Gene regulation of shell banding in a land snail from Israel

JOSEPH HELLER, MICHAL VOLOKITA

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

The Israeli land snail, Xeropicta vestalis, offers a particularly clear example of gene regulation in relation to natural selection, in that within each population the appropriate phenotype is generated only at the correct part of the animals life cycle, and a contrasting phenotype develops when the forces of natural selection change. In the mountains of Jerusalem, where the winter is cold, the shells are dark. Westwards, towards the coastal plain where the winter is warmer, the shells gradually become paler. As dark shells absorb more radiation than pale ones, this clinal variation in morph frequencies can be explained in thermal terms. (Banded shells are also more cryptic than non‐banded shells, so that in the mountains visual selection by predators may be an additional force which favours dark shells.) Xeropicta vestalis is an annual, semelparous species: the snails hatch in winter, become mature within one year, reproduce, and then die. In the coastal plain the snails are active throughout most of the year, and they have a long period in which to grow to reach adult size. In the mountains and hills, on the other hand, the snails are active for only a very short period. They spend most of their lives as small snails, in a state of aestivation. Xeropicta vestalis must be dark in mountains because when it finally awakens, it must very rapidly and hastily reach reproduction size. A dark shell, by speeding up temperature‐dependent processes in this critical stage, assists the snail to mature rapidly. Shell darkness varies with age: in the mountains and hills the shells are moderately dark when they hatch, but become darker whilst growing in early winter. In the coastal plain also, the snails are moderately dark when they hatch; but here they become paler, whilst growing in winter and spring. In both cases, each snail is darker in the colder months and paler in the hot ones. A strategy of gene regulation of shell colour is thus favoured when the subsequent forces of the environment are very contrasting in their direction, very severe—yet also very predictable.

Original languageEnglish
Pages (from-to)261-277
Number of pages17
JournalBiological Journal of the Linnean Society
Volume16
Issue number4
DOIs
StatePublished - 1 Jan 1981
Externally publishedYes

Keywords

  • Israel ‐
  • Land snail ‐
  • Xeropicta vestalis ‐
  • clinal variation ‐
  • gene regulation ‐
  • natural selection.
  • shell bands ‐

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

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