Interbreeding and gene flow in the genus Trichinella.

Breeding experiments between isolates of Trichinella spiralis--Trichinella (pig; 43 degrees 00'N, 81 degrees 00'W; 1952), Trichinella (polar bear; 58 degrees 00'N, 95 degrees 00'W; 1976), and Trichinella (wolverine; 55 degrees 00'N, 100 degrees 00'W; 1979)--and T. spiralis var. pseudospiralis were undertaken. Results from breeding experiments differed, such as the inability of the strain isolated from pigs and T. spiralis var. pseudospiralis to breed. The pig isolate was capable of breeding with both arctic isolates (wolverine and polar bear) and the arctic isolates both were capable of breeding with T. spiralis var. pseudospiralis. These observations indicated that gene flow occurs between these isolates of Trichinella and suggests a latitudinal cline of variants but not distinct species. It is hypothesized that T. spiralis consists of a series of semispecies or incipient species in various stages of speciation.