Odd couples: extraordinary differences between the sexes in the animal kingdom

The roots of sexual differences : why male and female animals differ

Elephant seals : harems, hierarchies, and giant males

Great bustards : gorgeous males and choosy females

Shell-carrying cichlids : protective males and furtive females

Yellow garden spiders : sedentary females and roving males

Blanket octopuses : drifting females and dwarf males

Giant seadevils : fearsome females and parasitic males

Bone-eating worms : female tubeworms with harems of minuscule males

Shell-burrowing barnacles : sac-like females with harems of phallic males

The diversity of sexual differences : differences between males and females across the animal kingdom.