Intraspecific Variation in the Secretion and Morphology of the Scent Glands of a Neotropical Harvestman (Opiliones, Cosmetidae)

Abstract

Relatively little is known about intraspecific variation in the use of chemical defenses by cosmetid harvestmen. In this study, we investigated sexual and ontogenetic variation in the emission of secretions from the scent glands and the morphology of the ozopores of Erginulus clavotibialis, a Neotropical species from Belize. Most individuals (> 94%) did not secrete when seized by leg IV, however, when the body was subsequently grasped firmly with forceps, 76% of the harvestmen (n = 96) responded by releasing enteric fluid (clear, no odor) or secretions from the scent glands (reddish-brown, distinct odor), most commonly in the form of globules near the ozopores. Adults and penultimate nymphs rarely (less than 5% of all trials) exhibited leg dabbing, an unusual behavior generally associated with cosmetid harvestmen. Males released enteric fluid (without scent gland secretions) significantly more than females or nymphs. Nymphs emitted secretions from scent glands at a significantly greater frequency than males or females. Using SEM, we examined the ozopores and the dorsal processes of coxae I and II and found that the morphology of these structures varies between adults and nymphs but not between males and females. The openings of the ozopores of nymphs are circular and are not obscured by the dorsal posterior process of coxa I and the dorsal anterior process of coxa II. In contrast, adults have subtriangular ozopores that are difficult to observe without dissection because they are partially blocked by the dorsal processes of coxae I and II.