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Interactions among Escovopsis, Antagonistic Microfungi Associated with the Fungus-Growing Ant Symbiosis. J Fungi (Basel) 2021; 7:jof7121007. [PMID: 34946990 PMCID: PMC8703566 DOI: 10.3390/jof7121007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 11/12/2021] [Accepted: 11/13/2021] [Indexed: 11/17/2022] Open
Abstract
Fungi in the genus Escovopsis (Ascomycota: Hypocreales) are prevalent associates of the complex symbiosis between fungus-growing ants (Tribe Attini), the ants' cultivated basidiomycete fungi and a consortium of both beneficial and harmful microbes found within the ants' garden communities. Some Escovopsis spp. have been shown to attack the ants' cultivated fungi, and co-infections by multiple Escovopsis spp. are common in gardens in nature. Yet, little is known about how Escovopsis strains impact each other. Since microbe-microbe interactions play a central role in microbial ecology and evolution, we conducted experiments to assay the types of interactions that govern Escovopsis-Escovopsis relationships. We isolated Escovopsis strains from the gardens of 10 attine ant genera representing basal (lower) and derived groups in the attine ant phylogeny. We conducted in vitro experiments to determine the outcome of both intraclonal and interclonal Escovopsis confrontations. When paired with self (intraclonal interactions), Escovopsis isolated from lower attine colonies exhibited antagonistic (inhibitory) responses, while strains isolated from derived attine colonies exhibited neutral or mutualistic interactions, leading to a clear phylogenetic pattern of interaction outcome. Interclonal interactions were more varied, exhibiting less phylogenetic signal. These results can serve as the basis for future studies on the costs and benefits of Escovopsis coinfection, and on the genetic and chemical mechanisms that regulate the compatibility and incompatibility observed here.
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Abstract
The evolution of a mutualism requires reciprocal interactions whereby one species provides a service that the other species cannot perform or performs less efficiently. Services exchanged in insect-fungus mutualisms include nutrition, protection, and dispersal. In ectosymbioses, which are the focus of this review, fungi can be consumed by insects or can degrade plant polymers or defensive compounds, thereby making a substrate available to insects. They can also protect against environmental factors and produce compounds antagonistic to microbial competitors. Insects disperse fungi and can also provide fungal growth substrates and protection. Insect-fungus mutualisms can transition from facultative to obligate, whereby each partner is no longer viable on its own. Obligate dependency has (a) resulted in the evolution of morphological adaptations in insects and fungi, (b) driven the evolution of social behaviors in some groups of insects, and (c) led to the loss of sexuality in some fungal mutualists.
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Affiliation(s)
- Peter H W Biedermann
- Research Group Insect-Fungus Symbiosis, Department of Animal Ecology and Tropical Biology, University of Würzburg, 97074 Würzburg, Germany;
| | - Fernando E Vega
- Sustainable Perennial Crops Laboratory, United States Department of Agriculture, Agricultural Research Service, Beltsville, Maryland 20705, USA;
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Lindstedt C, Murphy L, Mappes J. Antipredator strategies of pupae: how to avoid predation in an immobile life stage? Philos Trans R Soc Lond B Biol Sci 2019; 374:20190069. [PMID: 31438812 DOI: 10.1098/rstb.2019.0069] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Antipredator strategies of the pupal stage in insects have received little attention in comparison to larval or adult stages. This is despite the fact that predation risk can be high during the pupal stage, making it a critical stage for subsequent fitness. The immobile pupae are not, however, defenceless; a wide range of antipredator strategies have evolved against invertebrate and vertebrate predators. The most common strategy seems to be 'avoiding encounters with predators' by actively hiding in vegetation and soil or via cryptic coloration and masquerade. Pupae have also evolved behavioural and secondary defences such as defensive toxins, physical defences or deimatic movements and sounds. Interestingly, warning coloration used to advertise unprofitability has evolved very rarely, even though the pupal stage often contains defensive toxins in chemically defended species. In some species, pupae gain protection from conspecifics or mimic chemical and auditory signals and thereby manipulate other species to protect them. Our literature survey highlights the importance of studying selection pressures across an individual's life stages to predict how ontogenetic variation in selective environments shapes individual fitness and population dynamics in insects. Finally, we also suggest interesting avenues for future research to pursue. This article is part of the theme issue 'The evolution of complete metamorphosis'.
