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Methods of studying wild-reared interactions

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1 Methods of studying wild-reared interactions
T. F. Cross Department of Zoology, Ecology & Plant Science National University of Ireland, Cork, Ireland

2 The problem: Cultured fish inadvertently escape
from farms or wander from ranching exercises OR are deliberately introduced by stocking ALL OF THESE SOURCES CAN BE EQUALLY DAMAGING

3 Cultured species breed with wild
conspecifics or closely-related species. Offspring have reduced fitness compared with wild populations or species, but in some cases replace them Cultured strains may out-compete wild populations, or can transfer diseases, so leading to reduced Ne PRODUCTIVITY DECLINES (carrying capacity)

4 Direct and indirect genetic effects
Interbreeding with wild conspecific populations or with closely related species (most studied aspects to date) Indirect Cultured organisms compete successfully with wild individuals, and so lead to population decline (reduced Ne) Disease transfer from cultured to wild organisms

5 Definition: fitness = reproductive fitness
Most European experiments have concentrated on Atlantic salmon These have generally shown reduced fitness in reared and/or translocated salmon, compared with natives WHY?

6 Loss of genetic variability due to use of
small numbers of broodstock (so-called inbreeding effects, also leading to loss of local adaptation). 2. Introduced organisms maladapted in non-native area (breakdown of co-adapted gene complexes/ genetic architecture; outbreeding depression in subsequent generations). Must be major factor in translocations without rearing? 3. Domestication selection (relaxation of natural selection/hatchery selection) Only a factor where rearing involved but seems to happen quickly!

7 Are there likely to be similar problems with other
European species? Taking cod as an example: Wild stocks are overfished Genetic variability often much lower in cultured strains than wild progenitors (Bekkevold et al.) BUT not enough known of wild population structure, extent of philopatry and local adaptation (Norwegian & Danish examples?) Also about domestication in reared cod

8 With reared cod Some knowledge of fate of deliberate releases
Farm escapes occur (eggs, net chewing) Do they interbreed with wild conspecifics? What is the relative fitness of progeny?

9 Potential for loss of genetic variability!
Armitage, with SAMS Ardtoe Seven females & seven males in mass spawning M1 M2 M3 M4 M5 M6 M7 SIRE F1 2 13 1 24 40 F2 F3 3 6 F4 F5 7 11 F6 F7 DAM 17 32 57 Potential for loss of genetic variability!

10 Opportunist situations
Where escape or stocking/ranching exercise has occurred and interactions are in progress e.g. Clifford et al. in Donegal, Ireland Escapes from big freshwater farm and from sea cages ID with mtDNA and minisatellites Evidence for breeding in the wild Reduction of cultured influence over time Effects not quantifiable

11 Highly variable loci best-microsatellites (or many
SNP loci, chosen to give the greatest degree of ascertainment) Use individual assignment methods to allocate individuals. Based on genotypes thus giving more power than methods based on allele frequencies (two alleles, three genotypes; three alleles, five genotypes etc.) The more loci used the more accurate (less error) in the assignment (typically microsatellites)

12 Microsatellite locus

13 Manipulated situations
Common-garden field experiments (Burrishoole) Know actual parents so can use parental assignment which is more accurate than individual assignment (exclusion methods like PAPA or FAP-Arden & Jones) Accuracy improves to near 100% as number of loci is increased Usually about six loci are optimal Can then look at morphological traits of identified individuals, since environment “common”

14 FIELD EXPERIMENT Assessing the potential impact on native salmon from farmed escapes in Ireland (McGinnity et al. 1997, 2003)

15 How general are Irish salmon findings?
AIR project had Scottish and Spanish components-performance of natives better than non-natives “Common-garden” comparison in Ireland of native versus non-native wild progeny, showed significantly higher survival of former Similarly in Imsa study in Norway (Fleming et al.)

16 INDIRECT EFFECTS: Disease from cultured salmon affecting wild
salmonids EU SALIMPACT-Neth, UK, Nor, Irl Major Histocompatibility Complex investigated

17 Examining temporal samples of sea trout from a river in the west of Ireland with a history of aquaculture Burrishoole – freshwater Atlantic salmon hatchery, ranching and sea cages

18 Burrishoole Upstream from Furnace Downstream from Feeagh
Salmon Leap trap

19 Aquaculture activity- Atlantic salmon (hatchery and ranching c1960)
MI smolt unit

20 Allelic richness Significant loss of allelic richness/genetic diversity at MHC I after 1958 but subsequent recovery Relative stability at neutral loci

21 Putative agent of selection
Furunculosis associated with development of smolt release programme - reducing genetic variability at MHC Aquaculture activities can cause changes at immune response genes in cohabiting salmonid species, in addition to changes caused by interbreeding, either within or between species

22 Marine species differ from salmon:
Census populations much larger (low drift) Population (“stock”) structure far less defined Is gene flow high? Reduced interpopulation differences in latter group often attributed to far greater gene flow (poor natal homing) Might also (or instead) be due to far less genetic drift?

23 Known that salmon home natally and are locally
adapted. Are marine species? “Walls in ocean?” Gyral retention of larvae Heterogeneity of spawning habitat Hybrid zones (Baltic/Atlantic-Nielsen et al.)

24 Challenge to study in “open” system
Maybe, invoke genetic “tagging” (breeding for genotype that is rare in wild, but functionally equivalent to other genotypes) May have to use opportunist situations, since experimental systems in ocean likely to be too costly and uncontrollable (except in semi-isolated habitats/Borgenfjord)

25 How can aquaculture grow without
further impinging on wild populations, themselves threatened by overfishing, pollution, habitat destruction and climate change?

26 “When elements of a species are domesticated, the remaining wild
To quote a distinguished mammalologist: “When elements of a species are domesticated, the remaining wild populations quickly go extinct” Can we prevent this with aquatic species?

27 Thank you!

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