Ultrastructural analysis of spermiogenesis in Admetus pomilio (Arachnida, amblypygi)

Area of Science:

• * Zoology
• * Spermatology
• * Arachnology

Background:

• * The spermatozoon is the mature male gamete responsible for fertilization.
• * Sperm ultrastructure varies significantly across species, reflecting diverse reproductive strategies.
• * Understanding sperm morphology is crucial for evolutionary and reproductive biology.

Purpose of the Study:

• * To describe the detailed ultrastructure of the mature spermatozoon of Admetus pomilio.
• * To identify key morphological features of Admetus pomilio sperm, including nuclear and flagellar organization.
• * To compare the observed ultrastructure with that of other arachnid groups, particularly primitive ones.

Main Methods:

• * Transmission electron microscopy was used to examine the ultrastructure of Admetus pomilio spermatids and spermatozoa.
• * Detailed morphological analysis focused on the nucleus, acrosome, flagellum, and mitochondrial sheath.
• * Comparative analysis was performed with existing literature on spider spermatid ultrastructure.

Main Results:

• * Admetus pomilio spermatozoa are spherical with a nucleus and a tightly coiled flagellum.
• * Key features include a helical nucleus with twisted chromatin filaments, a long perforatorium, and a spiral mitochondrial sheath surrounding the axoneme.
• * The late spermatid exhibits further contortions, with the nucleus coiling and the flagellum winding within the cell body.

Conclusions:

• * The ultrastructure of Admetus pomilio spermatids, particularly the helical nuclear and flagellar morphology, is distinct.
• * These ultrastructural characteristics show notable resemblance to those observed in the primitive Liphistiomorpha spiders.
• * The findings contribute to our understanding of sperm evolution and phylogenetic relationships within spiders.