Selection for
GIANT sperm…
Selection for
GIANT sperm…
Differences in sperm length appear driven by
differences in length of female reproductive tract
D. bifurca testes are 11% of body weight,
each sperm is 20X length of male
Drosophila bifurca
Drosophila pseudoobscura
0.36 mm sperm
GIANT sperm…
Sperm competition
How to test experimentally?
Bidirectional artificial selection for
seminal receptacle (SR) length (in females)
and sperm length (in males)
Sperm production in D. bifurca only 6X faster
than egg production – recall Bateman’s rule
Long-sperm male
Short SR female
Measure
fertilization success
among male-female
pairs from these
four groups
Male fertilization success
Selection for
Drosophila bifurca
58.3 mm sperm
Short male
Long female
SR length
Sperm competition driving some
species back toward isogamy?
Selection for Giant sperm
of 1
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