Mature Colonies Research Articles

Latitudinal variation in reproductive synchrony in Acropora assemblages: Japan vs. Australia

Abstract The annual mass spawning of scleractinian corals on the Great Barrier Reef (GBR), Australia, is purported to be unprecedented in terms of the taxonomic and geographical scale of spawning synchrony. Here, we compare spawning synchrony both within and among coral species in four regions spanning 10°of latitude on the GBR and compare this with four regions separated by a similar latitudinal range within the Japanese tropical and sub-tropical Archipelago. On the GBR, peak reproductive activity at all latitudes occurred in November whereas there was a clear disjunction in the period of peak reproductive activity among the four regions in Japan, with tropical locations spawning up to 3 months earlier. In Sekesei Lagoon (22°N), a high proportion of Acropora colonies were mature following the full moon in April; at Akajima Island (26°N) peak reproductive activity occurred in May; at Oku (28°N) peak reproductive activity occurred in June and in Amakusa (31°N), reproductive activity likely peaked in July. However, mature colonies of Acropora were found prior to every full moon for at least 5 months at two regions examined in detail (The Whitsundays Islands on the GBR and Akajima Island). While these regions on GBR appear to act more homogeneously than regions over a similar latitudinal range in Japan with respect to the timing of peak reproductive activity, and the proportion of colonies mature was often higher during these peaks, the reproductive season on the GBR is much longer (5 months) than is typically appreciated.

Army Ants as Research and Collection Tools

Ants that fall prey to the raids of army ants commonly respond by evacuating their nests. This documented behavior has been underexploited by researchers as an efficient research tool. This study focuses on the evacuation response of the southwestern desert ant Aphaenogaster cockerelli André (Hymenoptera: Formicidae) to the army ant Newamyrmex nigrescens Cresson. It is shown that army ants can be used to collect mature colonies of ants. The applicability of this tool to ecologically meaningful areas of research is discussed.

How the distribution of colonies of the hydroid Laomedea flexuosa is limited to a narrow belt along the lower littoral zone

In the White Sea the colonial hydroid Laomedea flexuosa inhabits a narrow belt of the lower littoral zone. How is so limited a habitat determined? We studied the time of planula release and the behaviour of larvae during the free-swimming stage and settlement in natural and laboratory conditions. Three methods were used to record the tidal-dependent dynamic of planula release: (1) plankton collecting bags around Fucus distichus macrophytes with mature hydroid colonies; (2) active stirring of Fucus with hydroids in a container with water, which is an old way to stimulate planula release; and (3) direct counts of the mature planulae in gonangia. The dynamic intensity of L. flexuosa planula release was investigated according to 3–4 phases of the tidal cycle. A moment of general release of larvae was shown to be correlated with a period of low water. Following the incoming tide keeps planulae in the littoral area. The planulae of L. flexuosa have a short period of swimming (less than 30 minutes), unlike those of Gonothyrae loveni and Dynamena pumila whose swimming period is about 36 hours. Quick settlement and tidal planula release could explain the strong spatial limitation in the distribution of L. flexuosa within the lower level of the intertidal zone. It is hypothesized that distribution over large areas is most likely by drift of colonies attached to detached seaweeds. Our outlook about the biological ways of ecological niche differentiation among marine organisms is broadened by the results of this study.

Colony characteristics of Vespula germanica (F.) (Hymenoptera, Vespidae) in a Mediterranean climate (southern Australia)

