Reproductive Timing and Allele Length Variation in the PolyQ Domain of the Clock Gene in Cyprinid Fishes of the Middle Rio Grande, New Mexico

The exact timing of spawning is critically important for reproductive success of minnows and other fishes.  Previous studies have shown that allele length polymorphism in one gene, Circadian Locomotor Output Cycles Kaput (Clock), is correlated with timing of migration and reproduction in phylogenetically-disparate organisms such as salmon and songbirds.  Allele length polymorphism in Clock in these taxa is largely due to variation in a polyglutamine repeat domain (PolyQ).  We hypothesized that allelic variation in the PolyQ domain plays an important role in spawning seasonality differences among five species of minnows (family Cyprinidae) native to the Rio Grande.  We used DNA sequencing to partially characterize the Clock1 paralog, including the PolyQ domain, in individuals of these five species.  PolyQ domains in these species varied in length from 59 to 76 amino acids.  We discuss the relationship of PolyQ length and timing of spawning.  This study has important implications for the conservation of threatened and endangered species, such as Rio Grande silvery minnow, Hybognathus amarus.