Variation In Colony Size Research Articles

Modeling Physical and Physiological Processes Reveals the Role of Turbulence in the Prerequisites for Microcystis Blooms

AbstractHarmful algal blooms of Microcystis have become a global problem. Turbulence, a determining factor affecting blooms, not only disperses surface scum but also controls the growth of Microcystis. Numerous studies have analyzed the effects of turbulence on the growth and colony size of Microcystis in laboratories, but the turbulence thresholds for Microcystis growth and colony disaggregation in the field are difficult to determine due to the complex environment. In addition, the quantitative contribution of turbulence‐driven blooms and the intrinsic mechanisms of the spatial distribution responding to turbulence are unclear. In this study, a fully integrated filed scale computational model focusing on turbulence‐driven blooms was developed, which incorporates physical processes (turbulence‐induced vertical mixing, VMT) and physiological processes such as buoyancy‐controlling transport (BCT), turbulence‐induced colony size variation (CSV), and growth rate variation (GRV). We performed model sensitivity analysis and evaluated the effects of turbulence intensity and duration on the biomass and vertical distribution of Microcystis. The results show that the optimal turbulence dissipation rate for Microcystis growth in the field is 1.0 × 10−5 m2/s3 and the critical turbulence dissipation rate for aggregation distribution is 3.81 × 10−6 m2/s3 in shallow lakes. A quantitative comparison of the effects of physical/physiological processes on blooms shows that physiological processes (CSV, GRV, and BCT) are critical for biomass enrichment, and the accumulation of Microcystis at the water surface is dominated by physical processes (VMT). This study reveals the mechanisms of turbulence‐driven Microcystis blooms and provides new insights for algal bloom prediction and control.

A comparison of the population ecology of 4 Cryptomys hottentotus subspecies

Abstract Selection pressures underpinning the evolution of mammalian sociality and body mass variation have spurred great interest for several decades. Because they inhabit a wide range of geographic localities and habitats, African mole-rat subspecies of Cryptomys hottentotus present a unique opportunity to further our understanding of intra- and interspecific variation of sociality and body mass in mammalian species. We compared the demographics and body masses among 4 C. hottentotus subspecies: the Mahali mole-rat, C. h. mahali; highveld mole-rat, C. h. pretoriae; Natal mole-rat, C. h. natalensis; and common mole-rat, C. h. hottentotus within the context of their respective microclimates and evolutionary history. We propose that all ancestral C. hottentotus subspecies were arid-adapted and thus formed large colonies (as found today in the Mahali mole-rat). However, as the subspecies dispersed to occupy habitats of varying aridity and temperature across South Africa, selection for a particular colony size range in each subspecies arose to provide an adaptive fitness benefit to survive in its habitat. Consequently, the Mahali mole-rat—which remained in a warm and arid environment—retained the largest mean colony size, followed by the Natal mole-rat, which—even though inhabiting a hyper-mesic environment—selected for increased colony sizes to offset the energy requirement of thermoregulation (through huddling) in the cooler montane environments they prefer. The common mole-rat and the highveld mole-rat possessed the smallest mean colony sizes, likely the result of inhabiting a mesic and warm environment. At the same time, body mass variation in the C. hottentotus complex is likely linked to colony size variation, with subspecies having the largest colonies possessing the lowest individual body mass.

Variation in North American bumble bee nest success and colony sizes under captive rearing conditions.

Of the 265 known bumble bee (Bombus) species, knowledge of colony lifecycle is derived from relatively few species. As interest in Bombus commercialization and conservation grows, it is becoming increasingly important to understand colony growth dynamics across a variety of species since variation exists in nest success, colony growth, and reproductive output. In this study, we reported successful nest initiation and establishment rates of colonies and generated a timeline of colony development for 15 western North American Bombus species, which were captively reared from wild-caught gynes from 2009 to 2019. Additionally, we assessed variation in colony size among 5 western North American Bombus species from 2015 to 2018. Nest initiation and establishment rates varied greatly among species, ranging from 5-76.1% and 0-54.6%, respectively. Bombus griseocollis had the highest rates of nest success across the 11-yr period, followed by B. occidentalis, B. vosnesenskii, and B. huntii. Furthermore, days to nest initiation and days to nest establishment varied among species, ranging from 8.4 to 27.7 days and 32.7 to 47 days. Colony size also differed significantly among species with B. huntii and B. vosnesenskii producing more worker/drone cells than B. griseocollis, B. occidentalis, and B. vancouverensis. Additionally, gyne production differed significantly among species with B. huntii colonies producing more gynes than B. vosnesenskii. Results from this study increase knowledge of systematic nesting biology for numerous western North American Bombus species under captive rearing conditions, which can further improve rearing techniques available to conservationists and researchers.

