1. ¹Department of Earth and Life Sciences, Osaka Prefecture University, 1-1 Gakuen-Cho, Sakai 599-8531, Japan
2. ²Department of Applied Biology, Kyoto Institute of Technology, Kyoto 606-8585, Japan
3. ³Department of Biology, Loyola University of Chicago, Chicago, IL 60626, USA

Correspondence: S Gamo, Department of Earth and Life Sciences, Osaka Prefecture University, 1-1 Gakuen-Cho, Sakai 599-8531, Japan. E-mail: gamo@las.osakafu-u.ac.jp

⁴Current address: Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, USA.

⁵Current address: Graduate School of Molecular Biology, Nara Institute of Science and Technology, Nara, Japan.

Received 19 August 2005; Accepted 16 February 2006; Published online 26 April 2006.

Abstract

We studied the dynamics of hobo elements of Drosophila melanogaster in Japan with the goal of better understanding the invasion and evolution of transposons in natural populations. One hundred and twenty-six isofemale lines and 11 older stocks were tested for the presence and genetic phenotype of hobo elements. The oldest H strain, containing complete and deleted hobo elements, is Hikone-H (1957), but Hikone-R (1952) has no hobo-homologous sequences. The findings suggest that the hobo element invaded Japanese populations in the mid-1950s, at about the same time as the P element invasion in Japan. This chronology is consistent with the hypothesis of a recent worldwide hobo element invasion into D. melanogaster in the mid-1950s. In recently collected populations, H° strains (low hobo activity and high repression potency) are predominant, whereas H⁺ strains (high hobo activity and high repression potency) are predominant in the Sakishima Islands, the most southwestern islands of the Japanese archipelago. H' strains (high hobo activity and low repression potency) were first found in limited island populations. Japanese populations have not only full-size hobo elements and 1.5 kb Th elements but also characteristic deletion derivatives (1.6 and 1.8 kb XhoI fragments) that we have named Jh elements. These results are consistent with transgenic experiments with complete hobo elements, in which populations evolved to H⁺ or H° via H', and in which 1.8 kb fragments appeared. We conclude that hobo elements invaded the central region of Japan, spread to the far islands, and that the invasion is currently at an intermediate, nonequilibrium stage.