Abstract

A highly specialized form of egg deposition occurs in the dragonfly Micrathyria dictynna, which attaches egg-masses onto the underside of leaves high above shallow streams in Central American rainforests. Here, we describe the ultrastructure of the egg chorion of M. dictynna to reveal structural adaptations related to this unusual form of oviposition. We find that the egg chorion is generally divided into a thin, sticky exochorion and a tough, hard, smooth endochorion. The exochorion of eggs collected from the peripheral region of egg masses, however, shows a separation into outer and inner exochorionic layers. The space formed between these layers develops numerous pillars. In eggs collected from the area between the periphery and central region of an egg mass, the exochorion exhibits irregular interconnected patches of elevated areas containing very fine superficial linear reticulations. We propose that the exochorion of peripheral eggs is functionally modified to form a plastron that regulates respiration and restricts water loss of eggs in the inner layers of the egg mass.

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