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GENETIC DIFFERENTIATION, SYMPATRIC SPECIATION, AND THE ORIGIN OF A DIPLOID SPECIES OF STEPHANOMERIA
Author(s) -
Gottlieb L. D.
Publication year - 1973
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1973.tb05956.x
Subject(s) - biology , sympatric speciation , reproductive isolation , population , evolutionary biology , ploidy , hybrid zone , gene flow , pollination , ecological speciation , obligate , zoology , ecology , genetic variation , genetics , pollen , gene , demography , sociology
Evidence is presented that a geographically peripheral population of the annual Stephanomcria exigua ssp. coronaria (Compositae), a widespread and ecologically diverse species, has recently given rise by a process of sympatric speciation to a diploid species presently designated “Malheurensis.” The new species comprises less than 250 individuals and is found only at a single locality in eastern Oregon where it grows interspersed with its parental population. Stephanomeria exigua ssp. coronaria is an obligate outcrosser and “Malheurensis” is highly self‐pollinating. Reproductive isolation is maintained by differences in breeding system, a crossability barrier that reduces seed set following cross‐pollination between them, and reduction in hybrid fertility caused by chromosomal structural differences. They are very similar morphologically. Electrophoretic analyses of seven enzyme systems demonstrate that all the alleles but one at the controlling 13 gene loci in “Malheurensis” are identical to alleles in ssp. coronaria . The new species displays certain maladapted features including loss of the specific requirements for seed germination characteristic of the progenitor population of ssp. coronaria . The origin of “Malheurensis” appears to be an exception to the theory of geographical speciation because spatial isolation is not necessary at any time for the origin or establishment of its reproductive isolating barriers. The nature of these barriers plus the genetic homogeneity of the species are compatible with the hypothesis that it derives from a single progenitor individual. Very little genetic change is involved initially in this mode of speciation.