DOI: 10.5061/dryad.ht76hdrn1
title: Latitudinal patterns in a reproductive trait driven by sexual selection

description: Many organisms with broad distributions show latitudinal variations in
 morphological phenotypes and life history traits, such as body size and
 phenology, in relation to environmental changes such as temperature along
 latitude. Such variations have usually been considered the result of
 natural selection, but sexual selection may also lead to these latitudinal
 patterns. Although a recent study has shown the latitudinal pattern in the
 strength of male‒male competition in medaka fish, such a latitudinal
 pattern related to sexual selection is rarely known in other organisms.
 Here, we show the latitudinal pattern of a reproductive trait driven by
 sexual selection in the Japanese black salamander (Hynobius nigrescens),
 where snout-vent length (SVL) in males predicts the outcome of male‒male
 competition over egg sacs. First, we conducted phylogenetic analyses to
 examine the phylogenetic pattern along latitude. From the constructed
 phylogenetic tree, this species was split into five lineages that were
 roughly divided along latitude. We also used field surveys to examine
 whether the operational sex ratio (OSR: an index of the strength of
 male‒male competition) varies across lineages with latitude. We found that
 the OSR was more biased toward males in a lineage distributed at lower
 latitudes due to its longer breeding period. We measured the SVLs of
 collected samples to determine if the latitudinal pattern also exists for
 SVL. Indeed, male SVLs were longer in lineages distributed at lower
 latitudes, whereas those in females did not differ among lineages. Our
 common garden experiment also showed that the individuals from a lineage
 distributed at lower latitudes had longer SVLs even when they grew under
 the same environmental conditions, suggesting that the latitudinal pattern
 in SVL is genetically determined. These results suggest that males at
 lower latitudes have evolved longer SVLs, driven by stronger male‒male
 competition. Our study provides the first example, to the best of our
 knowledge, of a latitudinal pattern driven by sexual selection and its
 evolutionary determinant in detail in the wild.
description: # Latitudinal patterns in a reproductive trait driven by sexual selection
 #### **Description of the data and file structure** Sample
 information.xlsx: Sheet 1 contains the details of all samples used in this
 study. Collection site numbers and collection site names are the same as
 those in “morphological analysis data.xlsx” and “Phylogenetic analysis
 data.xlsx”. Experiment numbers are the same as those in the text. In the
 column named "Egg acquisition", "1" indicates a
 winning male, and "0" indicates a background male. Experimental
 data for latitudinal patterns of SVLs in larvae and juveniles are
 indicated as Experiment S10 (corresponding to Appendix S1: Fig. S10).
 Sheet 2 contains the details of the data in the experiment for “breeding
 period of male individuals” and “overall breeding period of females” in
 Experiment 2-1. Sheet 3 contains the details of the data in the experiment
 for the operational sex ratio in Experiment 2-2. The operational sex ratio
 was calculated as the number of female individuals per day/the number of
 male individuals participating in breeding (= total number of pairs of egg
 sacs × proportion of sexually receptive male individuals). The latitude
 and longitude of the sampling sites are not shown here to discourage
 overhunting and habitat disturbance. Morphological analysis data.xlsx:
 Information on sampling sites and the numbers of adult males, adult
 females, larvae and juveniles of H. nigrescens used in morphological
 analysis. Phylogenetic analysis data.xlsx: Information on sampling sites
 and the number of individuals in each lineage split by phylogenetic
 analysis in H. nigrescens. \#Experiment 2-1_Breeding periods of male
 individuals Relative_breeding_period.csv: In Experiment 2-1, this data was
 used for statistical analysis. Please refer to
 "Experiment2-1_Script.txt". Experiment2-1_Script.txt: Scripts
 for statistical analysis in Experiment 2-1. We used the relative breeding
 period of the male as the response variable, and the lineage as the
 explanatory variable. RBP_Central-eastern_vs_Central-western.csv: Data
 used for the post-hoc test in Experiment 2-1 to compare the relative
 breeding periods between central-eastern lineage and central-western
 lineage. Please refer to "Experiment 2-1_Script.txt"
 RBP_Central-eastern_vs_Southern.csv: Data used for the post-hoc test in
 Experiment 2-1 to compare the relative breeding periods between
 central-eastern lineage and southern lineage. Please refer to
 "Experiment 2-1_Script.txt" RBP_Central-western_vs_Southern.csv:
 Data used for the post-hoc test in Experiment 2-1 to compare the relative
 breeding periods between central-western lineage and southern lineage.
