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Abstract
We report a functional switching valve within the female genitalia of the Brazilian cave insect Neotrogla. The valve complex is composed of two plate-like sclerites, a closure element, and in-and-outflow canals. Females have a penis-like intromittent organ to coercively anchor males and obtain voluminous semen. The semen is packed in a capsule, whose formation is initiated by seminal injection. It is not only used for fertilization but also consumed by the female as nutrition. The valve complex has two slots for insemination so that Neotrogla can continue mating while the first slot is occupied. In conjunction with the female penis, this switching valve is a morphological novelty enabling females to compete for seminal gifts in their nutrient-poor cave habitats through long copulation times and multiple seminal injections. The evolution of this switching valve may have been a prerequisite for the reversal of the intromittent organ in Neotrogla.
Highlights
Many man-made engineering solutions have evolved already in insects
We investigated the structure of the spermathecal plate by using a combination of confocal laser scanning microscopy (CLSM) and high-resolution synchrotron microcomputed tomography (HR-mCT) to assess the functional morphology of sperm storage and control of seminal flow
Sc 2 is a bowl-shaped chitinous structure harboring a fan-like muscle, which originates at its ventral part and attaches to a thumb-shaped controller/closure element (CE: Figures 1CD and 2A–D)
Summary
Many man-made engineering solutions have evolved already in insects. Such examples include hinges (flapping flight enabled by the wing base: Brodsky, 1994), on-off valves (spiracle openings to regulate airflow: Chapman, 1998), backflow valves (the bombardier beetle’s defensive spray: Arndt et al, 2015), coiling mechanisms (genital tubes: Matsumura et al, 2017a) or catapult-like mechanisms (the legs of many jumping insects: Burrows, 2013). Studies of micron-scale biological structures can be rewarding as they illuminate construction principles in insects that could be applied to technical solutions in engineering (Matsumura et al, 2017b). The genus Neotrogla (family Prionoglarididae) is a minute Brazilian cave insect belonging to the order Psocodea (booklice, barklice, and parasitic lice). This genus is of special evolutionary and morphological interest because of the reversal in its genital structures (Yoshizawa et al, 2014).
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