Abstract
The evolution of trait variation among populations of animals is difficult to study due to the many overlapping genetic and environmental influences that control phenotypic expression. But, in a group of animals called bryozoans, it is possible to isolate genetic contributions to phenotypic variation, due to the modular nature of bryozoan colonies. Each bryozoan colony represents a snapshot of the phenotypes that correspond to a single genotype, which can be summarized as a phenotypic distribution. We test whether these phenotypic distributions are evolvable across a generation of colonies in two sister species of the bryozoan Stylopoma, grown and bred in a common garden breeding experiment. We find that components of phenotypic distributions, specifically median trait values of colony members, are evolvable between generations of colonies. Furthermore, this evolvability has macroevolutionary importance because it correlates with the morphological distance between these two species. Because parts of the phenotypic distributions are evolvable, and this evolvability corresponds to evolutionary divergence between species, we infer that these distributions can shift and change shape over macroevolutionary timescales. Such changes to phenotypic distributions across many generations of colonies may underpin the emergence of colony-level traits, like division of labor in colonies.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
email: sarah.leventhal{at}colorado.edu
Methods updated to focus on evolvability rather than heritability; Results section revised to show results from revised methodology; Figure 2 revised to reflect new evolvability analyses; Figure 3 removed; new tables included to show evolvability values; Discussion section revised to complement new results section