Avian diet and visual perception suggests avian predation selects for color pattern mimicry in bumble bees

Maddux, John Michael

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https://hdl.handle.net/2142/88090 Copy

Description

Title

Avian diet and visual perception suggests avian predation selects for color pattern mimicry in bumble bees

Author(s)

Maddux, John Michael

Issue Date

2015-07-20

Director of Research (if dissertation) or Advisor (if thesis)

Cameron, Sydney A.

Department of Study

Entomology

Discipline

Entomology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Müllerian mimicry
• Bombus
• birds

Abstract

Mimicry theory was developed by H. W. Bates and F. Müller based on their observations of similarities among butterflies, and since publication their theories have been used to explain numerous other mimicry systems. Bumble bees can be found in throughout the temperate parts of the word, as well as the high mountains and polar regions. In any given area, the local bumble bee species tend to share the same color patterns. Statistical confirmation of these trends has resulted in the hypothesis that these similarity groups are Müllerian mimicry rings. Bumble bee color patterns are thought to convey protection from avian predators, thus creating selection for fewer, more effective color patterns. Evidence for birds as predators of bumble bees primarily comprises logical arguments bolstered by only a few laboratory studies and empirical accounts. Although the hypothesis that birds are bumble bee predators driving the evolution of Müllerian mimicry is well reasoned and has some evidential support, strong experimental data are lacking. To test the effects of bumble bee color pattern on avian attack frequency, I created bumble bee models from soft plasticine with local, novel, and non-aposematic color patterns. I then presented these models to birds in the field using presentation apparatus to simulate bumble bees in flight and foraging on flowers; despite numerous attempts to optimize the apparatus, however, models were not effectively engaged by birds and statistically significant trends were not detected. A larger sample size may be needed, or the presentation system may require further modification. Requisite to birds displaying preferences with regard to bumble bee color patters, is that birds are major predators of bumble bees in nature, which has not been conclusively shown. To investigate this premise, I recruited the assistance of bird banders from across the country as collaborators in the collection of dietary samples from a large number of birds representing multiple species. I then designed and conducted a PCR assay to detect the presence of bumble bee tissue in the samples. Samples yielding electrophoresis bands were sequenced for verification. My results indicate widespread bumble bee predation across multiple bird species. Many of these birds have large populations and distributions, suggesting that they are able to exert significant selective forces on bumble bee populations. The large number of individual birds and bird species found to consume bumble bees provides strong affirmative evidence for the claim that birds are bumble bee predators and possible participants in the evolution of mimicry groups. I found bumble bee predation to be more likely in older birds, contrary to what would be expected if learned avoidance of bumble bees was occurring. The relationships between birds and bumble bees appears to be complex and conform poorly to general trends such as “birds avoid bumble bees.” Mimicry theory has been applied to bumble bees to explain the observed color pattern similarities in species with overlapping geographical distributions. All research in this area is based on the human-centric observation that these similarity groups exist. Animals possess diverse visual systems, however, and it should not be taken for granted that predators of bumble bees, no matter what they are, see the same color pattern convergence that humans do. I asked the question of whether birds’ perceptions of bumble bee color patterns are likely to parallel our own. To test this, I used reflectance spectroscopy to measure bumble bee color patches and generated hue scores based on avian color perception. I then compared these scores to human-assigned color classifications and found strong statistical association between human and avian perception of bumble bee colors. I also found that white bumble bee color patches consistently display relatively high ultraviolet reflectance invisible to human, but not avian, eyes. Consistent association of ultraviolet reflectance with only white color patches suggests that this reflectance does not add variation to bumble bee coloration that humans cannot perceive. I conclude that existing studies indicating color pattern convergence in bumble bees based on human vision are likely valid from the avian visual perspective, as well. My analysis of bird dietary samples show that birds are eating bumble bees in large numbers sufficient to result in powerful selection for color pattern convergence in bumble bees if foraging preferences based on color pattern exist. Additionally, reflectance data indicate that human-observed groups of bumble bees with similar color patterns are seen by birds, indicating that birds could be generalizing these patterns to create functional mimicry rings. The question remains, however, of whether birds learn to recognize and avoid bumble bees in the wild. My experiments were unable to demonstrate any effects of coloration on avian attack rates in the field, while my examination of the effects of age on the likelihood of finding bumble bee tissue in a birds’ diets showed a pattern inconsistent with that expected in a mimetic system. While I have shown that birds play a significant role in the ecology of bumble bees, and that putative bumble bee mimicry rings are visible to birds as well as humans, the role of birds in creating these mimicry rings remains uncertain.

Graduation Semester

2015-8

Type of Resource

text

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http://hdl.handle.net/2142/88090

Copyright and License Information

Copyright 2015 John Maddux

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