BIO 117P Lecture Notes - Lecture 2: Female Sperm Storage, Damselfly

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5 Feb 2017
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Waage 1979 Dual Function of the Damselfly Penis: Sperm Removal and Transfer
Most insect eggs are fertilized at oviposition
o Oviposition the storage of sperm by the female from previous matings
o When multiple males mate with a female, their sperms do not have the
same chances in fertilization (in fact, the last mate usually has the majority
of the children)
Evidence for sperm displacement is indirect and lacks controls
Three experiments
o Compared the amounts of sperm in females after one v. two matings
Females were tethered and presented to males
Copulations were timed
After the copulations, the female abdomens were removed and
immediately preserved in 70% ethanol
The external dimensions of the sperm mass were measured with an
ocular grid
Was used to determine sperm volume stored by a female
Result the volume for group 1 (one mating) was equal to
group 2 (two matings)
o Comparisons of sperm volume in females caught in the field during several
stages (i. perching on the shore; ii. Flying in tandem with males before
copulation; iii. After copulation, but before oviposition; iv. In copula, but
stopped before completion
Results the first three had no difference in sperm volume. The last
one had little or no sperm in their copulatrix
INTERPERTATION females prior to mating carrier substantial
amounts of sperm and that this sperm is expelled or removed
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