DOI: 10.5061/dryad.c866t1ghd
title: Natural selection, rather than sexual selection, plays a dominant role in the formation of body coloration in Drosophila suzukii

description: Drosophila suzukii, a widely distributed pest globally, causes significant
 economic losses to the fruit industry. The body color of D. suzukii
 exhibits plasticity, with the color changing according to the season: it
 is lighter in summer and darker in winter. Currently, research on the body
 color of D. suzukii mainly focuses on its functional aspects. However, a
 notable deficiency exists in current understanding of how plastic body
 color traits in D. suzukii are formed, highlighting a significant area for
 future research. Given the important roles of natural and sexual selection
 in the formation of insect traits, we deduced that both natural and sexual
 selection play key roles in the development of body coloration in D.
 suzukii. In order to test this hypothesis, we measured the dorsal
 abdominal melanization rate, chill coma duration, and mating success rate
 in D. suzukii and we also calculated the contributions of natural
 selection and sexual selection to the formation of plastic body color
 traits. Our results showed that the melanization rate of D. suzukii
 developed under 15°C temperature conditions is significantly higher than
 that of individuals developed under 25°C temperature conditions; the chill
 coma recovery duration of D. suzukii developed under 15°C temperature
 conditions is significantly shorter than that of individuals developed
 under 25°C temperature conditions; Natural selection and sexual selection
 accounted for 89.02% and 10.92% of the total selection differential,
 respectively. Thus, natural selection, rather than sexual selection, plays
 a dominant role in the formation of body coloration in D. suzukii. Our
 study is the first to quantitatively elucidate the relative contributions
 of natural and sexual selection to the formation of the plastic body color
 phenotype in D. suzukii. Future research could further investigate how
 natural selection influences the allele frequencies of body color-related
 genes in D. suzukii.
description: <strong>Fly stocks</strong> Adult
 <em>D. suzukii</em> were collected from a Hui Wang blueberry
 orchard in Nanling, Anhui Province, China, in 2022 (30.92°N, 118.34°E).
 And all <em>D. suzukii </em>used in this study were collected
 from the wild and used in experiments within five generations. Under
 laboratory conditions, adults <em>D. suzukii</em> were
 independently reared in nylon cube cages (35×35×35 cm) at artificial
 climate chambers with 65% humidity. Three different temperature and
 photoperiod conditions were used as the experimental subjects: (1) 15°C
 with L:D =10h:14h, (2) 20°C with L:D (Light: Dark) =12h:12h, (3) 25°C with
 L:D =14h:10h. <em>D. suzukii</em> were fed a 240-mL plastic
 cup containing 80 mL of solid food (water: 1000.00 mL, corn flour: 44.67
 g, sucrose: 71.33 g, agar: 16.00 g, yeast: 25.00 g, propionic acid: 6.30
 mL, 100% ethanol: 22.30 mL) (Gonzalez-Cabrera et al. 2018), which was
 changed daily. <strong>Dorsal abdominal
 melanization measurement</strong> Thirty
 3-day-old male and Thirty 3-day-old female <em>D. suzukii</em>
 were collected from each of the three temperature and photoperiod rearing
 artificial climate chambers. The dorsal side of the abdomen of
 <em>D. suzukii</em> was photographed under a microscope
 (VHX-5000, Osaka Japan, Keyence Corporation) at 30x magnification, then,
 all images were converted to grayscale using ImageJ (version 1.54g)
 software, where each pixel is represented by 8 bits, indicating a
 grayscale level from 0 to 255. We used the “Subtract Background” function
 to adjust the images and invert the brightness and darkness. At last, we
 set the threshold at 97 to mark the melanization area of the abdomen, so
 that the software could automatically calculate the abdominal melanization
 rate. All <em>D. suzuki</em>i were collected and subsequently
 reared in artificial climate chambers after the melanization rate
 measurement to prepare for the chill coma recovery experiment.
 <strong>Chill coma recovery
 experiment</strong> 4-day-old male and female
 <em>D. suzukii</em> adults were collected from each of the
 three temperature and photoperiod rearing chambers, with each individual
 placed separately in a 1.5 mL EP tube. And then, the EP tubes were placed
 in the - 20°C freezer (BCD-310, Qingdao China, Haier Corporation)
 compartment for 15 min and 30 sec (a duration that ensures cold-induced
 immobilization without causing death). Afterward, the EP tubes were
 quickly removed from the freezer and placed at room temperature, and the
 time from immobilization to standing was recorded for each <em>D.
 suzukii</em>. One hundred male and female <em>D.
 suzukii</em> from each of the three temperature and photoperiod
 rearing conditions were used in this experiment. Data from <em>D.
