Relations between allometry, male–male interactions and dispersal in a sap beetle, Librodor japonicus

doi:10.1016/j.anbehav.2006.09.020

Animal Behaviour

Volume 74, Issue 4, October 2007, Pages 749-755

https://doi.org/10.1016/j.anbehav.2006.09.020 Get rights and content

Status-dependent tactics of males trying to gain access to females were examined in relation to morphology, male–male interactions and dispersal in a sap beetle, Librodor japonicus. Males of this species have sexually dimorphic enlarged mandibles which they use in fights for mates on a sap site. Morphological analyses revealed a switchpoint at which the linear slopes of mandible and hindwing width to body length increased and decreased, respectively. Larger males frequently fought with other males in an experimental arena, whereas smaller males often showed sneaking behaviour without fighting. Mark–release–recapture experiments showed a size-dependent difference in dispersal ability of males in the field. The longest dispersal distance was seen in intermediate-sized males, and the shortest dispersal distances were observed in the largest and smallest males. In females, no relation was found between body size and dispersal distance. The largest males thus remain on sap sites and fight with other males, the smallest males also remain on sap sites and try to sneak access to females, and intermediate-sized males move among sap sites and settle on one without a larger male. The results suggest a nondichotomous difference in optimal behavioural tactics of males even though male dimorphism has been detected in armed beetles.

Section snippets

Beetles

Librodor japonicus (Motschulsky) is distributed throughout Japan except for the Ryukyu Archipelago and is commonly found at sites where sap exudes from Quercus trees (Kurosawa et al. 1985). The larvae grow at sap sites, and copulation and male–male fighting occur at sap sites on Quercus variabilis (Okada & Miyatake 2004).

We collected adult beetles with banana bait traps: a clear plastic bottle (500 ml) containing fermented banana fruit (35 g). Several traps were placed on the trunks of Quercus

Male Dimorphism

The test for nonlinearity of relations between prothorax length and the seven traits yielded significant values of α₂ only in the mandible length, head width and hindwing 4 length in males (Table 1). We therefore conducted further analyses only on these relations (Fig. 2). In equation (2), coefficient β₂ was significant in the relation between prothorax length and both mandible length (β₂ = 1.09 ± 0.19, P < 0.0001) and head width (β₂ = 0.82 ± 0.19, P < 0.0001). Significant coefficients β₂ (−0.80 ± 0.31, P <

Discussion

Morphological and behavioural changes in relation to body size corresponded well in L. japonicus. There were switchpoints, in which the linear slopes between the prothorax length and other traits coincided, for mandible length, head width and hindwing size. The slopes increased from the switchpoint in the former two traits and decreased in the latter trait in males (Fig. 2, prothorax length = 2.31 mm), indicating male dimorphisms in L. japonicus. In equation (2), coefficient β₃ was not

Acknowledgments

We thank Drs S. Sanada-Morimura and K. Matsuura, Okayama University, for helpful discussions, and two anonymous referees for useful comments. This work was supported in part by Research Fellowships for Young Scientists (JSPS 195563) to K.O. and a Grant-in-Aid for Scientific Research (KAKENHI 19370011) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, the Ryobi-Teien Memorial Foundation and the Yakumo Foundation for Environmental Science to T.M.

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Relations between allometry, male–male interactions and dispersal in a sap beetle, Librodor japonicus

Section snippets

Beetles

Male Dimorphism

Discussion

Acknowledgments

Animal Behaviour

Trends in Ecology & Evolution

Animal Behaviour

Sexual Selection

The morphology and behavior of dimorphic males in Perdita portalis (Hymenoptera: Andrenidae)

Behavioral Ecology and Sociobiology

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American Naturalist

Male dimorphisms in beetles and earwigs and the question of developmental constraints

Evolution

Costs and the diversification of exaggerated animal structures

Science

The development and evolution of exaggerated morphologies in insects

Annual Review of Entomology

Status-dependent selection in the dimorphic beetle Onthophagus taurus

Proceedings of the Royal Society of London, Series B

Horn and wing allometry and male dimorphism in giant rhinoceros beetles (Coleoptera: Scarabaeidae) of tropical Asia and America

Annals of the Entomological Society of America

Trade-offs during the development of primary and secondary sexual traits in a horned beetle

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Proceedings of the National Academy of Sciences, U.S.A.