Adaptations to stag beetle weaponry and its ecological consequences Jana Goyens, Joris Dirckx, Peter...
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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 #