Social variety in the yellow-bellied marmot (Marmota flaviventris)

The social behaviour of high and medium elevation colonies of yellow-bellied marmots in Rocky Mountain National Park, Colorado, were studied. The medium elevation animals were consistently larger, exhibiting greater physical spacing, lower frequencies of greeting and upright playfighting, and a higher agonistic component than did those of the more closely-integrated high-elevation colony. These results are interpreted as part of a complex series of adaptations within the genus Marmota to variations in ecology related to growing season.     

Persistent social interactions beget more pronounced personalities in a desert-dwelling social spider

The social niche specialization hypothesis predicts that repeated social interactions will generate social niches within groups, thereby promoting consistent individual differences in behaviour. Current support for this hypothesis is mixed, probably because the importance of social niches is dependent upon the ecology of the species. We test whether repeated interactions among group mates generate consistent individual differences in boldness in the social spider, Stegodyphus dumicola. In support of the social niche specialization hypothesis, we found that consistent individual differences in boldness increased with longer group tenure. Interestingly, these differences took longer to appear than in previous work suggesting this species needs more persistent social interactions to shape its behaviour. Recently disturbed colonies were shyer than older colonies, possibly reflecting differences in predation risk. Our study emphasizes the importance of the social environment in generating animal personalities, but also suggests that the pattern of personality development can depend on subtle differences in species'' ecologies.     

The social behaviour of the hoary marmot (Marmota caligata)

The social behaviour of four colonies of hoary marmots (Marmota caligata) was studied in Glacier National Park, Montana, during the summer of 1970. Colony structure involved a dominant male with a few females (3 years or older), 2-year-olds, yearlings and pups. Patterns of burrow use, greetings, play, and aggressive chasing are described, indicating a closely-integrated social structure with reproductive patterns suggesting late dispersal and maturation. A close resemblance to the behaviour of the Olympic marmot (M. olympus) is proposed.     

Ectoparasites,Fitness, and Social Behaviour of Yellow-Bellied Marmots

Parasites can cause a loss of fitness for their hosts, potentially influencing social behaviour patterns of the host that promote or hinder parasite transmission. I studied yellow-bellied marmots (Marmota flaviventris) and their ectoparasites to determine if ectoparasites reduce the fitness of marmots and to test whether ectoparasite loads differ according to social behaviour. Three taxa of ectoparasites were identified, fleas (Oropsylla Stanfordi), lice (Linognathoides marmotae), and mites (family Dermanyssidae). High ectoparasite loads were related to slower growth, lower overwinter survival, and reduced reproduction, suggesting that ectoparasites are a fitness cost for marmots. Ectoparasite loads were not higher in colonial than in noncolonial marmots, nor in polygynous than in monogamous adult males. There was a trend, however, toward higher ectoparasite loads in marmots that were dispersing rather than philopatric. Further, ectoparasite loads differed among groups of marmots that nested or hibernated communally, indicating that spatial scale is important in understanding the relationships between parasites and social behaviour.     

The legacy effects of keystone individuals on collective behaviour scale to how long they remain within a group

The collective behaviour of social groups is often strongly influenced by one or few individuals, termed here ‘keystone individuals’. We examined whether the influence of keystone individuals on collective behaviour lingers after their departure and whether these lingering effects scale with their tenure in the group. In the social spider, Stegodyphus dumicola, colonies'' boldest individuals wield a disproportionately large influence over colony behaviour. We experimentally manipulated keystones'' tenure in laboratory-housed colonies and tracked their legacy effects on collective prey capture following their removal. We found that bolder keystones caused more aggressive collective foraging behaviour and catalysed greater inter-individual variation in boldness within their colonies. The longer keystones remained in a colony, the longer both of these effects lingered after their departure. Our data demonstrate that, long after their disappearance, keystones have large and lasting effects on social dynamics at both the individual and colony levels.     

