Behaviour 143, 3 (March 2006)
http://www.ingentaconnect.com/content/brill/beh/2006/00000143/00000003
(Abstracts below)
Rossi-Santos, MR & J Podos (2006) Latitudinal variation in whistle structure of
the estuarine dolphin Sotalia guianensis. Behaviour 143: 347-364.
Laidre, ME (2006) Manipulation without mind-reading: information suppression
and leakage during food discovery by mandrills (Mandrillus sphinx). Behaviour
143: 365-392.
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Abstracts
Rossi-Santos, MR & J Podos (2006) Latitudinal variation in whistle structure of
the estuarine dolphin Sotalia guianensis. Behaviour 143: 347-364.
Analyses of intraspecific variation in behaviour can provide insights into the
process of behavioural diversification. In this study we characterized
geographic variation in whistle structure of the estuarine dolphin, Sotalia
guianensis, at 10 sites of a â?¼4000 km transect along the coast of Brazil.
Whistles were recorded, digitized (N = 527), and six acoustic parameters
measured from spectrograms. ANOVA revealed geographic variation in all six
parameters. Post-hoc analyses indicated that pairs of sites with similar
whistle parameters tended to be adjacent to each other, and discriminant
functions analysis (DFA) revealed that the greatest differences in whistle
structure tended to occur between the most distant sites. Whistle parameters
did not, however, express simple clinal variation, and DFA was a poor predictor
of site (29.0% accuracy). Mantel tests revealed significant correlations
between geographic distance and variation in three of six whistle parameters.
Linear reg
ression analyses for our data set, pooled with data from Azevedo & Van Sluys
(2005, J. Acoust. Soc. Am. 117:1456), revealed significantly lower starting and
minimum frequencies for southern populations relative to northern populations.
A geographic discontinuity in these two features is observed, varying on either
side of the easternmost tip of South America. Possible ecological and
evolutionary explanations for these patterns are discussed.
Laidre, ME (2006) Manipulation without mind-reading: information suppression
and leakage during food discovery by mandrills (Mandrillus sphinx). Behaviour
143: 365-392.
At an ultimate, evolutionary level, manipulation entails behaviour that
enhances the fitness of the manipulator even if at times inflicting a cost on
the fitness of the manipulated. At a proximate, mechanistic level, mind-reading
entails an ability on the part of a manipulator to attribute beliefs to those
it manipulates. Both manipulation and mind-reading were investigated during a
study of food-associated calling by semi free-ranging mandrills in Gabon.
Mandrills were initially provisioned at a feeding cage (whose opening generated
loud noises) and under these conditions calling occurred at high rates,
particularly among middle-ranking individuals. When mandrills were then fed
away from the cage (where potential alerting cues were absent) the calling rate
dropped drastically and discoverers of the resource suppressed loud calls,
producing only soft grunts. The latter conditions provided an increased
opportunity for solitary consumption, and analyses showed that discoverers
benefited substantially in terms of ingested food from a reduced presence of
group mates. Loud calls, however, were produced by later arrivals and a
correlation existed between the production of these calls and more group mates
arriving at the resource. Loud calls may have enabled later arrivals to access
monopolized resources, since by divulging information they could attract other,
particularly lower-ranking group mates whose arrival engendered a diversion.
Withholding calls (information suppression) and producing calls (information
leakage) thus each appeared functionally manipulative, their usage depending
only on whether they benefited the signaler. Acoustic playbacks were consistent
with this hypothesis: compared to controls, food-associated calls resulted in
more arrivals and also a trend toward quicker resource depletion and increased
consumption by mandrills other than the discoverer. Yet upon hearing playbacks
of a group mate's calls, non-vocal discoverers consumin
g the resource did not disguise their actions in anticipation of their group
mates' arrival. In fact, some of their actions (like making repeated forays
with unconcealed food) appeared wholly inconsistent with mind-reading.
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