Inter specific hybridization

Interspecific Hybridization, a Matter of
Pioneering? Insights from Atlantic
Salmon and Brown Trout

1. WELCOME TO MY PRESENTATION ON Interspecific Hybridization, a Matter of Pioneering? Insights from Atlantic Salmon and Brown Trout . JOSE L. HORREO,FERNANDO AYLLO N ́ 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.

13. 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.

14. 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

15. THANKS TO ALL