Browsing by Subject "behavioral senescence"

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    Female swamp sparrows do not show evidence of discriminating between the songs of peak-aged and senescent males
    (Ethology, 2021-01-01) Zipple, MN; Peters, S; Searcy, WA; Nowicki, S
    Sexual selection theory predicts that females face contrasting selection pressures when choosing the age of their mate. On the one hand, older males have demonstrated their ability to survive and they may be more experienced than younger males. At the same time, however, younger males are expected to have accumulated fewer deleterious mutations in their germline as compared to older males. These contrasting pressures on female preference may result in a preference for intermediate-aged males. A preference for males of a particular age can only be expressed, however, if females are able to identify males of different ages. We have previously shown that male swamp sparrows display age-related changes in vocal quality, such that males display sharp increases in vocal quality in early adulthood, followed by gradual senescent declines thereafter. We have also shown that territorial males discriminate these within-individual differences, giving stronger aggressive responses to songs of peak-aged males than to those of senescent males. Here, we use a copulation solicitation assay to test whether females also discriminate these within-signaler markers of senescence in song. Contrary to our prediction, females did not show any evidence of discriminating between songs recorded from peak-aged males as compared to songs from the same males following song senescence. We suggest that this difference in demonstrated discrimination between males and females may be the result of the two sexes attending to different song characteristics.
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    Sounds of senescence: Male swamp sparrows respond less aggressively to the songs of older individuals
    (Behavioral Ecology, 2021-01-01) Zipple, MN; Peters, S; Searcy, WA; Nowicki, S
    Age-related changes in assessment signals occur in a diverse array of animals, including humans. Age-related decline in vocal quality in humans is known to affect perceived attractiveness by potential mates and voters, but whether such changes have functional implications for nonhuman animals is poorly understood. Most studies of age-related change in animal signals focus on increases in signal quality that occur soon after the age of first breeding (“delayed maturation”), but a few have shown that signal quality declines in older individuals after a mid-life peak (“behavioral senescence”). Whether other individuals are able to detect this senescent decline of assessment signals has not previously been tested. Here we use playback experiments to show that wild male swamp sparrows (Melospiza georgiana) respond more aggressively to songs from 2-year-old males as compared with songs from the same males when they are 10 years old. Senescence in signals that, like birdsong, affect reproductive success through intrasexual competition or mate choice may be of evolutionary significance. Lay Summary: Using playback experiments with wild swamp sparrows (Melospiza georgiana), we demonstrate that listeners both detect and respond to age-related declines in vocal quality. Two previous studies have shown that some song characteristics deteriorate with age later in life in songbirds, but to our knowledge this is the first demonstration outside of humans that such deterioration affects receiver response. Discrimination of songs from males of different ages may have evolutionary implications.