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Size and shape variation in the male dimorphic head weapons of an anthribid weevil (Hoherius meinertzhageni)

Abstract

Allometry is a common technique used by biologists to quantify and describe the exaggerated sexually selected traits of beetles. While horned species have dominated studies documenting weapon evolution among beetles, there is remarkable diversity in weapon type, including enormous mandibles, robust hind legs and elongated rostra. Here, I characterise intrasexual and intraspecific variation in body size, head size and shape in the anthribid weevil Hoherius meinertzhageni using traditional linear and 2D geometric morphometric approaches. Large males possess a broadened, shield-like head, which is much smaller in females and small-bodied males. Males were significantly larger in head and body size than females, and showed higher levels of variation in head and mandible size. Males exhibited an intrasexual dimorphism in head width and mandible length, but not head or antenna length. Overall, male head and mandible size showed hyperallometry, but minor males showed significantly steeper allometric slopes compared to major males and females. Geometric morphometrics revealed distinct differences in head shape between all groups (major and minor males, females). There were significant differences in the magnitude and direction of trajectories in size-shape space between males and females, with males showing more shape change per unit of size than females. In addition, there were significant differences in trajectory length but not slope angle between minor and major males. Overall, this combined approach using allometry with both traditional linear morphometrics and geometric morphometrics suggests that sexual selection is driving divergence in weapon size and shape among males and between the sexes. Preliminary behavioural observations support the hypothesis that weapon morphology corresponds to alternative mating tactics, although a more thorough investigation into the mating system of H. meinertzhageni is required.

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taken from H. meinertzhageni including head width (HW), head length (HL) and mandible length (ML). Illustration by Emma Scheltema

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Code availability

R code used in all analyses will be made publicly available at the Open Science Framework after publication.

Data availability

Collection locality and measurement data are provided in Supplementary table 1. Shape data based on geometric morphometrics will be publicly available at the Open Science Framework after publication.

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Acknowledgements

Thank you to Oriane David for assistance with specimen landmarking, Pete McGregor for sharing locality and behaviour information and photographs of H. meinertzhageni, as well as sharing videos of the species behaviour, Greg Holwell for helpful comments on a draft of this manuscript, Emma Sherratt and Jaimi Gray for helpful geomorph advice, Grace Hall, Cor Vink and Phil Sirvid for assistance in the arthropod collections of New Zealand, Birgit Rhodes for assistance using the imaging microscope at Landcare Research, and Emma Scheltema for the illustrations. I thank Emma Sherratt for very helpful guidance as handling editor and two anonymous reviewers for their constructive suggestions. Finally, thank you to Robert Hoare for pointing out this fascinating beetle to me in the first place.

Funding

I was supported by a Kate Edgar Educational Trust postdoctoral award during data collection, and a Rutherford Postdoctoral Fellowship during manuscript preparation.

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Contributions

CJP conceived and designed the study, collected and analysed the data, and wrote the manuscript.

Corresponding author

Correspondence to Christina J. Painting.

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I have none to declare.

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Supplementary Information

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Supplementary file1 (XLSX 18 kb)

Supplementary file2 (DOCX 12 kb)

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Painting, C.J. Size and shape variation in the male dimorphic head weapons of an anthribid weevil (Hoherius meinertzhageni). Evol Ecol 36, 643–662 (2022). https://doi.org/10.1007/s10682-021-10127-8

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  • DOI: https://doi.org/10.1007/s10682-021-10127-8

Keywords

  • Anthribidae
  • Male dimorphism
  • Sexual dimorphism
  • Sexual selection
  • Geometric morphometrics
  • Weaponry