DOI: 10.5061/dryad.1ns1rn946
title: Asymmetric oviposition behaviour between Drosophila suzukii and D. subpulchrella suggests competition for the shared niche in their native range

description: Release from competitors is one of the mechanisms ascribed to the
 ecological success of invasive species outside their native range
 (competitive release hypothesis). However, studies describing the natural
 competitors of invasive species in their homeland are limited. Drosophila
 suzukii, the spotted-wing drosophila, is an invasive pest of small fruits
 expanding its range worldwide, whereas D. subpulchrella, the most closely
 related species to D. suzukii, remains endemic to the native range of D.
 suzukii. D. subpulchrella is inferior to D. suzukii in terms of the host
 usage capability, and it has not been considered as a major competitor of
 D. suzukii. This study examined the interaction between the two species in
 egg-laying behaviour. A field survey revealed that 11% of wild berries
 were co-infected by both species. In the laboratory
 experiments, D. suzukii avoided oviposition substrates that had
 already been oviposited by either conspecific or D. subpulchrella females,
 whereas D. subpulchrella did not show any preference/avoidance toward the
 substrates oviposited by either species. This asymmetric interaction
 indicates that D. subpulchrella may have a negative effect on the
 D. suzukii propagation as a niche-sharing competitor in their homeland,
 raising a possibility that the release from competition with D.
 subpulchrella helped the expansion of D. suzukii populations in invaded
 areas.
description: # Asymmetric oviposition behaviour between *Drosophila suzukii* and *D.
 subpulchrella* suggests competition for the shared niche in their native
 range
 [https://doi.org/10.5061/dryad.1ns1rn946](https://doi.org/10.5061/dryad.1ns1rn946) ## Description of the data and file structure Field survey Wild berries (*Rubus hirsutus, R. palmatus, R. crataegifolius, R. microphyllus, Cerasus jamasakura, Morus australis*) were collected in a mountainous area (450 ~ 650 m of elevation) in Hachioji, Tokyo once in a week from May to June in 2023. The field consists of two sites, separated from each other by 600 m in the horizontal distance and 200 m in the altitude. At each site, berries were collected from several patches, each selected to be at least 20 m distant from the other patches. At each patch, 10 fruits were collected. The fruits were individually transferred into glass vials within the day and maintained at 20°C until adults emerged. The species and sex of the emerged Drosophila flies were recorded. Oviposition assay An oviposition chamber consisted of a glass cup (24 mm diameter and 40 mm high) at the bottom of which was placed a disc of wet paper and two oviposition substrates (Fig. 1A). The substrates were made of 1% agar (Seakem® LE Agarose, Lonza, Basel, Switzerland) and 1% glucose (FUJIFILM Wako Pure Chemical Corp., Osaka, Japan) cast in a silicone mould for UV-resin craft to give a hemispherical shape (7.5 mm diameter, 100 µl in volume), which promote oviposition of Drosophila species including *D. suzukii* (Akutsu and Matsuo 2022; Akutsu and Matsuo 2023)  Females at the age of 9~13 days old were used for both pretreatment and two-choice assays. For pretreatment (conditioning of substrates), a female (conditioning female) was allowed to lay eggs on two newly prepared substrates for 18 h (from 2 h before the end of the light phase to 4 h after the end of the dark phase). Control substrates were prepared in the same way without females. Eggs laid on each substrate were counted and removed using fine forceps, which were cleaned with ethanol every time. A conditioned substrate and a control substrate were placed in a new chamber. To compensate for the effect of the holes left on the conditioned substrates, the same number of holes as the paired conditioned substrate were made on the control substrates using clean forceps. A new female (choosing female) was introduced into the chamber and allowed to lay eggs for 18 h (start and end times were the same as those in the pretreatment). The number of eggs on each substrate was counted. At least 20 replications were prepared for each combination of treatments to secure the enough statistical power. References Akutsu, J. & Matsuo, T. (2022) *Drosophila suzukii* preferentially lays eggs on spherical surfaces with a smaller radius. *Scientific Reports*, 12, 15792. [https://doi.org/10.1038/s41598-022-20022-z](https://doi.org/10.1038/s41598-022-20022-z)  Akutsu, J. & Matsuo, T.  (2023) Oviposition preference for spherical surfaces is shared among multiple Drosophila species except *D. melanogaster* (Diptera: Drosophilidae). *Entomological Science*, 26, e12560. [https://doi.org/10.1111/ens.12560](https://doi.org/10.1111/ens.12560) ### Files and variables #### File: Field\_survey.csv **Description:** Infection rate of wild berries by Drosophila fruit flies. ##### Variables * Date_of_collection: On which the wild berry fruits were collected. * Site_ID: Identity among two sites. * Patch_ID: Identity of collection patches. Note that Patch IDs are not consistent between different collection dates. * Host_species: Name of the wild berry. * Fruit_ID: Identity of fruits within each collection patch. * D.suzukii_male: Number of adults emerged from the focal fruit. * D.suzukii_female: Number of adults emerged from the focal fruit. * D.subpulchrella_male: Number of adults emerged from the focal fruit. * D.subpulchrella_female: Number of adults emerged from the focal fruit. * D.rufa_male: Number of adults emerged from the focal fruit. * D.rufa_female: Number of adults emerged from the focal fruit. * D.immigrans_male: Number of adults emerged from the focal fruit. * D.immigrans_female: Number of adults emerged from the focal fruit. #### File: Oviposition\_assay.csv **Description:** Results of the two choice assay using artificial substrates conditioned with other females. ##### Variables * Date: On which each experiment started. * Pretreatment_ID: Identity of the vial in the pretreatment step. Each pretreatment vial contained two substrates. * Conditioning_strain: Strain name of the conditioning female. * Conditioning_species: Species name of the conditioning female. suz: *D. suzukii*; sub: *D. subpulchrella*. * Eggs_pretreatment: Number of eggs laid by the conditioning female on the conditioned substrate, which was removed before the following two-choice assay. * Choice_assay_ID: Identity of the vial in the two-choice assay performed on the same day. * Choosing_strain: Strain name of the choosing female. * Choosing_species: Species name of the choosing female. * Eggs_on_conditioned: Number of eggs laid by the choosing female on the conditioned substrate. * Eggs_on_control: Number of eggs laid by the choosing female on the control substrate.