45 Introduction to Sexual Selection

By the end of your reading you will be able to:

  1. Define the following terms:
    • intrasexual selection
    • intersexual selection
    • anisomagy
    • parental care
    • secondary sexual traits
    • sexual dimorphism
    • cryptic female choice
    • sperm competition
    • satellite behavior
    • sexual mimicry
    • traumatic insemination
  2. Understand the differences between natural selection and sexual selection.
  3. Identify the two forms of sexual selection and the types of traits that result from each process.
  4. Explain why males and females have different reproductive strategies and how this can lead to sexual conflict
  5. Describe the different behaviors that males and females engage in before, during, and after sex that are subject to sexual selection

The case of the silent crickets

If you have ever tried to escape the sounds of the city at night, you probably realized that nature can be just as loud! All the insects buzzing, frogs croaking, owls hooting- these are the sounds of animals looking for love. Most of these sounds are emitted by individuals, often times males, seeking mating partners. The Pacific field cricket, Teleogryllus oceanicus, is no exception. Like most crickets, males of this species sing to attract females.

So then, how can we understand the presence of non-calling males? In a recently studied population of Hawaiian crickets, non-calling males made up 50% of the population on the island of Oahu and over 90% on the island of Kauai. Knowing how natural selection operates, how can we understand the presence of these non-calling males? How do these non-calling males pass on their genetic material to the next generation, if they cannot sing to attract a mate?

Selection has operated on sexually reproducing organisms in many ways, including ways specific to attracting and retaining mates. This type of selection is called sexual selection, and is the focus of this chapter. Read about sexual selection, and then we’ll return to the problem of the non-calling male crickets at the end of the chapter.

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