Colony Mortality Research Articles

Marked annual coral bleaching resilience of an inshore patch reef in the Florida Keys: A nugget of hope, aberrance, or last man standing?

Annual coral bleaching events, which are predicted to occur as early as the next decade in the Florida Keys, are expected to cause catastrophic coral mortality. Despite this, there is little field data on how Caribbean coral communities respond to annual thermal stress events. At Cheeca Rocks, an inshore patch reef near Islamorada, FL, the condition of 4234 coral colonies was followed over 2 yr of subsequent bleaching in 2014 and 2015, the two hottest summers on record for the Florida Keys. In 2014, this site experienced 7.7 degree heating weeks (DHW) and as a result 38.0% of corals bleached and an additional 36.6% were pale or partially bleached. In situ temperatures in summer of 2015 were even warmer, with the site experiencing 9.5 DHW. Despite the increased thermal stress in 2015, only 12.1% of corals were bleached in 2015, which was 3.1 times less than 2014. Partial mortality dropped from 17.6% of surveyed corals to 4.3% between 2014 and 2015, and total colony mortality declined from 3.4 to 1.9% between years. Total colony mortality was low over both years of coral bleaching with 94.7% of colonies surviving from 2014 to 2016. The reduction in bleaching severity and coral mortality associated with a second stronger thermal anomaly provides evidence that the response of Caribbean coral communities to annual bleaching is not strictly temperature dose dependent and that acclimatization responses may be possible even with short recovery periods. Whether the results from Cheeca Rocks represent an aberration or a true resilience potential is the subject of ongoing research.

Drivers of colony losses.

Over the past decade, in some regions of the world, honey bee (Apis mellifera L.) colonies have experienced rates of colony loss that are difficult for beekeepers to sustain. The reasons for losses are complex and interacting, with major drivers including Varroaand related viruses, pesticides, nutrition and beekeeper practices. In these endeavors it has also become apparent that defining a dead colony, and singling out the effects of specific drivers of loss, is not so straightforward. Using the class of neonicotinoid pesticides as an example we explain why quantifying risk factor impact at the colony level is at times elusive and in some cases unpractical. In this review, we discuss the caveats of defining and quantifying dead colonies. We also summarize the current leading drivers of colony losses, their interactions and the most recent research on their effects on colony mortality.

Epormenis cestri secretions in Sebastiania schottiana trees cause mass death of honey bee Apis mellifera larvae in Uruguay.

For more than 60 years, sporadic cases of massive summer honey bee larvae mortality in colonies located near freshwater systems with abundant riparian vegetation have been reported in Uruguay. This odd phenomenon, known as “River disease” by beekeepers, can lead to colony death by depopulation. The aim of this study was to detect the causes of larvae death. Different experiments and analyses were performed using affected apiaries located between two important water courses. 1 day old larvae were the most susceptible and substances that killed the larvae were present in the nectar but not in the pollen. A palynological analysis of nectar samples showed that bees collect this resource from commonly pollinated floral species in the country. However, abundant fungi spores and conidia were found, which indicates that the bees also collected honeydews. In the riparian vegetation, bees were observed collecting the secretions of the planthopper Epormenis cestri on Sebastiania schottiana trees. It was found that the mortality period of larvae overlaps with the presence of E. cestri. Larvae maintained in the laboratory were fed (i) nectar from healthy colonies, (ii) nectar from affected colonies, and (iii) secretions of E. cestri. The mortality of the larvae that received nectar from colonies affected with River disease and secretions of E. cestri was higher than the mortality of those receiving nectar from healthy colonies. This represents the first report of planthopper honeydew causing mass larval mortality in honey bees.

Toxicity and poisoning symptoms of selected insecticides to honey bees (Apis mellifera mellifera L.)

