Population, sex, and ontogenetic differences in the procurrent rays of the caudal fin in threespine sticklebacks (Gasterosteusaculeatus)

Abstract

The procurrent rays occur at the leading edge of the caudal fin in bony fishes and are taxonomically variable and possibly important to caudal motion. Using radiographs, as well as stained and cleared specimens, of threespine sticklebacks (Gasterosteus aculeatus L., 1758) from lakes on Haida Gwaii, British Columbia, we examined the extent of individual and population variabilities in these rays. Among 1113 fish from Drizzle Lake, 53% of individuals were dorsoventrally asymmetric in number of rays of which 95% had greater number of rays on the dorsal lobe. On 274 fish, we also quantified dorsal to ventral (D/V) ratios of the width of the most posterior procurrent rays and found ontogenetic shifts with symmetrical D/V ratios in subadults shifting to significant dorsal biases on the larger fish (60–90 mm standard length (SL)). Males have proportionally greater dorsal bias than females of equivalent size in both number and width of procurrent rays. We examined D/V width ratios in 105 stained and cleared specimens from 13 additional allopatric lake populations on Haida Gwaii. Eight populations were symmetrical for width of dorsal and ventral rays, while three populations were ventrally biased and two populations were dorsally biased. D/V ratios were best predicted by positive associations with adult body size and negative associations with total number of gill rakers.