Galls and Fungi: Fading away, an oak gall’s last hurra(

Fading away, an oak gall’s last hurrah

Jason, Sean, Sonja


Oak galls induced by cynipid wasps are models of ecological inquiries (Wetzel et al. 2014, Prices et al. 2004).  Not only do oak trees and their gall-forming wasp represent a system of co-evolution and diversity (Stone and Schonrogge 2003, Abrahamson et al. 2003) but also the galls serve a secondary function as shelter for other arthropods after wasp emergence (Wetzel et al. 2014). Oak galls eventually fall to the ground, covering the understory and potentially filling a tertiary role in decomposition and the bottom-up food web. One avenue of interest intersects the chemical properties of oak trees and the oak galls. For instance, galls on trees exhibit high tannin levels and act as a defense against fungal invasion; which, in turn protects the developing cynipid wasp (Taper et al. 1986). It follows, that galls across multiple tree taxa exhibit secondary compound and nutrient levels distinct from ungalled leaf tissue (Hartley 1998, Nyman and Julkunen-Titto 2000). Connecting this with studies showing chemical properties in leaf litter change soil chemistry (Jackson et al. 1990) one can infer oak galls generate unique decomposition interactions with the below ground food webs.

Questions Does biomass production of fungi differ in an environment with a high proportion of decomposing galls relative to soil without gall decomposition? Additionally, can we attribute differences of fungi biomass to biotic organisms or to the chemical composition of galls? Furthermore, do the resulting fungi grown support different levels of biodiversity between each treatment?

Materials & Methods

Initial Survey

Gall specific chemicals will be identified in existing soil and tannin concentrations replicated in a mushroom growing medium by the addition of crushed galls.  Suggested laboratories for analysis include the UC Davis Analytic Lab ( and Dellavalle Lab (, suggested by Mike Davis (UC Davis Professor of Plant Pathology).  A meeting with Douglas Adams (UC Davis Professor of Viticulture/Enology) has been scheduled to further explore local cost effective tannin analysis solutions.  Power analysis will be performed to determine statistical significance requirements on replicate numbers and to further pinpoint treatment variation specifics.


Tentative treatment variations are: Agaricus spp. grown in compost with; (a) no galls, (b) crushed galls in high concentrations that mimic native soil found under trees with galls (c) then autoclaved galls to assess potential effects of microbial community.


Growth rates of mushrooms in each treatment will be measured and correlated to gall presence.  Insect activity associated with mushrooms will be observed. Mushroom treatment replicates will be taken back to the lab for insect rearing. Lastly, insects will be identified and diversity between treatments will be recorded.

Expected Results

Biomass growth, chemical composition, and biodiversity of the three treatment groups will be compared through ANOVA or other statistical comparison tests. The most probable outcome would be to expect mushrooms grown under trees with high concentrations of galls to be suppressed in biomass production due to the unfavorable soil conditions created by the decomposing galls. This prediction comes from studies that reveal valley oaks galls are high in tannin concentration (Abrahamson et al. 2003) and others showing that soil high in tannin concentration reduces biomass growth in many fungal species (Chang and Yu 1989). Also, if the introduction of microbial communities is indeed a contributing factor to fungal growth, then the autoclaved group would experience less fungal biomass growth than the non-autoclaved group. Predicting a difference in the three group’s supported biodiversity is difficult to predict due to a lack of available information on these types of biotic interactions.    


Collecting galls 1 day Preparing boxes for mushroom rearing 1.5 weeks

  • determine amount galls to add
  • sterilizing galls
  • inoculating Agaricus mushrooms

Rearing Agaricus 4 weeks Set into the field for 3 days Rear insects 1.5 week References

  1. Abrahamson, W.G., et al., 2003. Cynipid gall-wasp communities correlate with oak chemistry. Jou. Chem. Ecol. 29:1
  2. Chang, Shu Ting, Yu, Marilyn. 1989, Tolerance of tannin by the shiitake mushroom, Lentinus edodes. M1RCENJournal, 1989, 5,375-378.
  3. Hartley, S.E. 1998. The chemical composition of plant galls: are levels of nutrients and secondary compounds controlled by the gall-former? Oecologia 113:492-501.
  4. Jackson, L.E., R.B. Strauss, M.K. Firestone, J.W Bartolome, 1990. Influence of tree canopies on grassland productivity and nitrogen dynamics in deciduous oak savanna. Agri. Ecosys. Environ. 32:89-105
  5. Nyman, T., R. Julkunen-Tiitto, 2000. Manipulation of the phenolic chemistry of willows by gall-inducing sawflies. PNAS 97:24
  6. Price, W.P., 2004. Using galls wasps on oaks to test broad ecological concepts. Conser. Biol 18:5
  7. Stone, G.N., K. Schonrogge, 2003. The adaptive significance of insect gall morphology. TRENDS in Ecol. and Evo. 18:10
  8. Taper, M.L., E.M. Zimmerman, T.J. Case, 1986. Sources of mortality for a cynipid gall-wasp (Dryocosmus dubiosus (Hymenoptera:Cynipidae)): The importance of the Tannin/Fungus interaction. Oecologia. 68:437-445.

