The developmental stream of cottonwoods affects ramet growth and resistance to galling aphids

Michakl J.C. Kearslfy, Thomas G. Whitham

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

We define the 'developmental stream' of a plant as the gradient of increasingly mature phenotypes its shoots express over its lifetime. This pattern has important implications for studies of morphology, physiology, reproduction, and interactions with other organisms. Using cottonwoods, we test two major hypotheses about their developmental streams. First, within a tree, the developmental stage expressed by a shoot is dependent on its growth distance from the ground. Second, the distribution and fitness of Pemphigus betae, an aphid that is sensitive to host maturity, are positively related to increasingly mature shoot phenotypes within a tree. We show that the developmental variation in plant morphology and reproductive output within a tree are as great as that found among different-aged trees within a clone. In addition, we show that within-tree patterns of variation are stable from year to year and that P. betae responds to this variation by preferentially colonizing branches expressing more mature phenotypes. This pattern of branch selection is adaptive; aphids transferred to branches with shoots expressing mature phenotypes have expected fitnesses >80% higher than those transferred to branches expressing juvenile phenotypes. These findings have several general implications. First, a within-tree series of developmental stages provides a heritable mechanism for creating mosaics of variability in host quality within plants that create host selection problems for herbivores. Second, herbivores sensitive to developmental changes in their hosts will be concentrated in areas of high quality where they will be subject to the detrimental effects of competition, predation, and parasitism. Third, simulation models of plant growth based on the behavior of repeating plant parts (e.g., shoots) must be sensitive to developmental changes in these parts during plant development. Fourth, the developmental streams of plants may affect the evolution of such herbivore traits as territoriality, deme formation, and virulence. Fifth, the use of clonally propagated stock for the study of the genetic components of resistance to herbivory must be carried out with an understanding of the effects of host development on herbivores.

Original languageEnglish (US)
Pages (from-to)178-191
Number of pages14
JournalEcology
Volume79
Issue number1
DOIs
StatePublished - Jan 1 1998

Keywords

  • Aphid
  • Cottonwood
  • Gall
  • Herbivory
  • Heterochronic evolution
  • Host development
  • Metamerism
  • Mosaicism
  • Pemphigus
  • Phase change
  • Populus
  • Resistance

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

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