Rapid anti-pathogen response in ant societies relies on high genetic diversity

Social organisms are constantly exposed to infectious agents via physical contact with conspecifics. While previous work has shown that disease susceptibility at the individual and group level is influenced by genetic diversity within and between group members, it remains poorly understood how group-level resistance to pathogens relates directly to individual physiology, defence behaviour and social interactions. We investigated the effects of high versus low genetic diversity on both the individual and collective disease defences in the ant Cardiocondyla obscurior. We compared the antiseptic behaviours (grooming and hygienic behaviour) of workers from genetically homogeneous and diverse colonies after exposure of their brood to the entomopathogenic fungus Metarhizium anisopliae. While workers from diverse colonies performed intensive allogrooming and quickly removed larvae covered with live fungal spores from the nest, workers from homogeneous colonies only removed sick larvae late after infection. This difference was not caused by a reduced repertoire of antiseptic behaviours or a generally decreased brood care activity in ants from homogeneous colonies. Our data instead suggest that reduced genetic diversity compromises the ability of Cardiocondyla colonies to quickly detect or react to the presence of pathogenic fungal spores before an infection is established, thereby affecting the dynamics of social immunity in the colony.     

Reproductive success in a socially polymorphic spider: social individuals experience depressed reproductive success in isolation

1. Correlated individual differences in behaviour across ecological contexts, or behavioural syndromes, can theoretically constrain individuals' ability to optimally adjust their behaviour for specific contexts. 2. Female Anelosimus studiosus exhibit a unique behavioural polymorphism: ‘social’ females are tolerant of conspecifics and aggregate in multi‐female colonies, while ‘solitary’ females aggressively defend their singleton webs from intrusion by adult female conspecifics. Previous work found that social females are also less aggressive toward prey and are more fearful of predators. 3. In this study we quantify potential fitness consequences of these correlated behaviours by examining the potential and realised fecundities of the two phenotypes in naturally occurring colonies, and by quantifying their ability to rear offspring as singleton individuals. 4. There were no differences in the fecundities of laboratory‐reared females between the phenotypes, nor were there differences in field‐collected brooding females from naturally occurring solitary and social nests. 5. Brooding females from solitary and social colonies that were isolated in new nests for the growing season were both capable of rearing their broods; however, females from solitary nests had significantly greater success. 6. These results suggest a fitness consequence to the reduced‐aggression syndrome of social females that may represent a general impediment to the evolution of sociality in spiders.     

No Genetic Tradeoffs between Hygienic Behaviour and Individual Innate Immunity in the Honey Bee,Apis mellifera

Many animals have individual and social mechanisms for combating pathogens. Animals may exhibit short-term physiological tradeoffs between social and individual immunity because the latter is often energetically costly. Genetic tradeoffs between these two traits can also occur if mutations that enhance social immunity diminish individual immunity, or vice versa. Physiological tradeoffs between individual and social immunity have been previously documented in insects, but there has been no study of genetic tradeoffs involving these traits. There is strong evidence that some genes influence both innate immunity and behaviour in social insects – a prerequisite for genetic tradeoffs. Quantifying genetic tradeoffs is critical for understanding the evolution of immunity in social insects and for devising effective strategies for breeding disease-resistant pollinator populations. We conducted two experiments to test the hypothesis of a genetic tradeoff between social and individual immunity in the honey bee, Apis mellifera. First, we estimated the relative contribution of genetics to individual variation in innate immunity of honey bee workers, as only heritable traits can experience genetic tradeoffs. Second, we examined if worker bees with hygienic sisters have reduced individual innate immune response. We genotyped several hundred workers from two colonies and found that patriline genotype does not significantly influence the antimicrobial activity of a worker’s hemolymph. Further, we did not find a negative correlation between hygienic behaviour and the average antimicrobial activity of a worker’s hemolymph across 30 honey bee colonies. Taken together, our work indicates no genetic tradeoffs between hygienic behaviour and innate immunity in honey bees. Our work suggests that using artificial selection to increase hygienic behaviour of honey bee colonies is not expected to concurrently compromise individual innate immunity of worker bees.     

Habitat preferences in gray marmots (Marmota baibacina)

We examined habitat preferences of the Southern Altai subspecies of gray marmots (Marmota baibacina baibacina) both at the small and large scale. Considerable differences in habitat use among the gray marmot (sub)species complex have been described; Marmota kastschenkoi possibly represents the only forest-dwelling Palearctic marmot. Our results show that habitat use in Southern Altai marmots is determined mainly by vegetation type. The Altai marmots preferred grasslands and shrublands and their distribution was limited to the alpine zone above timberline. Marmots clearly avoided woodlands, even the forest edges and forest-steppe areas with a tree cover greater than 10 %. Gray marmots occur rarely in habitats occupied by alpine pikas, whereas presence of ground squirrels had no effect on marmot distribution. Altai marmots preferred mesic habitats with permeable subsoil layers. Livestock grazing and human disturbance did not affect marmot occurrence. Habitat requirements of examined Altai subspecies M. baibacina baibacina differ from the forest-steppe M. kastschenkoi; nevertheless, the ecological factors to which the forest-dwelling species responds remain to be analyzed. A recent speciation process in gray marmot complex was followed by the evolution of ecological requirements resulting in adaptation to forest dwelling.     

