Kinship and social dynamics in juvenile Atlantic salmon and rainbow trout : the adaptive role of kin discrimination

Brown, Grant Edwin (1993) Kinship and social dynamics in juvenile Atlantic salmon and rainbow trout : the adaptive role of kin discrimination. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

I conducted a series of experiments designed to examine the regulating mechanisms and the functional value of kin discrimination in two juvenile salmonids: Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss ). The first two studies documented kin discrimination abilites in these species and also determined the possible recognition mechanism responsible for kin discrimination abilities in these species. When given the 'choice', individual salmon and trout fry spent a significantly greater proportion of time in waters conditioned by kin versus non-kin (Chapter 2). When I controlled for familiarity (Chapter 3), individual trout fry spent a significantly greater proportion of time in water conditioned by either familiar (reared together) or unfamiliar (reared apart) kin versus non-kin, but exhibited no significant discrimination between familiar versus unfamiliar kin. These data suggest that these species are capable of kin discrimination based on water-borne chemosensory cues and that direct familiarity is not the recognition mechanism regulating this ability. Support for the phenotype matching hypothesis was found. -- I conducted a third study (Chapter 4) designed to examine the effects of kinship on the territorial defence behaviour of juvenile salmon and trout. Kin groups initiated significantly fewer aggressive interactions, utilized a lower proportion of 'overtly aggressive' behaviour types and defended significantly smaller territories than did non-kin groups in an artificial stream channel. This study suggests the possibility for significant inclusive fitness benefits associated with kin-biased territorial behaviour. -- I examined the effects of varying territory quality on these kin-biased territorial defence behaviour in juvenile rainbow trout in the fourth study (Chapter 5). Food availability and predator presentation rates were altered in order to manipulate territory quality. Kin groups were always observed to initiate significantly fewer aggressive interactions and to defend significantly smaller territories than were non-kin groups. Kin-biased territorial defence behaviour were always observed, though the magnitude of the difference between kin and non-kin groups was reduced at the low territory quality conditions. Kin groups also exhibited higher mean weight increases (fitness benefits) when compared to non-kin groups, regardless of territory quality. -- The final study (Chapter 6) examines the influence of kinship on the foraging behaviour and the distribution of benefits in groups of kin and non-kin salmon and trout. Both salmon and trout kin groups exhibited significantly higher mean weight increases with significantly less variability among individual weight gains when compared to non-kin groups. Foraging rates among subordinate kin were higher and aggressive interactions among dominant kin were reduced compared to non-kin groups. These results suggest that with decreased territorial defence behaviour, individuals can devote more time to foraging and hence exhibit higher and less variable fitness benefits. -- Taken together, these data suggest that there is significant kin selection pressure on the territorial defence behaviour of these juvenile salmonids. By defending territories near kin preferentially, both juvenile salmon and trout are able to reduce the frequency of aggressive interactions and the costs associated with territorial defence behaviours, resulting in significant direct and inclusive fitness benefits to the individual.

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