Researchers at University of Tsukuba investigated secondary contact zones, hybridization, and genetic introgression in two closely related species of spider mites, haplodiploid organisms found at different elevations in Japan, a mountainous country. The results suggest that secondary contact zones are widespread in the mountainous areas from the Shizuoka Prefecture to Kyushu and that the two species mate in these regions but with low genetic introgression.

Tsukuba, Japan—Speciation is an important research area, as it increases biodiversity on Earth. When closely related species with incomplete reproductive isolation expand their distribution after some degree of differentiation and form secondary contact zones, the status of hybridization and genetic introgression provides important information for understanding speciation. To date, speciation studies have primarily focused on diploid organisms, but haplodiploid organisms have not been investigated in depth.

In this study, researchers focused on two species of related haplodiploid spider mites found at different elevations in Japan and investigated their secondary contact zones on Mt. Amagi (Shizuoka Prefecture) as well as hybridization and genetic introgression in that area. Analyses of male morphology, sex ratio, single nucleotide polymorphism using multiplexed Inter-Simple Sequence Repeat (ISSR) genotyping by sequencing (MIG-seq), and crossing experiments confirmed extensively overlapping distribution of these two species on the mountainside. Taken together with previous studies, the results suggest widespread secondary contact zones of the two species in the mountainside from the Shizuoka Prefecture to Kyushu. A few hybrids were obtained from crossing experiments in the laboratory, but no obvious hybrids were found in the fields. Nonetheless, the sex ratio in the field suggested interspecific mating in the secondary contact zone. In addition, genetic introgression was detected, although very low. Moreover, a male with abnormal morphology was found, but with an unclear association with hybridization.

This study is the first to reveal hybridization and genetic introgression in spider mites in a secondary contact zone. Further research on speciation of haplodiploid spider mites is needed for complete understanding of their speciation.

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This research was supported in part by JSPS KAKENHI, Grant Number 20K06810 (Grant-in-Aid for Scientific Research C to Y. Sato), by JSPS KAKENHI, Grant Number 24H00055 (Grant-in-Aid for Scientific Research S to Y. Tsumura), by Nakatsuji Foresight Foundation (to Y. Sato), by The Research Enhancement Project of Mountain Science Center, University of Tsukuba (to Y. Sato), and by The Suzuki Takahisa Memorial Grant, University of Tsukuba (to Y. Sato).

Original Paper

Title of original paper:

Secondary contact zone and genetic introgression in closely related haplodiploid social spider mites

Journal:

Heredity

DOI:

10.1038/s41437-024-00708-y

Correspondence

Assistant Professor SATO Yukie
Institute of Life and Environmental Sciences, University of Tsukuba

Post Doctoral Fellow HIROTA Shun K.
Botanical Gardens, Osaka Metropolitan University

Professor SUYAMA Yoshihisa
Field Science Center, Graduate School of Agricultural Science, Tohoku University

Related Link

Institute of Life and Environmental Sciences