Dose and life stage-dependent effects of dietary beta-carotene supplementation on the growth and development of the Booroolong frog

Carotenoids are known for their antioxidant capacity and are considered to play an important role in vertebrate growth and development. However, evidence for their beneficial effects remains limited, possibly because very few studies have tested for dose effects across different life stages. The present study investigated the effect of various doses of dietary beta-carotene supplements on the growth and development of larval and post-metamorphic Booroolong frogs (Litoria booroolongensis). Larval and post-metamorphic basal diets (containing 0.015 and 0.005 mg g−1 total carotenoids, respectively) were supplemented with beta-carotene at one of four concentrations: 0 mg g−1 , 0.1 mg g−1 , 1 mg g−1 and 10 mg g−1 . Each treatment included 72 replicate individuals, and individuals remained on the same diet treatment over both life stages (spanning 53 experimental weeks). Our results show that larvae receiving an intermediate (1 mg g−1 ) beta-carotene supplement dose grew faster than unsupplemented larvae (0 mg g−1 ), and metamorphosed earlier. After metamorphosis, there was no effect of the lowest supplement dose (0.1 mg g−1 ) on growth and development. However, juveniles fed the highest supplement dose (10 mg g−1 ) displayed significantly smaller body mass and lower body condition, compared to all other supplement doses, from 4-months through to sexual maturity (7-months). These findings indicate that beta-carotene supplementation has positive effects on growth and development, but only at intermediate doses, and only in the larval life stage. This knowledge may assist with amphibian conservation by expediting the rate that metamorphs can be generated in captive breeding programmes. More broadly, this is the first study to demonstrate both dose and life stagedependent effects of dietary beta-carotene supplementation on vertebrate growth and development.