Abstract Vespula germanica has been accidentally introduced into Australia, where it has now established as a horticultural, agricultural, environmental and nuisance pest. Despite comprehensive and often expensive eradication programs, remarkably little information exists for the species in Australia. Most previous studies were conducted in its native range in England, and in New Zealand where V. germanica has also been introduced. Data on nesting sites in Adelaide were collected over two seasons, with a total of 2640 nests surveyed. The majority of nests (67%) were found below ground, mostly in soil. Twenty‐nine percent of nests were found in artificial structures, while the remainder of nests was located above ground. Variation among different habitat types suggests that the species can utilise whatever nest sites are available. Colony duration, timing and seasonal development were also examined by collecting wasp nests over three seasons. Nests were found between November and May. Average mature colonies contained over 9500 small (worker) and 3600 large (queen and male) cells, with some large nests consisting of over 27 500 cells. By the end of May, such colonies have 15 000 wasps emerging from small cells and 2500 wasps emerging from large cells. This is 35–80% more than the numbers of adults produced by V. germanica colonies in England. In addition, in southern Australia a proportion of nests overwinter and survive into the next season, whereas all nests collapse and die out at this time in England. A significant linear relationship was found between wasp traffic and various measures of nest size. These results indicate that in the absence of an adverse climate, V. germanica nests can attain a substantial size. Greater numbers of queens produced in nests may also facilitate a faster rate of population increase in Australia.

Sperm length evolution in the fungus-growing ants

Eusocial insects offer special opportunities for the comparative study of sperm traits because sperm competition is absent (in species with obligatory monandry) or constrained (in lineages where queens mate multiply but never remate later in life). We measured sperm length in 19 species of fungus-growing ants, representing 9 of the 12 recognized genera, and mapped these onto the ant phylogeny. We show that average sperm length across species is highly variable and decreases with mature colony size in basal genera with singly mated queens, suggesting that sperm production or storage constraints affect the evolution of sperm length. Sperm length does not decrease further in multiply mating leaf-cutting ants, despite substantial further increases in colony size. In a combined analysis, sexual dimorphism explained 63.1% of the variance in sperm length between species. As colony size was not a significant predictor in this analysis, we conclude that sperm production trade-offs in males have been the major selective force affecting sperm length across the fungus-growing ants, rather than storage constraints in females. The relationship between sperm length and sexual dimorphism remained robust in phylogenetically independent contrasts. Some of the remaining variation was explained by the relative size of the sperm-storage organ, but only in the multiply mating leaf-cutting ants, suggesting that sperm-storage constraints become important for the evolution of sperm length in this derived group. Mate number affected sperm length to a minor extent, and only in interaction with other predictor variables, suggesting that sperm competition has not been a major selective force for sperm length evolution in these ants.

Endosporium, a new endoconidial genus allied to the Myriangiales

A new endoconidial genus, Endosporium gen. nov., is reported from Alberta, Canada. Two species are described: Endosporium populi-tremuloidis Tsuneda sp. nov. (type species) isolated from a heavily colonized bud of Populus tremuloides Michx., and Endosporium aviarium Tsuneda sp. nov. isolated from the skin of Bombycilla garrulus (L.) (Bohemian waxwing) and a twig of Populus balsamifera L. This genus is morphologically similar to Phaeotheca in forming black, slow-growing colonies (conidiomata) containing numerous, conidiogenous, cellular clumps, but different in that (i) colonies possess aerial, determinate hyphae on the surface; (ii) mature colonies eventually collapse to release a mixture of conidiogenous cellular clumps, endoconidia, and blastic conidia in slimy liquid; and (iii) endoconidia are hyaline. Phylogenetic analyses of nuclear rDNA SSU, LSU, and ITS sequences indicate that Endosporium is phylogenetically distant from other endoconidial taxa, including Phaeotheca, and is most closely related to the Myriangiales (Dothideomycetes). Similarities in stroma and conidioma development as well as ecology between the two taxa suggest that Endosporium can be accommodated within this order, making it the first endoconidial and first black meristematic genus reported in the Myriangiales.

