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THE EVOLUTION OF CALIFORNIA'S WILD RADISH HAS RESULTED IN THE EXTINCTION OF ITS PROGENITORS
Author(s) -
Hegde Subray G.,
Nason John D.,
Clegg Janet M.,
Ellstrand Norman C.
Publication year - 2006
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.0014-3820.2006.tb01197.x
Subject(s) - biology , introgression , lineage (genetic) , extinction (optical mineralogy) , hybrid , gene flow , evolutionary biology , population , transgressive segregation , gene pool , taxon , genetics , zoology , ecology , gene , genetic diversity , genetic variation , botany , quantitative trait locus , demography , paleontology , sociology
If two previously isolated taxa mutually assimilate through hybridization and subsequent biparental introgression, and if their introgressed descendants have the same or higher fitness than their parents, then gene flow should result in the local extinction of parental taxa via replacement by hybrid derivatives. These dramatic events may occur rapidly, even in a few generations. Given the speed at which such extinction by hybridization may occur, it may be difficult to identify that the process has occurred. Thus, documented instances of extinction by hybridization are rare, and especially so for cases in which both parents are replaced by the hybrid lineage. Here we report morphological and allozyme evidence for the local extinction of two Raphanus species in California via replacement by their hybridderived descendants. The results from a greenhouse experiment demonstrate that California wild radishes have a specific combination of traits from their progenitors, and comparison of our results to that of an earlier report indicate that pure parental types are no longer present in the wild. Our results also show the hybrid‐derived lineage has transgressive fruit weight compared to its parents. Allozyme analysis demonstrates that California wild radishes are derived from hybridization between the putative parental species. However, that analysis also demonstrates that California wild radish has now become an evolutionary entity separate from both of its parents. We suggest that the aggressive colonizing behavior of the hybrid‐derived lineage probably results from a novel combination of parental traits, rather than genetic variability of the population per se.