An assessment of terminology for intraspecific diversity in fishes, with a focus on “ecotypes” and “life histories”

Abstract Understanding and preserving intraspecific diversity (ISD) is important for species conservation. However, ISD units do not have taxonomic standards and are not universally recognized. The terminology used to describe ISD is varied and often used ambiguously. We compared definitions of terms used to describe ISD with use in recent studies of three fish taxa: sticklebacks (Gasterosteidae), Pacific salmon and trout (Oncorhynchus spp., “PST”), and lampreys (Petromyzontiformes). Life history describes the phenotypic responses of organisms to environments and includes biological parameters that affect population growth or decline. Life‐history pathway(s) are the result of different organismal routes of development that can result in different life histories. These terms can be used to describe recognizable life‐history traits. Life history is generally used in organismal‐ and ecology‐based journals. The terms paired species/species pairs have been used to describe two different phenotypes, whereas in some species and situations a continuum of phenotypes may be expressed. Our review revealed overlapping definitions for race and subspecies, and subspecies and ecotypes. Ecotypes are genotypic adaptations to particular environments, and this term is often used in genetic‐ and evolution‐based journals. “Satellite species” is used for situations in which a parasitic lamprey yields two or more derived, nonparasitic lamprey species. Designatable Units, Evolutionary Significant Units (ESUs), and Distinct Population Segments (DPS) are used by some governments to classify ISD of vertebrate species within distinct and evolutionary significant criteria. In situations where the genetic or life‐history components of ISD are not well understood, a conservative approach would be to call them phenotypes.

variable roles of phenotype, genotype, and phenotypic plasticity (interactions of the genotype with the environment): Variability Phenotype = Variability Genotype + Variability Environment + Variability G enotype × Environment (DeWitt & Scheiner, 2004). Some researchers assess 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 (Chavarie et al., 2013;Collyer et al., 2015;Lessios & Weinberg, 1994); ecotypes (Arostegui et al., 2018;Cruz-Font et al., 2019;Gregor, 1944) species pairs (Taylor, 1999); ecomorphotypes (Baker et al., 1998;Kloh et al., 2019;Segura-Trujillo et al., 2018); ecophenotypes (Proćków et al., 2018;Schönborn & Peschke, 1988;Sorensen & Lindberg, 1991); polymorphisms (Jamie & Meier, 2020;Skúlason et al., 2019;Skúlason & Smith, 1995); and life histories (Stearns, 1989;Winemiller & Rose, 1992). Several of these terms have common roots and are often used interchangeably or in combination (e.g., Baker et al., 1998;Brannon et al., 2004;Chavarie et al., 2013;Palacios et al., 2012;Wood et al., 2008). 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 intraspecies diversity using classical and authoritative sources that set a precedent and articulate clear definitions; (2) provide a meta-review of evolution, traits, and ISD; (3) analyze trends over the last three decades  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 & Foster, 1994;Docker, 2015Docker, , 2019Groot & Margolis, 1991;Hardisty, 2006;Hendry et al., 2013;Orlov & Beamish, 2016a, b;Quinn, 2005;Wootton, 2009).

| Objective 1: Definitions
We found early uses of the terms ecotypes and life history in the literature. In papers that make a distinction across various animal taxa, we focused on information provided for fishes, for example, as by Haig et al. (2006). Our literature search included locating the first use of the term "ecotype" in the early 1900s and key publications by Stearns (1989Stearns ( , 1992. In addition, we found definitions for other terms that have been used synonymously with ecotype and life history.

| Objective 2: Meta-review of fish taxa
We conducted broad and succinct reviews of sticklebacks, PST, and lampreys that focused on books, book chapters, review articles, and other peer-reviewed literature to provide and describe the number of species, their evolution, trait diversity, and use of terms to describe ISD. We chose to do a meta-literature review because the exponential increase in articles for these species (e.g., Wootton, 2009) rendered exhaustive reviews untenable for the scope of this paper.

