Latitudinal gradients in sea ice and primary production determine Arctic seabird colony size in Greenland

Sea ice loss will indirectly alter energy transfer through the pelagic food web and ultimately impact apex predators. We quantified spring-time trends in sea ice recession around each of 46 thick-billed murre (Uria lomvia) colonies in west Greenland across 20 degrees of latitude and investigated the magnitude and timing of the associated spring-time primary production. A geographical information system was used to extract satellite-based observations of sea ice concentration from the Nimbus-7 scanning multichannel microwave radiometer (SMMR, 1979-1987) and the Defence Meteorological Satellite Programs Special Sensor Microwave/Imager (SSMI, 1987-2004), and satellite-based observations of chlorophyll a from the moderate resolution imaging spectroradiometer (MODIS: EOS-Terra satellite) in weekly intervals in circular buffers around each colony site (150 km in radius). Rapid recession of high Arctic seasonal ice cover created a temporally predictable primary production bloom and associated trophic cascade in water gradually exposed to solar radiation. This pattern was largely absent from lower latitudes where little to no sea ice resulted in a temporally variable primary production bloom driven by nutrient cycling and upwelling uncoupled to ice. The relationship between the rate and variability of sea ice recession and colony size of thick-billed murres shows that periodical confinement of the trophic cascade at high latitudes determines the carrying capacity for Arctic seabirds during the breeding period.     

Salt marsh vegetation: Latitudinal gradients in the zonation patterns

Summary Zonation patterns of salt marsh vegetation were examined at latitudes ranging from 44°40N at Halifax, Nova Scotia, to 58°50N at Churchill, Manitoba. It was found that in all areas examined the landward boundaries of the species' zones were more nearly coincident (i.e., more clustered) than their seaward boundaries. A conspicuous latitudinal trend was found: the clustering of both landward and seaward boundaries increased with increasing latitude. Evidence that between-species competition influences the locations of zone boundaries was also obtained. Possible implications of the results in terms of a relationship between intrapopulation polymorphism and latitude are discussed.     

Latitudinal patterns in the size of European butterflies

The importance of seasonality in shaping latitudinal size patterns was investigated in 16 species of lycaenine and satyrine butterflies with distributions in Sweden and continental Europe. Species without shifts in voltinism within the study area generally displayed clear size clines, increasing in size from north to south within Sweden. These species were also larger in continental Europe than in Sweden. In northern temperate areas a linear model for mean size at different latitudes seems to be a reasonable approximation for most species in this category. The size patterns for three species with shifts from univoltinism to bivoltinism at latitudes within Sweden were more reminiscent of the "saw-tooth"-pattern predicted by theory for such cases. The results suggest that size patterns in European butterflies to a large extent is governed by the length of the favorable season at different latitudes, affecting selection for development time and size. Altitude and drought also affect the effective season length and may amplify or complicate latitudinal patterns.     

Altruism and relatedness at colony foundation in social insects

Cooperative nest initiation in social insects is most easily explained when cooperating females are relatives, as is common in polistine wasps. However, recent research has revealed that unrelated ant queens also initiate colonies together. Reproductive dominance hierarchies are absent among unrelated foundresses, which contrasts with the rigid dominance hierarchies found among related foundresses. New field studies of joint nest founding among non-relatives show that cooperation is favored where colonies are clumped and brood raiding is common, so that attaining a large worker force quickly is critical to colony survival. These studies enrich our understanding of the role of relatedness in social groups.     

Latitudinal patterns in European ant assemblages: variation in species richness and body size

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.     

Colony size,social complexity and reproductive conflict in social insects

The broad limits of mature colony size in social insect species are likely to be set by ecological factors. However, any change in colony size has a number of important social consequences. The most fundamental is a change in the expected reproductive potential of workers. If colony size rises, workers experience a fall in their chances of becoming replacement reproductives and, it is shown, increasing selection for mutual inhibition of one another's reproduction (worker policing). As workers’ reproductive potential falls, the degree of dimorphism between reproductive and worker castes (morphological skew) can rise. This helps explain why small societies have low morphological skew and tend to be simple in organization, whereas large societies have high morphological skew and tend to be complex. The social consequences of change in colony size may also alter colony size itself in a process of positive feedback. For these reasons, small societies should be characterized by intense, direct conflict over reproduction and caste determination. By contrast, conflict in large societies should predominantly be over brood composition, and members of these societies should be relatively compliant to manipulation of their caste. Colony size therefore deserves fuller recognition as a key determinant, along with kin structure, of social complexity, the reproductive potential of helpers, the degree of caste differentiation, and the nature of within-group conflict.     

