article : Are you know, What the Sexusl Dimorphism?

By Laura Klappenbach, About.com

Question: What is Sexual Dimorphism?

Answer: Sexual dimorphism is the difference in form between male and female members of the same species. Sexual dimorphism includes differences in size, coloration, or body structure between the sexes. For example, the male northern cardinal (Cardinalis cardinalis) has a bright red plumage while the female has a duller plumage. Male lions (Panthera leo) have a mane, female lions do not. Below are some additional examples of sexual dimorphism:

• Male elk (Cervus canadensis) grow antlers, while female elk do not have antlers.
• Male elephant seals (Mirounga sp.) develop an elongated snout and fleshy nose that they inflate as a sign of aggression when competing with other males during the mating season.
• Male birds of paradise (Family Paradisaeidae) are noted for their elaborate plumage and complex mating dances. Females are far less ornate.

In most cases when size differences exist between the male and female of a species, it is the male that is the larger of the two sexes. But in a few species, such as birds of prey and owls, it is the female is the larger of the sexes and such a size difference is referred to as reverse sexual dimorphism. One rather extreme case of reverse sexual dimorphism exists in a species of deepwater anglerfish called the triplewart seadevils (Cryptopsaras couesii). The female triplewart seadevil grows much larger than the male and develops the characteristic illicium that serves as a lure to prey. The male, about one tenth the size of the female, attaches itself to the female as a parasite.

Sources

• Folkens, P. 2002. National Audubon Society Guide to Marine Mammals of the World. New York: Alfred A. Knopff.
• Sexual Dimorphism. 2007 (Accessed online). Wikipedia.