Capitula on stick insect eggs and elaiosomes on seeds: convergent adaptations for burial by ants

The eggs of many stick insect species (Phasmatodea) bear a striking resemblance to seeds. These eggs are not only similar in size, shape, colour and texture to seeds, but in many species bear a knob-like structure known as a capitulum. This structure resembles an elaiosome, a lipid-rich appendage on some seeds known to be an adaptation for burial by ants. Capitula, like elaiosomes, promote removal of eggs to ant nests and buried eggs suffer reduced rates of parasitism by wasps. Phasmatid nymphs are capable of emerging from eggs buried under 6 cm of soil. Capitula are found only in those phasmatid species which drop eggs freely on to litter and not in species which bury eggs or glue them to vegetation. Elaiosomes and capitula are both adaptations to use ant mutualists for burial, a striking example of evolutionary convergence between the plant and animal kingdoms. -from Authors