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.

Evolution of Obligate Siblicide in Boobies. 1. A Test of the Insurance-Egg Hypothesis

David J. Anderson
The American Naturalist
Vol. 135, No. 3 (Mar., 1990), pp. 334-350
Stable URL: http://www.jstor.org/stable/2462250
Page Count: 17
  • Read Online (Free)
  • Download ($19.00)
  • 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.
Preview not available

Abstract

Obligate siblicide, the unconditional killing of an individual by its sibling, occurs in a small number of bird species. Although clutches of two eggs are frequently laid, obligate siblicide eliminates the younger hatchling before it reaches the age of independence. The phenomenon presents a challenge to adaptationist evolutionary theory because parents produce chicks that are virtually certain to be killed and because surviving offspring actively sacrifice the inclusive-fitness increment represented by the victim. Dorward's (1962) insurance-egg hypothesis explains the production of a second egg as insurance against the first egg's failure. The insurance-egg hypothesis predicts that, if a second egg sometimes produces a fledgling after a first egg fails, then the evolution of insurance-egg production in single-chick species is governed by the ratio of the benefit of the increased probability of producing a hatchling to the cost of egg production. A field study of the obligately siblicidal masked booby (Sula dactylatra) demonstrated that second eggs contribute a surviving hatchling after the first egg's failure in 19.2% of two-egg clutches. The primary source of hatching failure was exceptionally high infertility or early embryonic death. Not all single-chick booby species produce insurance eggs, however, and the prediction of the insurance-egg hypothesis that the occurrence of insurance eggs is associated with the high benefit-to-cost ratio was supported by a compilation of booby breeding parameters. Because females make similar relative investments in each egg, the cost of insurance eggs is assumed to be constant across species, but benefits differ: hatching success in obligately siblicidal species ranges from 51% to 61%, whereas that in single-egg species is at least 85%.

Page Thumbnails

  • 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
  • Thumbnail: Page 
344
    344
  • Thumbnail: Page 
345
    345
  • Thumbnail: Page 
346
    346
  • Thumbnail: Page 
347
    347
  • Thumbnail: Page 
348
    348
  • Thumbnail: Page 
349
    349
  • Thumbnail: Page 
350
    350