From genes, to cells, to physiology, to morphology, the team aims to understand how body size and reproduction traits are connected by studying the repeated evolution of small body size in reptiles
The island rule is a phenomenon where animals that get isolated on islands often evolve to be bigger or smaller than their mainland ancestors. Throughout history, island dwarfism has played out on islands across the world with evidence in the fossil record of miniature elephants, hobbit-sized humans (Homo floresiensis), and tiny deer that demonstrate this miniaturization can happen in as little as 6000 years of separation from the mainland. We understand now that getting stuck on islands not only affects body size but also life-history traits such as growth rate, reproduction, and maybe even lifespan. These life-history traits, like many human and animal traits, are complex such that they are defined by both the environment and many genes that work together. While hypotheses related to resource (like food) limitation on islands may explain why island dwarfism happens, the molecular mechanisms (the genes, hormones, cell signaling) determine how island dwarfism happens and how complex life history traits are entwined.
The beauty of this research is that nature has already conducted the experiment for us, many times. Animals get stuck on islands and over many generations they evolve to adapt to their new environment, often changing their body size. We harness the power of one of these natural experiments where three species of reptiles (two snakes and a lizard) have each independently evolved small body size on the California Channel Islands relative to populations on the mainland California, in contrast to two species of lizards that did not diminish body size when isolated on the islands.
We will integrate data across multiple levels of biological organization, and quantify the relationship between physiology and life-history traits in natural populations. Using mark-recapture and field ultrasound alongside molecular assays we aim to define relationships among molecular regulators and body size, growth, and reproduction (a) among individuals within each population, (b) between dwarf & non-dwarf populations, and (c) between species that have independently evolved island dwarfism.
We will quantify divergence in cellular physiology and intracellular signaling using reptile cell culture to define the relative cell growth in reptiles. We will use the cell lines to conduct common garden cell culture experiments to test whether cell lines derived from mainland versus island dwarf individuals have diverged in either their response to endocrine regulators, or in their response to nutrient environments.
We will evaluate genetic divergence of molecular networks among island and mainland populations using whole genome sequencing data to test if repeated occurrences of insular dwarfism are convergent at the level of the genetic divergence in specific nodes of molecular network.
The integration of molecular data on the genetics, the cell metabolism, and the hormones produced in the animals into statistical models will further our understanding of their relationships to life history traits such as growth rate, body size and reproductive variables. In the process of conducting the research, novel tools will be developed to investigate the genetics and hormone physiology of reptiles that will also be useful for understanding the health of natural and zoo populations to aid in conservation and agriculture. These research findings will further our understanding of how genes and environment determine complex traits, and more specifically identify mechanisms that are shared across animal species to regulate body size and reproduction in natural populations.
Our Journey So Far
Amanda Sparkman and Tonia Schwartz find incredible diversity in the IGF1 protein sequence among reptiles while PhD students at Iowa State University, unknowing initiating a longterm collaboration
Dr. Amanda Sparkman, as a new professor at Westmont College initiates long-term mark-recapture studies of the reptiles on the Channel Islands.