Colony Fusion Research Articles

Intracolony relatedness and polydomy in the Australian meat ant, Iridomyrmex purpureus

In polydomous ants, individuals belonging to a single colony occupy a variable number of neighbouring nests. Polydomy is frequently associated with polygyny and species are often both facultatively polydomous and facultatively polygynous. In this study we test the generality of this association by investigating the genetic and spatial structure of polydomous colonies of Iridomyrmex purpureus in New South Wales, Australia. Genetic analysis of 15 colonies revealed high relatedness within all but one of the colonies, indicating that the workers are mostly produced by one, singly inseminated queen. Polydomy in this population therefore is not associated with polygyny. Intriguingly, our behavioural data suggests that the colony with low within-colony relatedness had been recently formed by colony fusion. While genotypes were not distributed homogenously throughout this newly formed colony, there was an obvious exchange of genotypes between the nests of the two former colonies. During 2 years of field observations in which we observed 140 colonies comprising over 1000 nests, we observed colony fusion only twice. We discuss these findings in relation to the current theories on the relationship between polydomy and polygyny.

Colony structure and sex allocation ratios in the ant Temnothorax crassispinus

We analyzed the impact of ecological parameters, such as nest density and nest site availability, on colony organization and investment patterns in two populations of the ant Temnothorax crassispinus, a parapatric sibling species of the well-studied T. nylanderi (Temnothorax was until recently referred to as Leptothorax (Myrafant); Bolton, 1993). As in T. nylanderi, sex allocation ratios were strongly associated with total sexual reproduction, i. e., nests with large sexual investment produced mainly female sexuals. Furthermore, nest site quality affected sex allocation ratios, with colonies from ephemeral nest sites producing a more male-biased sex allocation ratio than colonies from sturdy nest sites. In contrast to T. nylanderi, workers in colonies of T. crassispinus were mostly fullsisters both in a dense and a sparsely populated area, suggesting that colony fusion and colony usurpation are rare in this species. In addition, the presence of a queen in a local nest unit strongly influenced sex ratio decisions, in that these nests raised a more male biased allocation ratio compared to queenless nests. This also suggests that colony structure is more stable in T. crassispinus than in T. nylanderi. We conclude that sibling species, though often very similar in their morphology and ecological requirements, may nevertheless react very differently to ecological variation.

GETTING BIGGER FASTER: MEDIATION OF SIZE-SPECIFIC MORTALITY VIA FUSION IN JUVENILE CORAL TRANSPLANTS

Size-specific mortality can determine whether coral transplants become successfully established in a reef rehabilitation effort. Presented here are results of a study of size-specific mortality in laboratory-cultured transplants, and the mediating effect of fusion on their survival and growth. Culturing seeded colonies for transplantation minimizes impacts to source reefs. This strategy provides an opportunity to enhance survival of a transplanted population by incorporating selected aspects of colonial modular biology, such as fusion, into the culture phase. Despite efforts to develop a completely field-based method, settlement and early survival of juveniles of the scleractinian Pocillopora damicornis were much higher in laboratory aquaria than among those settled on reef substrate, highlighting the difficulty of direct seeding and justifying the higher effort involved in laboratory rearing. Juvenile colonies from four size cohorts (≤3 mm, 3.1–6 mm, 6.1–10 mm, and 10.1–29 mm), outplanted to a reef in August 1997, showed one-year survival of 0%, 2.5%, 16.3%, and 47.5%, respectively, illustrating significant size-specific mortality. Colony fusion resulted in lower 6-mo mortality (unfused colonies: 34.5% ± 0.4%, fused pairs: 14.0% ± 2.5%, fused groups: 8.3% ± 4.8%; means ± 1 se), and chimeras of >2 fused colonies produced polyps faster. Tissue necrosis along fusing colony borders was observed between 8-mo-old colonies. This suggested a rejection response, though colonies fusing prior to this age remained stable for up to one year. A transition matrix revealed that fused colonies showed greater probability of growth to the next size class, while unfused colonies showed higher mortality and stasis. Growth trajectories based on transition probabilities suggested that fused colonies would reach reproductive size much earlier than unfused colonies. To test the hypothesis that larvae aggregatively settle to increase their chances of fusing, settlement patterns were determined in larvae of same- vs. mixed-parent groups. Settled larvae were aggregatively distributed, with no difference in aggregation strength in larvae of same- vs. mixed-parent groups. Results suggest a benefit of fusion to survival and growth within the first eight months in juvenile coral colonies. Fusion could be used as a strategy to obtain larger colonies faster, provided they remain stable over time. Laboratory seeding and rearing of juveniles to 10 mm provides a workable alternative to fragment transplantation in brooding coral species, and similar strategies may also be developed for spawning species.

