Table 4.

Microglial density and microglia/neuron ratio in different cortical sites^a

	Gray matter (microglia/mg)							White matter (microglia/mg)					Wilcoxon I/mg versus white matter
	I/mg				M vs. I, (exponent and p value)	I/N		I/mg				M vs. I, (exponent and p value)
	(range and mean ± SE)	(I/mg vs I, Spearman ρ and p value)	(I/mg vs N/mg, Spearman ρ andp value)	(I/mg vs N/mg, exponent and p value)		(I/mg vs N/mg, exponent, and p value)	(I vs I/mg, exponent, and p value)	(range and mean ± SE)	(I/mg vs I, Spearman ρ, andp value)	(I/mg vs O/mg, Spearman ρ, andp value)	(I/mg vs O/mg exponent, and p value)
All clades	[106-16 061] 3620 ± 63	ρ=0.2942 p < 0.0001	ρ=−0.1108 p = 0.0005	−0.025 ± 0.016 p = 0.1165	0.882 ± 0.010 p < 0.0001	−1.020 ± 0.016 p < 0.0001	1.104 ± 0.063 p < 0.0001	[271-19 827] 5016 ± 93	ρ=0.1614 p < 0.0001	ρ=0.2172 p < 0.0001	0.596 ± 0.064 p < 0.0001	0.945 ± 0.012 p < 0.0001	p < 0.0001
Per clade
Afrotheria	[930-7971] 4140 ± 97	ρ=0.3005 p = 0.0009	ρ=0.1538 p = 0.0936	0.083 ± 0.066 p = 0.2094	0.760 ± 0.050 p < 0.0001	−0.917 ± 0.066 p < 0.0001	0.840 ± 0.126 p < 0.0001	[371-10 673] 4482 ± 163	ρ=0.4252 p < 0.0001	ρ=0.5710 p < 0.0001	1.144 ± 0.149 p < 0.0001	0.628 ± 0.054 p < 0.0001	p = 0.2835
Artiodactyla	[1075-15 647] 4975 ± 345	ρ=0.4382 p = 0.0006	ρ=0.5049 p = 0.0001	0.715 ± 0.136 p < 0.0001	0.847 ± 0.071 p < 0.0001	−0.285 ± 0.136 p = 0.0397	0.536 ± 0.088 p < 0.0001	[2576-16 518] 6833 ± 387	ρ=0.2862 p = 0.0309	ρ=0.7154 p < 0.0001	1.472 ± 0.202 p < 0.0001	0.882 ± 0.039 p < 0.0001	p = 0.0002
Carnivora	[919-10 728] 3722 ± 98	ρ=0.2386 p = 0.0003	ρ=0.2954 p < 0.0001	0.122 ± 0.026 p < 0.0001	0.863 ± 0.025 p < 0.0001	−0.878 ± 0.026 p < 0.0001	0.276 ± 0.156 p = 0.0775	[741-19 827] 6740 ± 242	ρ=0.3512 p < 0.0001	ρ=0.7023 p < 0.0001	1.323 ± 0.103 p < 0.0001	0.844 ± 0.028 p < 0.0001	p < 0.0001
Marsupialia	[600-15 098] 4648 ± 175	ρ=0.2954 p = 0.0003	ρ=0.3813 p < 0.0001	0.368 ± 0.092 p = 0.0001	0.791 ± 0.040 p < 0.0001	−0.632 ± 0.092 p < 0.0001	0.730 ± 0.068 p < 0.0001	[1220-12 132] 5242 ± 162	ρ=0.2362 p = 0.0080	ρ=0.4062 p < 0.0001	0.474 ± 0.128 p = 0.0003	0.890 ± 0.026 p < 0.0001	p = 0.0151
