Nathan Rank

Sonoma State University

Local adaptation in montane leaf beetles
Geographic variation in enzyme polymorphisms (Page 2 of 4)

Introduction & Collaborators

Enzyme polymorphisms

Environmental Gradients & Stress Proteins

Study Objectives

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See also research summary.

  • Different forms of the enzyme phosphoglucose isomerase are found in beetle populations living in different drainages.
  • Allele 1 predominates in the northern drainage Rock Creek (p = 0.9), and it is the most common allele in Bishop Creek (p = 0.7), but it is relatively rare in Big Pine Creek (p = 0.2).
  • The unusual pattern at PGI succests that natural selection acts on it. In Bishop Creek, allele 1 has increased in frequency since 1988, supporting the hypothesis that PGI is under natural selection.

  • Four of 8 beetles in Big Pine Creek are homozygous for PGI allele 4 and four are heterozygotes with Allele 1.
  • Seven of 11 beetles from Bishop Creek are homozygous for PGI allele 1 and four are heterozygotes with allele 4.
  • All six beetles from Rock Creek are homozygous for PGI allele 1

Variation in PGI-1 frequencies. Because PGI-4 is the only other common allele, it decreases in frequency as PGI-1 increases. For example, in BPC, the frequency of PGI-4 is 0.8, while in RC it is 0.1.

Spatial and Temporal PGI variation

  • We collected1600 beetles in 1988 and 1300 beetles in 1996 and screened them at five polymorphic enzymes.
  • PGI-1 predominated in RC, but was rare in BPC. PGI-4 was rare in RC but predominated in BPC.
  • PGI frequencies did not change in BPC and RC during the 8 years between samples. In BC, PGI-1 frequencies increased by 15%.

Evidence for selection on PGI in Bishop Creek

  • PGI-1 increased in frequency at all four sites between 1988 and 1996.
  • No other enzyme showed a consistent increase in frequency of a single allele.
  • This indicates that PGI-1 was selectively favored between 1988 and 1996.


PGI-1 frequencies in BC, shown for each site in the drainage.

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January 23, 1999 NER