A grand experiment in evolution: the Drosophila subobscura colonization of the Americas

Abstract

Drosophila subobscura is a Palearctic species that has been extensively studied by population and evolutionary geneticists for nearly half a century. In 1978, it appeared in Puerto Montt, Chile; within a few years it extended over much of Chile and into Argentina and became the most common drosophilid in many places. In 1982, it appeared in the American northwest; shortly thereafter it was found extensively distributed from southern British Columbia, through Washington and Oregon, into southern California, west of Sierra Nevada. In North America also it has become a common drosophilid in many places. The source of the colonizers has been sought with four lines of research: sequence arrangement of the polytene chromosomes, allozyme polymorphisms, mitochondrial DNA restriction patterns, and frequency of lethal alleles. The origin of the colonizers remains uncertain, although all evidence indicates that both the North American and the South American colonizers derive from the same Palearctic population. The overall configuration of the chromosomal and allozyme frequencies suggests a western Mediterranean origin, which is consistent with the mtDNA data. The presence of a particular chromosome arrangement, O5, suggests a northern European origin. Lethal allelism has opened up the possibility of discovering the precise origin of the colonizers: all O5 chromosomes in the Americas carry a particular recessive lethal gene. There is strong evidence that the number of founders was not very small and not very large, perhaps between 10 individuals and several score. The chromosomal polymorphisms of D. subobscura exhibit well-defined latitudinal clines in the Old World. In the few years since the colonization, clines in every chromosome have evolved in the Americas that have identical latitudinal polarity with those in the Old World. This would seem strong evidence that the polymorphisms and the clines are adaptive.Key words: chromosomal polymorphism, mitochondrial DNA evolution, allozyme polymorphism, lethal allelism, adaptation, geographic clines.

Relationship between Chromosomal Races/Subraces in the Brachypterous Grasshopper Podisma sapporensis (Orthoptera: Acrididae) Inferred from Mitochondrial ND2 and COI Gene Sequences

“…In fact, a north-south cline for paracentric inversions in Europe has repeated itself in the Pacific coast of North America, and it reversed and became a south-north cline in the Pacific coast of South America. This invasion of the New World by an Old World species has been called by Ayala et al (1989) "a grand experiment in evolution." A similar pattern of latitudinal clines in both hemispheres exists for D. melanogaster (Lemeunier and Aulard 1992).…”

Size and seasonal temperature in free-ranging Drosophila subobscura

“…The invadinḡ ies spread rapidly on both continents, and populations within continents became genetically subdivided soon after the introductions (Ayala et al, 1989;Brncic, 1995). The invasions have been very successful.…”

Genetic Variation in the Spread of Drosophila Subobscura From a Nonequilibrium Population

“…These findings are consistent with genetic drift causing allele frequency differences between populations in the eastward spread of D. subobscura across North America, as by founder effect(s). We do not think that selection acting on chromosomal inversions in this species contributed to these results, given the genetic similarity between the distant west coast populations, the observed association of inversion arrangements with latitude (Prevosti et al 1988), and the lack of significant clines in North American populations for inversions on the A-chromosome (Ayala et al 1989).…”

“…The recent colonization of the New World by Drosophila subobscura has offered researchers many empirical opportunities for examining the genetic consequences of founder effects (e.g., Ayala et al 1989;Prevosti et al 1989;Balanya et al 1994). Drosophila subobscura is believed to have invaded North America from Eurasia sometime between 1975 and 1982 (Prevosti et al 1988;Ayala et al 1989), spreading very quickly across the United States and Canadian west coasts and to the Sierra Nevada and the Okanagan Mountains Noor 1994Noor , 1998.…”

“…Drosophila subobscura is believed to have invaded North America from Eurasia sometime between 1975 and 1982 (Prevosti et al 1988;Ayala et al 1989), spreading very quickly across the United States and Canadian west coasts and to the Sierra Nevada and the Okanagan Mountains Noor 1994Noor , 1998. Analyses of chromosomal inversion polymorphisms (e.g., Prevosti et al 1988), allozyme allele frequencies (e.g., Balanya et al 1994), mitochondrial DNA restriction haplotypes (e.g., Latorre et al 1986;Rozas et al 1990), restriction haplotypes of the rp49 region (Rozas and Aguade 1991), and the frequency and allelism of lethal genes (Mestres et al 1990) have been conducted on North American and European populations of this species.…”