Resistance be affected by the relative fitness costs

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Resistance be affected by the relative fitness costs

 Resistance and tolerance
are two plant defence strategies against natural enemies like herbivores. Substantial
evidence shows that plants allocate resources simultaneously to both tolerance
and resistance. Both strategies are considered adaptive and are assumed to
imply fitness costs to a plant’s phenotype. As a result, the evolution and
maintenance of each defensive strategy in plant populations should be affected
by the relative fitness costs and benefits that each strategy involves. Authors
reviewed different models for the joint evolution of tolerance and resistance,
to test the hypothesis whether a mixed pattern of defence allocation to
tolerance and resistance constitute evolutionary stable phenotype equilibrium.

 

Defensive traits
expressed by plants to herbivory damage may also serve other functions and
hence be selected by agents other than herbivores. Resistant traits are often correlated
with other fitness-enhancing traits, which represent a constraint to the
evolution of increasing levels of resistance. This cost of allocating resources
to defence may be expressed as a direct reduction in fitness in an
herbivore-free environment, or as an indirect effect of altering the phenotypic
expression of other traits that also increase fitness. Changes in the physical
and biotic environment can also affect the phenotypic expression of plant
defensive traits. Putative traits of tolerance are often associated with plant
growth. Thus, any selective agent acting on growth could select potentially to
increase or decrease tolerance.

To date, a combination
of resistance and tolerance was favoured, however population differences in the
cost/benefit ratio for tolerance and resistance can vary, promoting the evolution
of either tolerance or resistance but not both. In conclusion, selective forces
constraining the evolution of maximal resistance or tolerance that leads to the
mixed pattern of allocation to both strategies appear to be evolutionarily
unstable.

I will cite this information to support
my argument that there is a correlation between two strategies. By exploring
the strategies plant use to defend themselves and their links with other traits
and environmental conditions, I will address the ecological factors that may
constrain the simultaneous evolution of resistance and tolerance. 

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