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Affiliation(s)
- Carita Lindstedt
- Department of Biological and Environmental Sciences, P.O. Box 35, FI-40014 University of Jyväskylä, Jyväskylä, Finland
| | - Liam Murphy
- Department of Biological and Environmental Sciences, P.O. Box 35, FI-40014 University of Jyväskylä, Jyväskylä, Finland
| | - Johanna Mappes
- Department of Biological and Environmental Sciences, P.O. Box 35, FI-40014 University of Jyväskylä, Jyväskylä, Finland
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Bonadies E, Wcislo WT, Gálvez D, Hughes WOH, Fernández-Marín H. Hygiene Defense Behaviors Used by a Fungus-Growing Ant Depend on the Fungal Pathogen Stages. INSECTS 2019; 10:insects10050130. [PMID: 31060310 PMCID: PMC6572560 DOI: 10.3390/insects10050130] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 04/09/2019] [Accepted: 04/11/2019] [Indexed: 11/24/2022]
Abstract
Parasites and their hosts use different strategies to overcome the defenses of the other, often resulting in an evolutionary arms race. Limited animal studies have explored the differential responses of hosts when challenged by differential parasite loads and different developmental stages of a parasite. The fungus-growing ant Trachymyrmex sp. 10 employs three different hygienic strategies to control fungal pathogens: Grooming the antibiotic-producing metapleural glands (MGs) and planting or weeding their mutualistic fungal crop. By inoculating Trachymyrmex colonies with different parasite concentrations (Metarhizium) or stages (germinated conidia or ungermianted conidia of Metarhizium and Escovopsis), we tested whether ants modulate and change hygienic strategies depending on the nature of the parasite challenge. There was no effect of the concentration of parasite on the frequencies of the defensive behaviors, indicating that the ants did not change defensive strategy according to the level of threat. However, when challenged with conidia of Escovopsis sp. and Metarhizium brunneum that were germinated or not-germinated, the ants adjusted their thygienic behavior to fungal planting and MG grooming behaviors using strategies depending on the conidia germination status. Our study suggests that fungus-growing ants can adjust the use of hygienic strategies based on the nature of the parasites.
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Affiliation(s)
- Ernesto Bonadies
- Centro de Biodiversidad y Descubrimiento de Drogas, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología (INDICASAT AIP), Apartado 0843-01103, Panamá, República de Panamá.
- Programa de Maestría en Entomología, Vicerrectoría de Investigación y Postgrado, Estafeta Universitaria 0824, Universidad de Panamá, República de Panamá.
- Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Panamá, República de Panamá.
| | - William T Wcislo
- Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Panamá, República de Panamá.
| | - Dumas Gálvez
- Programa de Maestría en Entomología, Vicerrectoría de Investigación y Postgrado, Estafeta Universitaria 0824, Universidad de Panamá, República de Panamá.
| | | | - Hermógenes Fernández-Marín
- Centro de Biodiversidad y Descubrimiento de Drogas, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología (INDICASAT AIP), Apartado 0843-01103, Panamá, República de Panamá.
