Chapter Index
Population database index

Asymmetry; variation within populations

Lateral differences for instance of limb measurements have been found (B. Meier, pers. comm.; Seth 1969). In forms in which only few animals are available for examination, it might therefore be good to increase sample size by measuring both left and right
limbs and other bilaterally occurring parts of the body in each animal (according to Swindler, 1976, in teeth there is no noticeable difference between right and left side; Schwartz and Beutel, 1995, however, recorded bilaterally different tooth measurements).
In addition, comparison of individual size and asymmetry with the average values of the population may allow some conclusions concerning heterozygosity: in a diversity of species, relatively heterozygous individuals were found to have reduced fluctuating
asymmetry and reduced morphological variation, suggesting a relationship beween heterozygosity and developmental stability. Individuals with extreme values for a morphological character whose variation is largely due to additive genetic variation will tend to
be homozygous at the loci that influence the trait; they are also expected to be more asymmetric than those with central values. Relationship between extremity of measurements and asymmetry is highly dependant on how strongly variation of the morphological
character in question is controlled by additive genetic variation and how many loci are involved. If the number of loci is large, then extremeness may provide a good estimate of genomic heterozygosity (Allendorf, Leary 1986).

Average relative asymmetry of a series of specimens: average of all individual percentual differences between left and right measurement, including cases of bilateral symmetry.

In the following formula, ri is the measurement on the right side of i-th specimen (i = 1,2,...n) and l i the measurement on the left side of the i-th specimen. The individual deviation Di of the larger measurement from the smaller one in the i-th specimen is:

Meaning of similarity / variation between populations

Degree of similarity between populations or species in relation to the variability of certain characters under investigation, in specimens of corresponding stages of development:


Average value in population a = 150.0; maximum value in a specimen in population a = 160.0;
Difference: 10.0: (specimen with maximum value lies 10.0 index units above the average value of the population)

Average value in population a = 150.0; average value in population b = 155.2;
Difference: 5.2 index units between the average values, representing the absolute deviation of population a from population b

The following formula is valid for A = average, m a = maximum, m i = minimum measurement of an examined sample of animals; x = measurement of a new specimen or average measurement of another sample to be compared with the former one.

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Draft for a measuring standard Last amendment: 9 August 2002

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