 suzukii </em>that did not recover from chill coma in this experiment
 will not be included in the analysis. All surviving <em>D.
 suzukii</em> were collected and reared in artificial climate
 chambers for 24 hr to prepare for the mate choice preference
 experiment. <strong><em>D.
 suzukii</em> mate choice preference
 experiment</strong> 6-day-old male and female
 <em>D. suzukii</em> adults were collected from each of the
 three temperature and photoperiod rearing chambers, with each individual
 placed separately in a 1.5 mL EP tube. We used non-choice experiments to
 test the mating preference of female <em>D. suzukii</em> for
 male <em>D. suzukii</em>. The non-choice experimental groups
 are as follows: (1) Randomly select 3 females reared at 15°C, pairing each
 with a male reared at 15°C, 20°C, or 25°C, respectively; (2) Randomly
 select 3 females reared at 20°C, pairing each with a male reared at 15°C,
 20°C, or 25°C, respectively; (3) Randomly select 3 females reared at 25°C,
 pairing each with a male reared at 15°C, 20°C, or 25°C, respectively. Each
 pair is placed in a separate culture dish (35×10 mm). For each of the
 above three groups, 10 replicates were performed. As the morning is the
 peak mating period for <em>D. suzukii</em> (Revadi et al.
 2015), the sexual selection experiments were conducted from 7:00 AM to
 11:00 AM, during which the mate choice behavior of females was recorded
 over a 50-minute period. <strong>Statistical
 analyses</strong> The Kolmogorov-Smirnov test was
 used to assess the normality of the obtained melanization rates and chill
 coma recovery data. Subsequently, a one-way analysis of variance (ANOVA)
 was performed. To evaluate natural and sexual selection on the character
 of abdominal melanization rates, we employed the method proposed by Arnold
 and Wade (1984) (Arnold and Wade 1984). According to the theory of
 measuring natural and sexual selection, assessing selection on phenotypic
 characters does not require knowledge of their genetic background. The
 statistical relationship between fitness and phenotypic characters can be
 deduced from the change that occur within a generation in the mean,
 variances, and covariances of phenotypic traits (Arnold and Wade 1984). In
 this research, we view sexual selection as selection arising from variance
 in copulation success and natural selection as selection arising from
 variance in cold tolerance. Since natural selection and sexual selection
 act on different life stages of D. suzukii, so that whole selection
 procedure can be divided into two selection episodes. We regarded cold
 tolerance as the first selection force and copulation success as the
 second, because if D. suzukii is unable to survive cold environments, it
 would result in the loss of copulating opportunities.
 The parameters and formulas used in this study are as follows
 (Table1, Table3): (1) p, initial frequency distribution
 of the phenotypes, changes as a result of each episode: from p to p1, p1=
 pw1 after the first episode, to p2=p1w2 after the second episode and so
 forth; (2) , the mean of phenotypic character before
 selection;  is a column vector representing the change in the mean of each
 phenotypic character from one generation to the next generation;
 (3) S, selection differential, covariance between relative
 fitness and character, S = m-, m is the mean after m episodes of
 selection; (4) Wk, the absolute fitness at episode k of
 selection; (5) k , the average absolute fitness at the
 kth epiaode, k = pk-1Wk; (6) wk, the relative fitness
 at episode k of selection, wk = Wk/k; (7) , univariate
 selection gradient, partial regression of relative fitness on
 character; (8) P, the phenotypic variance-covariance
 matrix assessed before selection, P = S/; (9) , the
 standardized selection differential (intensity of selection),  =
 S/P1/2
description: # Natural selection, rather than sexual selection, plays a dominant role
 in the formation of body coloration in *Drosophila suzukii*
 [https://doi.org/10.5061/dryad.c866t1ghd](https://doi.org/10.5061/dryad.c866t1ghd) ## Description of the data and file structure The dataset consists of a data.xlsx, which consists of dorsal abdominal melanization rate and chill coma recovery duration of *D. suzukii.* ### Files and variables #### File: data.xlsx **Description:** The data on the abdominal dorsal melanization rate and the recovery duration of chill coma in *Drosophila suzukii* under three different temperature rearing conditions. ##### The data file consists of the following sheets: * Abdominal dorsal melanization rate: The table presents dorsal abdominal melanization values across three temperature treatments (15°C, 20°C, and 25°C) for both males and females. The values likely represent mean melanization scores or proportions for individual samples or replicates under each condition. * Chill coma recovery duration in seconds: This table presents the duration it took for individuals to recover from chill coma across three temperature treatments (15°C, 20°C, 25°C) and two sexes (male and female). Each value represents the recovery time for a single subject or replicate. ## Code/software Use Microsoft Office software to open the data spreadsheet.