 Please refer to "Experiment 2-1_Script.txt"
 RBP_Northern_vs_Central-eastern.csv: Data used for the post-hoc test in
 Experiment 2-1 to compare the relative breeding periods between northern
 lineage and central-eastern lineage. Please refer to "Experiment
 2-1_Script.txt" RBP_Northern_vs_Central-western.csv: Data used for
 the post-hoc test in Experiment 2-1 to compare the relative breeding
 periods between northern lineage and central-western lineage. Please refer
 to "Experiment 2-1_Script.txt" RBP_Northern_vs_Southern.csv:
 Data used for the post-hoc test in Experiment 2-1 to compare the relative
 breeding periods between northern lineage and southern lineage. Please
 refer to "Experiment 2-1_Script.txt". \#Experiment
 2-2_Operational sex ratio in the wild OSR.csv: In Experiment 2-2, this
 data was used for statistical analysis. Please refer to "Experiment
 2-2_Script.txt". OSR_Central-eastern_vs_Central-western.csv: Data
 used for the post-hoc test in Experiment 2-2 to compare the operational
 sex ratio between Central-eastern lineage and Central-western lineage.
 Please refer to "Experiment 2-2_Script.txt".
 OSR_Central-eastern_vs_Southern.csv: Data used for the post-hoc test in
 Experiment 2-2 to compare the operational sex ratio between
 central-eastern lineage and southern lineage. Please refer to
 "Experiment 2-2_Script.txt".
 OSR_Central-western_vs_Southern.csv: Data used for the post-hoc test in
 Experiment 2-2 to compare the operational sex ratio between
 central-western lineage and southern lineage. Please refer to
 "Experiment 2-2_Script.txt".
 OSR_Northern_vs_Central-eastern.csv: Data used for the post-hoc test in
 Experiment 2-2 to compare the operational sex ratio between northern
 lineage and central-eastern lineage. Please refer to "Experiment
 2-2_Script.txt". OSR_Northern_vs_Central-western.csv: Data used for
 the post-hoc test in Experiment 2-2 to compare the operational sex ratio
 between northern lineage and central-western lineage. Please refer to
 "Experiment 2-2_Script.txt". OSR_Northern_vs_Southern.csv: Data
 used for the post-hoc test in Experiment 2-2 to compare the operational
 sex ratio between northern lineage and southern lineage. Please refer to
 "Experiment 2-2_Script.txt". Experiment 2-2_Script.txt: Scripts
 for statistical analysis in Experiment 2-2. We used the OSR as the
 response variable and the lineage as the explanatory variable.
 \#Experiment 3 \_Morphology of males that obtained egg sacs
 Egg_acquisition.csv: In Experiment 3, this data was used for statistical
 analysis and for drawing the figure. Please refer to "Experiment
 3_SVL_relative_to_TOL_Script.txt", "Experiment
 3_TOL_Script.txt" and "Experiment 3_Figure_Script.txt".
 Experiment 3_SVL_relative_to_TOL_Script.txt: Scripts for statistical
 analysis in Experiment 3. We used egg acquisition as the response
 variable, and SVL relative to TOL (SVL/TOL) as explanatory variable.