Genetic regulation of colony social organization in fire ants: an integrative overview

Expression of colony social organization in fire ants appears to be under the control of a single Mendelian factor of large effect. Variation in colony queen number in Solenopsis invicta and its relatives is associated with allelic variation at the gene Gp-9, but not with variation at other unlinked genes; workers regulate queen identity and number on the basis of Gp-9 genotypic compatibility. Nongenetic factors, such as prior social experience, queen reproductive status, and local environment, have negligible effects on queen numbers which illustrates the nearly complete penetrance of Gp-9. As predicted, queen number can be manipulated experimentally by altering worker Gp-9 genotype frequencies. The Gp-9 allele lineage associated with polygyny in South American fire ants has been retained across multiple speciation events, which may signal the action of balancing selection to maintain social polymorphism in these species. Moreover, positive selection is implicated in driving the molecular evolution of Gp-9 in association with the origin of polygyny. The identity of the product of Gp-9 as an odorant-binding protein suggests plausible scenarios for its direct involvement in the regulation of queen number via a role in chemical communication. While these and other lines of evidence show that Gp-9 represents a legitimate candidate gene of major effect, studies aimed at determining (i) the biochemical pathways in which GP-9 functions; (ii) the phenotypic effects of molecular variation at Gp-9 and other pathway genes; and (iii) the potential involvement of genes in linkage disequilibrium with Gp-9 are needed to elucidate the genetic architecture underlying social organization in fire ants. Information that reveals the links between molecular variation, individual phenotype, and colony-level behaviors, combined with behavioral models that incorporate details of the chemical communication involved in regulating queen number, will yield a novel integrated view of the evolutionary changes underlying a key social adaptation.     

The role of colony organization on pathogen transmission in social insects

Social organisms are especially vulnerable to pathogens due to the homogeneity of the colony, and the close proximity and extensive interactions among its members. However, the social organization of these groups also offers the potential to provide an effective barrier against the transmission of pathogens within the colony. Social insects with their elaborate colony organizations provide an ideal model system to develop and test this hypothesis. While the different elements of colony organization are generally assumed to be products of ergonomic selection, in this paper we address how the same elements could influence the transmission of pathogens. By developing a simple model, we explore how three parameters of colony organization, division of labor, interaction network and colony demography could influence the transmission of pathogens. We find that heterogeneity among individuals in terms of division of labor alone has little effect on the spread of an infection in the colony and the scenario is indistinguishable from one in which all the individuals are homogeneous. However, division of labor, combined with heterogeneity in the interaction network and demographic schedules reduce the spread of an infection.     

A genetic model for disruptive selection on colony social organisation,reproduction, and ecotype distribution in wood ants inhabiting different woodland habitats

Summary Wood ants of theFormica rufa species complex are typically bound to woodland habitats and their eventual colonization of more open habitats depends on the presence of a sufficient number of woody plants. Computer simulations of the long-term development of large wood ant populations in woodland systems of differing structure were performed. A cellular, stochastic automation model simulated the alternatives of a compact, coherent woodland system and a fragmented, coarse-grained woodland system. The simulation of a compact woodland system gave evidence that disruptive selection alone may be sufficient to produce two distinct ectotypes, which are known asFormica rufa andFormica polyctena, even if there is a full fertility of the crosses. The simulation of a fragmented, coarse-grained woodland system has supported the view, that a high local frequency of nests with intermediate phenotypes might be explainable by a particular woodland pattern which favour mixed strategies. It was shown that queen dominance and intraspecific social parasitism are likely to be important factors in the dynamics of large wood ant populations.     

Colony spatial structure in polydomous ants: complimentary approaches reveal different patterns

Eusocial insects often live in colonies comprised of an extensive network of interconnected nests and estimating colony spatial structure and colony boundaries may be difficult, especially in cryptic, subterranean species. A combination of aggression assays and protein marking was used to estimate nest spatial distribution in field populations of the highly polydomous cornfield ant, Lasius neoniger. The estimates were first obtained via 1-on-1 aggression tests for workers collected from different nests within the research plots. The aggression tests were followed by mark-recapture field studies which utilized rabbit IgG protein. The ants were allowed to self-mark by feeding on sucrose solution spiked with the IgG protein. Colony spatial structure was detected by sampling ants from different nests and analyzing them for the presence of the marker using an ELISA test. Estimates based on aggression tests were substantially higher relative to those based on protein marking. The average colony size based on aggression tests was 2.0 ± 0.2 m² and was significantly higher than the 1.1 ± 0.4 m² estimate based on protein marking. The estimate based on protein marking was even lower, 0.2 ± 0.1 m², when a Fluon-coated ring restricted ant feeding to the focal nest and prevented ants from other nests from feeding on the protein-marked sucrose. No significant correlation was detected between internest aggression and internest distance. Likewise, no correlation was detected between distance from the focal nest and the percentage of workers testing positive for the protein marker. The results show that both approaches have their own limitations, but their simultaneous use allows for a more accurate assessment of colony spatial structure. The advantages and limitations of each technique are discussed.     