Negative regulation of Jak2 by its auto-phosphorylation at tyrosine 913 via the Epo signaling pathway

Janus kinase 2 (Jak2) has a pivotal role in erythropoietin (Epo) signaling pathway, including erythrocyte differentiation and Stat5 activation. In the course of screening for critical phosphorylation of tyrosine residues in Jak2, we identified tyrosine 913 (Y 913) as a novel and functional phosphorylation site, which negatively regulates Jak2. Phosphorylation at Y 913 rapidly occurred and was sustained for at least 120 min after Epo stimulation, in contrast to the transient phosphorylation of Y 1007/1008 in the activation loop of Jak2. Interestingly, phosphorylation defective mutation of Y 913 (Y 913F) results in a significant enhancement of Epo-induced Jak2 activation, whereas phosphorylation mimic mutation of Y 913 (Y 913E) completely abrogated its activation. Furthermore, Jak2 deficient fetal liver cells expressing Y 913F mutant generated many mature erythroid BFU-E and CFU-E colonies, while Y 913E mutant failed to reconstitute Jak2 deficiency. We also demonstrate, in Jak1, phosphorylation of Y 939, a corresponding tyrosine residue with Y 913, negatively regulated Jak1 signaling pathway. Accordingly, our results suggest that this tyrosine phosphorylation in JH1 domain may be involved in common negative regulation mechanism for Jak family.

Parabiosis between basal fungus-growing ants (Formicidae, Attini)

We describe the first observation of parabiosis between two Attini ants (Apterostigma urichii Forel and Cyphomyrmex faunulus Wheeler) found in northern Manaus, AM, Brazil. Complete, mature colonies of both species were found in a single cavity inside a rotten log, sharing and tending a single combined fungus garden, made up of two distinct halves, each cultivated by one species. Workers of one species often antennated workers of the other species and showed no aggression toward each other or toward each other’s workers, queens, or immatures. Laboratory observations suggest that immatures of both species feed on hyphae from either half of the fungus garden. We were not able to find other parabiotic pairs involving the same species in the same locality, although we found colonies of both species sharing trails and foraging territories.

Effect of colony size and age on resource allocation between growth and reproduction in the corals Goniastrea aspera and Favites chinensis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 354:133-139 (2008) - DOI: https://doi.org/10.3354/meps07216 Effect of colony size and age on resource allocation between growth and reproduction in the corals Goniastrea aspera and Favites chinensis Sayaka Kai*, Kazuhiko Sakai Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, 3422 Sesoko, Motobu, Okinawa 905-0227, Japan *Email: k058553@eve.u-ryukyu.ac.jp ABSTRACT: The effect of colony size and age on growth and sexual reproduction was examined by taking small-sized fragments from large mature donor colonies of Goniastrea aspera and Favites chinensis. Both species are massive colonial corals in the family Faviidae. Monopolyp and oligopolyp (5 to 8 polyps) fragments were established. The fragments were cultured in running seawater aquaria for 22 mo, and growth and gamete production were measured. In both species, monopolyp fragments had higher growth rates than oligopolyp fragments. F. chinensis had higher growth rates than G. aspera in both fragment sizes. Polyps tended to bud when there was open space, and smaller colonies had higher growth rates, probably because the polyps of smaller colonies had more open space. In G. aspera, both the monopolyp and oligopolyp fragments produced gametes, whereas in F. chinensis, neither type of fragment produced gametes. These results suggest that sexual maturity is determined by colony age in G. aspera and by colony size in F. chinensis. Our results also suggest that polyps are integrated at the colony level. Polyp integration activity in a colony may be determined by the age of the colony in G. aspera and by the size of the colony in F. chinensis, likely maximizing colony fitness. KEY WORDS: Resource allocation · Colonial corals · Growth · Reproduction · Colony size · Colony age · Integration Full text in pdf format PreviousNextCite this article as: Kai S, Sakai K (2008) Effect of colony size and age on resource allocation between growth and reproduction in the corals Goniastrea aspera and Favites chinensis. Mar Ecol Prog Ser 354:133-139. https://doi.org/10.3354/meps07216 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 354. Online publication date: February 07, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Intraspecific competition in the ant Camponotus cruentatus: should we expect the ‘dear enemy’ effect?

