Introgression in laboratory populations of Drosophila persimilis and D. pseudoobscura

A natural population of Drosophila transferred to a laboratory environment

“…By contrast, D. pseudoobscura and D. persimilis are often sympatric but not interbreeding in nature. Van Valen (1963) reported that a " hybrid swarm" was formed in population cages with a mixture of the two species held at 25° C. Our data provide no support for this claim, but they are not necessarily in contradiction. Among other differences in experimental designs, our experiments used progenies of wild-collected flies, while those of Van Valen used mutants which had been kept in laboratory cultures for many generations, and which may have had their ethological isolation weakened.…”

Genetic Interactions and Natural Selection in Louisiana Iris Hybrids

“…authors have reported the occurrence of favorable interactions between divergent parental genomes at both the nuclear and cytonuclear levels (e.g., Anderson and Stebbins 1954;Van Valen 1963;Lewontin and Birch 1966;MacRae and Anderson 1988;Hutter and Rand 1995;Rieseberg et al 1996). This phenomenon has been documented at the interpopulational and interspecific levels in plants and animals and suggests that, in addition to promoting postmating reproductive isolation between lineages, recombination and segregation of the parental genomes may sometimes generate adaptive genetic variation.…”

Introgression Between Closely Related Species of Drosophila in Panama

“…With a similar criterion, no crossing in natural populations between D. arizonensis and race B of D. mo javensis was found by Mettler and Nagle (1966); between D. pavani and D. gaucha by Koref-Santibafiez and del Solar (1961); between eastern and western strains of D. athabasca by Miller and Westphal (1965); between the Orinocan and Amazonian strains of D. paulistorum by Dobzhansky and Spassky (1959);or between "light" and "dark" D. ananassae (Futch, in Johnson et al, 1966). Although D. persimilis and D. pseudoobscura will introgress in the laboratory when no choice of mates is given and temperature is held at 25 C, species hybrids in nature are extremely rare (Van Valen, 1963). Natural sterile male hybrids be-tween D. aldrichi and D. mulleri, detectable by the reduced size of their testes seen through the ventral abdominal wall, are found only in regions where D. aldrichi males exceed one-third the male population of both species (Patterson and Stone, 1952).…”