| Objective 3: Trends in use of "life history" and "ecotype"
We conducted three independent searches for the use of the terms, "ecotypes" and "life history" for sticklebacks, PST, and lampreys using the advanced search option in the Web of Science search engine for articles in English, over 30 years (for years 1990-2019). Each search included the words "stickleback" or "Oncorhyhnchus" or "lamprey," with at least one of the terms "ecotype life history" in the title of the article, using the operators: (TI=(ecotype OR life history) AND TI=(stickleback)). The same was done for "Oncorhynchus" and "lamprey." These searches were executed between November 2020 and February 2021. Each article was reviewed to determine the focal species and phenotypes assessed; whether a genetic basis was identified for the diversity in phenotypes; and whether an article used both terms (ecotypes and life history) synonymously or both, but independently or used only one of the terms. Finally, the frequency of term use was calculated and compared among papers.

| Objective 4: Compare definitions with term use and make recommendations
We compared definitions (Objective 1) with the meta-review (Objective 2) and trends in use of the terms ecotypes and life history (Objective 3). We addressed the questions: Are there clear patterns in how terms are used in particular contexts? Do redundancies or ambiguities exist in the use of some terms that suggest that some terms ought not to be used?

| Objective 1: Definitions
In our search for definitions of ecotype and life history, it became apparent that several terms are used more-or-less synonymously (e.g., "species pairs", "ecotypes", and "life histories" in Taylor, 1999 and "races", "phenotype", "types", and "subspecies" in Brannon et al., 2004). This entanglement of phenotypic terms was noted over eight decades ago: "The questions of what is a species, or a subspecies, or a race, or any classificatory category of specific or lower rank, cannot be disassociated from one another" (Ginsburg, 1937).
We compiled definitions of common terms used to describe ISD (Table 1). Generic terms used to describe ISD include "form" and "type." Life history describes the phenotypic responses of organisms to environments and includes biological parameters that affect population growth and decline, including birth, survival, reproductive timing, reproductive investment, and mortality. Life-history pathway(s) are the result of different developmental routes by an organism that are contingent upon the physiological status and genetic thresholds of that organism. The different developmental routes can result in different life histories. The terms paired species/species pairs have been used to describe two different phenotypes such as benthic versus limnetic sticklebacks or freshwater resident kokanee versus anadromous sockeye salmon (O. nerka; Taylor, 1999) and freshwater resident, nonfeeding brook lampreys versus anadromous and parasitic lampreys (Docker, 2009;Docker & Potter, 2019;Salewski, 2003). However, for lampreys, the more appropriate term would be "satellite species" and not "species pairs" (see below).
Species pairs implies two phenotypes, whereas in some species and situations a continuum of phenotypes may be expressed. Our review revealed the ambiguity of the term, race, and the overlap in definitions of this term with subspecies. Classification of subspecies is controversial among taxonomists (Haig et al., 2006;Patten, 2015;de Queiroz, 2020), and a commonly accepted definition of subspecies remains elusive (Haig et al., 2006). Nevertheless, subspecies have recently been defined as components of a species that are incompletely speciated (Patten, 2015;de Queiroz, 2020; Table 1). We also found an overlap in definitions between subspecies and ecotypes.
Ecotype was originally used to describe patterns in traits (genes) and ecology in the early 1900s (Gregor, 1944;Turesson, 1922). In essence, ecotypes are genotypic adaptations to particular environments. "Satellite species" is used for situations in which a parasitic lamprey yields two or more derived, nonparasitic lamprey species (Docker, 2009;Salewski, 2003;Vladykov & Kott, 1979). In some situations, these closely related lamprey species may not be distinct species (Docker, 2009

| Sticklebacks
Research on sticklebacks has focused primarily on one species, the threespine stickleback, Gasterosteus aculeatus, with fewer studies on ninespine stickleback, Pungitius pungitius (e.g., Table 2). The threespine stickleback has been a model organism for studying behavior, host-parasite relationships, morphology, evolutionary ecology, and speciation (e.g., Baker et al., 2008;Bell & Foster, 1994;Hendry et al., 2009Hendry et al., , 2013McKinnon & Rundle, 2002;Schluter, 2010;Wootton, 2009). The overall trend with studies on the threespine stickleback has been the identification of numerous species, followed by lumping into one species, followed by a return to splitting the phenotypes back out into individual species in some geographical areas.
In the early 1900s, taxonomists struggled with the wide phenotypic diversity of threespine stickleback and several phenotypes were initially believed to be separate species (Wootton, 2009). This diversity is captured in the following quote: "Race ranking may be accorded forms, like local types of Gasterosteus aculeatus, which are so confusingly numerous or so complex in characters, and so complicated in genetic and geographical relationship, as to transcend any ordinary scheme of zoological nomenclature" (Hubbs, 1943). It has since been argued that the threespine stickleback is a "raceme" (persistent lineage [marine phenotype] out of which multiple lineages [anadromous and freshwater phenotypes] diverge and quickly end in extinction) or "species complex," composed of thousands of diverse populations that have evolved numerous times in particular locations (Bell & Foster, 1994;Hendry et al., 2013;Schluter & Conte, 2009;Wootton, 2009). Others refer to the diversity within threespine stickleback by calling the species a "superspecies" (Baker et al., 2008).

