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

Abstract

Nearly half of the animal phyla contain species that propagate asexually via agametic reproduction, often forming colonies of genetically identical modules, that is, ramets, zooids, or polyps. Clonal reproduction, colony formation, and modular organization have important consequences for many aspects of organismal biology. Theories in ecology, evolution, and development are often based on unitary and, mainly, strictly sexually reproducing organisms, and though colonial animals dominate many marine ecosystems and habitats, recognized concepts for the study of clonal species are often lacking. In this review, we present an overview of the study of colonial and clonal animals, from the historic interests in this subject to modern research in a range of topics, including immunology, stem cell biology, aging, biogeography, and ecology. We attempt to portray the fundamental questions lying behind the biology of colonial animals, focusing on how colonial animals challenge several dogmas in biology as well as the remaining puzzles still to be answered, of which there are many.

Differential Gene Expression Between Polymorphic Zooids of the Marine BryozoanBugulina stolonifera

“…Ultimately, comparing the genetic processes behind establishing division of labor in bryozoans to those in other colonial taxa may help reveal clues about the enigmatic evolution of polymorphism in some colonial animals (Hiebert et al 2020) and more broadly, the processes involved in the evolution of colonial animals in general (Simpson et al 2020).…”

“…This includes the transition from single celled to multicellular organisms, from asexual populations to sexual populations, and from solitary organismal associations to colonial organisms (Szathmáry and Smith 1995;Simpson 2012, Hiebert et al 2020. Of all the metazoan phyla with colonial animals, only the Cnidaria, Bryozoa, and Chordata have representatives with division of labor among asexually budded and physiologically connected colony modules, or zooids.…”

From the individual to the colony: Marine invertebrates as models to understand levels of biological organization

“…This origin story for colonies—one of increasing complexity and interconnection between originally clonal animals—is treated as an assumption, often being used to define colonial organisms themselves. However, there is no strong evidence that incomplete cloning underlies every evolutionary transition to coloniality (Hiebert et al 2020, in this issue).…”

Evolution of animal coloniality and modularity: Emerging themes

“…As the first and opening article (review) for the special issue, three instructors (L. Hiebert, C. Simpson, and S. Tiozzo) of the Evolution of Coloniality and Modularity course, which took place at the Centre for Marine Biology of University of São Paulo (CEBIMar/USP), compile a superb recount of concepts about animal coloniality in historical scholarly literature, and discuss implications of animal coloniality in a number of active research topics in biology, such as regeneration, aging, functional specialization (i.e., polymorphism), phenotypic plasticity, ecological dynamics, or allorecognition (Hiebert et al, 2021, This issue)⁠.…”