期刊
ECOLOGICAL ENTOMOLOGY
卷 34, 期 5, 页码 551-561出版社
WILEY
DOI: 10.1111/j.1365-2311.2009.01107.x
关键词
Danaus plexippus; density-dependent prophylaxis; host-parasite interaction; melanism; monarch butterfly; neogregarine protozoan; Ophryocystis elektroscirrha
类别
资金
- The National Science Foundation [ISE-0104600, DEB-0643831]
- Xerces Society
- University of Minnesota Extension Service and Monarchs
- Graduate Division of Biological and Biomedical Sciences at Emory University [NSF DGE-0231900]
- PRISM Fellowship
- Summer Undergraduate Research Program (SURE)
- Scholarly Inquiry Research Experience (SIRE) at Emory University
1. Hosts experiencing frequent variation in density are thought to benefit from allocating more resources to parasite defence when density is high ('density-dependent prophylaxis'). However, high density conditions can increase intra-specific competition and induce physiological stress, hence increasing host susceptibility to infection ('crowding-stress hypothesis'). 2. We studied monarch butterflies (Danaus plexippus) and quantified the effects of larval rearing density on susceptibility to the protozoan parasite Ophryocystis elektroscirrha. Larvae were inoculated with parasite spores and reared at three density treatments: low, moderate, and high. We examined the effects of larval density on parasite loads, host survival, development rates, body size, and wing melanism. 3. Results showed an increase in infection probability with greater larval density. Monarchs in the moderate and high density treatments also suffered the greatest negative effects of parasite infection on body size, development rate, and adult longevity. 4. We observed greater body sizes and shorter development times for monarchs reared at moderate densities, and this was true for both unparasitised and parasite-treated monarchs. We hypothesise that this effect could result from greater larval feeding rates at moderate densities, combined with greater physiological stress at the highest densities. 5. Although monarch larvae are assumed to occur at very low densities in the wild, an analysis of continent-wide monarch larval abundance data showed that larval densities can reach high levels in year-round resident populations and during the late phase of the breeding season. Treatment levels used in our experiment captured ecologically-relevant variation in larval density observed in the wild.
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