ABSTRACT

Unilateral postzygotic paternal care is extremely rare among animals. The giant water bug family Belostomatidae contains most of the arthropod species known to exhibit this unusual behavior. In the subfamily Lethocerinae, males brood eggs laid on emergent vegetation. Brooding in this group involves watering eggs, shading them, and defending them against predation. In the subfamily Belostomatinae, males employ a variety of behavior patterns to aerate eggs attached to their backs by their mates. Brooding is obligatory in all belostomatid species studied; unattended eggs invariably die if left in the open air or submersed.

This chapter explores the biology, phylogeny and fossil record of the Belostomatidae and related taxa in an attempt to discern the selection forces, the constraints, and the sequence of historical events responsible for the evolution of this unusual behavior and its subsequent diversification. Selection for large bug size, in order to take advantage of vertebrate prey, together with the dual phylogenetic constraints of Dyar's Law and the apparent inability of heteropterans to add molts, coupled egg size to body size. Thus selection for large bugs also produced large eggs: too large to develop unattended submersed in water. A past history of eggs being laid in water left these larger eggs lacking the necessary adaptations to survive desiccation when laid unattended in the open air. Consequently, large eggs created selection for an innovation to lift egg–size limitations on imago size. Ergo, emergent brooding evolved in the lethocerine lineage.