Genome Size Reversely Correlates With Host Plant Range in Helicoverpa Species

Abstract

In organisms with very low percentages of transposable elements (TEs), genome size may positively or negatively correlate with host range, depending on whether host adaptation or host modification is the main route to host generalism. To test if this holds true for insect herbivores with greater percentages of TEs, we conducted flow cytometry to measure the endopolyploidy levels and C-values of the host modification (salivary gland and mandibular gland in head), host adaptation (midgut), and host use-independent tissues (male gonad, hemolymph, and Malpighian tubules) of the generalist Helicoverpa armigera and the head of its older specialist sister H. assulta. Larval salivary gland displayed a consecutive chain of endopolyploidy particles from 8Cx to higher than 32Cx and larval head and midgut had endopolyploidy nuclei clusters of 16Cx and 32Cx, whereas larval male gonad, hemolymph, and Malpighian tubules possessed no endopolyploidy nuclei of higher than 8Cx. The estimated genome size of the Solanaceae plant specialist H. assulta is 430 Mb, significantly larger than that of its older generalist sister Heliothis virescens (408 Mb) and those of its two generalist descendants H. armigera (394 Mb) and H. zea (363 Mb). These data not only reveal a negative correlation between host plant range and genome size in this terminal lineage, but also imply that Helicoverpa species appear to depend more on host modification than on host adaptation to achieve polyphagy.

Genome size evolution in the beetle genusDiabrotica

“…Cases of negative correlation of genome size with pupal development have been reported in ladybird beetles and with the overall development rate in Tribolium (Carreras et al, 1991;Gregory et al, 2003). It has been previously hypothesized that genome size negatively correlates with the host range in insect herbivores (Zhang et al, 2019). However, there are also studies showing that genome size may be positively correlated with the host range in insect herbivores (Matsubayashi & Ohshima, 2015;Calatayud et al, 2016).…”

Genome Size Estimation of Callipogon relictus Semenov (Coleoptera: Cerambycidae), an Endangered Species and a Korea Natural Monument

“…Flow cytometry is a fluorescence-based technique used to detects the intensity of fluorescence emitted by DNA stained with propidium iodide [ 12 ]. As a relatively quick and reliable method for accurately estimate the size of even large genomes, flow cytometry has been widely used to analyze various insect genomes, such as in firefly [ 13 ], the stick insect Clitarchus hookeri [ 14 ], Neotropical mutualistic ant [ 15 ], and Helicoverpa moths [ 16 ]. Nevertheless, the application of flow cytometry is limited by the availability of intact tissue [ 17 ] and the estimate is also affected by chromatin condensation and the proportion of cells in G 0 to G 1 phases.…”

“…Nevertheless, the application of flow cytometry is limited by the availability of intact tissue [ 17 ] and the estimate is also affected by chromatin condensation and the proportion of cells in G 0 to G 1 phases. Given that insect tissues may show high levels of endoreplication, the use of appropriate tissue for the analysis and selection of proper standard species with well-known genome size are critical for accurate size estimation using flow cytometry [ 16 , 18 ].…”

Transcriptional response to host chemical cues underpins expansion of host range in a fungal plant pathogen lineage

“…In this lineage, horizontal gene transfers contributed to host range expansion (Zhang et al, 2019a). By contrast, genome size was inversely correlated with host range in Helicoverpa butterflies (Zhang et al, 2019b). The genome of the generalist aphid Myzus persicae has a gene count half that of Acyrthosyphon pisum , which is specialized on pea.…”