The association of coloniality with parental care of embryos

Abstract

Many colonial marine animals care for embryos by brooding them on or in their bodies. For brooding to occur, features of the animals must allow it, and brooding must be at least as advantageous as releasing gametes or zygotes. Shared features of diverse colonial brooders are suspension feeding and a body composed of small modules that are indefinitely repeated and can function semi‐autonomously, such as polyps or zooids. Suspension feeding permits capture of sperm for fertilization of ova that are retained by the parent. Distribution of broods among numerous small polyps, zooids, or other small modules facilitates supply of oxygen to embryos that are retained and protected by the parent. Brooding increases survival of offspring, controls dispersal, and can provide other developmental advantages. Colonial ascidians, pterobranch hemichordates, and entoprocts brood; most bryozoans and many colonial cnidarians brood. An unanswered question is why so many colonial anthozoans do not brood. Sponges share with colonies capacities for capturing sperm and separating numerous retained embryos yet many do not brood. Hypotheses for nonbrooding by colonies and sponges necessarily must apply to particular taxa. Few have been tested.

Reproductive and environmental traits explain the variation in egg size among Medusozoa (Cnidaria)

“…This is consistent with the view that the cost of brooding is associated with oxygen provision [81], as smaller and more spaced embryos facilitate oxygen supply (e.g. [82]), and in the case of modular colonies, could favour the occurrence of brooding [83].These different patterns would have consequences from basic physiology (e.g. energetic demand of the different reproductive system and trade off with other systems) to species interaction (e.g.…”

Evolution of animal coloniality and modularity: Emerging themes

“…Several of these features of animal colonies are also common to plants. These parallels, as well as common challenges due to their sessile and modular architecture—for example, how to achieve fertilization or how to optimize sex allocation—allow us to compare theoretical frameworks developed to respond similar evolutionary problems, and as a result may allow us to articulate a more comprehensive understanding of how modular organisms evolve (Dias et al, 2021, This issue; Hiebert et al, 2021, This issue; Hughes, 2005; Strathmann, 2021, This issue)⁠.…”

“…His comparative study mainly focuses on benthic and sessile colonial animals because of the intrinsic functional differences with pelagic colonies (e.g., particular adaptations resulting from distinct susceptibilities to water currents among benthic and pelagic colonies). As a result, R. Strathmann raises many questions and hypotheses about the consequence of brooding, or in some cases not‐brooding, for the life history and reproduction of the different taxa (Strathmann, 2021, This issue)⁠.Unsatisfied with the all the attention given to genetic relatedness and inclusive fitness as major evolutionary drivers for the evolution of polymorphism in eusocial insects, C. Simpson—in the fourth article (research article)—develops a new theoretical framework to propose a new hypothesis that he terms the “life‐history ratchet.” The focus of this hypothesis is placed on the evolution of new body types (i.e., polymorph types) as a way to release colonies from ancestral life history strategy constraints, generated by the reduced numbers of body types. Mechanisms of colonial development Dias et al (2021, This issue)⁠ (research article) contribute with an elegant ecological study and experimental transplantation in a marina; they document phenotypic responses of bryozoan colonies to heteregeneous environments that affect overall morphology of the colonies, as well as the composition of polymorphic zooids in the colony, demonstrating a trade‐off between clonal growth and defense (density of avicularia).By comparing developmental mechanisms of budding, Alié et al (2021, This issue)⁠ (review) do a superb job to highlight the different cells and tissues that have been coopted in budding in the different groups of ascidians, suggesting a highly plastic nature of cell and tissues in this phylum. They raise the importance of tunicate diverse mechanisms of budding, as a goldmine to study evolutionary plastic developmental traits.By using positive selection tests on orthologous genes, followed by independent gene tree analyses, using several transcriptomes of entoprocts, bryozoans, and phoronids, Santagata (2021, This issue)⁠ (research article) identifies a pool of genes potentially related to the convergent evolution of coloniality among entoprocts and bryozoans, and probably also the “colonial‐like” (highly aggregate) phoronids. Signaling in colony regeneration and patterning In a laboratory experimental setting, Luz et al (2021, This issue)⁠ (research article) report predominant effects of fragment size in the process of regeneration in a group of invasive colonial dendrophylliid corals and show that Wnt and FGF—signaling pathways known to function in regeneration—are expressed during whole‐body regeneration in Tubastraea coccinea , a calcified anthozoan species fostered by the authors as a laboratory model.Cartwright et al (2021, This issue)⁠ (review) review variation and plasticity of colony forms in the hydrozoans and hypothesize that Wnt signaling may play an important role in colony patterning and morphology. From unicellular to multicellular colonies Cellular behaviors and developmental mechanisms that regulate the formation of colonies in aggregative bacteria have evolved multiple times.…”

“…His comparative study mainly focuses on benthic and sessile colonial animals because of the intrinsic functional differences with pelagic colonies (e.g., particular adaptations resulting from distinct susceptibilities to water currents among benthic and pelagic colonies). As a result, R. Strathmann raises many questions and hypotheses about the consequence of brooding, or in some cases not‐brooding, for the life history and reproduction of the different taxa (Strathmann, 2021, This issue)⁠.…”

An ecological driver for the macroevolution of morphological polymorphism within colonial invertebrates

“…The colony, formed by large numbers of asexually produced organisms, has the possibility to take on different patterns of energetic investment than individual members can which provides species that evolve colonial growth with potential new ecological opportunities (Buss, 1979). Colonial organisms occur in many phyla, and despite the differences in their phylum‐specific body plans and inherent constraints of life‐histories, as colonies, they share many major features of life‐history and ecology (Buss, 1979; Jackson, 1986a; Jackson & Coates, 1986), including a tendency for colonial species of all phyla to brood larvae (Strathmann, 2020).…”