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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

Presentation Layout• Hybridization

• Inter specific hybridization

• Introgressive hybridyzation

• Colonization

• Background

• Case study

• Sampling

• Analysis

• Result & discussion

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 betweenlabeo rohita & labio calbasu) are sometimes known as interspecific hybrids orcrosses.

Introgressive hybridyzationIntrogression, also known as introgressive hybridization, in genetics (particularlyplant genetics) is the movement of a gene (gene flow) from one species into thegene pool of another by the repeated backcrossing of an interspecifichybrid with one of its parent species. Purposeful introgression is a long-termprocess; 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",

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.

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.

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.

NATURAL HYBRIDIZATION

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

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.

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

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

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.

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.

• 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

THANKS TO ALL