Inter-population variation in fin sexual dimorphism in medaka (Oryzias latipes)
Data files
Jun 27, 2025 version files 236.29 KB
Abstract
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.
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.