Primata	[106-16 061] 2890 ± 92	ρ=0.1876 p = 0.0001	ρ=0.3226 p < 0.0001	0.301 ± 0.036 p < 0.0001	0.893 ± 0.022 p < 0.0001	−0.657 ± 0.037 p < 0.0001	0.537 ± 0.054 p < 0.0001	[271-12 511] 3965 ± 123	ρ=−0.0689 p = 0.2197	ρ=0.3998 p < 0.0001	0.864 ± 0.088 p < 0.0001	1.019 ± 0.027 p < 0.0001	p < 0.0001
Per species
Afrotheria*
L. africana	[930-7971] 4170 ± 97	ρ=0.2704 p = 0.0032	ρ=0.1538 p = 0.0936	0.280 ± 0.080 p = 0.0006	0.791 ± 0.054 p < 0.0001	−0.719 ± 0.080 p < 0.0001	0.652 ± 0.099 p < 0.0001	[371-10 673] 4511 ± 166	ρ=0.4081 p < 0.0001	ρ=0.5491 p = 0.0001	1.240 ± 0.154 p < 0.0001	0.604 ± 0.058 p < 0.0001	p = 0.2732
Artiodactyla
G. camelopardalis	[2764-9975] 5825 ± 352	ρ=0.6361 p = 0.0026	ρ=0.2060 p = 0.3835	0.228 ± 0.170 p = 0.1969	0.604 ± 0.141 p = 0.0004	−0.772 ± 0.170 p = 0.0003	0.602 ± 0.297 p = 0.0576	[3769-10 746] 7197 ± 466	ρ=0.5789 p = 0.0075	ρ=0.4226 p = 0.0634	0.827 ± 0.365 p = 0.0361	0.876 ± 0.101 p < 0.0001	p = 0.0223
T. strepsiceros	[1075-4298] 2847 ± 214	ρ=0.6118 p = 0.0118	ρ=0.6824 p = 0.0036	1.066 ± 0.211 p = 0.0002	0.658 ± 0.133 p = 0.0002	0.066 ± 0.211 p = 0.7581	0.394 ± 0.120 p = 0.0054	[3502-6804] 5070 ± 231	ρ=0.5353 p = 0.0326	ρ=0.4471 p = 0.0825	0.432 ± 0.373 p = 0.2663	0.933 ± 0.032 p < 0.0001	p < 0.0001
S. scrofa domesticus	[5584-15 647] 8481 ± 939	ρ=0.1879 p = 0.6032	ρ=−0.1758 p = 0.6272	0.400 ± 0.250 p = 0.1478	1.170 ± 0.089 p < 0.0001	−0.600 ± 0.250 p = 0.0430	0.393 ± 0.379 p = 0.3305	[8595-16 518] 11 742 ± 803	ρ=0.5333 p = 0.1392	ρ=0.5000 p = 0.1705	0.983 ± 0.525 p = 0.1032	0.907 ± 0.139 p = 0.0003	p = 0.0101
A. marsupialis	[1941-6161] 3476 ± 377	ρ=−0.1189 p = 0.7129	ρ=0.8531 p = 0.0004	0.625 ± 0.114 p = 0.0003	1.138 ± 0.164 p < 0.0001	−0.375 ± 0.114 p = 0.0080	−0.203 ± 0.218 p = 0.3754	[2576-7398] 4894 ± 399	ρ=0.4685 p = 0.1245	ρ=0.9231 p < 0.0001	1.285 ± 0.220 p = 0.0002	0.831 ± 0.041 p < 0.0001	p = 0.0194
Carnivora
M. mongo	[919-2130] 1400 ± 172	ρ=0.3214 p = 0.4821	ρ=0.7857 p = 0.0362	0.698 ± 0.201 p = 0.0177	0.398 ± 0.511 p = 0.4715	−0.302 ± 0.201 p = 0.1926	−0.014 ± 0.292 p = 0.9642	[740-2918] 1926 ± 156	ρ=0.7343 p = 0.0065	ρ=0.1678 p = 0.6021	1.391 ± 0.916 p = 0.1600	0.250 ± 0.193 p = 0.2235	p = 0.0572
