Algal-diet Enhances Sexual Ornament, Growth And Reproduction in the Guppy

Abstract

Carotenoids often influence male coloration, and the carotenoid-based coloration is used for female mate choice in some animals. The positive influence of carotenoids on a variety of physiological systems in animals is also known. Because animals have to obtain carotenoids from their food, the conspicuousness of carotenoid-based coloration may indicate the male's foraging ability for carotenoid-rich food. It is possible, therefore, that females can obtain benefits of the high-foraging ability and, thus, health or vigor of their offspring through their mate preference for the male coloration. In order to test this prediction, we examined the influence of algae-intake (carotenoid-resource in nature) on guppies. By algae-supplement, not only male orange coloration but also growth of both sexes and female reproduction were enhanced compared with fish in control groups, although they got the same amount of energy from their food. However, carotenoid-supplementation did not show the positive influence on growth and reproduction, though male orange coloration became conspicuous. It is possible to explain the difference of the influence on growth and reproduction between algae- and carotenoid-supplement groups in two ways. First, some kinds of carotenoids within algae other than carotenoids used for carotenoid-supplementation play an important role for enhancement of growth and reproduction. Second, other substances (e.g. non-digestible carbohydrates) within algae influenced growth and reproduction through the positive effect on digestive system. Since algae-intake enhanced not only male orange coloration but also growth and reproduction, female guppies may obtain benefits through mate preference for males having brighter coloration and, hence, greater foraging ability for algae.