A multivariate view of the speciation continuum

Abstract

The concept of a “speciation continuum” has gained popularity in recent decades. It emphasizes speciation as a continuous process that may be studied by comparing contemporary population pairs that show differing levels of divergence. In their recent perspective article in Evolution, Stankowski and Ravinet provided a valuable service by formally defining the speciation continuum as a continuum of reproductive isolation, based on opinions gathered from a survey of speciation researchers. While we agree that the speciation continuum has been a useful concept to advance the understanding of the speciation process, some intrinsic limitations exist. Here, we advocate for a multivariate extension, the speciation hypercube, first proposed by Dieckmann et al. in 2004, but rarely used since. We extend the idea of the speciation cube and suggest it has strong conceptual and practical advantages over a one-dimensional model. We illustrate how the speciation hypercube can be used to visualize and compare different speciation trajectories, providing new insights into the processes and mechanisms of speciation. A key strength of the speciation hypercube is that it provides a unifying framework for speciation research, as it allows questions from apparently disparate subfields to be addressed in a single conceptual model.

A speciation continuum within repeated origin of hypertrophied lips in cyprinid fish from East Africa

“…Similar situation of the sympatric differentiation is reported for the cichlid genus Amphilophus which demonstrates a speciation continuum from incipient to fully completed (Torres-Dowdall & Meyer, 2021;Sowersby et al, 2021). These examples correspond to the concept of speciation continuum that is considered a speciation as a continuum of stages of reproductive (and other) isolations (Drès & Mallet, 2002;Stankowski & Ravinet, 2021;Bolnick et al, 2023). It is noteworthy that such a continuum is found in Labeobarbuspopulations inhabiting the rivers while all previous examples (among fishes) came from the lacustrine environment.…”

Speciation and repeated origins of hypertrophied lips in parallel adaptive radiations of cyprinid fish from East Africa

“…These examples correspond to the concept of the speciation continuum that is considered a speciation as a continuum of stages of reproductive (and other) isolations (Bolnick et al, 2023;Drès & Mallet, 2002;Stankowski & Ravinet, 2021). It is noteworthy that such a continuum is found in Labeobarbus populations inhabiting the rivers while all previous examples (among fishes) came from the lacustrine environment.…”

Genomic evidence for homoploid hybrid speciation in a marine mammal apex predator

“…S17). Thus, it is expected that the genomic results attesting to the evolutionary independence of Pfs hybrid genome align with other relevant axes of divergence ( 13 ). These include morphological, behavioral, and ecological differences between the Pfs and its donor species ( 23 , 25 ).…”

“…Determining whether the RI of the new lineage was directly derived from the hybridization event may be very difficult in ancient hybridizations ( 9 , 12 ), and artificial crosses allowing inference of hybrid fitness ( 11 ) apply to only a subset of organisms. Moreover, the mode and strength of RI deemed relevant for speciation differ by species concept and taxon ( 13 ), blurring the criteria that could be applied across the tree of life. Experimental evidence for hybrid speciation remains accordingly scarce ( 9 , 14 , 15 ).…”