A novel transient structure with phylogenetic implications found in ratite spermatids

Area of Science:

• * Reproductive Biology
• * Evolutionary Biology
• * Cell Biology

Background:

• * A novel transient structure was identified in the spermatids of three ratite species.
• * This observation was made using transmission electron microscopy.

Purpose of the Study:

• * To describe a novel transient structure observed in ratite spermatids.
• * To investigate the potential phylogenetic significance of this sperm ultrastructure.

Main Methods:

• * Transmission electron microscopy was employed to examine spermatids.
• * Sperm development stages, including the circular and longitudinal manchette phases, were analyzed.

Main Results:

• * A unique cogwheel-like structure, composed of finger-like projections (30 nm long, 14 nm wide), was observed associated with the outer nuclear membrane.
• * This structure appeared during the circular manchette stage, was prominent during the longitudinal manchette phase, and disappeared before spermiation.
• * While similar structures exist in some reptiles, this is the first report in birds.

Conclusions:

• * The unique ratite spermatid structure may serve as a phylogenetic marker, suggesting a link between reptiles and birds.
• * This finding supports the basal monophyletic positioning of ratites within the avian phylogenetic tree.