The mechanisms of competition and resource domination were analysed in the Mediterranean ant Camponotus cruentatus. In a plot located in southern Spain mature colonies are overdispersed, which is indicative of territoriality in other species. Unexpectedly, however, workers from neighbouring colonies commonly foraged in areas that overlapped by more than 44%. This suggests that while mature colonies possibly prevent the establishment of new colonies in the vicinity of their nests, they do not limit the intrusion of alien foragers. In contrast, rich food sources located in common foraging areas are aggressively defended, generally leading to their domination by the nest that discovered them first. Resource exploitation further requires rapid recruitment of foragers and soldiers to transport food as well as to exclude competitors. Complementary to the field experiments we conducted laboratory bioassays to assess intercolonial aggression. Group encounters showed that workers of C. cruentatus were equally aggressive towards alien ants irrespective of whether they were sympatric neighbours (and had possibly had contact), sympatric nonneighbours (which had probably had no contact), or allopatric. This was corroborated by analysis of the hydrocarbons that generally serve as colony recognition cues. This mixture, which contains an unusual proportion of trimethylalkanes, showed important colony specificity. The high intraspecific aggression shown indiscriminately by workers indicates that the ‘dear enemy’ effect does not exist in this species and suggests that scarce resources are worth defending against intraspecific competitors. We discuss several proximate and ultimate constraints that may prevent the general occurrence of this process in ants.

Changes in composition of cuticular biochemicals of the facultatively polygynous ant Petalomyrmex phylax during range expansion in Cameroon with respect to social, spatial and genetic variation

In social insects, biochemicals found at the surface of the cuticle are involved in the recognition process and in protection against desiccation and pathogens. However, the relative contribution of evolutionary forces in shaping diversity of these biochemicals remains largely unresolved in ants. We determined the composition of epicuticular biochemicals for workers sampled in 12 populations of the ant Petalomyrmex phylax from Cameroon. Genetic variation at 12 microsatellite markers was used to infer population history and to provide null expectations under the neutrality hypothesis. Genetic data suggest a recent southward range expansion of this ant species. Furthermore, there is a decline southward in the numbers of queens present in mature colonies. Here, we contrast the pattern of biochemical variation against genetic, social and spatial parameters. We thus provide the first estimates of the relative contribution of neutral and selective processes on variation of ant cuticular profile. Populations in migration-drift disequilibrium showed reduction of within-population variation for genetic markers as well as for cuticular profiles. In these populations, the cuticular profile became biased towards a limited number of high molecular weight molecules. Within- and among-population biochemical variation was explained by both genetic and social variation and by the spatial distribution of populations. We therefore propose that during range expansion of P. phylax, the composition of epicuticular compounds has been affected by a combination of neutral processes - genetic drift and spatially limited dispersal - and spatially varying selection, social organization and environmental effects.

Targeted Removal of Ant Colonies in Ecological Experiments, Using Hot Water

Ecological experiments on fire ants cannot, or should not, use poison baits to eliminate the fire ants because such baits are not specific to fire ants, or even to ants. Hot water is an extremely effective and specific killing agent for fire ant colonies, but producing large amounts of hot water in the field, and making the production apparatus mobile have been problematical. The construction and use of a charcoal-fired kiln made from a 55-gal. oil drum lined with a sand-fireclay mixture is described. An automobile heater fan powered from a 12-v battery provided a draft. Dual bilge pumps pumped water from a large tank through a long coil of copper tubing within the kiln to produce 4 to 5 l. of hot water per min. The hot water was collected in 20 l. buckets and poured into fire ant nests previously opened by piercing with a stick. The entire assembly was transported in and operated from the back of a pickup truck.Five experimental plots containing 32 to 38 colonies of the fire ant, Solenopsis invicta, Buren (Hymenoptera: Formicidae), were treated with hot water over a period of two years. All colonies on the treatment plots were treated twice with hot water early in 2004, reducing their numbers to zero. However new colonies were formed, and mature colonies expanded into the plots. A third treatment was made in the spring of 2005, after which fire ant populations were suppressed for over a year. Whereas the 5 control plots contained a total of 166 mostly large colonies, the 5 treatment plots contained no live colonies at all. Averaged over a two-year period, a 70% reduction in total number of colonies was achieved (P < 0.001) on the treatment plots, and a 93% reduction of large, mature colonies. Over this same time span, the number of colonies in control plots remained stable. The reduction in colony numbers on the treatment plots was reflected in the pitfall trap samples that recorded a 60% reduction in fire ants.

