DOI: 10.5061/dryad.zgmsbccmj
title: Inter-population variation in fin sexual dimorphism in medaka (Oryzias latipes)

description: Multiple factors can influence the strength of sexual selection in
 populations; variation in these factors can result directly or indirectly
 from environmental factors, including climatic ones, and this variation
 can, in turn, result in among-population variation in the strength of
 sexual selection. Populations with intense sexual selection can have
 greater divergence between the sexes for sexually selected traits, but
 this is less likely for traits that are not under sexual selection. In
 this study, taking advantage of a cline in conditions that could impact
 the strength of sexual selection, we asked which environmental factors
 best predicted among-population variation in the degree of sexual
 dimorphism in sexually selected traits. We predicted that populations with
 environmental factors that extend the length of the breeding season would
 have increased sexual dimorphism in those traits; this is because, as the
 breeding season gets longer, the receptivity of the sexes can become
 asynchronous and bias the operational sex ratio and, in turn, alter the
 strength of sexual selection. We did not expect the degree of dimorphism
 in non-sexually selected traits to be affected in this way. For this
 study, we asked if factors, including breeding season length, monthly
 temperature, and latitude, have impacted several morphological traits in
 Oryzias latipes (medaka) from wild populations in Japan. We selected anal
 fin and dorsal fin lengths as our sexually selected traits, as males use
 these fins to clasp females during mating. As predicted, in conditions
 expected to affect the intensity of SS, anal fins lengths were most
 sexually dimorphic when sampled from a tropical population where the
 length of the breeding season was longest. However, when this population
 was excluded, the degree of anal fin dimorphism did not vary significantly
 across the semi-tropical and temperate sites. Other traits, related to
 swimming performance, were not significantly dimorphic.
description: **Data files required to reproduce Downer-Bartholomew and Rodd (2025):
 Inter-population variation in fin sexual dimorphism in medaka (*Oryzias
 latipes*).** This file contains the data needed to reproduce the
 statistical analyses presented in Downer-Bartholomew and Rodd (2025). Each
 column contains a different variable, see the list below for details on
 each. Each row contains the values and details for a given specimen (N =
 284). **File name: DownerBartholomew and Rodd 2025_Specimen Data.csv**
 Column name: Description Specimen: Unique specimen number. Provided by
 Kanagawa Prefecture Natural History Museum (KPMNH). Subpopulation:
 Subpopulation the specimen belongs to. Provided by KPMNH. District:
 District-prefecture that the specimen was collected from. Provided by
 KPMNH. City: City that the specimen was collected from. Provided by KPMNH.
 Town: Town that the specimen was collected from. Provided by KPMNH.
 WaterBody: Water body/river that the specimen was collected from. Provided
 by KPMNH. Blank entries were sites where no local water body/river was
 listed by KPMNH. Habitat: Habitat type that the specimen was collected
 from. This was determined based on the other sampling location details
 provided by KPMNH. Specimens where there was not enough detail to estimate
 habitat type are listed as having none under this column. LocalityName:
 Name of the location where the specimens were collected from. Lat:
 Latitude of sampling location. Long: Longitude of sampling location.
 Yearly_TMN_30: Mean monthly minimum temperature (°C) from a 30-year period
 (1989-2019) for a given site. Yearly_TMP_30: Mean monthly mean temperature
 (°C) from a 30-year period (1989-2019) for a given site. Yearly_TMX_30:
 Mean monthly maximum temperature (°C) from a 30-year period (1989-2019)
 for a given site. Yearly_PRE_30: Mean monthly precipitation from a 30-year
 period (1989-2019) for a given site. Months_TMX30: Number of months in the
 specimen’s collection year that exceeded a maximum monthly temperature of
 30 °C. BS_Start: Estimated starting month of the breeding season for the
 site that the specimen was sampled from. BS_End: Estimated ending month of
 the breeding season for the site that the specimen was sampled from.
 BS_Length: Our estimated length of the breeding season in number of
 months. We obtained this estimate based on estimated start and end month
 of the breeding season. See main text (Downer-Bartholomew and Rodd 2025)
 for how this was determined. Coll_Month: Numeric month of the year (Jan.
 =1, Dec. =12) that the specimen was collected in, provided by KPMNH.
 Entires of NA occur when that specimen was not provided with a collection
 month. Coll_Year: Year in which the specimen was collected, provided by
 KPMNH. Entires of NA occur when that specimen was not provided with a
 collection year. Sex: Sex of the specimen. SL_1, SL_2, SL_3: These are
 three different columns that contain standard length (mm) measures. AFL_1,
 AFL_2, AFL_3: These are three different columns that contain anal fin
 length (mm). DFL_1, DFL_2, DFL_3: These are three different columns that
 contain dorsal fin length (mm). Mean_SL: The mean standard length (mm) of
 a specimen. Mean was calculated using SL_1, SL_2 and SL_3. Mean_AFL: The
 mean anal fin length (mm) of a specimen. Mean was calculated using AFL_1,
 AFL_2 and AFL_3. Mean_DFL: The mean dorsal fin length (mm) of a specimen.
