Asexual propagation in the marine bryozoan Cupuladria exfragminis

Abstract

Colonies of the free-living bryozoan Cupuladria exfragminis [Herrera-Cubilla, A., Dick, M.H., Sanner, J., Jackson, J.B.C., 2006. Neogene Cupuladriidae of Tropical America. I:. Taxonomy of Recent Cupuladria from opposite sides of the Isthmus of Panama. Journal of Paleontology. 80, 245–263.] from the Gulf of Panama are observed to separate into viable fragments without external force. The process, termed autofragmentation, involves the development of distinctive morphologies designed to assist in colony division. Culturing C. exfragminis shows that fragments that are a consequence of autofragmentation are significantly better able to regenerate than fragments originating from mechanical fragmentation. However, the relative importance of auto- versus mechanical fragmentation in natural populations remains unknown. Autofragmentation in C. exfragminis is found to be stimulated by cooling waters, and analysis of growth in natural populations demonstrates that colonies undergo periodic fragmentation coincident with lowered water temperatures during seasonal upwelling in the Gulf of Panama. These observations suggest that C. exfragminis uses the drop in temperature that occurs during upwelling as a cue to indicate times of increased food availability which may assist in the successful regeneration of fragments. These results are discussed in the context of the morphological, ecological and evolutionary significance of autofragmentation as a method of asexual propagation in cupuladriids.