Aquifer microbial community assembly:do neutral processes dominate?

Presenter: Michael Strack (@mixtrak)

MQ SupervisorsGrant HoseAdam StowDavid Nipperess

UTS supervisorJohn Ellis

Structure1. Background – Groundwater & community ecology

2. Project overview

3. Evidence for dispersal limitation

4. Evidence for environmental selection

5. Conclusions & current work

Chand Baori, Rajasthan

Chennai, Tamil NaduWe rely on groundwater

Global liquid freshwater(Shiklomanov, 1998)

Groundwater Everything else

Wetlands rely on groundwater

Microbes regulate water quality

Processes structuring communities?

Theory of Community Ecology (TOCE)(Vellend, 2010)

Sampling design

Water chemistry & flora

ArchaeaBacteriaFungiEukarya generally

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Dispersal limitation

Sampling design

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Hypothesis• More DOC, higher richnessApproachMultiple linear regression (MLR): richness vs.• Total organic carbon (TOC)• Inorganic carbon (IC)• Nitrate (NO3)• Dissolved oxygen (DO)• Salinity (conductivity, “cond”)• Depth to water table (water.table)

If not dispersal, what about selection? (sensu Vellend)

Environmental structuring – richness MLRn = 36

Taxon Model p Adjusted R2Predictor variablesp < 0.05 (*), p < 0.01 (**), p < 0.001 (***)

Archaea < 0.001 0.5665 +NO3***, +cond**, -water.table***

Bacteria 0.001 0.2755 -IC**

Fungi 0.013 0.2016 -TOC**

Eukarya n.s. n.s. n.s.

Aggregate 0.016 0.1412 -TOC*

Compositional similarityHypothesis• More similar environments = more similar communities

Approach• Distance-based redundancy analysis• Multivariate extension of linear regression• How much variation in response variables is explained by predictors?• Response = matrix of Jaccard distances of communities (i.e. dissimilarity

matrix)• Predictors = environmental variables + region (factor) + richness• Constrained (canonical) ordination – significance testing etc.

Archaeap = 0.006R2 = 0.05

Bacteriap = 0.001R2 = 0.12

Fungip = 0.001R2 = 0.14

Eukaryap = 0.001R2 = 0.15

Summary

• Richness• Catchment

Taxon IC TOC NO3 Conductivity

Archaea + ++ +

Bacteria ++ +

Fungi ++ + +

Eukarya ++

Conclusions• Models significant (p < 0.01) BUT low R2 (< 0.16)• Experimental power? N = 36

OR

Selection & dispersal limitation weak forces in GW?• Oligotrophic - selection slow relative to other processes• Functional redundancy (i.e. small fitness differences)• Sparse populations & limited selective interactions• Resilience: metabolic flexibility, dormancy, resistant structures• Environmental stability, niche construction, refugia, micro-habitats Neutral ecosystem?

Current work

Thank you

Acknowledgements• Supervisors: Grant Hose, Adam Stow, David Nipperess, John Ellis• WRS: Martin Anderson, Peter Graham• Funding: ARC/MQ• Mentoring & molbio: Paulsen & Emma V labs

@mixtrak