Evolution and Environment of Tropical American Cupuladriid Bryozoa

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

ABSTRACT Evolution and Environment of Tropical American Cupuladriid Bryozoa Jeremy Jackson, Scripps Institute of Oceanography EAR-0345471 PIs will determine the extent to which major environmental change in the Caribbean Sea has driven the macroevolutionary patterns of cupuladriid bryozoans over the past 15 million years. Cupuladriids are small, free-living colonial animals whose skeletons are among the most abundant and well-preserved fossils from tropical America. They vary greatly in their life histories, from entirely sexual to almost exclusively asexual species, and these differences are well preserved in the budding patterns and shapes of colonies. Cupuladriids also record changes in the mean annual range of temperature and total productivity in the environment through seasonal variations in size of their modular living chambers called zooids. Thus we have the opportunity to precisely observe major evolutionary and environmental changes from the same fossils. Preliminary work suggests that the Caribbean closely resembled the tropical eastern Pacific until about 10 million years ago when there was still strong oceanographic mixing between the Atlantic and Pacific through the Panamanian Strait. At that time, seasonal upwelling, temperature fluctuations, and high biological productivity occurred in both oceans. Then, as the Isthmus rose and connections between the oceans diminished, the Caribbean slowly became more stable with little upwelling and low seasonal variations and productivity. There is also evidence that the cupuladriid bryozoans shifted from predominantly asexual reproduction and dominance of the genus Discoporella to predominantly sexual reproduction and dominance by the genus Cupuladria - conditions that are observed between the eastern Pacific and Caribbean today. PIs will test all these patterns using abundant, replicate collections in both space and time to document in great detail the changes in environmental conditions and corresponding changes in bryozoan life histories and taxonomic composition. By using the same samples for measures of both environment and biological change they will be able to reconstruct the relations between evolution and environment with high statistical confidence, thereby avoiding the broad-brush approach and lack of precision that have plagued earlier studies of this nature.