Date of Award
12-24-2025
Date Published
January 2026
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Biology
Advisor(s)
Scott Pitnick
Second Advisor
Stephen Dorus
Keywords
Chymomyza procnemis;ejaculate structure;polymorphism;postcopulatory sexual selection;sperm length;spermatogenesis
Abstract
Sperm heteromorphism, the production of two or more discrete sperm types or morphs within a single testis, occurs in diverse taxa. This phenomenon is believed to represent a division of labor by male gametes, with only one morph (the "eusperm") participating in fertilization and the other morph(s) specialized to perform some other (typically unknown) function within the female reproductive tract. One of the most intensively investigated systems is the Drosophila obscura species group, for which sperm heteromorphism evolved once in the common ancestor to the group, with all examined descendent species exhibiting sperm length heteromorphism. The absence of additional sperm heteromorphism origins among drosophilids has precluded comparative evolutionary analyses. Here, we report the discovery of a second origin within the Drosophilidae, in which Chymomyza procnemis exhibits the most extreme sperm length heteromorphism known (>15-fold difference). Males were found to produce and transfer to females approximately twice as many short sperm as long sperm. Shortly after insemination, female ejected most of the short morph sperm, yet relatively few of the long morph sperm from their reproductive tracts, which resulted in a preponderance of long morph sperm occupying the female’s sperm-storage organs. Furthermore, after the start of egg laying, few-to-no short morph sperm were detectable in the female reproductive tract. Thus, we conclude that only the long sperm morph is likely to participate in fertilization. Although C. procnemis have very long eusperm and the highest relative investment (Gonadosomatic Index; GSI) in testes for any drosophilid species, a comparative analysis across 149 species of Drosophila revealed no significant coevolutionary relationship between sperm heteromorphism and either sperm length or GSI. Continued investigations with Chymomyza will advance our understanding of how sperm heteromorphism arises, persists, and diversifies across lineages.
Access
Open Access
Recommended Citation
Bhatt, Karan, "NOVEL ORIGIN OF SPERM HETEROMORPHISM IN THE DROSOPHILIDAE" (2025). Theses - ALL. 993.
https://surface.syr.edu/thesis/993
