Unfertilized eggs retained their ability to be fertilized
for at least 40 min at 28C (i.e. there was no association
between egg age and the percentage of eggs developing
within the range tested). Sperm could fertilize eggs up to
20 h after ejaculation but sperm that was less than 2 h old
was significantly more likely to fertilize eggs than sperm
that was more than 5 h old (chi-square test: 2
3=23.5,
N=83, P<0.0001). Sperm had the potential, then, to
fertilize eggs well after they were spawned.
Despite this potential, extragroup fertilization rarely
occurred: in 39 of 40 clutches, paternity of all eggs was
consistent with the males present when the clutch was
laid. No eggs were fertilized by males that had departed
after completing the preceding clutch (five cases). In the
single clutch where offspring genotypes were inconsistent
with any putative father, only two of 24 eggs were
inconsistent. These two cases could be due to mutation,
misgenotyping or fertilization by extragroup sperm. As
discussed above, the probability of detecting an extragroup
fertilization was above 50%. Because only two of
846 eggs were inconsistent with any of the putative
males, we conclude that fertilization by extragroup sperm
was rare and can be ignored.
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