Inheritance and reproductive role of rare males in a parthenogenetic population of the brine shrimp,Artemia parthenogenetica

The occurrence and potential reproductive role of rare males produced by obligately parthenogenetic brine shrimp were examined. The study of sex ratios in offspring from 30 different parental lines through three generations indicated the existence of two groups of females (Group A and Group B), which were genetically distinct with regard to their tendency to produce males. Group A females consistently produced fewer males than did the Group B females, and thus had a lower ratio of males to females among their offspring than the average population sex ratio. A significant increase in ratios of males to females in broods of the Group B females in the third generation suggests that selection for females expressing this trait may have occurred.Histological examination of parthenogenetically produced males revealed the presence of sperm in the testes and in the vas deferens. Sperm of these males were significantly larger than those of sexual males (6.6 m vs. 4.1 in diameter). Mating experiments between parthenogenetically derived males and both parthenogenetic siblings and sexual females gave no indication that these males contributed to any aspect of reproduction. However, further experiments are needed before these males can be characterized as reproductively sterile.