Objective 1: Definitions
In our search for classical and authoritative 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, 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” (Table
1). Our review revealed the ambiguity of terms such as “races” and
“subspecies”, and the extent to which these two terms appear to be
used less by scientists now than in the past. Classification of
subspecies is controversial among taxonomists (Haig et al. 2006; Patten
2015; de Queiroz 2020), and a common accepted definition of the
subspecies remains elusive (Haig et al. 2006). 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, and a striking similarity
between the terms, ecotype and reaction norms. Ecotype was originally
used to describe patterns in traits (genes) and ecology in the early
1900s (Turesson 1922; Gregor 1944). Life history, by contrast, includes
biological parameters that affect abundance and population growth or
decline, including parameters related to birth, survival, reproductive
timing, reproductive investment, and mortality (Stearns 1992). The terms
paired species/species pairs have been used to describe a dichotomy of
two different phenotypes such as benthic versus limnetic sticklebacks or
freshwater resident kokanee versus anadromous sockeye salmon (O.
kisutch ; Taylor 1999) and freshwater resident, non-feeding brook
lampreys vs. anadromous and parasitic lampreys (Salewski 2003; Docker
2009; Docker and Potter 2019). The term, satellite species is generally
used to describe situations in which one lamprey species yields two or
more derived species (Vladykov and Kott 1979; Salewski 2003; Docker
2009). Evolutionary Significant Units (ESUs) have been used primarily
for PST.