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Armitage SAO, Fernández-Marín H, Boomsma JJ, Wcislo WT. Slowing them down will make them lose: a role for attine ant crop fungus in defending pupae against infections? J Anim Ecol 2016; 85:1210-21. [PMID: 27136600 PMCID: PMC6084299 DOI: 10.1111/1365-2656.12543] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 04/12/2016] [Indexed: 02/05/2023]
Abstract
Fungus-growing ants (Attini) have evolved an obligate dependency upon a basidiomycete fungus that they cultivate as their food. Less well known is that the crop fungus is also used by many attine species to cover their eggs, larvae and pupae. The adaptive functional significance of this brood covering is poorly understood. One hypothesis to account for this behaviour is that it is part of the pathogen protection portfolio when many thousands of sister workers live in close proximity and larvae and pupae are not protected by cells, as in bees and wasps, and are immobile. We performed behavioural observations on brood covering in the leaf-cutting ant Acromyrmex echinatior, and we experimentally manipulated mycelial cover on pupae and exposed them to the entomopathogenic fungus Metarhizium brunneum to test for a role in pathogen resistance. Our results show that active mycelial brood covering by workers is a behaviourally plastic trait that varies temporally, and across life stages and castes. The presence of a fungal cover on the pupae reduced the rate at which conidia appeared and the percentage of pupal surface that produced pathogen spores, compared to pupae that had fungal cover experimentally removed or naturally had no mycelial cover. Infected pupae with mycelium had higher survival rates than infected pupae without the cover, although this depended upon the time at which adult sister workers were allowed to interact with pupae. Finally, workers employed higher rates of metapleural gland grooming to infected pupae without mycelium than to infected pupae with mycelium. Our results imply that mycelial brood covering may play a significant role in suppressing the growth and subsequent spread of disease, thus adding a novel layer of protection to their defence portfolio.
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Affiliation(s)
- Sophie A O Armitage
- Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark
| | - Hermógenes Fernández-Marín
- Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark.,Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, Edificio 219, Ciudad del Saber, Clayton, Panamá City, Panamá,Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancón, Panamá
| | - Jacobus J Boomsma
- Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark
| | - William T Wcislo
- Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancón, Panamá
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Fernández-Marín H, Nash DR, Higginbotham S, Estrada C, van Zweden JS, d'Ettorre P, Wcislo WT, Boomsma JJ. Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants. Proc Biol Sci 2016; 282:20150212. [PMID: 25925100 DOI: 10.1098/rspb.2015.0212] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens.
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Affiliation(s)
- Hermógenes Fernández-Marín
- Centro de Biodiversidad y Descubrimiento de Drogas, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología, Edificio 219, Ciudad del Saber, Clayton, Panamá Centre for Social Evolution, Department of Biology, University of Copenhagen Universitetsparken 15, Copenhagen 2100, Denmark Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panamá
| | - David R Nash
- Centre for Social Evolution, Department of Biology, University of Copenhagen Universitetsparken 15, Copenhagen 2100, Denmark
| | - Sarah Higginbotham
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panamá
| | - Catalina Estrada
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panamá
| | - Jelle S van Zweden
- Centre for Social Evolution, Department of Biology, University of Copenhagen Universitetsparken 15, Copenhagen 2100, Denmark Laboratory of Socioecology and Social Evolution, Zoological Institute, University of Leuven, Naamsestraat 59, box 2466, Leuven 3000, Belgium
| | - Patrizia d'Ettorre
- Centre for Social Evolution, Department of Biology, University of Copenhagen Universitetsparken 15, Copenhagen 2100, Denmark Laboratoire d'Ethologie Expérimentale et Comparée (LEEC), University of Paris 13, Sorbonne Paris Cité, France
| | - William T Wcislo
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panamá
| | - Jacobus J Boomsma
- Centre for Social Evolution, Department of Biology, University of Copenhagen Universitetsparken 15, Copenhagen 2100, Denmark
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8
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Andersen SB, Yek SH, Nash DR, Boomsma JJ. Interaction specificity between leaf-cutting ants and vertically transmitted Pseudonocardia bacteria. BMC Evol Biol 2015; 15:27. [PMID: 25886448 PMCID: PMC4346108 DOI: 10.1186/s12862-015-0308-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 02/16/2015] [Indexed: 01/12/2023] Open
Abstract
Background The obligate mutualism between fungus-growing ants and microbial symbionts offers excellent opportunities to study the specificity and stability of multi-species interactions. In addition to cultivating fungus gardens, these ants have domesticated actinomycete bacteria to defend gardens against the fungal parasite Escovopsis and possibly other pathogens. Panamanian Acromyrmex echinatior leaf-cutting ants primarily associate with actinomycetes of the genus Pseudonocardia. Colonies are inoculated with one of two vertically transmitted phylotypes (Ps1 or Ps2), and maintain the same phylotype over their lifetime. We performed a cross-fostering experiment to test whether co-adaptations between ants and bacterial phylotypes have evolved, and how this affects bacterial growth and ant prophylactic behavior after infection with Escovopsis. Results We show that Pseudonocardia readily colonized ants irrespective of their colony of origin, but that the Ps2 phylotype, which was previously shown to be better able to maintain its monocultural integrity after workers became foragers than Ps1, reached a higher final cover when grown on its native host than on alternative hosts. The frequencies of major grooming and weeding behaviors co-varied with symbiont/host combinations, showing that ant behavior also was affected when cuticular actinomycete phylotypes were swapped. Conclusion These results show that the interactions between leaf-cutting ants and Pseudonocardia bear signatures of mutual co-adaptation within a single ant population. Electronic supplementary material The online version of this article (doi:10.1186/s12862-015-0308-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Sandra B Andersen
- Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark. .,Current address: Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Hørsholm, Denmark.
