Activation of parasperm and eusperm upon ejaculation in Lepidoptera

Area of Science:

• Reproductive Biology
• Insect Physiology
• Sperm Biology

Background:

• Lepidoptera produce two sperm types: nucleated eusperm (eupyrene) and anucleate parasperm (apyrene).
• Both sperm types are activated upon ejaculation, transitioning from inactivity to motility.
• Existing research suggests proteases activate parasperm, but this is not universally applicable.

Purpose of the Study:

• To investigate the male-derived activators of both eusperm and parasperm in diverse Lepidoptera species.
• To elucidate the distinct mechanisms underlying the activation of anucleate and nucleated spermatozoa.
• To explore the potential evolutionary origins and functional significance of these unique sperm activation processes.

Main Methods:

• Analysis of male secretions and their effects on sperm motility and bundle dissociation.
• Use of protease inhibitors and ionophores to probe the activation pathways of parasperm.
• Biochemical characterization of male proteins involved in sperm activation, including molecular weight determination.

Main Results:

• A male protein of approximately 37.7 kDa activates both parasperm and eusperm across diverse Lepidoptera.
• Parasperm activation involves a trans-membrane ionic event, not solely protease-dependent, as shown in Manduca sexta.
• A distinct, protease-sensitive male protein dissociates eusperm bundles, unlike the parasperm activator.

Conclusions:

• The identified sperm activators differ from previously proposed initiators like Bombyx mori initiatorin.
• Parasperm activation mechanisms are more complex than previously thought, involving ionic events.
• These findings highlight a crucial, yet understudied, role for parasperm in lepidopteran reproductive physiology and behavior.