CER-Variation and Sexual
Dichromatism
Sexual dimorphism is the
condition where sexes of the same
species exhibit different. These
may include differences in size,
weight, color, markings, or behavioral traits. Lions, for
instance, exhibit dimorphism in that the males are
larger and have manes.
Sexual dichromatism is a form of sexual dimorphism
that refers to a difference in coloration between sexes
within a species.
Parrots comprise one of the most colorful groups of
birds. Their unique pigments and nesting habits are
two potential explanations for their colorful character.
However, plumage (feather) color varies substantially
between parrot species and sometimes also between
males and females of the same species
The graph below shows variation in color and sexual
dichromatism in parrots.
Colour elaboration
Resource competition
Mutual mate choice
Social selection
or
Colour elaboration
Sexual dichromatism
Predation risk
Sexual selection on males
Extra-pair paternity
O+
Sexual dichromatism
Body size
The study examines how size and color may correlate
to other factors in the environment, such as resource
competition and predation.
https://doi.org/10.1111/jeb. 13690
1. Provide another example (not one listed) of animals
that exhibit sexual dimorphism:
2. What is dichromatism?
3. The graph shows two variables studied, color
elaboration (brightness) and sexual dichromatism as
they relate to body size. Which group (small vs large)
tend to exhibit more elaborate colors?
4. Examine the description of those parrots, which
outlines some of the interspecific effects within that
group. Explain why resource competition would
influence the size of those birds.
5. Smaller birds tend to exhibit less elaboration.
Suggest a reason for this observation.
6. Sexual selection on males describes the female
behavior where females choose their mates based on
color. Why might the smaller birds exhibit more
dimorphism than the larger birds?
7. Would you expect a medium sized parrot with few
predators and abundant resources to exhibit greater
or lesser sexual dichromatism? Explain your choice.
8. Summarize the graph, explaining how external
factors influence color in birds.
