Mature Colonies Research Articles

Genetic Structure within Septobasidium Colonies Suggests Outcrossing and Frequent Non Self-Fusion

Abstract Fungi in the genus Septobasidium form colonies that envelop and infect multiple scale insects. Infection of each insect is thought to occur only via meiotic basidiospores. In this study, we investigated the genetic status of colonies by genotyping different phases of the Septobasidium life cycle including single spore isolates, mature colony tissue isolates, and infected insects. Meiotic analyses showed segregation of two alleles at multiple loci among the progeny from a single fungal colony. Genotyping of multiple tissue isolates demonstrated that individual Septobasidium colonies were composed of a single heterozygous dikaryotic mycelium. Fungi from insects fused to a colony of S. ramorum had identical genotypes to each other, but insects not yet fused to a colony sometimes had unique genotypes. Based on these studies, Septobasidium species are suggested to be predominantly outcrossing, with colonies maintaining their genetic identity despite frequent non self-fusions.

Bionomics and Formation of “Bonsai” Colonies With Long-Term Rearing of Coptotermes formosanus (Isoptera: Rhinotermitidae).

This laboratory study reports the ability of Formosan subterranean termite, Coptotermes formosanus Shiraki, colonies to survive for at least 9 yr while restricted to a sweater box. Colonies survived by limiting queen size and worker numbers, allowing these bonsai colonies to thrive. Queen physogastry appeared to plateau with 9-yr-old queens not larger than 6-yr-old queens, but nearly triple the size of 2-yr-old queens. Nine-year-old colony worker numbers were not greater than 6-yr-old colonies, but worker numbers were greater than in 2-yr-old colonies. Such colony survival under conditions of restricted resources provides a mechanism for re-infestation of areas following extensive area-wide control efforts. “Bonsai” colonies are relevant to the ability of marginalized colonies to avoid detection and then expand and invade into areas once the large, mature colonies are eliminated, and their potential to produce alates to start new C. formosanus colonies in areas which have been subjected to colony elimination programs impacts termite management strategies.

Population structure and genetic diversity in the nannandrous moss Homalothecium lutescens: does the dwarf male system facilitate gene flow?

BackgroundNannandry is a sexual system where males (”dwarf males”) are much smaller than the conspecific females. Dwarf males occur in a wide range of unrelated organisms but the evolutionary advantages of this condition are poorly understood. The dwarf male sexual system results in differences in the mode of dispersal and establishment as well as the life span between males and females. Such differences must have profound effects on the population dynamics and genetic structures. We have studied four populations of the nannandrous moss Homalothecium lutescens in southern Sweden. We genotyped dwarf males and female shoots with the aim of describing the genetic diversity and structure of the populations.ResultsDwarf males were most related to their host shoot, then their colony (within 0.5 m2) and then the rest of the population, which suggests restricted spore dispersal. However, a few dwarf males in each population appeared to originate from other colonies and sometimes even other populations. Genetic diversity of dwarf males was generally high but showed no tendency to be consistently higher or lower than female genetic diversity within the four populations.ConclusionsAlthough most dwarf males have local origin, sporadic dispersal events occur. The ability of the dwarf males to establish in high numbers in mature colonies facilitates gene flow between populations as well as increases the potential to accumulate genetic diversity within populations.

Rare Production of Nymphs in an Asian Subterranean Termite (Isoptera: Rhinotermitidae) Incipient Colony

Coptotermes colonies usually produce nymphs when a colony reaches maturity. In this study, we describe a rare case of nymph production from a 10-mo-old colony that previously had lost a primary reproductive. Such replacement reproductives are not functional. We suggest that the unusual developmental plasticity we observed may be the result of a vestigial developmental pathway that may partially regain its functionality in mature colonies.

Multiple functions of fire ant Solenopsis invicta mandibular gland products

AbstractAlarm pheromones of social insects are best known for their role in the defence and maintenance of colony integrity. Previous studies with the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) demonstrate that the mandibular glands of workers (sterile females) and male and female sexuals produce an alarm pheromone, 2‐ethyl‐3,6‐dimethylpyrazine. The function of alarm pheromones in worker ants is well understood and divergent from the function of these compounds in the winged sexual forms. The present study quantifies the amount of pyrazine in the mandibular glands from male and female alate sexuals, as well as queens. Pyrazine production in female alates starts in the late pupal stage and increases until they reach mating flight‐ready maturity; however, after mating flight participation, the pyrazine level declines by >50%. Interestingly, mature male alates lose >85% of their mandibular gland pyrazine during mating flight activity. The results of the present study indicate that male and female sexuals use mandibular gland secretions for mating flight initiation and during mating flights. Furthermore, the ontogeny of mandibular gland products (pyrazine as the marker) from newly‐mated queens to mature colony queens shows a more than two‐fold increase in the amount of pyrazine by 6 months after mating. However, this is followed by a decline to trace amounts in mature colony queens (>2 years old), suggesting a function for mandibular gland products during colony development. Multifunctional use of social insect pheromones is well documented and data are reported in the present study suggesting new roles for mandibular gland products in fire ants.

