Abstract
Insect fecundity is a quantitative phenotype strongly affected by genotypes and the environment. However, interactions between genotypes and environmental factors in modulating insect fecundity remain largely unknown. This study investigated the impact of population density on the fecundity of Nilaparvata lugens (brown planthopper; BPH) carrying homozygous high- (HFG) or low- (LFG) fecundity homozygous genotypes. Under low population densities, the fecundity and population growth rate of both genotypes showed similar increasing trends across generations, while the trends between HFG and LFG under high population densities were opposite. Through a combination of temporal analysis and weighted gene co-expression network analyses on RNA-seq data of HFG and LFG under low and high population densities in the 1st, 3rd, and 5th generations, we identified 2 gene modules that were associated with these density-dependent progenitive phenotypes. Four pathways related to the neural system were simultaneously enriched by the 2 gene modules. Furthermore, Nlpale, which encodes a tyrosine hydroxylase, was identified as a key gene. The RNA interference of this gene and manipulation of its downstream product dopamine significantly affected the basic and density-dependent progenitive phenotypes of BPH. These findings indicated that dopamine biosynthesis is the key regulatory factor that determines fecundity in response to density changes in different BPH genotypes. Thus, this study provides insights into the interaction of a typical environmental factor and insect genotype during the process of population regulation.
Highlights
10, 50, 90, 130 and 170 newly (
There was no significant difference between most adjacent generations in low-fecundity genotype (LFG)
The LFG demonstrated similar change in the population growth rate under low densities, the changing of the population growth rate was not obvious for LFG under high densities (Fig. 1B). These findings suggested that BPH populations with different fecundity-determined genotypes were quite different in their strategies of population regulation to density changes
Summary
Insects comprise the most diverse class of animals due to their excellent adaptability and high reproductive capacity (Grimaldi and Engel 2005). The reproductive fitness of insects is a quantitative phenotype determined by both of genotypes and the environmental factors. Genotypic factors usually refer to genetic variants that change the function of fecundity-related proteins (Watt 1992; Edward et al 2014). Environmental factors associated with insect fecundity usually include predators (Rosenheim 1998), temperature (Geister et al 2008), xenobiotics (Ge et al 2011), nutrition (Winkler et al 2006), and the density of insect populations (Stiling 1988). Population density acting as a dynamic factor that closely related to insect diet and the available nutrition, has great impact on the population growth of insects
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