 Experiment 3_TOL_Script.txt: Scripts for statistical analysis in
 Experiment 3. We used egg acquisition as the response variable, and TOL as
 explanatory variable. Experiment 3_Figure_Script.txt: Scripts for the
 drawing of the figure in Experiment 3. Egg_acquisition_Nishimeya.csv: Data
 of egg acquisition in site 7 (northern lineage). In Experiment 3, this
 data was used to plot the data of site 7. Please refer to "Experiment
 3_Figure_Script". Egg_acquisition_Tokamachi.csv: Data of egg
 acquisition in site 66 (central-western lineage). In Experiment 3, this
 data was used to plot the data of site 66. Please refer to
 "Experiment 3_Figure_Script". \#Experiment 4_Plasticity of the
 latitudinal pattern in snout-vent length in common garden experiment
 Rearing.csv: In Experiment 4, this data was used for statistical analysis
 and for the drawing of the figure. Please refer to "Experiment
 4_Script.txt:" and "Experiment 4_Figure_Script.txt".
 Experiment 4_Script.txt: Scripts for statistical analysis in Experiment 4.
 We used SVL as the response variable and TOL, the lineage, the interaction
 between TOL and lineage and rearing temperature (15°C or 20°C) as
 explanatory variables. Rearing_Northern.csv: Data of northern lineage in
 Experiment 4. This data was used for the drawing of the figure. Please
 refer to "Experiment 4_Figure_Script.txt". Rearing_Southern.csv:
 Data of southern lineage in Experiment 4. This data was used for the
 drawing of the figure. Please refer to "Experiment
 4_Figure_Script.txt". Rearing_Northern15.csv: Data of northern
 lineage reared at 15°C in Experiment 4. This data was used for the drawing
 of the figure. Please refer to "Experiment 4_Figure_Script.txt".
 Rearing_Northern20.csv: Data of northern lineage reared at 20°C in
 Experiment 4. This data was used for the drawing of the figure. Please
 refer to "Experiment 4_Figure_Script.txt".
 Rearing_Southern15.csv: Data of southern lineage reared at 15°C in
 Experiment 4. This data was used for the drawing of the figure. Please
 refer to "Experiment 4_Figure_Script.txt".
 Rearing_Southern20.csv: Data of southern lineage reared at 20°C in
 Experiment 4. This data was used for the drawing of the figure. Please
 refer to "Experiment 4_Figure_Script.txt". Experiment
 4_Figure_Script.txt: Scripts for the drawing of the figure in Experiment
 4. \#Experiment 5_Latitudinal pattern of snout-vent length in adult
 females in the wild Female.csv: In Experiment 5, this data was used for
 statistical analysis and for the drawing of the figure in female. Please
 refer to "Experiment 5_Female_Script.txt" and "Experiment
 5_Female_Figure_Script.txt".
 Fe_Central-eastern_vs_Central-western.csv: Data used for the post-hoc test
 of female in Experiment 5 to compare the SVLs of females between
 central-eastern lineage and central-western lineage. Please refer to
 "Experiment 5_Female_Script.txt".
 Fe_Central-eastern_vs_Southern.csv: Data used for the post-hoc test of
 female in Experiment 5 to compare the SVLs of females between
 central-eastern lineage and southern lineage. Please refer to
 "Experiment 5_Female_Script.txt".
 Fe_Central-western_vs_Southern.csv: Data used for the post-hoc test of
 female in Experiment 5 to compare the SVLs of females between
 central-western lineage and southern lineage. Please refer to
 "Experiment 5_Female_Script.txt"
 Fe_Northern_vs_Central-eastern.csv: Data used for the post-hoc test of
 female in Experiment 5 to compare the SVLs of females between northern
 lineage and central-eastern lineage. Please refer to "Experiment
 5_Female_Script.txt" Fe_Northern_vs_Central-western.csv: Data used
 for the post-hoc test of female in Experiment 5 to compare the SVLs of
 females between northern lineage and central-western lineage. Please refer
 to "Experiment 5_Female_Script.txt" Fe_Northern_vs_Southern.csv:
 Data used for the post-hoc test of female in Experiment 5 to compare the
 SVLs of females between northern lineage and southern lineage. Please
 refer to "Experiment 5_Female_Script.txt" Experiment
 5_Female_Script.txt: Scripts for statistical analysis of female in
 Experiment 5. We used SVL as the response variable and TOL, the lineage,
 and the interaction between TOL and lineage as explanatory variables.
