Evolution des Polymorphismus bei Bryozoa

1) Wider research context / theoretical framework Division of labor is thought to increase organismal
efficiency. Thus, it is often considered a key factor in the evolution of increased size and complexity. It is most
striking in colonial organisms that exhibit polymorphism (morphological specialization of colony members).
Curiously, many colonial organisms either lack polymorphism or have secondarily lost it. 2)
Hypotheses/research questions /objectives We will investigate four questions. 1) Are polymorphic lineages
more successful in terms of species richness and diversification rate? 2) What factors promote the evolution
or loss of polymorphism? Previous hypotheses suggest that environmental stability, size, and
compartmentalization of colony modules may be important. 3) Does polymorph morphology influence
extinction risk? 4) Do developmental biases (trait relationships) quickly breakdown during the evolution of
polymorphism? 3) Approach/methods Cheilostome bryozoans will be as a model organism due to the wide
range of polymorphism they exhibit, and their rich fossil record. To investigate whether polymorphism is
linked to increased diversification rates, we will construct a database of cheilostome traits from the literature
and museum collections. Using this data, we will quantify the impact of polymorphism on species success
using a series of state-speciation-exitinction models and multi-trait-dependent extinction models. We will
then investigate four hypotheses about which factors promote the evolution of polymorphism. First we will
test whether environmental stability is correlated with degree of polymorphism as predicted by the ergonomic
hypothesis. Then, we will run several phylogenetic generalized least squares analyses to determine if degree
of polymorphism is linked to increased colony size, the variability of colony modules, or degree of
compartmentalization between modules. Next we will investigate the phenotypic evolution of one type of
polymorph, the avicularium. First we will determine how many times avicularia have evolved, and then we will
measure avicularium morphology in museum specimens. Then we will test which model of phenotypic
evolution fits our data. Finally, we will test whether lineages with more extreme avicularium morphologies are
more extinction prone using PyRate software. Lastly, we will investigate whether developmental biases are
conserved in polymorph evolution. Using modern and fossil specimens, we will calculate G matrices for
homologous traits in autozooids and avicularia. This will reveal whether developmental biases are conserved
within/across lineages, and whether developmental biases are impacted by increasing morphological
integration. 4) Level of originality / innovation This proposal combines phylogenetics with morphology, using
modern and fossil species to investigate a range of hypotheses on the evolution of polymorphism. 5) Primary
researchers involved Dr. Carolann Schack and Dr. Andrei Ostrovski