Chimpanzee Extraversion scores vary with epigenetic modification of dopamine receptor gene D2 (DRD2) and early rearing conditions

Figures & data

Table 1. Adjectives loading onto varimax-rotated chimpanzee personality traits.

Method	Trait	Adjectives/behaviours
Rating	Reactivity/ Undependability	+ Irritable + Temp./moody + Deceptive + Impulsive + Defiant + Mischievous + Jealous + Manipulative + Stingy + Bullying + Aggressive + Eccentric + Socially inept + Excitable + Autistic – Calm
	Dominance	+ Bold + Relaxed + Dominant – Fearful – Timid – Cautious – Dependent – Anxious
	Extraversion	+ Active + Playful + Sexual + Affiliative- Solitary – Depressed
	Openness	+ Human oriented + Inquisitive/curious + Inventive + Intelligent + Affectionate/ Friendly + Persistent
	Agreeableness	+ Protective + Considerate
	Methodical	+ Self-caring + Methodical

Data were reproduced with permission from Freeman et al. (2003) [1] .

Figure 1. Correlation between peripheral blood CpG methylation levels and methylation at same sites in tissue from (a] the prefrontal cortex, and (b) the cerebellum.

Table 2. 16 Chimpanzee DRD2 CpG sites identified and included in this study.

CpG ID	CpG name	CHR	Coordinate Pantro2.1.4	Location	Coordinate hg19	DIST
DRD2-1	cg22404572	11	111,327,207	Body	113,289,673	NA
DRD2-2	cg02198192	11	111,332,873	5’UTR	113295379	5666
DRD2-3	cg19804476	11	111,333,002	5’UTR	113295509	129
DRD2-4	cg11323042	11	111,333,019	5’UTR	113295526	17
DRD2-5	cg14809166	11	111,334,320	5’UTR	113296828	1301
DRD2-6	cg16823554	11	111,339,746	5’UTR	113300731	5426
DRD2-7	cg00525373	11	111,346,866	5’UTR	113307871	7120
DRD2-8	cg21141217	11	111,349,863	5’UTR	113310882	2997
DRD2-9	cg03608783	11	111,356,104	5’UTR	113317120	6241
DRD2-10	cg18248586	11	111,368,000	5’UTR	113329026	11,896
DRD2-11	cg02332042	11	111,369,061	5’UTR	113330091	1061
DRD2-12	cg20016411	11	111,383,594	5’UTR	113344987	14,533
DRD2-13	cg23881278	11	111,384,919	TSS1500	113,346,299	1325
DRD2-14	cg12758687	11	111,384,947	TSS1500	113,346,327	28
DRD2-15	cg12176709	11	111,385,105	TSS1500	113,346,485	158
DRD2-16	cg20629239	11	111,385,111	TSS1500	113,346,491	6

CHR = Chromosome number, 5’ UTR = 5 end untranslated region, TSS1500 = Promotor region 1500bp upstream of transcription site, DIST = distance to neighbouring CpG site

Table 3. CpG factor item loadings on varimax-rotated factors.

CpG ID	CpG name	PC1	PC2	PC3	PC4	h^2
DRD2-5	cg14809166	0.93	0.078	0.115	−0.157	0.91
DRD2-9	cg03608783	0.914	0.223	0.148	−0.126	0.923
DRD2-8	cg21141217	0.879	0.136	0.067	−0.109	0.807
DRD2-13	cg23881278	−0.874	−0.044	0.095	0.276	0.851
DRD2-2	cg02198192	0.869	0.275	0.044	−0.132	0.85
DRD2-6	cg16823554	0.85	0.384	−0.008	−0.005	0.87
DRD2-14	cg12758687	−0.701	−0.001	0.157	0.431	0.702
DRD2-10	cg18248586	−0.572	−0.221	−0.052	−0.429	0.563
DRD2-15	cg12176709	−0.09	−0.806	−0.037	0.284	0.739
DRD2-4	cg11323042	0.265	0.738	−0.206	0.243	0.716
DRD2-16	cg20629239	−0.37	−0.677	0.112	0.404	0.771
DRD2-7	cg00525373	0.037	−0.02	−0.819	−0.061	0.677
DRD2-1	cg22404572	−0.049	−0.126	0.79	0.003	0.643
DRD2-11	cg02332042	0.21	−0.039	0.732	0.04	0.583
DRD2-12	cg20016411	−0.197	−0.108	0.172	0.734	0.62
DRD2-3	cg19804476	0.31	0.226	0.153	−0.506	0.427
Eigenvalue		6.912	2.174	1.31	1.254
% variance explained		43.202	13.587	8.189	7.837

h² indicates communalities, boldface indicates items with salient loadings >|0.5|

Figure 2. Association between personality scores and composite DRD2 CpG composite measure scores. Higher scores are associated with (a) higher Extraversion for PC1; (b) lower Extraversion for PC3 (c) lower Extraversion for PC4 (d) lower Openness for PC3.

Figure 3. Methylation levels for individual DRD2 CpG sites loading onto composite measures PC1 and PC4. Each point represents methylation values for each individual at each CpG site and is coloured by that individual’s Extraversion score. Lines are loess smoothed methylation values for each quartile for Extraversion score. TSS 1500 = within 1500 bp of a transcription start site and 5’ UTR = within the 5’ untranslated region of DRD2. Chromosomal coordinates are in base pairs and refer to human genome build hg19.

Table 4. Model statistics for DRD2 CpG composite measure scores and their association with personality dimensions in chimpanzees.

Personality trait	CpG component	Est	SE	t	p
Extraversion	DRD2_PC1	0.169	0.064	2.650	0.011
	DRD2_PC2	0.070	0.054	1.307	0.198
	DRD2_PC3	−0.129	0.053	−2.429	0.019
	DRD2_PC4	−0.159	0.057	−2.781	0.008
Openness	DRD2_PC1	0.053	0.073	0.722	0.474
	DRD2_PC2	0.081	0.061	1.326	0.192
	DRD2_PC3	−0.168	0.060	−2.771	0.008
	DRD2_PC4	−0.144	0.065	−2.216	0.032
Agreeableness	DRD2_PC1	−0.019	0.077	−0.249	0.804
	DRD2_PC2	0.140	0.099	1.416	0.164
	DRD2_PC3	−0.087	0.062	−1.402	0.168
	DRD2_PC4	−0.019	0.068	−0.278	0.782
Dominance	DRD2_PC1	−0.011	0.084	−0.126	0.901
	DRD2_PC2	0.083	0.070	1.183	0.243
	DRD2_PC3	−0.076	0.071	−1.072	0.290
	DRD2_PC4	−0.132	0.076	−1.726	0.091
Reactivity	DRD2_PC1	0.094	0.077	1.216	0.231
	DRD2_PC2	0.071	0.064	1.113	0.272
	DRD2_PC3	−0.028	0.065	−0.428	0.671
	DRD2_PC4	−0.141	0.070	−2.012	0.051

Est = estimate, SE = Standard error, t = t-value, p = p value, boldface indicates p-value significant after FDR correction

Figure 4. The influence of rearing background on the association between PC4 methylation and Extraversion. A negative association was found between PC4 scores and Extraversion in nursery-reared but not mother-reared individuals.

Freeman HD, Brosnan SF, Hopper, LM et al. Developing a comprehensive and comparative questionnaire for measuring personality in chimpanzees using a simultaneous top-down/bottom-up design. Am J Primatol. 2013;75(10):1042–1053.

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Data availability statement

The authors confirm that the data supporting the findings of this study are available within the supplementary materials https://doi.org/10.1080/15592294.2022.2058224.