Table 4 Summary results from general linear mixed models testing for differences in head morphology (extracted from the principal component analysis, gillraker number and gillraker length) of threespine sticklebacks from 25 freshwater locations

Head shape (PC1)

Intercept

0.023 ± 0.011

0.038

R² = 0.57

Littoral carbon (α)

1

−0.004 ± 0.003

1.76

0.185

N fish = 482

Trophic position (Tpos)

1

−0.000 ± 0.003

0.04

0.833

N populations = 25

Sex

1

0.005 ± 0.001

79.20

< 0.001

Total length (cm)

1

−0.004 ± 0.001

12.42

< 0.001

Head shape (PC2)

Intercept

−0.011 ± 0.011

0.295

R² = 0.25

Littoral carbon (α)

1

0.004 ± 0.003

1.64

0.203

N fish = 482

Trophic position (Tpos)

1

0.002 ± 0.003

0.71

0.401

N populations = 25

Sex

1

0.005 ± 0.000

58.81

< 0.001

Total length (cm)

1

−0.000 ± 0.001

0.04

0.836

Head shape (PC3)

Intercept

−0.039 ± 0.009

< 0.001

R² = 0.42

Littoral carbon (α)

1

−0.002 ± 0.002

0.99

0.322

N fish = 482

Trophic position (Tpos)

1

0.002 ± 0.002

0.53

0.467

N populations = 25

Sex

1

−0.000 ± 0.000

3.64

0.057

Total length (cm)

1

0.008 ± 0.001

65.20

< 0.001

Head shape (PC4)

Intercept

0.018 ± 0.008

0.036

R² = 0.33

Littoral carbon (α)

1

−0.000 ± 0.002

0.00

0.988

N fish = 482

Trophic position (Tpos)

1

0.002 ± 0.002

0.61

0.435

N populations = 25

Sex

1

0.000 ± 0.000

1.63

0.203

Total length (cm)

1

−0.005 ± 0.001

30.25

< 0.001

Gillraker number

Intercept

19.474 ± 1.055

< 0.001

R² = 0.30

Littoral carbon (α)

1

−0.176 ± 0.294

0.36

0.550

N fish = 481

Trophic position (Tpos)

1

−0.153 ± 0.274

0.31

0.578

N populations = 25

Sex

1

−0.173 ± 0.060

8.34

0.004

Total length (cm)

1

0.050 ± 0.125

0.16

0.693

Gillraker length

Intercept

0.190 ± 0.095

0.046

R² = 0.42

Littoral carbon (α)

1

0.075 ± 0.026

8.41

0.004

N fish = 481

Trophic position (Tpos)

1

−0.016 ± 0.025

0.42

0.515

N populations = 25

Sex

1

−0.045 ± 0.006

67.84

< 0.001

Total length (cm)

1

0.139 ± 0.011

148.80

< 0.001