Host race formation in the Acari

Abstract

Host race formation generates diversity within species and may even lead to speciation. This phenomenon could be particularly prevalent in the Acari due to the often intimate interaction these species have with their hosts. In this review, we explore the process of host race formation, whether it is likely to occur in this group and what features may favour its evolution. Although few studies are currently available and tend to be biased toward two model species, results suggest that host races are indeed common in this group, and more likely to occur when hosts are long-lived. We discuss future directions for research on host-associated adaptations in this group of organisms and the potential relevance of host race formation for the biodiversity of mites and ticks.

Trans-oceanic host dispersal explains high seabird tick diversity on Cape Verde islands

“…parasite diversity is expected to be low and spatially restricted [16]). While sympatric host race formation and local adaptation may be common in ticks [7,17], our phylogenetic analyses indicate that the primary factor responsible for standing diversity within Cape Verde is multiple independent colonization events. A similar scenario of multiple colonizations and intra-island diversification has been recently reported for avian blood-parasites [6], but at a smaller spatial scale.…”

Reproductive incompatibility between genetically differentiated populations of Tetranychus urticae from different host plants

“…However, such extreme polyphagy at the species level may be harbouring several specialised, genetically differentiated populations adapted on different hosts, as is often the case with generalist feeders (Fox andMorrow 1981, Thompson 1994). Indeed, at the population level some degree of specialisation has been found in T. urticae, as evidenced by the observation of genetically differentiated populations associated with particular host species (reviewed in Magalhães et al 2007).…”

“…of populations partly reproductively isolated due to adaptation on different hosts (Diehl and Bush 1984), is an intermediate stage in this process and has in fact often been implicated to support the plausibility of sympatric speciation (Drès and Mallet 2002). Host race formation, which reduces variation at the population level and increases it at the species level, is not uncommon in the Acari, given their low dispersal ability, strong association with their hosts, host-associated mating, high reproductive rates and short generation times (Magalhães et al 2007). …”

“…The evidence shows that T. urticae populations adapt very rapidly to initially unfavourable hosts, in only a few generations (Gould 1979, Fry 1990, Agrawal 2000, Magalhães et al 2007), although not much evidence exists that artificial selection on different hosts results in reproductive isolation (Fry 1999). In natural populations of T. urticae, some studies have revealed host race formation, some have failed to and some show mixed results.…”

“…Also, different patterns emerge from the application of different markers, possibly because they operate at different time scales . Another hypothesis that can be formulated is that T. urticae may be more likely to form host races on plants that -like citrus and rose bay -produce increased levels of toxic chemicals, exerting high selection pressure on the herbivore, and are long-lived, providing more opportunity for a stable association (Magalhães et al 2007).…”