Relationship between body size and sexual size dimorphism in syringophilid quill mites

Lajos Rózsa,Evelyn Moldovan

doi:10.1007/s00436-022-07437-3

Lajos Rózsa, Evelyn Moldovan

Open Access

https://doi.org/10.1007/s00436-022-07437-3

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Abstract

A positive relationship of body size and sexual size dimorphism (males’ size relative to females), called Rensch’s rule, is often observed in comparisons within non-parasitic taxa. However, this allometric relationship has rarely been tested in comparisons across closely related parasite species. Since male sexual rivalry is often regarded as the main cause of this phenomenon, the present study tests this rule in a taxon where sexual selection is almost totally absent in males. Body size data of (non-physogastric) female and male quill mites (Acari: Syringophilidae) were gathered from the literature to investigate this relationship. The data set consisted of 113 species representing 8 genera. For the data set as a whole, increasing body size came together with decreasing relative body size of males (relative to females), a phenomenon known as converse Rensch’s rule. Repeating the same analysis for the 8 genera separately, similar patterns were found in 4 significant and 3 non-significant cases. There was a significant tendency to comply with Rensch’s rule only in one genus, the Neoaulonastus. Thus, converse Rensch’s rule is the primary trend in syringophilid quill mites that appears repeatedly and independently in several genera. This phenomenon is probably caused by their extreme inbreeding, which strongly reduces sexual competition among males in this taxon.

Highlights

Most parasites reproduce sexually, or at least both sexually and asexually, giving rise to sexual selection as a potentially influential force on their evolution
In comparisons across closely related species, male body size relative to female size tends to increase with the average size of the species, an allometric relationship called Rensch’s rule (RR)
RR postulates that sexual size dimorphism decreases with the species body size in taxa where males are smaller than females, and it increases in taxa where males are larger than females (Rensch 1959)

Summary

Introduction

At least both sexually and asexually, giving rise to sexual selection as a potentially influential force on their evolution. Most often only its indirect effects are detected, such as the sexually selected morphological traits of parasites. Sexual dimorphism in body size is widespread among dioecious parasites, such as in nematodes, acanthocephalans, gamasid mites, fleas, and lice (see, e.g., Poulin 1997; Caddigan et al 2017; Surkova et al 2018; Piross et al 2019). RR postulates that sexual size dimorphism decreases with the species body size in taxa where males are smaller than females, and it increases in taxa where males are larger than females (Rensch 1959). Several free-living (i.e., non-parasitic) animals, and most often vertebrates, have been analyzed in this respect, and a

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