Table 3 Effect of communal litter size and litter birth order on relative investment gained from partner mother.

Effect	Fixed effect	χ²	df	p^a
*All pups*^b
Communal litter size	−0.006 ± 0.003	5.83	1	0.016
Pup from 1^st vs 2^nd born litter	−0.035 ± 0.017	4.09	1	0.043
Partner food intake^c	1.675 ± 0.110	68.24	1	<0.0001
Partner relatedness	−0.001 ± 0.016	0.01	1	0.94
4 way interaction		20.18	11	0.043
Relatedness × communal litter size × birth order		10.49	5	0.063
*First-born litters*^d
Communal litter size	−0.005 ± 0.003	2.34	1	0.13
Partner food intake	1.696 ± 0.144	38.63	1	<0.0001
Partner relatedness	−0.018 ± 0.020	0.81	1	0.37
*Second-born litters*^d
Communal litter size	−0.007 ± 0.004	3.61	1	0.057
Partner food intake	1.683 ± 0.160	31.06	1	<0.0001
Partner relatedness	0.020 ± 0.025	0.64	1	0.42
Relatedness × communal litter size × partner food intake		13.70	4	0.008
Relatedness × communal litter size		9.34	1	0.002
*Second-born litters in sister nests*^d
Communal litter size		0.14	1	0.71
Partner food intake		21.30	1	<0.0001
*Second-born litters in unrelated nests*^d
Communal litter size		12.84	1	0.0003
Partner food intake		11.68	1	0.0007

^aValues in bolded text are statistically significant (p < 0.05).
^bMixed-effects models of relative investment gained from partner mother (mother included as a random effect in each model; pair had zero variance and so was not included). Interactions that had significant effects are shown. Data for all pups from 16 communal nests (n = 44 first born and n = 33 second born pups in sister nests; n = 41 first born and n = 40 second born pups in unrelated female nests), shown in Fig. 4 and Supplementary Data 1.
^cProportion of food intake over the labelling period that was due to partner mother.
^dAnalysis broken down into four different subsets to interpret the significant 4 way interaction for all pups. Adjustment for multiple post hoc comparisons using a conservative Bonferroni correction has a threshold for significance of p < 0.0125.

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