2013; Collyer et al. 2015); ecotypes (Gregor 1944; Arostegui et al. 2018; Cruz-Font 2019); species pairs (Taylor 1999); satellite species (Salewski 2003); ecomorphotypes (Baker et al. 1998; Segura-Trujillo et al. 2018; Kloh et al. 2019); ecophenotypes (Schönborn and Peschke 1988; Sorensen and Lindberg 1991; Proćków et al. 2018); polymorphisms (Skúlason and Smith 1995; Skúlason et al. 2019; Jamie and Meier 2020); and life histories (Stearns 1989; Winemiller and Rose 1992). Several of these terms have common roots, and are often used inter-changeably or in combination (e.g., Baker et al. 1998; Chavarie et al. 2013; Brannon et al. 2004; Wood et al. 2008; Palacios et al. 2012). The use of these terms may suggest perceived or actual novelty, a unique take on biological phenomena, or an attempt to follow precedents of other published works. Although a diverse terminology can be useful in describing the existing diversity of evolved or expressed phenotypes, careful use of terms could improve knowledge transfer and clarity of understanding among scientists, policy makers and fisheries managers. Here, we assess the use of terms to describe ISD in the peer-reviewed scientific literature. We focused on two ISD terms that we believe have been used inconsistently and interchangeably — life histories and ecotypes.
Our goals were to assess the terminology for ISD and make recommendations for future use of these terms. Our four objectives were to: 1) define key terms for intra-species diversity using classical and authoritative sources that set a precedent and articulate clear definitions; 2) provide a meta-review of evolution, traits, and ISD for the three aforementioned taxa; 3) analyze trends over the last three decades (1990 – 2019) in the use of the terms “life history” and “ecotype” in the peer-reviewed literature; and 4) compare the authoritative definitions with the trends in use of life history and ecotypes and make recommendations on future term use. For objectives 2 and 3, we focused on three fish taxa, including sticklebacks (Gasterosteidae), Pacific salmon and trout (Oncorhynchus spp., herein, “PST”), and lampreys (Petromyzontiformes) that represent a rich history of classical ecology and evolutionary studies (Bell and Foster 1994; Woottton 2009; Hendry et al. 2013; Groot and Margolis 1991; Hendry and Stearns 2004; Quinn 2005; Hardisty 2006; Docker 2015; 2019; Orlov and Beamish 2016a, b).