Evidence of social niche construction: persistent and repeated social interactions generate stronger personalities in a social spider

While there are now a number of theoretical models predicting how consistent individual differences in behaviour may be generated and maintained, so far, there are few empirical tests. The social niche specialization hypothesis predicts that repeated social interactions among individuals may generate among-individual differences and reinforce within-individual consistency through positive feedback mechanisms. Here, we test this hypothesis using groups of the social spider Stegodyphus mimosarum that differ in their level of familiarity. In support of the social niche specialization hypothesis, individuals in groups of spiders that were more familiar with each other showed greater repeatable among-individual variation in behaviour. Additionally, individuals that were more familiar with each other exhibited lower within-individual variation in behaviour, providing one of the first examples of how the social environment can influence behavioural consistency. Our study demonstrates the potential for the social environment to generate and reinforce consistent individual differences in behaviour and provides a potentially general mechanism to explain this type of behavioural variation in animals with stable social groups.     

The relationship between population size,amount of brood,and individual foraging behaviour in the honey bee,Apis mellifera L.

This study experimentally examines the relationship between colony state and the behaviour of individual pollen and nectar foragers in the honey bee, Apis mellifera L. In the first experiment we test the prediction that individual pollen foragers from colonies with higher brood quantities should exhibit a greater work effort for pollen resources than individual pollen foragers from colonies with low brood quantities. Eight colonies were assigned into two treatment groups; HIGH brood colonies were manipulated to contain 9600±480 cm² brood area; LOW brood colonies were manipulated to contain 1600±80 cm² brood area. We measured colony brood levels over the course of the experiment and collected individual pollen loads from returning pollen foragers. We found that, while colonies remained significantly different in brood levels, individual pollen foragers from HIGH brood colonies collected larger loads than individuals from LOW brood colonies. In the second experiment we investigated the influence of colony size on the behaviour of individual nectar foragers. We assigned eight colonies to two treatment groups; LARGE colonies were manipulated to contain 35000±1700 adult workers with 3500±175 cm² brood area, and SMALL colonies were manipulated to contain 10000±500 adult workers with 1000±50 cm² brood area. We observed foraging trips of individually marked workers and found that individuals from LARGE colonies made longer foraging trips than those from SMALL colonies (LARGE: 1666.7±126.4 seconds, SMALL: 1210.8±157.6 seconds), and collected larter nectar loads (LARGE: 19.2±1.0 l, SMALL: 14.6±0.8 l). These results indicate that individual nectar foragers from LARGE colonies tend to work harder than individuals from SMALL colonies. Both experiments indicate that the values of nectar and pollen resources to a colony change depend on colony state, and that individual foragers modify their behaviour accordingly.     

Ecological,Evolutionary and Social Constraints on Reproductive Effort: Are Hoary Marmots Really Biennial Breeders?

Biennial breeding is a rare life-history trait observed in animal species living in harsh, unproductive environments. This reproductive pattern is thought to occur in 10 of 14 species in the genus Marmota, making marmots useful model organisms for studying its ecological and evolutionary implications. Biennial breeding in marmots has been described as an obligate pattern which evolved as a mechanism to mitigate the energetic costs of reproduction (Evolved Constraint hypothesis). However, recent anecdotal evidence suggests that it is a facultative pattern controlled by annual variation in climate and food availability (Environmental Constraint hypothesis). Finally, in social animals like marmots, biennial breeding could result from reproductive competition between females within social groups (Social Constraint hypothesis). We evaluated these three hypotheses using mark-recapture data from an 8-year study of hoary marmot (Marmota caligata) population dynamics in the Yukon. Annual variation in breeding probability was modeled using multi-state mark-recapture models, while other reproductive life-history traits were modeled with generalized linear mixed models. Hoary marmots were neither obligate nor facultative biennial breeders, and breeding probability was insensitive to evolved, environmental, or social factors. However, newly mature females were significantly less likely to breed than older individuals. Annual breeding did not result in increased mortality. Female survival and, to a lesser extent, average fecundity were correlated with winter climate, as indexed by the Pacific Decadal Oscillation. Hoary marmots are less conservative breeders than previously believed, and the evidence for biennial breeding throughout Marmota, and in other arctic/alpine/antarctic animals, should be re-examined. Prediction of future population dynamics requires an accurate understanding of life history strategies, and of how life history traits allow animals to cope with changes in weather and other demographic influences.     

