Crowded conditions muddle frogs’ mating choices

(Press-News.org) Female treefrogs prefer a mate with an impressive call, but the crowded environments give unattractive males an edge, according to a new international study led by Assistant Professor Jessie Tanner of the University of Tennessee, Knoxville.

When choosing among only two males, female gray treefrogs pick the mate with faster and more regular calls. Faced with four or eight types of calls, however, their choices were inconsistent, according to the study recently published in the biological sciences journal Proceedings of the Royal Society B.

In the wild, frogs usually are choosing mates in noisy, crowded environments called choruses, with many males calling at the same time. “Our study suggests that female treefrogs might not be able to get what they want when they choose in naturally crowded choruses,” said Tanner, a faculty member in both the Department of Ecology and Evolutionary Biology and the Department of Psychology and Neuroscience. She collaborated with scientists at Colorado State University, the University of Minnesota, and Tel Aviv University in Israel on the study.

“Because female mate choice can drive evolution, our results suggest that evolution might happen more slowly than we thought before,” she said. “Some males that are fairly unattractive could still mate, especially if they take advantage of crowded spaces where females might be less able to discriminate between attractive and unattractive males.”

Examining Choice Overload

Researchers designed the study to investigate “choice overload,” when having too many options hampers decision-making. Humans faced with too many types of toothpaste at the grocery store or profiles on a dating app might choose something they would not usually choose, take longer to decide, or put off a decision until later, Tanner explained.

“We wanted to understand how having to make mating decisions in crowded environments, where choice overload could be a problem, might drive the evolution of calls,” she said. “Since males that are chosen by females pass on their genes to the next generation, this mate choice can cause the population to change over time.”

Expanding Animal Behavior Studies

Tanner also has been studying choice overload in animals with Assistant Professor Claire Hemingway under UT’s Collaborative for Animal Behavior (CoLAB).

“Our lab is working to understand how choice overload and noise may each contribute to the difficulty female treefrogs face in making mating decisions,” Tanner said. “We are also working to understand whether this choice overload is something that occurs generally in many different kinds of animals or is more specific to individual species.”

Tanner is collaborating with Hemingway to study choice overload in bumblebees, and both are working with Professor Todd Freeberg to understand whether wood roaches experience choice overload.

Tanner began behavior research on mate choice as an undergraduate, but she also had an interest in acoustic phenomena, fueled by her fascination with language and music. As a postdoctoral researcher she led a study to understand how noise affects mate choice in crickets, which also use acoustic signals to attract mates. 

“During that study, it became clear that our work was consistent with both the possibility that many simultaneous cricket songs created noise that made it hard for females to hear, and the possibility that the females were experiencing choice overload,” Tanner said. “Our current work looks to disentangle those ideas.”

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