Table 1a–d.

Multiple regression analyses controlling for phylogeny (GLS) of sperm morphometry in relation to testis mass and body mass within families and across all species. (A t-test was used to compare the slopes against 0. The fitted model including the maximum likelihood value of λ was compared against the models including λ=1 and 0: superscripts after the λ value indicate significance levels of the likelihood ratio tests (first position, against λ=1; second position, λ=0; significance levels, ^n.s.not significant, ^*p<0.05). Effect size r calculated from the t value and the non-central 95% confidence intervals are presented. CLs excluding 0 indicate a significant relationship whereas CLs including 0 indicate no statistical significance. The data of the monogamous Sylviidae are a subset of the data of Sylviidae.)

sperm trait	predictor	slope	t	p	λ	r	CL
(a) Fringillidae (n=12)
head	testis mass	−0.65	−2.03	0.07	<0.001*,n.s	−0.58	−0.83 to 0.07
	body mass	−0.21	−0.77	0.46		−0.26	−0.07 to 0.40
midpiece	testis mass	397.91	3.01	0.02	<0.001*,n.s	0.73	0.18 to 0.89
	body mass	−144.34	−1.30	0.23		−0.42	−0.76 to 0.27
flagellum	testis mass	365.38	3.06	0.01	<0.001*,n.s	0.73	0.19 to 0.89
	body mass	−144.96	−1.45	0.18		−0.46	0.78 to 0.23
total length	testis mass	355.98	3.04	0.01	<0.001*,n.s	0.73	0.19 to 0.89
	body mass	−148.35	−1.51	0.17		−0.47	−0.78 to 0.21
(b) Sylviidae (n=14)
head	testis mass	0.03	1.17	0.27	<0.001n.s.,n.s	0.35	−0.06 to 0.79
	body mass	−0.24	−2.86	0.02		−0.67	−0.85 to −0.15
midpiece	testis mass	−0.10	−4.43	0.001	0.14n.s.,n.s	−0.81	−0.91 to −0.46
	body mass	−0.25	−3.94	0.002		−0.78	−0.90 to −0.38
flagellum	testis mass	−0.09	−3.69	0.004	0.69n.s.,n.s	−0.76	−0.89 to −0.33
	body mass	−0.21	−3.55	0.005		−0.75	−0.89 to −0.33
total length	testis mass	−0.07	−3.40	0.006	0.80n.s.,n.s	−0.73	−0.88 to −0.27
	body mass	−0.29	−4.12	0.002		−0.79	−0.91 to −0.41
(c) monogamous Sylviidae (n=7)
head	testis mass	0.73	0.29	0.79	<0.001n.s.,n.s	0.17	−0.70 to 0.79
	body mass	−13.60	−3.26	0.03		−0.88	−0.97 to 0.02
midpiece	testis mass	−0.50	−3.69	0.02	<0.001n.s.,n.s	−0.91	−0.97 to −0.13
	body mass	−0.55	−2.49	0.07		−0.82	−0.95 to 0.18
flagellum	testis mass	−35.28	−3.09	0.04	<0.001n.s.,n.s	−0.87	−0.96 to 0.02
	body mass	−25.93	−1.40	0.23		−0.63	−0.90 to 0.47
total length	testis mass	−33.90	−3.31	0.03	<0.001n.s.,n.s	−0.89	−0.97 to −0.03
	body mass	−33.85	−2.04	0.11		−0.76	−0.93 to 0.30
(d) across passerine species (n=50)
head	testis mass	0.04	2.21	0.03	0.37n.s, *	0.31	0.04 to 0.61
	body mass	−0.08	−3.82	<0.001		−0.49	−0.82 to −0.25
midpiece	testis mass	3.83	0.52	0.61	0.84n.s.,*	0.08	−0.21 to 0.37
	body mass	−17.68	−1.88	0.07		−0.27	−0.56 to 0.01
flagellum	testis mass	0.07	1.29	0.20	0.93n.s.,*	0.19	−0.09 to 0.48
	body mass	−0.20	−2.59	0.01		−0.26	−0.55 to 0.02
total length	testis mass	7.44	1.15	0.25	0.80n.s.,*	0.17	−0.11 to 0.46
	body mass	−17.56	−2.19	0.04		−0.31	−0.61 to −0.35