 Mean was calculated using DFL_1, DFL_2 and DFL_3. lnSL: Natural log of
 standard length. lnAFL: Natural log of anal fin length. lnDFL: Natural log
 of dorsal fin length. BD: Body depth (mm). CH: Caudal fin height (mm). PL:
 Pectoral fin length (mm). CA: Caudal fin area (mm2). PA: Pectoral fin area
 (mm2). sqrCA: Square root of caudal fin area. sqrPA: Square root of
 pectoral fin area. LNsqrCA: Natural log of the square root of caudal fin
 area. LNsqrPA: Natural log of the square root of pectoral fin area. CAR:
 Caudal fin aspect ratio. FR: Fineness ratio. PAR: Pectoral fin aspect
 ratio. lnBD: Natural log of body depth. lnCA: Natural log of caudal fin
 area. lnPA: Natural log of pectoral fin area. lnCAR: Natural log of caudal
 fin aspect ratio. lnPAR: Natural log of pectoral fin aspect ratio. lnFR:
 Natural log of the fineness ratio. Group: Indicates what group
 (major/minor) that the given specimen was classified as. See main text of
 Downer-Bartholomew and Rodd (2025) for details on these two groups.
 PC1_morph: PC scores from axis 1 of our morphology PCA. PC2_morph: PC
 scores from axis 2 of our morphology PCA. PC3_morph: PC scores from axis 3
 of our morphology PCA. PC4_morph: PC scores from axis 4 of our morphology
 PCA. PC5_morph: PC scores from axis 5 of our morphology PCA. PC6_morph: PC
 scores from axis 6 of our morphology PCA. Env_PC1: PC scores from axis 1
 of our environmental PCA. Env_PC2: PC scores from axis 2 of our
 environmental PCA. Env_PC3: PC scores from axis 3 of our environmental
 PCA. Env_PC4: PC scores from axis 4 of our environmental PCA. Env_PC5: PC
 scores from axis 5 of our environmental PCA. Env_PC6: PC scores from axis
 6 of our environmental PCA. Env_PC7: PC scores from axis 7 of our
 environmental PCA. Env_PC8: PC scores from axis 8 of our environmental
 PCA. **File name: DownerBartholomew and Rodd 2025_Environmental PCA.csv**
 This file contains the data that we used for our environmental PCA. The
 columns contain the environmental factors included in this analysis, and
 the name of each locality. Each row represents a sampling
 location/locality (N =34 localities). Column name: Description Lat:
 Latitude of site Long: Longitude of site TMN30: Mean monthly minimum
 temperature from a 30-year period (1989-2019) for a given site. TMP30:
 Mean monthly mean temperature from a 30-year period (1989-2019) for a
 given site. TMX30: Mean monthly maximum temperature from a 30-year period
 (1989-2019) for a given site. PRE30: Mean monthly precipitation from a
 30-year period (1989-2019) for a given site. MONTH30: Number of months in
 a year where the maximum temperature exceeded 30 °C. BSL: Estimate of
 breeding season length at a given site. Breeding season begins in the
 spring when the maximum temperature exceeds a critical threshold and ends
 in the autumn when there were fewer than 13 hours of light per day. See
 main text (Downer-Bartholomew and Rodd 2025) for how this was determined.
 LocName: Name of the locality. GSI_Group: Name of the medaka population
 from Shinomiya et al. (2023) that this sampling location was closest to.
 We used this to determine the photoperiods and temperatures needed to
 trigger the start of the breeding season. **File name: DownerBartholomew
 and Rodd 2025_Morphological PCA.csv** This file contains the data that we
 used for our morphological PCA. The columns contain the natural log of a
 given trait (N = 9 traits) included in this analysis, the sex of the
 specimen and what group (major/minor) that the specimen is in. Each row
 represents a specimen (N = 284 specimens). Column name: Description lnBD:
 Natural log of body bepth. LNsqrCA: Natural log of the square root of
 caudal fin area. LNsqrPA: Natural log of the square root of pectoral fin
 area. lnCAR: Natural log of caudal fin aspect ratio. lnPAR: Natural log of
 pectoral fin aspect ratio. lnFR: Natural log of the fineness ratio. lnSL:
 Natural log of standard length. lnAFL: Natural log of anal fin length.
 lnDFL: Natural log of dorsal fin length. Sex: Sex of the specimen. Group:
 What grouping the specimen belongs to (major/minor). See main text
 (Downer-Bartholomew and Rodd 2025) for how specimens were assigned to
 these groups.