U. arctos	[1432-5774] 2801 ± 94	ρ=0.1660 p = 0.1828	ρ=−0.0423 p = 0.7359	0.022 ± 0.088 p = 0.8050	0.953 ± 0.032 p < 0.0001	−0.978 ± 0.088 p < 0.0001	0.956 ± 0.178 p < 0.0001	[1970-11 965] 5738 ± 281	ρ=0.3883 p = 0.0058	ρ=0.5573 p < 0.0001	1.178 ± 0.184 p < 0.0001	0.953 ± 0.047 p < 0.0001	p < 0.0001
F. catus	[1536-4755] 2902 ± 186	ρ=0.3510 p = 0.0726	ρ=0.4829 p = 0.0107	0.588 ± 0.211 p = 0.0101	0.846 ± 0.078 p < 0.0001	−0.412 ± 0.211 p = 0.0622	0.598 ± 0.145 p = 0.0004	[2276-5590] 3406 ± 227	ρ=0.6941 p = 0.0029	ρ=0.3824 p = 0.1439	0.492 ± 0.376 p = 0.2117	0.850 ± 0.070 p < 0.0001	p = 0.0899
C. familiaris	[1867-6866] 4170 ± 132	ρ=0.2634 p = 0.0646	ρ=0.1200 p = 0.4065	0.085 ± 0.076 p = 0.2666	0.948 ± 0.041 p < 0.0001	−0.915 ± 0.076 p < 0.0001	0.699 ± 0.268 p = 0.0121	[4846-15 717] 8094 ± 358	ρ=0.2406 p = 0.1773	ρ=0.6086 p = 0.0002	0.668 ± 0.142 p < 0.0001	1.018 ± 0.048 p < 0.0001	p < 0.0001
M. putorius furo	[4523-10 728] 7366 ± 525	ρ=0.1636 p = 0.6307	ρ=0.4455 p = 0.1697	0.260 ± 0.160 p = 0.1396	0.892 ± 0.190 p = 0.0011	−0.740 ± 0.160 p = 0.0013	0.131 ± 0.536 p = 0.8119	[10 348-19 827] 13 278 ± 909	ρ=−0.0833 p = 0.8312	ρ=−0.1333 p = 0.7324	−0.583 ± 0.562 p = 0.3343	1.039 ± 0.144 p = 0.0002	p = 0.0003
P. leo	[2192-8166] 4285 ± 126	ρ=0.2756 p = 0.0263	ρ=0.0137 p = 0.9139	0.081 ± 0.070 p = 0.2482	0.895 ± 0.051 p < 0.0001	−0.919 ± 0.070 p < 0.0001	0.740 ± 0.223 p = 0.0015	[5816-10 588] 8123 ± 199	ρ=0.4866 p = 0.0013	ρ=0.3747 p = 0.0158	0.472 ± 0.132 p = 0.0010	0.943 ± 0.026 p < 0.0001	p < 0.0001
Marsupialia
M. rufogriseus	[4090-7414] 5753 ± 225	ρ=0.0610 p = 0.7927	ρ=0.1117 p = 0.6298	0.058 ± 0.075 p = 0.4500	1.053 ± 0.087 p < 0.0001	−0.942 ± 0.075 p < 0.0001	0.476 ± 0.679 p = 0.4919	[5303-9640] 6775 ± 257	ρ=−0.0561 p = 0.8194	ρ=0.2614 p = 0.2797	0.224 ± 0.247 p = 0.3770	1.053 ± 0.053 p < 0.0001	p = 0.0127
D. aurita	[3290-8565] 5801 ± 425	ρ=0.8576 p < 0.0001	ρ=0.6182 p = 0.0063	0.485 ± 0.173 p = 0.0126	0.461 ± 0.100 p = 0.0003	−0.515 ± 0.173 p = 0.0088	0.319 ± 0.242 p = 0.2069	[4113-8611] 5506 ± 402	ρ=0.1678 p = 0.6021	ρ=0.6573 p = 0.0202	0.553 ± 0.131 p = 0.0018	0.884 ± 0.166 p = 0.0003	p = 0.5677