Bees are potential pollinators of wide variety of crops. The European dark bee, Apis mellifera mellifera (L.) is widely used for crop pollination. However, pesticide usage in modern agriculture has threatened the plant-bee pollinator interaction. There is lack of data regarding lethal time, insecticide concentration and poisoning symptoms, especially for formulated insecticides that are widely used in insect management. This study shows that the intrinsic toxicity of insecticides (LC 50 ) to A. mellifera mellifera (L.) was in the following order: imidacloprid (0.0070) > fipronil (0.0125) > indoxacarb (0.0266)> cypermethrin (0.0370) > dimethoate (0.0385). The lethal time (LT 50 ) values (h) in the ascending order of toxicity of insecticides were as follows: fipronil (6.56), cypermethrin (6.69), dimethoate (8.00), imidacloprid (9.85) and indoxacarb (13.45). Distinct poisoning symptoms observed in A. mellifera mellifera were extended proboscis, expanded wings, unhooked wings, extended legs and twisted bodies, defecation on cage covers, sting in release-out position and anus with excreta. All the tested pesticides are harmful to the honey bee except azadirachtin. The tested pesticides exhibited different poisoning symptoms in bees, which could be useful for beekeepers in identifying the cause of colony mortality. In conclusion, the pesticide toxicological research on bees is an important safety aspect for beneficial organisms. This study reveals a realistic acute toxicity in the field of commonly used insecticides. The information is important for insecticide selection in order to minimize direct killing of foraging honey bees while maintaining effective management of crop pests. https://doi.org/10.2298/ABS170131020P Received: January 31, 2017; Revised: April 26, 2017; Accepted: May 16, 2017; Published online: June 12, 2017 How to cite this article: Pashte VV, Patil CS. Toxicity and poisoning symptoms of selected insecticides to honey bees (Apis mellifera mellifera L.). Arch Biol Sci. 2018;70(1):5-12.

Demographics and Population Dynamics Project the Future of Hard Coral Assemblages in Little Cayman

Individual hard coral colonies from four representative reef sites around Little Cayman were surveyed yearly between 2010 and 2015, a period of non-disturbance between two elevated seawater temperature anomalies. Photographic censuses produced 7069 annual transitions that were used to describe the demographics (size class frequencies, abundance, area cover) and population dynamics under non-disturbance environmental conditions. Agariciids, Porites asteroides, and Siderastrea radians have replaced acroporids as the predominant massive corals. Recruitment rates were generally low (2), except for a fourfold recruitment pulse of S. radians that occurred in 2011. On average, 42% of coral recruits survived their first year but only 10% lived longer than four years. Temporal comparisons allowed correction factors to be calculated for in-situ methods that overestimate recruitment of colonies ≤2 cm in diameter and overlook larger colonies. Size class transitions included growth (~33%), stasis (~33%), partial mortality (10% - 33%), and whole colony mortality, which decreased with increasing colony size (typically 30 cm2). Transition matrices indicated that Little Cayman assemblages have declining hard coral populations (λ 150 cm2 surface areas, live area cover may remain relatively stable. Projection models indicated that downward population trends would be exacerbated even by mild disturbance (5% - 10% mortality) scenarios. The fate of hard corals on Little Cayman’s reefs was determined to be heavily dependent on the health and transitions of agariciid colonies. Conservation strategies that currently focus on restoration of Caribbean acroporids should be expanded to include agariciids, which were previously considered “weeds”.

Ecosystem-based management affecting Brandt's Cormorant resources and populations in the central California Current region

The Brandt's Cormorant of the California Current is a “boom-or-bust” species like its congeners in other eastern boundary, upwelling driven ecosystems, and like many of the prey upon which they depend. These birds produce many recruits when fish availability is high, leading to rapidly increasing populations, but few recruits, and may even exhibit die-offs, when the opposite is true. Unlike cormorants in the Peru and Benguela currents, however, Brandt's Cormorant population changes have yet to be correlated with those of its prey. Herein, using multi-decadal time series of cormorant colony size, diet, prey availability and mortality, in the context of changes in breeding site and fishery management, we provide insight into why central California colonies near San Francisco — a major portion of this species' global population — expanded from principally one offshore island in the 1960–70s to include a large mainland component by the 1990s. Involved were increases and decreases, respectively, of northern anchovy, a coastal forage species, and young-of-the year rockfish, more prevalent offshore. With protection of breeding sites and a shift towards ecosystem-based fisheries management by the 1990s, variations of the central California Brandt's Cormorant population are now driven naturally by forage fish availability, and perhaps inter- and intraspecific competition for prey and space when population sizes are high. This species, owing to its “boom-or-bust” natural history and the relative ease of assessing breeding population size and diet, may be ideal for monitoring the state of the central California Current food web.