A note on bat faunal assessment in Karuna bat cave, Baglung, Nepal

Abstract In 2019, we surveyed the Karuna bat cave during spring and autumn seasons and recorded two species of fruit bats; Rousettus leschenaultii and Eonycteris spelaea, and two species of insectivorous bats; Hipposideros armiger and Rhinolophus macrotis. Although there was no variation in colony size of insectivorous bats, the fruit bat population (around 38,000 individuals) was only recorded in autumn which indicated seasonal migration. Occasional killing of bats, unsustainable guano extraction, and tourism development threaten this major cave for bats in Nepal. The study recommends prioritizing scientific research and bat friendly cave conservation actions.

The influence of subcolony-scale nesting habitat on the reproductive success of Ad\xe9lie penguins

Group-size variation is common in colonially breeding species, including seabirds, whose breeding colonies can vary in size by several orders of magnitude. Seabirds are some of the most threatened marine taxa and understanding the drivers of colony size variation is more important than ever. Reproductive success is an important demographic parameter that can impact colony size, and it varies in association with a number of factors, including nesting habitat quality. Within colonies, seabirds often aggregate into distinct groups or subcolonies that may vary in quality. We used data from two colonies of Adélie penguins 73 km apart on Ross Island, Antarctica, one large and one small to investigate (1) How subcolony habitat characteristics influence reproductive success and (2) How these relationships differ at a small (Cape Royds) and large (Cape Crozier) colony with different terrain characteristics. Subcolonies were characterized using terrain attributes (elevation, slope aspect, slope steepness, wind shelter, flow accumulation), as well group characteristics (area/size, perimeter-to-area ratio, and proximity to nest predators). Reproductive success was higher and less variable at the larger colony while subcolony characteristics explained more of the variance in reproductive success at the small colony. The most important variable influencing subcolony quality at both colonies was perimeter-to-area ratio, likely reflecting the importance of nest predation by south polar skuas along subcolony edges. The small colony contained a higher proportion of edge nests thus higher potential impact from skua nest predation. Stochastic environmental events may facilitate smaller colonies becoming “trapped” by nest predation: a rapid decline in the number of breeding individuals may increase the proportion of edge nests, leading to higher relative nest predation and hindering population recovery. Several terrain covariates were retained in the final models but which variables, the shapes of the relationships, and importance varied between colonies.

Two-year moving aeration controls cyanobacterial blooms in an extremely eutrophic shallow pond: Variation in phytoplankton community and Microcystis colony size

Artificial mixing is considered as one of the most effective methods for controlling cyanobacterial blooms. However, the success rate of this method is still very low, and whether it could be successfully applied to shallow waters remains unclear. In the current study, a self-designed moving aeration device was employed in an extremely eutrophic shallow pond with water depth of 1.5 m. A similar pond without aeration was set as the control. The experiment was performed over two years (2019–2020). There were no significant differences in the mean values of all water quality parameters (except for ammonia concentration) between the two ponds. Nevertheless, the occurrence of blooms was eliminated in the treated pond in the second year, while cyanobacterial blooms still occurred frequently in the control pond. In the second year of the experiment, Cyanobacteria was the dominant phytoplankton phylum in the control pond, comprising up to 68% of the total community. However, in the treated pond, the maximum proportion of Cyanobacteria was just 30%, while the proportions of Bacillariophyta and Chlorophyta reached approximately 80%. Microcystis was the dominant genus in the control pond, while Scenedesmus and Pediastrum became dominant in the treated pond in the second year. Microcystis colony size decreased substantially in the treated pond in the second year. The results suggest that moving aeration is an environmentally friendly method of controlling cyanobacterial blooms in shallow ponds and lakes. The aeration could disaggregate Microcystis colonies and shift the phytoplankton community from Cyanobacteria to Chlorophyta and Bacillariophyta.

