Abstract
Species are fundamental units in many biological disciplines, but there is continuing disagreement as to what species are, how to define them, and even whether the concept is useful. While some of this debate can be attributed to inadequate data and insufficient statistical frameworks in alpha taxonomy, an equal part results from the ambiguity over what species are expected to represent by the many who use them. Here, mtDNA data, microsatellite data, and sequence data from 17 nuclear loci are used in an integrated and quantitative manner to resolve the presence of evolutionary lineages, their contemporary and historical structure, and their correspondence to species, in a species complex of Amazonian peacock “bass” cichlids (Cichla pinima sensu lato). Results suggest that the historical narrative for these populations is more complex than can be portrayed by recognizing them as one, two, or four species: their history and contemporary dynamics cannot be unambiguously rendered as discrete units (taxa) at any level without both choosing the supremacy of one delimitation criterion and obscuring the very information that provides insight into the diversification process. This calls into question the utility of species as a rank, term, or concept, and suggests that while biologists may have a reasonable grasp of the structure of evolution, our methods of conveying these insights need updating. The lack of correspondence between evolutionary phenomena and discrete species should serve as a null hypothesis, and researchers should focus on quantifying the diversity in nature at whatever hierarchical level it occurs.
Highlights
Despite a “renaissance” of species delimitation [1], there is continuing disagreement among evolutionary biologists and systematists as to what species are, how to define them, and even whether the concept is useful to broader goals of biology and conservation [2]
In our recent work [31], we examined the correspondence of combined molecular data from over a thousand individuals with the 15 species identified by K&F, who cited a phylogenetic species concept [32]
The historical narrative for the populations of Cichla pinima sensu lato is more complex than can be portrayed by recognizing them as one, two, or four species: their history and contemporary dynamics cannot be unambiguously rendered as discrete units at any level without both choosing the supremacy of one delimitation criterion and obscuring the very information that provides insight into the diversification process
Summary
Despite a “renaissance” of species delimitation [1], there is continuing disagreement among evolutionary biologists and systematists as to what species are, how to define them, and even whether the concept is useful to broader goals of biology and conservation [2]. In contrast are researchers who see “species” as an ontological concept wholly separate from species’ “contingent properties” and who emphasize that traits used by operationalists may arise in different orders if at all during speciation [4, 5]. This viewpoint portrays the tips of the tree of life as a discrete series of units, albeit ones challenging to delimit, but does not question how well this dichotomy reflects biological reality [4]. Many authors argue that multiple, integrated datasets should be used to recognize species [6, 7]
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