This presentation summarizes research on interspecific hybridization between Atlantic salmon and brown trout. The study examined hybridization in rivers in northern Spain where one species colonized areas inhabited by the other. When Atlantic salmon colonized brown trout areas, 5-10% of juveniles were found to be hybrids, with Atlantic salmon as the maternal species. Similarly, when brown trout colonized an area, 5-7% of juveniles were hybrids with brown trout as the maternal species. The research suggests that the colonizing female species exhibits relaxed mate choice, leading to initial hybridization. However, as the colonizing species expands, hybridization decreases or changes direction. Introgression between the species occurs at low levels and is unlikely

1. WELCOME TO
MY PRESENTATION
ON
Interspecific Hybridization, a Matter of Pioneering?
Insights from Atlantic Salmon and Brown Trout.
JOSE L. HORREO,FERNANDO AYLLON
́
AL MAMUN
10-05-2386

2. Presentation Layout
• Hybridization
• Inter specific hybridization
• Introgressive hybridyzation
• Colonization
• Background
• Case study
• Sampling
• Analysis
• Result & discussion

3. What is hybridization?
any offspring resulting from the breeding of two genetically distinct individuals.
In other word crossing of two individual.
What is interspecific hybridization?
Hybrids between different species within the same genus (such as between
labeo rohita & labio calbasu) are sometimes known as interspecific hybrids or
crosses.
Introgressive hybridyzation
Introgression, also known as introgressive hybridization, in genetics (particularly
plant genetics) is the movement of a gene (gene flow) from one species into the
gene pool of another by the repeated backcrossing of an interspecific
hybrid with one of its parent species. Purposeful introgression is a long-term
process; it may take many hybrid generations before the backcrossing occurs.
Colonization
occurs whenever any one or more species populate an area. The term,
which is derived from the Latin colere, "to inhabit, cultivate, frequent
practice, tend, guard, respect",

4. Background
• Introgressive hybridization can be interpreted as an
invasion of the genome by foreign genes.
• Increased interspecific hybridization is one of the
consequences of species translocations, invasions
because secondary contacts between formerly isolated
species contribute to break reproductive barriers and
lead to introgressive hybridization.

5. Background
• When a fraction of a nonnative species enters in a new area
and encounters a native species, a contact wave front is
originated where the new species (the colonizer) is generally
much scarcer than the native one. Newly arrived
• females (colonizers) may relax mate choice for avoiding
gamete losses in absence of high-quality or just suitable
breeders; they would mate with the most abundant males,
conspecific or not.
• whereas females of the native species would reject mating
with (scarce) alien males.
• the scarcer species providing generally the female in
interspecific crosses.

6. Background
• Aquatic organisms provide examples of interactions between
native and colonizer species due to escapes or deliberate
releases of farmed fish and shellfish.
• Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)
are sympatric species that exhibit introgressive hybridization
in the wild in all their distribution areas.
• Interspecific hybridization seems increased by different
factors, such as escapes or releases of domestic individuals and
alternative mating behavior like male sneaking.

7. NATURAL HYBRIDIZATION

8. Case study
Atlantic Salmon as a Colonizer
• In North Spain (South Europe; lat 43°N), streams support
brown trout and Atlantic salmon sympatric populations.
• Rivers are short and subject to variable conditions of water
level and flow (e.g., Moran et al. 2005) depending on
snowfall,rainfall, and temperature.
• When an upstream area is made accessible, adult salmon may
colonize it from downstream searching for new spawning
areas and enter in secondary contact with resident brown trout

9. Case study
Brown Trout as a Colonizer
• After salmon acclimatization, brown trout arrived in the
Korrigans system by migration from neighbor rivers.
• In only 3 generations, brown trout displaced completely.
• Found hybrids as a signal of interspecific hybridization.
• In the Armor system, the salmon population was resident.

10. Sampling
• When a new species colonizes a river, hybridization occurs in
the lower portions of the river systems, and the occurrence and
degree of hybridization decrease with upstream distance from
the source of the colonizing species.
• Those areas were systematically electrofished: the first 200
mjust upstream the obstacle and sections 100–200 m long
every500 m for several kilometers upstream (whenever
possible).
• Sampling was carried out in summer/autumn (August– October
in Spain and December–January in Kerguelen).
• Juvenile salmonids were caught by 2 or 3 electrofishing passes
in the selected stream sections to obtain adipose fin biopsies,
which were preserved in ethanol until DNA analysis

11. Genetic analysis
• For determining the species of each sample, the 5S ribosomal
RNA nuclear marker was polymerase chain reaction amplified
with the primers ,which yield amplification fragments of
255 bp for Atlantic salmon and
276 bp for brown trout,
• For determining the maternal species of hybrids, the
mitochondrial cytochrome b gene was amplified

12. Result
• The percentage of interspecific hybridization between these
species has been very different according to the cases studied
until now.
• These percentages ranged between 0.74% in the case of parents
of domestic origin in hybrid crosses and 41.5% when both
species were reintroduced in a river section.
• When Atlantic salmon colonized rivers where brown trout was
the only resident,
the percentage of interspecific hybrids ranged in our samples
between 3.03% and 9.84% (mean 5.84%).maternal sp.Atlantic
salmon.
• Where brown trout was the colonizer (Korrigan’s)
the percentage of interspecific hybrids was 5.56% and
6.58%.maternal sp brown trout.

14. Discussion:
• the maternal species of the hybrids, which appeared in first
contact areas, was always the colonizer species.
• colonizer salmonid females exhibited relaxed mate choice and
hybridized since the beginning of the secondary contact, likely
because flexible behavior is advantageous in such
circumstances.
• When the colonizers have expanded after few generations of
colonization, hybridization patterns seem to change, decreasing
or disappearing or giving chance to crosses in the opposite
direction.
• when Atlantic salmon became more abundant than , relaxed
mate choice is happened
• Brown trout possess highly aggressive and dominant during
courtship and relaxed female mate choice would be no longer
necessary.

15. • Interspecific gene flow (introgression) can affect specie
integrity but introgression between these Salmo species occurs
via allotriploids with very low offspring survival and is likely
minimal.
• Therefore it seems unlikely that extinction will be caused by
introgressive hybridization, which is especially important in the
context of conservation and persistence of these species where
they come into artificial (human mediated) secondary contact

16. THANKS TO ALL