Date of Award

4-22-2015

Document Type

Thesis and Dissertation

Degree Name

Master of Science (MS)

Department

School of Biological Sciences

First Advisor

Scott K. Sakaluk

Second Advisor

Anne-Katrin Eggert

Abstract

Male Nicrophorus burying beetles utilize two alternative mate-finding tactics, representing an ideal model system to test the influence of environmental cues on the expression of alternative tactics. The "searching" tactic involves flying in search of a carcass on which to mate. This tactic can result in high levels of paternity, but is risky in that carcasses are rare and competition for carcasses is fierce. The "signaling" tactic, which involves emitting pheromone in the absence of a carcass to attract females, is energetically less costly, but a signalling male must mate with multiple females to achieve the same reproductive returns as a successful searcher. Most male burying beetles employ both tactics, but the amount of time spent employing each tactic differs between individuals. Because all males are phenotypically plastic in the time invested in alternative behaviors, the expression of the tactics is likely to be condition dependent. While size has been shown to have an effect on tactic expression, it does not explain all of the variation. As a conditional-strategy, an environmental cue, such as the availability of reproductive resources, may influence the "switchpoint" of when one tactic yields higher fitness than the other.

We tested how the expression of alternative tactics is influenced by previous mating experience and the perceived availability of females versus carcasses by using a repeated-measures design in which mate-finding behavior of males was observed before and after exposure to: 1) multiple females but no carcasses, 2) multiple females and multiple carcasses, 3) multiple carcasses but no females, or 4) no females of carcasses (control). We found a significant time-by-treatment interaction for time invested in signaling, with both the control and multiple-female groups significantly increasing signaling time. Although the overall time-by-treatment interaction was not quite significant for time invested in searching, pairwise comparisons revealed that control, multiple-female, and multiple-carcass groups all significantly decreased time spent searching. Our results demonstrate that environmental cues do affect which alternative tactic male burying beetles employ, and that the chosen tactic is influenced by the availability of both receptive females and carcasses on which to breed.

Comments

Imported from ProQuest Mulrey_ilstu_0092N_10535.pdf

Page Count

42

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