Correlation between the spatial distribution and colony size was common for monogenetic bacteria in laboratory conditions

BackgroundGeographically separated population growth of microbes is a common phenomenon in microbial ecology. Colonies are representative of the morphological characteristics of this structured population growth. Pattern formation by single colonies has been intensively studied, whereas the spatial distribution of colonies is poorly investigated.ResultsThe present study describes a first trial to address the questions of whether and how the spatial distribution of colonies determines the final colony size using the model microorganism Escherichia coli, colonies of which can be grown under well-controlled laboratory conditions. A computational tool for image processing was developed to evaluate colony density, colony size and size variation, and the Voronoi diagram was applied for spatial analysis of colonies with identical space resources. A positive correlation between the final colony size and the Voronoi area was commonly identified, independent of genomic and nutritional differences, which disturbed the colony size and size variation.ConclusionsThis novel finding of a universal correlation between the spatial distribution and colony size not only indicated the fair distribution of spatial resources for monogenetic colonies growing with identical space resources but also indicated that the initial localization of the microbial colonies decided by chance determined the fate of the subsequent population growth. This study provides a valuable example for quantitative analysis of the complex microbial ecosystems by means of experimental ecology.

Partitioning colony size variation into growth and partial mortality.

Body size is a trait that broadly influences the demography and ecology of organisms. In unitary organisms, body size tends to increase with age. In modular organisms, body size can either increase or decrease with age, with size changes being the net difference between modules added through growth and modules lost through partial mortality. Rates of colony extension are independent of body size, but net growth is allometric, suggesting a significant role of size-dependent mortality. In this study, we develop a generalizable model of partitioned growth and partial mortality and apply it to data from 11 species of reef-building coral. We show that corals generally grow at constant radial increments that are size independent, and that partial mortality acts more strongly on small colonies. We also show a clear life-history trade-off between growth and partial mortality that is governed by growth form. This decomposition of net growth can provide mechanistic insights into the relative demographic effects of the intrinsic factors (e.g. acquisition of food and life-history strategy), which tend to affect growth, and extrinsic factors (e.g. physical damage, and predation), which tend to affect mortality.

Sequence of Microcystis colony formation during recruitment under natural conditions

Colony formation by Microcystis is considered to play an important role in bloom development. Population dynamics of benthic and pelagic Microcystis colonies and single cells were investigated in Lake Taihu during recruitment from the sediment. Our results showed that the number of Microcystis single cells in both the water column and sediment was much higher than that of colonies during winter and early spring. In late May, cell density of single cells in the water column was greater than 1 × 105 cells ml−1. This result also suggested that only a portion of the Microcystis single cells formed colonies during recruitment. Microcystis single cells formed colonies on the surface of the sediment where the temperature and light intensity were lower than in the water column. The temporal variation in morphology and colony size of Microcystis in both the water column and sediment demonstrated that a possible sequence of Microcystis colony formation is that colony-forming process begins with loose amorphous colonies formed from single cells in the sediment, then changing to firm amorphous colonies. Afterwards, firm amorphous colonies rise into the water column and some form typical M. ichthyoblabe colony morphology.

The spatial and metabolic basis of colony size variation

Spatial structure impacts microbial growth and interactions, with ecological and evolutionary consequences. It is therefore important to quantitatively understand how spatial proximity affects interactions in different environments. We tested how proximity influences colony size when either Escherichia coli or Salmonella enterica are grown on various carbon sources. The importance of colony location changed with species and carbon source. Spatially explicit, genome-scale metabolic modeling recapitulated observed colony size variation. Competitors that determine territory size, according to Voronoi diagrams, were the most important drivers of variation in colony size. However, the relative importance of different competitors changed through time. Further, the effect of location increased when colonies took up resources quickly relative to the diffusion of limiting resources. These analyses made it apparent that the importance of location was smaller than expected for experiments with S. enterica growing on glucose. The accumulation of toxic byproducts appeared to limit the growth of large colonies and reduced variation in colony size. Our work provides an experimentally and theoretically grounded understanding of how location interacts with metabolism and diffusion to influence microbial interactions.

Progenitor cells from different zones of human cartilage and their correlation with histopathological osteoarthritis progression.