D. goodfellowi	[1780-7000] 3465 ± 239	ρ=0.2591 p = 0.2214	ρ=0.2417 p = 0.2551	0.275 ± 0.168 p = 0.1174	0.991 ± 0.076 p < 0.0001	−0.725 ± 0.168 p = 0.0003	0.608 ± 0.241 p = 0.0192	[3536-7873] 5382 ± 246	ρ=0.4442 p = 0.0437	ρ=0.1558 p = 0.4999	0.259 ± 0.272 p = 0.3529	0.826 ± 0.068 p < 0.0001	p < 0.0001
M. parma	[2351-15 098] 5547 ± 640	ρ=−0.0912 p = 0.7103	ρ=0.7123 p = 0.0006	0.510 ± 0.164 p = 0.0063	1.117 ± 0.174 p < 0.0001	−0.490 ± 0.164 p = 0.0082	0.287 ± 0.228 p = 0.2257	[2671-5518] 4316 ± 222	ρ=0.4071 p = 0.1320	ρ=0.5179 p = 0.0480	0.484 ± 0.248 p = 0.0730	0.831 ± 0.067 p < 0.0001	p = 0.1270
W. bicolor	[1163-8680] 6191 ± 330	ρ=0.3468 p = 0.1049	ρ=−0.0524 p = 0.8124	−0.136 ± 0.209 p = 0.5223	0.736 ± 0.076 p < 0.0001	−1.136 ± 0.209 p < 0.0001	1.145 ± 0.223 p = 0.000044	[4194-12 132] 6966 ± 429	ρ=0.2403 p = 0.2942	ρ=0.5026 p = 0.0202	0.238 ± 0.179 p = 0.1987	0.937 ± 0.066 p < 0.0001	p = 0.6052
S. harrisii	[600-2571] 1394 ± 156	ρ=0.3187 p = 0.2886	ρ=0.5495 p = 0.0518	0.945 ± 0.411 p = 0.0422	0.807 ± 0.226 p = 0.0045	−0.055 ± 0.411 p = 0.8956	0.657 ± 0.149 p = 0.0011	[1220-4633] 2971 ± 324	ρ=0.7273 p = 0.0074	ρ=0.3007 p = 0.3423	0.483 ± 0.634 p = 0.4638	0.765 ± 0.146 p = 0.0004	p = 0.0006
M. fuliginosus	[2113-5441] 3725 ± 197	ρ=0.5047 p = 0.0062	ρ=0.2906 p = 0.1335	0.328 ± 0.171 p = 0.0657	0.916 ± 0.060 p < 0.0001	−0.672 ± 0.171 p = 0.0006	0.621 ± 0.197 p = 0.0041	[1945-5161] 4029 ± 166	ρ=0.2538 p = 0.2208	ρ=0.5646 p = 0.0033	0.881 ± 0.301 p = 0.0076	0.832 ± 0.026 p < 0.0001	p = 0.1277
Primata
P. anubiscynocephalus	[856-8907] 2402 ± 154	ρ=0.0651 p = 0.6337	ρ=0.2333 p = 0.0865	0.200 ± 0.087 p = 0.0254	1.023 ± 0.050 p < 0.0001	−0.800 ± 0.087 p < 0.0001	0.546 ± 0.197 p = 0.0077	[1983-11 992] 4385 ± 320	ρ=0.2047 p = 0.1724	ρ=0.6150 p < 0.0001	1.071 ± 0.169 p < 0.0001	0.960 ± 0.103 p < 0.0001	p < 0.0001
M. fascicularis	[989-11 057] 3718 ± 257	ρ=0.6443 p < 0.0001	ρ=0.4089 p = 0.0097	0.482 ± 0.178 p = 0.0102	0.756 ± 0.048 p < 0.0001	−0.518 ± 0.178 p = 0.0061	0.657 ± 0.127 p < 0.0001	[1620-10 255] 5997 ± 348	ρ=0.3559 p = 0.0306	ρ=0.1566 p = 0.3764	0.095 ± 0.220 p = 0.6700	0.873 ± 0.059 p < 0.0001	p < 0.0001
O. garnettii	[3384-16 061] 9259 ± 909	ρ=0.2264 p = 0.4364	ρ=0.0637 p = 0.8286	0.021 ± 0.291 p = 0.9434	0.472 ± 0.265 p = 0.1001	−0.979 ± 0.291 p = 0.0057	0.979 ± 0.286 p = 0.0050	[2226-12 240] 7912 ± 1172	ρ=0.8833 p = 0.0016	ρ=0.5000 p = 0.1705	1.251 ± 0.341 p = 0.0080	−0.063 ± 0.221 p = 0.7835	p = 0.3951
