Cryptic or pseudocryptic: can morphological methods inform copepod taxonomy? An analysis of publications and a case study of theEurytemora affinisspecies complex

Abstract

Interest in cryptic species has increased significantly with current progress in genetic methods. The large number of cryptic species suggests that the resolution of traditional morphological techniques may be insufficient for taxonomical research. However, some species now considered to be cryptic may, in fact, be designated pseudocryptic after close morphological examination. Thus the “cryptic or pseudocryptic” dilemma speaks to the resolution of morphological analysis and its utility for identifying species. We address this dilemma first by systematically reviewing data published from 1980 to 2013 on cryptic species of Copepoda and then by performing an in-depth morphological study of the former Eurytemora affinis complex of cryptic species. Analyzing the published data showed that, in 5 of 24 revisions eligible for systematic review, cryptic species assignment was based solely on the genetic variation of forms without detailed morphological analysis to confirm the assignment. Therefore, some newly described cryptic species might be designated pseudocryptic under more detailed morphological analysis as happened with Eurytemora affinis complex. Recent genetic analyses of the complex found high levels of heterogeneity without morphological differences; it is argued to be cryptic. However, next detailed morphological analyses allowed to describe a number of valid species. Our study, using deep statistical analyses usually not applied for new species describing, of this species complex confirmed considerable differences between former cryptic species. In particular, fluctuating asymmetry (FA), the random variation of left and right structures, was significantly different between forms and provided independent information about their status. Our work showed that multivariate statistical approaches, such as principal component analysis, can be powerful techniques for the morphological discrimination of cryptic taxons. Despite increasing cryptic species designations, morphological techniques have great potential in determining copepod taxonomy.

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

“…Noteworthy, some authors have already coined a term “pseudo‐cryptic” to distinguish “completely identical species” from “morphologically diagnosable species” (Achurra, Rodriguez, & Erséus, ; Knowlton, ; Sáez & Lozano, ). This classification may lead to questions such as “When are species similar enough to be considered morphologically cryptic?” (Karanovic et al., ; Lajus, Sukhikh, & Alekseev, ). This question is at risk to remain without epilogue.…”

“…This classification may lead to questions such as "When are species similar enough to be considered morphologically cryptic?" (Karanovic et al, 2016;Lajus, Sukhikh, & Alekseev, 2015). This question is at risk to remain without epilogue.…”

Rangeomorph classification schemes and intra-specific variation: are all characters created equal?

“…The techniques used most commonly include dimensionality reduction analyses, such as principal components analysis and multiple correspondence analysis (Lajus et al 2015), as well as clustering algorithms (Jardine & Sibson 1971;Dunn & Everitt 2004;Bonder et al 2012;Pagni et al 2013). The approach adopted in the present study is to combine clustering methods with multivariate analytical techniques.…”

Advances on Dipterology in the 21st century and extinction rates

“…Although money itself would not guarantee qualified taxonomic work, "governments, science funders and environmental agencies need to invest" (Hochkirch, 2016, p. 141). The decline of funding from governmental and private agencies, and the tendency of students moving towards more in vogue and fancy areas of scientific investigation jeopardize the ability of the area to accomplish its goals and the urgent need of development (Lajus et al, 2015). The 'taxonomic impediment' -i.e., the small and inadequate number of proficient taxonomists, and the consequential lack of keys and other resources for accurate identification -is a reality (Carvalho et al, 2005;Evenhuis, 2007) and may affect entomologists in general and dipterists in particular.…”