Comparison of three methods to multiply honey bee (Apis mellifera) colonies

In Canada, there is a growing need for additional honey bee colonies to satisfy the demand for pollination services and compensate for high winter colony mortality. The objective of our study was to compare methodologies that would be both better structured and adapted to producing new colonies in today’s beekeeping industry. Efficacy of three colony production techniques was compared at the Deschambault Research Center for Animal Sciences, Quebec: package bees, one brood frame, two brood frames. Experimental colonies were monitored from July 2014 to June 2015, and several parameters were measured to evaluate their strength and the presence of pathogens. Results showed no statistical difference in colony strength between methods. However, making nuclei from one brood frame offered the greatest multiplication potential and the most advantageous economically. This study also confirmed that nuclei production reduces swarming and varroa infestation levels in mother colonies.

Evolution of the optimal reproductive schedule in the ant Camponotus (Colobopsis) nipponicus (wheeler): a demographic approach

1. Traits are hypothesised to optimise via natural selection. The schedule of reproduction is an important adaptive trait, but its evolution is difficult to study, as measuring parameters is usually difficult. However, the sufficient amounts of demographic data enable us to estimate these parameters.2. Here, it is shown that the reproductive schedule of the ant Camponotus (Colobopsis) nipponicus is tuned to maximise the lifetime production of alates.3. A colony started its reproduction 4 years after the colony founding, at which time they were far smaller than well‐developed colonies. This contradicts the prediction of the bang‐bang strategy theory. The size distribution of colonies in the study area showed that the mortality of small colonies is much higher than that of large colonies.4. A simulation analysis suggests that the colonies that are smaller than the threshold can still achieve significant improvement in colny survival to the following year by investing all resources in colony growth instead of reproduction. A sensitivity analysis for the starting year of reproduction showed that the observed schedule maximises lifetime alate production. The demographic data suggest a stable population, which is required for optimisation through this maximisation.5. The observed reproductive schedule must be optimised, and the breakdown of the bang‐bang theory is due to higher mortalities during the incipient stage of colonies. This study demonstrates that having enough demographic data creates a useful tool for studying the evolution of life‐history characteristics.

Honey bee (Apis mellifera) colony health and pathogen composition in migratory beekeeping operations involved in California almond pollination.

Honey bees are important pollinators of agricultural crops. Pathogens and other factors have been implicated in high annual losses of honey bee colonies in North America and some European countries. To further investigate the relationship between multiple factors, including pathogen prevalence and abundance and colony health, we monitored commercially managed migratory honey bee colonies involved in California almond pollination in 2014. At each sampling event, honey bee colony health was assessed, using colony population size as a proxy for health, and the prevalence and abundance of seven honey bee pathogens was evaluated using PCR and quantitative PCR, respectively. In this sample cohort, pathogen prevalence and abundance did not correlate with colony health, but did correlate with the date of sampling. In general, pathogen prevalence (i.e., the number of specific pathogens harbored within a colony) was lower early in the year (January—March) and was greater in the summer, with peak prevalence occurring in June. Pathogen abundance in individual honey bee colonies varied throughout the year and was strongly associated with the sampling date, and was influenced by beekeeping operation, colony health, and mite infestation level. Together, data from this and other observational cohort studies that monitor individual honey bee colonies and precisely account for sampling date (i.e., day of year) will lead to a better understanding of the influence of pathogens on colony mortality and the effects of other factors on these associations.

Disruption of oxidative balance in the gut of the western honeybee Apis mellifera exposed to the intracellular parasite Nosema ceranae and to the insecticide fipronil

SummaryThe causes underlying the increased mortality of honeybee colonies remain unclear and may involve multiple stressors acting together, including both pathogens and pesticides. Previous studies suggested that infection by the gut parasite Nosema ceranae combined with chronic exposure to sublethal doses of the insecticide fipronil generated an increase in oxidative stress in the midgut of honeybees. To explore the impact of these two stressors on oxidative balance, we experimentally infected bees with N. ceranae and/or chronically exposed to fipronil at low doses for 22 days, and we measured soluble reactive oxygen species (ROS) and ROS damage by quantifying both protein and lipid oxidation in the midgut. Our results revealed a disruption of the oxidative balance, with a decrease in both the amount of ROS and ROS damage in the presence of the parasite alone. However, protein oxidation was significantly increased in the N. ceranae/fipronil combination, revealing an increase in oxidative damage and suggesting higher fipronil toxicity in infected bees. Furthermore, our results highlighted a temporal order in the appearance of oxidation events in the intestinal cells and revealed that all samples tended to undergo protein oxidation during ageing, regardless of treatment.