Unpaved roads alter foraging patterns of the leafcutter ant Atta colombica

Leaf cutting ants are dominant herbivores and influential ecosystem engineers in the Neotropics. It has been suggested that habitat disturbances alter the architecture of foraging trail systems for colonies in their vicinity; however, the evidence remains scarce. In this study we investigated the effect of unpaved roads dissecting tropical lowland forest habitat on the structure of leafcutter foraging trail systems and foraging effort. We mapped trail systems for 16 mature Atta colombica colonies located at different distances from unpaved roads. Our results suggest exploitation of unpaved roads by leafcutters provides favorable foraging conditions, causing significant differences in foraging trail structure.

Dispersal Flights of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae).

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is a pest of major economic concern. This termite is particularly known for its tendency to establish populations in nonendemic areas via maritime vessels as well as human-aided transport of infested materials. The natural spread of this species after new introductions occurs in part by dispersal flights originating from mature colonies. Dispersal flight activity is also the primary variable for the evaluation of area-wide management programs. Few studies exist describing the dynamics and distribution of a typical dispersal flight for this species. The present study used data collected by mark-recapture of C. formosanus alates over 12 individual evenings of dispersal flights in the New Orleans French Quarter. In this study, we found that for one selected flight dispersal location, which was not affected by a high density of trap locations nearby, alates flew on average 621 m from their parent colony. A new record of a 1,300-m dispersal flight was recorded. Spatial analysis showed that neither wind nor light affected the direction of flight, which may, however, be attributed to scarce light and wind measurements in the study region.

Body Size of the Monomorphic AntLasius niger: Young Colonies along a Metal Pollution Gradient

Metal pollution may cause the decrease in the individual body size. In ants, the morphological diversity within and between colonies may be much higher than that considered before, even in monomorphic ants. In this study we measured the body size, expressed as head width, ofLasius nigerworkers collected from 44 young colonies in their ergonomic stage along a well-known gradient exhibiting chronic metal pollution. We calculated statistics describing the body size distribution curve, namely, average, median, data range, skewness, and kurtosis. None of these statistics correlated with the pollution level. Contrary to our previous study performed on mature colonies, workers from young colonies do not display pollution-related morphological changes. The results stress the importance of developmental stage of colony on diversifying body size of the worker cast, in monomorphic ants living in metal-polluted areas.

Occurrence of sexuals of African weaver ant (Oecophylla longinoda Latreille) (Hymenoptera: Formicidae) under a bimodal rainfall pattern in eastern Tanzania

The African weaver ant, Oecophylla longinoda, is being utilized as a biocontrol agent and may also be targeted for future protein production. Rearing of mated queens in nurseries for colony production is needed to cater for such demands. Thus, newly mated queens must be collected for use as seed stocks in the nurseries. To collect mated queens efficiently it is important to identify when sexuals occur in mature colonies. We studied the occurrence of sexuals in O. longinoda colonies for 2 years in Tanga, Tanzania, a region characterized by a bimodal rainfall pattern. We found that O. longinoda sexuals occurred almost throughout the year with abundance peaks from January to April. Production of sexuals appeared to be triggered by rainfall, suggesting that populations in areas with long rainy periods may show prolonged mating periods compared to populations experiencing extended dry periods. The bimodal rain pattern may thus cause a low production over a long period. The average yearly production of queens per tree and per colony was estimated to be 449 and 2753, respectively. The average number of queens per nest was 17. Worker abundance declined from January to March with minimum by the end of this period, being inversely proportional to the production of sexuals. In conclusion, mated queens may be collected almost throughout the year, but most efficiently by the onset of the long rainy season when the majority disperse.

