Abstract
Nucleic acids help clarify variation in species richness of insects having different metamorphosis modes, a biological conundrum. Here we analyse nucleic acid contents of 639 specimens of aquatic insects collected from four high mountain streams of Sierra Nevada in southern Spain to test whether the allocation to RNA or DNA content differs during ontogeny between juvenile insects undergoing direct (hemimetabolous) or indirect (holometabolous) metamorphosis. The results show that RNA content as a function of body mass was negatively correlated to insect body length in four out of six and three out of six of the holometabolan and hemimetabolan taxa, respectively. Although no significant differences in RNA content were found between holometabolans and hemimetabolans, the significant interaction between body length and metamorphosis mode for RNA and RNA:DNA indicates a strong ontogenetic component to RNA allocation. In addition, our finding of lower DNA content in holometabolans relative to hemimetabolans agree with the analysis of empirical genome data in aquatic and terrestrial insects, and extend to this class of arthropods the “growth rate-genome size-nutrient limitation” hypothesis that differences in allocation between RNA and DNA may reflect fundamental evolutionary trade-off of life-history strategies associated with high growth rates (and RNA content) in holometabolans at the expense of diminished genome sizes.
Highlights
Nucleic acids help clarify variation in species richness of insects having different metamorphosis modes, a biological conundrum
Our results showed that RNA content was not significantly different between holometabolans and hemimetabolans
We found negative correlations between body length and RNA in four out of six holometabolans, and in three out of six hemimetabolans (Fig. 2)
Summary
Nucleic acids help clarify variation in species richness of insects having different metamorphosis modes, a biological conundrum. No significant differences in RNA content were found between holometabolans and hemimetabolans, the significant interaction between body length and metamorphosis mode for RNA and RNA:DNA indicates a strong ontogenetic component to RNA allocation. Profound causal links between RNA and DNA content have been cited by one research team as an explanation, among o thers[14] (the “bulk DNA” or the “selfish DNA”), for the variation in the genome size of o rganisms[15] These latter researchers hypothesised that the evolutionary mechanism by which intracellular allocation of P from DNA to RNA would accelerate growth rates but reduce the genome size in fast-growing cladocerans compared to long-lived copepods facing chronic P limitation (“growth rate-genome size-nutrient limitation” hypothesis).
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