Genetic diversity within honeybee colonies prevents severe infections and promotes colony growth

Multiple mating by social insect queens increases the genetic diversity among colony members, thereby reducing intracolony relatedness and lowering the potential inclusive fitness gains of altruistic workers. Increased genetic diversity may be adaptive, however, by reducing the prevalence of disease within a nest. Honeybees, whose queens have the highest levels of multiple mating among social insects, were investigated to determine whether genetic variation helps to prevent chronic infections. I instrumentally inseminated honeybee queens with semen that was either genetically similar (from one male) or genetically diverse (from multiple males), and then inoculated their colonies with spores of Ascosphaera apis, a fungal pathogen that kills developing brood. I show that genetically diverse colonies had a lower variance in disease prevalence than genetically similar colonies, which suggests that genetic diversity may benefit colonies by preventing severe infections.     

Genetic variation within social insect colonies reduces parasite load

In colonies of social Hymenoptera (ants, bees and wasps), workers are often not very closely related to each other, because queens mate with several different males (polyandry) or because several functional queens are present (polygyny). Both characteristics increase genetic variation among the queens'' reproductive and worker offspring, but the benefits of this increased variation remain obscure. Here we report an experiment where genetically homogeneous and genetically heterogeneous colonies of the bumble bee, Bombus terrestris, have been exposed to parasitism under field conditions. Colonies of high or low genetic variation were achieved by adding and removing brood from donor colonies. The results showed a consistent effect in that genetically variable colonies experienced reduced parasite loads, i.e. lower prevalence, intensity and parasite species richness, for a range of protozoa, nematodes, mites or parasitoids affecting the workers. We therefore propose that polyandry and/or polygyny of social insects may be beneficial under parasitism.     

Genetic diversity increases insect herbivory on oak saplings

A growing body of evidence from community genetics studies suggests that ecosystem functions supported by plant species richness can also be provided by genetic diversity within plant species. This is not yet true for the diversity-resistance relationship as it is still unclear whether damage by insect herbivores responds to genetic diversity in host plant populations. We developed a manipulative field experiment based on a synthetic community approach, with 15 mixtures of one to four oak (Quercus robur) half-sib families. We quantified genetic diversity at the plot level by genotyping all oak saplings and assessed overall damage caused by ectophagous and endophagous herbivores along a gradient of increasing genetic diversity. Damage due to ectophagous herbivores increased with the genetic diversity in oak sapling populations as a result of higher levels of damage in mixtures than in monocultures for all families (complementarity effect) rather than because of the presence of more susceptible oak genotypes in mixtures (selection effect). Assemblages of different oak genotypes would benefit polyphagous herbivores via improved host patch location, spill over among neighbouring saplings and diet mixing. By contrast, genetic diversity was a poor predictor of the abundance of endophagous herbivores, which increased with individual sapling apparency. Plant genetic diversity may not provide sufficient functional contrast to prevent tree sapling colonization by specialist herbivores while enhancing the foraging of generalist herbivores. Long term studies are nevertheless required to test whether the effect of genetic diversity on herbivory change with the ontogeny of trees and local adaptation of specialist herbivores.     

Energetic inequivalence in eusocial insect colonies

The energetic equivalence rule states that population-level metabolic rate is independent of average body size. This rule has been both supported and refuted by allometric studies of abundance and individual metabolic rate, but no study, to my knowledge, has tested the rule with direct measurements of whole-population metabolic rate. Here, I find a positive scaling of whole-colony metabolic rate with body size for eusocial insects. Individual metabolic rates in these colonies scaled with body size more steeply than expected from laboratory studies on insects, while population size was independent of body size. Using consumer-resource models, I suggest that the colony-level metabolic rate scaling observed here may arise from a change in the scaling of individual metabolic rate resulting from a change in the body size dependence of mortality rates.     

Genetic diversity within honeybee colonies increases signal production by waggle-dancing foragers

Recent work has demonstrated considerable benefits of intracolonial genetic diversity for the productivity of honeybee colonies: single-patriline colonies have depressed foraging rates, smaller food stores and slower weight gain relative to multiple-patriline colonies. We explored whether differences in the use of foraging-related communication behaviour (waggle dances and shaking signals) underlie differences in foraging effort of genetically diverse and genetically uniform colonies. We created three pairs of colonies; each pair had one colony headed by a multiply mated queen (inseminated by 15 drones) and one colony headed by a singly mated queen. For each pair, we monitored the production of foraging-related signals over the course of 3 days. Foragers in genetically diverse colonies had substantially more information available to them about food resources than foragers in uniform colonies. On average, in genetically diverse colonies compared with genetically uniform colonies, 36% more waggle dances were identified daily, dancers performed 62% more waggle runs per dance, foragers reported food discoveries that were farther from the nest and 91% more shaking signals were exchanged among workers each morning prior to foraging. Extreme polyandry by honeybee queens enhances the production of worker-worker communication signals that facilitate the swift discovery and exploitation of food resources.     

