The consequences of predation by Chaoborus americanus on Daphnia pulex
Spitze, Ken Rollin
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https://hdl.handle.net/2142/20230
Description
Title
The consequences of predation by Chaoborus americanus on Daphnia pulex
Author(s)
Spitze, Ken Rollin
Issue Date
1989
Doctoral Committee Chair(s)
Lynche, Mike
Department of Study
Biology
Discipline
Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, General
Language
eng
Abstract
The direct and indirect effects of predation by the aquatic dipteran larva Chaoborus americanus on the crustacean Daphnia pulex were investigated with a combination of laboratory and field assessments. All approaches indicated that Chaoborus inflict a pattern of size-specific mortality on Daphnia that can be well approximated by a Gaussian function. Maximum vulnerability is experienced by Daphnia with body size of about 1 mm. Daphnia larger that 2 mm were essentially invulnerable. Several techniques are presented that remove biases that exist in previous methods used to assess size-specific vulnerability.
C. americanus emits a water soluble chemical that induces a morphological change within clones of D. pulex, most notably, the formation of a small horn on the dorsal margin of the head. Controlled laboratory experiments indicate that the horned morph experiences a 34-67% reduction in mortality, relative to the normal morph. Life table assays of many clones that compared the induced and non-induced morphs of each clone under identical conditions (except for induction factor) indicate substantial genotype x environment interaction for life history characters. Some clones showed a dramatic increase in body size, growth, and reproduction while other clones displayed a delay in reproduction, indicating a potential energetic cost to the induced morph. The significant genotype x environment interactions for many life-history characters indicate substantial genetic variance for the phenotypic plasticity.
Assessments from large genetically diverse replicate laboratory populations indicate that Chaoborus predation can have significant effects on the clonal composition of Daphnia populations. Life table studies of laboratory populations in the presence and absence of Chaoborus indicate that Chaoborus predation leads to significant changes in mean population life history. Increased immature body size and delayed maturity were the most significant effects attributable directly to Chaoborus predation.
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