| | - Sze Huei Yek
- Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark. .,Current address: Department of Genetics, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa.
| | - David R Nash
- Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark.
| | - Jacobus J Boomsma
- Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen, Denmark.
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Flórez LV, Biedermann PHW, Engl T, Kaltenpoth M. Defensive symbioses of animals with prokaryotic and eukaryotic microorganisms. Nat Prod Rep 2015; 32:904-36. [DOI: 10.1039/c5np00010f] [Citation(s) in RCA: 233] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Many organisms team up with symbiotic microbes for defense against predators, parasites, parasitoids, or pathogens. Here we review the known defensive symbioses in animals and the microbial secondary metabolites responsible for providing protection to the host.
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Affiliation(s)
- Laura V. Flórez
- Max Planck Institute for Chemical Ecology
- Insect Symbiosis Research Group
- 07745 Jena
- Germany
| | - Peter H. W. Biedermann
- Max Planck Institute for Chemical Ecology
- Insect Symbiosis Research Group
- 07745 Jena
- Germany
| | - Tobias Engl
- Max Planck Institute for Chemical Ecology
- Insect Symbiosis Research Group
- 07745 Jena
- Germany
| | - Martin Kaltenpoth
- Max Planck Institute for Chemical Ecology
- Insect Symbiosis Research Group
- 07745 Jena
- Germany
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10
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Ferguson-Gow H, Sumner S, Bourke AFG, Jones KE. Colony size predicts division of labour in attine ants. Proc Biol Sci 2014; 281:20141411. [PMID: 25165765 PMCID: PMC4173680 DOI: 10.1098/rspb.2014.1411] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 08/01/2014] [Indexed: 01/11/2023] Open
Abstract
Division of labour is central to the ecological success of eusocial insects, yet the evolutionary factors driving increases in complexity in division of labour are little known. The size-complexity hypothesis proposes that, as larger colonies evolve, both non-reproductive and reproductive division of labour become more complex as workers and queens act to maximize inclusive fitness. Using a statistically robust phylogenetic comparative analysis of social and environmental traits of species within the ant tribe Attini, we show that colony size is positively related to both non-reproductive (worker size variation) and reproductive (queen-worker dimorphism) division of labour. The results also suggested that colony size acts on non-reproductive and reproductive division of labour in different ways. Environmental factors, including measures of variation in temperature and precipitation, had no significant effects on any division of labour measure or colony size. Overall, these results support the size-complexity hypothesis for the evolution of social complexity and division of labour in eusocial insects. Determining the evolutionary drivers of colony size may help contribute to our understanding of the evolution of social complexity.
