Leafcutter ants, fungi, and bacteria - microbewiki
Ingenious leafcutter ants have developed a successful symbiotic relationship with the fungi they farm. New genetic analysis helps pinpoint. Leafcutter ants constitue 41 species of ant across the genera Atta and Indeed, their unique relationship with a symbiotic fungus has been compared to the. Some tropical ants collect leaves which they use to grow fungi in their undergound nests. The ants cannot digest the The ants and their fungi form a true symbiosis, with both partners benefiting from the relationship. The ants benefit by.
Workers, however, should prefer a 1: When there is more than one queen or when queens are multiply mated, predicting and measuring sex-ratio conflict in social insect colonies become more complex Bourke and Franks, ; Crozier and Pamilo, ; Mehdiabadi et al. The presence of heterospecific symbionts in a social insect colony, such as fungus-growing ants, causes further complications for studying conflict over the sex ratio.
In such cases, three parties may have conflicting interests: Besides the conflict of interests between queen and workers, the fungus itself should prefer the production of only female reproductives as only virgin queens disperse the fungus they carry small pieces of the natal fungus to start their own garden; Huber, ab ; Ihering, ; Mueller et al.
From the evolutionary viewpoint of the fungus, then, males are a waste of colony resources. Indeed, it seems possible for the fungus to manipulate the ant sex ratio because brood are covered with and are embedded in the fungus Weber, ; Mehdiabadi NJ, personal observation.
The goal of this study was to explore whether sex-ratio conflict occurs between the ants and the cultivar in a primitive attine ant-fungus system, as well as to identify and measure aspects of ant-fungus cooperation in this symbiosis. For this study, we used the primitive attines Cyphomyrmex longiscapus and Cyphomyrmex muelleri Mueller and Wcislo, ; Schultz et al.
Population genetic analyses using allozyme and microsatellite markers showed that the previously recognized C. These two species are sympatric in Panama, and reproductive isolation between them is indicated by the absence of heterozygotes at differentially fixed microsatellite and allozyme loci Schultz et al. Each of these cryptic species cultivates only one type of fungus, and these two cultivars are distantly related Mueller et al. Nevertheless, horizontal transmission is common for members of this genus Green et al.
Leaf Cutter Ants
Nevertheless, the ability to remove a native, coevolved cutivar and replace it with a novel, non-coevolved cultivar allows us to examine aspects of cooperation and conflict in this mutualism.
What aspects of cooperation derive from the mutualistic association? The prediction is that colonies that switch to a novel fungus, which occurs occasionally under horizontal transmission of cultivars between colonies Green et al. We measured cooperation by estimating fitness of both the fungus and the ants in switched nests and controls. A correlate of fitness for the fungus is garden biomass. We assume that the larger the biomass of a garden, the greater the chance of fungal propagation.
Such propagation is a benefit not only to the fungus but also to the ants as a larger garden biomass means more food for the ants. In addition, we estimated ant colony fitness by measuring worker population size as well as the production of reproductives.
A larger colony size and a greater number of reproductives increase the fitness for the colony as well as for the fungus, unless the colony sex ratio becomes male biased.
What forms of conflict are involved in this mutualism?
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We focused on the potential for conflict over the sex ratio between the ants and the fungus. Sex allocation varies from one colony to another for both C. Such differences might be explained by the differential ability of fungal cultivars to manipulate the ant sex ratio to become more female biased. Specifically, we examined the potential for fungal manipulation of the ant sex ratio by measuring numerical sex ratios after eclosion of reproductive brood, even though such manipulation can occur at earlier developmental stages.
Nevertheless, adult reproductives can remain in nests for long periods of time until nuptial flights, representing an energy cost to the colony Mueller UG, personal observation. As noted above, these parties should have conflicting sex-ratio interests, with the fungus predicted to prefer a sex ratio exclusively or highly biased toward females and the queens and workers predicted to prefer a less female-biased sex ratio i.
Collection and construction of colonies We used 60 queenright colonies i. All four treatments were replicated 15 times for a total of 60 colonies. Using a block design, we standardized worker number and garden biomass within each of the 15 replicates. Colony size ranged from 6 to 42 workers average colony size of a field-collected C.
For example, all four treatments from replicate one had six workers and a garden biomass of Before the experiment began, we removed brood eggs, all larval instars, and pupae and reproductives from all colonies by carefully searching through the entire garden under a microscope. Newly emerged workers or reproductives produced within the first 4 weeks of the experiment were not counted in case some brood was missed during the removal process.
Nevertheless, only a few colonies produced new workers within this time period.
Maintenance of colonies Each colony was housed in a square plastic nest-box side, 7. Each week we moistened the plaster on the bottom of the nest-boxes and placed UV-sterilized organic oats, ad libitum, in the second chambers for use as garden substrate. We reared colonies under an approximate 8: Data collection and analyses For all colonies, we measured ant mortality weekly i. To minimize disturbance to colonies, we kept all ants on their cultivars during garden biomass measurements.
Nevertheless, ant biomass was negligible relative to fungal biomass Mehdiabadi NJ, unpublished data. In addition to collecting data on ant mortality and garden biomass, we counted the number of live and dead reproductives produced by each colony at the end of the experiment. The fixed effect in each analysis was treatment, and the random effect was colony each of the four colonies per replicate standardized according to worker number and garden biomass.
Differences among pairs of treatments were determined using Tukey honestly significant difference HSD post hoc tests. Differences among treatments in number of reproductives produced were analyzed with a general linear model with Poisson errors in SAS SAS Institute, Survivorship of reproductives on a novel fungus This experiment tested whether survivorship of male and female reproductives changed when they were switched to a novel cultivar in the absence of any potential sex-ratio influences from the queen and workers i.
Collection and setup We used 22 colonies of C. From colonies of both species, we reared only male and female reproductives on their native fungus controls. We also reared reproductives of C. We used a paired design: For all replicates, we standardized the number of reproductives and garden biomass: This fungus turns a cheery yellow ear of corn into a deformed and grey mass. These grey tumor-masses are actually kernels that have been infected by U. In all but central Mexico, this fungus is considered a bothersome disease, but there it is quite the culinary delicacy The American Phytopathological Society, Another example of a parasitic relationship is that of the genus Cordyceps of which there are many species and a poor insect host E.
In this most unfortunate relationship a spore will land in some fashion on a fly and germinate, then stromata a visible clavate or sometimes branched structure coming out of insect body segments will form outside of the body.
These structures contain the sexual components of the fungi which will release spores when mature. This allows the spores to eventually be released in the most prime conditions and location for eventual germination on another unsuspecting ant.
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Things are much prettier on the mutualism side of things. The concept of mycorrhizal associations between a fungal partner and a plant partner is the mutualistic symbiosis most commonly referred to when talking about fungi.
Microscope Ectomycorrhizae — http: For instance, the fungus growing around or in some cases in the roots of the plant allows for greater surface area of those roots. This greater surface area allows for greater access to water. In return, the plant shares some of the carbon created during photosynthesis.