Nonclonal coloniality: Genetically chimeric colonies through fusion of sexually produced polyps in the hydrozoanEctopleura larynx

Abstract

Hydrozoans typically develop colonies through asexual budding of polyps. Although colonies of Ectopleura are similar to other hydrozoans in that they consist of multiple polyps physically connected through continuous epithelia and shared gastrovascular cavity, Ectopleura larynx does not asexually bud polyps indeterminately. Instead, after an initial phase of limited budding in a young colony, E. larynx achieves its large colony size through the aggregation and fusion of sexually (nonclonally) produced polyps. The apparent chimerism within a physiologically integrated colony presents a potential source of conflict between distinct genetic lineages, which may vary in their ability to access the germline. To determine the extent to which the potential for genetic conflict exists, we characterized the types of genetic relationships between polyps within colonies, using a RAD‐Seq approach. Our results indicate that E. larynx colonies are indeed comprised of polyps that are clones and sexually reproduced siblings and offspring, consistent with their life history. In addition, we found that colonies also contain polyps that are genetically unrelated, and that estimates of genome‐wide relatedness suggests a potential for conflict within a colony. Taken together, our data suggest that there are distinct categories of relationships in colonies of E. larynx, likely achieved through a range of processes including budding, regeneration, and fusion of progeny and unrelated polyps, with the possibility for a genetic conflict resolution mechanism. Together these processes contribute to the reevolution of the ecologically important trait of coloniality in E. larynx.

Phenotypic plasticity rather than genotype drives reproductive choices in Hydra populations

“…To describe population genetic structure in H. oligactis we employed restriction‐site associated DNA sequencing (RAD‐Seq, Andrews et al, 2016; Baird et al, 2008; Davey & Blaxter, 2010). The use of RAD‐Seq in population genomics is becoming increasingly popular and it has been successfully applied in cnidarians to infer phylogeographical patterns in sea anemones (Reitzel et al, 2013), chimerism among colonial hydrozoans (Chang et al, 2018), and other phenomena, such as identification of introgressive hybridization (Combosch & Vollmer, 2015) and sex determination (Pratlong et al, 2017) in corals. Specifically, we aimed to obtain detailed genetic data on population structure of this model system and thus to obtain more insight on the evolution of distinct reproductive strategies.…”

Frizzled3 expression and colony development in hydractiniid hydrozoans

“…A close relative of Hydra, Ectopleura larynx is technically colonial, but their colonies form primarily from fusion of sexually reproduced juvenile polyps (Nawrocki and Cartwright, 2012;Chang et al, 2018). Unlike Hydra, Ectopleura retains colonyspecific tissue aboral to the polyp that it uses to build the chimeric colony (Nawrocki and Cartwright, 2012).…”

Coloniality, clonality, and modularity in animals: The elephant in the room

“…Though aggressive rejection can put the colony at risk, the cost is balanced by the potential benefit of competition for space. In some cases, colony formation occurs by the fusion of nonclonal (sexually derived) individuals such as in the case of some hydrozoans (Chang, Orive, & Cartwright, 2018; Nawrocki & Cartwright, 2012).…”