Sexual dimorphism in fin size and shape in North American Killifish
Data files
Apr 24, 2025 version files 70.61 KB
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Davis_etal_killi.csv
66.29 KB
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README.md
4.32 KB
Abstract
Sexual dimorphism is intriguing because it suggests that males and females differ in phenotypic optima for traits and that sex-specific trait values can evolve despite a shared genome. Differences in sexual dimorphism across populations or species suggest that the nature of sexual selection and/or genetic constraints differs among species. Here, we measured sexual dimorphism in 20 species of North American killifish (Fundulidae) in size and shape of dorsal, anal, and caudal fins. We observed profound sexual dimorphism in anal and dorsal fin size and shape across all species, suggesting a common direction of selection. Sexual dimorphism was also present in caudal fin size and shape but was much lower in magnitude, with several species not differing from a null expectation of zero. There was little evidence for a phylogenetic signal in the levels of sexual dimorphism in dorsal and anal fin traits. We also found a strong phylogenetic correlation between sexual dimorphism in anal and dorsal fin shape but no phylogenetic correlation between fin area, base length, or ray length across different fins. Our results indicate that there is pronounced sexual dimorphism in anal and dorsal fin size and shape across fundulids. Similar patterns of sexual dimorphism in anal and dorsal fin properties have been documented in other groups, including gars, bichirs, graylings, minnows, and many species in the Atherinomorpha, suggesting that this pattern may be common across Actinopterygii.
https://doi.org/10.5061/dryad.wm37pvmz6
Description of the data and file structure
Files and variables
File: Davis_etal_killi.csv
Description:
Variables
- Fish_ID: ID number for code in original photo
- Genus:self-explanatory
- Species:self-explanatory
- Sex: male or female
- SL: standard length; length in mm from the tip of the snout to the base of the caudal peduncle
- Dor_Base: dorsal fin base length (mm)
- Dor_RF: dorsal first fin ray length (mm)
- Dor_RQ1: dorsal first quartile fin ray length (mm)
- Dor_RQ2: dorsal median fin ray length (mm)
- Dor_RQ3: dorsal third quartile fin ray length (mm)
- Dor_RL: dorsal last fin ray length (mm)
- Dor_Area: dorsal fin area calculated as the product of dorsal base length times the average dorsal fin ray length (mm^2)
- Anal_Base: anal fin base length (mm)
- Anal_RF: anal first fin ray length (mm)
- Anal_RQ1: anal first quartile fin ray length (mm)
- Anal_RQ2: anal median fin ray length (mm)
- Anal_RQ3: anal third quartile fin ray length (mm)
- Anal_RL: anal last fin ray length (mm)
- Anal_Area: anal fin area calculated as the product of anal base length times the average anal fin ray length (mm^2)
- Caud_Base: caudal fin base length (mm); same as the caudal peduncle width (mm)
- Caud_DM: caudal fin dorsal ray length (mm)
- Caud_Mid: caudal median fin ray length (mm)
- Caud_VM: caudal fin ventral ray length (mm)
- Caudal_Area: caudal fin area (measured from photo) (mm^2)
Tree File
The tree file is the median fundulid tree pruned to include only the taxa included in the morphological data.
R Files
There is one large file that contains all of the analyses presented in the paper. It has the code to create the 4 main data tables in the paper (Tables 2-5) and to create 6 of the figures (figures 3-8).
Table 2 is the correlations between trait values and standard length.
Table 3 presents the analyses for each major trait, including the F-values from an Analysis of Variance that considers the effects of Species, Sex, and their interaction. It also lists the value for sexual dimorphism as measured as the effect size due to sex. It presents statistics on the extent to which there is a phylogenentic signal on standard length and other fin traits after being corrected for standard length. It also examines whether sexual dimorphism has a strong phylognetic signals. Finally, it presents the across-species correlation between male and female values after having corrected for phylogeny.
Table 4 presents the same analyses above, except that it is performed on individual fin ray measurements.
Table 5 presents data on the extent to which sexual dimorphism is correlated across different fin traits (i.e., is sexual dimorphism in dorsal fin area correlated with sexual dimorphism in anal fin area) across species after having accounted for the phylogenetic history.
Figure 3 presents boxplots for standard length across all 20 species.
Figure 4 presents the overall effect size of sex on different fin traits across the entire family.
Figure 5 gives a visualization of dorsal fin size and shape after being corrected for standard length. For each species, the emmeans for the two sexes was determined, while holding constant the effect of standard length. The position of the fin rays was accounted for by using the mean fin base length for males and females and accounting for the position of the first fin ray, first quantile fin ray, median fin ray, third quantile fin ray, and last fin ray. This visualization allows one to see the size and shape of dorsal fins of males and females in different species.
Figure 6 is the same as figure 5, except that it shows anal fin size and shape.
Figure 7 shows the effect sizes due to sex for the area of dorsal, anal, and caudal fins across all 20 species of killifish.
Figure 8 shows the effect sizes due to sex for the shape of dorsal, anal, and caudal fins across all 20 species of killifish.
Code/software
These data were processed using R version 4.4.2 (2024-10-31) -- "Pile of Leaves".
The following packages were used: ape, diversitree, rfishbase, phytools, geiger, emmeans, broom, ggplot2, ggpubr, dplyr, car, and broom.
Here, we measured sexual dimorphism in 20 species of North American killifish (Fundulidae) in size and shape of dorsal, anal, and caudal fins. We took digital photos of 363 individuals across 20 species. We measured standard length and fin base length for the dorsal, anal, and caudal fins. For the dorsal and anal fins, we also measured the lengths of the first and last fin rays as well as the lengths of median, first quartile, and third quartile fin rays. For the caudal fin, we measured the median fin ray length and the length of the upper dorsal and lower ventral fin ray. From these data, we estimated fin area. We also used published genbank data to estimate a phylogeny for the group. We analyzed the data in R. Because there is pronounced variation in standard length (i.e., size) across these species, we first performed a linear regression of the log of the trait value on the log of standard length and used the residuals as a measure of size-corrected fin traits.