Revision of the oribatid mite genus Austronothrus Hammer (Acari:Oribatida):sexual dimorphism and a re-evaluation of the phylogenetic relationships of the family Crotoniidae

Abstract

The Gondwanan relict oribatid mite family Crotoniidae contains the genera Austronothrus Hammer, 1966, Crotonia Thorell, 1876 and Holonothrus Wallwork, 1963. This family is of considerable interest biogeographically and also because the members of the family may have re-evolved sexuality from thelytokous parthenogenetic ancestors. Crotonia and Holonothrus are speciose and widely distributed whereas Austronothrus is obscure, hitherto monospecific and known only from New Zealand. We revise Austronothrus and compare it with its better-known congeners. Two new species of Austronothrus are described from New Zealand, namely A. clarki, sp. nov., and A. flagellatus, sp. nov. The only previously known species, Austronothrus curviseta Hammer, 1966, is redescribed and the genus is redefined. The presence of male specimens of all species confirmed Austronothrus as a sexual genus, like its congeners. Secondary sexual characteristics within Austronothrus and Crotonia include significant differences in body size and proportion, as well as the lengths and shapes of various setae, predominantly those of the notogastral region. Because these characters are frequently used by taxonomists to separate and define species within the Crotoniidae, it is important that the sex of adult specimens be determined to avoid describing conspecific males and females as separate species. A phylogenetic analysis based on morphological characters shows the crotoniid genera nested within the Camisiidae, with Camisia von Heyden, 1826 basal to the crotoniid clade of Austronothrus, Holonothrus and Crotonia, and with a clade of Platynothrus Berlese, 1913, Heminothrus Berlese, 1913 and Paracamisia Olszanowski & Norton, 2002 (Camisiidae) forming the sister clade of Camisia + Crotoniidae. Thus, Camisiidae is paraphyletic with respect to Crotoniidae. The family Crotoniidae is revised in light of the cladistic analysis, and relegated to subfamily rank. Three subfamilies are defined within the Camisiidae : Crotoniinae (containing Crotonia, Austronothrus and Holonothrus), Camisiinae (containing Camisia) and Heminothridae, subfam. nov. (containing Heminothrus, Platynothrus and Neonothrus Forsslund, 1955). Nothrus maximus Trägårdh, 1901 belongs to the genus Platynothrus and is recombined.

Mites on Plants

“…the rocky intertidal zone (Krisper and Schuster 2008 ) and semi-aquatic habitats (Behan-Pelletier 1996 ). At least in their latter instars, crotoniine oribatids are largely associated with the epiphytes growing on bark and tree limbs, and they are unusual in being the only sexual lineage (with moderate sexual dimporphism) in a cluster of parthenogenetic lineages (Colloff and Cameron 2009 ). Some parthenogenetic lineages of Crotonioidea also are arboreal, but it is interesting that sexual dimorphism and extreme habitats are again associated.…”

The Crotonia fauna of New Zealand revisited (Acari: Oribatida): taxonomy, <br />phylogeny, ecological distribution and biogeography

“…The oribatid genus Crotonia is of biogeographical and evolutionary significance for its combination of harmonic Gondwanan and disjunct trans-Pacific vicariant distribution patterns (Colloff 2009b;2010a). In a phylogenetic analysis, Colloff and Cameron (2009) recognised the subfamily Crotoniinae, containing Crotonia, Holonothrus and Austronothrus. Despite recent findings of Austronothrus on Norfolk Island and Borneo (Colloff & Cameron 2014), New Zealand is the only place where all three genera have been recorded.…”

Revealing the Hyperdiverse Mite Fauna of Subarctic Canada through DNA Barcoding

“…Despite their diversity and abundance, mites are rarely included in biodiversity assessments because of serious taxonomic barriers. The status of many species is uncertain due to synonymies [19] , morphotypes which are distinct species [20] , and sexual dimorphisms [21] . Immature life stages are also excluded from surveys as they lack diagnostic morphological characters.…”