Adaptations to stag beetle weaponry and its ecological consequences

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Adaptations to stag beetle weaponryand its ecological consequencesJana Goyens, Joris Dirckx, Peter AertsLaboratory for Functional MorphologyUniversity of Antwerp, BelgiumLaboratory of BioMedical Physics

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Introduction: stag beetle armature Stag beetle family: Large male mandibles (jaws)High diversity in size and shape:

Prosopocoilus umhangiAegognathus waterhousei Allotopus moellenkampiCyclommatus metallifer#

Introduction: stag beetle armature Mandibles used as armature in fightsMales fight each other over mating opportunities:

Youtube, Tammy Bergstrm

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Introduction: stag beetle armature

Aims: Adaptations of head morphology to make mandibles useful tools? mandible bite force

Morphological adaptations to move around with heavy and large armature? stability and efficiency

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Mandible bite forceMales bite more forcefully:

: 6.9 2.0 N normalized: 849.2

: 1.1 0.4 N normalized: 285.2

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Mandible bite forceHigher male bite force DESPITE mechanical disadvantage (output lever)Explanations:Longer input lever: compensation for long output leverLarger bite muscles (microCT-scans)Males and females almost optimal muscle fiber direction (CT-scans)

Conclusion:Male head size and shape drastically changedto produce high bite forces

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LocomotionHeavy male head CAUSES impaired running:

(static) instability:

Alternating tripod gait

Static stability possible

Stability margin:

Perpendicular distance to edge support triangle

Negative when outside triangle#

LocomotionHeavy male head CAUSES impaired running:

(static) instability:

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LocomotionHeavy male head CAUSES impaired running:

(static) instability:

Very cost inefficient

Cost of transport:: 4.15 1.13 Jm-1kg-1: 2.52 0.76 Jm-1kg-1

Males 40% higher cost of transport

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Conclusions

Male stag beetles are completely adapted to male-male fights:Diversification and enlargement of mandibles troughout Lucanidae family

Head size and shape adapted for high bite forces

Large ecological consequencesStatic instability: males occasionally bounce against the ground with their headHigh locomotion cost

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Thank you for your attention!

Acknowledgements:Ministry of Youth and Sport of Azerbaijan RepublicAzerbaijan Young Scientists, Postgraduate and Masters Union (AYSPMU)EurodocUniversity of Antwerp Dehousse grant #