Strict monandry in the ponerine army ant genus Simopelta suggests that colony size and complexity drive mating system evolution in social insects

Altruism in social insects has evolved between closely related full-siblings. It is therefore of considerable interest why some groups have secondarily evolved low within-colony relatedness, which in turn affects the relatedness incentives of within-colony cooperation and conflict. The highest queen mating frequencies, and therefore among the lowest degrees of colony relatedness, occur in Apis honeybees and army ants of the subfamilies Aenictinae, Ecitoninae, and Dorylinae, suggesting that common life history features such as reproduction by colony fission and male biased numerical sex-ratios have convergently shaped these mating systems. Here we show that ponerine army ants of the genus Simopelta, which are distantly related but similar in general biology to other army ants, have strictly monandrous queens. Preliminary data suggest that workers reproduce in queenright colonies, which is in sharp contrast to other army ants. We hypothesize that differences in mature colony size and social complexity may explain these striking discrepancies.     

Optimal colony fissioning in social insects: testing an inclusive fitness model with honey bees

In most species of social insects, when a queen departs from her parental nest to found a new colony, she leaves on her own. In some species, however, the departing queen leaves accompanied by a portion of the parental colony’s workers and there is a permanent fissioning of the worker force. Little is known about how the adult workers in colonies of fissioning species distribute themselves between the old and the new colonies. We examined this problem, building on Bulmer’s (J Theor Biol 100: 329–339, 1983) model for the optimal splitting of a colony’s adult workforce during colony reproduction. We first created an inclusive fitness model of optimal colony fissioning that applies to species in which fissioning gives rise to two autonomous colonies. The model predicts the optimal “swarm fraction”, which we define as the proportion of the adult workers in a fissioning colony that join the departing queen. We then tested the model by comparing the predicted and observed swarm fractions in honey bees. We found a close match between predicted (0.76–0.77) and observed (0.72 ± 0.04) swarm fractions. Evidently, worker honey bees distribute themselves between the old and new colonies in a way that jointly maximizes the inclusive fitness of each worker. We conclude by discussing additional ways to test the model.     

Variance-based selection may explain general mating patterns in social insects

Female mating frequency is one of the key parameters of social insect evolution. Several hypotheses have been suggested to explain multiple mating and considerable empirical research has led to conflicting results. Building on several earlier analyses, we present a simple general model that links the number of queen matings to variance in colony performance and this variance to average colony fitness. The model predicts selection for multiple mating if the average colony succeeds in a focal task, and selection for single mating if the average colony fails, irrespective of the proximate mechanism that links genetic diversity to colony fitness. Empirical support comes from interspecific comparisons, e.g. between the bee genera Apis and Bombus, and from data on several ant species, but more comprehensive empirical tests are needed.     

Brood care and social evolution in termites

Cooperative brood care is assumed to be the common driving factor leading to sociality. While this seems to be true for social Hymenoptera and many cooperatively breeding vertebrates, the importance of brood care for the evolution of eusociality in termites is unclear. A first step in elucidating this problem is an assessment of the ancestral condition in termites. We investigated this by determining the overall level of brood care behaviour across four termite species that cover the phylogenetic diversity of the lower termites. Brood care was low in the three species (all from different families) that had an ancestral wood-dwelling lifestyle of living in a single piece of wood that serves as food and shelter. In the fourth species, a lower termite that evolved outside foraging, brood care was more common. Together with data for higher termites, this suggests that brood care in termites only becomes important when switching from a wood-dwelling to a foraging lifestyle. These results imply that early social evolution in termites was driven by benefits of increased defence, while eusociality in Hymenoptera and cooperative breeding in birds and mammals are primarily based on brood care.     

白蚁的社会组织和社会行为

白蚁属于等翅目昆虫,共有7科2 750种,这是昆虫纲中唯一的一个目,其所有的种类都靠消化道内共生的鞭毛类、原生动物利用和消化纤维素。介绍了白蚁社会组织和社会存为的特点,比较了白蚁与蚂蚁的异同,并指出两者相似是由于趋同进化,而两者不同是由于亲缘关系相距甚远,各来自不同祖先。