Reflections on distribution and origin of the halacarid genus Isobactrus (Acari: Halacaridae)

Abstract

Isobactrus is a worldwide-spread genus. Most species live in the upper and middle area of a more or less regularly emerged zone. The species diversity is distinctly higher in the northern than in the southern hemisphere. At present, the genus consists of 29 species. An analysis of the geographical distribution of 36 external morphological characters revealed a uniformity in the combination of states of northern Pacific species, but a heterogeneity in the characters of northern Atlantic species. Several character states demonstrate a distinct north/south or north/tropics/south distribution. A parsimony analysis revealed basal northern Atlantic clades, a northern Pacific clade that also includes Northern Atlantic species and an Indo-Pacific clade with a tropical area cluster. The present data suggest that the genus Isobactrus evolved in the Palaearctic Ocean and might represent a basal lineage within the family Halacaridae.