Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Hybridization as a Source of Variation for Adaptation to New Environments

R. C. Lewontin and L. C. Birch
Evolution
Vol. 20, No. 3 (Sep., 1966), pp. 315-336
DOI: 10.2307/2406633
Stable URL: http://www.jstor.org/stable/2406633
Page Count: 22
  • Read Online (Free)
  • Download ($4.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Hybridization as a Source of Variation for Adaptation to New Environments
Preview not available

Abstract

Dacus tryoni, the Queensland fruit fly, has extended its geographical range sharply in the last hundred years. This extension is not a result of an expansion of food resource but involved a physiological adaptation to extreme temperatures. There is evidence that shows past and present crossing between D. tryoni and a closely related species, D. neohumeralis. This crossing is probably a result of the breakdown of isolating mechanisms with the advent of large-scale production of fruit to which Dacus is preadapted. We hypothesize that the genetic variation necessary to allow Dacus tryoni to increase its ecological tolerance came from introgression of genes from D. neohumeralis. In order to see whether such a mechanism is a reasonable one, an experiment was performed. Populations of D. tryoni and hybrids between D. tryoni and D. neohumeralis were maintained for nearly two years at 20⚬ C., 25⚬ C., and 31.5⚬ C. During these two years the production of pupae by the population was measured. During the first half of the experiment hybrids were clearly poorer than "pure" tryoni, but over the last half there was no difference. Also, during this time the composition of the hybrid population changed to resemble that of the tryoni population. At the end of two years various components of the rate of increase were measured. At 20⚬ C. and 25⚬ C., there was little or no difference between the hybrid populations and the tryoni populations. At 31.5⚬ C., however, the hybrids were clearly superior in various life-cycle components and in their intrinsic rate of increase. The results also show that 31.5⚬ C. is a stress temperature as compared with the lower temperatures. We interpret these results as supporting the hypothesis that introgression of genes, not adaptive per se, can lead to rapid adaptive evolution.

Page Thumbnails

  • Thumbnail: Page 
315
    315
  • Thumbnail: Page 
316
    316
  • Thumbnail: Page 
317
    317
  • Thumbnail: Page 
318
    318
  • Thumbnail: Page 
319
    319
  • Thumbnail: Page 
320
    320
  • Thumbnail: Page 
321
    321
  • Thumbnail: Page 
322
    322
  • Thumbnail: Page 
323
    323
  • Thumbnail: Page 
324
    324
  • Thumbnail: Page 
325
    325
  • Thumbnail: Page 
326
    326
  • Thumbnail: Page 
327
    327
  • Thumbnail: Page 
328
    328
  • Thumbnail: Page 
329
    329
  • Thumbnail: Page 
330
    330
  • Thumbnail: Page 
331
    331
  • Thumbnail: Page 
332
    332
  • Thumbnail: Page 
333
    333
  • Thumbnail: Page 
334
    334
  • Thumbnail: Page 
335
    335
  • Thumbnail: Page 
336
    336