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.

Seasonal Variation in the Morphology of Drosophila robusta Sturtevant

Harrison D. Stalker and Hampton L. Carson
Evolution
Vol. 3, No. 4 (Dec., 1949), pp. 330-343
DOI: 10.2307/2405719
Stable URL: http://www.jstor.org/stable/2405719
Page Count: 14
  • 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.
Seasonal Variation in the Morphology of Drosophila robusta Sturtevant
Preview not available

Abstract

A study of genetically controlled seasonal variation in morphology was made of a natural population of Drosophila robusta near St. Louis, Missouri. Five hundred F2 progenies from wild flies captured in the period from February to September 1946 were reared under uniform laboratory conditions, and five adult females were measured from each progeny. Of the five characters measured, thorax-length, head-width, femur-length, wing-length and wing-width, all showed significant seasonal heterogeneity. Using the compound measurement D2 (Fisher's Discriminant Function), as an indication of northernness or southernness of the morphology it was shown that the population underwent a regular, highly significant shift toward a southern morphology during the summer months June through August. This shift during the hot weather was in the direction expected if the southern morphology has high temperature adaptive value, and if the species undergoes a rapid selective response to seasonal temperature fluctuations. The seasonal changes in morphology are in marked contrast to the essential stability of the gene arrangement frequencies. Since such stability seems to indicate a relatively large breeding population it is felt that the observed morphological changes cannot be attributed to genetic drift, and are probably the result of natural selection. In order to determine the direct, nongenetic effect of the temperature of rearing on the morphology, five geographically diverse strains were used in which flies reared at 25.5⚬C and those reared at 17.6⚬ C. were compared morphologically. It was found that the low temperature group were more northern in their morphology than those reared at high temperatures. The northernness of the low temperature group was indicated both by their D2 values and by the typically northern shift in the proportion of head-width and wing-length. By comparing the F2 progenies coming from wild parents carrying different gene arrangements it was shown that the arrangements XR and XR-1 are associated with different morphological characteristics.

Page Thumbnails

  • 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
  • Thumbnail: Page 
337
    337
  • Thumbnail: Page 
338
    338
  • Thumbnail: Page 
339
    339
  • Thumbnail: Page 
340
    340
  • Thumbnail: Page 
341
    341
  • Thumbnail: Page 
342
    342
  • Thumbnail: Page 
343
    343