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Balancing selection is important for the maintenance of polymorphism as it
can prevent either fixation of one morph through directional selection or
genetic drift, or speciation by disruptive selection. Polychromatism, the
presence of multiple genetically determined colour phenotypes, can be
maintained if the fitness of alternative morphs depends on the relative
frequency in a population. In aggressive species, negative
frequency-dependent antagonism can prevent an increase in the frequency of
rare morphs as they would only benefit from increased fitness while they
are rare. Heterospecific aggression is common in nature and has the
potential to contribute to rare morph advantage. Here we carry out field
observations and laboratory aggression experiments with mbuna cichlids
from Lake Malawi, to investigate the role of con- and heterospecific
aggression in the maintenance of polychromatism and identify benefits to
rare morphs which are likely to result from reduced aggression. We
hypothesise that rare morph individuals receive less aggression than
common morph individuals and therefore have an ecological advantage.
Within species we found that males and females bias aggression towards
their own morph, adding to the evidence that inherent own-morph aggression
biases can contribute to balancing selection. Over-representation of rare
morph territory owners may be influenced by two factors; higher tolerance
of different morph individuals as neighbours, and ability of rare morphs
to spend more time feeding. Reduced aggression to rare morph individuals
by heterospecifics may also contribute to rare morph advantage.
135 views reported since publication in 2021.