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

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.