Abstract
Accurate estimation of species richness is often complex as genetic divergence is not always accompanied by appreciable morphological differentiation. In consequence, cryptic lineages or species evolve. Cryptic speciation is common especially in taxa characterized by small and simplified bodies, what makes their proper identification challenging. The cereal rust mite, Abacarus hystrix, was regarded for a long time as a species associated with a wide range of grass hosts, whereas wide host ranges are rather rare in eriophyoid mites. Therefore, the generalist status of A. hystrix was questioned. In this paper we demonstrate that the diversity within Abacarus species associated with grasses is more complex than it was previously thought. The 78 Abacarus mtDNA COI sequences used in this study formed 10 highly supported clades (bootstrap value 99%) and four more distinct genetic lineages were represented by unique sequences. The genetic distances between them ranged from 6.6 to 26.5%. Moreover, morphological study and genetic approach based on the combination of the Poisson Tree Processes model for species delimitation (PTP) and a Bayesian implementation of PTP (bPTP), and Neighbour Joining analyses led to delimitation of a new species within the Abacarus complex: Abacarus plumiger, specialized on smooth brome (Bromus inermis). Furthermore, our analyses demonstrated a pattern of host-associated differentiation within the complex. Overall, our study indicates that cryptic speciation occurs in the grass-associated Abacarus genus, and suggests the need for more extensive sampling using integrative methods.
Highlights
The genetic divergence leading to speciation is not always accompanied by appreciable morphological differentiation
Some sequences of brome-associated mites clustered on the D2 28S rDNA tree together with Abacarus acutatus Sukhareva, another grass-inhabiting eriophyoid species. This unresolved relationship between A. hystrix and A. acutatus led to the conclusion that the whole grass-associated Abacarus genus complex needs revision (Skoracka and Dabert 2010). These analyses showed that A. hystrix does not exist as a monophyletic taxon and the diversity of the whole grass-associated Abacarus genus complex may be higher than it was thought to be, whereas DNA barcoding based on mtDNA cytochrome oxidase subunit I (COI) is a valuable tool for identification of morphologically similar eriophyoid species
Cryptic speciation is a common phenomenon in all mite taxa (Skoracka et al 2015; Coimbra-Dores et al 2016; García-Jiménez et al 2017; de Rojas et al 2018; Stork 2018), including obligatory phytophagous eriophyoid mites (Lewandowski et al 2014; Cvrković et al 2016)
Summary
The genetic divergence leading to speciation is not always accompanied by appreciable morphological differentiation. Over the last 30 years, there has been an exponential increase in the number of studies that demonstrated the existence of cryptic diversity (Bickford et al 2007; Poulin 2014; Espíndola et al 2016; Živković et al 2017). This rising trend is linked to increasing access to wide array of technologies that enable effective species delimitation. Many of them, before correct identification with aid of genetic methods, had been suspected to be species complexes on the basis of their biological and ecological features (Henry and Wells 2010; Nygren et al 2010; Skoracka and Dabert 2010)
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