Does disturbance favor dispersal? An analysis of ant migration using the colony-based lattice model

Spatially explicit models that simulate the evolution of dispersal strategies have not considered colonial organisms. Here we develop the colony-based lattice model, in which a colony, rather than an individual, occupies each lattice site. With this model we investigate why invasive tramp ant species usually lack long-distance dispersal, despite living in frequently disturbed habitats. We assume a new trade-off between the dispersal distance and the offspring colony size in the competition between two extreme strategies: the short-distance dispersal strategy (the S strategy, simulating budding or fission), which splits a colony in half with one of the two halves moving to a neighboring site, and the long-distance dispersal strategy (the L strategy, assuming colony-founding by winged queens), which allocates a minimal resource to an offspring colony that disperses to a randomly chosen site. Mortality of a colony is assumed to depend on the size; the L strategy suffers from costs due to small initial colony size (i.e., high mortality and late colony maturity). Disturbance causes additional mortality to both types of colonies and is controlled by disturbance frequency, p, and a stochastic parameter determining the spatial autocorrelation of disturbance, q. Simulations show that the S strategy is favored under frequent but spatially small-scale disturbances (high p and low q ), whereas large-scale disturbances (low p and high q ) favor the L strategy. When mortality is generally high or particularly high in small colonies, the S strategy tends to be advantageous. In contrast, when colony mortality is generally low, the L strategy is favored. We discuss the importance of colony size dynamics and the trade-off between colony size and the dispersal distance in the evolution of dispersal strategies in ants and other more or less sessile organisms.

Phosphoinositide 3-kinase signalling regulates early development and developmental haemopoiesis

Phosphoinositide 3-kinase (PI3K)-dependent signalling regulates a wide variety of cellular functions including proliferation and differentiation. Disruption of class I(A) PI3K isoforms has implicated PI3K-mediated signalling in development of the early embryo and lymphohaemopoietic system. We have used embryonic stem (ES) cells as an in vitro model to study the involvement of PI3K-dependent signalling during early development and haemopoiesis. Both pharmacological inhibition and genetic manipulation of PI3K-dependent signalling demonstrate that PI3K-mediated signals, most likely via 3-phosphoinositide-dependent protein kinase 1 (PDK1), are required for proliferation of cells within developing embryoid bodies (EBs). Surprisingly, the haemopoietic potential of EB-derived cells was not blocked upon PI3K inhibition but rather enhanced, correlating with modest increases in expression of haemopoietic marker genes. By contrast, PDK1-deficient EB-derived progeny failed to generate terminally differentiated haemopoietic lineages. This deficiency appeared to be due to a requirement for PI3K signalling during the proliferative phase of blast-colony-forming cell (BL-CFC) expansion, rather than as a result of effects on differentiation per se. We also demonstrate that PI3K-dependent signalling is required for optimal generation of erythroid and myeloid progenitors and their differentiation into mature haemopoietic colony types. These data demonstrate that PI3K-dependent signals play important roles at different stages of haemopoietic development.

