Can you see any differences between these millimeter-long male and female ostracodes (tiny ocean animals)? Microscope photos of fossil ostracodes.
(Bottom, left) In this species of tiny animal called an ostracod, males are smaller than females and have special light organs that they use to compete for females by emitting flashes of bioluminesence. (Gene Hunt, Smithsonian/Jim G. Morin)
What does mate choice have to do with extinction?
February 06, 2017
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In the animal kingdom, sexual reproduction is the rule. This is even true for tiny ocean animals. One example is ostracodes. With just a few exceptions to the rule, male sex cells must fertilize female sex cells. That is how they make offspring. Some animals, such as male and female clams, release sex cells into the water for chance encounters. But reproduction in many animals requires that males and females find each other.
Attracting individuals of the same species is achieved in a startling variety of ways. They can make creative use of the senses. This activity can range from singing by frogs to dancing by jumping spiders to luminescing by deep-sea animals. Once found, a potential mate may need to be convinced to go forward with the mating relationship. Generally, it's the male doing the convincing. This is because females usually make the larger investment in creating and raising offspring. So females are choosier about who to mate with.
Let's take birds as an example. In birds, males invite females to their territories by singing, sporting bright feathers and doing courtship dances. The more flamboyant males tend to be more successful at attracting females. This activity by males drives a sort of evolutionary arms race. Which one can have the showiest feather plumage? Showier plumage may lead to more mating opportunities. This leads to more offspring. That perpetuates showier plumage in the population of birds.
This form of natural selection driven by mate choice is called "sexual selection." While it has inspired spectacular characteristics in animals, from feathers to antlers to lion manes, it might have a dark side. Peacocks with larger tails may be easier for wild dogs to catch, for example. Elks with larger antlers might not be as agile against wolf attacks. And a lit-up squid might attract a hungry fish instead of a mate. Species with more extreme differences between males and females ("sexual dimorphism") might be more susceptible to extinction in the long run.
Smithsonian paleontologist Dr. Gene Hunt is using tiny ocean ostracodes as a model to examine a hypothesis. It is that sexual selection plays a role in extinction. Learn more about what his studies of ostracodes are revealing in a live "Smithsonian Science How" webcast. It airs on Thursday, Feb. 9. In "What Tiny Marine Fossils Reveal about Extinction" (airs at 11 a.m. and 2 p.m. EST on the Q?rius website), Gene will show you how he tests hypotheses. He also will answer your questions live. You can also get teaching resources to use with the webcast.
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CRITICAL THINKING QUESTION
How might species with more extreme differences between males and females be more susceptible to extinction?
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