Symbiotic physiology promotes homeostasis in Daisyworld

A connection is hypothesized between the physiological consequences of mutualistic symbiosis and life's average long-term impact on certain highly biologically conserved environmental variables. This hypothesis is developed analytically and with a variant of the Daisyworld model. Biological homeostasis is frequently effective due to co-ordination between opposing physiological “rein” functions, which buffer an organism in response to an external (often environmental) perturbation. It is proposed that during evolutionary history the pooling of different species' physiological functions in mutualistic symbioses increased the range of suboptimal environmental conditions that could be buffered against—a mutual tolerance benefit sometimes sufficient to outweigh the cost of cooperation. A related argument is that for a small number of biologically-crucial physical variables (i) the difference between organism interiors and the life-environment interface is relatively low, and (ii) the biologically optimum level of that variable is relatively highly conserved across different species. For such variables, symbiosis tends to cause (at a cost) an increase in the number of environmental buffering functions per unit of selection, which in turn biases the overall impact of the biota on the state of the variable towards the biological optimum. When a costly but more temperature-tolerant and physiologically versatile symbiosis between one black (warming) and one white (cooling) “daisy” is added to the (otherwise unaltered) Daisyworld parable, four new results emerge: (1) The extension of habitability to a wider luminosity range, (2) resistance to the impact of “cheater” white daisies with cold optima, that derive short-term benefit from environmental destabilisation, (3) the capacity to maintain residual, oscillatory regulation in response to forcings that change more rapidly than allele frequencies and (crucially) (4) “succession”-type dynamics in which the tolerant symbiosis colonises and to an extent makes habitable an otherwise lifeless environment, but is later displaced by free-living genotypes that have higher local fitness once conditions improve. The final result is arguably analogous to lichen colonisation of the Neoproterozoic land surface, followed by the Phanerozoic rise of vascular plants. Caution is necessary in extrapolating from the Daisyworld parable to real ecology/geochemistry, but sufficiently conserved variables may be water potential, macronutrient stoichiometry and (to a lesser extent) the temperature window for metabolic activity.     

Conditions favoring queen execution in young social insect colonies

Summary. Previous attempts to explain worker aggression against extra queens in young social insect colonies have used kin selection arguments. These have been inconsistent with experimental evidence demonstrating aggression against extra queens without strong evidence of kin discrimination. Using a game theoretical model, I suggest a series of decision rules that are consistent with the current experimental evidence from study of young colonies of the fire ant Solenopsis invicta. These decision rules are: 1) When workers cannot directly determine which queen is their mother, they should behave in favor of a queen that maximizes the product of the chance that a queen is the workers mother multiplied by the chance that it will survive to colony maturity. In some cases, the survival potential of the different queens may be the only character that influences the workers decision. 2) Workers should delay aggression against extra queens until the workers can gain their greatest advantage through such aggression. 3) Queens may adopt strategies that allow them to dominate rivals, either by gaining an advantage in fights among the queens or by increasing their attractiveness to workers.Received 2 June 2004; revised 5 July 2004; accepted 14 July 2004.     

Genetic diversity in laboratory colonies of western corn rootworm (Coleoptera: Chrysomelidae), including a nondiapause colony

Laboratory-reared western corn rootworms, Diabrotica virgifera virgifera, from colonies maintained at the North Central Agricultural Research Laboratory (NCARL) in Brookings, SD, are used extensively by many researchers in studies of the biology, ecology, behavior, and genetics of this major insect pest. A nondiapause colony developed through artificial selection in the early 1970s is particularly attractive for many studies because its generation time is much shorter than that of typical diapause colonies. However, the nondiapause colony has been in culture for approximately 190 generations without out-crossing. We compared variation at six microsatellite loci among individuals from the NCARL nondiapause colony (approximately 190 generations), main diapause colony (approximately 22 generations), four regional diapause colonies (3-8 generations), and four wild populations. Genetic diversity was very similar among the diapause laboratory colonies and wild populations. However, the nondiapause colony showed approximately 15-39% loss of diversity depending on the measure. Pairwise estimates of F(ST) were very low, revealing little genetic differentiation among laboratory colonies and natural populations. The nondiapause colony showed the greatest genetic differentiation with an average pairwise F(ST) of 0.153. There was little evidence that the laboratory colonies had undergone genetic bottlenecks except for the nondiapause colony. The nondiapause colony has suffered a moderate loss in genetic diversity and is somewhat differentiated from wild populations. This was not unexpected given its history of artificial selection for the nondiapause trait, and the large number of generations in culture. In contrast, the results indicate that the diapause colonies maintained at NCARL are genetically similar to wild populations.     

