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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Organismic and Evolutionary Biology

Year Degree Awarded

2016

Month Degree Awarded

May

First Advisor

Benjamin B. Normark

Second Advisor

Lynn S. Adler

Third Advisor

Aaron Ellison

Fourth Advisor

Laura A. Katz

Subject Categories

Evolution

Abstract

Ant agricultural mutualisms are common, well studied, and receive attention from scientific and public spheres due to shared similarities with human agriculture (i.e. ant/fungus ‘crop farming’ and ant/insect ‘dairy farming’). They also serve as important model systems for studying many facets of mutualism. This study reveals that the repertoire of ant agriculture may also include ‘meat farming’. Predatory mutualisms occur between Melissotarsus ants and various species of armored scale insects. This dissertation employs a multi-disciplinary approach to investigate the evolutionary history and nature of ant/diaspidid mutualisms. Chapter 1 reviews the current state of knowledge regarding species composition of these associations and includes descriptions of three new diaspidid species. Also included is a discussion on new observations of foraging behaviors gathered from multiple colonies of Melissotarsus emeryi in South Africa. Chapter 2 reconstructs the phylogeny of the Aspidiotini tribe of armored scale insects from molecular data for 127 species from 31 genera. Nearly all known ant-associated diaspidids belong to the tribe Aspidiotini. The majority of aspidiotine genera are found to be paraphyletic as currently defined and recommendations to increase taxonomic stability for this tribe are provided. Myrmecophily among diaspidids has evolved no fewer than six times independently, four times within the Aspidiotini and two additional origins recorded from the Diaspidini. Relationships between ants/diaspidids are labile at the species level and partnerships can shift. However, several clades of ant-specialized diaspidids have evolved indicating that some relationships can be stable on an evolutionary timescale. Chapter 3 investigates the diet and relative trophic position of Melissotarsus ants by analyzing stable isotopic enrichment of δ15N and δ13C, and by assaying ant gut contents for diaspidid COI mtDNA fragments. Diaspidid DNA is consistently amplified from gut contents of worker ants. Isotopic analyses indicate a strong positive relationship between δ15N and δ13C isotopes of worker ants and associated diaspidids; most variation in worker isotopes can be explained by variation in diaspidid isotopes. Worker ants are calculated to be approximately one trophic level above associated diaspidids. These dietary studies indicate that Melissotarsus ants are predators of mutualistically associated diaspidids. Predation plays a central role in the establishment and maintenance of ant/diaspidid mutualisms.

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Evolution Commons

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