David Reznick: UC Riverside Department of Biology

An unanswered question in biology is “how do complex traits evolve?”. This question endures as an area of controversy because of a paucity of empirical evidence and because the process unfolds on a time scale that is far longer than human experience. I am developing a model system for the evolution of complexity by studying the evolution of the placenta in the fish subfamily Poeciliinae. This group of fish offers a unique opportunity to study the evolution of complexity because placental adaptation exhibits: 1) dynamic variation: placentas appear to have evolved five or more times in the family, 2) serial variation: in several cases, closely related species exhibit either no placentas, intermediate stages, or highly developed placentas, and 3) quantitative variation: an objective criterion for pre- versus post-fertilization maternal provisioning exists which provides an index of placental performance. Furthermore, these fish are readily reared and bred in captivity, are easily studied in nature, and have an excellent prior history as subjects in laboratory and field studies. Evaluating the evolution of complexity demands integrated studies at different levels of biological organization. I envision the ongoing research as creating a template that will facilitate such work because it will define independent origins of placentas and groups of closely related species that either do not have a placenta or have a placenta in an intermediate stage of development. These sets of species represent the likely sequence of events associated with the evolution of the placenta and become the targets of further study.
I am my collaborators are using a combination of molecular and morphological systematics to define relationships within the subfamily and the relation of the subfamily to the remainder of its order. We are quantifying the life histories of these fish so that we can combine life history and phylogeny data, then apply statistical methods that will allow us to infer the patterns of evolution of life histories in the subfamily. We will also use these methods to develop hypotheses for how and why the placenta evolved. Finally, we are executing a series of laboratory experiments that test predictions and assumptions derived from recently developed theory for the evolution of placentas.
http://www.bec.ucla.edu/papers/Reznick_1-24-05.pdf