GENETICS OF

Abstract

The brine shrimp Artcinia solina is a crustacean (Order Anostraca) which lives in the saline lakes and coastal salterns of five continents. (Salterns are ponds where sea water is concentrated by solar evaporation for the commercial production of sodium chloride.) Some populations are bisexual whereas others consist only of females which reproduce parthenogenetically. Some populations are diploid whereas others have been reported to be triploid, tetraploid, pentaploid, or octaploid on the basis of cytological studies. The morphological and cytological studies of Artcinia populations have been reviewed by Stella (1933), Goldschmidt (1952), Barigozzi (1957), Dutrieu (1960), Gilchrist (1960), and Stefani (1961). The author knows of only two papers in which hybridization studies were mentioned. Gilchrist (1960, page 233) stated that North African shrimp and Calif ornian shrimp would not interbreed. Barigozzi and Tosi (1959) mated Great Salt Lake shrimp to a diploid stock which evidently came from the Gulf of California. The purpose of the present study was to determine whether nine wild populations of Arteinia were reproductively isolated from one another. Evidence of reproductive isolation would be : ( 1 ) inability of the two populations to live in the same medium (habitat isolation), (2) failure of the male to clasp the female (ethological isolation), (3) failure to produce a viable F x (due to mechanical isolation, gametic or zygote mortality, or hybrid inviability), or (4) hybrid sterility (absence of an F 2 or production of a deficient F 2 ). These isolating mechanisms have been defined and discussed by Mayr (1963, pp. 91 to 109). This paper describes a series of hybridizations in which wild-type shrimp were out-crossed either to wild shrimp from different localities or to inbred stocks homozygous for recessive mutant genes. It was found that the shrimp from Mono Lake and from Sete were reproductively isolated from each other and from the other seven populations. However, there was no barrier to gene exchange among