4 Interactions of Wild and Reared Fish and Invertebrates
139
4.5.2 Indirect Effects
Presuming there is a drastic reduction the size of natural populations (and also of
N e ), exponential increase in genetic drift may result in a loss of potentially adaptative
population structure, due to loss of alleles and alteration of allele frequencies. In
other cases it may be difficult to distinguish between direct and indirect effects of
interactions and it is conceivable that indirect effects may be masked by the
consequences of interbreeding. Because of this problem, together with a lack of
knowledge about functional genomics (e.g., immune response genes) in many
species and a poor understanding of long-term ecological implications, many of the
consequences of indirect interactions for wild populations are unknown.
4.6 Establishing the Severity of the Problems Caused
by Wild/Reared Interactions with Different Species
Two types of scenarios are recognised where the consequences of interaction
between wild and cultured individuals can be assessed, opportunist and experimental
situations.
4.6.1 Opportunist Situations
These are defined as situations where escapes or deliberate introductions have
already occurred, and the aim is to quantify the extent of the subsequent direct or
indirect interactions. In this case, a range of molecular markers (Box 4.1) are
investigated in the wild population/s and reared strain/s involved, searching for
marker loci either with completely different alleles or haplotypes in the wild and
reared groups (referred to as an absolute or qualitative marker), or at least loci
which show substantially different allele frequency differences (termed quantitative
markers). While a proportion of absolute markers can usually be found between
congeneric or more distantly related species, they are rare within species, unless
reared and wild individuals come from different major population groupings (but
see Clifford et al. 1998). Thus, in the conspecific case it is usually necessary to rely
on allele frequency differences at quantitative markers as defined above. With this
type of marker, the discriminatory power increases with the number of individual
loci or haplotypes included. Using a number of quantitative markers, individuals
can be assigned to one or other group although certain markers will be intrinsically
better when seeking high levels of discrimination. Microsatellite loci because of
their high mutation rate and high allele number are particularly useful in this
respect, as is the 5′ end of the d-loop region of the mitochondrial genome. With
mtDNA, in addition to rapid mutation rate, there is a four times lower N e (assuming
139
4.5.2 Indirect Effects
Presuming there is a drastic reduction the size of natural populations (and also of
N e ), exponential increase in genetic drift may result in a loss of potentially adaptative
population structure, due to loss of alleles and alteration of allele frequencies. In
other cases it may be difficult to distinguish between direct and indirect effects of
interactions and it is conceivable that indirect effects may be masked by the
consequences of interbreeding. Because of this problem, together with a lack of
knowledge about functional genomics (e.g., immune response genes) in many
species and a poor understanding of long-term ecological implications, many of the
consequences of indirect interactions for wild populations are unknown.
4.6 Establishing the Severity of the Problems Caused
by Wild/Reared Interactions with Different Species
Two types of scenarios are recognised where the consequences of interaction
between wild and cultured individuals can be assessed, opportunist and experimental
situations.
4.6.1 Opportunist Situations
These are defined as situations where escapes or deliberate introductions have
already occurred, and the aim is to quantify the extent of the subsequent direct or
indirect interactions. In this case, a range of molecular markers (Box 4.1) are
investigated in the wild population/s and reared strain/s involved, searching for
marker loci either with completely different alleles or haplotypes in the wild and
reared groups (referred to as an absolute or qualitative marker), or at least loci
which show substantially different allele frequency differences (termed quantitative
markers). While a proportion of absolute markers can usually be found between
congeneric or more distantly related species, they are rare within species, unless
reared and wild individuals come from different major population groupings (but
see Clifford et al. 1998). Thus, in the conspecific case it is usually necessary to rely
on allele frequency differences at quantitative markers as defined above. With this
type of marker, the discriminatory power increases with the number of individual
loci or haplotypes included. Using a number of quantitative markers, individuals
can be assigned to one or other group although certain markers will be intrinsically
better when seeking high levels of discrimination. Microsatellite loci because of
their high mutation rate and high allele number are particularly useful in this
respect, as is the 5′ end of the d-loop region of the mitochondrial genome. With
mtDNA, in addition to rapid mutation rate, there is a four times lower N e (assuming