Comparative study of resistance to heat in two species of leaf-cutting ants

Atta laevigata and Atta capiguara are two species of leaf-cutting ants that are found in the pastures of Central Brazil and build huge underground nests linked to the outdoor environment by underground tunnels, which can reach several tens of meters and further extend through foraging trails to distant foraging grounds. The tunnels built by mature colonies of A. capiguara are usually longer and deeper than those built by mature colonies of A. laevigata. The physical trails are also shorter on average. We hypothesized that these differences could be related to differences in thermotolerance between the two species. To test this we collected ants on foraging trails and placed them individually in waterproof test tubes plunged in a thermostatic bath at 25 °C (control), 37 and 39 °C (test temperatures). The results showed that at both 37 and 39 °C, the survival time of A. laevigata was much more extended than that of A. capiguara. A possible explanation for the longer and deeper underground foraging tunnels, as well as the shorter foraging trails, built by A. capiguara may thus be their lower resistance to heat stress. The longer tunnels built by A. capiguara colonies may reduce the exposure to heat of the foraging workers that commute between their nest and the foraging grounds or act as a thermal refuge in which the workers can find temporary protection against high outdoor temperatures.

Developmental instability in incipient colonies of social insects.

Social insect colonies can provide homeostatic conditions that buffer the incidence of environmental fluctuations on individuals, which have contributed to their ecological success. Coptotermes (Isoptera: Rhinotermitidae) is a highly invasive termite genus and several species have important economic impact in many areas of the world. Mature Coptotermes colonies with millions of individuals can provide optimal environmental condition and nurturing capacity for the developing brood. However, it was previously suggested that contrary to mature colonies, incipient colonies may be exposed to critical stress, which may explain for the low success rate of establishment within the first year of the life of a termite colony. We here investigated the stress imposed on individuals of incipient colonies by comparing the developmental instability of individuals between incipient and mature colonies of two Coptotermes species, C. formosanus Shiraki and C. gestroi (Wasmann). We assessed the developmental instability by measuring the asymmetry of morphological traits from the head capsule of the soldier caste. Soldiers from incipient colonies of both species displayed strong asymmetrical traits in comparison to soldiers from mature colonies. We suggest that homeostatic conditions for optimal development are reached as the colony matures, and confirmed that the incipient colony remains a critical bottleneck where individuals are exposed to high developmental stress.

Characterization of the Neurospora crassa cell fusion proteins, HAM-6, HAM-7, HAM-8, HAM-9, HAM-10, AMPH-1 and WHI-2.

Intercellular communication of vegetative cells and their subsequent cell fusion is vital for different aspects of growth, fitness, and differentiation of filamentous fungi. Cell fusion between germinating spores is important for early colony establishment, while hyphal fusion in the mature colony facilitates the movement of resources and organelles throughout an established colony. Approximately 50 proteins have been shown to be important for somatic cell-cell communication and fusion in the model filamentous fungus Neurospora crassa. Genetic, biochemical, and microscopic techniques were used to characterize the functions of seven previously poorly characterized cell fusion proteins. HAM-6, HAM-7 and HAM-8 share functional characteristics and are proposed to function in the same signaling network. Our data suggest that these proteins may form a sensor complex at the cell wall/plasma membrane for the MAK-1 cell wall integrity mitogen-activated protein kinase (MAPK) pathway. We also demonstrate that HAM-9, HAM-10, AMPH-1 and WHI-2 have more general functions and are required for normal growth and development. The activation status of the MAK-1 and MAK-2 MAPK pathways are altered in mutants lacking these proteins. We propose that these proteins may function to coordinate the activities of the two MAPK modules with other signaling pathways during cell fusion.

Bacterial signalling mechanisms: Checking out the neighbourhood

In much the same way that people check out the neighbourhood and ask their friends for advice before they decide to move to a new house, bacteria perceive, integrate and respond to various different environmental and social cues during the processes of surface colonization and biofilm formation. These integrated signalling responses determine whether bacteria adopt a free-living individualist lifestyle associated with motility and elevated virulence, or whether they form a complex multicellular community known as a biofilm. Biofilms consist of large surface-attached multicellular structures, where the individual bacteria are encased in a matrix of proteins, exopolysaccharides and extracellular DNA strands. Within the biofilm, discrete bacterial subpopulations fulfil distinct phenotypic roles. These include support cells, persister cells that can resist high concentrations of antibiotics, and swarmer cells that burst from the surfaces of mature biofilms and colonies into new environments. As the majority of chronic hospital-acquired and implant-associated infections are biofilm-based, understanding the signalling networks that underpin bacterial biofilm formation is of vital importance.

Bumblebee size polymorphism and worker response to queen pheromone.

