Data from: Male responses to sperm competition risk when rivals vary in their number and familiarity

Males of many species adjust their reproductive investment to the number
of rivals present simultaneously. However, few studies have investigated
whether males sum previous encounters with rivals, and the total level of
competition has never been explicitly separated from social familiarity.
Social familiarity can be an important component of kin recognition and
has been suggested as a cue that males use to avoid harming females when
competing with relatives. Previous work has succeeded in independently
manipulating social familiarity and relatedness among rivals, but
experimental manipulations of familiarity are confounded with
manipulations of the total number of rivals that males encounter. Using
the seed beetle Callosobruchus maculatus we manipulated three factors:
familiarity among rival males, the number of rivals encountered
simultaneously, and the total number of rivals encountered over a 48-hour
period. Males produced smaller ejaculates when exposed to more rivals in
total, regardless of the maximum number of rivals they encountered
simultaneously. Males did not respond to familiarity. Our results
demonstrate that males of this species can sum the number of rivals
encountered over separate days, and therefore the confounding of
familiarity with the total level of competition in previous studies should
not be ignored.