|Year : 2016 | Volume
| Issue : 2 | Page : 42-47
Sexual dimorphism in epidermal ridge density and thickness asymmetry indices among hausa population of Kano State Nigeria
Lawan Hassan Adamu1, Samuel Adeniyi Ojo2, Barnabas Danborno3, Samuel Sunday Adebisi3, Magaji Garba Taura4
1 Department of Anatomy, Faculty of Basic Medical Sciences, Bayero University, Kano, Nigeria
2 Department of Human Anatomy, Faculty of Medicine, Ahmadu Bello University, Zaria, Kaduna, Nigeria
3 Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, Kaduna, Nigeria
4 Department of Anatomy, Faculty of Basic Medical Sciences, Bayero University, Kano, Nigeria; Department of Anatomy, College of Medicine, University of Bisha, Bisha, Saudi Arabia
|Date of Web Publication||16-Aug-2018|
Dr. Lawan Hassan Adamu
Department of Anatomy, Faculty of Basic Medical Sciences, Bayero University Kano, PMB 3011, Kano
Source of Support: None, Conflict of Interest: None
Background: The small deviations from perfect symmetry between body sides for bilateral characters may result in random errors. This is measured using the type of symmetry called fluctuating asymmetry (FA). Objectives: The objectives of the present study were to determine the sexual dimorphism in asymmetry indices using thumbprints ridge count and thickness among the Hausa ethnic group. To also investigate the existence of FA using thumbprint ridge count and thickness among the Hausa population, of Kano state. Materials and Methods: This is a cross-sectional study. A total of 217 participants comprising 112 males and 105 females participated in the study. From plain thumbprint 25 mm2 ulnar, radial and proximal areas were defined for ridge count and thickness determination. Results: The result showed a significant sex differences in signed asymmetry (SA) in ulnar ridge counts with males and females exhibited leftward and rightward asymmetry, respectively. In radial and proximal ridge counts in both sexes, the asymmetry was leftward and rightward, respectively. In the ulnar area, significant sexual dimorphism was observed in both absolute and composited asymmetry with females having higher means asymmetry indices. In the entire sample, females had a higher mean value of asymmetry. SA is not significantly different from the mean of zero in both males and females. All the counts and thickness exhibit fluctuating type of asymmetry in both sexes. Conclusion: males have a low level of asymmetry compared to females in this population. The possible existence of fluctuating type of asymmetry was observed. The ridge density and thickness may be used to study the level of developmental stability and stress during intrauterine life in this population.
Keywords: Developmental stability, fluctuating asymmetry, ridge count and thickness, sexual dimorphism
|How to cite this article:|
Adamu LH, Ojo SA, Danborno B, Adebisi SS, Taura MG. Sexual dimorphism in epidermal ridge density and thickness asymmetry indices among hausa population of Kano State Nigeria. Niger J Exp Clin Biosci 2016;4:42-7
|How to cite this URL:|
Adamu LH, Ojo SA, Danborno B, Adebisi SS, Taura MG. Sexual dimorphism in epidermal ridge density and thickness asymmetry indices among hausa population of Kano State Nigeria. Niger J Exp Clin Biosci [serial online] 2016 [cited 2018 Nov 12];4:42-7. Available from: http://www.njecbonline.org/text.asp?2016/4/2/42/239100
| Introduction|| |
In a bilaterally structured organism, developmental stability can be explained as the ability of an individual to form the optimal phenotype that may be interpreted as perfect symmetry.,,,,, The ability for the phenotypic feature of a particular trait to deviate from the value expected for an individual of a given genotype in a given environment is termed developmental instability. The small deviations from perfect symmetry between body sides for bilateral characters may result in random errors. This was reported to be controlled genetically through such mechanisms as levels of whole-genome heterozygosity or genomic co-adaptation. However, this was suggested to be character, taxon, and environment specific., Direct observations of random error on given traits are a difficult phenomenon, but these can be predicted from the increased variance in the asymmetry of bilateral characters across the population.,
Fluctuating asymmetry (FA) is a measure of small random departures from perfect symmetry in a bilaterally symmetrical structure., FA is considered to be a good indicator of the level of stress, and it also reflects how individuals cope with environmental or genetic perturbations., FA could be also a good predictor of developmental instability in an organism; this is because the same underlying genotype in a bilaterally symmetrical organism should be identical in the same environment., Bilateral asymmetry is one of the least understood aspects of the dermal ridge patterns. The measure of asymmetry which has mainly been used in population and genetic studies is the right and left difference in the total finger ridge count. The assessment of ridge asymmetry receives less attention among Hausa population. It was also reported that certain dermatoglyphic areas such as a thumb and interdigital area a-b are more vulnerable to developmental/environmental insults compared to other areas, and therefore the two areas may be considered as predictors of stress in an individual or population. This type of study may be considered as one of the usefulness of thumbprints in the assessment of the level of developmental stability and stress using genetically determined features such as fingerprints ridge density. The objectives of this study were to determine the sexual dimorphism in asymmetry indices using thumbprints ridge count and thickness among the Hausa population of Kano state Nigeria. To also investigate the existence of FA using thumbprint ridge count and thickness among the Hausa population, of Kano state.
