Marianne Marcoux, Luke Rendell and Hal Whitehead (2007): Indications of
fitness differences among vocal clans of sperm whales. Behav. Ecol.
Sociobiol. 61(7), 1093-1098.
Abstract: Cultural variation can affect the genetic evolution of a species
if there are consistent cultural differences that contribute to fitness
variation between groups of individuals. In this study, measures of the
reproductive success of groups of sperm whales from different cultural
clans are used as proxies for fitness. We measure reproductive success
using population length distributions from acoustic and photographic
measurements and visual observations of the presence of calves. The
results obtained are generally consistent between methods; there are large
and significant differences between the clans in the measures of
reproductive success. The results from this study strengthen the case for
cultural hitchhiking in sperm whales by indicating that differences in
culture between clans correlate with differences in fitness.
Gail L. Patricelli, Marc S. Dantzker and Jack W. Bradbury (2007):
Differences in acoustic directionality among vocalizations of the male
red-winged blackbird ( Agelaius pheoniceus ) are related to function in
communication. Behav. Ecol. Sociobiol. 61(7), 1099-1110.
Abstract: Studies of animal acoustic communication have found that the
frequency and temporal structure of acoustic signals can be shaped by
selection for efficient communication. The directionality of acoustic
radiation may also be adapted for communication, but we know relatively
little about how directionality varies with signal function, sender
morphology, and the environment in which the sound is transmitted. We
tested the hypothesis that the directionality of a vocalization is adapted
to its function in communication. This hypothesis predicts that
vocalizations that are directed to multiple conspecifics (e.g.,
advertisements and alarms) will be relatively omnidirectional because this
will maximize the number of neighbors and mates that receive the signal,
and that vocalizations directed to particular individuals will be
relatively directional because this will maximize detection of the signal
by the targeted receiver and minimize eavesdropping. To test these
predictions, we measured the directionality and amplitude of red-winged
blackbird (Agelaius pheoniceus) vocalizations in the field by recording
vocalizations simultaneously on eight calibrated microphones encircling
the bird. We found significant variation in directionality among
vocalizations. Supporting our predictions, we found that the most
omnidirectional vocalizations were those used to alert conspecifics to
danger, and the most directional vocalizations are those used during
courtship and solicitation of copulation, when the costs of eavesdropping
are likely to be high. These results suggest that the directionality of
red-winged blackbird vocalizations is shaped by selection for effective
communication. This study is the first to provide statistical support for
the hypothesis that directionality is related to the function of a signal
in communication.
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Kind regards
Sonja Amoser
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