''Drosophila bifurca'' is a species of
fruit fly. Males of this species are known to have the longest
sperm cells of any organism on Earth—5.8 cm long when uncoiled, over twenty times the entire body length of the male.
The cells are mostly tail, and are delivered to the females in tangled coils. A male can only make a few hundred such cells during its lifetime. The other members of the genus ''
Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...
'' also make very few, giant sperm cells, with ''D. bifurca'' being the longest. The sperm cells are produced in
testes
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...
6.7 cm long, which comprise 11% of the male's body mass. Males of the species become sexually mature 17 days after
emergence, instead of 7 days for females, which suggests testes development is costly in time and energy.
Such sperm gigantism is thought to have evolved via a
Fisherian runaway
Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of ostentatious male ornamentation by persistent, directional fem ...
process, with a genetic link between sperm length and the length of the female seminal receptacle (sperm-storage organ) length, combined with an increasing competitive advantage of longer sperm as the seminal receptacle evolves to be longer.
References
External links
LiveScience article
bifurca
{{Drosophilidae-stub