Chimerism following fusion in a clonal ascidian (Urochordata)

Many marine invertebrates bud vegetatively to produce a modular colony of individuals derived from a single zygote. Fusion of different colonies to produce a genetically composite entity (a chimera) is known from experiments on sponges, hydroids, corals, bryozoans and ascidians – groups which together dominate sessile faunas on marine hard substrates. Random amplified polymorphic DNA–polymerase chain reaction (RAPD–PCR) analysis was applied to individual modules (zooids) dissected from colonies of a colonial ascidian, Diplosoma listerianum (Milne Edwards), to investigate the presence and extent of chimerism. The technique revealed chimerism in wild material. In total, 288 colonies from eight different natural populations were analysed. Chimeric colonies were present in all populations, at frequencies of up to 61%, with up to six different genotypes present in some colonies. Zooids of different genetic origin often intermingled within a chimeric colony to produce a zooidal mosaic. Although fusion of colonies has been observed directly in the laboratory, an unknown proportion of the chimerism detected in wild populations might have arisen through somatic mutation. To assess this possibility, tissue of 12 clones in culture was sampled repeatedly over a period of 3 years and subjected to RAPD–PCR analysis. RAPD banding patterns were generally very stable; the changes noted mostly involved minor bands that would not, on their own, have been taken as evidence for chimerism under the conservative criteria adopted for the study of wild populations. It was concluded that a large proportion of natural chimerism is attributable to colony fusion.

Colony fusion in a termite: What makes the society "open"?

Sociobiological theories assume that insect societies are closed, i.e., members always act aggressively toward alien conspecific individuals. However, introduction of non-nestmate workers into a host colony of a lower termite, Reticulitermes speratus revealed various levels of agonism: from genocide to colony fusion. Members of the host colony attacked and killed the intruders having a higher nymph ratio (the number of nymphs/the number of workers) than the host colony had. In contrast, the intruders were accepted if they had a lower nymph ratio than the host colony. Acceptance of a lower-nymph-ratio colony could be beneficial for the host colony because it would gain additional labor force to feed its own nymphs. However, acceptance of a higher-nymph-ratio colony might be disadvantageous because the workers must rear non-relative nymphs additionally. Here we show that termites facultatively change their agonistic response toward non-nestmates according to the cost and benefit of colony fusion. Contrary to the existent concept, we report for the first time that colony fusion is an adaptive tactic in social insects.

Random amplified polymorphic DNA (RAPD) analysis reveals extensive natural chimerism in a marine protochordate

Random amplified polymorphic DNA (RAPD) analysis was applied to individual modules (zooids) of a colonial ascidian to investigate the presence and extent of chimerism, the parabiotic association of different genetic entities. The technique proved to be rapid and efficient for distinguishing different genotypes present in a colony, and revealed genetic mosaicism in wild material, as well as in laboratory cultures following planned fusion. Approximately one‐third of colonies in the natural population studied possessed multiple genotypes, presumably as the result of fusion of different colonies. Furthermore, individual zooids of different genetic origin often intermingled after colony fusion, spreading each genotype throughout a larger total area.

