DOI: 10.5061/dryad.n5tb2rc78
title: Data from: Scaling of ovipositor size in Drosophila suzukii and D. subpulchrella: Altered genital-coupling mechanisms and evolution of allometric slopes

description: Animal genitalia typically exhibit limited size variation relative to
 overall body size, a pattern known as negative allometry. The
 “one-size-fits-all” hypothesis suggests that genital compatibility between
 sexes constrains the evolution of extreme genital sizes, yet direct
 evidence remains scarce. Drosophila suzukii presents a unique opportunity
 to test this hypothesis from the female perspective. This species has
 evolved an enlarged, sclerotized ovipositor capable of piercing intact
 fruit skins. However, this innovation necessitated an altered genital
 coupling mechanism, as the modified ovipositor—also functioning as part of
 the female genitalia—posed a mechanical obstacle to copulation. In
 contrast, D. subpulchrella, the closest relative of D. suzukii, retains
 the ancestral coupling mechanism, which depends on genital size
 compatibility between sexes. Allometric analyses revealed that D.
 subpulchrella ovipositors exhibit shallower scaling slopes than other body
 parts, consistent with the negative allometry rule. Conversely, D. suzukii
 ovipositors display significantly steeper slopes, suggesting that the new
 coupling mechanism has relaxed the constraint on genital size. These
 findings support the one-size-fits-all hypothesis from a novel perspective
 at an unprecedented resolution.
description: Sample collection
 Two pairs of sympatric populations of <em>D.
 suzukii</em> and <em>D. subpulchrella</em>, collected in
 Tokyo and Yamagata, Japan, were used to confirm the consistency across
 populations of different localities. For the Tokyo populations, the adults
 that emerged from wild berries (<em>Rubus hirsutus</em>,
 <em>R. palmatus</em>, <em>R. crataegifolius</em>,
 <em>R. microphyllus</em>, <em>Cerasus
 jamasakura</em>, <em>Morus australis</em>) were directly
 used for morphological measurements. Ripe fruits were collected from a
 mountainous area in Hachioji, Tokyo, once a week from May to June in 2024.
 They were individually maintained in glass vials at 20°C in the laboratory
 until adults emerged. For the Yamagata populations, laboratory-maintained
 strains were used for the measurements. These strains were originally
 established from multiple pairs that emerged from Chinese dogwood fruits
 (Cornus kousa) collected in Minorigaoka, Yamagata, in 2021. They have
 since been maintained on standard Drosophila medium consisting of
 cornmeal, glucose, and dry yeast at 20°C with a 12L:12D light
 cycle. Morphological
 measurements For each female, head width, thorax length,
 ovipositor length, and ovipositor width were measured. The head, thorax,
 and terminal segments of the abdomen were dissected from the rest of the
 body. Images of the head and the thorax were captured with a digital
 camera (FLEXACAM C1, Leica Microsystems, Wetzlar, Germany) mounted on a
 dissection microscope (MZ FL3, Leica Microsystems). The abdominal segments
 containing the ovipositor were immersed in 10% potassium hydrate overnight
 to clear the tissues before being mounted on slides with Hoyer’s mountant
 (Neo-Shigaral, Shiga Insect Company, Tokyo, Japan). The ovipositor
 consists of a pair of hypogynial valves. They were dissected apart so that
 both could be measured. Images were captured with a digital camera
 (FLEXACAM C1) mounted on a phase-contrast microscope (CK X31, Olympus,
 Tokyo, Japan). To obtain the trait length in pixel number, the obtained
 images were analysed using a custom MATLAB script that returns the
 dimensions of a rectangle drawn on the image. The same process was applied
 to the images of a micrometre to convert pixel values into real
 length.
description: # Data from: Scaling of ovipositor size in Drosophila suzukii and D.
 subpulchrella: Altered genital-coupling mechanisms and evolution of
 allometric slopes Dataset DOI:
 [10.5061/dryad.n5tb2rc78](10.5061/dryad.n5tb2rc78) ## Description of the
 data and file structure ### Files and variables #### File: Trait_size.xlsx
 **Description:** The values of measured traits and accompanied information
 for each individual used in the study. ##### Variables * Sample_ID: a
 unique number for all individuals used in the analysis. * Date of
 collection: the date of the host fruit was collected. * Date of
 dissection: the date of sample treatment performed on the emerged adults
 (dissection, mounting, and image acquisition). * Host: host name. *
 Population: locality of the samples collected. {Tokyo|Yamagata} * Species:
 species name of the corresponding individual. {suzukii|subpulchrella} *
 head-width: length in μm. * thorax-length: length in μm. * ovp1-length:
 length of a ovipositor in μm. * ovp1-width: width of the same ovipositor
 in μm. * ovp2-length: length of the ovipositor on the other side in μm. *
 ovp2-width: width of the ovipositor on the other side in μm. *
 px_head-width, px_thorax-length, px_ovp1-length, px_ovp1-width,
 px_ovp2-length, px_vp2-width: values in pixel number originally obtained
 by analysis of the digital images.