Abstract:
The reproductive behaviour of the field cricket, Gryllus
integer, was systematically observed in indoor arenas to
determine the extent of female Choice and male-male competition
at different sex ratios representing two male densities
(12:6 and 6:6). The costs and benefits to males and females
in those two densities were analyzed according to the theory
of the evolution o£ leks. Observations were conducted during
the dark hours when most calling occurred since hourly rates of
courtship song and mating did not fluctuate significantly over
a 24 h period. Female mating rates were not significantly
different between densities, therefore males at high densities
were not advantaged because of increased female tendencies to
mate when social stimulation was increased. Mean rates of
acoustical signalling (calling and courtin"g) did not differ
significantly between densities. Mean rates of fighting by
males at the high density were significantly greater than those
of males at the low density.
Mating benefits associated with callin~courting and
fighting were measured. Mating rates did not vary with rates
of calling at either density. Calling was not a prerequisite
to mating. Courtship song preceded all matings. There was a
significant power fit between male mating and courting rates,
and male mating and fighting rates at the low, but not at the
high, density. Density differences in the benefits associated
with increased courting and fighting may relate, in part, to
greater economic defensibility and monopoly of females due
to reduced male competition at the low density.
Dominant males may be preferentially chosen by females or
better able to monopolize mating opportunities than subordinate
males. Three criteria were used to determine whether
dominant males were preferentially chosen by females. The
number of matings by males who won fights (within 30 min of
mating) was significantly greater than the number of matings by
males who were defeated in such fights. Mating rates did not
vary significantly with rates of winning at either density.
There was a significant power fit between male mating rates
and the percentage of fights a male won (irrespective of his
fighting-frequency) at the low density.
The mean duration a male guarded the female after mating
did not vary significantly between densities. There was a
significant linear relationship between the duration a spermatophore
was retained and the duration a male guarded the female
after mating. Courtship song apparently stimulated spermatophore
removal. Male guarding involved inter-male aggression and
reduced courtship attempts by other males.
Males at the high density received no apparent reproductive
benefits associated with increased social stimulation. Conclusive
evidence for preferential choice of males by females, using
the criteria examined here, is lacking. Males at the lower
density had fewer competitors and could monopolize females more
effectively.