Cell-based therapies development for the treatment of osteoarthritis (OA) requires an understanding of the disease progression and attributes of the cells resident in cartilage. This study focused on quantitative assessment of the concentration and biological potential of stem and progenitor cells resident in different zones of cartilage displaying macroscopic Outerbridge grade 1-2 OA, and their correlation with OA progression based on established histologic scoring system. Lateral femoral condyles were collected from 15 patients with idiopathic OA and varus knees undergoing total knee arthroplasty. Superficial(Csp , top ∼ 500 µm) and deep cartilage(Cdp ) was separated. Chondrogenic Connective Tissue Progenitors (CTP-C) were assayed by standardized Colony-Forming-Unit assay using automated image analysis (ColonyzeTM ) based on ASTM standard F-2944-12. Cell concentration (cells/mg) was significantly greater in Csp (median: 7,000; range: 3,440-17,600) than Cdp (median: 5,340; range: 3,393-9,660), p = 0.039. Prevalence (CTPs/million cells) was not different between Csp (median: 1,274; range: 0-3,898) and Cdp (median:1,365; range:0-6,330), p = 0.42. In vitro performance of CTP-C progeny varied widely within and between patients, manifest by variation in colony size and morphology. Mean histopathological Mankin score was 4.7 (SD = 1.2), representing mild to moderate OA. Tidemark breach by blood vessels was associated with lower Csp cell concentration (p = 0.02). Matrix degradation was associated with lower Cdp cell and CTP-C concentration (p = 0.015 and p = 0.095, respectively), independent of articular surface changes. These findings suggest that the initiation of OA may occur in either superficial or deep zones. The pathological changes affect CTP-Cs in Csp and Cdp cartilage zones differently. The heterogeneity among the available CTP-Cs in Csp and Cdp suggests performance-based selection to optimize cell-sourcing strategies for therapy. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1728-1738, 2018.

The ecology and evolution of colony-size variation

Animals often breed in colonies that can vary in size by several orders of magnitude. Colony-size variation is perplexing because individuals in some colony sizes have lower fitness than those in other colony sizes, yet extensive size variation persists in most populations. Natural variation in colony size has allowed us to better quantify the costs and benefits of coloniality, but what causes and maintains size variation is in general unknown. Ecological correlates of colony-size variation potentially include local availability of resources, such as food or nesting sites, and may also reflect individuals’ sorting among colonies (based on life-history traits, morphology, or behavioral propensities) to find the social environment to which they are best suited. Preferences for particular colony sizes are genetically based in some species. The fitness differences observed among colony sizes may reflect unmeasured tradeoffs among life-history components and also could vary temporally or spatially. Colony-size variation might be maintained by fluctuating directional or stabilizing selection that alternately favors individuals in different group sizes and leads to stasis in the colony-size distribution over the long term. Recent focus on the cues individuals use to select breeding habitat (e.g., conspecific attraction, reproductive success of others) does not satisfactorily explain variation in colony size. Costs of dispersal, reliance on imperfect information, and collective nonrandom movement can also lead to colony-size variation in the absence of fitness-based site selection. Our understanding of factors generating and maintaining variation in colony size remains in its infancy and offers many opportunities for future research with broad implications for behavioral ecology.

Asynchronous spore germination in isogenic natural isolates of Saccharomyces paradoxus.

Spores from wild yeast isolates often show great variation in the size of colonies they produce, for largely unknown reasons. Here we measure the colonies produced from single spores from six different wild Saccharomyces paradoxus strains. We found remarkable variation in spore colony sizes, even among spores that were genetically identical. Different strains had different amounts of variation in spore colony sizes, and variation was not affected by the number of preceding meioses, or by spore maturation time. We used time-lapse photography to show that wild strains also have high variation in spore germination timing, providing a likely mechanism for the variation in spore colony sizes. When some spores from a laboratory strain make small colonies, or no colonies, it usually indicates a genetic or meiotic fault. Here, we demonstrate that in wild strains spore colony size variation is normal. We discuss and assess potential adaptive and non-adaptive explanations for this variation.

Trade-offs in the evolution of bumblebee colony and body size: a comparative analysis.

