Biodiv Sci ›› 2016, Vol. 24 ›› Issue (9): 1056-1061.

• Orginal Article •

### Frequency dependent fitness in different evolved Escherichia coli lines

Chuan Ni, Biru Zhu, Dayong Zhang*()

1. Key Laboratory for Biodiversity Science and Ecological Engineering of Ministry of Education, Beijing Normal University, Beijing 100875
• Online:2016-09-20 Published:2016-10-09
• Contact: Zhang Dayong

Abstract:

Differences in fitness between two species or genotypes is usually assumed to be constant when competition experiments are used to measure relative fitness in evolutionary experiments. However, interactions between competitors may lead to frequency-dependence in fitness. We measured the relative fitness of two types of evolved lines of Escherichia coli under different initial relative frequencies to analyze the effects of initial relative frequency on relative fitness. Competed with the low nitrogen evolved lines, the high nitrogen evolved lines displayed increased relative fitness with decreased initial relative frequency, which suggests negative frequency dependence. Both types did not grow in the filtrate from high nitrogen evolved lines, but grew in the filtrate from low nitrogen evolved lines. However, the number of cell doublings of the high nitrogen evolved lines was three times higher than that of the low nitrogen evolved lines. One probable explanation for the negative frequency dependent fitness was that the low nitrogen evolved lines had weaker resource competitive ability and could not sufficiently use resources. Another explanation was that the high nitrogen evolved lines could use some metabolites produced by the low nitrogen evolved lines, which suggests the existence of cross-feeding interaction. Different interactions may lead to different relationships between relative fitness and initial relative frequency. Therefore, we need to account for the effects of initial relative frequency on relative fitness to more accurately measure fitness in evolutionary experiments.

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