Trends in Parasitology
OpinionSpecies Concepts: What about Ticks?
Section snippets
The Species Problem
For a long time, philosophers and taxonomists have tried to classify different forms of life. This is what taxonomy is about: the science (and practice) of identifying, naming, classifying, and describing organisms. For instance, as early as the 4th century BC, the Greek philosopher Aristotle, in his book series Ton peri ta zoia historion (translated into English as ‘History of Animals’), grouped animals according to their morphology: for example, birds have feathers, wings, beaks, and two bony
The ‘Tic-Tac’: Tick Evolution
Ticks are arthropods belonging to the order Ixodida, which is traditionally subdivided into three families: Argasidae, Ixodidae, and Nuttalliellidae [4]. Recently, a new, extinct family, namely Deinocrotonidae, was proposed based on adult ticks found in a Burmese amber from the Cretaceous (circa 99 million years ago) [5].
Ticks diverged from other Acari millions of years ago, probably as parasites of the ancestors of modern reptiles, amphibians, or both. An early hypothesis placed the origin of
Tick Taxonomy: From Linnaeus to Present Days
Ticks have been known since ancient times [12]. Linnaeus’ first endeavour to describe and classify ticks appeared in 1746, in his Fauna Svecicaiii. Nonetheless, the International Commission on Zoological Nomenclature arbitrarily fixed the date January 1, 1758 as the starting point of zoological nomenclature. Consequently, tick taxonomy is considered to be born in 1758, with the 10th edition of Systema Naturae, when Linnaeus described different tick species, including the lone star tick
Species Concepts in Ticks
The oldest and the newest valid tick species descriptions were based on morphology. In fact, morphology was, and still is, the most widely used criterion for species delineation, nowadays with much more refined descriptions [16] – with some exceptions [17]. High-quality light microscopy and, eventually, scanning electron microscopy have been used in recent species descriptions, providing additional morphological details previously overlooked 18, 19, 20. Furthermore, new methodological
Okay, Let Us Talk Biology and Genetics
Biological and genetic studies are becoming more widely used in modern tick taxonomy, shedding new light on old taxonomic issues, but also uncovering novel taxonomic problems to be solved. In fact, results from biological and genetic analyses may not always be congruent.
According to the BSC, species are groups of natural populations that actually or potentially interbreed and that are reproductively isolated from other such groups. Reproductive isolation may occur due to prezygotic barriers
Concluding Remarks
While several criteria have been used to delimit and delineate tick species, the typological approach is still the most widely used in tick taxonomy. When assessing whether a tick (or group of ticks) represents a new species on morphological grounds, one should keep in mind that intraspecific variability does exist and that threshold between intraspecific and interspecific variabilities is still poorly understood, especially when dealing with species complexes 41, 43. Thus, cautiousness is
Note added in Proof
One of the outstanding questions raised in this article is: ‘Can we reach a consensus about the genus-level classification of the family Argasidae?’ (see Outstanding Questions). After this article was written, a new study dealing with this question was published [68]. The authors sequenced the mitochondrial genomes of several soft tick species and proposed a revised genus-level classification for the family Argasidae. The authors also presented an updated list of soft tick species, which
Acknowledgments
Thanks to Professor Chris Arme and Professor Andrey José de Andrade for their critical review of an early draft of this article. Thanks also to my research group (Vector-Borne Diseases: A One Health Approach) for the scientific discussions during the preparation of this article and for their suggestions on Figure 1.
Disclaimer Statement
The content of this article is the sole responsibility of the author.
Glossary
- Basal lineage
- a genetic lineage that connects a variant allele (type) possessed by a more common ancestor that evolves into two descendant variants possessed by a branch ancestor.
- Crossbreeding
- the mating of organisms of different breeds, varieties, or species.
- Cryptic species
- two or more distinct species that are morphologically similar or identical.
- Diagnosability
- the quality of being diagnosable.
- Evolutionary lineage
- a temporal series of organisms, populations, cells, or genes connected by a
References (68)
Next-generation sequencing as means to retrieve tick systematic markers, with the focus on Nuttalliella namaqua (Ixodoidea: Nuttalliellidae)
Ticks Tick Borne Dis.
(2015)Molecular phylogeny of soft ticks (Ixodida: Argasidae) inferred from mitochondrial genome and nuclear rRNA sequences
Ticks Tick Borne Dis.
(2014)Reassessment of the taxonomic status of Amblyomma cajennense (Fabricius, 1787) with the description of three new species, Amblyomma tonelliae n. sp., Amblyomma interandinum n. sp. and Amblyomma patinoi n. sp., and reinstatement of Amblyomma mixtum Koch, 1844, and Amblyomma sculptum Berlese, 1888 (Ixodida: Ixodidae)
Ticks Tick Borne Dis.
(2014)Integrative taxonomy of Afrotropical Ornithodoros (Ornithodoros) (Acari: Ixodida: Argasidae)
Ticks Tick Borne Dis.
(2018)Linking morphometric and genetic divergence with host use in the tick complex, Ornithodoros capensis sensu lato
Infect. Genet. Evol.
(2016)Different lines of evidence used to delimit species in ticks: A study of the South American populations of Amblyomma parvum (Acari: Ixodidae)
Ticks Tick Borne Dis.
