The dynamics of reproductive allocation in Hippodamia convergens as a function of female age and body size

Reproducing organisms face a trade-off between the size and number of their offspring. In lady beetles, egg size is relatively fixed, whereas clutch size is more variable. However, maternal effects (female age and body size) may generate some variation in egg size, with consequences for offspring fitness. We studied the reproduction of Hippodamia convergens females that, as larvae, were provided access to food (eggs of Ephestia kuehniella) for either 30 minutes, six hours, or ad libitum daily. These treatments produced three different body sizes (small, medium and large) and developmental rates (slow, medium, fast). Observations on clutch size, egg size and fertility were made daily throughout adult life. Some females entered reproductive diapause and exhibited reduced fecundity, fertility and reproductive days when diapause was broken two months later. In non-diapausing females, egg weight and clutch size were both correlated with body size, especially early in oviposition. Egg size increased over the course of 10 to 17 clutches for large and medium females, respectively, whereas that of small females declined. The fertility of small females also declined more steeply than that of larger females. Changes in clutch size over 25 reproductive days were parabolic in large and medium females, but linear and declining in small females. Changes in egg size and clutch size with female age represent dynamic shifts in reproductive allocation that are likely adaptive within the context of aphidophagy where females face 'boom and bust' cycles of resource availability.