Genetic analysis along an invasion pathway reveals endemic cryptic taxa, but a single species with little population structure in the introduced range

Abstract

Aim The invasion pathways of pest arthropods can be traced using genetic tools to develop an understanding of the processes that have shaped successful invasions and to inform both pest management and conservation strategies in their non-native and native ranges, respectively. The redlegged earth mite, Halotydeus destructor, is a major economic pest in Australia, successfully establishing and spreading after arrival from South Africa more than 100 years ago. Halotydeus destructor has recently expanded its range and evolved resistance to numerous pesticides in Australia, raising questions around its origin and spread.Location South Africa and Australia.Methods We sampled H. destructor populations in South Africa and Australia and developed a microsatellite marker library. We then examined genetic variation using mtDNA and microsatellite markers across both native and invasive ranges to determine endemic genetic diversity within South Africa, identify the likely origin of invasive populations and test genetic divergence across Australia.Results The data show that H. destructor comprises a cryptic species complex in South Africa, with putative climatic/host plant associations that may correspond to regional variation. A lineage similar to that found near Cape Town has spread throughout Western and eastern Australia, where populations remain genetically similar.Main conclusions Tracing the invasion pathway of this economically important pest revealed cryptic lineages in South Africa which points to the need for a taxonomic revision. The absence of significant genetic structure across the wide invasive range of H. destructor within Australia has implications for the development (and spread) of pesticide resistance and also points to recent local adaptation in physiological traits.

A cryptic diapause strategy in Halotydeus destructor (Tucker) (Trombidiformes: Penthaleidae) induced by multiple cues

“…The presence of different types of diapause eggs raises the question of whether these reflect adaptive responses to different recurring environmental conditions and different levels of environmental variability. This could be further tested by comparing the incidence of diapause strategies across populations of mites given that H. destructor in Australia covers a wide range of climatic conditions and there is evidence for adaptive differentiation in H. destructor populations …”

“…In addition to the individual differences in female mites observed in our study, evolutionary changes are probably involved in diapause characteristics of H. destructor, which entered Australia from South Africa over a century ago and have undergone genetic adaptation. 28 In comparison with South African populations, Australian populations have expanded into hotter and drier inland areas and have become more thermoresistant. [55][56][57] Pesticide resistance against pyrethroids 58,59 and organophosphates 39 has also evolved in H. destructor populations in Australia.…”

“…This could be further tested by comparing the incidence of diapause strategies across populations of mites given that H. destructor in Australia covers a wide range of climatic conditions and there is evidence for adaptive differentiation in H. destructor populations. 28,56,57…”

“…Winter diapause of eggs in Acari has been reported in seven species from the Tetranychoidea superfamily. Summer diapause is known in at least five species from the Eupodoidea superfamily, including Halotydeus destructor (Tucker) (Trombidiformes: Penthaleidae), an invasive pest from South Africa introduced into Australia, which attacks pastures, grains and vegetables . Although legumes are the preferred hosts of this polyphagous species, broadleaf weeds and microflora also provide moist habitat and supplementary nutrition .…”

“…Summer diapause is known in at least five species from the Eupodoidea superfamily, 16 including Halotydeus destructor (Tucker) (Trombidiformes: Penthaleidae), an invasive pest from South Africa introduced into Australia, which attacks pastures, grains and vegetables. [26][27][28] Although legumes are the preferred hosts of this polyphagous species, broadleaf weeds and microflora also provide moist habitat and supplementary nutrition. [29][30][31][32] In Australia, this pest is active in the cool and wet months, typically between April and November, completing at least three generations a year.…”