(2016)Distribution and genetic variation of Amblyomma triste (Acari: Ixodidae) in Argentina
Ticks Tick Borne Dis.
(2013)Description of all the stages of Ixodes inopinatus n. sp. (Acari: Ixodidae)
Ticks Tick Borne Dis.
(2014)Phylogenetic analysis of mitochondrial genome sequences indicates that the cattle tick, Rhipicephalus (Boophilus) microplus, contains a cryptic species
Mol. Phylogenet. Evol.
(2014)Morphological and phylogenetic analyses of Rhipicephalus microplus ticks from Bangladesh, Pakistan and Myanmar
Ticks Tick Borne Dis.
(2018)
Further thoughts on the taxonomy and vector role of Rhipicephalus sanguineus group ticks
Vet. Parasitol.
The taxonomic status of Rhipicephalus sanguineus (Latreille, 1806)
Vet. Parasitol.
Rhipicephalus sanguineus (Latreille, 1806): neotype designation, morphological re-description of all parasitic stages and molecular characterization
Ticks Tick Borne Dis.
Molecules and morphology: evidence for cryptic hybridization in African Hyalomma (Acari: Ixodidae)
Mol. Phylogenet. Evol.
Ecological explanations for (incomplete) speciation
Trends Ecol. Evol.
Natural hybridization of the ticks Ixodes persulcatus and Ixodes pavlovskyi in their sympatric populations in Western Siberia
Infect. Genet. Evol.
Natural hybridization between Ixodes ricinus and Ixodes persulcatus ticks evidenced by molecular genetics methods
Ticks Tick Borne Dis.
Ancestral reconstruction of tick lineages
Ticks Tick Borne Dis.
Coalescent-based species delimitation in an integrative taxonomy
Trends Ecol. Evol.
Implications of different species concepts for conserving biodiversity
Biol. Conserv.
Biology and systematics of Echinococcus
Adv. Parasitol.
The application of species criteria in avian taxonomy and its implications for the debate over species concepts
Biol. Rev. Camb. Philos. Soc.
Species concepts, diversity, and evolution in primates: lessons to be learned from mouse lemurs
Evol. Anthropol.
Species delimitation based on diagnosis and monophyly, and its importance for advancing mammalian taxonomy
Zool. Res.
Biology of Ticks
Ticks parasitised feathered dinosaurs as revealed by Cretaceous amber assemblages
Nat. Commun.
The mitochondrial genomes of Nuttalliella namaqua (Ixodoidea: Nuttalliellidae) and Argas africolumbae (Ixodoidae: Argasidae): estimation of divergence dates for the major tick lineages and reconstruction of ancestral blood-feeding characters
PLoS One
The fossil record and the origin of ticks revisited
Exp. Appl. Acarol.
Haemaphysalis cretacea a nymph of a new species of hard tick in Burmese amber
Parasitology
Nuttalliella namaqua: a living fossil and closest relative to the ancestral tick lineage: implications for the evolution of blood-feeding in ticks
PLoS One
The enigma of the dog mummy from ancient Egypt and the origin of ‘Rhipicephalus sanguineus'
Parasit. Vectors
Names for Ixodidae (Acari: Ixodoidea): valid, synonyms, incertae sedis, nomina dubia, nomina nuda, lapsus, incorrect and suppressed names – with notes on confusions and misidentifications
Zootaxa
The Argasidae, Ixodidae and Nuttalliellidae (Acari: Ixodida) of the world: a list of valid species names
Zootaxa
Cited by (45)
Biocontrol potential of entomopathogenic nematodes against camel tick, Hyalomma dromedarii (Acari: Ixodidae)
2024, Journal of King Saud University - ScienceNon-invasive detection of Orthohalarachne attenuata (Banks, 1910) and Orthohalarachne diminuata (Doetschman, 1944) (Acari: Halarachnidae) in free-ranging synanthropic South American sea lions Otaria flavescens (Shaw, 1800)
2023, International Journal for Parasitology: Parasites and WildlifeMALDI-TOF MS identification of cattle ticks from Cameroon
2023, Ticks and Tick-borne DiseasesRhipicephalus Capensis (Acari: Ixodidae), A geographically restricted South African tick, returning with a human traveler to the United States
2022, Ticks and Tick-borne DiseasesCitation Excerpt :We note further, for perspective, that the surface area of South Africa is approximately 13% that of the U.S., and yet nationwide South African tick diversity is surprisingly equal to the number of tick species living in the U.S. (i.e., 96 species, JWM unpublished records). Disregarding extralimital tick species documented only once in the Fynbos region on non-native hosts, introduced/established exotic species, and also other species now locally extirpated and absent (Horak et al., 2018), the present resident diversity of ticks in the Fynbos comprises 30 ixodid species and 4 argasids (3.5% of the world diversity) (Walker, 1991; Horak et al., 2018; Dantas-Torres, 2018; Mans et al., 2019, 2021). Of the overall South African tick diversity, no soft ticks, but seven species (6.4%) of the hard ticks are endemic (or nearly so) to the Fynbos, and R. capensis is one of the two endemic Rhipicephalus spp. ticks.