Figure 1

Heritable evolution of gill raker number and spacing in three freshwater populations. (A, B) Alizarin red-stained left anterior (row 1) gill rakers from an adult lab-reared Little Campbell (LITC) marine (A) and Fishtrap Creek (FTC) freshwater (B) fish. Scale bar = 500 um. Additional images labeling anatomical features of the branchial skeleton are presented in Additional file 1: Figure S1. (C, D) Mean row 1 to 9 ventral gill raker number (C) and left row 1 ventral gill raker spacing (D) for wild-caught and/or lab-raised fish from LITC, FTC, Paxton Benthic freshwater (PAXB), or Bear Paw freshwater (BEPA). LITC and FTC wild raker number and spacing differences are maintained in lab-reared fish, and fish from the three freshwater populations (blue) have fewer gill rakers that are more widely spaced than fish from the marine population (red). Data in (D) are back-transformed residuals from a standard length regression for a mean length of 40 mm. Error bars depict mean +/- SD. n > =19 per condition. ***P <0.001, Tukey’s HSD test.