| Materials and Methods|| |
The study was conducted among one original Hausa states; Kano state of Nigeria [Figure 1]. Kano is the most populous state in Nigeria, with about 9,383,682 million people. The principal inhabitants of the city are the Hausa people. This is a cross-sectional study. A total of 217 participants comprising 112 males and 105 females participated in the study. Any participant who was Hausas up to level of grandfather, apparently healthy whose thumbs were free from any inflammation, or deformity were included in the study. To minimize the effect of age on the thumbprint ridges only participants within the age range of 18–25 years were considered. Before the commencement of the research, ethical approval was obtained from the Ethical Committee of Kano state Hospitals Management Board and Ahmadu Bello University Teaching Hospitals Faculty of Medicine (ABUTHZ/HREC/506/2015). Informed consent was obtained from the participants and persons whose photographs appear in the study.
|Figure 1: Location of the study area (Kano) and it's local governments on the map of Nigeria|
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A direct sensing method  was used to capture plain fingerprints using a scanner (Digitapersona, China). The plain fingerprints were saved in JPEG format for ridge density determination using Bioanalyzer (a software designed using Microsoft visual basic version 6.0 programming language). The fingerprints were classified into one of the three basic patterns, namely, loops, whorls, and arches. Ridge density was measured from the count of ridges found diagonally within a 5 mm 2 × 5 mm 2 on the fingertip surface of an areas located on the ulnar, radial and the proximal side of each finger [Figure 2]., The indirect method of the ridge thickness measurement was adopted. However, the estimation of ridge thickness was carried out by dividing 7.07 mm length of diagonal line with a number of counted ridges within 25 mm 2 area. To facilitate counting, the ridge count was carried out using the magnified image. To ensure real size measurements, an ink method was used to collect the thumbprints of the 30 randomly selected participants.
|Figure 2: Spaces (5 mm × 5 mm) on ulnar, radial and proximal of fingerprint for ridge density and thickness determination for three the classes of fingerprint|
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Three indices of asymmetry, differences between left (L) and right (R) used include signed asymmetry (SA), absolute asymmetry (AA), and composite asymmetry (CA). These were determined by the following formulae; SA = R-L, AA = √ (R-L) 2, CA = −√(R-L) 2/n, where n is the sample size. The existence of directional asymmetry was detected by subjecting the mean value of SA to one sample t-test., An asymmetry was directional if the mean value of signed symmetry differs significantly from zero. Otherwise, it was considered as fluctuating symmetry.
To quantify precision, two sets of measurements were taken where with each method was compared using technical error of measurement (TEM). The absolute TEM was expressed as percentages. The percentage scores were divided into five precision categories, scores <1% was deemed excellent, and scores exceeding 10% were deemed poor. The r was computed to reveal the strength of the relationship (similarities) between two measurements. Intraclass correlation of 0.6 to <0.8 is considered as substantial reliability and 1 as perfect reliability. Independent sample t-test was used to test for sex differences in the variables. SPSS version 20 statistical software (IBM Corporation, NY, USA) was used for the statistical analysis and P < 0.05 was set as the level of significance.
| Results|| |
From [Table 1], the mean ridge counts showed that the proximal count had lowest mean value in both sexes and sides of the thumb. This also corresponds to the highest thickness in the proximal area of the thumb. In was observed that the minimum ridge count of the study population was 6 ridges/unit 25 mm 2 and the maximum was 15 ridges/25 mm 2. Similarly, for ridge thickness, the minimum ridge count of the study population was 0.45 mm and the maximum was 1.27 mm. The statistically significant mean differences were observed between male and female in ulnar and proximal areas only.
|Table 1: Descriptive statistics for thumbprint ridge density and thickness in the radial, ulnar, and proximal areas for males and female|
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Significant sex differences were observed in SA in ulnar ridge counts where males and females exhibited leftward and rightward asymmetry, respectively. In radial and proximal ridge counts in both sexes, the asymmetry is leftward and rightward, respectively. In the ulnar area, significant sexual dimorphism was observed in both absolute and CAs with females having higher means asymmetry indices. In CA significant differences were observed in both radial and proximal areas, and for AA, the differences were only in the radial area. In all the cases, females had a higher mean value of asymmetry [Table 2].
|Table 2: Sexual dimorphism in asymmetry indices of thumbprint ridge density among Hausa ethnic group of Kano, Nigeria|
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Females were found to have higher mean asymmetry in the ridge thickness in three asymmetry indices in the ulnar. In SA index females exhibited rightward asymmetry only radial area while males exhibited in all the areas. Significant sexual dimorphism was observed only in CAs in the radial area. In proximal area, both absolute and CAs showed significance sexual dimorphism [Table 3].
|Table 3: Sexual dimorphism in asymmetry indices of thumbprint ridge thickness among Hausa ethnic group of Kano, Nigeria|
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Based on one sample t-test, it was observed that the SA is not significantly different from the mean of zero in both males and females. All the counts and thickness exhibit fluctuating type of asymmetry in both sexes [Table 4].
|Table 4: Evaluation of fluctuating asymmetry among Hausa ethnic group of Kano, Nigeria|
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| Discussion|| |
Bilateral asymmetry is one of the least understood aspects of the dermal ridge patterns. The measure of asymmetry which has mainly been used in population and genetic studies is the right and left the difference in the total finger ridge count. Considering thumb as a digit that is more vulnerable to developmental/environmental insults compared to other digits. The present study investigated the existence of sexual dimorphisms in the three asymmetry indices using thumbprint ridge density. The existence of fluctuating type of asymmetry with respect to ridge density was also evaluated among the Hausa populations of Kano state.
