Low Fecundity Population Research Articles

Regulation of NlE74A on vitellogenin may be mediated by angiotensin converting enzyme through a fecundity-related SNP in the brown planthopper, Nilaparvata lugens

The major yolk protein precursors (YPP) gene, vitellogenin (Vg), usually considered as a reproductive indicator and molecular marker for evaluating insect fecundity, is controlled by insect hormone (mainly ecdysteroids and juvenile hormone), transcription factors and many other fecundity-related genes. To better understand the underlying molecular regulation mechanisms of the NlVg in the brown planthopper Nilaparvata lugens (N. lugens), the correlation between one early ecdysone response gene E74 and one important fecundity-related gene angiotensin converting enzyme (ACE) on the regulation of Vg gene expression, was investigated. We first showed that the mRNA expression level of NlACE were significantly higher in a high-fecundity population (HFP) than a low-fecundity population (LFP) at different development stages, and knockdown of NlACE expression by RNA interference (RNAi) results in a reduced level of NlVg expression and N. lugens fecundity. Subsequently, we analyzed the promoter of NlACE and found an E74A binding site, which was also differentially expressed in HFP and LFP. Then a gene putatively encoding E74A, namely NlE74A, predominant in the ovary and fat body was cloned and characterized. Furthermore, the developmental profile during female adult and the tissue-specific expression pattern of NlACE and NlE74A were similar to the expression pattern of NlVg gene, implying that both NlACE and NlE74A may be involved in regulating the expression of NlVg. Finally, after injecting the dsRNA of NlE74A, the NlACE expression levels were significantly reduced simultaneously at 24 h and 48 h post-injection, and the NlVg expression level was significant reduced at 24 h post-injection and the downswing was more significant at 48 h post-injection. These results imply that regulation of NlE74A on NlVg transcription might be mediated by NlACE through the E74 binding site at the NlACE promoter region in N. lugens.

Transcriptional regulation of the vitellogenin gene through a fecundity-related single nucleotide polymorphism within a GATA-1 binding motif in the brown planthopper, Nilaparvata lugens.

Identifying the Single Nucleotide Polymorphisms (SNPs) with functions in insect fecundity promises to provide novel insight into genetic mechanisms of adaptation and to aid in effective control of insect populations. We previously identified several SNPs within the vitellogenin (Vg) promoter region between a high-fecundity population (HFP) and a low-fecundity population (LFP) of the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae). Here, we found that an A-to-T (HFP allele to LFP allele) transversion at nucleotide -953 upstream of Vg in a Nilaparvata lugens GATA-1 (NlGATA-1) binding motif is associated with the level of Vg transcription. We also characterized NlGATA-1, containing a double CX2 CX17 CX2 C zinc finger, which has been implicated in the activation of Vg gene expression. Knockdown of the NlGATA-1 gene results in a reduced basal level of expression of the Vg gene and fewer offspring of N.lugens in vivo, whereas overexpression of NlGATA-1 in cells increased Vg promoter activity. Moreover, upon cotransfection with NlGATA-1 expression vector, the luciferase activities of Vg reporter vectors with the A allele were significantly higher than those with the T allele. These findings support a mechanism in which a SNP within the promoter of Vg is associated with the level of Vg transcription by altering the binding activity of NlGATA-1 and subsequently affecting fecundity in N.lugens.

Discovery and functional identification of fecundity-related genes in the brown planthopper by large-scale RNA interference.

Recently, transcriptome and proteome data have increasingly been used to identify potential novel genes related to insect phenotypes. However, there are few studies reporting the large-scale functional identification of such genes in insects. To identify novel genes related to fecundity in the brown planthopper (BPH), Nilaparvata lugens, 115 genes were selected from the transcriptomic and proteomic data previously obtained from high- and low-fecundity populations in our laboratory. The results of RNA interference (RNAi) feeding experiments showed that 91.21% of the genes were involved in the regulation of vitellogenin (Vg) expression and may influence BPH fecundity. After RNAi injection experiments, 12 annotated genes were confirmed as fecundity-related genes and three novel genes were identified in the BPH. Finally, C-terminal binding protein (CtBP) was shown to play an important role in BPH fecundity. Knockdown of CtBP not only led to lower survival, underdeveloped ovaries and fewer eggs laid but also resulted in a reduction in Vg protein expression. The novel gene resources gained from this study will be useful for constructing a Vg regulation network and may provide potential target genes for RNAi-based pest control.

The genetic basis of population fecundity prediction across multiple field populations of Nilaparvata lugens.

