Biology ETDs

Publication Date

7-1-2015

Abstract

The tendency for flying organisms to possess small genomes has been interpreted as evidence of natural selection acting on the physical size of the genome. Nonetheless, the flight-genome link and its mechanistic basis have yet to be well established by comparative studies within a volant clade. Is there a particular functional aspect of flight such as brisk metabolism, lift production, or maneuverability that impinges on the physical genome? I measured genome sizes, wing dimensions, and heart, flight muscle, and body masses from a phylogenetically diverse set of bird species. In phylogenetically controlled analyses, I found that genome size was negatively correlated with relative flight muscle size and heart index (i.e., ratio of heart to body mass) but positively correlated with body mass and wing loading. The proportional masses of the flight muscles and heart were the most important parameters explaining variation in genome size in multivariate models. Hence, the metabolic intensity of powered flight appears to have driven genome size reduction in birds. Birds evolving on islands have been the subject of thousands of scientific studies. These studies have revealed a tendency for island populations to adapt to a generalist niche. I found consistent shifts in shape, but not body size, following island colonization. Island-restricted volant species evolved smaller flight muscles than their continental relatives, with the degree of reduction greatest on islands of low species diversity. The decrease in flight muscle size was accompanied by an increase in leg length, reflecting a shift in investment from forelimbs to hindlimbs. Evolution along the trajectory toward flightlessness occurred in island bird populations from all nine families studied. I tested how reduced flight muscles and longer legs affect take-off performance in birds on the small, depauperate island of Tobago. I found that birds on Tobago had slower maximum velocity and maximum acceleration during take-off relative to conspecifics on the larger island of Trinidad. Initiation of wingbeats occurred later during take-off in populations on the island of Tobago in two species. Across all individuals, birds with smaller flight muscles initiated wingbeats later and achieved peak acceleration earlier during take-off. Lower predation pressures on small, species-poor islands likely permit the slower take-off velocities that result from island birds reduced flight muscles. These predictable evolutionary changes in the avian bauplan may explain why volant island birds are particularly vulnerable to introduced predators.

Project Sponsors

National Science Foundation National Institutes of Health American Ornithologists' Union Robert W. Dickerman University of New Mexico Department of Biology Scholarship Fund

Language

English

Keywords

birds, genome size, island biogeography, flight muscles

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Long, Jeffery

Second Committee Member

Brown, James

Third Committee Member

Wolf, Blair

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