Stickleback speciation is complex and involves multiple traits.
This speciation occurs rapidly in diverse geographical areas. Natural selection, sexual selection, standing genetic variation, mutation, and genetic recombination have led to rapid reproductive isolation and speciation that has occurred since the last glaciers ca. 9,000-13,000 years ago McKinnon & Rundle, 2002;Schluter, 2010;Schluter & Conte, 2009;Wootton, 2009). In the midto late-1900s, research on sticklebacks examined the variation and adaptive significance of phenotypic traits including body shape and size, body armor (bony plates), spines and skeletal structure, spawning coloration, life-history characteristics, and behavior. In the latter part of this period, research focused on the adaptive radiation and reproductive isolation of sticklebacks in lakes. In the 2000s, genomic TA B L E 1 Terms used to define diverse phenotypes of plants and animals, and the processes driving within-species diversification. The terms are generally arranged from top to bottom by simple adaptive bifurcation to adaptive radiation. Italicized terms ("life history" and "ecotype") are the focus of the present paper Life history Phenotypes of the same or similar species differing with respect to various life-history parameters that are interrelated by trade-offs among these parameters (Stearns, 1989). ?
The life-history parameters include, among others, birth, size, growth characteristics, age and size at maturity, fecundity, offspring size and sex ratio, reproductive investments relative to age and size, mortality relative to age and size, and duration of life (Stearns, 1992).
Reproductive effort related to age or life stage, and in response to factors that influence fecundity and survival. Thus, life histories reflect the expression of fitness-related traits, including the timing and expression of the number, size, and life span of offspring, and size and age at maturity (Hutchings, 2004). ?

Life-history pathway
Alternative pathways of development that yield different life-history traits, depending on the physiological status and genetic thresholds of a species. This can result in a diversity of life histories rather than a particular life history (Thorpe et al., 1998).

Phenotypic plasticity
Paired species/ species pair Two phenotypes of the same species that differ in morphology, behavior, genetics, and ecology (Taylor, 1999).

Incipient ecological speciation
Speciation may occur at different rates in different locations and for different species, along a continuum of states (Hendry, 2009).
Although species may go through a subspecies stage, all subspecies may not become species (Patten, 2015).
? "Unlike races, subspecies are animal kinds which are sufficiently clear-cut as to be thought worthy of a place in the nomenclatorial system, but which do not give evidence of being completely differentiated"; "Incompleteness versus completeness of differentiation is the main test by which subspecies may be distinguished from species…"; "…subspecies in fishes are being shown to be ecological (or microgeographical) forms, which occupy diverse habitats in the same or in very broadly overlapping areas" (Hubbs, 1943).
Phenotypic and genotypic differences in threespine stickleback have been found among marine, anadromous, freshwater resident populations (lakes and streams), and between phenotypes within these habitats (e.g., limnetic vs. benthic phenotypes/species; Table 2). This diversity has been identified as "species pairs" Taylor, 1999;Wootton, 2009), "ecomorph pairs" (Wootton, 2009), and "ecotypes" (Table 2; Hendry et al., 2013;Taylor, 1999). Life-history diversity has also been examined (Table 2; Baker et al., 2008), and "life history" can be used to describe phenotypic characteristics in life-history parameters across multiple lineages without having to demonstrate a genotypic associationunlike "ecotypes." Some of these phenotypes of threespine stickleback show sufficient reproductive isolation and phenotypic and genotypic differences to warrant calling them separate species, although they still bear the same scientific name (Schluter, 2010;Wootton, 2009). For example, "limnetic" and "benthic" phenotypes/ species have been shown to be adaptive in the littoral zone (benthic species/phenotype) and limnetic zone (limnetic species/phenotype)

