Cryptic species as a window into the paradigm shift of the species concept

Abstract

The species concept is the cornerstone of biodiversity science, and any paradigm shift in the delimitation of species affects many research fields. Many biologists now are embracing a new "species" paradigm as separately evolving populations using different delimitation criteria. Individual criteria can emerge during different periods of speciation; some may never evolve. As such, a paradigm shift in the species concept relates to this inherent heterogeneity in the speciation process and species category-which is fundamentally overlooked in biodiversity research. Cryptic species fall within this paradigm shift: they are continuously being reported from diverse animal phyla but are poorly considered in current tests of ecological and evolutionary theory. The aim of this review is to integrate cryptic species in biodiversity science. In the first section, we address that the absence of morphological diversification is an evolutionary phenomenon, a "process" counterpart to the long-studied mechanisms of morphological diversification. In the next section regarding taxonomy, we show that molecular delimitation of cryptic species is heavily biased towards distance-based methods. We also stress the importance of formally naming of cryptic species for better integration into research fields that use species as units of analysis. Finally, we show that incorporating cryptic species leads to novel insights regarding biodiversity patterns and processes, including large-scale biodiversity assessments, geographic variation in species distribution and species coexistence. It is time for incorporating multicriteria species approaches aiming to understand speciation across space and taxa, thus allowing integration into biodiversity conservation while accommodating for species uncertainty.

Mediterranean Lithophyllum stictiforme (Corallinales, Rhodophyta) is a genetically diverse species complex: implications for species circumscription, biogeography and conservation of coralligenous habitats

“…In recent years, cryptic diversity has become a key topic in evolutionary biology and examples of this diversity have been demonstrated in numerous groups of organisms, including those that are complex and large‐sized (Fišer et al. ).Theoretical considerations suggest that cryptic diversity can be expected to abound in marine macroalgae, particularly in forms with simple morphologies (Verbruggen ). This prediction has been confirmed in recent years, sometimes to extreme levels, especially when methods for algorithmic delimitation of species have been used (e.g., Payo et al.…”

Cryptic and extensive hybridization between ancient lineages of American crows

“…Phenotypic characters have historically been a primary basis for distinguishing between species (Bickford et al, 2007), but the increasing availability of DNA evidence has made clear that speciation is not always accompanied by morphological change (Fišer, Robinson, & Malard, 2018). Genomic analyses of morphologically conserved groups have uncovered cryptic species across the tree of life (e.g., Hotaling et al, 2016; Larsen, Miller, Rhodes, & Wiens, 2017; Pfenninger & Schwenk, 2007; Satler, Carstens, & Hedin, 2013), yet not all morphologically diagnosed species show genomic differences (e.g., Mason & Taylor, 2015).…”

Deep segregation in the open ocean: Macaronesia as an evolutionary hotspot for low dispersal marine invertebrates

“…Diniz‐Filho, Loyola, Raia, Mooers, & Bini, ). In addition, it may be difficult to describe species based solely on morphological characters (Beheregaray & Caccone, ; Fišer, Robinson, & Malard, ; Knowlton, ). In peracarids, for example, even family‐level diagnostic characters can change with development and sex, making identification problematic (Larsen, ; Larsen & Wilson, ).…”