A response to recent proposals for integrative taxonomy

Abstract

Several proposals have been launched under the new concept 'integrative taxonomy' to frame the future development of species discovery and description. We consider that some of those proposals have failed to be truly integrative, by not acknowledging the limitations of operational definitions of species, by defending some kinds of evidence as universally superior, by considering taxonomy to be irreconcilable with population genetics, or by ignoring that the heterogeneity of evolutionary processes often precludes full character congruence in species. Here we defend a taxonomy where species exist, but not in any particular way everyone might want them to exist; a taxonomy open to data and methods from population biology, phylogeography and phylogenetics, as well as any other discipline providing evidence about the origin and evolution of species. This new taxonomy embraces all the consequences of considering species as lineages of reproductive populations, encouraging the use of as many lines of evidence as possible, but without negating that a single line may also be the only one providing evidence for a particular species. Species cannot only be those reproductive populations showing broad character congruence and/or reproductive isolation, due to the different degrees of character congruence, as well as of reproductive isolation, that result from the heterogeneity of evolutionary processes causing lineage splitting and divergence. Also, any kind of character -and not only those established by tradition or fashion -is potentially relevant as evidence of lineage divergence. To conciliate the authors who only see species supported by broad character congruence as good species hypotheses, we explain how a hypothesis can gain corroboration using single or multiple lines of evidence, even in cases of discordance with other lines of evidence. Finally, we propose guidelines to identify the expected degree of stability (preliminary, unstable, and stable) of species hypotheses.

An integrative approach to species delineation incorporating different species concepts: a case study of Limnadopsis (Branchiopoda: Spinicaudata)

“…These different types of data complement each other by solving ambiguities or by pointing out erroneous assumptions on the basis of any single character set. Consistency among the data strengthens the proposed species delineation, but, in most cases, conflicts among datasets can be expected (Padial & de la Riva, 2010). Such conflicts may indicate ongoing speciation processes that have not yet been finalized, e.g.…”

“…on the basis of genetic data, allopatric populations are delineated into several lineages, but mechanisms for reproductive isolation are still missing. Padial & de la Riva (2010) argued that full congruence among data from various sources cannot be demanded or even expected. As a result of heterogeneous evolutionary forces, not all characters will be equally affected during speciation processes, implying that congruence among data is desirable, but not mandatory, for species delineation.…”

“…To overcome these problems, several authors have argued for an 'integrative taxonomy', combining molecular, morphological and any other available data to delineate and identify species (Dayrat, 2005;Will, Mishler & Wheeler, 2005;Padial & de la Riva, 2010). Several studies have already applied such integrative approaches (Ballard, Chernoff & James, 2002;Wiens & Penkrot, 2002;Laamanen, Petersen & Meier, 2003;Page, Choy & Hughes, 2005;Sanders, Malhotra & Thrope, 2006;Roe & Sperling, 2007;Alström et al, 2008;Tan et al, 2010), but the integration of the various data is not straightforward.…”

“…The classification of a group of individuals or populations to one or several species requires the explicit use of a species concept. As all data types used in integrative approaches differ in their relevance for the various species concepts, species boundaries may differ for each data type (Padial & de la Riva, 2010) and species concept (Laamanen et al, 2003;Tan et al, 2008). Such differences do not impede species delineation; instead, they enable biologists to take different lines of argumentation into account, leading to well-founded conclusions regarding the delineation of the studied species.…”

Phortica eparmata species complex (Diptera, Drosophildae) from the Oriental Region, with DNA barcoding information of Chinese species

“…Although genetic divergence is low in these species of the genus Phortica, the differences in genital morphology are considered as the most reliable characters to delimit these species. The integration of morphological and DNA-based approaches has revealed an effective way to improve accuracy for species identification (An et al 2015;Dayrat 2005;Lumley & Sperling 2010;Padial & Riva 2010). However, the present study raises concern as to the extent to which species delineation can be defined based on COI, which is a widely used gene for barcoding in Drosophila, and emphasizes the necessity of exploring potentially effective morphological diagnosis when lower resolution of molecular data is observed.…”