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Because of the biased operational sex ratio, males and females have different strategies for maximizing their fitness.

Males Compete for Mates

• for males, the more matings, the more fitness
• often there are many more males than (receptive) females
• therefore, males compete against each other for access to females

Females Select Among Mates

• a female doesn't need many matings to fertilize her eggs
• she can produce better offspring if she selects a particularly "good" mate (some males can be preferable to other males in a variety of ways)
• therefore, females choose from among available males for the preferable one.

Mouse over the images to see them in color. The spider on the left is a female H. amicus, the one on the right is a male H. amiucs. Images Copyright © 1994-1995 W. Maddison. All rights reserved.

Male Ornamentation

Because males often must persuade females to select them, and not some other male, males of many animal species are brightly colored or ornamented, whereas the females are drab. If the goal is to get a female, any female, the male isn't choosy -- so it doesn't matter to the male what the female looks like. But if a female is choosing among several males, bright color or spectacular ornaments might influence her choice.

Jumping spiders possess excellent vision, and the males are conspicuous for their bright colors and ornaments:

See colorful jumping spider males (combined size of all images: 154kb)

Drab females and their colorful male counterparts (images: 338kb total)

Next: How does this difference between males and females in sexual strategy affect mating behavior?