 Fe_Northern.csv: Data of female in northern lineage in Experiment 5. This
 data was used for the drawing of the figure. Please refer to
 "Experiment 5_Female_Figure_Script.txt". Fe_Central-eastern.csv:
 Data of female in central-eastern lineage in Experiment 5. This data was
 used for the drawing of the figure. Please refer to "Experiment
 5_Female_Figure_Script.txt". Fe_Central-western.csv: Data of female
 in central-western lineage in Experiment 5. This data was used for the
 drawing of the figure. Please refer to "Experiment
 5_Female_Figure_Script.txt". Fe_Southern.csv: Data of female in
 southern lineage in Experiment 5. This data was used for the drawing of
 the figure. Please refer to "Experiment
 5_Female_Figure_Script.txt". Experiment 5_Female_Figure_Script.txt:
 Scripts for the drawing of the figure of female in Experiment 5.
 \#Experiment 5_Latitudinal pattern of snout-vent length in adult males in
 the wild Male.csv: In Experiment 5, this data was used for statistical
 analysis and for the drawing of the figure in male. Please refer to
 "Experiment 5_Male_Script.txt" and "Experiment
 5_Male_Figure_Script.txt". Ma_Central-eastern_vs_Central-western.csv:
 Data used for the post-hoc test of male in Experiment 5 to compare the
 SVLs of males between central-eastern lineage and central-western lineage.
 Please refer to "Experiment 5_Male_Script.txt".
 Ma_Central-eastern_vs_Southern.csv: Data used for the post-hoc test of
 male in Experiment 5 to compare the SVLs of males between central-eastern
 lineage and southern lineage. Please refer to "Experiment
 5_Male_Script.txt". Ma_Central-western_vs_Southern.csv: Data used for
 the post-hoc test of male in Experiment 5 to compare the SVLs of males
 between central-western lineage and southern lineage. Please refer to
 "Experiment 5_Male_Script.txt".
 Ma_Northern_vs_Central-eastern.csv: Data used for the post-hoc test of
 male in Experiment 5 to compare the SVLs of males between northern lineage
 and central-eastern lineage. Please refer to "Experiment
 5_Male_Script.txt". Ma_Northern_vs_Central-western.csv: Data used for
 the post-hoc test of male in Experiment 5 to compare the SVLs of males
 between northern lineage and central-western lineage. Please refer to
 "Experiment 5_Male_Script.txt". Ma_Northern_vs_Southern.csv:
 Data used for the post-hoc test of male in Experiment 5 to compare the
 SVLs of males between northern lineage and southern lineage. Please refer
 to "Experiment 5_Male_Script.txt". Experiment 5_Male_Script.txt:
 Scripts for statistical analysis of male in Experiment 5. We used SVL as
 the response variable and TOL, the lineage, and the interaction between
 TOL and lineage as explanatory variables. Ma_Northern.csv: Data of male in
 northern lineage in Experiment 5. This data was used for the drawing of
 the figure. Please refer to "Experiment
 5_Male_Figure_Script.txt". Ma_Central-eastern.csv: Data of male in
 central-eastern lineage in Experiment 5. This data was used for the
 drawing of the figure. Please refer to "Experiment
 5_Male_Figure_Script.txt". Ma_Central-western.csv: Data of male in
 central-western lineage in Experiment 5. This data was used for the
 drawing of the figure. Please refer to "Experiment
 5_Male_Figure_Script.txt". Ma_Southern.csv: Data of male in southern
 lineage in Experiment 5. This data was used for the drawing of the figure.
 Please refer to "Experiment 5_Male_Figure_Script.txt".
