Function and evolution of reptile eggs
Evolution over millions of years has shaped the diversity of forms and functions we see today in avian and reptilian eggs. Eggs are multifunctional structures, and are likely an innovation that allowed early vertebrates to colonize new habitats. To date, there is a fundamental lack of knowledge about the basic properties of eggshells, particularly those of reptiles, from their chemical composition and ultrastructure to their essential material properties. This project uses an integrative approach to unravel the ecological and environmental drivers of eggshell evolution in birds and reptiles. Two main questions I want to answer are: 1) What are the ecological correlates of the functional properties and morphology of eggs and 2) Do eggshells provide suitable models for the development of new functional materials?
Antimicrobial defenses in vertebrate eggs
I have been investigating some of the mechanisms of the remarkable network of antimicrobial defenses in birds with high risk of egg infection. Megapodes, for example, avoid egg microbial infection despite the high microbial abundance in their mounds, Their eggshells are coated with a thick layer of mineral nanospheres that prevent bacterial attachment. I also found that other bird species that nest in humid environments also coat their eggs with this type of cuticle.
During incubation, vertebrate eggs are models of successful microbial inhibition and control. I am interested in the chemical and physical antimicrobial features of eggshells. I am studying the success of eggshells with varying characteristics (antimicrobial concentration, porosity) at preventing microbial invasion and the role that abiotic factors may play in increasing susceptibility of eggs to infection.
Currently, I am narrowing the focus of this research towards reptiles, for which reproductive antimicrobial strategies are largely unexplored.
Mechanisms and Evolution of
As in other animals, the colors of bird feathers are produced by a variety of pigment molecules, nanostructures, or a combination of both. This mechanistic diversity provides complex opportunities for natural and sexual selection on the many functions of plumage color. One objective in this project has been to investigate the diversity in morphology of feather and skin melanosomes (melanin-containing organelles) and its association with the production of color.
By performing discriminant analyses on data from a wide range of bird species, we have been able to predict colors of both non-avialan dinosaurs and basal birds. Three of our published papers performing use these color reconstructions address questions about the evolution of color patterns and novel structural colors in the avian lineage.
Collaborators: Julia Clarke, Matthew Shawkey, Jakob Vinther, Li Quanguo, Gao Ke-Qin
Funding Body : NSF
A second aspect of this research focuses on mammal coloration. Traditionally, fur coloration has been considered to originate simply from the deposition of melanin (eu- or pheomelanin) in hairs. However, we are starting to gain a deeper insight into the relative contribution of hair structure and pigments to the diversity of colors we see in mammals.
I have been interested in knowing how the physical environment, by constraining the way energy is gained and expended, determines the capacity of organisms to invest in reproduction, growth or in resistance to stress.
I have studied some of the different strategies that individuals follow during the various phases of bird reproduction such as nest-site selection, resource allocation during egg formation, incubation and chick rearing.
Nest-site selection and incubation
Long term effects of developmental conditions
I find incubation especially interesting because it represents an energetically demanding event that can set limits to current and future reproductive success in birds. My PhD thesis investigated the importance of the thermal environment and nesting habitat on the reproductive performance of a sea duck, the Common Eider (Somateria mollissima) breeding in a cold environment.
In essence the questions of my project were 1) how does the nest site influence the microclimate of incubation, 2) what is the effect of microclimate on incubation performance? And 3) what role does the macroclimate play in population dynamics?
I have also worked in a study looking at the way the environment of a developing individual can shape adult phenotype. Specifically, we looked at consequences of the elevation of stress hormone levels during development and how this affects reproductive effort/success on later stages in life using the zebra finch as model species. This project was performed in collaboration with Prof. Pat Monaghan, Prof. Neil Evans and Dr. Karen Spencer.