Table 2.

Mixed linear model investigating variance in total and PO activity as a function of population, sex and carotenoid concentration, and variance in carotenoid concentration as a function of population and sex, in samples of G. pulex collected for the second study.

source	covariance parameter estimates				type 3 tests of fixed effects
	parameter	estimate ±s.e.	wald's Z	p	effect	estimate ±s.e.	Fd.f.	p
total activity	population	1.16±0.60	1.93	0.03	sexa	0.52±0.21b	6.381,413	0.01
	residual	4.27±0.30	14.32	<0.0001	carotenoids	0.17±0.03	36.481,419	<0.0001
	likelihood ratio test: Χ21df=65.09, p<0.0001
PO activity	population	0.007±0.004	1.64	0.05	sexc	−0.08±0.03b	7.551,414	0.006
	residual	0.084±0.006	14.29	<0.0001	carotenoids	0.02±0.004	40.551,401	<0.0001
	likelihood ratio test: Χ21df=16.56, p<0.0001
carotenoids	population	3.21±1.66	1.93	0.03	sexd	0.13±0.36b	0.121,420	0.73
	residual	13.14±0.91	14.44	<0.0001
	likelihood ratio test: Χ21df=63.52, p<0.0001

^aMean±s.e. taken on raw data (measured as maximum change in optical density per minute); females, 3.37±0.22 milliunit min⁻¹; males, 4.03±0.22 milliunit min⁻¹.

^bEstimate of males relative to females taken as the reference (estimate=0).

^cFemales, 0.72±0.08 milliunit min⁻¹; males, 0.50±0.08 milliunit min⁻¹.

^dFemales, 213±9 ng μl⁻¹; males, 205±7 ng μl⁻¹.