 Experiment 5_Male_Figure_Script.txt: Scripts for the drawing of the figure
 of male in Experiment 5. \#Experiment 5_Latitudinal pattern of sexual
 dimorphism in adults in the wild Sexual_dimorphism_Northern.csv: This data
 was used for statistical analysis and for drawing of the figure to examine
 the difference between sexes in northern lineage. Please refer to
 "Sexual dimprphism_Script.txt" and "Sexual
 dimorphism_Figure_Script.txt". Sexual_dimorphism_Central-eastern.csv:
 This data was used for statistical analysis and for drawing of the figure
 to examine the difference between sexes in central-eastern lineage. Please
 refer to "Sexual dimprphism_Script.txt" and "Sexual
 dimorphism_Figure_Script.txt". Sexual_dimorphism_Central-western.csv:
 This data was used for statistical analysis and for drawing of the figure
 to examine the difference between sexes in central-western lineage. Please
 refer to "Sexual dimprphism_Script.txt" and "Sexual
 dimorphism_Figure_Script.txt". Sexual_dimorphism_Southern.csv: This
 data was used for statistical analysis and for drawing of the figure to
 examine the difference between sexes in southern lineage. Please refer to
 "Sexual dimprphism_Script.txt" and "Sexual
 dimorphism_Figure_Script.txt". Experiment
 5_Sexual_dimorphism_Script.txt: Scripts for statistical analysis to
 examine the difference between sexes in each lineage. We used SVL as the
 response variable and TOL, sex, and the interaction between TOL and sex as
 explanatory variables. Fe_Sexual_dimorphism_Northern.csv: Data of female
 to draw a figure of sexual dimorphism in northern lineage. Please refer to
 "Sexual dimorphism_Figure_Script.txt".
 Ma_Sexual_dimorphism_Northern.csv: Data of male to draw a figure of sexual
 dimorphism in northern lineage. Please refer to "Sexual
 dimorphism_Figure_Script.txt".
 Fe_Sexual_dimorphism_Central-eastern.csv: Data of female to draw a figure
 of sexual dimorphism in central-eastern lineage. Please refer to
 "Sexual dimorphism_Figure_Script.txt".
 Ma_Sexual_dimorphism_Central-eastern.csv: Data of male to draw a figure of
 sexual dimorphism in central-eastern lineage. Please refer to "Sexual
 dimorphism_Figure_Script.txt".
 Fe_Sexual_dimorphism_Central-western.csv: Data of female to draw a figure
 of sexual dimorphism in central-western lineage. Please refer to
 "Sexual dimorphism_Figure_Script.txt".
 Ma_Sexual_dimorphism_Central-western.csv: Data of male to draw a figure of
 sexual dimorphism in central-western lineage. Please refer to "Sexual
 dimorphism_Figure_Script.txt". Fe_Sexual_dimorphism_Southern.csv:
 Data of female to draw a figure of sexual dimorphism in southern lineage.
 Please refer to "Sexual dimorphism_Figure_Script.txt".
 Ma_Sexual_dimorphism_Southern.csv: Data of male to draw a figure of sexual
 dimorphism in southern lineage. Please refer to "Sexual
 dimorphism_Figure_Script.txt". Experiment 5_Sexual
 dimorphism_Figure_Script.txt: Scripts for drawing a figure of sexual
 dimorphism. \#Experiment 5_Relationship between OSR and SSD PGLS.csv: The
 data for statistical analysis and for drawing figure in PGLS. Please refer
 to "PGLS_OSR_and_SSD_Script" and
 "PGLS_OSR_and_SSD_Figure_Script". PGLS_OSR_and_SSD_Script.txt:
 Scripts for statistical analysis in PGLS. We used SSD as the response
 variable and OSR and annual mean temperature as explanatory variables.
 ultrametric_OSR_and_SSD.nwk: This data was used for statistical analysis
 and for drawing figure in PGLS. Please refer to
 "PGLS_OSR_and_SSD_Script" and
 "PGLS_OSR_and_SSD_Figure_Script". Northern.csv: Data used to
 draw the figure of the relationship between SSD and OSR in the northern
 lineage. Please refer to " PGLS_OSR_and_SSD_Figure_Script.txt".
