Fighting, dispersing, and sneaking: body‐size dependent mating tactics by male Librodor japonicus beetles

Abstract

1. Scaling relations between weapons and body size depart from linearity in many male beetles. In many previous studies, these males have been divided into major and minor males with a switch point, that is male dimorphism. Major and minor males adopt strikingly different reproductive tactics.2. We found three size‐dependent behaviours, i.e. fighting, dispersing, and sneaking, however, among Librodor japonicus males with dimorphic mandibles. We statistically classified males into large, medium, and small (L‐, M‐, and S‐males) sizes and then compared the dispersal of males from a foraging site, behaviours to gain access to females, and sizes of mandibles, wings, and testes.3. M‐males dispersed earlier than L‐ and S‐males from a territory in a field, but no difference in the frequency of dispersal was observed between L‐ and S‐males. Observations of male–male interactions in the laboratory showed that L‐males frequently fought with other males in a fighting arena, while S‐males often showed sneaking behaviour without fighting.4. On the basis of the morphological analysis, we concluded that S‐males invested their available resources more in sperm (= testes), M‐males more in wings, and L‐males more in mandibles in L. japonicus.5. Even though a morphological male dimorphism was detected, it might be possible to classify the males of the armed beetles into more than two behavioural tactics if we examine their behaviours.

Plasticity of size and allometry in multiple sexually selected traits in an armed beetle Gnatocerus cornutus

“…There is also some evidence that males are able to adjust their sexual traits in response to the environment factors (Emlen 1994;Cotton et al 2004;Bonduriansky 2007). Therefore, exaggerated traits such as ornaments and weapons often show high phenotypic variance (Green 1992;Kodric-Brown et al 2006) and scaling relationships between exaggerated traits and body size, i.e., allometry, sometimes depart from linearity (Unrug et al 2004;Tomkins et al 2005a;Okada et al 2007Okada et al , 2008. In addition the allometric slopes and intercepts also change in response to environmental fluctuation (allometric plasticity, sensu Emlen 1997).…”

Dispersal and ejaculatory strategies associated with exaggeration of weapon in an armed beetle

“…Of 150 males of each line, each individual was introduced into the container, and the number of males dispersing from the container was observed every hour during scotophase under a red light for 8 h. We compared the male dispersal tendencies between selection regimes at 8 h after the introduction. Several previous studies indicated that the dispersal tendency in weapon-bearing male beetles is positively associated with the dispersal ability in the field (see Okada et al 2007Okada et al , 2008.…”

Histone deacetylases control module-specific phenotypic plasticity in beetle weapons

“…In the case of sexually selected exaggerated traits, condition-dependent selections for fighting or sneaking/dispersal are thought to generate the evolution of heightened plasticity (6)(7)(8). In contrast, other body modules, such as genitalia, are under stabilizing selection that favors the production of uniform organ size irrespective of developmental conditions (i.e., canalization) (10)(11)(12).…”