Somatic and germ cell parasitism in a colonial ascidian: Possible role for a highly polymorphic allorecognition system

A colonial protochordate, Botryllus schlosseri, undergoes a natural transplantation reaction in the wild that results alternatively in colony fusion (chimera formation) or inflammatory rejection. A single, highly polymorphic histocompatibility locus (called Fu/HC) is responsible for rejection versus fusion. Gonads are seeded and gametogenesis can occur in colonies well after fusion, and involves circulating germ-line progenitors. Buss proposed that colonial organisms might develop self/non-self histocompatibility systems to limit the possibility of interindividual germ cell “parasitism” (GCP) to histocompatible kin [Buss, L. W. (1982) Proc. Natl. Acad. Sci. USA 79, 5337–5341 and Buss, L. W. (1987) The Evolution of Individuality (Princeton Univ. Press, Princeton]. Here we demonstrate in laboratory and field experiments that both somatic cell and (more importantly) germ-line parasitism are a common occurrence in fused chimeras. These experiments support the tenet in Buss’s hypothesis that germ cell and somatic cell parasitism can occur in fused chimeras and that a somatic appearance may mask the winner of a gametic war. They also provide an interesting challenge to develop formulas that describe the inheritance of competing germ lines rather than competing individuals. The fact that fused B. schlosseri have higher rates of GCP than unfused colonies additionally provides a rational explanation for the generation and maintenance of a high degree of Fu/HC polymorphism, largely limiting GCP to sibling offspring.

Somatic and germ cell parasitism in a colonial ascidian: possible role for a highly polymorphic allorecognition system.

A colonial protochordate, Botryllus schlosseri, undergoes a natural transplantation reaction in the wild that results alternatively in colony fusion (chimera formation) or inflammatory rejection. A single, highly polymorphic histocompatibility locus (called Fu/HC) is responsible for rejection versus fusion. Gonads are seeded and gametogenesis can occur in colonies well after fusion, and involves circulating germ-line progenitors. Buss proposed that colonial organisms might develop self/non-self histocompatibility systems to limit the possibility of interindividual germ cell "parasitism" (GCP) to histocompatible kin [Buss, L. W. (1982) Proc. Natl. Acad. Sci. USA 79, 5337-5341 and Buss, L. W. (1987) The Evolution of Individuality (Princeton Univ. Press, Princeton]. Here we demonstrate in laboratory and field experiments that both somatic cell and (more importantly) germ-line parasitism are a common occurrence in fused chimeras. These experiments support the tenet in Buss's hypothesis that germ cell and somatic cell parasitism can occur in fused chimeras and that a somatic appearance may mask the winner of a gametic war. They also provide an interesting challenge to develop formulas that describe the inheritance of competing germ lines rather than competing individuals. The fact that fused B. schlosseri have higher rates of GCP than unfused colonies additionally provides a rational explanation for the generation and maintenance of a high degree of Fu/HC polymorphism, largely limiting GCP to sibling offspring.

Intraspecific interactions in a community of arboreal nesting termites (Isoptera: Termitidae)

In coconut plantations of northern New Guinea, the arboreal nesting termite community comprises three species:Nasutitermes princeps, N. novarumhebridarum, andMicrocerotermes biroi. In orde to assess the importance of intraspecific interactions in this community, we conducted pairwise encounters between batches of individuals in the laboratory and between entire nest populations in seminantural conditions. Three levels of agonism were defined in laboratory bioassays: anagonism, moderate agonism, and strong agonism. Anagonism was observed during all control tests with homocolonical groups and in some tests with allocolonial groups of all species. Moderate agonism included initial aggressiveness that subsequently faded out, and initially passive encounters where aggression progressively built up and led to fighting. Strong agonism corresponded to initial aggressiveness and fighting. Results obtained in alboratory bioassays were consistent with bioassays in seminatural conditions. WhenNasutitermes colonies were anagonists in laboratory bioassays, their foraging trails merged without aggression in field tests.N. princeps nests that were moderately agonistic in laboratory tests fought and either continued to avoid each other or finally joined after elimination of the most aggressive individuals. The most aggressiveM. biroi andN. princeps colonies fought and their foraging trails diverged afterward. Direct attacks on alien nests were winnessed inM. biroi. In all species, anagonism occurred in 21–34% of the combinations tested, between either geographically close or distantcolonies. An exeption was a group of 112 anagonist nests ofN. princeps, which most probably constituted a supercolony. The level of agonism betweenNasutitermes colonies was constant during the wet and dry season. Termite colonies excluded each other, both intra- and interspecifically, from the coconut trees, and their territories seem distributed in a mosaic pattern. Agonism between colonies may result in the elimination of the weakest colonies or in trail divergence, maintaining this mosaic. In cotrast, lack of agonism between some colonies suggests the possibility of colony fusion and gene exchanges without nuptial flights.

