Sex-related growth patterns in a caecilian amphibian (genus Ichthyophis): evidence from laboratory data

Abstract

Post-metamorphic growth patterns were analysed in the tropical caecilian amphibian Ichthyophis cf. kohtaoensis (Amphibia: Gymnophiona) experimentally in captivity over 6 years. Two questions were addressed. (1) Does this Ichthyophis display sexual dimorphism for size? (2) Do ichthyophiid caecilians express an indeterminate growth pattern? Total length did not differ between sexes in the first, second or third year after metamorphosis. In the fourth, fifth and sixth years, females were significantly larger than males. The index of sexual size dimorphism increased from zero in the first year after metamorphosis to 0.104 in the sixth year. Relative growth rates of total length were different for each sex. In the first two growth seasons males grew at higher rates, while from the third growth season females grew faster than males. In general, growth rates increased from the first to the second year after metamorphosis and decreased dramatically after both sexes became mature. As all Ichthyophis in this study grew constantly throughout the first 6 years after metamorphosis, indeterminate growth probably occurs in caecilians as reported for frogs and salamanders. Additionally, growth curves for both sexes of Ichthyophis cf. kohtaoensis were estimated based on the von Bertalanffy model.