Term Definition
Process Notes "Distinct genotypes (or populations) within a species, resulting from adaptation to local environmental conditions; capable of interbreeding with other ecotypes or epitypes of the same species" (Hufford & Mazer, 2003).
? "The term ecotype is proposed here as ecological unit to cover the product arising as a result of the genotypical response of an ecospecies to a particular habitat. The ecotypes are then the ecological subunits of the ecospecies, while the genotypes are purely Mendelian subunits of the genospecies. Knowledge of the ecology of an ecospecies presupposes knowledge of its most important ecotypes, and the knowledge of the ecology of the latter involves primarily a study of the variation and the distribution in nature of each of these ecotypes" (Turesson, 1922). ?

Satellite species
Describes situations in which a single parasitic lamprey species gives rise to one or more nonparasitic species (Vladykov & Kott, 1979).
Incipient ecological speciation to speciation (Docker, 2009) In some situations, these closely related lamprey species may not be distinct species (Docker, 2009 Any subspecies or distinct population segment of vertebrate species that interbreeds is reproductively isolated and is an evolutionarily significant unit (i.e., it provides a significant contribution to the genetic and ecological diversity) of the species (ESA, 1973;Waples, 2006 (1973), to include distinct vertebrate populations with unique genetic diversity (Waples, 1991(Waples, , 1995(Waples, , 2006.

Human constructs and speciation
Based largely on Pacific salmon Context-dependent population or population group that is arbitrarily chosen based on biological components (reproductively isolated, displays unique genetic, phenotypic, and ecological components), and economic, cultural, and social considerations (reviewed in Ford, 2004).

TA B L E 1 (Continued)
TA B L E 2 Papers identified through Web of Science search (see text for details). The papers are arranged by sticklebacks, then Oncorhynchus spp., and then lampreys. Within each of these three taxa, the papers are organized by year of publication, and then alphabetically, by the authors' last names. For terms, "1" = "life history" or "life histories"; "2" = "ecotype(s)"; "3" = both terms 1 and 2 were used synonymously; and "4" = both terms 1 and 2 were used independently (i.e., not synonymously)