9.Wetzel et al. 2014. Ecosystem engineering by a gall-forming wasp indirectly suppresses diversity and density on oak trees. (manuscript)


Peer Review

copy/paste style

Questions about Intro

  • more big picture in intro
  • studies have observed Nitrogen pool fluxes with increased oak leaf litter as well as increased oak leaf herbivory (Jackson et al 1990, Hollinger 1986).
  • Mushrooms are a temporary food source for insects (temporary pulse)
  • *Mark Hunter comments:
    • 1) in almost every system studied to date, gall forming insects reduce the rate at which their individual leaves decompose.
    • 2) in almost all of those systems, condensed tannins have been implicated as the mechanism behind slowed decomposition.
    • 3) so high gall populations could reduce the rate at which leaves decompose under trees,
    • 4) that might have implications for the rate of nutrient recycling (particularly N release) from those leaves. ( (This might be the paper Mark is referring to.)
    • 5) if gall formers reduce the rate at which N cycles, it could reduce subsequent N concentrations in plant foliage and therefore feed back to influence the performance of herbivores
  • Are oak galls made on leaves, or on branches?
    •  (certain galls can be formed on valley oak leaves (jumping galls) although since our experimental timeframe is in the winter/early spring we will focus specifically on valley oak apple galls which are formed on branches)
  • talk about how fungi are affected by soil chemistry?
    • we have papers showing the negative correlation between tannin soil concentration and fungi growth rate. how are they affected by other gall chemicals
    • Background:  “The soil microbial community is responsible for most nutrient transformations in soil, regenerating minerals that limit plant productivity. Fungi and bacteria are the two groups that dominate the microbial decomposer community, and, crudely defined, they share the function of decomposing organic matter in soil, indicating that there is a strong potential for interaction.” -( )(<- interesting implications about autoclaved vs non autoclaved treatments)ohhhh yeah. bam.
    • Check this! not as great as I thought…  Ok article


Questions about questions

  • add hypothesis?
    •  “Biomass production of mushrooms should have a negative correlation with gall presence in the soil. This correlation should be attributed to the soil chemistry change caused by the composition of galls, with possible additive effects from microbial communities harbored within the galls . The resulting fungi grown may also support varying levels of biodiversity between treatments.”


  • Additional study potential
    • (Using mushrooms as a case study, this experiment could be applied to various  other ground-level organisms living under oak trees and their interactions with decomposing galls)
    • ( An interesting follow up study would be to isolate the leaf litter from the gall litter to see just how much galls contribute to soil composition change on top of the change caused by leaves),
    • (Another avenue to explore could be associated with how galls affect the fungal breakdown of the growth medium),
    • (Yet another, if we have enough viable fungal colonies, putting some at trees along the riverbank could provide for additional data gathering opportunities associated with exploration of an abiotic gradient)

Questions about Methods:

  • However, in revision it would be helpful to have more detail in the methods including citations. Using personal communication for citation would be helpful to other readers in several cases.
    • (planning on the mushroom rearing process has taken place with advice from Mike Davis, resident fungal expert and professor here)

Species specific

  • Would it be feasible and interesting to also sample the plant and/or insect community under oaks with galls and with no galls as an additional observational study on the bottom-up effects of galls? What level of enrichment would this provide the project? Plots or pit traps or both could be located in the same blocks as mushrooms were planted.
    • (Yes! but can we use the data from the previous class? I think they sampled from the base of the oak trees), (sampling from the site while the mushrooms are propagating would allow for additional exploration of subsequent colonization of galls after falling from the trees)
  • How will mushrooms be measured
    • Rear boxes specifically for fitness. Sacrifice some for harvesting/weighing
  • Insect rearing and ID process
    • (emailed M.Turelli about what exactly we can expect in mushrooms.)
    • Rearing insects really depends. I hope it would be 1.5 week. ID insects could take 1 week depending on if we do family level vs morhphotype (depends on how big the diversity is)
  • Looking at the mobile arthropod community would also be interesting; however I’m not sure how to do that without scaring away the bugs if we wanted to recover the mushrooms.
    • (Visual observations and notes can be taken at each box. The ones we are going to be interested in will hopefully have larva to be reared out.)
    • (if mobile arthropods are to be collected, quickly bagging the sample should allow most of the mobile insect species to be recovered.
  • There would likely be insect underneath the boxes as well and a protocol could be developed on how to best collect data associated with such.
    • (Underneath the boxes might be not the best for collecting. I would just want to count insects who we see in the boxes.)