Identifying the molecular markers for complex quantitative traits in natural populations promises to provide novel insight into genetic mechanisms of adaptation and to aid in forecasting population dynamics. In this study, we investigated single nucleotide polymorphisms (SNPs) using candidate gene approach from high- and low-fecundity populations of the brown planthopper (BPH) Nilaparvata lugens Stål (Hemiptera: Delphacidae) divergently selected for fecundity. We also tested whether the population fecundity can be predicted by a few SNPs. Seven genes (ACE, fizzy, HMGCR, LpR, Sxl, Vg and VgR) were inspected for SNPs in N. lugens, which is a serious insect pest of rice. By direct sequencing of the complementary DNA and promoter sequences of these candidate genes, 1033 SNPs were discovered within high- and low-fecundity BPH populations. A panel of 121 candidate SNPs were selected and genotyped in 215 individuals from 2 laboratory populations (HFP and LFP) and 3 field populations (GZP, SGP and ZSP). Prior to association tests, population structure and linkage disequilibrium (LD) among the 3 field populations were analysed. The association results showed that 7 SNPs were significantly associated with population fecundity in BPH. These significant SNPs were used for constructing general liner models with stepwise regression. The best predictive model was composed of 2 SNPs (ACE-862 and VgR-816 ) with very good fitting degree. We found that 29% of the phenotypic variation in fecundity could be accounted for by only two markers. Using two laboratory populations and a complete independent field population, the predictive accuracy was 84.35-92.39%. The predictive model provides an efficient molecular method to predict BPH fecundity of field populations and provides novel insights for insect population management.

Proteomic and Transcriptomic Analyses of Fecundity in the Brown Planthopper Nilaparvata lugens (Stål)

As an r-strategy insect species, the brown planthopper (BPH) Nilaparvata lugens (Stål) is a serious pest of rice crops in the temperate and tropical regions of Asia and Australia, which may be due to its robust fecundity. Here we combined 2-DE comparative proteomic and RNA-seq transcriptomic analyses to identify fecundity-related proteins and genes. Using high- and low-fecundity populations as sample groups, a total of 54 and 75 proteins were significantly altered in the third and sixth day brachypterous female stages, respectively, and 39 and 54 of these proteins were identified by MALDI-TOF/TOF MS. In addition, 71,966 unigenes were quantified by Illumina sequencing. On the basis of the transcriptomic analysis, 7408 and 1639 unigenes demonstrated higher expression levels in the high-fecundity population in the second day brachypterous female adults and the second day fifth instar nymphs, respectively, and 411 unigenes were up-regulated in both groups. Of these dozens of proteins and thousands of unigenes, five were differentially expressed at both the protein and mRNA levels at all four time points, suggesting that these genes may regulate fecundity. Glutamine synthetase (GS) was chosen for further functional studies. RNAi knockdown of the GS gene reduced the fecundity of N. lugens by 64.6%, disrupted ovary development, and inhibited vitellogenin (Vg) expression. Our results show that a combination of proteomic and transcriptomic analyses provided five candidate proteins and genes for further study. The knowledge gained from this study may lead to a more fundamental understanding of the fecundity of this important agricultural insect pest.

Variation in extinction risk among birds: chance or evolutionary predisposition?

Collar et al. (1994) estimate that of the 9,672 extant species of bird, 1,111 are threatened by extinction. Here, we test whether these threatened species are simply a random sample of birds, or whether there is something about their biology that predisposes them to extinction. We ask three specific questions. First, is extinction risk randomly distributed among families? Second, which families, if any, contain more, or less, threatened species than would be expected by chance? Third, is variation between taxa in extinction risk associated with variation in either body size or fecundity? Extinction risk is not randomly distributed among families. The families which contain significantly more threatened species than expected are the parrots (Psittacidae), pheasants and allies (Phasianidae), albatrosses and allies (Procellariidae), rails (Rallidae), cranes (Gruidae), cracids (Cracidae), megapodes (Megapodidae) and pigeons (Columbidae). The only family which contains significantly fewer threatened species than expected is the woodpeckers (Picidae). Extinction risk is also not distributed randomly with respect to fecundity or body size. Once phylogeny has been controlled for, increases in extinction risk are independently associated with increases in body size and decreases in fecundity. We suggest that this is because low rates of fecundity, which evolved many tens of millions of years ago, predisposed certain lineages to extinction. Low-fecundity populations take longer to recover if they are reduced to small sizes and are, therefore, more likely to go extinct if an external force causes an increase in the rate of mortality, thereby perturbing the natural balance between fecundity and mortality.