Threespine stickleback, Gasterosteus aculeatus
Age and body size at maturity, reproductive effort, and fecundity of ocean and lake phenotypes within some lakes (Schluter, 2010) and phenotypes associated with different lake substrates (lava vs. mud; Kristjánsson et al., 2002) in ways that reduce competition for resources (Schluter, 2010). In addition, some phenotypic and genotypic divergence in lakes has been attributed to predators and prey (Miller et al., 2019;Millet et al., 2013), and parasitism may also influence divergence leading to speciation between limnetic and benthic threespine sticklebacks (Schluter, 2010). The appropriate terminology for describing threespine stickleback diversity may depend on the population(s) in question. This is because speciation within sticklebacks occurs along a continuum, from "continuous variation within panmictic populations" on one end to "complete and irreversible reproductive isolation" on the other, with factors affecting the divergence of populations along this continuum . Hendry et al. (2009) reported that most stickleback populations are on the front end of this spectrum, "… even though some of these [populations] show evidence of disruptive selection and positive assortative mating."
Modern PST are approximately 6-20 million years old, and further speciation and intraspecific diversification has been occurring ever since (Stearley & Smith, 1993;Montgomery, 2000;Penaluna et al., 2016). Significant geologic activity, including tectonic action, volcanism, and cycles of glaciation and deglaciation, occurred and thus has been implicated in influencing the speciation of PST (Montgomery, 2000;Penaluna et al., 2016). This geologic activity would have also resulted in creation of river drainages and thus geographical isolation that influenced PST speciation (Montgomery, 2000). Pacific salmon and trout exhibit a general pattern of isolation-by-distance, with populations near each other being more closely related than those further away (apart from sockeye salmon O. nerka; Wood et al., 2008).
Pacific salmon and trout home to their natal streams and lakes, and this results in structured populations that are locally adapted to particular environments (Brannon et al., 2004;Hendry et al., 2004a;Quinn, 2005;Waples et al., 2001. Pacific salmon and trout have been described as "…different populations [that] represent ecological types referred to as spring-, summer-, fall and winter-run segments, as well as stream-and ocean-type, or stream-and oceanmaturing life history forms" (Brannon et al., 2004).
Important diversification in PST occurs below the species level (Behnke, 2002). Traits of PST that diverge at the intraspecific level include run timing (Brannon et al., 2004;Groot & Margolis, 1991), anadromy/freshwater residency (Hendry et al., 2004b;Quinn & Myers, 2004), ocean residency, fecundity, territoriality, iteroparity/ semelparity, and precocity versus larger and older spawning types (Table 2; see also Fleming & Reynolds, 2004;Quinn & Myers, 2004;Quinn, 2005). This ISD is a continuum determined by a suite of traits that are influenced along seasonal changes in environmental conditions (i.e., temporal clines). One key temporal cline is water temperature, which affects larval development, juvenile residence, and spawn timing (Brannon et al., 2004;Quinn & Myers, 2004;Waples et al., 2001). The diversity in life histories and genetics within PST exhibits a direct and strong correlation (Waples et al., 2001). In addition, life-history traits in PST are directly related to evolutionary fitness and thus are subjected to strong and consistent selection (Carlson & Seamons, 2008;Hutchings, 2004). Nevertheless, many questions remain about the extent to which the ISD in PST is a result of phenotypic plasticity versus genetic adaptation (Hendry et al., 2004b;Waples et al., 2001;Waples & Hendry, 2008).
Some authors combine use of terms such as "life history ecotypes" (Wood et al., 2008). In addition, some PST populations have received the designation of ESUs (Table 1). This designation enables tracking of demographic characteristics relative to population status.
The brook lampreys are relatively small in body size and females exhibit low fecundity, whereas the anadromous lampreys are relatively large and exhibit correspondingly higher fecundities (Docker, 2009;Docker & Potter, 2019;Salewski, 2003). The closely related pairs or groups of brook and anadromous lampreys have been termed "paired species" or "species pairs," "satellite species" (more than two species), "life histories" (Docker, 2009;Docker & Potter, 2019;Salewski, 2003;Vladykov & Kott, 1979), and recently "ecotypes" (Docker & Potter, 2019;Rougemont et al., 2017). We argue that paired species/species pairs confuses ISD and interspecies diversity of lampreys with that of teleosts (e.g., Taylor, 1999); thus, these two terms should probably be avoided when discussing diversity in lampreys. By contrast, satellite species has a historical context (Vladykov & Kott, 1979) and makes sense because of the definition provided, which encompasses both ISD and interspecies diversity (Table 1).
Ecotypes are gaining in use for lampreys (Table 2), though it makes more sense to use this term in terms ISD and not for interspecies diversity. Life history could reasonably be used to describe recognizable differences in life-history traits for ISD in lampreys. A review of studies on parasitic and nonparasitic species pairs of lampreys identified a continuum of genetic and phenotypic divergence withinspecies pairs, with the term "ecotype" being used to indicate different phenotypic expression and partial or full reproductive isolation, whereas life history was used to indicate trade-offs in body size and fecundity associated with feeding type (parasitic or nonfeeding) and anadromy versus freshwater residency (Docker & Potter, 2019).
The level of genetic relatedness between species pairs depends on the geographic location and circumstances. In some situations, closely related parasitic lamprey and nonparasitic brook lamprey can reproduce together; thus, they may more aptly be called phenotypes of the same species. Examples of this include the European river lamprey (Lampetra fluviatilis) and European brook lamprey (L. planeri; Rougemont et al., 2015), and the resident parasitic silver lamprey (Ichthyomyzon unicuspis), and nonparasitic northern brook lamprey (I. fossor; Docker et al., 2012). In other situations, these phenotypes exhibit discrete genetic differences, such as among specimens of parasitic western river lamprey (L. ayresii) and the closely related western brook lamprey (L. richardsoni) and other Lampetra species along the west coast of North America (Boguski et al., 2012), and among allopatric European river lamprey and European brook lamprey (Rougemont et al., 2017). These satellite species were originally identified as separate species (Docker, 2009;Vladykov & Kott, 1979). Resident brook lampreys are expected to display more population structure within a particular river basin than anadromous lampreys, as demonstrated for western brook lamprey (L. richardsoni; Spice et al., 2019). Anadromous lampreys do not home to their natal streams, and so they display less genetic stock structure (Bergstedt and Seelye., 1995;Bryan et al., 2005;Spice et al., 2012).
More recently, research into Pacific lamprey, Entosphenus tridentatus, has revealed another form of phenotypic diversity beyond feeding and migratory behavior: bimodal differences in maturation timing.
Research into body morphology, gonadosomatic index (GSI), and maturation levels (determined by gonadal histology) revealed phenotypic differences in maturation timing, which were named "stream maturing" and "ocean maturing" Pacific lamprey (Clemens et al., 2013). It was hypothesized that the less-mature life history or phenotype was the commonly recognized stream maturing phenotype that would be expected to spawn one or more years after entering freshwater, whereas the formerly unrecognized ocean maturing form (which is more sexually mature upon entering freshwater) might spawn within the same year of entering freshwater (Clemens et al., 2013). The ocean maturing phenotype was found in the Klamath River estuary (California, USA, at the river mouth, river kilometer 0). A separate study conducted at this same location verified the existence of stream maturing and ocean maturing ISD in Pacific lamprey, via single nucleotide polymorphism markers and GSI. This phenotypic diversity was initially referred to as "life histories" (Clemens et al., 2013) and then more recently as "ecotypes" (Parker et al., 2019). Ecotypes should be used in terms of ISD and not for interspecies diversity. Life history could reasonably be used to describe recognizable differences in life-history traits for ISD in lampreys.
Nine articles found by the Web of Science literature search were omitted from our analyses because these papers focused on life stage differences rather than intraspecific differences. Journals with a general focus on organismal biology and ecology tended to use the term(s) "life history/life histories," whereas journals focusing on evolution and genetics tended to use the term "ecotype(s)"  (2016) would have been missed because "life history" is in the title of that paper. However, in the other papers "ecotypes" was included as a keyword Neave et al., 2019) or in the running title (Rougemont et al., 2015), rather than in the title. In other instances, use of the word "ecotypic" rather than "ecotype" (e.g., Keeley et al., 2005Keeley et al., , 2007