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Affiliation(s)
- Henry Ferguson-Gow
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, UK Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
| | - Seirian Sumner
- Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
| | - Andrew F G Bourke
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, UK
| | - Kate E Jones
- Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK Centre for Biodiversity and Environment Research, Department of Genetics, Evolution and Environment, University College London, Gower St., London WC1E 6BT, UK
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11
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Stürup M, Nash DR, Hughes WOH, Boomsma JJ. Sperm mixing in the polyandrous leaf-cutting ant Acromyrmex echinatior. Ecol Evol 2014; 4:3571-82. [PMID: 25478149 PMCID: PMC4224532 DOI: 10.1002/ece3.1176] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Revised: 06/25/2014] [Accepted: 07/02/2014] [Indexed: 11/08/2022] Open
Abstract
The insemination of queens by sperm from multiple males (polyandry) has evolved in a number of eusocial insect lineages despite the likely costs of the behavior. The selective advantages in terms of colony fitness must therefore also be significant and there is now good evidence that polyandry increases genetic variation among workers, thereby improving the efficiency of division of labor, resistance against disease, and diluting the impact of genetically incompatible matings. However, these advantages will only be maximized if the sperm of initially discrete ejaculates are mixed when stored in queen spermathecae and used for egg fertilization in a "fair raffle." Remarkably, however, very few studies have addressed the level of sperm mixing in social insects. Here we analyzed sperm use over time in the highly polyandrous leaf-cutting ant Acromyrmex echinatior. We genotyped cohorts of workers produced either 2 months apart or up to over a year apart, and batches of eggs laid up to over 2 years apart, and tested whether fluctuations in patriline distributions deviated from random. We show that the representation of father males in both egg and worker cohorts does not change over time, consistent with obligatorily polyandrous queens maximizing their fitness when workers are as genetically diverse as possible.
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Affiliation(s)
- Marlene Stürup
- Department of Biology, Centre for Social Evolution, University of Copenhagen Universitetsparken 15, Copenhagen, 2100, Denmark
| | - David R Nash
- Department of Biology, Centre for Social Evolution, University of Copenhagen Universitetsparken 15, Copenhagen, 2100, Denmark
| | - William O H Hughes
- Department of Biology, Centre for Social Evolution, University of Copenhagen Universitetsparken 15, Copenhagen, 2100, Denmark ; School of Life Sciences, University of Sussex Brighton, BN1 9QG, UK
| | - Jacobus J Boomsma
- Department of Biology, Centre for Social Evolution, University of Copenhagen Universitetsparken 15, Copenhagen, 2100, Denmark
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12
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Shik JZ, Santos JC, Seal JN, Kay A, Mueller UG, Kaspari M. Metabolism and the rise of fungus cultivation by ants. Am Nat 2014; 184:364-73. [PMID: 25141145 DOI: 10.1086/677296] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Most ant colonies are comprised of workers that cooperate to harvest resources and feed developing larvae. Around 50 million years ago (MYA), ants of the attine lineage adopted an alternative strategy, harvesting resources used as compost to produce fungal gardens. While fungus cultivation is considered a major breakthrough in ant evolution, the associated ecological consequences remain poorly understood. Here, we compare the energetics of attine colony-farms and ancestral hunter-gatherer colonies using metabolic scaling principles within a phylogenetic context. We find two major energetic transitions. First, the earliest lower-attine farmers transitioned to lower mass-specific metabolic rates while shifting significant fractions of biomass from ant tissue to fungus gardens. Second, a transition 20 MYA to specialized cultivars in the higher-attine clade was associated with increased colony metabolism (without changes in garden fungal content) and with metabolic scaling nearly identical to hypometry observed in hunter-gatherer ants, although only the hunter-gatherer slope was distinguishable from isometry. Based on these evolutionary transitions, we propose that shifting living-tissue storage from ants to fungal mutualists provided energetic storage advantages contributing to attine diversification and outline critical assumptions that, when tested, will help link metabolism, farming efficiency, and colony fitness.
