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SUMMARY:Contributed Talk 5: Successive range expansions of interacting mic
 robial populations promote spatial diversity - Goldschmidt\, F (ETH Zrich)
DTSTART:20141028T150000Z
DTEND:20141028T151500Z
UID:TALK55741@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Succession of species is a process that is widespread in natur
 e. Succession occurs when a pioneering species that expands into new terri
 tory is followed by a secondary species that depends on the change in the 
 formerly pristine environment caused by the primary species. It is known t
 hat when species expand their territory\, genetic drift leads to a reducti
 on of diversity in this species. On the other hand was recently shown that
  interactions between species\, like mutualistic dependencies\, can oppose
  genetic drift during simultaneous expansion. However\, it remains unclear
  how genetic drift affects diversity during successive expansions of inter
 acting species. Our main questions are two-fold\; first\, can a temporally
  segregated interaction can oppose genetic drift during the succession and
  if this affects mainly the secondary or also the primary pioneer? \n\nTo 
 address our questions\, we constructed a system of two syntrophic bacteria
  that undergo successive range expansions. The producing strain degrades a
  parent substrate into an intermediate\, which is then excreted. The consu
 ming strain then consumes the secreted intermediate. We manipulate the int
 eraction between the two strains from commensal to a non-obligate mutualis
 m by changing the reactivity of the intermediate using the pH (i.e.\, the 
 toxicity of the intermediate increases as the pH decreases).\n\nWe found t
 hat the producing strain forms a regular wave front\, while the consuming 
 strain\, which has to penetrate the biofilm of the producing strain\, form
 s dendritic structures with fractal properties. There are two processes th
 at oppose the diversity reducing effect of genetic drift during the succes
 sive expansion. First the number of expanding dendrites is higher at non-o
 bligate mutualistic conditions. This process maintains the initial diversi
 ty. Second the degree of dendritic branching is higher at commensal condit
 ions. Branching generates new spatial diversity by splitting up the popula
 tions into small sub-populations. In short we find that successive expansi
 on promotes diversity by maintenance of pre-existing diversity and generat
 ion of new diversity during the expansion.\n
LOCATION:Seminar Room 1\, Newton Institute
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