Objective 4: Compare definitions with term use and make
recommendations
Ecotype originally was used to describe patterns in traits (gene)
combinations in particular environments. This term also tends to
describe a genetic basis for ISD and is often used in genetic- and
evolution-based journals during 1990 – 2019. Thus, a general
consistency between the classical definition and the current use of
ecotype exists. Ecotype would therefore be an obvious term for
geneticists and evolutionary biologists wishing to address patterns in
genes associated with particular habitats. Significant overlap in
meaning exists between ecotype and reaction norms, and the nuanced
differences in these terms should be carefully parsed out by authors.
The classical definition of “life history” is clear and
straightforward on demographic trade-offs (e.g., Stearns 1989, 1992).
Life history has strong demographic connotations (Table 1), and thus the
general trend for its use in organismal- and ecology-based journals
during 1990 – 2019 makes sense. Life history types implies
discontinuity in phenotypic expressions, whereas life history pathways
(e.g., Thorpe et al. 1998) implies continuity in phenotypic expression
(Table 1). The term, species pairs implies two phenotypes, whereas in
some species and situations, more than one phenotype or a continuum of
phenotypes, akin to life history pathways, may be expressed. Race is
generally synonymous with subspecies. “Satellite species” is used for
lampreys, but not for sticklebacks or PST.
Although we did not assess the use of derivative terms such as
morphotypes, ecomorphotypes, ecophenotypes, these terms arguably do not
offer insight into ISD, and we therefore recommend that authors either
should not use these terms or use them sparingly. All attempts to
describe ISD would benefit from clear definitions. In situations where
the genetic and demographic components of ISD are not well understood, a
conservative approach would be to forego categorization of the diversity
as ecotypes or life history types / life history pathways and to call
them phenotypes.
We speculate that if, for some reason, cultural, recreational, and
economic roles of species were reversed so that sticklebacks and
lampreys became more important than PST, that perhaps the research focus
of sticklebacks and lampreys would have tended more towards demographic
and life history assessments and less towards evolutionary assessments
— even though these disciplines are connected (e.g., Frank and Leggett
1994; Hutchings 2000; Waples and Hendry 2008). If this were to have
occurred, we wonder the extent to which the diversity within
sticklebacks and lampreys might be more classified by life histories,
races, and subspecies, whereas the diversity of Pacific salmon and trout
might be more towards ecotypes. With this simple thought experiment, we
speculate that the scope and breadth of human interests in particular
taxa could influence the epistemology of how these organisms are
studied, and hence the way we describe their diversity. We realize this
thought experiment is somewhat overly simplified, however, in that
species characteristics that can determine their commercial and
recreational interests (e.g., large body size and hence longer
generation times, as in Oncorhynchus spp.) also make these
animals more challenging to study (Stearns and Hendry 2004). By
contrast, the relatively small-bodied sticklebacks, which do not have a
known commercial or recreational interest are comparatively short-lived
and this therefore makes them tractable study animals. In addition, the
evolutionary histories of these three fish taxa are very different, with
the oldest by far being the lampreys, followed by the PST, and then
sticklebacks. Although some of the same past geological events may have
influenced the evolutionary trajectories of these taxa (e.g.,
glaciation; Bell and Andrews 1997), these events would have worked at
different time frames and to different extents. The foregoing rationale
suggests that terminology to describe ISD may not be directly
transferable between taxa. For example, the abundant delineation of
Pacific trouts to subspecies may make more sense for that taxon, given
their population structure and distribution into geographically isolated
streams (that can be geologically and ecologically diverse; Behnke 2002;
Penaluna et al. 2016) than it would for either sticklebacks or lampreys.
On the other hand, some terminology may have broader applicability —
such as life history and ecotypes (Table 2).
In conclusion, understanding and preserving ISD is important for species
conservation. Ecotype was originally used to describe patterns in genes
and ecology, and recent studies generally use this term in a 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. The nature of human interests (i.e., scientific,
commercial, recreational, cultural) in particular taxa could influence
the epistemology of how these organisms are studied, and hence the ways
in which their ISD is understood, described, and conserved.