Variation in body size in the giant rhinoceros beetle Trypoxylus dichotomus is mediated by maternal effects on egg size

Abstract

1. The egg size of insects can vary depending on maternal body size or resource status, and it may influence offspring body size by determining initial resource level. 2. The giant rhinoceros beetle Trypoxylus dichotomus exhibits considerable variation in body size, some of which is attributed to the variation in larval food (humus) quality, although a substantial amount of variation in body size remains unexplained. In the present study, changes in the egg size and offspring body size in response to several maternal variables were examined (i.e. body size, age, and, nutritional status). 3. Nutritional intake of the females during the adult stage did not affect the egg size. Larvae hatched from small eggs partially recovered from the initial disadvantage during their ontogenetic processes by increasing growth rate (i.e. compensatory growth); however, there was still a positive relationship between egg size and pupal body size. 4. Older females produced small eggs, but because of compensatory growth, the pupae were no longer small. By contrast, due to a lack of compensatory growth, small females produced small eggs as well as small pupae. 5. These results suggest that maternal body size affects offspring body size through effects on egg size. This transgenerational effect may account for some of the variation in adult body size of T. dichotomus.

Catch‐up growth in the rhinoceros beetle Trypoxylus dichotomus (Coleoptera: Scarabaeidae): Smaller neonates gain relatively more body mass during larval development

“…B). This confirmed the findings by Kojima (). The SDI was significantly negative at the end of instar 1 and the later developmental stages; the SDI magnitude continuously increased with larval development (Fig.…”

“…Catch‐up growth was found significantly or as a tendency at each instar for both sexes in T. dichotomus . For the total larval growth of this species, catch‐up growth was notable in both sexes, supporting the suggestion by Kojima (). For other insects, few studies have examined the size dependence of larval growth increments by appropriate methods.…”

“…; Tammaru et al . ; Kojima ; the present study). This trend among insect groups might have developed because catch‐up growth occurs among a wide range of insect groups.…”

“…Therefore, catch‐up growth is most likely adaptive for T. dichotomus males with small bodies at birth. For female T. dichotomus , the egg number is positively correlated with the maternal body size (Kojima ). This suggests that catch‐up growth is adaptive for T. dichotomus females with small bodies at birth.…”

“…The body mass of neonates markedly varies in T. dichotomus (Kojima 2015). Catch-up growth was suggested (Kojima 2015), but it has not been directly examined. This beetle shows a malebiased SSD (Siva-Jothy 1987;Johns et al 2014;Kojima 2015), but the SSD development has not been examined by larval instars.…”