The ruff sandpiper is a shorebird that exhibits three genetically distinct types of males, which differ markedly in body size, ornaments, hormones, and mating behavior. Aggressive Independents represent the type that evolved first. Semi-cooperative Satellites and female-mimicking Faeders evolved later through a specific type of genetic rearrangement called ‘inversion’ where a chromosome segment becomes inverted. Due to the nature of this inversion, Satellite and Faeder chromosomes cannot recombine and are expected to deteriorate over time.
However, it remains unclear whether the genetic differences between these morphs, which affect physiological and behavioral traits, also translate into differences in sperm traits. We used a captive population of ruffs to compare sperm velocity and morphology between the three types of males. Consistent with expectations based on genetic deterioration over time, Faeder sperm was the slowest. However, against our expectations, the sperm of Independents does not appear to have better performance characteristics. Furthermore, although the midpiece of sperm is responsible for energy production, the length of the midpiece did not appear to affect sperm swimming speed.
To conclude, the three genetically determined types of ruffs displayed only minor differences in sperm traits, and these differences were not strongly linked to variation in sperm velocity, suggesting limited potential for morph-specific sperm adaptations in ruffs.