A contrast of CentralAndes versus Mapuche ancestry is associated with

The contrast CentralAndes versus Mapuche in the full CANDELA sample is sig- nificantly associated with variation in several facial features (Figure 6.3). To take one example, Figure 6.4 shows a scatterplot with the regression line for one of the associated traits, Nose Bridge Breadth.

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171 Figure 6.3. Sub-continental ancestry and physical appearance.

(A) -log P-values for a linear regression of variation in the 28 traits described in section 6.2.1 (with categorical traits listed in grey and quantitative traits in black) against the contrasts between two sub-continental ancestry components estimated by SOURCEFIND. The left column details results for the Portugal/WestSpain and North- WestEurope1 contrast in the Brazilian sample (Br). The two right columns present the contrast between CentralAndes and Mapuche in the full CANDELA sample (all) or re- stricted to Chile (Ch). Bonferroni-corrected P-value significance threshold (alpha=0.05) is shown on the –log P-value scale as 3.22. (B) Regression coefficients (Betas), divided by the standard deviation (SD) for that trait, for the contrasts in (A) (hence in units of SD). In panels (A) and (B) colour intensity reflects variation in –log P-values or beta coeffi- cients, as indicated on the scale. Bonferroni-corrected significant values are highlighted with a dot. Adapted from Chacón-Duque et al. (2018). Generated by J.C. Chacón-Duque and K. Adhikari.

CHAPTER 6. SUB-CONTINENTAL ANCESTRY AND PHYSICAL APPEARANCE

Validation analyses using the same contrast but limited to Peru and Chile or only to Chile, an equivalent contrast generated from unsupervised ADMIXTURE re- sults (K=7) and PC7 produced similar results, showing consistency for several phenotypes, with four traits significantly associated in all analyses: Eye Fold, Chin Protrusion, Nose Protrusion and Nose tip angle (Figure 6.5 and Table 6.1).

Figure 6.4. Scatterplot and regression line (with 95% confidence interval) for nose bridge breadth and the SOURCEFIND contrast between CentralAndes and Mapuche in Peru and Chile.

Adapted from Chacón-Duque et al. (2018). Generated by J.C. Chacón-Duque and K. Adhikari.

The associations with nose-related traits are perhaps the most interesting given previous evidence. In the analysis I present here, the Mapuche sub-component is associated with a less protruded nose (-log P-value=4.61) and equivalently with a broader nose tip angle (-log P-value=6.83), consistent with physical anthropol- ogy studies indicating that the Mapuche have a flatter, wider nose compared to Aymaras and Quechuas, the two main Central Andean groups (Bustamante et al. 2011b; Comas 1960; Davies 1932). Furthermore, this variation has also been documented in world-wide human populations (including some Andean and Southern Chilean populations) and an association between nose protrusion and dry and cold conditions has been found, interpreted as an evidence for climatic adaptation (Davies 1932; Hubbe et al. 2009; Leong and Eccles 2009).

A research that compared the divergence of quantitative nose shape traits and neutral molecular markers (using 𝑄𝑆𝑇− 𝐹𝑆𝑇 comparisons, (Leinonen et al. 2013;

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173

Wright 1951)) has also suggested that features related to nose width have been influenced by adaptation to cold/dry versus hot/humid environments, as they seem to have differentiated more than it would be expected under genetic drift compared to other nose shape traits (Zaidi et al. 2017).

Figure 6.5. Scatterplot of –log P-values from additional phenotypic regression analyses involving CentralAndes versus Mapuche contrast.

The values used are presented in Table 6.1. The X-axis refers to P-values from the pri- mary analysis using SOURCEFIND estimates (SF) and all the CANDELA data, as shown in the second column of Figure 6.3. The Y-axis refers to –log P-values from four other regression analyses using related ancestry components defined by ADMIXTURE (Adm) at K=7 in all the CANDELA data or using SOURCEFIND or PCA (PC7) ancestry compo- nents limited to the Peruvian and/or Chilean data (chapter 3, section 3.8). Sample sizes: all data N=5.794, Peruvian and Chileans N=2.594, Chileans N=1.542. Adapted from Chacón-Duque et al. (2018). Generated by J.C. Chacón-Duque and K. Adhikari.

