MICHIGAN STATE (US) — Larger female hyenas have more offspring and live longer after beginning to reproduce than smaller females, but overall size isn’t the reason.
Size can be one of the most important traits affecting an animal’s life, influencing eating, getting eaten, speed and agility, and attractiveness to potential mates, but how it’s measured is important—overall height and weight may not capture differences in more specific traits like leg length that might be more important in survival.
“We were able to document that larger female hyenas have more cubs over their lifetime than do smaller females as well as develop a novel approach for estimating body size,” says Eli Swanson, a graduate student working with Kay Holekamp, professor of zoology and Ian Dworkin, assistant professor of zoology at Michigan State University.
Details of the research are reported in the journal Proceedings of the Royal Society B.
To identify the most-important traits, researchers sedated hyenas in Kenya and took 13 measurements on each subject, including total body length, skull size, and leg length. While overall size didn’t affect reproductive success, clusters of traits did.
The length of the lower leg, the height at the shoulder, and body length were all individually associated with more reproductive success.
“Our results highlight the importance of choosing appropriate measures when estimating animal body size,” Swanson says. “They also suggest researchers should take caution in interpreting selection on size-related traits as selection on size itself.”
Spotted hyenas are particularly interesting because females are larger than males, extremely unusual among mammals, where for the most part larger males get more food and attract more females.
Females are faced with a tradeoff between their own body size and the energy needed for pregnancy and lactation. Large female hyenas reproduce more often and live longer after beginning to reproduce, when compared to smaller females.
Estimating fitness—or success at surviving and reproducing—is difficult with spotted hyenas, which can live at least 19 years in the wild. The current field of study has been ongoing for more than 20 years, so researchers can count the number of surviving offspring produced by a female in her lifetime, as well as the length of her total reproductive lifespan.
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