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Affiliation(s)
- Jonathan Z Shik
- Smithsonian Tropical Research Institute, Balboa, Ancon, Republic of Panama
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Römer D, Roces F. Nest enlargement in leaf-cutting ants: relocated brood and fungus trigger the excavation of new chambers. PLoS One 2014; 9:e97872. [PMID: 24830633 PMCID: PMC4022738 DOI: 10.1371/journal.pone.0097872] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 04/25/2014] [Indexed: 11/18/2022] Open
Abstract
During colony growth, leaf-cutting ants enlarge their nests by excavating tunnels and chambers housing their fungus gardens and brood. Workers are expected to excavate new nest chambers at locations across the soil profile that offer suitable environmental conditions for brood and fungus rearing. It is an open question whether new chambers are excavated in advance, or will emerge around brood or fungus initially relocated to a suitable site in a previously-excavated tunnel. In the laboratory, we investigated the mechanisms underlying the excavation of new nest chambers in the leaf-cutting ant Acromyrmex lundi. Specifically, we asked whether workers relocate brood and fungus to suitable nest locations, and to what extent the relocated items trigger the excavation of a nest chamber and influence its shape. When brood and fungus were exposed to unfavorable environmental conditions, either low temperatures or low humidity, both were relocated, but ants clearly preferred to relocate the brood first. Workers relocated fungus to places containing brood, demonstrating that subsequent fungus relocation spatially follows the brood deposition. In addition, more ants aggregated at sites containing brood. When presented with a choice between two otherwise identical digging sites, but one containing brood, ants' excavation activity was higher at this site, and the shape of the excavated cavity was more rounded and chamber-like. The presence of fungus also led to the excavation of rounder shapes, with higher excavation activity at the site that also contained brood. We argue that during colony growth, workers preferentially relocate brood to suitable locations along a tunnel, and that relocated brood spatially guides fungus relocation and leads to increased digging activity around them. We suggest that nest chambers are not excavated in advance, but emerge through a self-organized process resulting from the aggregation of workers and their density-dependent digging behavior around the relocated brood and fungus.
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Affiliation(s)
- Daniela Römer
- Department of Behavioural Physiology and Sociobiology (Zoology II), Biocenter, University of Würzburg, Würzburg, Germany
- * E-mail:
| | - Flavio Roces
- Department of Behavioural Physiology and Sociobiology (Zoology II), Biocenter, University of Würzburg, Würzburg, Germany
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14
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Tragust S, Ugelvig LV, Chapuisat M, Heinze J, Cremer S. Pupal cocoons affect sanitary brood care and limit fungal infections in ant colonies. BMC Evol Biol 2013; 13:225. [PMID: 24125481 PMCID: PMC3854126 DOI: 10.1186/1471-2148-13-225] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Accepted: 08/29/2013] [Indexed: 12/02/2022] Open
Abstract
BACKGROUND The brood of ants and other social insects is highly susceptible to pathogens, particularly those that penetrate the soft larval and pupal cuticle. We here test whether the presence of a pupal cocoon, which occurs in some ant species but not in others, affects the sanitary brood care and fungal infection patterns after exposure to the entomopathogenic fungus Metarhizium brunneum. We use a) a comparative approach analysing four species with either naked or cocooned pupae and b) a within-species analysis of a single ant species, in which both pupal types co-exist in the same colony. RESULTS We found that the presence of a cocoon did not compromise fungal pathogen detection by the ants and that species with cocooned pupae increased brood grooming after pathogen exposure. All tested ant species further removed brood from their nests, which was predominantly expressed towards larvae and naked pupae treated with the live fungal pathogen. In contrast, cocooned pupae exposed to live fungus were not removed at higher rates than cocooned pupae exposed to dead fungus or a sham control. Consistent with this, exposure to the live fungus caused high numbers of infections and fungal outgrowth in larvae and naked pupae, but not in cocooned pupae. Moreover, the ants consistently removed the brood prior to fungal outgrowth, ensuring a clean brood chamber. CONCLUSION Our study suggests that the pupal cocoon has a protective effect against fungal infection, causing an adaptive change in sanitary behaviours by the ants. It further demonstrates that brood removal-originally described for honeybees as "hygienic behaviour"-is a widespread sanitary behaviour in ants, which likely has important implications on disease dynamics in social insect colonies.
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Affiliation(s)
- Simon Tragust
- Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400 Klosterneuburg, Austria
- Evolution, Behaviour and Genetics, Biology I, University of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany
- Animal Ecology I, University of Bayreuth, 95440 Bayreuth, Germany
| | - Line V Ugelvig
- Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400 Klosterneuburg, Austria
- Evolution, Behaviour and Genetics, Biology I, University of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany
| | - Michel Chapuisat
- Department of Ecology and Evolution, Biophore, UNIL-Sorge, University of Lausanne, 1015 Lausanne, Switzerland
| | - Jürgen Heinze
- Evolution, Behaviour and Genetics, Biology I, University of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany
| | - Sylvia Cremer
- Evolutionary Biology, IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400 Klosterneuburg, Austria
- Evolution, Behaviour and Genetics, Biology I, University of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany
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