Experimental design
How colonial animals evolve
Sci Adv, Jan 8, 2020; DOI: 10.1126/sciadv.aaw9530

Here, we use colonies that were grown in a previous breeding experiment. The specimens were used previously to tell whether skeletons are enough to tell species apart (28), whether selection or random change drove differentiation between species (29), and a phylogenetic estimate of the tempo of speciation (32). The scientific versatility of these specimens is due to the controlled way that they were grown and bred. From wild-caught colonies, two generations of colonies with known maternity were born. Furthermore, offspring colonies grown in a common garden experiment, allowing generations of scientists to tease apart the complex processes involved in phenotypic macroevolution.

The experimental design was modified from one developed by Maturo (42). This experiment was designed to strictly limit the number of possible paternal colonies that could fertilize maternal colonies and then to use the limited dispersal ability of Stylopoma larvae to know the maternal colonies that gave rise to offspring colonies. The experiment was conducted at the Smithsonian field station just east of San Blas Point on the Caribbean coast of the Republic of Panamá. Using this field station allowed offspring colonies to be grown in a common garden with a shared environment that allows the quantification of the impact of the environment on phenotypic expression. Bryozoans were collected from one to five sites, depending on species, between Holandes Cays and Isla Grande in depths of <1 to >40 m and were maintained in running sea water for usually no more than 1 day before use. Maternal colonies of two Stylopoma species were collected from the localities shown on this map. Colonies were collected in the 1980s from the following localities: Isla Grande, the west and eastern shores of Ulaksukan, West Palina, and southwest and northeast Aguadargana.

As described in Jackson and Cheetham (28) and Cheetham et al. (29), corals with Stylopoma colonies containing embryos were collected from these Caribbean localities. These coral substrata were cleaned of other organisms and isolated in transport chambers made from plastic food containers with sides cut open and replaced by plankton nets. Filtered sea water was run through the top of the chambers and exited through the nets in the walls. A single maternal colony was kept in each container under a piece of bare coral for daughter colonies to settle. After 5 to 10 days, the coral substratum with newly settled F1 colonies were removed and attached to concrete blocks on a sandy bottom about −0.5 m below low water at the Smithsonian field station just east of San Blas Point on the Caribbean coast of the Republic of Panamá (Fig. 4). Every month, the condition of the colonies was assessed, and the colonies and substrata were cleaned of other organisms.