Queen pheromones are chemical signals produced by reproductive individuals in social insect colonies. In many species they are key to the maintenance of reproductive division of labor, with workers beginning to reproduce individually once the queen pheromone disappears. Recently, a queen pheromone that negatively affects worker fecundity was discovered in the bumblebee Bombus terrestris, presenting an exciting opportunity for comparisons with analogous queen pheromones in independently-evolved eusocial lineages such as honey bees, ants, wasps and termites. I set out to replicate this discovery and verify its reproducibility. Using blind, controlled experiments, I found that n-pentacosane (C25) does indeed negatively affect worker ovary development. Moreover, the pheromone affects both large and small workers, and applies to workers from large, mature colonies as well as young colonies. Given that C25 is readily available and that bumblebees are popular study organisms, I hope that this replication will encourage other researchers to tackle the many research questions enabled by the discovery of a queen pheromone.

A simple mathematical model that describes the growth of the area and the number of total and viable cells in yeast colonies

We propose a model, based on the Gompertz equation, to describe the growth of yeasts colonies on agar medium. This model presents several advantages: (i) one equation describes the colony growth, which previously needed two separate ones (linear increase of radius and of the squared radius); (ii) a similar equation can be applied to total and viable cells, colony area or colony radius, because the number of total cells in mature colonies is proportional to their area; and (iii) its parameters estimate the cell yield, the cell concentration that triggers growth limitation and the effect of this limitation on the specific growth rate. To elaborate the model, area, total and viable cells of 600 colonies of Saccharomyces cerevisiae, Debaryomyces fabryi, Zygosaccharomyces rouxii and Rhodotorula glutinis have been measured. With low inocula, viable cells showed an initial short exponential phase when colonies were not visible. This phase was shortened with higher inocula. In visible or mature colonies, cell growth displayed Gompertz-type kinetics. It was concluded that the cells growth in colonies is similar to liquid cultures only during the first hours, the rest of the time they grow, with near-zero specific growth rates, at least for 3weeks. Mathematical models used to predict microbial growth are based on liquid cultures data. Models describing growth on solid surfaces, highlighting the differences with liquids cultures, are scarce. In this work, we have demonstrated that a single Gompertz equation describes accurately the increase of the yeast colonies, up to the point where they reach their maximum size. The model can be used to quantify the differences in growth kinetics between solid and liquid media. Moreover, as all its parameters have biological meaning, it could be used to build secondary models predicting yeast growth on solid surfaces under several environmental conditions.

Quantitative analysis of morphological changes in yeast colonies growing on solid medium: the eccentricity and Fourier indices.

The colony shape of four yeast species growing on agar medium was measured for 116 days by image analysis. Initially, all the colonies are circular, with regular edges. The loss of circularity can be quantitatively estimated by the eccentricity index, Ei , calculated as the ratio between their orthogonal vertical and horizontal diameters. Ei can increase from 1 (complete circularity) to a maximum of 1.17-1.30, depending on the species. One colony inhibits its neighbour only when it has reached a threshold area. Then, Ei of the inhibited colony increases proportionally to the area of the inhibitory colony. The initial distance between colonies affects those threshold values but not the proportionality, Ei /area; this inhibition affects the shape but not the total surface of the colony. The appearance of irregularities in the edges is associated, in all the species, not with age but with nutrient exhaustion. The edge irregularity can be quantified by the Fourier index, Fi , calculated by the minimum number of Fourier coefficients that are needed to describe the colony contour with 99% fitness. An ad hoc function has been developed in Matlab v. 7.0 to automate the computation of the Fourier coefficients. In young colonies, Fi has a value between 2 (circumference) and 3 (ellipse). These values are maintained in mature colonies of Debaryomyces, but can reach values up to 14 in Saccharomyces. All the species studied showed the inhibition of growth in facing colony edges, but only three species showed edge irregularities associated with substrate exhaustion.

The influence of repetitive thermal stresses on the dominance of reef-building Acropora spp. (Scleractinia) on coral reefs of the Maldive Islands

The distribution and size-age structure of Acropora corals were studied in two Maldivian atolls that differ in their geographic position and sea surface temperature regimes. The frequency and strength of thermal anomalies for the last 2 decades had a significant influence on the abundance, mortality rates, and age structures of acroporid communities. The long-term temperature amplitude was higher and the maxima were more pronounced in the northernmost Ihavandippolu Atoll than those in the equatorial South Huvadhoo Atoll. These differences resulted in a 10.4% mean cover of Acropora at Ihavandippolu Atoll, whereas the Acropora cover in the South Huvadhoo Atoll reached 59.5%. In the northern atoll, the coral mortality rate after the 2010 thermal anomaly was 3 times higher than that in the southern atoll. Younger acroporid colonies (up to 2 years old) dominated the northern atoll reefs, while the southern atoll showed a high proportion of older mature colonies. In both atolls, healthy table colonies of Acropora cytherea with a disk diameter greater than 2 m were observed that apparently survived three thermal anomalies since 1998. The mechanisms of acclimatization of Acropora and the prospects for its dominance in the Maldives under changing environmental conditions are discussed.

