Sperm
Sperm (the thin green cells) from a human bedbug Cimex lectularis, swimming out of the female’s secondary set of genitalia (the round cells) into her body cavity on their way to the ovaries. Oh, evolution.
My PhD research focused on the evolution of sperm morphology, especially in the obscura sub-genus of Drosophila. These ~55 species of fruitflies are fairly unusual, in that they have two discrete sperm morphs: one is longer and is capable of fertilisation, and the other is short and apparently never fertilises eggs. My PhD tried to figure out why the flies have evolved two types of sperm when most species do fine with just one. We found some evidence that the smaller sperm improve the survival of their larger brothers after mating, though I’d like to revisit this problem someday and figure it out once and for all!