The statistically significant higher mean value in mean ridge density asymmetry indices in females may indicate a higher level of small random error in males compared to females and more tendency of the directional type of asymmetry in females. This may also indicate higher level of developmental stress and instability in female compared to their male counterparts. It was reported that high level of FA could be used as a proxy in determining developmental instability in an individual. It has also been considered as a good indicator of stress which may reflect the inability of individuals to cope with environmental or genetic perturbations., Evolutionary biologists argue that a well-developed, symmetrical phenotype indicates the ability of an individual to oppose the challenges of developmental stress in particular environments. To further support the expression of higher asymmetry in females, Trivers et al. reported that in the elbow and fourth digit boys are less asymmetric than girls. A similar finding was reported by Gray and Marlowe, who reported women of Tanzania as being more asymmetric than men.
The sex differences observed in the three asymmetry indices may explain the level of intrauterine exposure to the environmental stress in the study population. This may be supported by the fact that asymmetry of fingerprint ridges originates in the first trimester of pregnancy and remains unchanged thereafter. It is also suggested that environmental stress during early fetal life may be the principle reason for bilateral finger ridge count asymmetry. Among Andhra Pradesh, Indian population similar intensity of developmental stress was reported. Some previous studies assumed that the genetic information for both sides of the body is the same and therefore the observed inequality at birth is attributed to intra-uterine developmental stress., It was also reported that random error assessed through asymmetry might be controlled genetically through such mechanisms as levels of whole-genome heterozygosity or genomic co-adaptation. It was also documented that the fingerprints of individuals are genetically determined and once established around the 16th week of development remained unchanged throughout the life of an individual., This leads to the suggestion that the influence of environmental factor on genetically determine feature like fingerprints may occur before the final formation of the prints features.
Population-based comparison indicated differences in expression of sexual dimorphism in ridge asymmetry. Contrary to the present study, there is no significant sexual dimorphism in both mean signed and means AA in the thumb among the Indian population. This indicates population and finger-specific variation of sexual dimorphism in the asymmetry indices. It can also be appreciated that the study of ridge asymmetry is necessary for different populations and even in the same population due to different environmental conditions. This may suggest the potential of fingerprint asymmetry as a good index in the study of population variability in dermatoglyphics.
Leftward asymmetry exhibited in males in this study may be because the ridges of the right hand were found to be coarser than the left hand. Thus, for the same area, the right hand would have a fewer ridges than the left hand. Moreover, it was evident that ridge density in both sexes among Spanish Caucasians population, where the ridge density was greater in the areas of the left hand, thus showing finer ridges than in the right hand. It was also observed that mean ridge breadth is greater for right fingers than for left fingers. Previous findings concluded that males with higher circulating testosterone had more ridges on their left hand than their right. Similarly, male with higher hand masculinity scores (which may reflect the effect of androgens on development) had lower ridge count asymmetry scores. This means that men with masculine hands had more ridges on their left fingers compared to their right. This may be different with respect to the area of the fingertips. For example, it was reported that in the proximal area, there is the existence of rightward asymmetry as opposed to the other two areas (ulna and radial). This may be linked to differences in developmental instruction that may vary from one area to another of the same finger. It can also postulate that certain areas are more prone to developmental error compared to others. Each area needs to be considered as a separate entity when explaining the type and direction of asymmetry in a given population.
Using one sample t-test, it was observed that all the SA in counts and thickness in this population have mean that is not >0, thus exhibiting fluctuating type of asymmetry in both sexes. This is because asymmetry is considered fluctuating type when the differences between right and left are centered on the mean zero., it may be stated that thumbprints features such as ridge density and thickness may be used as a model in the prediction of the level of environmental stress a given population is exposed to.
| Conclusion|| |
The present study has established the presence of sexual dimorphism in ridge density asymmetry indices. Males had a low level of asymmetry compared to females' counterpart in this population. The possible existence of fluctuating type of asymmetry was observed using one sample t-test as a screening tool of the type of asymmetry. The ridge density may be used to study the level of developmental stability and stress during intrauterine life in a given population.
We would like to thank all those who volunteered to participate in this research. In addition, our thanks also go to Sanusi Aminu who helped in the development of the software used as well as other technical assistance.
Financial support and sponsorship
This work is an extract of a Ph.D. dissertation which was sponsored by Bayero University Research Grant Unit and Tertiary Education Trust Fund (TETfund) of Nigeria.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]