Abstract:
Sperm competition is the competition for fertilizations between
ejaculates, within a female, following multiple mating. There are
four sperm utilization or precedence patterns: first male precedence,
where the first male to mate fertilizes most of the eggs laid by a
female; last male precedence, where the last male to mate fertilizes
most of the eggs laid by a female; "all-or-none" pattern, where sperm
from either male fertilizes all the eggs laid by a female but which
male's sperm that is used is random; or sperm mixing, where sperm from
each male is used equally in fertilizing eggs laid by a female.
Intermediate utilization patterns are also possible. Sperm
competition occurs in a wide variety of insect species as well as
other animals. This study was undertaken to study sperm competition
in the field cricket, Gryllus integer. Four experiments were
conducted: a radiation and sterilization experiment, a diapause
experiment, and 2 competition experiments. It was found that 7,000
rad of gamma radiation sterilized adult ~ integer males. There was
no diapause in the laboratory in ~ integer eggs. In the first
competition experiment, three groups of females were used: females
mated with a normal male, then with a second normal male (NN group);
females mated with a normal male, and then with a sterile male (NR
group); and females mated with a sterile male, and then with a normal
male (RN group). The results obtained from this experiment showed
that the mean proportion of eggs hatched was significantly different
between 3 groups of females, with the proportion hatched much greater
in the NN group than in either the NR or RN groups. The pattern for
the proportion of eggs hatched following a double mating most closely
resembled a pattern expected if sperm mixing is occurring. Results
obtained in the replicate competition experiment showed that the mean
proportion of eggs hatched for the females in the NR group was
significantly lower than the proportion hatched in the other two
groups. This also supports a model of sperm mixing as a precedence
pattern. Values calculated following Boorman and Parker (1976), for
the proportion of eggs fertilized by the second male to mate following
a double mating, were 0.57 in competition experiment 1 and 0.62 in the
replicate. These values indicate that sperm mixing occurs in~
integer.
