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Two Distinct Genotypes of Spissistilus festinus (Say, 1830) (Hemiptera, Membracidae) in the United States Revealed by Phylogenetic and Morphological Analyses
Open AccessArticle

Allometry and Fighting Behaviour of a Dimorphic Stag Beetle Cyclommatus mniszechi (Coleoptera: Lucanidae)

Department of Life Science, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Rd., Taipei 11677, Taiwan
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Author to whom correspondence should be addressed.
These authors have contributed equally to this work.
Insects 2020, 11(2), 81; https://doi.org/10.3390/insects11020081
Received: 2 December 2019 / Revised: 16 January 2020 / Accepted: 20 January 2020 / Published: 23 January 2020
Male stag beetles (Coleoptera: Lucanidae) use their mandibles as weapons to compete for resources and reproduction. Mandible size in stag beetles can be associated with different behaviours and the outcome of male contests. We investigated the allometric relationship between mandible and body size in males of the stag beetle Cyclommatus mniszechi to uncover distinct morphs. The results divided male C. mniszechi into majors and minors with the switch point of mandible length at 14.01 mm. The allometric slope of mandibles was positive for both morphs but was steeper for the minors. We also characterised the fighting behaviour of the different morphs in size-matched contests using sequential analyses. Males matched each other’s behaviour in contests with many physical contacts, no injury and a progression from low towards high aggression and rare de-escalation. Major and minor males employed the same behavioural elements in contests, but major males were more likely to escalate directly into more aggressive phases and minor males tended to stay within phases. This finding suggests that major males may compete more aggressively than minor males in contests.
Keywords: body size; male–male competition; mandible; sequential analysis; sexual selection; weapon body size; male–male competition; mandible; sequential analysis; sexual selection; weapon
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    Doi: 10.5281/zenodo.3603560
    Description: Supplementary Materials: Table S1. The morphological measurements of males of Cyclommatus mniszechi used for allometry analyses. Table S2. The behavioural sequence data used for sequential analyses of size-matched contests in major males of Cyclommatus mniszechi. Table S3. The behavioural sequence data used for sequential analyses of size-matched contests in minor males of Cyclommatus mniszechi. Video S1. The behavioural sequence of males of Cyclommatus mniszechi in fighting contests under the laboratory setups. One of the opponents walked to the other and touched it (00:07), and then both of them displayed ‘defensive posture’ (00:08) after ‘touch’. Once both individuals approached each other, they accelerated antennation and raised their mandibles and prothoracic parts. The contest then progressed into ‘body raising’ (00:14). They then performed ‘attack’ and ‘push’ to each other several times and then escalated to ‘tussle’ (00:20) and interlocked their mandibles until one of the contestants was clamped (‘clamp1’) in the air by the other for a second and flipped (00:50). The winner dropped the loser and kept attacking and pushing the loser while the loser retreated and moved backwards (00:51).
MDPI and ACS Style

Chen, Z.-Y.; Hsu, Y.; Lin, C.-P. Allometry and Fighting Behaviour of a Dimorphic Stag Beetle Cyclommatus mniszechi (Coleoptera: Lucanidae). Insects 2020, 11, 81.

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