Thermal stress exposure, bleaching response, and mortality in the threatened coral Acropora palmata

Demographic data for Elkhorn coral, Acropora palmata, and in situ water temperature data from seven upper Florida Keys (USA) reefs revealed three warm thermal stress events between 2010 and 2016. During a mild bleaching event in 2011, up to 59% of colonies bleached, but no mortality resulted. In both 2014 and 2015, severe and unprecedented bleaching was observed with up to 100% of colonies bleached. A. palmata live tissue cover declined by one-third following the 2014–2015 events. Colony mortality of mildly- and non-bleached colonies did not differ but increased significantly with more severe bleaching. Increased bleaching prevalence corresponded to maximum daily average water temperatures above 31.3°C. However, the cumulative days with daily average exceeding 31.0°C provided a better predictor of bleaching response. The bleaching response of surviving colonies in 2015 was not consistent with acclimatization as most individual colonies bleached at least as badly as in 2014.

The virulent, emerging genotype B of Deformed wing virus is closely linked to overwinter honeybee worker loss

Bees are considered to be threatened globally, with severe overwinter losses of the most important commercial pollinator, the Western honeybee, a major concern in the Northern Hemisphere. Emerging infectious diseases have risen to prominence due to their temporal correlation with colony losses. Among these is Deformed wing virus (DWV), which has been frequently linked to colony mortality. We now provide evidence of a strong statistical association between overwintering colony decline in the field and the presence of DWV genotype-B (DWV-B), a genetic variant of DWV that has recently been shown to be more virulent than the original DWV genotype-A. We link the prevalence of DWV-B directly to a quantitative measure of overwinter decline (workforce mortality) of honeybee colonies in the field. We demonstrate that increased prevalence of virus infection in individual bees is associated with higher overwinter mortality. We also observed a substantial reduction of infected colonies in the spring, suggesting that virus-infected individuals had died during the winter. Our findings demonstrate that DWV-B, plus possible A/B recombinants exhibiting DWV-B at PCR primer binding sites, may be a major cause of elevated overwinter honeybee loss. Its potential emergence in naïve populations of bees may have far-reaching ecological and economic impacts.

Persistence of subclinical deformed wing virus infections in honeybees following Varroa mite removal and a bee population turnover

Deformed wing virus (DWV) is a lethal virus of honeybees (Apis mellifera) implicated in elevated colony mortality rates worldwide and facilitated through vector transmission by the ectoparasitic mite Varroa destructor. Clinical, symptomatic DWV infections are almost exclusively associated with high virus titres during pupal development, usually acquired through feeding by Varroa mites when reproducing on bee pupae. Control of the mite population, generally through acaricide treatment, is essential for breaking the DWV epidemic and minimizing colony losses. In this study, we evaluated the effectiveness of remedial mite control on clearing DWV from a colony. DWV titres in adult bees and pupae were monitored at 2 week intervals through summer and autumn in acaricide-treated and untreated colonies. The DWV titres in Apistan treated colonies was reduced 1000-fold relative to untreated colonies, which coincided with both the removal of mites and also a turnover of the bee population in the colony. This adult bee population turnover is probably more critical than previously realized for effective clearing of DWV infections. After this initial reduction, subclinical DWV titres persisted and even increased again gradually during autumn, demonstrating that alternative non-Varroa transmission routes can maintain the DWV titres at significant subclinical levels even after mite removal. The implications of these results for practical recommendations to mitigate deleterious subclinical DWV infections and improving honeybee health management are discussed.

The ecological and genetic basis of annual worker production in the desert seed harvesting ant, Veromessor pergandei

