Fossil brooders and modern reproductive strategies

The proposed research will comprise the first comparative morphological and anatomical studies of the earliest and subsequent stages in the evolution of parental care in fossil and Recent Cheilostomata (Bryozoa), one of the dominant groups of colonial marine invertebrates. The aim of the project is to reconstruct the sequence of evolutionary events leading to brooding behaviour and associated structures and resulting in different reproductive patterns. A complex approach will be employed, using both light and scanning electron microscopy. The order Cheilostomata originated in the latest Jurassic and underwent explosive diversification, supposedly triggered by retention of the embryo and larva in the Late Cretaceous. Hence, possible factors promoting retention might have included novel structures and behaviour. The following hypotheses will be tested: (1) brooding originated several times in cheilostome history, and the earliest brood chambers may have been constructed of modified spines; (2) the evolution of parental care may have triggered new reproductive patterns since brooding could potentially have induced variations in oogenesis; further, (3) extra-embryonal placental nutrition in brood chambers may have evolved independently in some groups; and (4) a transition from external to internal brooding occurred in other groups. All of these developments would have influenced the reproductive biology of cheilostomes, contributing to their remarkable radiation and evolutionary success: this clade comprises about 75% of living bryozoans. The proposed project will be combined with parallel studies of frontal body-wall evolution to create an integrated picture of the phylogeny of Cheilostomata. The morphological data on reproduction and brooding structures will be added to the list of cheilostome characters and character-states being developed for bryozoan classification based on cladistic analysis. The results of the project will have particular relevance to the cheilostome volume of the Treatise on Invertebrate Paleontology Series (currently in preparation), and will provide additional keys for investigating bryozoan evolution and biodiversity in particular, and for understanding reproductive ecology in clonal sessile organisms in general.