Zoological Research ›› 2019, Vol. 40 ›› Issue (3): 219-225.doi: 10.24272/j.issn.2095-8137.2019.022

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Depressed female cynomolgus monkeys (Macaca fascicularis) display a higher second-to-fourth (2D:4D) digit ratio

Wei Li1,2,3,Ling-Yun Luo4,Xun Yang2,3,Yong He2,3,Bin Lian2,3,Chao-Hua Qu2,3,Qing-Yuan Wu2,Jian-Guo Zhang3,Peng Xie2,3()   

  1. 1. Department of Neurology, Army Medical Center of PLA, Chongqing 400042, China
    2. Institute of Neuroscience, Chongqing Medical University, Chongqing 400016, China
    3. Chongqing Key Laboratory of Neurobiology of Chongqing Medical University, Chongqing 400016, China
    4. Department of Neurology, the Third Affiliated Hospital of Sun Yat-Sen Universlty Yuedong Hospital, Guangzhou Guangdong 514700, China
  • Received:2018-07-07 Accepted:2019-01-24 Online:2019-05-18 Published:2019-04-19
  • Contact: Peng Xie E-mail:xiepeng@cqmu.edu.cn
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (816 01207) and National Basic Research Program of China (973 Program) (2017YFA 0505700)


This research aimed to provide evidence of a relationship between digit ratio and depression status in the cynomolgus monkey (Macaca fascicularis). In stable cynomolgus monkey social groups, we selected 15 depressed monkeys based on depressive-like behavioral criteria and 16 normal control monkeys. All animals were video recorded for two weeks, with the duration and frequency of the core depressive behaviors and 58 other behaviors in 12 behavioral categories then evaluated via behavioral analysis. Finger lengths from the right and left forelimb hands of both groups were measured by X-ray imaging. Finger length and digit ratio comparisons between the two groups were conducted using Student’s t-test. In terms of the duration of each behavior, significant differences emerged in “Huddling” and five other behavioral categories, including Ingestive, Amicable, Parental, Locomotive, and Resting. In addition to the above five behavioral categories, we found that depressed monkeys spent less time in parental and rubbing ‘ and forth behaviors than the control group. Furthermore, the 4th fingers were significantly longer in the left and right hands in the control group relative to the depressed monkeys. The second-to-fourth (2D:4D) digit ratio in the left and right forelimb hands was significantly lower in the control group than that in the depressed group. Our findings revealed significant differences in finger lengths and digit ratios between depressed monkeys and healthy controls, which concords with our view that relatively high fetal testosterone exposure may be a protective factor against developing depressive symptoms (or that low fetal testosterone exposure is a risk factor).

Key words: Finger length, Digit ratio, Major depressive disorder, Cynomolgus monkey

Figure 1

Core depressive behavior (“Huddling”) in a cynomolgus monkey "

Figure 2

Forelimb hand X-ray image"

Table 2

Frequency of behaviors observed in depressed and control subjects"

Behavior Frequency
Behavioral category Behavior Depressed group Control subjects P value Adjusted P value
Core behavior Huddling*** 1.53±2.17 0.51±1.25 P<0.001 P<0.001
Ingestive behavior Feeding while hanging*** 0.11±0.63 0.05±0.28 P<0.001 P<0.001
Feeding while sitting** 0.85±2.15 1.11±2.47 P<0.001 P<0.01
Drinking*** 0.20±0.86 0.51±1.59 P<0.001 P<0.001
Amicable behavior Mutual grooming*** 0.74±1.83 1.33±2.40 P<0.001 P<0.001
Mating behavior Copulation* 0.08±0.35 0.12±0.53 P=0.0007 P=0.0418
Parental behavior Nursing* 0.28±1.01 0.40±1.44 P=0.0002 P=0.0129
Resting behavior Hanging on iron chain rest*** 0.02±0.22 0.23±0.80 P<0.001 P<0.001
Hanging on skylight rest*** 0.29±1.63 0.10±0.62 P<0.001 P<0.001
Locomotive behavior Walking along iron chain*** 0.03±0.21 0.10±0.53 P<0.001 P<0.001
Miscellaneous behavior Rub hand back and forth*** 0.02±0.15 0.06±0.43 P<0.001 P<0.001

Table 3

Digit length in right and left forelimbs of depressed and control subjects (cm)"

Left/Right Digit? Control (n=16) Depressed (n=15)
Mean SD Mean SD
Left 2 29.76 2.46 29.28 2.62
4* 37.75 2.60 35.45 3.17
Right 2 30.25 2.67 29.04 2.78
4* 37.14 2.64 35.09 3.24

Table 4

2D:4D ratio in the right and left forelimb hands of depressed and control subjects"





Control Depressed P value
n Mean SD n Mean SD
Left 2D:4D 16 0.79 0.04 15 0.83 0.03 0.002**
Right 2D:4D 16 0.81 0.03 15 0.84 0.05 0.0372*

Table 1

Duration of behaviors observed in depressed and control subjects"

Behavior Duration
Behavioral category Behavior Depressed group Control subjects P value Adjusted P value
Core behavior Huddling*** 365.44±514.14 159.00±355.08 P<0.001 P<0.001
Ingestive behavior Drinking*** 2.51±13.09 5.92±21.59 P<0.001 P<0.001
Feeding while hanging* 6.16±33.19 3.56±24.14 P=0.0004 P=0.0243
Lick food residue off cage* 1.29±13.78 0.44±3.24 P=0.0007 P=0.0419
Feeding while sitting*** 29.73±89.06 63.29±171.94 P<0.001 P<0.001
Amicable behavior Mutual grooming*** 51.96±153.61 114.13±226.53 P<0.001 P<0.001
Being groomed*** 51.75±120.17 97.94±198.63 P<0.001 P<0.001
Parental behavior Nursing* 7.33±36.69 11.75±57.42 P=0.0006 P=0.0334
Locomotive behavior Quadrupedal walking on floor*** 62.82±58.99 82.03±75.68 P<0.001 P<0.001
Walking along iron chain*** 0.13±1.26 0.85±5.62 P<0.001 P<0.001
Standing* 9.75±25.35 13.94±29.95 P=0.0006 P=0.0378
Resting behavior Hanging on iron chain rest*** 5.85±71.70 45.35±176.59 P<0.001 P<0.001
Hanging on skylight rest*** 23.18±143.93 8.88±81.59 P<0.001 P<0.001
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