Behavioral Ecology Vol. 12 No. 3: 340-347
© 2001 International Society for Behavioral Ecology
Experimental demonstration of the insurance value of extra eggs in an obligately siblicidal seabird
Department of Biology, Wake Forest University, Winston-Salem, NC 27109, USA
Address correspondence to L.D. Clifford. E-mail: cliffld5{at}wfu.edu .
A variety of organisms regularly produce more offspring than they raise. Despite the apparent energetic waste of such a reproductive tactic, overproduction may be favored by natural selection in some cases. One such case is when surplus offspring can serve as replacements, or insurance, for failed siblings. We tested the Insurance Egg Hypothesis (IEH) as an explanation for the overproduction of offspring in an obligately siblicidal seabird, the Nazca booby (Sula grant)i, which fledges a maximum of one nestling regardless of its clutch size. We manipulated clutch sizes within the range of natural variation encountered in this species (one-two eggs). The IEH predicts that parents with two-egg clutches should have higher reproductive success than those with one-egg clutches because the second egg can provide a nestling when the first egg fails to hatch, or when the first chick dies young. Consistent with the IEH, natural one-egg clutches that were enlarged to two eggs produced more hatchlings and fledglings than control one-egg clutches did, and natural two-egg clutches that were reduced to one egg produced fewer hatchlings and fledglings than control two-egg clutches did. We also evaluated aspects of the Individual Optimization Hypothesis, which proposes that individual optimal clutch sizes differ, as an explanation for clutch size variation in this species. In Nazca boobies, selection driven by replacement value appears to favor clutches larger than one even though final brood size is invariably one. One-egg clutches may be produced by parents experiencing some proximate limitation, such as a lack of food.
Key words: clutch size, Individual Optimization Hypothesis, Insurance Egg Hypothesis, Nazca booby, siblicide, Sula granti, surplus offspring.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  H. M. Townsend and D. J. Anderson Production of insurance eggs in Nazca boobies: costs, benefits, and variable parental quality Behav. Ecol., September 1, 2007; 18(5): 841 - 848. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. J.A. Cunningham and S. Lewis Parasitism of maternal investment selects for increased clutch size and brood reduction in a host Behav. Ecol., January 1, 2006; 17(1): 126 - 131. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. D. Clifford and D. J. Anderson Clutch size variation in the Nazca booby: a test of the egg quality hypothesis Behav. Ecol., March 1, 2002; 13(2): 274 - 279. [Abstract] [Full Text] [PDF]
|
|