Maternal hatching synchronization in a subsocial burrower bug mitigates the risk of future sibling cannibalism.

Hiromi Mukai,Shintaro Nomakuchi,Sumio Tojo,Mantaro Hironaka

doi:10.1002/ece3.3894

Abstract

Sibling cannibalism—the killing and consumption of conspecifics within broods—carries a high risk of direct and inclusive fitness loss for parents and offspring. We reported previously that a unique vibrational behavior shown by the mother of the subsocial burrower bug, Adomerus rotundus (Heteroptera: Cydnidae), induced synchronous hatching. Maternal regulation may be one of the most effective mechanisms for preventing or limiting sibling cannibalism. Here, we tested the hypothesis that synchronous hatching induced by maternal vibration in A. rotundus prevents sibling cannibalism. Mothers and their mature egg masses were allocated to three groups: synchronous hatching by maternal vibration (SHmv), synchronous hatching by artificial vibration (SHav), and asynchronous hatching (AH). We then investigated the influence of each hatching strategy on the occurrence of sibling cannibalism of eggs and early‐instar nymphs in the laboratory. No difference in the proportion of eggs cannibalized was observed among the three groups. However, the proportion of nymphs cannibalized was higher in the AH group than in the SHmv group. The difference in the number of days to first molting within clutch was significantly higher in the AH group than in the SHmv group. Junior nymphs were sometimes eaten by senior nymphs. However, immediately after molting, senior nymphs were at a high risk of being eaten by junior nymphs. Our results indicate that synchronous hatching of A. rotundus is necessary to mitigate the risk of sibling cannibalism.

Highlights

Cannibalism is observed in many animal taxa exhibiting various feeding habits and in predators and in herbivores (Elgar & Crespi, 1992; Polis, 1981)
Seventy mothers and their mature egg masses were allocated to three groups: synchronous hatching by maternal vibration (SHmv), synchronous hatching by artificial vibration (SHav), and asynchronous hatching (AH)
We found that the absence of maternal or artificial vibration facilitated AH of egg mass and induced asynchronous molting, which increased the rate of cannibalism between junior and senior nymphs

Summary

| INTRODUCTION

Cannibalism is observed in many animal taxa exhibiting various feeding habits and in predators and in herbivores (Elgar & Crespi, 1992; Polis, 1981). Hatching is extremely well synchronized in some species of burrower bugs and closely related shield bugs (Mukai, Hironaka, Tojo, & Nomakuchi, 2012, 2014) These species show complex maternal care, including egg guarding, production of trophic eggs, protection of nymphs, and progressive provisioning (Baba et al, 2011; Filippi, Hironaka, & Nomakuchi, 2001; Filippi et al, 2009; Hironaka, Nomakuchi, Iwakuma, & Filippi, 2005; Inadomi et al, 2014; Mukai et al, 2010; Nakahira, 1994; Tsukamoto & Tojo, 1992). While holding their egg masses, Adomerus rotundus (Heteroptera: Cydnidae) mothers produce physical vibrations that regulate and synchronize hatching (Figure 1; Mukai et al, 2012). This sophisticated care behavior probably has the adaptive function of supporting the young offspring. We prepared unsynchronized and naturally or artificially synchronized hatching broods and investigated the effects on the occurrence of sibling cannibalism during early development in the laboratory

| MATERIALS AND METHODS

| Experimental procedures

Findings

| DISCUSSION