Ruminant herbivores gain from the microflora in their gut through digestion of cellulose and in return, the microflora gets the nutrients from the ruminants. The shark doesn't benefit from the remora but the remora gets a free ride from the shark and it feeds on the leftovers from the shark's meal. The human host loses nutrients because the tapeworm gets to eat the food provided by the host. Cats provide shelter and food for the flea but the cat becomes anemic because of blood loss from its parasites.
eDNA from the skin cells of a fish can be found in water
Troposphere.
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It is an example of directional selection.
The different kinds of natural selection can influence the distribution of phenotypes within a population. In stabilizing selection, an average phenotype is preferred.
In directional selection, a modification in the surrounding changes the spectrum of the observed phenotypes, and in diversifying selection the extreme values for a trait are preferred over the transitional values. This kind of selection usually pushes speciation.
The directional selection, in the field of population genetics, refers to a mode of natural selection in which an extreme phenotype is preferred over other phenotypes, making the allele frequency to change with time in the orientation of that phenotype.
