The Amblyomma maculatum Koch, 1844 (Acari: Ixodidae) group of ticks: phenotypic plasticity or incipient speciation?

Abstract

BackgroundThe goal of this study was to reassess the taxonomic status of A. maculatum, A. triste and A. tigrinum by phylogenetic analysis of five molecular markers [four mitochondrial: 12S rDNA, 16S rDNA, the control region (DL) and cytochrome c oxidase 1 (cox1), and one nuclear: ribosomal intergenic transcribed spacer 2 (ITS2)]. In addition, the phenotypic diversity of adult ticks identified as A. maculatum and A. triste from geographically distinct populations was thoroughly re-examined.ResultsMicroscopic examination identified four putative morphotypes distinguishable by disjunct geographical ranges, but very scant fixed characters. Analysis of the separated mitochondrial datasets mostly resulted in conflicting tree topologies. Nuclear gene sequences were almost identical throughout the geographical ranges of the two species, suggesting a very recent, almost explosive radiation of the terminal operational taxonomic units. Analysis of concatenated molecular datasets was more informative and indicated that, although genetically very close to the A. maculatum - A. triste lineage, A. tigrinum was a monophyletic separate entity. Within the A. maculatum - A. triste cluster, three main clades were supported. The two morphotypes, corresponding to the western North American and eastern North American populations, consistently grouped in a single monophyletic clade with many shared mitochondrial sequences among ticks of the two areas. Ticks from the two remaining morphotypes, south-eastern South America and Peruvian, corresponded to two distinct clades.ConclusionsGiven the paucity of morphological characters, the minimal genetic distance separating morphotypes, and more importantly the fact that two morphotypes are genetically indistinguishable, our data suggest that A. maculatum and A. triste should be synonymized and that morphological differences merely reflect very recent local adaptation to distinct environments in taxa that might be undergoing the first steps of speciation but have yet to complete lineage sorting. Nonetheless, future investigations using more sensitive nuclear markers and/or crossbreeding experiments might reveal the occurrence of very rapid speciation events in this group of taxa. Tentative node dating revealed that the A. tigrinum and A. maculatum - A. triste clades split about 2 Mya, while the A. maculatum - A.triste cluster radiated no earlier than 700,000 years ago.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3186-9) contains supplementary material, which is available to authorized users.

Pathogens, endosymbionts, and blood-meal sources of host-seeking ticks in the fast-changing Maasai Mara wildlife ecosystem

“…Also, one individual, which was provisionally termed Amblyomma sp., had a distinct morphology, and was genetically closest by its ITS-2 sequence to a tick recovered from a traveler in Lope National Park in Gabon [28]. Although we could not conclusively deduce from the evidence in this study, whether these ticks were different species or morphotypes of known species, intraspecific morphological variations are known to occur in Amblyomma species [31] with studies elsewhere demonstrating phenotypic plasticity within this genus [32]. Morphotypic variation in Am.…”

Pathogens, endosymbionts, and blood-meal sources of host-seeking ticks in the fast-changing Maasai Mara wildlife ecosystem

“…gemma has been reported by Walker and co-workers [22], where a minority of populations may exhibit incomplete fusion of the posteromedial and falciform stripes, as is evident in this study. Intraspecific morphological variations are also known to occur in other Amblyomma species with studies elsewhere demonstrating phenotypic plasticity within this genus [34,35]. These findings highlight the important of utmost care in morphological identification of ticks and the need for concurrent genetic studies with nuclear and mitochondrial markers.…”

An Assessment of the Molecular Diversity of Ticks and Tick-Borne Microorganisms of Small Ruminants in Pakistan

“…For Rh. haemaphysaloides , the genetic differences (0.2–7.6%) in cox 1 sequences inferred here suggest the existence of two distinct lineages or even distinct species as their genetic similarity is < 95%, the value generally considered to be the threshold of conspecificity for these genes in ticks [ 52 , 53 , 54 , 55 , 56 ]. However, due to limited genetic data being available for this tick species, it is challenging to define a threshold for species delineation.…”