Colony founding by the ant Myrmelachista flavocotea

Identifying key life history characters is crucial to understanding the selective forces that influence species interactions and reciprocal evolution. We often know little about colony-founding behavior and colony structure of ants involved in obligate interactions with plants. Here, I describe colony-founding behavior of Myrmelachista flavocotea (Formicidae: Formicinae) on its obligate host plants Ocoteaatirrensis and O. dendrodaphne (Lauraceae) in a lowland Caribbean rainforest at La Selva Biological Station, Costa Rica. Ocotea seedlings produce specialized nodules on the main stem that are used as domatia by founding queens. In this study, Ocotea seedlings were colonized by multiple haplometrotically founding M.flavocotea queens. Mature colonies typically had only a single queen, apparently as a result of secondary monogyny. The number of foundress queens per tree was positively correlated with seedling height and stem diameter (nesting space) at time of colony founding. The extent to which foundress queens cooperate in colony founding is not known. Nonetheless, colony establishment by multiple foundress queens may be critical in ensuring the successful founding by at least one queen, thus allowing the perpetuation of the Myrmelachista-Ocotea interaction.

Differences in Forage-Acquisition and Fungal Enzyme Activity Contribute to Niche Segregation in Panamanian Leaf-Cutting Ants

The genera Atta and Acromyrmex are often grouped as leaf-cutting ants for pest management assessments and ecological surveys, although their mature colony sizes and foraging niches may differ substantially. Few studies have addressed such interspecific differences at the same site, which prompted us to conduct a comparative study across six sympatric leaf-cutting ant species in Central Panama. We show that foraging rates during the transition between dry and wet season differ about 60 fold between genera, but are relatively constant across species within genera. These differences appear to match overall differences in colony size, especially when Atta workers that return to their nests without leaves are assumed to carry liquid food. We confirm that Panamanian Atta specialize primarily on tree-leaves whereas Acromyrmex focus on collecting flowers and herbal leaves and that species within genera are similar in these overall foraging strategies. Species within genera tended to be spaced out over the three habitat categories that we distinguished (forest, forest edge, open grassland), but each of these habitats normally had only a single predominant Atta and Acromyrmex species. We measured activities of twelve fungus garden decomposition enzymes, belonging to the amylases, cellulases, hemicellulases, pectinases and proteinases, and show that average enzyme activity per unit of fungal mass in Atta gardens is lower than in Acromyrmex gardens. Expression profiles of fungal enzymes in Atta also appeared to be more specialized than in Acromyrmex, possibly reflecting variation in forage material. Our results suggest that species- and genus-level identities of leaf-cutting ants and habitat-specific foraging profiles may give predictable differences in the expression of fungal genes coding for decomposition enzymes.

Colony age-dependent pathway in caste development of Coptotermes formosanus Shiraki

The caste developmental pathway for the production of soldiers and nymphs in termite colonies is variable among species and limited numbers of studies have properly categorized such pathways. In this study, the developmental pathway for the production of soldiers and nymphs in Coptotermes formosanus Shiraki has been re-analyzed using the data from previous studies in light of new observations. Five distinct colony life stages were determined based on the caste developmental pathway used by the colony at each stage, which we here redefined as: incipient colony, immature colony, juvenile colony, mature colony, and senescent colony. We determined that in incipient colonies, the first soldier (nanitic) emerges from a second instar larva. We suggest that the production of a nanitic soldier is cost-effective as it allows the colony to focus on the production of workers from the first cohort of individuals. However, in an immature colony, the origin for the production of soldiers shifts to first and second instar workers. In juvenile colonies, soldiers are essentially produced from second instar workers. In mature colonies (>5 years), soldiers are mostly produced from second instar workers, occasionally from third instar workers, and we suggest that nymphs are primarily produced from second instar larvae. Finally, in senescent colonies, the absence of brood leads to the accumulation of old individuals. We concluded that descriptions from previous studies may have overlooked the group dynamics within a colony and that the caste developmental pathway in C. formosanus is dependent on the age of the colony.