Colony size is an important predictor of annual survival and reproduction in social insects. By tracking monthly forager turn over, we measured the size-specific production rates necessary to counteract forager mortality in wild Veromessor pergandei colonies. Between 31,180 and 237,980 individuals appeared as foragers annually, representing an eightfold difference in production between neighboring nests. Highly productive colonies housed 26,000 foragers at one time, turned over 34,000 foragers in a single month, and produced 470 g of worker biomass during the year. Each forager population turned over approximately 20 times during the year, cumulatively returning 3.4 kg of biomass per hectare (with 14 nests per hectare). Forager longevity was not influenced by forager number, season, or pressure from neighboring conspecifics. Genotyping at three microsatellite loci revealed that all colonies contained a single queen and one to seven patrilines (mean m observed = 3.8; m e = 2.56). The most productive colonies had significantly fewer patrilines, a larger peak forager population, and a larger annual foraging range. Colonies varied in their ability to replace lost workers, adding anywhere from 2 to 42 new foragers per death during peak forager allocation. Seasonal increases in forager population size corresponded to decreases in worker body size, suggesting a trade-off during production earlier in the year. Together, these findings demonstrate how the combination of individual colony-member characteristics influence whole colony survival across multiple years. The survival of an animal society can depend on its size and stability. We measured the seasonal relationships between mortality and production of new colony members, with respect to foraging range size, paternity, neighbor pressure, and body size in a desert seed harvesting ant. Mortality rate was stable across seasons, but the ability of colonies to replace dead individuals corresponded to increased foraging range size, decreased patriline number, and seasonal decreases in body size. Our findings reveal the characteristics that allow colonies to respond to worker mortality on an annual scale.

Is Acarapis woodi mite currently infesting Apis mellifera colonies in Argentina?

The honey bee tracheal mite Acarapis woodi (Rennie) (Acari: Tarsonemidae) is an internal obligate parasite of the respiratory system of adult honey bees (Apis mellifera), which may be one of the factors causing the loss of bee colonies and the decrease in the beekeeping industry. In Argentina, the last prevalence study of A. woodi was in 1998, and therefore there is no current data on the prevalence and impact of the mite in colonies of A. mellifera in this country. For this reason, the objective of this study was to determine the prevalence of A. woodi in honey bee colonies of apiaries belonging to different geographic regions of Argentina (Northwest, Chaco, Mesopotamic, Pampean and Patagonic) using two different methods of diagnosis. One method was traditional microscopy, which is based on direct visualization of A. woodi in the prothoracic tracheas of bees, and the other technique was molecular analysis using real-time PCR with specific primers to amplify CO1 gene of A. woodi. To perform the analysis of prevalence, bees were collected during winter, because during this season, populations of A. woodi are more abundant in bee colonies. The results were negative for both methods of diagnosis, with prevalence equal to 0%. Considering that in recent years it has been reported an increased mortality in bee colonies in Argentina, we note that acarapisosis is not currently impacting on the disappearance of A. mellifera colonies in Argentina.

Response of sea fans to infection with Aspergillus sp. (Fungi)

Mass mortalities of sea fans (Gorgonia spp.) off the South and Central American coasts were reported in the 1980s. In some cases, populations never recovered. Widespread tissue mortality in G. ventalina and G. flabellum throughout the Caribbean was reported in 1997. Although colony mortality was apparently lower in the more recent epizootic, the geographic distribution of the disease appeared much greater. Tissue samples of affected colonies were found to be infected with a fungus (Aspergillus sp.) with was shown to be able to cause the disease in healthy sea fans. We describe observations on the early infection process and subsequent development of the disease. Based on these observations, we report the response of Gorgina spp. to infection by Aspergillus.

Causes of colony mortality in bumblebees

AbstractDespite considerable interest in bumblebees and their conservation, few data are available on basic life‐history parameters such as rates of nest predation and the proportion of wild nests that survive to reproduction. Here, we use a combination of data collected by volunteers and our own direct observations which together describe the fate of 908 bumblebee nests in the UK between 2008 and 2013. Overall, 75% of nests produced gynes, with marked differences between species; the recently arrived species, Bombus hypnorum, had the highest proportion of colonies surviving to gyne production (96%), with the long‐tongued Bombus hortorum having the lowest success in reaching gyne production (41%). There were also large differences between bumblebee species in the timing of nesting, gyne production and nest mortality, with B. hypnorum and Bombus pratorum nests starting early, producing most gynes before mid‐summer, and then dying off in June, whereas at the other end of the spectrum Bombus pascuorum nests started late and produced gynes mainly in August. There was evidence for the partial or complete destruction of 100 nests. The main reported causes were excavation by a large mammal, probably primarily Meles meles (50%). Human disturbance was the second greatest cause of nest mortality (26%), followed by flooding (7%). Wax moth infestations were common (55% of nests), with B. hypnorum nests most frequently infested. However, infestation did not results in reduced likelihood of gyne production, perhaps because infestations often do not become severe until after some gynes have been produced. Our study provides novel insights into the little‐studied biology of wild bumblebee nests and factors affecting their survival; collecting similar datasets in the future would enable fascinating comparisons as to how parameters such as nest survival and reproduction are changing over time, and are affected by management interventions for bees.