Trade-offs between life-history traits - such as fecundity and survival - have been demonstrated in several studies. In eusocial insects, the number of organisms and their body sizes can affect the fitness of the colony. Large-than-average body sizes as well as more individuals can improve a colony's thermoregulation, foraging efficiency, and fecundity. However, in bumblebees, large colonies and large body sizes depend largely on high temperatures and a large amount of food resources. Bumblebee taxa can be found in temperate and tropical regions of the world and differ markedly in their colony sizes and body sizes. Variation in colony size and body size may be explained by the costs and benefits associated with the evolutionary history of each species in a particular environment. In this study, we explored the effect of temperature and precipitation (the latter was used as an indirect indicator of food availability) on the colony and body size of twenty-one bumblebee taxa. A comparative analysis controlling for phylogenetic effects as well as for the body size of queens, workers, and males in bumblebee taxa from temperate and tropical regions indicated that both temperature and precipitation affect colony and body size. We found a negative association between colony size and the rainiest trimester, and a positive association between the colony size and the warmest month of the year. In addition, male bumblebees tend to evolve larger body sizes in places where the rain occurs mostly in the summer and the overall temperature is warmer. Moreover, we found a negative relationship between colony size and body sizes of queens, workers, and males, suggesting potential trade-offs in the evolution of bumblebee colony and body size.

Collective Behavior and the Respiratory Physiology of Social Insect Colonies

The ecological success of social insect colonies depends on the functional integration of metabolism and behavior by a multitude of physically independent individuals. To understand the physiological basis of social organization in ant colonies, it is necessary to investigate the respiratory dynamics of social insects across levels of biological organization. Using synchrotron x-ray phase contrast imaging and flow-through respirometry, individual ant workers exhibited discontinuous ventilation and patterns of tracheal compression. In whole colonies, flow-through respirometry revealed a relatively high degree of respiratory synchrony compared to models simulating the collective ventilation of insect groups and parameterized with data from individual-level recordings. Whole colonies consistently exhibited hypometric metabolic allometry with colony size, both based on natural variation in colony size and following experimental manipulation of colony size. In a study of colonies collected from across latitudinal and temperature gradients, the scaling exponent of whole-colony metabolic allometry was not affected by collection location or rearing environment, but did significantly increase with the experimentally manipulated ambient temperature during measurement. These findings support the hypothesis that the metabolism of collective groups is a nonlinear phenomenon dependent on the interactions between individuals within the group and their physical and social environment. This research was conducted with support from the National Science Foundation IOS-1110796 and the James S. McDonnell Foundation. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357].

All you can eat: is food supply unlimited in a colonially breeding bird?

Food availability is generally considered to determine breeding site selection and therefore plays an important role in hypotheses explaining the evolution of colony formation. Hypotheses trying to explain why birds join a colony usually assume that food is not limited, whereas those explaining variation in colony size suggest that food is under constraint. In this study, we investigate the composition and amount of food items not eaten by the nestlings and found in nest burrows of colonially nesting European bee-eaters (Merops apiaster). We aimed to determine whether this unconsumed food is an indicator of unlimited food supply, the result of mistakes during food transfer between parents and chicks or foraging selectivity of chicks. Therefore, we investigated the amount of dropped food for each nest in relation to reproductive performance and parameters reflecting parental quality. Our data suggest that parents carry more food to the nest than chicks can eat and, hence, food is not limited. This assumption is supported by the facts that there is a positive relationship between dropped food found in a nest and the number of fledglings, nestling age, and chick health condition and that the amount of dropped food is independent of colony size. There is variation in the amount of dropped food within colonies, suggesting that parent foraging efficiency may also be an important determinant. Pairs nesting in the center of a colony performed better than those nesting on the edge, which supports the assumption that quality differences between parents are important as well. However, dropped food cannot be used as an indicator of local food availability as (1) within-colony variation in dropped food is larger than between colony variation and, (2) the average amount of dropped food is not related to colony size.

Variation in age composition among colony sizes in Cliff Swallows.

Variation in group size is characteristic of most social species. The extent to which individuals sort among group sizes based on age may yield insight into why groups vary in size and the age-specific costs and benefits of different social environments. We investigated the age composition of Cliff Swallow (Petrochelidon pyrrhonota) colonies of different sizes over 18 years at a long-term study site in western Nebraska, USA. Using years elapsed since banding as a relative measure of age for over 194,000 birds, we found that the proportion of age-class-1 swallows (birds banded as nestlings or juveniles or adults in the year of banding) of both sexes increased in larger colonies and at colony sites becoming active later in the summer. Age composition was unrelated to how often a particular colony site was used. The effect of colony size most likely reflected the fact that older birds return to the same colony site in successive years even when the colony size there decreases, and that yearlings and immigrants benefit more from larger colonies than do older, more experienced individuals. The date effect probably resulted in part from later spring arrival by younger and/or immigrant swallows. At fumigated sites where ectoparasitic swallow bugs (Oeciacus vicarius) had been removed, age composition did not vary with either colony size or colony initiation date. The patterns reported here appear to be driven partially by the presence of ectoparasites and suggest that the hematophagous bugs influence variation in Cliff Swallow group composition. Our results are consistent with the hypothesis that variation in colony size reflects, in part, age-based sorting of individuals among groups.

