Ontogenetic coupling of growth rate with RNA and P contents in five species of Drosophila

Summary1 We studied the associations among growth rate, RNA content and P content at ∼12‐h intervals during the larval stage in five species of Drosophilids that specialize on host foods that differ substantially in P content. 2 Consistent with expectations based on the ‘growth rate hypothesis’ (GRH), within each species there were significant positive correlations between growth rates and RNA and P contents and in each species variation in P content was largely determined by differences in RNA content. However, there was a significant difference among species in how these three parameters were associated with each other, primarily due to differences in the intercept of the relationships rather than in their slopes. 3 Consistent with the GRH, we also observed positive associations among the average growth rates, RNA contents and P contents of the five species. Furthermore, these differences were broadly consistent with differences in the P content of their host resources: for example, Drosophila falleni , a species that specializes on P‐rich mushrooms, had the highest growth rates and P and RNA contents while D. pachea and D. mettleri , species that specialize in low‐P exudates from necrotic cacti and trees, had the lowest growth rates and P and RNA contents. 4 While data for additional species are needed, our findings provide further evidence consistent with the GRH and highlight a potential role of P limitation in shaping growth rate evolution in the Drosophilids .