Sexual dimorphism and allometry in two seed beetles (Coleoptera: Bruchidae)

Abstract

Male Callosobruchus chinensis (Coleoptera: Bruchidae) have elaborated, pectinate antennae, which are absent from conspecific females and both sexes of a congener, Callosobruchus maculatus. To begin to unravel the mechanisms producing this striking dimorphism, we examined which morphological traits best explain body size variation in bruchid beetles and quantified sexual dimorphism of antenna size through allometric analyses. Using principal component analyses, we found that elytron length and pronotum width were significantly correlated with the first principal component, which was interpreted as explaining variation in body size. Regressions of log-transformed body size measures on log-transformed antenna length revealed that males of both species had longer antennae than conspecific females for any given body size, although most of this effect was attributable to higher intercepts, rather than increased allometry, in males. Comparisons among heterospecific males revealed that C. maculatus males have noticeably longer antennae than C. chinensis males at large body sizes. Callosobruchus chinensis males, thus, appear to have increased the receptive area of their antennae by adding to the width of, rather than further elongating, their antennae. Finally, we found evidence for positive allometry between log-transformed antenna length and log-transformed antenna width in C. chinensis males. We discuss our results in the context of evidence supporting the presence of an additional, and potentially unique, sex pheromone in C. chinensis females.

Female size constrains egg size via the influence of reproductive organ size and resource storage in the seed beetle Callosobruchus chinensis

“…The mechanism for this is related to the pattern of development which is a reflection of underlying immutable properties of a development system (Emlen and Nijhout, 2000;Frankino et al, 2005) and has a functional significance which means that the width of ovipositor relative to body size is too large to hold capital resource and mature eggs and locomotion for heavy of it (Sivinski et al, 2001); thus, there is tight scaling between individual body parts and overall size. The lengths of the body parts of C. chinensis and the congeneric species C. maculatus were positively correlated with total body mass (Colgoni and Vamosi, 2006). Egg size increased with female body size in these two seed beetles (Fox, 1993;Kawecki, 1995;Yanagi and Miyatake, 2002).…”

Sexual selection, phenotypic variation, and allometry in genitalic and non-genitalic traits in the sexually size-dimorphic stick insectMicrarchus hystriculeus

“…By contrast, others argue that sexually-selected traits should have higher phenotypic variance than nonsexual traits because high phenotypic variance is an outcome of the genetic or phenotypic condition dependence of traits under directional sexual selection (Price, Schluter & Heckman, 1993;Pomiankowski & Møller, 1995;Rowe & Houle, 1996;Tomkins et al, 2004). The empirical data support both sides of this argument because a variety of sexually-selected traits show low (Colgoni & Vamosi, 2006;Kelly, Bussiere & Gwynne, 2010;Reinhold, 2011) and high (Palestrini et al, 2000;Cotton, Fowler & Pomiankowski, 2004;Fairn, Schulte-Hostedde & Alarie, 2007;Cothran & Jeyasingh, 2010) phenotypic variance. As with the allometric patterns of sexuallyselected traits, the expected high phenotypic variance of sexually-selected traits might be an artefact of biased sampling (sensu Bonduriansky, 2007).…”

“…These less‐exaggerated but nonetheless sexually‐selected, traits tend to be isometric or negatively allometric. For example, the legs of males in a number of arthropods can be either isometric or negatively allometric (Bonduriansky, ); antennal length in male Callosobruchus chinensis beetles is isometric (Colgoni & Vamosi, ) and the forelimbs in several anuran amphibians are isometric (Schulte‐Hostedde et al ., ). Evidence is accumulating that naturally selected traits can also scale with positive allometry (Bergmann & Berk, ).…”

The interaction effect between intraspecific competition and seed quality on the life‐history traits of the seed‐feeding beetleAcanthoscelides macrophthalmus

“…Using image analysis software (Leica Image Analysis v.4.2.0), elytron length (EL), elytron width (EW), and pronotum width (PW) were measured per individual. Two of these morphological traits -EL and PWhave been considered the most appropriate traits to assess body size variation in bruchines (Colgoni & Vamosi, 2006). EL was estimated by calculating the mean value from the longest portion of both elytra.…”