Allorecognition elements on a urochordate histocompatibility locus indicate unprecedented extensive polymorphism

Tissue contacts between different colonies of the cosmopolitan urochordate Botryllus schlosseri resulted either in fusion between allogenic blood vessels or in the formation of rejections, characterized by necrotic areas. This colony specificity is manifested by a single, highly polymorphic mendelian locus, with codominantly expressed alleles, called the tunicate fusibility/histocompatibility (Fu/HC) haplotype. Two colonies sharing even one allele at the Fu/HC locus may fuse; rejecting colonies share no alleles. Previous studies have revealed up to 100 alleles on the Fu/HC locus in different natural populations. We studied Fu/HC polymorphism in three populations (> 1000 colonies) along the Mediterranean coast of Israel, 12-36 km apart. By using the protocol of colony allorecognition assays (CAAS) on 444 tests within localities, 58-306 alleles per locality were calculated. We also estimate a total of 479-560 Fu/HC alleles in the three Israeli populations. An additional 103 interpopulation CAAS resulted in zero fusion, an outcome which contradicts previous findings showing 4.4-12.0% fusions between more remote B. schlosseri populations such as those from Israel versus Monterey, California, and California versus Japan assays. We propose that the recorded unprecedented Fu/HC polymorphism is maintained through overdominant selection, which is promoted by the gregarious settlement of Fu/HC-compatible larvae and by the subsequent threat of germ cell parasitism following colony fusion.

C-kit ligand augments granulocyte-macrophage colony growth from patients with 5q- syndrome.

In vitro studies may serve as a guide to clinical strategies with cytokines. In this study, marrows from 26 patients with myelodysplastic syndrome (MDS) were assayed for myeloid progenitor cells in agar gel. Colony stimulating activity was provided by the recombinant human colony stimulating factors granulocyte-macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), interleukin 3 (IL-3), fusion protein (FP), c-kit ligand (KL) or GM-CSF combined with other cytokines (KL, IL-3). Decreased colony forming units granulocyte-macrophage (CFU-GM) were detected in most cases (69%) compared with normal controls. Neither FP nor the combination of GM-CSF + IL-3 produced more colonies than GM-CSF alone. The number of CFU-GM did not correlate with French American British (FAB) class. All marrows (7) from patients with 5q- showed augmentation of GM-CSF induced colonies with the addition of KL. In contrast, KL augmentation was noted in only 42% of other MDS marrows (p = 0.01). This in vitro result suggests that 5q- may predict a group of MDS patients with a likelihood to respond to the combination of GM-CSF + KL.

Chimeras vs Genetically Homogeneous Individuals: Potential Fitness Costs and Benefits

Colonies of the compound tunicate Botryllus schlosseri show the capacity for colony specificity resulting either in vascular fusion or in rejection between genetically distinct colonies. Cosettlement of kin colonies increases the probability of fusion between allogeneic colonies. However, laboratory studies revealed that fusion terminates in the resorption of one partner, and that fusion raises the threat of somatic/germ cell parasitism. Here we tested in a laboratory study, done with 88 oozooids from 4 gravid colonies, the suggestion that colony fusion between relatives may be beneficial to one or both members of a chimera by increasing the size, the fecundity and/or survivorship.

Do Corals Lie About Their Age? Some Demographic Consequences of Partial Mortality, Fission, and Fusion

Population dynamics of corals and other colonial animals are complicated by their modular construction and growth. Partial colony mortality, colony fission, and colony fusion distort any simple relationship between size and age among reef corals.

GENETIC AND DEVELOPMENTAL STUDIES ON BOTRYLLUS SCHLOSSERI.

1. Properties of Botryllus schlosseri which give it outstanding promise for studies in developmental genetics are reviewed. 2. Laboratory culture procedures, in vitro fertilization, and a method for raising embryos in vitro are described. Controlled successions of complete life cycles can now be achieved in any laboratory. 3. Experiments involving colony fusion, subsequent vascular budding, and the analysis of color patterns in resultant systems suggest that cells of the simple vessel walls govern the morphology of the regenerated zooids. 4. Results of some preliminary genetic crosses are reported.