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R Soc Open Sci. 2017 Sep 13;4(9):171108. doi: 10.1098/rsos.171108. eCollection 2017 Sep.

How tight are beetle hugs? Attachment in mating leaf beetles.

Author information

1
Institute for Botany, Technische Universität Dresden, 01062 Dresden, Germany.
2
Department of Mechanical Engineering, Technion-Israel Institute of Technology, Technion City, 32000 Haifa, Israel.
3
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332, USA.

Abstract

Similar to other leaf beetles, rosemary beetles Chrysolina americana exhibit a distinct sexual dimorphism in tarsal attachment setae. Setal discoid terminals occur only in males, and they have been previously associated with a long-term attachment to the female's back (elytra) during copulation and mate guarding. For the first time, we studied living males and females holding to female's elytra. Pull-off force measurements with a custom-made tribometer featuring a self-aligning sample holder confirmed stronger attachment to female elytra compared with glass in both males and females; corresponding to 45 and 30 times the body weight, respectively. In line with previous studies, males generated significantly higher forces than females on convex elytra and flat glass, 1.2 times and 6.8 times, respectively. Convex substrates like elytra seem to improve the attachment ability of rosemary beetles, because they can hold more strongly due to favourable shear angles of legs, tarsi and adhesive setae. A self-aligning sample holder is found to be suitable for running force measurement tests with living biological samples.

KEYWORDS:

adhesive setae; attachment; copulation; discoid; sexual dimorphism; sexual selection

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