Morphometric discrimination of wild from farmed Dybowski’s frog (Rana dybowskii) based on hindlimb length

Abstract

Commercial farming of anuran species that are declining in the wild raises a need to discriminate wild from farmed frogs. We hypothesized wild frogs might have extended hindlimbs due to greater frequency or intensity of jumping relative to farmed frogs, highlighting a morphometric approach to discrimination of wild from farmed frogs using hindlimb length. In the present study, Dybowski’s frog (Rana dybowskii) was used to test this hypothesis. We measured body mass (Mb) and hindlimb length (Lh) of 2-year old farmed frogs and wild frogs aged 2 to 5 years. Dybowski’s frog demonstrated significant dimorphism in Mb and Lh. Mb was significantly greater among farmed 2-year old frogs in both sexes (p=0.000), while only among females was Lh significantly greater for wild frogs (p=0.000). Lh/Mb was used as an index for origin discrimination to eliminate the influence of Mb due to variation of husbandry conditions among farms. Mean Lh/Mb for farmed frogs was significantly lower than for wild frogs (p=0.000) in the 2-year old age class. Discrimination correctly classified 84.4% of farmed and 96.3% of wild male frogs. Among females, 92.9% of farmed frogs and 90.1% wild frogs were correctly classified. The overall correctness of classification was 92.1% and 90.8% for males and females, respectively. However, Lh/Mb revealed variation with age, resulting in reduced discriminative power for frogs ≥3 years old. We introduced a coefficient Ce to adjust the Lh/Mb of frogs ≥3 years to the level equivalent to 2-year frogs. The adjustment achieved 89.5% for overall correctness of origin for wild males and 92.4% for wild females ≥3 years old. These results show that Lh/Mb is an effective index to discriminate wild from farmed Dybowski’s frog. Since the physical demands of jumping are common among anurans, this index is also potentially applicable to other anuran species.