Table 3.

Seminal vesicle masses of competing males predict the number of sperm in competition

Factor	Estimate ± SE	t	P
A) Sperm no. in uterus from second male
Intercept	116.03 ± 32.15	3.61
Seminal vesicle mass of first male	−0.23 ± 0.07	−3.22	<0.01**
Cauda sperm count of second male	0.28 ± 0.10	2.79	0.02*
B) Sperm no. in uterus from second male
Intercept	−12.32 ± 28.27	−0.44
Seminal vesicle mass of second male	0.19 ± 0.08	2.48	0.02*
Cauda sperm count of second male	0.32 ± 0.10	3.21	<0.01**

When two males mate with the same female, the number of sperm from the second male recovered from the uterus: A) decreases with seminal vesicle mass of the first male, and B) increases with seminal vesicle mass of the second male. Cauda sperm count of the second male (measured postmortem as an index of sperm production) is included as a covariate with the aim of controlling for variation in the number of sperm ejaculated (see Results and Discussion). Results are shown for linear mixed models fit by restricted maximum likelihood (REML), for 18 double copulations with 18 males mating second and 11 males mating first. The identity of the first male to mate is included as a random factor in the analysis. Bold text indicates statistical significance (*P < 0.05; **P < 0.01). t = t value.