Rj. Wootton et al., A REVIEW OF REPRODUCTIVE RATES IN STICKLEBACKS IN RELATION TO PARENTAL EXPENDITURE AND OPERATIONAL SEX-RATIOS, Behaviour, 132, 1995, pp. 915-933
1. The expenditures of time and energy on parental activities of femal
e and male threespine sticklebacks, Gasterosteus aculeatus L., are rev
iewed in the context of sex differences in competition for and choice
of mates. 2. The female's parental contribution is mainly cytoplasmic
in the form of provisioned eggs. In energy units each clutch spawned r
epresents about 200% of the daily maintenance ration of a sexually mat
ure female. Each egg in a clutch represents about 2% of that ration. T
he 'time out', during which the female is sexually unreceptive between
spawnings, varies from about 3 to 15 days, and is inversely correlate
d with the rate of food consumption. 3. The male's parental contributi
on is primarily behavioural. The daily energy expenditure of a parenta
l male is equivalent to a daily ration of about 6% of the male's body
weight, a value not dissimilar to that of a reproductively active fema
le. The pattern of 'time-outs' of males differs from that of females,
with the periods of sexual receptivity and unreceptivity both longer.
4. A crude simulation model of the effect of sex differences in the pa
ttern and length of 'time outs' suggested that the operational sex rat
io (OSR) would usually be male-biased favouring inter-male competition
for mates and mate choice by females. 5. However, both environmental
factors such as food availability, and demographic factors such as sex
differences in mortality rates, together with the sex differences in
'time out' could cause the OSR to vary within breeding seasons, betwee
n breeding seasons and between populations. This leads to the predicti
on that there will be corresponding variations in the intensities of m
ale-male and female-female competition for males and hence in the deve
lopment of secondary sexual characteristics.