Kinship and sociality in coastal river otters: are they related?
Gail M. Blundell
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2
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Merav Ben-David
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3
Pamela Groves
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2
R. Terry Bowyer
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Eli Geffen
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uwyo.edu. Received 21 February 2003; revised 23 February 2004; accepted 16 March 2004
1
Institute for Nature Conservation Research, Tel Aviv University
, Ramat Aviv, 69978,
Israel
2
Institute of Arctic Biology, University of Alaska Fairbanks
, Fairbanks,
AK 99775, USA
3
Department of Zoology and Physiology, 1000 East University Avenue, University of Wyoming
, Laramie,
WY 82071, USA
4
Division of Wildlife Conservation, Alaska Department of Fish and Game
, Douglas,
Alaska 99824, USA
Previous studies of coastal river otters (Lontra canadensis) in Prince William Sound, Alaska, USA, documented atypical social organization for mammals. Social groups were composed largely of males, but some males remained solitary year-round and most females were asocial. Because, in carnivores, groups are usually composed of highly related individuals but group living also provides advantages unrelated to kinship, we concurrently evaluated the role of relatedness and ecological benefits in sociality among coastal river otters. By using DNA microsatellite analysis and radiotelemetry, we were able to reject the hypothesis that social groups of otters were kin based. In addition, we found no indication of kin avoidance, as would be expected from low dispersal and high local competition. Sociality conferred no reproductive benefits or costs to otters; number of offspring and number of relatives in the population did not differ between social and solitary animals. Solitary males were not older or larger than were social males, and there was no relation between male size and number of offspring, indicating that sexual selection did not mask a potential relation between sociality and reproductive success. Among coastal river otters in this region, sociality could be explained by the benefits obtained from cooperative foraging on high-quality schooling pelagic fishes. Such benefits did not require association with kin, resulting in no selection pressure for kin-based groups. The prediction that the degree of sociality in the population will fluctuate relative to the abundance of schooling pelagic fishes merits further investigation. Key words: Alaska, kin selection, Lontra canadensis, microsatellite DNA, reproductive success, schooling pelagic fishes, sexual selection. [Behav Ecol 15:705-714 (2004)]
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Ebenefits gained relative to costs. Benefits include reduced
volution of sociality among animals has been attributed to
risk of predation and increased access to resources (Alcock,
1993; Alexander, 1974; Rubenstein, 1978), whereas costs
include reproductive suppression, intraspecific competition
for resources or reproductive opportunities, and increased
potential for parasite and disease transmission (Alexander,
1974; Armitage, 1986; Packer et al., 1991; West et al., 2002;
Wrangham and Rubenstein, 1986). Fitness benefits have been
hypothesized to occur directly, at the level of the individual,
through maximized reproductive success (Williams, 1966), or
indirectly through reproductive success of related individuals
(i.e., kin selection; Hamilton 1964). Although reciprocity,
mutualism (Connor, 1986, 1995; Mesterton-Gibbons and
Dugatkin, 1992), or ecological benefits from associations with
nonkin could influence direct fitness (Gompper and Wayne,
1996; Hughes, 1998), benefits obtained from association with
kin may affect both direct and indirect fitness (Gompper and
Wayne, 1996; Hughes, 1998). Nonetheless, under limited
dispersal and high local competition, association with kin may
negatively affect both (West et al., 2002). Thus, to better
understand the role of kinship in formation of groups,
a concurrent evaluation of ecological benefits and relatedness
is required.
In several marine mammals and carnivores, relatedness
among group members is high especially when dispersal is
limited (Clutton-Brock 2002; Wrangham and Rubenstein,
1986). Examples include pods of pilot whales (Globicephala
melas: Amos et al. 1993), packs of dwarf mongooses (Helogale
parvula: Creel and Waser, 1994; Keane et al., 1994), female
groups of coatis (Nasua narica: Gompper 1996; Gompper et al.
1997), packs of African hunting dogs (Lycaon pictus: Girman et
al., 1997), prides of African lions (Panthera leo: Packer et al.,
1991), and wolves (Canis lupus: for review, see Gompper and
Wayne, 1996). Nonetheless, in many cases ecological benefits
such as counter-action against infanticide (lions: Packer et al.,
1991), counter-action against cleptoparasitism (African
hunting dog: Girman et al., 1997), food source manipulation
(coati: Gompper, 1996), and confinement of prey (cetaceans:
Herzing and Johnson, 1997) were recorded, suggesting that
relatedness may not be the sole determinant of formation or
maintenance of social groups in carnivores.
River otters (Lontra canadensis), like other mammalian
species (Lott, 1991), exhibit high intraspecific variation in
social systems. Th (...truncated)