Social structure and facultative mating systems of hoary marmots (Marmota caligata)

Mate-choice theory predicts different optimal mating systems depending on resource availability and habitat stability. Regions with limited resources are thought to promote monogamy. We tested predictions of monogamy in a social rodent, the hoary marmot (Marmota caligata), at the northern climatic extreme of its distribution. Mating systems, social structure and genetic relationships were investigated within and among neighbouring colonies of marmots within a 4 km(2) valley near Kluane National Park, Yukon, Canada, using 21 microsatellite loci. While both monogamous and polygynous populations of hoary marmots have been observed in the southern reaches of this species' range; northern populations of this species are thought to be predominantly monogamous. Contrary to previous studies, we did not find northern hoary marmot social groups to be predominantly monogamous; rather, the mating system seemed to be facultative, varying between monogamy and polygyny within, as well as among, social groups. These findings reveal that the mating systems within colonies of this species are more flexible than previously thought, potentially reflecting local variation in resource availability.     

Secretions of the interaural gland contain information about individuality and colony membership in the Bechstein's bat

Mammals use chemical signals for individual and kin recognition, to establish social hierarchies, mark territories and choose mates. The nocturnal and social lifestyle of bats suggests that, besides acoustic signals, they also use scent to communicate. We investigated in the communally breeding Bechstein's bat, Myotis bechsteinii, whether secretions of the facial interaural gland contain information that can be used for individual and colony recognition. Since female Bechstein's bats live in closed societies and show cooperative behaviour, we predicted they would recognize colony members. We analysed interaural gland secretions, which we repeatedly sampled from 85 females belonging to four free-ranging colonies. Gas chromatography/mass spectrometry profiles were individually specific and differed between colonies. Comparing odour profiles between colonies we found a relation between chemical similarity and the mitochondrial haplotype of colony members. Within colonies there was no correlation between mass spectrometer profile similarity and genetic relatedness. Our results suggest that female Bechstein's bats may use interaural gland secretions for individual and colony recognition but not to infer kinship directly.Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Social responses to variation in food supply and nest suitability in ants (Tapinoma erraticum)

The social organization of Tapinoma erraticum colonies has been studied in two environmental contexts: those of mild starvation and of disturbance inducing a complete change of nest site. Trophallactic activity was compared with brood transport behaviour in tests performed repeatedly on the same group of insects. Workers were individually marked enabling interactions to be analysed within the group. An age-dependent difference in behaviour exists during feeding. However, when the colony changed its location, certain workers were found to be transport specialists, whereas others remained inactive: the transport behaviour of T. erraticum workers does not appear to be agedependent, unlike feeding behaviour. A principal components analysis of the results indicated no link between these two types of activities at the individual level. This study indicates the existence of types of social organization which are specific to each of the activities performed.     

Reliability and the adaptive utility of discrimination among alarm callers

Unlike individually distinctive contact calls, or calls that aid in the recognition of young by their parents, the function or functions of individually distinctive alarm calls is less obvious. We conducted three experiments to study the importance of caller reliability in explaining individual-discriminative abilities in the alarm calls of yellow-bellied marmots (Marmota flaviventris). In our first two experiments, we found that calls from less reliable individuals and calls from individuals calling from a greater simulated distance were more evocative than calls from reliable individuals or nearby callers. These results are consistent with the hypothesis that marmots assess the reliability of callers to help them decide how much time to allocate to independent vigilance. The third experiment demonstrated that the number of callers influenced responsiveness, probably because situations where more than a single caller calls, are those when there is certain to be a predator present. Taken together, the results from all three experiments demonstrate the importance of reliability in explaining individual discrimination abilities in yellow-bellied marmots. Marmots' assessment of reliability acts by influencing the time allocated to individual assessment and thus the time not allocated to other activities.     