Plant diversity accurately predicts insect diversity in two tropical landscapes

Plant diversity surely determines arthropod diversity, but only moderate correlations between arthropod and plant species richness had been observed until Basset et al. (Science, 338, 2012 and 1481) finally undertook an unprecedentedly comprehensive sampling of a tropical forest and demonstrated that plant species richness could indeed accurately predict arthropod species richness. We now require a high‐throughput pipeline to operationalize this result so that we can (i) test competing explanations for tropical arthropod megadiversity, (ii) improve estimates of global eukaryotic species diversity, and (iii) use plant and arthropod communities as efficient proxies for each other, thus improving the efficiency of conservation planning and of detecting forest degradation and recovery. We therefore applied metabarcoding to Malaise‐trap samples across two tropical landscapes in China. We demonstrate that plant species richness can accurately predict arthropod (mostly insect) species richness and that plant and insect community compositions are highly correlated, even in landscapes that are large, heterogeneous and anthropogenically modified. Finally, we review how metabarcoding makes feasible highly replicated tests of the major competing explanations for tropical megadiversity.     

昆虫多样性三十年研究进展

当前, 全球昆虫数量和多样性均处于下降趋势, 而导致这一趋势的原因主要包括人为干扰及气候变化。本文基于森林、草地、农业、水生和土壤生态系统, 以植食性、访花、捕食性、寄生性、食果以及食腐昆虫为重点功能昆虫群, 综述了近三十年来国内外昆虫多样性研究领域的主要进展, 并分析了发展趋势。近年来, 昆虫多样性的研究维度不断拓展, 形态多样性研究不断深入, 系统发生多样性、功能多样性和遗传多样性等研究也显著加强。此外, 昆虫多样性研究的空间尺度也逐步扩大, 大尺度区域性研究甚至全球范围的调查持续增长。昆虫进化历史也被引入多样性格局研究中, 并随着系统发生信息学方法的普及而被整合到生态系统建成和生物多样性形成机制研究中。未来需要加强关键昆虫类群整合分类学研究、功能性状多样性、林冠昆虫多样性、互作网络结构等方向的研究。     

昆虫拟态的多样性

综述了昆虫拟态的常见类型及其研究动态 ,特别对光学拟态、声学拟态、化学拟态和拟态的多型现象及复杂性作了较详细的介绍     

Plant functional group diversity promotes soil protist diversity

We tested whether effects of plant diversity can propagate through food webs, down to heterotrophic protists not linked directly to plants. To this end we synthesised grassland ecosystems with varying numbers of plant functional groups (FGN) and assessed corresponding changes in testate amoebae communities. The number of plant species was kept constant. When FGN was increased from 1 to 3, species number and total community density of live testate amoebae were enhanced according to a linear and a saturating function, respectively. From FGN 1 to 2, the appearance of new testate amoebae species did not affect the presence of the resident species, whereas, from FGN 2 to 3 about one quarter of the resident testate amoebae species was replaced, without altering the total species number. Overall, density by species increased, while evenness of the testate amoebae community was not affected by FGN; although Trinema lineare, one of the most common species, became more abundant. The observed relationship between plant functional group diversity and testate amoebae diversity could shed new light on the biogeographical distribution patterns of protists.     

Social transfer of pathogenic fungus promotes active immunisation in ant colonies

Due to the omnipresent risk of epidemics, insect societies have evolved sophisticated disease defences at the individual and colony level. An intriguing yet little understood phenomenon is that social contact to pathogen-exposed individuals reduces susceptibility of previously naive nestmates to this pathogen. We tested whether such social immunisation in Lasius ants against the entomopathogenic fungus Metarhizium anisopliae is based on active upregulation of the immune system of nestmates following contact to an infectious individual or passive protection via transfer of immune effectors among group members--that is, active versus passive immunisation. We found no evidence for involvement of passive immunisation via transfer of antimicrobials among colony members. Instead, intensive allogrooming behaviour between naive and pathogen-exposed ants before fungal conidia firmly attached to their cuticle suggested passage of the pathogen from the exposed individuals to their nestmates. By tracing fluorescence-labelled conidia we indeed detected frequent pathogen transfer to the nestmates, where they caused low-level infections as revealed by growth of small numbers of fungal colony forming units from their dissected body content. These infections rarely led to death, but instead promoted an enhanced ability to inhibit fungal growth and an active upregulation of immune genes involved in antifungal defences (defensin and prophenoloxidase, PPO). Contrarily, there was no upregulation of the gene cathepsin L, which is associated with antibacterial and antiviral defences, and we found no increased antibacterial activity of nestmates of fungus-exposed ants. This indicates that social immunisation after fungal exposure is specific, similar to recent findings for individual-level immune priming in invertebrates. Epidemiological modeling further suggests that active social immunisation is adaptive, as it leads to faster elimination of the disease and lower death rates than passive immunisation. Interestingly, humans have also utilised the protective effect of low-level infections to fight smallpox by intentional transfer of low pathogen doses ("variolation" or "inoculation").