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Macroevolution is guided by sorting of interspecific variation ("species selection" [2]), as opposed to sorting of intraspecific variation in microevolution. [3] Species selection may occur as (a) effect-macroevolution, where organism-level traits (aggregate traits) affect speciation and extinction rates, and (b) strict-sense species selection, where species-level traits (e.g. geographical ...
The slope of this line is the specific growth rate of the organism, which is a measure of the number of divisions per cell per unit time. [5] The actual rate of this growth (i.e. the slope of the line in the figure) depends upon the growth conditions, which affect the frequency of cell division events and the probability of both daughter cells ...
[1] [3] [4] [5] Filamentation is also thought to protect bacteria from antibiotics, and is associated with other aspects of bacterial virulence such as biofilm formation. [ 6 ] [ 7 ] The number and length of filaments within a bacterial population increases when the bacteria are exposed to different physical, chemical and biological agents (e.g ...
As resources become more limited, the growth rate tapers off, and eventually, once growth rates are at the carrying capacity of the environment, the population size will taper off. [6] This S-shaped curve observed in logistic growth is a more accurate model than exponential growth for observing real-life population growth of organisms. [8]
Figure 1: A bi-phasic bacterial growth curve.. A growth curve is an empirical model of the evolution of a quantity over time. Growth curves are widely used in biology for quantities such as population size or biomass (in population ecology and demography, for population growth analysis), individual body height or biomass (in physiology, for growth analysis of individuals).
Bacteria are prokaryotic microorganisms that can either have a bacilli, spirilli, or cocci shape and measure between 0.5-20 micrometers. They were one of the first living cells to evolve [9] and have spread to inhabit a variety of different habitats including hydrothermal vents, glacial rocks, and other organisms.
The 12 E. coli LTEE populations on June 25, 2008. [1]The E. coli long-term evolution experiment (LTEE) is an ongoing study in experimental evolution begun by Richard Lenski at the University of California, Irvine, carried on by Lenski and colleagues at Michigan State University, [2] and currently overseen by Jeffrey Barrick at the University of Texas at Austin. [3]
On February 24, 1988, Lenski started growing twelve lineages of E. coli under identical growth conditions. [39] [40] When one of the populations evolved the ability to aerobically metabolize citrate from the growth medium and showed greatly increased growth, [41] this provided a dramatic observation of evolution in action. The experiment ...