The influence of the nutritional content of the adult male diet on testis mass, body condition and courtship vigour in a Hawaiian Drosophila

Abstract

1. The effects of the nutritional quality of the adult diet (primarily protein content) on testis mass, body condition and courtship vigour were studied in a Hawaiian Drosophila, D. grimshawi, a lek‐forming species under strong sexual selection. The primary goals of this study were to determine whether there is a trade‐off between investment in reproductive and somatic tissues, and to examine whether this trade‐off is influenced by quality of the adult diet. 2. Quality of the adult diet had a major influence on male body condition, courtship vigour and testis mass, but males varied in their investment patterns even within diet treatment. 3. Body condition, a measure of phenotypic quality, was significantly related to how much males invested in testis and body tissues, but the nature of the relationships differed between males fed high‐ or low‐quality diets. 4. Paragonia volume was significantly smaller for adult males fed low‐quality diets than for males fed high‐quality diets. Nutrient‐deficient diets apparently forced males to trade off investment in testes and body condition, and in body condition and courtship vigour, but nutrient‐rich diets did not result in severe trade‐offs. 5. Collectively, the results suggest that fluctuation in adult diet quality of male D. grimshawi might influence male reproductive quality in ways that might limit female reproductive output and/or be a factor for female choice in this species.