Ontogenetic Coupling of Growth Rate with RNA and P Contents in Five Species of Drosophila

1. 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.