Intraclutch egg‐size variation in acanthosomatid bugs: adaptive allocation of maternal investment?

Abstract

If there are differences in predation risk among the offspring within a clutch, parents may allocate less resources to the offspring facing higher risk. I examined parental investment in terms of egg size within clutches in five species of stink bugs (Heteroptera, Acanthosomatidae). In subsocial Elasmucha and Sastragala species, the female guards her eggs and first‐instar nymphs against invertebrate predators by covering her clutch with her body. Large differences in survival from predation between offspring at the centre and offspring at the periphery of the clutch have been reported in such subsocial insects. I found that Elasmucha and Sastragala females laid significantly smaller eggs in the peripheral (and thus more vulnerable) part of the clutch. Phenotypic trade‐offs between egg size and clutch size were detected in these subsocial species. Egg size was positively correlated with hatched first‐instar nymph size: smaller nymphs hatched from smaller peripheral eggs. In asocial Elasmostethus humeralis, however, no significant difference in size was detected between the eggs at the centre of and those at the periphery of the clutch. Thus, in subsocial acanthosomatid bugs, females seem to allocate their resources according to the different predation risks faced by the offspring within the clutch.

Juvenile exposure to predator cues induces a larger egg size in fish

“…Fontaine & Martin [12] observed a decrease in egg size and clutch mass in eight passerine species under increased nest predation risk. Similarly, in five species of acanthosomatid bugs, females laid smaller eggs at the peripheral, which represents a more vulnerable section of the clutch [11]. In these species, losses to predators occur during the brood care period.…”

“…In many insects and birds, mothers lay smaller eggs when these eggs are more likely to experience mortality owing to predation, either to save energy that can be redirected to other functions or to enable them to produce more young and thus to spread the risk [11][12][13]. This strategy is a 'selfish maternal effect' [14], as a smaller egg often strongly diminishes offspring fitness [15,16].…”

Coping with environmental uncertainty: dynamic bet hedging as a maternal effect

“…Mothers may increase egg size variability in order to increase arithmetic mean fitness. For example, in stinkbugs, Kudo (2001) found subsocial species to lay smaller eggs around the periphery of the clutch in response to the positional risk of egg predation, whereas asocial species produce offspring of similar size (Kudo 2001(Kudo , 2006. In this example, producing offspring of different sizes increases the number of surviving offspring in a constant and predictable environment.…”

Mothers modify eggs into shields to protect offspring from parasitism

“…In Adomerus triguttulus (Heteroptera: Cydnidae), fertile egg clutches are covered with inviable eggs that serve to provision offspring and may secondly protect them from natural enemies, but only the parental guard behaviour has been specifically tested as being an effective deterrent against predation [28]. In these systems, predation risk to eggs does not depend on size, but on their position [29]. Females may have been selected to invest less in peripheral eggs because it is less costly.…”