The Exposure of Honey Bees to Pesticide Residues in the Hive Environment with Regard to Winter Colony Losses

Abstract The present studies are the second part of the research project dedicated to finding the causes for increased winter mortality of honey bee colonies. The aim of this task was to investigate incidents of overwintered colonies′ death with regard to the potential interrelation to the exposure to pesticides. The samples of winter stores of bee bread and sugar food (honey or syrup processed by bees), beeswax and bees collected from apiaries with low and high rates of winter colony mortality were searched for acaricides used to control V. destructor and plant protection pesticides. The presence of acaricides used in apiculture has been detected in the 51% beeswax samples. The most abundant acaricide was tau-fluvalinate. The stores of bee bread and sugar food had a similar frequency of plant protection pesticide occurrence, ranging between 50-60%, but the number of active substances and their concentrations were substantially lower in sugar food samples. The most prevalent pesticides in pollen were fungicides (carbendazim and boscalid) and insecticides (acetamiprid and thiacloprid). Only a few pesticides were found in the several dead honey bees. The level of pesticide contamination (frequency, concentration, toxicity) of hive products and bees originating from apiaries with both a high and low winter colony survival rates, was similar, which created a similar extent of risk. Although the multiple varroacides and pesticides were present in the hive environment we not found unequivocal links between their residues and high winter colony mortality.

Modelling environmental drivers of black band disease outbreaks in populations of foliose corals in the genus Montipora

Seawater temperature anomalies associated with warming climate have been linked to increases in coral disease outbreaks that have contributed to coral reef declines globally. However, little is known about how seasonal scale variations in environmental factors influence disease dynamics at the level of individual coral colonies. In this study, we applied a multi-state Markov model (MSM) to investigate the dynamics of black band disease (BBD) developing from apparently healthy corals and/or a precursor-stage, termed ‘cyanobacterial patches’ (CP), in relation to seasonal variation in light and seawater temperature at two reef sites around Pelorus Island in the central sector of the Great Barrier Reef. The model predicted that the proportion of colonies transitioning from BBD to Healthy states within three months was approximately 57%, but 5.6% of BBD cases resulted in whole colony mortality. According to our modelling, healthy coral colonies were more susceptible to BBD during summer months when light levels were at their maxima and seawater temperatures were either rising or at their maxima. In contrast, CP mostly occurred during spring, when both light and seawater temperatures were rising. This suggests that environmental drivers for healthy coral colonies transitioning into a CP state are different from those driving transitions into BBD. Our model predicts that (1) the transition from healthy to CP state is best explained by increasing light, (2) the transition between Healthy to BBD occurs more frequently from early to late summer, (3) 20% of CP infected corals developed BBD, although light and temperature appeared to have limited impact on this state transition, and (4) the number of transitions from Healthy to BBD differed significantly between the two study sites, potentially reflecting differences in localised wave action regimes.

Decreasing worker size diversity does not affect colony performance during laboratory challenges in the ant Temnothorax nylanderi

Within-colony phenotypic diversity can play an essential role in some eusocial insect taxa by increasing the performance of division of labor, thereby increasing colony fitness. Empirical studies of the effect of phenotypic diversity on colony fitness mostly focused on species with discrete castes (workers, soldiers) or with continuously and highly morphologically variable workers, which is not the most common case. Indeed, most species exhibit continuous but limited worker morphological variation. It is still unclear whether this variation impacts colony fitness. To test this, we reduced the worker size diversity in 25 colonies of the ant Temnothorax nylanderi and compared their performances to 25 control colonies. We reared these colonies in the laboratory and measured the effect of treatment (reduced diversity or control) and colony size (number of workers) on colony performance at six challenges, as well as on worker mortality and brood production. The reduction of worker size diversity did not affect colony performance nor mortality and brood production. As expected, colony performance and brood production increased with colony size. These results suggest that worker size diversity may not be under positive selection in this species, but rather the product of a lack of developmental canalization. We propose that social life could decrease the selective pressures maintaining developmental canalization, subsequently leading to higher size diversity without necessarily increasing colony performance.