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ARS Home » Northeast Area » Newark, Delaware » Beneficial Insects Introduction Research Unit » Research » Publications at this Location » Publication #309943
Title: Variation in genome size and karyotype among closely related parasitoids of aphids

Author
item GOKHMAN, VLADIMIR - Moscow State University
item Kuhn, Kristen
item WOOLLEY, JAMES - Texas A&M University
item Hopper, Keith

Submitted to: Comparative Cytogenetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2017
Publication Date: 1/23/2017
Citation: Gokhman, V.E., Kuhn, K.L., Woolley, J.B., Hopper, K.R. 2017. Variation in genome size and karyotype among closely related parasitoids of aphids. Comparative Cytogenetics. 11:97-117.

Interpretive Summary: Genome sizes and the number and shapes of chromosomes can provide important information for genome assembly and genetic mapping. Flow cytometry, which involves measuring the contents of cells as they flow past a sensor, has been used to accurately measure genome size independently from genome assembly. Here we report genome sizes for females and males of nine species of wasps that parasitize aphids. Closely related species in two species complexes differed somewhat in genome size, and the two species complexes differed even more in genome size. The number and shapes of chromosomes also differed between these species complexes. The flow cytometry estimates of genome size are being used to guide the assembly of the genomes of these wasps. The genome assemblies and number and shapes of chromosomes are being used to study the genes affecting host specificity and climatic adaptation in these insects to improve their usefulness in controlling major pests of crops like soybean and wheat.

Technical Abstract: Genome sizes and karyotypes can provide crucial insights into important characteristics of genomes, as well as providing data for phylogenetic inferences. We measured genome sizes and determined the karyotypes of nine species of aphid parasitoids in the genus Aphelinus. Genome sizes estimated from flow cytometry were 1.1-1.5 times larger for species in the mali complex than those for the species in the daucicola and varipes complexes. The large genome size difference between species in the varipes complex versus those in the mali complex is matches the phylogenetic divergence between these complexes. Haploid karyotypes of the daucicola and mali complexes comprised five metacentric chromosomes of similar size, whereas those of the varipes complex had four chromosomes, including a larger and a smaller metacentric together with two small acrocentric chromosomes, except for A. kurdjumovi, in which the smaller metacentric chromosome was replaced by an acrocentric of similar length. Total lengths of female haploid chromosome sets correlated with genome sizes estimated from flow cytometry. Phylogenetic analysis of karyotypic variation revealed a chromosomal fusion together with pericentric inversions in the common ancestor of the varipes complex and further pericentric inversions in the clade comprising A. kurdjumovi and A. hordei. Fluorescence in situ hybridization (FISH) with 28S rDNA probe revealed a single rDNA site on chromosomes of the haploid karyotype of A. coreae. Differences in genome sizes were inversely correlated with likelihood of interspecific hybridization.