H. sapiens sapiens	[664-7812] 2379 ± 81	ρ=0.3915 p < 0.0001	ρ=−0.1368 p = 0.0695	−0.138 ± 0.058 p = 0.0192	0.889 ± 0.023 p < 0.0001	−0.993 ± 0.065 p < 0.0001	1.222 ± 0.087 p < 0.0001	[915-9079] 2891 ± 133	ρ=0.1703 p = 0.0713	ρ=0.6150 p < 0.0001	1.244 ± 0.201 p < 0.0001	0.999 ± 0.050 p < 0.0001	p = 0.0005
A. trivirgatus	[1155-4145] 2612 ± 180	ρ=0.4946 p = 0.0120	ρ=0.2215 p = 0.2872	0.099 ± 0.121 p = 0.4215	0.815 ± 0.090 p < 0.0001	−0.901 ± 0.121 p < 0.0001	0.714 ± 0.350 p = 0.0530	[1782-4366] 2863 ± 193	ρ=0.1909 p = 0.4479	ρ=0.5872 p = 0.0104	0.991 ± 0.254 p = 0.0013	0.966 ± 0.108 p < 0.0001	p = 0.4381
S. midas	[691-7771] 3304 ± 532	ρ=0.2750 p = 0.3212	ρ=0.5821 p = 0.0228	0.705 ± 0.230 p = 0.0089	0.491 ± 0.268 p = 0.0898	−0.295 ± 0.230 p = 0.2206	0.404 ± 0.194 p = 0.0582	[1987-8209] 4437 ± 550	ρ=0.2912 p = 0.3344	ρ=0.6648 p = 0.0132	1.194 ± 0.389 p = 0.0107	0.715 ± 0.305 p = 0.0390	p = 0.1173
M. nemestrina	[1413-8300] 3732 ± 223	ρ=0.0196 p = 0.8839	ρ=0.4969 p = 0.0001	0.469 ± 0.110 p < 0.0001	1.045 ± 0.062 p < 0.0001	−0.531 ± 0.110 p < 0.0001	0.467 ± 0.126 p = 0.0005	[1510-12 511] 4782 ± 295	ρ=0.2114 p = 0.1493	ρ=0.6303 p < 0.0001	1.112 ± 0.172 p < 0.0001	0.902 ± 0.080 p < 0.0001	p = 0.0030
C. apella	[106-2901] 1626 ± 96	ρ=0.4959 p = 0.0007	ρ=0.2610 p = 0.0950	0.505 ± 0.106 p < 0.0001	0.633 ± 0.081 p < 0.0001	−0.495 ± 0.106 p < 0.0001	0.282 ± 0.150 p = 0.0684	[271-7371] 2985 ± 244	ρ=0.5126 p = 0.0016	ρ=0.3580 p = 0.0376	0.856 ± 0.164 p < 0.0001	0.400 ± 0.146 p = 0.0100	p < 0.0001

^aI, Number of microglial cells; I/mg, number of microglial cells per milligram of structure; N/mg, number of neuronal cells per milligram of structure; O/mg, number of non-neuronal (other) cells per milligram of structure; M, structure mass; I/N, microglia/neuron ratio.

*For Afrotheria, analyses were done, including all the species of the clade (D. dorsalis, E. myurus, L. africana, P. tetradactylus, and P. capensis). Analyses within afrotherian species cortices were only possible where at least three data points were available (L. africana).