Stress in an underground empire

The naked mole-rat (Heterocephalus glaber) and the Damaraland mole-rat (Fukomys damarensis) live in large colonies in underground tunnel systems in sub-Saharan Africa. Most members of the colonies are suppressed from reproduction and they are unlikely to reproduce during their lifetime. Only one female and a small number of males reproduce. This extreme cooperative social system has fascinated researchers since the naked mole-rat was first described as eusocial. Despite much research into the mechanisms of social suppression, the exact mechanisms are still unclear. Much evidence points towards high glucocorticoid concentrations caused by agonistic behaviour by the breeding female suppressing reproduction of non-breeders, but laboratory studies have not found any differences in glucocorticoids between breeders and non-breeders. There is, however, considerable evidence from field studies and other social mole-rats that social stress may indeed be an important factor of social suppression in social mole-rats and that those mechanisms are affected by the stability of the colony and environmental conditions. This review aims to provide a summary of the current knowledge of the relationship between environmental conditions, colony stability, glucocorticoids and reproductive suppression in social mole-rat species and suggests some avenues for future research.     

Features of Interspecific Contacts and Hybridization of Ground Squirrels (Marmotinae,Sciuridae, Rodentia) in Mongolia

Using molecular genetic methods, we investigated the secondary contact zones of two pairs of species of ground squirrels of Mongolia. In common colonies of marmots M. sibirica and M. baibacina, we revealed a high frequency of occurrence of hybrid individuals that were viable and fertile. A hybridization between S. alaschanicus and S. pallidicauda was sporadic in nature. The hypothesis about an extensive hybrid zone in these species of ground squirrels was not confirmed. An occupation of suboptimal biotopes by individuals of different species was the main factor contributing to hybridization in both case. The complex social behavior in marmots affected on the localization and diffusion of the hybridization process.     

Reproductive suppression in female Alpine marmots, Marmota marmota

We studied mechanisms responsible for reproductive skew in female Alpine marmots. In each social group, only dominant females produced weaned young although subordinate females had similar body condition, were fertile as indicated by high levels of oestradiol during the mating season, and occasionally started pregnancies. During the period of gestation, dominant females initiated significantly more agonistic interactions against subordinate females, resulting in significantly increased levels of glucocorticoids and decreased levels of progesterone in subordinates. Results suggested that reproductive suppression in female Alpine marmots is mediated by the negative effects of stress (glucocorticoids) on the activity of the hypothalamic-pituitary-gonadal axis. The strength of competition between subordinate and dominant females was affected by their relatedness. Dominant females attacked unrelated subordinate females more, whereas amicable behaviour was observed mainly between dominant females and their daughters. These differences could be explained by differences in indirect fitness: related subordinate females benefited from warming the offspring of the dominant female during hibernation. Reproductive suppression was apparently costly for dominant females, because their reproductive success decreased as the number of adult subordinate females in a group increased. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Natural variation in colony inbreeding does not influence susceptibility to a fungal pathogen in a termite

Reduced genetic diversity through inbreeding can negatively affect pathogen resistance. This relationship becomes more complicated in social species, such as social insects, since the chance of disease transmission increases with the frequency of interactions among individuals. However, social insects may benefit from social immunity, whereby individual physiological defenses may be bolstered by collective‐level immune responses, such as grooming or sharing of antimicrobial substance through trophallaxis. We set out to determine whether differences in genetic diversity between colonies of the subterranean termite, Reticulitermes flavipes, accounts for colony survival against pathogens. We sampled colonies throughout the United States (Texas, North Carolina, Maryland, and Massachusetts) and determined the level of inbreeding of each colony. To assess whether genetically diverse colonies were better able to survive exposure to diverse pathogens, we challenged groups of termite workers with two strains of a pathogenic fungus, one local strain present in the soil surrounding sampled colonies and another naïve strain, collected outside the range of this species. We found natural variation in the level of inbreeding between colonies, but this variation did not explain differences in susceptibility to either pathogen. Although the naïve strain was found to be more hazardous than the local strain, colony resistance was correlated between two strains, meaning that colonies had either relatively high or low susceptibility to both strains regardless of their inbreeding coefficient. Overall, our findings may reflect differential virulence between the strains, immune priming of the colonies via prior exposure to the local strain, or a coevolved resistance toward this strain. They also suggest that colony survival may rely more upon additional factors, such as different behavioral response thresholds or the influence of a specific genetic background, rather than the overall genetic diversity of the colony.