The nasal cavity is an important regulator of inhaled air, temperature and humidity (Naftali et al. 2005). The nasal airways warm inspired air and saturate it with water vapour, in order to reach the right optimal temperature and moisture required in the respiratory tract (Negus 1954). Regarding the possible effect of environmental adaptation, it has been proposed that narrow respiratory cavities maximize the mucosal contact area in relation to the inhaled air volume, enhancing the airflow and facilitating the exchange of heat and moisture in cold or dry climates (Churchill et al. 2004). For instance, according to simulated data, narrower nasal

CHAPTER 6. SUB-CONTINENTAL ANCESTRY AND PHYSICAL APPEARANCE

airways could be helpful in colder climates as the airflow increases and helps to warm the air quickly (Zhu et al. 2011), suggesting that populations with these characteristics, like the Central Andeans, may have been adapting to altitude.

Table 6.1. –log P-values from additional phenotypic regression analyses involving Cen- tralAndes versus Mapuche contrast

Trait ADM.K=7 (all) SF (all) SF (Pe-Ch) SF (Ch) PC7 (Ch) Height 0.91 0.95 0.47 0.51 1 Monobrow 2.77 2.63 3.58 2.26 1.96 Eyebrow density 4 3.15 3.67 3.83 3.18 Beard density 0.97 0.74 0.07 0.29 0.65 Hair shape 0 0.23 0.7 0.04 0.02 Hair graying 0.97 0.82 0.42 0.28 0.09 Balding 1.29 1.79 0.5 0.79 0.6 Hair color 0.91 0.64 0 0.06 0.39

Skin Melanin index 4.63 2.54 2.36 2.56 1.11 Brow ridge protrusion 4.83 5.1 2.39 2.33 2.36

Eye fold 5.53 4.42 6.97 10.21 11.6

Chin Shape 2.29 2.4 1 0.75 1.46

Forehead profile 3.15 3.17 2.86 2.86 3.36 Nasion position 0.9 1.19 0.43 0.71 0.3 Nose bridge breadth 3.22 3.75 2.2 2.33 2.14 Nose wing breadth 0.03 0.31 0.38 0.22 0.1 Columella inclination 0.97 1 0.69 0.59 0.28 Nose protrusion 5.06 4.61 5.07 5.07 6.33 Nose tip angle 7.84 6.83 6.01 6.06 6.96 Chin protrusion 4.97 5.37 4.43 4.43 4.22 Facial flatness 3.6 4.63 2.29 2.12 1.41 Ear protrusion 0.74 0.82 1.3 1.33 1.38 Lobe attachment 0.11 0.05 0.01 0.01 0.25 Lobe size 0 0.31 0.16 0.23 0.27 Helix rolling 2.66 2.99 1.68 1.66 1.52 Fold of antihelix 0.15 0.37 0.16 0.4 0.2 Antitragus size 0.02 0.23 0.46 0.08 0.03 *ADM.: ADMIXTURE, SF: SOURCEFIND, Pe: Peru, Ch: Chile.

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It is important to consider that the correlation between nose shape and climate is not always present (Leong and Eccles 2009) and that other causes for this varia- tion must be taken into consideration. Another plausible explanation could be the effect of sexual selection (Darwin 1871), as proposed for other physical appear- ance traits like skin pigmentation (Aoki 2002) and height (Stulp et al. 2015). How- ever the evidences for sexual selection of facial traits in humans are scarce, so far being mainly supported by studies on the effect of facial attractiveness in mate choice (Little et al. 2011).

6.3.2 Allele frequencies in loci associated with variation in facial traits