# First Bisexually Dimorphic Phytoptid Taxon (Eriophyoidea, Phytoptidae) from Gondwanian Angiosperm Host

## TL;DR

This study identifies the first gall mite species with distinct seasonal forms in both males and females, associated with ancient Nothofagus trees in South America.

## Contribution

The first documented case of bisexually dimorphic gall mites in the family Phytoptidae, expanding understanding of eriophyoid life cycles and adaptations.

## Key findings

- Austracus havrylenkonis exhibits two distinct forms of both males and females, marking the first bisexually dimorphic taxon in Phytoptidae.
- Seasonal morphological changes in A. havrylenkonis include variations in dorsal opisthosoma annulation between summer and winter forms.
- The study highlights the need for further research on eriophyoid life cycles and their associations with Nothofagus in the Southern Hemisphere.

## Abstract

Gall mites (superfamily Eriophyoidea) are microscopic phytoparasites that transmit plant viruses and induce various abnormal growths, significantly affecting plant health and agricultural productivity. While most species within the Eriophyoidea superfamily are believed to have a simple life cycle, those with a complex life cycle often display seasonal dimorphism, characterized by two distinct female morphotypes: protogynes and deutogynes. In contrast, male dimorphism remains poorly understood due to the scarcity of males in populations and the historical focus on female morphology in Eriophyoidea systematics. Trisetacus kirghisorum (Nalepellidae), a conifer-associated species, is the only known eriophyoid taxon to exhibit seasonal dimorphism in both males and females. In this study, we analyzed morphological, molecular, and biological data from Austracus havrylenkonis, a gall mite species associated with Gondwanian relict host plants of the genus Nothofagus. Using material collected from Chile and Argentina, we demonstrated that this species exhibits two distinct forms of both males and females, marking it as the first known bisexually dimorphic taxon within the family Phytoptidae. We further discuss the gradual and discrete seasonal morphological changes observed in Eriophyoidea populations and emphasize the importance of additional studies on life cycles and faunistic surveys of gall mites associated with Nothofagus in Australasia.

Acariform mites of the superfamily Eriophyoidea are permanent parasites of higher vascular plants. Seasonal morphological dimorphism in females has been documented across various eriophyoid taxa, while male dimorphism remains poorly understood. In this study, we analyzed morphological, molecular, and biological data from the genus Austracus Keifer 1944, with a particular focus on the type species, A. havrylenkonis Keifer 1944, associated with Nothofagus. Using new material collected from Chile and Argentina, we demonstrated that this species exhibits two distinct forms of both males and females, making it the first known bisexually dimorphic taxon within the family Phytoptidae. The summer form of A. havrylenkonis displays the unstable annulation of the dorsal opisthosoma, characterized by a significant variation in the number of thin, microtuberculated dorsal annuli interspersed among the broader, plate-like annuli typical of the winter form. This finding aligns with the previous observations of atypical deuterogyny in Eriophyoidea and leads us to hypothesize that gall mites employ diverse adaptive strategies—manifesting as either gradual or discrete morphological changes—to cope with seasonal environmental fluctuations. Investigating the genetic mechanisms underlying these adaptive strategies, along with further studies of eriophyoids associated with Nothofagus in the Southern Hemisphere, represents a promising direction for future research.