N. Ryman, MINIMIZING ADVERSE-EFFECTS OF FISH CULTURE - UNDERSTANDING THE GENETICS OF POPULATIONS WITH OVERLAPPING GENERATIONS, ICES journal of marine science, 54(6), 1997, pp. 1149-1159
Although an increasing number of natural fish populations are being co
ntaminated by exogenous immigrants, knowledge is poor regarding the ge
netic changes expected to occur in a wild stock once an introgression
has taken place. One reason for this lack of knowledge appears to be t
hat the theory for the genetic dynamics is poorly developed and compli
cated for age-structured populations with overlapping generations. Usi
ng newly developed theory and results from computer simulations, the g
enetic aspects of age-structured populations with overlapping generati
ons are discussed, especially the detection of contamination and the g
enetic dynamics following hybridization. When generations overlap, the
amount of temporal allele frequency shift is generally larger than fo
r a population of equal genetically effective size with discrete gener
ations. This is even more pronounced for the separate cohorts than for
the population as a whole. Therefore, when testing for temporal genet
ic heterogeneity, a higher frequency of statistically significant resu
lts may be expected than can be explained by genetic drift caused by a
restricted effective population size. During introgression, a sudden
infusion of new genes initiates marked allele frequency fluctuations,
and in salmonids this ''genetic instability'' may persist for several
decades. In spite of these potentially dramatic fluctuations, even a m
assive influx of exogenous genes may be very difficult to detect, part
icularly in the absence of genetic and demographic monitoring data fro
m the natural population prior to immigration. A conservative attitude
is recommended when interpreting allele frequency differences within
populations where the history and the demographic characteristics are
poorly known. The risk of incorrect interpretations is particularly ap
parent for many salmonid species where only a subset of the existing a
ge classes may be available for sampling. (C) 1997 International Counc
il for the Exploration of the Sea.