Impacts of Hybridization

Published Date: 23 Jan 2018

Introduction

Hybridization is a process that happens when two animals or plants of different species reproduce resulting in the appearance of a new organism commonly called hybrids.

By only read this explanation we can assume that hybridization is beneficial, because it is in some cases, the origin point of new species but this is not necessarily true. It can also cause the extinction of numerous species, as it has already done, that is caused by the hybrids since they start to substitute the original genetic material of the population, which is done by mating with them and reproducing among them, their genetic material starts to spread causing a exponentially growth in the hybrid population and replacing the original specie. Other times the hybrid is not sexually viable and cannot reproduce and so it does not make an impact on the original population.

Habitat modifications that are human related may cause organisms to move to different places and so an opportunity for different species to come in contact can occur. (Allendorf et all 2001).

To be able to make a conservation study we must identify what kind of hybridization we are dealing with, if it’s natural or “man-made”, and so different conservation policies must be made to deal with different types of hybridization.

In this work a genetic characterization of a dog population for the conservation of the Iberian wolf (Canis lupus signatus) endangered sub-specie of the wolf (Canis lupus) is going to be made.

The appearance of the domestic dog (Canis lupus familiaris) can be pin point to the domestication of the grey wolf (Canis lupus), during the Pleistocene, it cannot be easily specified if it was a wolf population or more that during this Epoch was the point of origin of this new specie. But in fact this new specie provided early humans with a guard animal, a source of food, fur, and in some cases a beast of burden.

Throughout this Epoch the population of domesticated wolfs would certainly be capable to breed with the existent wolf population causing a wide genetic variety in their offspring. But at some point this population of domestic wolfs “transform" in what we call as dogs (Vilá et al 1997).

To be able to explain the changes suffered by these animals, studies indicate that domestic animals must have changed in ways that were useful to humans at the time. (Morey, D. F. 1994).In fact the owners of the first dogs may have treated them better because they look different, they had a curled tail, big eyes or were dearer than the rest of the litter (Clutton-Brock J. 2002).

The Iberian wolf (Canis lupus signatus) is a grey wolf subspecies that the most probable cause of appearance was caused by the isolation of theIberian Peninsulacaused by the ice age on the Pleistocene. A grey wolf population was isolated in this territory and changed into this sub-specie. It has some specific characteristics when compared to the grey wolf which are: it is a bit shorter, white marks on the upper lips, the dark marks on the tail and on its front legs (ICN, 2006) this marks are the reason of it subspecies name,signatus("marked").

The diet of the Iberian wolf consists in: wild boar, roe deer and deer, and in some cases some domestic animals like the sheep, goat, and chicken (Álvares, 2006; Cruz, 1999; Nunes, 2000). It can also feed on corpses and so can also be branded as a scavenger.

The Iberian Peninsula was in its major part inhabited by the Iberian wolf until 1900s, but in Portugal the numbers of wolfs are diminishing since 1940 (Nunes, 2000), which were caused by: hunting, loss of territory, hybridization witch is referred in this work and extermination campaigns extermination like the ones that occurred in Spain in 1950 to 1960 that almost decimated the animals in Spain except the north-western part of the country, where there is still a sizeable population in the Sierra de la Culebra, and Sierra Morena.

The wolf population in Portugal consists of two subpopulations: a subpopulation occurs north of the Douro River which is the continuity of Spanish population, and other subpopulation is situated south of the Douro River that seems to be isolated from the rest of the Iberian population and shows a high level of fragmentation ( Cabral et all, 2005). In this work the wolf population used is situated south of Douro River more precisely in Serra da Arada, Freita e Montemuro.

Invasive methods to obtain genetic data from the dog population will be used; they consist in fur and buccal swabs that will be collect from various dogs from Serra da Arada, Freita and Montemuro. Fur samples can be preserved by storing them at room temperature or in ethanol (Oka and Takenaka 2001), dry with or without disinfectant (Gagneux et al. 1997, Woods et al. 1999), or by freezing (Con- stable et al. 2001), buccal swabs can be preserved by freezing them until the time of use, from this samples a database will be created that will help to identify a hybrid or non-hybrid organism.

From the genetic material obtained, mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) can be extracted, but in this work only mitochondrial DNA will be used because from it we can discover what specie the female progenitor was (dog or wolf). A second laboratory procedure will be done that consists in the study of specific microsatellite (short tandem repeat or STR) which is done by a PCR (polymerase chain reaction) using specific PCR primers which connect to both sides of the microsatellite. The size of the DNA that was amplified is determinate by the numbers of repeats present in the microsatellite on that allele. Then it’s run on a gel that will separate the fragments based on size. Individuals usually have two alleles for all microsatellites. If the number of repetitions of an allele is different from the other, then two distinct bands in the gel would appear.

Therefore, as said by (Arif et all, 2010) “a single pair of PCR primers will work for every individual in the species and produce different sized products for each of the different length microsatellites” (short tandem repeat or STR) . In this work 25 microsatellites are used.

From the positions and differences of the microsatellites a comparison can be done that will allow us to verify if the specimen in study is a hybrid or not. With the results obtained the data base created will help us to identify the possible the number of wolf, and wolf –dog hybrid in the region and so help us define a conservation plan for the Iberian wolf in the region of study.

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