Date Thesis Awarded
Bachelors of Science (BS)
The cellular divisions in Rhabditis sp. SB347 male spermatogenesis have been modified to re-purpose an asymmetric division. This results in the dramatically skewed sex ratios observed in the progeny of males of this species. Here we confirm this asymmetry in the division of tubulin and major sperm protein (MSP). MSP, a necessary sperm component, is segregated exclusively into spermatids bearing the X chromosome while tubulin is segregated into the nullo-X sperm. Timing of the partitioning events reveals that MSP migration is not directly dependent on tubulin spindle asymmetry. Additionally, the endoplasmic reticulum is also segregated asymmetrically to the nullo-X spermatid during the partitioning phase of spermatogenesis. This results in only the X-bearing spermatids being functional, and thus the exclusive production of feminine offspring.
This pattern of asymmetry appears to not be isolated to SB347. We investigated several other species in the Rhabditis clade including SB372, JU1809, and JU1782. Using MSP and tubulin as markers, each species was noted to display asymmetric divisions very similar to those in SB347. This corresponds with data suggesting that these species demonstrate similar skews in the sex ratios of offspring (Pires daSilva, unpublished).
Not only do these species display unusual cellular divisions, but the size of the spermatids is greatly diminished compared to other closely related nematodes that have been studied. These two features make the species in the Rhabditis clade interesting subjects of study. They may serve as models to bolster our current understanding of cellular polarization in spermatogenesis and the mechanisms of distinction between residual body and spermatid. They may also yield important insights into the evolution of sex and gamete size.
Lastly, evidence suggests that the non-functional sperm, lacking the X chromosome, produced by Rhabditis sp. SB347 form large clusters in the male gonad. The fate of these aggregates is unknown, but they appear to be removed from the spermatid population. This draws some parallels to the apoptotic fate of the residual body in C. elegans. Study of the Rhabditis nematodes is just beginning, but it promises some interesting findings and novel insights into nematode biology.
Winter, Ethan S., "Evolutionary Conservation of a Modified Spermatogenesis Program in Rhabditis Nematodes with Skewed Sex Ratios" (2014). Undergraduate Honors Theses. Paper 79.