10.14 Wrapping Up: Understanding the silent crickets
Just like most animals, males of the Pacific field cricket, Teleogryllus oceanicus, signal to attract females. This song can grab the attention of female crickets from very far away. However, as you can imagine, the song is loud enough that it attracts predators as well. On the islands of Hawaii, this song attracts females of a parasitoid fly that lay eggs inside of singing males. These eggs then develop into larvae within the male cricket, and essentially eat the male from the inside out-killing him in the process. The larvae then emerge from the dead male cricket as flies that continue the same process as their mothers.
In this system, the presence of an alternative mating strategy, called satellite behavior, allows males to balance the relative costs and benefits associated with calling to mates. As you might imagine, any mechanism that would allow males to avoid the costs of this parasite would give these males a huge evolutionary advantage. So how do males attract females without attracting these deadly flies? Because of the relative risks of singing to attract females, male T. oceanicus will sometimes choose not to signal and instead will hang out near other males that are singing. Then when females approach that are attracted to the song that the singing male is producing, the non-signaler will intercept them. It’s almost as if the signaling male is acting as a “wing-man” to the non-signaling male. However, the signaling males do not get any benefit from having these non-signalers hang around them- they lose out on opportunities to mate with approaching females and they are more likely to be infected by fly larvae.
As a result of these behaviors, the Pacific field crickets in Hawaii have evolved remarkable morphological and behavioral novelties. For example, pre-existing flexibility in this satellite behavior has made way for a novel wing mutation, “flatwing”, that has caused individuals to lose all of the necessary wing structures for producing the songs used for attracting females. Subsequent selection on satellite behavior has led flatwings to gain greater success by targeting signaling individuals who are most likely to attract females. These mutant flatwing males now comprise 90% of the population on Kauai and 50% of the population on the island of Oahu.