Spatial and temporal unpredictability of colony size in Cliff Swallows across 30 years

Most colonially breeding animals occupy colonies that range in size from a few pairs to thousands of individuals, but the causes of colony size variation are largely unknown. Three general hypotheses are: (1) that variation in colony size is maintained by fluctuating selection via spatial and temporal changes in fitness associated with different colony sizes; (2) that colony formation reflects heterogeneity in habitat, with some sites having resources to support more individuals than others; and (3) that individuals assess the presence or annual reproductive success of current colony residents at each site and aggregate preferentially at high‐quality sites. These hypotheses make predictions about how consistent colony size should be across sites and among years. We examined temporal and spatial variability of colony size for >200 Cliff Swallow (Petrochelidon pyrrhonota) colony sites in western Nebraska across a 30‐year period. A colony's substrate type, annual population size in the study area, and whether the nesting season was relatively warm or cool, influenced average annual colony size. While some Cliff Swallow colony sites hosted perennially large colonies and others perennially small ones, between‐year variability in colony size at most sites was high. Annual colony size distributions were relatively stable over 30 years and provided no evidence for long‐term directional changes in colony size. The only ecological characteristic that was strongly associated with Cliff Swallow colony size at a site was the type of nesting substrate, with bridges tending to have larger colonies and being more frequently occupied than other substrates. Some sites showed annual changes in colony size consistent with the birds' basing their choice of colony on the presence or success of conspecifics, but many sites did not conform to a pattern expected if coloniality is a by‐product of traditional aggregation. Colony size in Cliff Swallows was temporally and spatially unpredictable when viewed across the 30 years of this study. Each of the three hypotheses to explain size variation may have applied at certain sites, but the pattern of colony size variability leant the most support to the hypothesis that fluctuating selection on group size maintains colonies of widely different sizes.

Colony-size effects on task organization in the harvester ant Pogonomyrmex californicus

Colony size is a fundamental attribute of insect societies that appears to play an important role in their organization of work. In the harvester ant Pogonomyrmex californicus, division of labor increases with colony size during colony ontogeny and among unmanipulated colonies of the same age. However, the mechanism(s) integrating individual task specialization and colony size is unknown. To test whether the scaling of division of labor is an emergent epiphenomenon, as predicted by self-organizational models of task performance, we manipulated colony size in P. californicus and quantified short-term behavioral responses of individuals and colonies. Variation in colony size failed to elicit a change in division of labor, suggesting that colony-size effects on task specialization are mediated by slower developmental processes and/or correlates of colony size that were missing from our experiment. In contrast, the proportional allocation of workers to tasks shifted with colony size, suggesting that task needs or priorities depend, in part, on colony size alone. Finally, although task allocation was flexible, colony members differed consistently in task performance and spatial tendency across colony size treatments. Sources of interindividual behavioral variability include worker age and genotype (matriline).

The Effectiveness of Antimicrobial Defenses Declines with Increasing Group Size and Genetic Similarity

ABSTBACT The secretion of cuticular antimicrobial compounds is an important defensive mechanism for social insects and recent studies have demonstrated their role in the evolution of sociality. However, the factors that might affect their production and effectiveness are not well understood. For example, natural variation in colony size and genetic diversity are predicted to influence susceptibility to disease and, as a consequence, we hypothesized that colonies adjust by varying antimicrobial production. We examined the effects of colony size and genetic diversity on the antimicrobial properties of cuticular compounds in 10 colonies of the Australian paper wasp, Polistes humilis F. ( Vespidae: Polistinae). The effectiveness of antimicrobial compounds produced by a colony was found to increase with genetic diversity but decrease with colony size. Further, genetic diversity appears to be the stronger factor in determining effectiveness of antimicrobial compounds and may compensate for larger group sizes. These data highlight a possible trade-off between increasing group size for work efficiency and maximizing relatedness for indirect fitness benefits, with disease risk being the underlying driving factor.