The degree of sexual size dimorphism is a factor that varies widely between breeds, whether domesticated
6,7 or wild species
5. In particular, the fact that dogs have different sizes and morphological structures, from Yorkshire Terrier to Doberman, brought with it intraspecific polyformism
12, which resulted in low interest in the evaluation of sexual dimorphism
13 as dogs have different sizes and visual morphology, they also show different skull typology distribution
16,20,21.
From the appendicular skeleton, sexual dimorphism has only been evaluated from the humerus bone of dogs so far, and it has been observed that this has 85% of estimation rate 15. In this study, the role of the femur, which is a bone that is widely used in determining gender in terms of humans 8-11, was investigated on sex determination in dogs with wide intraspecific polyformism 12.
There are many factors (genetics, race, species, etc.) that affect visual morphology and other important factor is sexual dimorphism, which reveals the size difference between male and female individuals 22. This reveals a noticeable difference in height and weight between males and females in many mammals 19. This contributes to the estimation of visual morphology over bones and also to reveal the existence of sexual dimorphism. It has been reported that a comparison between body sizes between males and females is possible with the contribution of osteometric comparisons in determining the sex of dog species 14. Therefore, morphological 15 and osteometric 23,24 methods are thought to be beneficial for animals. Similar to the widespread use of estimations based on morphometric data in humans 8-11, it has been tried to focus on how it should be used in animals, especially in dogs. The use of dog breeds of different sizes in this study, which are considered dolichocephalic 16, was due to the fact that sexual dimorphism is a factor affecting visual morphology 22. In the population including 22 breed and crossbred dogs, the differences between femur osteometric measurements of female and male individuals were significant at the P<0.01 level. This showed the change in osteometric measurements related to gender. The values of male individuals had a higher value than females especially in GL, Bp, DC, SD, CD and Bd values consecutively ; with the mean of 210, 96, 46.09, 23.11, 16.70, 56.86, 38.99 mm in males and 187.43, 41.22, 20.40, 16.36, 49.14, 34.37 mm in females.
Femur GL and diaphysis measurements (SD and CD) are widely used in making predictions such as shoulder height from visual morphological characteristics of dogs 25, body weight 25-27 and thinness index 25. The thought of sexual dimorphism affects visual morphology 22 supports the idea that body sizes differ in both two genders in many animal species. Males in larger species seem to be larger than females and males in smaller species 28, for instance male whippets, irish wolfhounds and standard poodles were found all significantly taller than their female individuals in Sutter et. al’s 7 study. In the light of these knowledge the variation observed in the GL value in this study was also due to the presence of dogs in different sizes and GL mean value of both males and females may have been a key point to understand sexual dimorphism 7.
SD and CD values were evaluated together with the GL value, the sexual dimorphism on these values became clearer. The thinness index is an important indicator of the strength of a particular item 23,25. Compared with the height of the withers, it provides a valuable measure of the structural feature of the legs of the animal in question, which correlates the robustness of the members with the relative weight of the animal, allowing it to be interpreted as stocky or slender 19. In males, the highest variation was found in the GL value, and the lowest variation was in the Bd value. The variation in GL and CD values was higher than the other parameters, indicating that dogs with different structural characteristics were used in the study. The GL value showed large-heavy male dogs, but when evaluated together with the SD value (high value), this definition could be made correctly. Otherwise, tall, slender-legged male dogs could also have a high GL value. Taken together, the graphical distribution of the SD value versus the GL value, supported a sexual dimorphism above the average with 15.51 mm.
Considering the coefficient of variation in femur osteometric measurements in both male and female dogs, it is seen that Bp and Bd values constitute the most reasonable variation and the most homogeneous distribution was seen in Bp and Bd values in terms of sexual dimorphism. When the distribution of Bp value within the overall average is compared to the Bd value, it was observed that females were more clustered below the overall average (Bp=43.62 mm) value, while males were more concentrated above this line. The ones observed below and above the mean line were likely due to the use of different phenotypic dogs in the study. Contrary to this evaluation, when the distribution of Bd value within the general average is compared to the Bp value, a similar situation to that of Bp was seen. It was observed that females clustered below the general mean line (Bd=36.65 mm), while males were over it.
These findings resembles the findings in Belahouse et al’s study that showed a relative strong female-biased dimorphism while for the other femoral variables, except length, the dimorphism is male-biased 13.
The scatter graph of (Bp+Bd+CD)/3 value, to which the GL and CD 25-27,29 values prominent in the prediction of visual morphology were added as addition to the values mentioned above, showed a difference in the distribution density of males and females with R2= 85.8 a predictive coefficient.
It was also possible to see some extremes in the scatterplots. These were the presence of females in the agglomeration of males or the presence of males in the heap of females. This was due to the presence of dogs with different morphological characteristics, because the morphology of the the bones were affected by size and body weight 28,30,31. It was normal for a female St. Bernard and a female Cocker Spaniel to differ slightly in distribution as the predictive rate (R2) had a value of 85.8%.
On the other hand, there were negative correlations between Bp*100/GL and Bd*100/GL indices and osteometric measurements, which was salient. There was a negative correlation between SD*100/GL index and GL and DC values. Although it had a low correlation coefficient, the increase in bone length had an effect on decreasing this index. A thinness index value with the appearance of long slender legs was emerging. This was probably the case for female individuals. Because the existence of a positive correlation of this index (SD*100/GL) with CD caused the index to increase as body weight increased. This is seen as an effect of the heavy and large-bodied appearance of male individuals 28,30,31. The statistical significance of the difference between the CD values of female and male individuals and the large difference observed between them are thought to be another factor in the large SD*100/GL index.
Although the effect of human choice and selection on the emergence of size differences between species was mentioned, according to the present study the argument of this effect was not very valid in determining sex in archaeological remaints by osteometric method 15 was a controversial subject. It is believed that the emergence of dog types with different sizes and morphological structures does not occur on a single gender, but covers both genders. Gender identification through bone morphology in dogs has so far been rather limited 11. Studies have generally focused on os coxae and sacrum 22,32-34. Although it is claimed that the osteometric method is inadequate in determining gender, the equations created by pelvis morphometry clearly reveal the existence of sexual dimorphism 22,35. The femoral osteometric measurements used in this study also clearly show the dimorphism between males and females. Obtained osteometric values are directly more decisive parameter than femur index values. The high positive correlations between osteometric values can also explain the higher size increase in males compared to females. An increase in one of the femoral parameters causes the other to increase as well, thus reflecting on the visual morphology. Although the index values of the femur do not have a determining effect on sexual dimorphism, it can provide a clear explanation of what kind of structural feature the limbs have. It is thought that the increase in the osteometric measurements has a negative effect on the indices, due to the fact that the increase in Bp, SD and Bd values is not at the desired level or in the negative direction compared to the rate of increase in the GL value.
On conclusion, although femur osteometric measurements of dogs in a wide morphological range do not provide us with 100% sexual discrimination, they will contribute greatly to the evaluations on this subject with a predictive coefficient of approximately 85%. The measurements in femur could correlate the most with sexual dimorphism in pelvic bones, both skeletal structures being involved in the movements of the hip joint like as pelvic dimensions especially depending on the individual’s breed. 13,31. Because it is well known that largest breeds show a highly male-biased sexaul dimorphism. And femur may be one of the indicator of sexual dimorphism genetically 30,31 and measurements of it could be applied to discriminate a male from a female canine in forensic investigations 31.
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