 Central-eastern.csv: Data used to draw the figure of the relationship
 between SSD and OSR in the central-eastern lineage. Please refer to "
 PGLS_OSR_and_SSD_Figure_Script.txt". Central-western.csv: Data used
 to draw the figure of the relationship between SSD and OSR in the
 central-western lineage. Please refer to "
 PGLS_OSR_and_SSD_Figure_Script.txt". Southern.csv: Data used to draw
 the figure of the relationship between SSD and OSR in the southern
 lineage. Please refer to " PGLS_OSR_and_SSD_Figure_Script.txt".
 PGLS_OSR_and_SSD_Figure_Script.txt: Scripts for drawing the figure showing
 the relationship between SSD and OSR in PGLS. Relationship between male
 total length and female total length genetic_correlation.csv: The data for
 statistical analysis and for drawing figure in PGLS. Please refer to
 "PGLS_genetic_correlation_TOL_Script.txt" and
 "PGLS_genetic_correlation_TOL_Figure_Script.txt".
 PGLS_genetic_correlation_TOL_Script.txt: Scripts for statistical analysis
 in PGLS. We used male TOL as the response variable and female TOL as the
 explanatory variable. PGLS_genetic_correlation_TOL_Figure_Script.txt:
 Scripts for drawing a figure showing the relationship between male TOL and
 female TOL in PGLS. ultrametric_genetic_correlation.nwk: This data was
 used for statistical analysis and for generating figure in PGLS. Please
 refer to "PGLS_genetic_correlation_TOL_Script.txt" and
 "PGLS_genetic_correlation_TOL_Figure_Script.txt". \#Latitudinal
 pattern of snout-vent length and total length in larvae in the wild
 Larva.csv: This data was used for statistical analysis and for drawing the
 figure in larvae. Please refer to "Larva_SVL_Script.txt",
 "Larva_TOL_Script.txt" and "Larva_Figure_Script.txt".
 Larva_SVL_Script.txt: Scripts for statistical analysis of the SVL in
 larvae. We used SVL as the response variable and TOL, lineage, the
 interaction between TOL and lineage, and annual mean temperature as
 explanatory variables. Larva_TOL_Script.txt: Scripts for statistical
 analysis of TOL in larvae. We used TOL as the response variable and
 lineage and annual mean temperature as explanatory variables.
 Larva_Northern.csv: Data of northern lineage in larva. This data was used
 for the drawing of the figure. Please refer to
 "Larva_Figure_Script.txt". Larva_Southern.csv: Data of southern
 lineage in larva. This data was used for the drawing of the figure. Please
 refer to "Larva_Figure_Script.txt". Larva_Figure_Script.txt:
 Scripts for drawing a figure showed relationship between TOL and SVL in
 larva. \#Latitudinal pattern of snout-vent length and total length in
 juveniles in the wild Juvenile.csv: This data was used for statistical
 analysis and for generating figure for juveniles. Please refer to
 "Juvenile_SVL_Script.txt", "Juvenile_TOL_Script.txt"
 and "Juveile_Figure_Script.txt". Juvenile_SVL_Script.txt:
 Scripts used for statistical analysis of SVL in juveniles. We used SVL as
 the response variable and TOL, lineage, the interaction between TOL and
 lineage, and annual mean temperature as explanatory variables.
 Juvenile_TOL_Script.txt: Scripts used for statistical analysis of TOL in
 juveniles. We used TOL as the response variable and lineage and annual
 mean temperature as explanatory variables. Juvenile_Northern.csv: Data of
 northern lineage in juvenile. This data was used for the drawing of the
 figure. Please refer to "Juvenile_Figure_Script.txt".
 Juvenile_Southern.csv: Data of southern lineage in juvenile. This data was
 used for the drawing of the figure. Please refer to
 "juvenile_Figure_Script.txt". Juvenile_Figure_Script.txt:
 Scripts for drawing a figure showed relationship between TOL and SVL in
 juvenile.