Birthday at Bowfin's.

http://deepblue.lib.umich.edu/bitstream/2027.42/52760/4/1192.pd

Kin Discrimination in Dictyostelium Social Amoebae

Presentation delivered at the symposium Evidence of Taxa, Clone, and Kin Discrimination in Protists: Ecological and Evolutionary Implications, VII European Congress of Protistology, University of Seville, 5–10 September 2015, Seville Spain. Evolved cooperation is stable only when the benefactor is compensated, either directly or through its relatives. Social amoebae cooperate by forming a mobile multicellular body in which, about 20% of participants ultimately die to form a stalk. This benefits the remaining individuals that become hardy spores at the top of the stalk, together making up the fruiting body. In studied species with stalked migration, P. violaceum, D. purpureum, and D. giganteum, sorting based on clone identity occurs in laboratory mixes, maintaining high relatedness within the fruiting bodies. D. discoideum has unstalked migration, where cell fate is not fixed until the slug forms a fruiting body. Laboratory mixes show some degree of both spatial and genotype-based sorting, yet most laboratory fruiting bodies remain chimeric. However, wild fruiting bodies are made up mostly of clonemates. A genetic mechanism for sorting is likely to be cell adhesion genes tgrB1 and tgrC1, which bind to each other. They are highly variable, as expected for a kin discrimination gene. It is a puzzle that these genes do not cause stronger discrimination between mixed wild clones, but laboratory conditions or strong sorting early in the social stage diminished by later slug fusion could be explanations

The distribution of Great Lakes shore plants around inland lakes.

http://deepblue.lib.umich.edu/bitstream/2027.42/52667/1/1100.pd

Ancient bacteria–amoeba relationships and pathogenic animal bacteria

Long before bacteria infected humans, they infected amoebas, which remain a potentially important reservoir for human disease. Diverse soil amoebas including Dictyostelium and Acanthamoeba can host intracellular bacteria. Though the internal environment of free-living amoebas is similar in many ways to that of mammalian macrophages, they differ in a number of important ways, including temperature. A new study in PLOS Biology by Taylor-Mulneix et al. demonstrates that Bordetella bronchiseptica has two different gene suites that are activated depending on whether the bacterium finds itself in a hot mammalian or cool amoeba host environment. This study specifically shows that B. bronchiseptica not only inhabits amoebas but can persist and multiply through the social stage of an amoeba host, Dictyostelium discoideum

Privatization and Property in Biology

Organisms evolve to control, preserve, protect and invest in their own bodies. When they do likewise with external resources they privatize those resources and convert them into their own property. Property is a neglected topic in biology, although examples include territories, domiciles and nest structures, food caching, mate guarding, and the resources and partners in mutualisms. Property is important because it represents a solution to the tragedy of the commons; to the extent that an individual exerts long-term control of its property, it can use it prudently, and even invest in it. Resources most worth privatizing are often high in value. To be useful to their owner in the future, they are typically durable and defensible. This may explain why property is relatively rare in animals compared to humans. The lack of institutional property rights in animals also contributes to their rarity, although owner–intruder conventions may represent a simple form of property rights. Resources are often privatized by force or threat of force, but privatization can also be achieved by hiding, by constructing barriers, and by carrying or incorporating the property. Social organisms often have property for two reasons. First, the returns on savings and investments can accrue to relatives, including descendants. Second, social groups can divide tasks among members, so they can simultaneously guard property and forage, for example. Privatization enhances the likelihood that the benefits of cooperation will go to relatives, thus facilitating the evolution of cooperation as in Hamilton\u27s rule or kin selection. Mutualisms often involve exchange of property and privatization of relationships. Privatization ensures the stability of such cooperation. The major transitions in evolution, both fraternal and egalitarian, generally involve the formation of private clubs with something analogous to the nonrivalrous club goods of economics

Fruiting bodies of the social amoeba \u3ci\u3eDictyostelium discoideum\u3c/i\u3e increase spore transport by Drosophila

Background: Many microbial phenotypes are the product of cooperative interactions among cells, but their putative fitness benefits are often not well understood. In the cellular slime mold Dictyostelium discoideum , unicellular amoebae aggregate when starved and form multicellular fruiting bodies in which stress-resistant spores are held aloft by dead stalk cells. Fruiting bodies are thought to be adaptations for dispersing spores to new feeding sites, but this has not been directly tested. Here we experimentally test whether fruiting bodies increase the rate at which spores are acquired by passing invertebrates. Results: Drosophila melanogaster accumulate spores on their surfaces more quickly when exposed to intact fruiting bodies than when exposed to fruiting bodies physically disrupted to dislodge spore masses from stalks. Flies also ingest and excrete spores that still express a red fluorescent protein marker. Conclusions: Multicellular fruiting bodies created by D. discoideum increase the likelihood that invertebrates acquire spores that can then be transported to new feeding sites. These results thus support the long-hypothesized dispersal benefits of altruism in a model system for microbial cooperation