CHANGES IN MATING SYSTEM AND SOCIAL STRUCTURE OF THE ANT PETALOMYRMEX PHYLAX ARE ASSOCIATED WITH RANGE EXPANSION IN CAMEROON

Past climate shifts have led to major oscillations in species distributions. Hence historical contingencies and selective processes occurring during such phases may be determinants for understanding the forces that have shaped extant phenotypes. In the plant-ant Petalomyrmex phylax (Formicinae), we observed spatial variation in number of queens in mature colonies, from several queens (high polygyny) in the median part of its distribution to a moderate number of queens (weak polygyny) or even only a single queen (monogyny) in the southwesternmost populations. This variation did not correlate with indicators of variation in current nest site availability and colony turnover, the supposedly determinant selective forces acting on gyny in ants. We show here that the variation in social structure correlates with a historical process corresponding to a progressive colonization of coastal southern Cameroon by the ant. Using microsatellite markers, we observed a clear pattern of isolation by distance except for the southernmost populations. Measures of genetic variability that do not take into account allele size were at equilibrium in all except the southernmost populations, suggesting recent foundation of the latter. Measures of genetic diversity taking into account allele size showed a clinal north-south decrease in variance of allele size. We propose that southern populations have yet to regain allele size variance after bottlenecks associated with the foundation of new populations, and that this variance is regained over time. Hence variation in social structure mirrors an old but still active southward colonization process or metapopulation dynamics, possibly in association with an expansion of the rain forest habitat during the late Holocene. A low number of queens in ant colonies is typically associated with strong dispersal capacity. We therefore suggest that the initial founders of new populations belong to the monogynous to weakly polygynous phenotype, and that queen number progressively increases in older populations.

Vasa expression in a colonial ascidian, Botrylloides violaceus

Evolution of solitary or colonial life histories in tunicates is accompanied by dramatic developmental changes that affect morphology and reproduction. We compared vasa expression in a solitary ascidian and a closely related colonial ascidian, in an effort to uncover developmental mechanisms important during the evolution of these contrasting life histories, including the ability to reproduce by budding. In this study, we explored the origin of germ cells in new buds developing by asexual reproduction in a colonial ascidian, Botrylloides violaceus and compared it to the source of germ cells in a solitary ascidian Boltenia villosa. We studied expression by in situ hybridization of vasa, a DEAD box RNA helicase gene found in germ cells across the metazoans. In B. villosa, bv-vasa mRNA was expressed in putative germ cells and oocytes of adult gonads, and was sequestered into a posterior lineage during embryogenesis. In mature colonies of the ascidian B. violaceus, bot-vasa mRNA was expressed in putative spermatogonia, in oocytes of zooids, and in some circulating cells in the zooids and differentiating buds. We propose that expression of vasa in cells other than gonadal germ cells of zooids in a colonial ascidian may serve as a source of germ-line stem cells in the colony.

Seasonal patterns of egg production in field colonies of the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

This is the first report on the annual egg production patterns in mature termite colonies in the field. Data on the seasonal patterns of egg production in field colonies are very important for understanding the annual colony growth schedule, resource allocation, and population dynamics of the termites. However, collecting the eggs from a sufficient number of colonies is extremely difficult in Reticulitermes termites because their multiple-site nesting makes it difficult to find the reproductive center of the colonies. Here, we first show the seasonal pattern of egg production in the subterranean termite Reticulitermes speratus by collecting the reproductive center of ten colonies each month from April through October. We had to destructively examine dozens of nests to find eggs from enough field colonies each month. Mature field colonies began to produce eggs in late May, soon after the swarming season, and the egg production rate (EPR) reached its maximum in early July. The eggs hatched until late October. The EPR was significantly correlated with the average monthly temperature. Additional investigation of the egg distributions in the nests showed that most eggs were kept around the royal cell, which contained the reproductives. The largest colony had 109 supplemental queens and 94,023 eggs, suggesting that each queen produced an average of 24.7 eggs per day, based on the known mean hatching period of an inseminated egg of 34.95±0.12 (SE) days.

