Kinship and the evolution of social behaviours in the sea

The Contribution of Clonality to Population Genetic Structure in the Sea Anemone, Diadumene lineata

Ecological and evolutionary processes differ depending on how genetic diversity is organized in space. For clonal organisms, the organization of both genetic and genotypic diversity can influence the fitness effects of competition, the mating system, and reproductive mode, which are key drivers of life cycle evolution. Understanding how individual reproductive behavior contributes to population genetic structure is essential for disentangling these forces, particularly in species with complex and plastic life cycles. The widespread sea anemone, Diadumene lineata, exhibits temperature-dependent fission, which contributes to predictable variation in clonal rate along the Atlantic coast of the United States, part of its non-native range. Because warmer conditions lead to higher rates of clonality, we expected to find lower genotypic and genetic diversity in lower versus higher latitude populations. We developed primers for 11 microsatellite loci and genotyped 207 anemones collected from 8 sites ranging from Florida to Massachusetts. We found clonal influence at all sites, and as predicted, the largest clones were found at lower latitude sites. We also found genetic signatures of sex in the parts of the range where gametogenesis is most common. Evidence of sex outside the native range is novel for this species and provides insights into the dynamics of this successful invader. Our findings also illustrate challenges that partially clonal taxa pose for eco-evolutionary studies, such as difficulty sampling statistically robust numbers of genets and interpretating common population genetic metrics. For example, we found high among-locus variation in FIS, which makes the meaning of mean multilocus FIS unclear.

Inbreeding shapes the evolution of marine invertebrates

Inbreeding is a potent evolutionary force shaping the distribution of genetic variation within and among populations of plants and animals. Yet, our understanding of the forces shaping the expression and evolution of nonrandom mating in general, and inbreeding in particular, remains remarkably incomplete. Most research on plant mating systems focuses on self-fertilization and its consequences for automatic selection, inbreeding depression, purging, and reproductive assurance, whereas studies of animal mating systems have often assumed that inbreeding is rare, and that natural selection favors traits that promote outbreeding. Given that many sessile and sedentary marine invertebrates and marine macroalgae share key life history features with seed plants (e.g., low mobility, modular construction, and the release of gametes into the environment), their mating systems may be similar. Here, we show that published estimates of inbreeding coefficients (F_IS ) for sessile and sedentary marine organisms are similar and at least as high as noted in terrestrial seed plants. We also found that variation in F_IS within invertebrates is related to the potential to self-fertilize, disperse, and choose mates. The similarity of F_IS for these organismal groups suggests that inbreeding could play a larger role in the evolution of sessile and sedentary marine organisms than is currently recognized. Specifically, associations between traits of marine invertebrates and F_IS suggest that inbreeding could drive evolutionary transitions between hermaphroditism and separate sexes, direct development and multiphasic life cycles, and external and internal fertilization.

Kin Discrimination in Protists: From Many Cells to Single Cells and Backwards

During four decades (1960-1990s), the conceptualization and experimental design of studies in kin recognition relied on work with multicellular eukaryotes, particularly Unikonta (including invertebrates and vertebrates) and some Bikonta (including plants). This pioneering research had an animal behavior approach. During the 2000s, work on taxa-, clone- and kin-discrimination and recognition in protists produced genetic and molecular evidence that unicellular organisms (e.g. Saccharomyces, Dictyostelium, Polysphondylium, Tetrahymena, Entamoeba and Plasmodium) could distinguish between same (self or clone) and different (diverse clones), as well as among conspecifics of close or distant genetic relatedness. Here, we discuss some of the research on the genetics of kin discrimination/recognition and highlight the scientific progress made by switching emphasis from investigating multicellular to unicellular systems (and backwards). We document how studies with protists are helping us to understand the microscopic, cellular origins and evolution of the mechanisms of kin discrimination/recognition and their significance for the advent of multicellularity. We emphasize that because protists are among the most ancient organisms on Earth, belong to multiple taxonomic groups and occupy all environments, they can be central to reexamining traditional hypotheses in the field of kin recognition, reformulating concepts, and generating new knowledge.

Evidence of Taxa-, Clone-, and Kin-discrimination in Protists: Ecological and Evolutionary Implications

Unicellular eukaryotes, or protists, are among the most ancient organisms on Earth. Protists belong to multiple taxonomic groups; they are widely distributed geographically and in all environments. Their ability to discriminate among con- and heterospecifics has been documented during the past decade. Here we discuss exemplar cases of taxa-, clone-, and possible kin-discrimination in five major lineages: Mycetozoa (Dictyostelium, Polysphondylium), Dikarya (Saccharomyces), Ciliophora (Tetrahymena), Apicomplexa (Plasmodium) and Archamoebae (Entamoeba). We summarize the proposed genetic mechanisms involved in discrimination-mediated aggregation (self versus different), including the csA, FLO and trg (formerly lag) genes, and the Proliferation Activation Factors (PAFs), which facilitate clustering in some protistan taxa. We caution about the experimental challenges intrinsic to studying recognition in protists, and highlight the opportunities for exploring the ecology and evolution of complex forms of cell-cell communication, including social behavior, in a polyphyletic, still superficially understood group of organisms. Because unicellular eukaryotes are the evolutionary precursors of multicellular life, we infer that their mechanisms of taxa-, clone-, and possible kin-discrimination gave origin to the complex diversification and sophistication of traits associated with species and kin recognition in plants, fungi, invertebrates and vertebrates.

Why is eusociality an almost exclusively terrestrial phenomenon?

Eusociality has evolved multiple times across diverse terrestrial taxa, and eusocial species fundamentally shape many terrestrial ecosystems. However, eusocial species are far less common and have much less ecological impact, in aquatic than terrestrial environments. Here, we offer a potential explanation for these observations. It appears that a precondition for the evolution of eusociality is the defence and repeated feeding of offspring in a nest or other protected cavity, and so eusocial species must be able to exploit a predator-safe, long-lasting (multigenerational) expandable nest. We argue that a range of factors mean that opportunities for such nests are much more widespread and the advantages more compelling in terrestrial than aquatic ecosystems.