Authors: Darren W Johnson, Keyne Monro, and Dustin J Marshall
Published in: Evolution, volume 67, issue 5 (May 2013)
Why are sperm so variable despite having a singular, critical function and an intimate relationship with fitness?
A key to under-standing the evolution of sperm morphology is identifying which traits enable sperm to be successful fertilizers. Several sperm traits (e.g., tail length, overall size) are implicated in sperm performance, but the benefits of these traits are likely to be highly con- text dependent.
Here, we examined phenotypic selection on sperm morphology of a broadcast spawning tube worm (Galeolaria gemineoa). We conducted laboratory experiments to measure the relationship between average sperm morphology and relative fertilization success across a range of sperm environments that were designed to approximate the range of sperm concentrations and ages encountered by eggs in nature.
We found that the strength and form of multivariate selection varied substantially across our environmental gradients. Sperm with long tails and small heads were favored in high-concentration environments, whereas sperm with long heads were favored at low concentrations and old ages.
We suggest variation in the local fertilization environment and resulting differences in selection can preserve variability in sperm morphology both within and among males.
Johnson D, Monro K, Marshall DJ (2013) The maintenance of sperm variability: context-dependent selection on sperm morphology in a broadcast spawning invertebrate. Evolution, 67-5: 1383–1395 PDF 889 KB doi:10.1111/evo.12022