| CON CLUS IONS
Understanding and preserving ISD is important for species conservation. Ecotype was originally used to describe genotypic adaptation to environments, and recent studies generally use this term in a  Table 3). These data indicate that organismal-and ecology-focused journals tended to use the term(s) "life history/life histories." By contrast, evolutionand genetic-focused journals tended to use the term "ecotype(s)." F I G U R E 2 Number of papers that used terms to describe intraspecific diversity in fishes. This data are the combined results of literature searches for sticklebacks, Oncorhynchus spp., and lampreys for 1990-2019. "Both terms (I)" = both terms were used independently. "Both terms (S)" = both terms were used synonymously. Numbers above the bars indicate the number of paper by term. These data indicate that studies that used the term "ecotype(s)" tended to find a genetic basis in the diversity examined. By contrast, papers that used the term(s) "life history/ life histories" did not tend to report a genetic basis for the diversity examined similar way. By contrast, life history includes biological parameters that affect abundance and population growth and decline, and recent studies generally use this term in a similar way. Ecotype and life history were used equally among recent studies on sticklebacks. By contrast, life history was used more frequently than ecotype among recent studies on PST and lampreys.

ACK N OWLED G M ENTS
This paper is dedicated to the memory of David L. G. Noakes , scientist, scholar, educator, mentor, collaborator, and friend.
We thank Tom Stahl for a review of an earlier draft of this paper.
This paper benefitted from discussions with Marc Johnson. Brian Sidlauskas provided recommendations for key literature to use. This paper benefitted from the constructive and critical reviews from Jon Hess, Margaret Docker, and an anonymous reviewer.
No research data were referenced for this paper. Any course data are included within the manuscript

CO N FLI C T O F I NTE R E S T
None declared.

DATA AVA I L A B I L I T Y S TAT E M E N T
No data were archived for this paper. All data are included within Variation in female life-history traits among Alaskan populations F I G U R E 3 Number of papers that used terms to describe intraspecific diversity in sticklebacks, Oncorhynchus spp., and lampreys for 1990-2019. Trends in term use, by taxa. "Both terms (I)" = both terms were used independently. "Both terms (S)" = both terms were used synonymously. These data indicate that the terms "ecotype(s)" and "life history/life histories" were used equally among studies on sticklebacks (a). By contrast, the term "life history/life histories" was used most among studies on Oncorhynchus spp. (b) and lampreys (c)