Timeline specific

  • Would it be possible to acquire some mushrooms that are already reared for a pilot study while the mushrooms for the main study were being reared?
    • (If we were only looking to have some preliminary ideas on the details involved with rearing insects found on or rearing eggs found in, while the bulk of the mushrooms are being propagated the button mushrooms could be purchased at a store and placed amongst oaks for a few days and then brought back to the lab to analyze)
  • Timeline looks good, but is 3 days long enough to keep the Agaricus in the field? Maybe it depends on the weather conditions at the time. This part could be flexible.
    • (Yeah 3 days should be fine / the mushrooms won’t last very long emailed Mike Davis the pilot study will help with this)

Site specific/Statistical issues with methodology

  • How would things differ along the river bank?
    • (Could be more closely reflecting a natural community if this was a worry)
    • (there could be a change of insect species type along the gradient)
  • the proposal indicates introducing fungal species to the oaks so my note would be to comment somewhere in the paper or find a way to address how this isn’t perfectly occurring in the natural system- wasn’t explicitly observed but can be extrapolated to relate to our study area
    • (Maybe add this as a note somewhere?) (we are using button mushrooms as a model to explore gall-fungal-insect relationships)
  • site repetition might be something to consider— doing it at this disturbed/manipulated location from the previous class’ experiment might alter the “realness” of the study. what is we could go to the oaks in the arb either by the horses or in the oak grove or some other place in davis? might help isolate the variables if we go to a previously unmanipulated study site
    • (along the river would be our best other option)
    • (it would be interesting although perhaps we wouldn’t be able to leverage existing research on the local insect community on Russell Ranch)

Autoclaving/Tannin specific

  • Real effects of autoclaving. What are they? how expensive is autoclaving? where is it done? (what exactly is it?)
    • (emailing Dave Rizzo about it)
    • (the basic idea is that we want to eliminate any anomalous results that could potentially be from microbe presence or absence,  it is basically a big oven that they use to sterilize all the dirt for the greenhouses)
    • (Tyler says that autoclaving probably would alter chemical properties of the galls.)
  • In the proposal it is hypothesized that autoclaving would remove beneficial microbes. Could it also remove antagonistic microbes and have a negative or neutral effect on mushroom growth?
    • ( IF AUTOCLAVING DID NOT MESS WITH THE GALLS; The nature of this interaction will be found experimentally by using an autoclaved treatment group and a non-autoclaved treatment group. If the autoclaved group results in increased mushroom growth compared to the non autoclaved group, then the microbial community overall has a suppressive effect on mushroom growth in combination with the gall composition. The reverse of this or neutral effects could also be possible)
  • can we use Douglas Adams as a resource? access to tools, papers, etc?
    • (Douglas Adams has provided personal information/readings regarding the analysis of phenolic plant metabolites. He can continue to be a resource throughout the experiment. Although he may not be able to provide the specific materials for soil chemical analysis, he probably knows where to get them.
  • ·      Would it be necessary to produce autoclaved no-gall soil as well? That way, the study can compare removal of the microbial community more accurately.
    • No, because we are not autoclaving sterilizing the compost part of the experiment)
  • While the study proposes replicating the tannin concentrations, what about the other chemicals in the galls? How to control for varying levels of tannins in oak galls.
    • (Maybe take out the tannins portion/make it broadly about chemicals in the analysis) (Other
    • studies have found that herbivore-induced changes in leaf chemistry can persist after senescence and have “afterlife effects” on decomposition and nutrient cycling (Choudhury 1988; Findlay et al. 1996; Schweitzer et al. 2005). (Maybe what Mike Davis was referring to)

Statistical/Results Questions


  • If a difference in biodiversity is found, what might it imply?
    • (Mushrooms have probably sequestered compounds in soil, caused by the increase in gall, which may create a more preferable/less preferable shelter/food source for arthropod community)


  • Instead of putting all the field observations under analysis, you should put them under the title of just methods. Analysis is how you’re going to look at the data, not how you’re going to collect the data. (easy fix!)

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