Dictyostelium development shows a novel pattern of evolutionary conservation

von Baer\u27s law states that early stages of animal development are the most conserved. More recent evidence supports a modified hourglass pattern in which an early but somewhat later stage is most conserved. Both patterns have been explained by the relative complexity of either temporal or spatial interactions; the greatest conservation and lowest evolvability occur at the time of the most complex interactions, because these cause larger effects that are harder for selection to alter. This general kind of explanation might apply universally across independent multicellular systems, as supported by the recent finding of the hourglass pattern in plants. We use RNA-seq expression data from the development of the slime mold Dictyostelium to demonstrate that it does not follow either of the two canonical patterns but instead tends to show the strongest conservation and weakest evolvability late in development. We propose that this is consistent with a version of the spatial constraints model, modified for organisms that never achieve a high degree of developmental modularity

Fine-scale spatial ecology drives kin selection relatedness among cooperating amoebae

Cooperation among microbes is important for traits as diverse as antibiotic resistance, pathogen virulence, and sporulation. The evolutionary stability of cooperation against “cheater” mutants depends critically on the extent to which microbes interact with genetically similar individuals. The causes of this genetic social structure in natural microbial systems, however, are unknown. Here, we show that social structure among cooperative Dictyostelium amoebae is driven by the population ecology of colonization, growth, and dispersal acting at spatial scales as small as fruiting bodies themselves. Despite the fact that amoebae disperse while grazing, all it takes to create substantial genetic clonality within multicellular fruiting bodies is a few millimeters distance between the cells colonizing a feeding site. Even adjacent fruiting bodies can consist of different genotypes. Soil populations of amoebae are sparse and patchily distributed at millimeter scales. The fine-scale spatial structure of cells and genotypes can thus account for the otherwise unexplained high genetic uniformity of spores in fruiting bodies from natural substrates. These results show how a full understanding of microbial cooperation requires understanding ecology and social structure at the small spatial scales microbes themselves experience

Sex ratio and gamete size across eastern North America in Dictyostelium discoideum, a social amoeba with three sexes

Theory indicates that numbers of mating types should tend towards infinity or remain at two. The social amoeba, Dictyostelium discoideum, however, has three mating types. It is therefore a mystery how this species has broken the threshold of two mating types, but has not increased towards a much higher number. Frequency-dependent selection on rare types in combination with isogamy, a form of reproduction involving gametes similar in size, could explain the evolution of multiple mating types in this system. Other factors, such as drift, may be preventing the evolution of more than three. We first looked for evidence of isogamy by measuring gamete size associated with each type. We found no evidence of size dissimilarities between gametes. We then looked for evidence of balancing selection, by examining mating type distributions in natural populations and comparing genetic differentiation at the mating type locus to that at more neutral loci. We found that mating type frequency varied among the three populations we examined, with only one of the three showing an even sex ratio, which does not support balancing selection. However, we found more population structure at neutral loci than the mating type locus, suggesting that the three mating types are indeed maintained at intermediate frequencies by balancing selection. Overall, the data are consistent with balancing selection acting on D. discoideum mating types, but with a sufficiently weak rare sex advantage to allow for drift, a potential explanation for why these amoebae have only three mating types

Limits to the spread of an obligate social cheater in the social amoeba Dictyostelium discoideum

Cooperation is widespread across life, but its existence can be threatened by exploitation. Social cheaters can be obligate, incapable of contributing to a necessary function, so that spread of the cheater leads to loss of the function. In the social amoeba Dictyostelium discoideum, obligate social cheaters cannot become dead stalk cells that lift spores up for dispersal, but instead depend on forming chimeras with fully functional altruistic individuals for forming a stalk. Obligate cheaters in D. discoideum are known to pay the cost of being unable to form fruiting bodies on their own. In this study we discovered that there are two additional costs that can apply to obligate cheaters. Even when there are wild-type cells to parasitize, the chimeric fruiting bodies that result have shorter stalks that are disadvantaged in spore dispersal. Furthermore, we found that obligate cheaters were overrepresented among spore cells in chimeras only when they were at low frequencies. Failure to develop into viable fruiting bodies on their own, negative frequency-dependent cheating, and shorter fruiting bodies represent three limits on obligate social cheating so it is not surprising that obligate cheaters have not been found in nature