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Experimental excursions on adaptive landscapes: Density-dependent selection on egg size

Svensson, Erik LU and Sinervo, B (2000) In Evolution 54(4). p.1396-1403
Abstract
Theories of density-dependent natural selection suggest that intraspecific competition will favor juveniles of high competitive ability. Empirical evidence has been provided from laboratory selection experiments, but field studies are lacking due to the logistical difficulties of experimentally manipulating population densities in natural settings. Here, we present data from a decade long experimental held study of side-blotched lizards, Uta stansburiana that overcomes these difficulties. We tested the hypothesis that density-dependent natural selection causes egg size to increase from early to late clutches in this and many other species. Using a novel combination of environmental manipulations of hatchling density and phenotypic... (More)
Theories of density-dependent natural selection suggest that intraspecific competition will favor juveniles of high competitive ability. Empirical evidence has been provided from laboratory selection experiments, but field studies are lacking due to the logistical difficulties of experimentally manipulating population densities in natural settings. Here, we present data from a decade long experimental held study of side-blotched lizards, Uta stansburiana that overcomes these difficulties. We tested the hypothesis that density-dependent natural selection causes egg size to increase from early to late clutches in this and many other species. Using a novel combination of environmental manipulations of hatchling density and phenotypic manipulations of egg size, we demonstrate that the nature of selection on egg size changes dramatically in the absence of older competitors. The strength of selection on egg size among later-clutch hatchlings released in areas without competitors from early clutches became almost doubled in magnitude, compared to that among hatchlings released in the presence of older competitors. These experimental findings demonstrate density-dependent natural selection on egg size; however, they contradict the classical idea that egg size increases during the reproductive season because of competition between early and late hadchlings. The results indicate that competitive age or size asymmetries between early and late hatchlings can override within-cohort asymmetries due to egg size. We suggest that competition could be an important mediator of oscillating selection pressures in this and other systems. Finally, we discuss the utility of "doubie-level," simultaneous experimental manipulation of both phenotypic traits that are targets of selection (e.g., egg size) as well the environmental agents of selection (e.g., population density). (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Evolution
volume
54
issue
4
pages
1396 - 1403
publisher
Wiley-Blackwell
external identifiers
  • scopus:0033831333
ISSN
1558-5646
language
English
LU publication?
yes
id
07b97445-bd16-4228-9763-694cde469686 (old id 145953)
alternative location
http://www.bioone.org/bioone/?request=get-document&issn=0014-3820&volume=054&issue=04&page=1396
date added to LUP
2007-06-26 12:21:21
date last changed
2017-11-12 03:54:28
@article{07b97445-bd16-4228-9763-694cde469686,
  abstract     = {Theories of density-dependent natural selection suggest that intraspecific competition will favor juveniles of high competitive ability. Empirical evidence has been provided from laboratory selection experiments, but field studies are lacking due to the logistical difficulties of experimentally manipulating population densities in natural settings. Here, we present data from a decade long experimental held study of side-blotched lizards, Uta stansburiana that overcomes these difficulties. We tested the hypothesis that density-dependent natural selection causes egg size to increase from early to late clutches in this and many other species. Using a novel combination of environmental manipulations of hatchling density and phenotypic manipulations of egg size, we demonstrate that the nature of selection on egg size changes dramatically in the absence of older competitors. The strength of selection on egg size among later-clutch hatchlings released in areas without competitors from early clutches became almost doubled in magnitude, compared to that among hatchlings released in the presence of older competitors. These experimental findings demonstrate density-dependent natural selection on egg size; however, they contradict the classical idea that egg size increases during the reproductive season because of competition between early and late hadchlings. The results indicate that competitive age or size asymmetries between early and late hatchlings can override within-cohort asymmetries due to egg size. We suggest that competition could be an important mediator of oscillating selection pressures in this and other systems. Finally, we discuss the utility of "doubie-level," simultaneous experimental manipulation of both phenotypic traits that are targets of selection (e.g., egg size) as well the environmental agents of selection (e.g., population density).},
  author       = {Svensson, Erik and Sinervo, B},
  issn         = {1558-5646},
  language     = {eng},
  number       = {4},
  pages        = {1396--1403},
  publisher    = {Wiley-Blackwell},
  series       = {Evolution},
  title        = {Experimental excursions on adaptive landscapes: Density-dependent selection on egg size},
  volume       = {54},
  year         = {2000},
}