  Bacteria typically reside in heterogeneous environments with various
chemogradients where motile cells can gain an advantage over non-motile cells.
Since motility is energetically costly, cells must optimize their swimming
speed and behavior to maximize their fitness. Here we investigate how cheating
strategies might evolve where slow or non-motile microbes exploit faster ones
by sticking together and hitching a ride. Starting with physical and biological
first-principles we computationally study the effects of sticking on the
evolution of motility in a controlled chemostat environment. We find stickiness
allows slow cheaters to dominate when nutrients are dispersed at intermediate
distances. Here, slow microbes exploit faster ones until they consume the
population, leading to a tragedy of commons. For long races, slow microbes do
gain an initial advantage from sticking, but eventually fall behind. Here, fast
microbes are more likely to stick to other fast microbes, and cooperate to
increase their own population. We therefore find the nature of the hitchhiking
interaction, parasitic or mutualistic, depends on the nutrient distribution.