Costs and benefits of joint colony founding in Australian Acacia thrips

Facultative joint colony founding by social insects (pleometrosis) provides an outstanding opportunity to analyze the costs and benefits of sociality. Pleometrosis has been documented for a range of social insects, but most studies on the adaptive benefits of this behavior are restricted to the Hymenoptera. In this study, we provide the first analysis of costs and benefits associated with pleometrosis for Australian Dunatothrips, which form domiciles by glueing together phyllodes (leaves) of their Acacia host plant. In Dunatothrips aneurae, the distribution of foundress numbers per nest indicated that females formed associations non-randomly. Furthermore, average group size was independent of both the number of foundresses on the host plant and the number of mature colonies, suggesting that this behavior was not simply a response to limited availability of nesting sites. Although per capita reproduction declined with increasing group size, we also identified two benefits of pleometrosis: (1) individual foundresses in groups had higher survival than solitary foundresses during the brood development period, and (2) larger colony sizes resulting from pleometrosis provided a benefit later in colony development, because a higher proportion of D. aneurae adults survived invasions by the kleptoparasite Xaniothrips mulga when colony size was larger. These results demonstrate that the reproductive costs of pleometrosis are at least partially counterbalanced by survival benefits.

Phenotypic Diversification and Adaptation ofSerratia marcescensMG1 Biofilm-Derived Morphotypes

We report here the characterization of dispersal variants from microcolony-type biofilms of Serratia marcescens MG1. Biofilm formation proceeds through a reproducible process of attachment, aggregation, microcolony development, hollow colony formation, and dispersal. From the time when hollow colonies were observed in flow cell biofilms after 3 to 4 days, at least six different morphological colony variants were consistently isolated from the biofilm effluent. The timing and pattern of variant formation were found to follow a predictable sequence, where some variants, such as a smooth variant with a sticky colony texture (SSV), could be consistently isolated at the time when mature hollow colonies were observed, whereas a variant that produced copious amounts of capsular polysaccharide (SUMV) was always isolated at late stages of biofilm development and coincided with cell death and biofilm dispersal or sloughing. The morphological variants differed extensively from the wild type in attachment, biofilm formation, and cell ultrastructure properties. For example, SSV formed two- to threefold more biofilm biomass than the wild type in batch biofilm assays, despite having a similar growth rate and attachment capacity. Interestingly, the SUMV, and no other variants, was readily isolated from an established SSV biofilm, indicating that the SUMV is a second-generation genetic variant derived from SSV. Planktonic cultures showed significantly lower frequencies of variant formation than the biofilms (5.05 x 10(-8) versus 4.83 x 10(-6), respectively), suggesting that there is strong, diversifying selection occurring within biofilms and that biofilm dispersal involves phenotypic radiation with divergent phenotypes.

BEHAVIORAL REGULATION OF GENETIC CASTE DETERMINATION IN A Pogonomyrmex POPULATION WITH DEPENDENT LINEAGES

The fate of a social insect colony is partially determined by its ability to allocate individuals to the caste most appropriate for the requirements for growth, maintenance, and reproduction. In pairs of dependent lineages of Pogonomyrmex barbatus, the allocation of individuals to the queen or worker caste is constrained by genotype, a system known as genetic caste determination (GCD). In mature GCD colonies, interlineage female eggs develop into sterile workers, while intralineage eggs become reproductively capable queens. Although the population-level consequences of this system have been intensively studied, the proximate mechanisms for GCD remain unknown. To elucidate these mechanisms, we brought newly mated queens into the laboratory and allowed them to establish colonies, nearly half of which unexpectedly produced virgin queens only seven months after colony founding. We genotyped eggs, workers, and the virgin queens from these colonies. Our results showed that queens in young colonies produce both interlineage and intralineage eggs, demonstrating that queens of GCD colonies indiscriminately use sperm of at least two lineages to fertilize their eggs. Intralineage eggs were more frequent in colonies producing virgin queens. These findings suggest that intralineage eggs are predetermined to become queens and that workers may cull these eggs when colonies are not producing queens. Virgin queens produced by young GCD colonies were smaller than field-caught virgin queens, and often had developmental problems. Hence, they are probably nonfunctional and represent an intense resource drain for developing colonies, not a contribution to colony fitness.