Version classiqueVersion mobile
OpenEdition Books

The Mediterranean region under climate change

 | 
Jean-Paul Moatti
, 
Stéphane Thiébault

Part 3. Adaptation, resilience, conservation of resources and prevention of risk

Sub-chapter 3.2.4. Managing genetic resources of small ruminants in a context of climate change

Anne Da Silva et Badr Benjelloun

Texte intégral

Introduction

1Locally adapted breeds of livestock are of major interest as reservoirs of biodiversity. They may play a key role in ensuring the sustainability of the breeding sector in a changing climate. The Mediterranean Basin is characterized by a wide diversity of small ruminant breeds, and more specifically, North Africa and Turkey constitute remarkable dry ecosystems which have enabled the emergence of breeds showing strong adaptation to harsh environments. This unique genetic heritage appears clearly endangered. One of the main threats is the deep lack of knowledge concerning the small ruminant livestock in these areas – some breeds have probably disappeared even before being recorded. Another issue concerns the erosion of the livestock gene pool with anarchic cross-breeding practices leading to genetic dilution and replacement of local breeds by exotic ones or by a reduced number of native breeds among the most productive. The recent availability of high-throughput sequencing is very promising, enabling the identification of unique allelic combinations underlying adaptation traits of the utmost importance in this context of global warming.

Context

2The majority of sheep and goat populations are found in developing countries and play a significant role in their national economies. Indeed, the ability to tolerate harsh climates and thrive on poor quality diets makes them one of the few species able to take advantage of low input farming systems. Breeds of small ruminants have evolved over the centuries managed by traditional pastoralists, enabling the emergence of wide diversity and of strong adaptations to a range of diverse environments. In developed countries the situation changed with the emergence of the breed concept (200 years ago), with a shift from “soft” selection to “harsh” selection for maximizing productivity (Taberlet 2008). As a result of practices focusing on performance improvement, genetic resources have been lost, because of the homogenization of industrial breeds subjected to strong selection and moreover, because of the replacement of traditional breeds by a limited number of high-performance breeds. Finally, intensive commercial production systems have led to the rupture of the link between the breed and its environment (Hoffmann 2010).

3Today, worldwide livestock diversity is threatened and the Mediterranean area is no exception: one domestic breed disappears every month in the world and 30 percent of livestock breeds are considered at risk of extinction (Food and Agriculture Organization (FAO), 2015). Animal genetic diversity determines the potential for adaptation in changing environments; hence preserving the biodiversity is crucial for the breeding sector, especially in a context of climate change.

4The Mediterranean Basin is characterized by semi-arid and arid areas which are noted for their desert climate in their southern part (mainly located in North Africa). Moreover, dryland mountain ecosystems, mostly encountered in Turkey and North Africa, represent extremely heterogeneous environments considered as biodiversity hotspots (FAO 2011). Breeds locally adapted to these particular ecosystems are the outstanding result of unique evolutionary phenomena, as they have developed the necessary specific features to deal with harsh environments (water scarcity, extreme hot and cold temperatures, unpredictable long drought periods, etc.). In the context of climate change, these highly resilient breeds are of primary interest. These countries, on the frontline of the climatic evolutions, are particularly vulnerable to the negative impacts of climate change. On the other hand, their livestock genetic heritage – a true reservoir of diversity – appears to be essential, offering a possible solution to deal with the global warming issue and related new diseases.

5Here we focus on the locally adapted breeds of particularly dry areas, and dry mountains of the Mediterranean Basin (i.e. North African countries and Turkey), with a view to identifying the major threats affecting them and the genetic field of investigation which could be developed with the aim of making agro-ecosystems of the Mediterranean area more resilient. This is a fundamental condition to ensure sustained-and if possible improved-productivity levels despite unfavorable environmental conditions.

Knowledge of Mediterranean small ruminant stock

6In DAD-IS, the Domestic Animal Diversity Information System hosted by FAO (http://dad.fao.org/​), breeds are classified in two groups (i) “local breeds” (i.e. breeds defined in the database as “occurring only in one country” and hence likely to develop adaptations to particular environments) and (ii) “transboundary breeds” (i.e. “breeds that occur in more than one country”). We have compiled this information in order to draw up an inventory of the current state of small ruminant “local breeds” in the Mediterranean area, considering the countries that surround the Mediterranean Basin and for which information is available (i.e. Albania, Algeria, Bosnia-Herzegovina, Croatia, Cyprus, Egypt, France, Greece, Italy, Israel, Libya, Malta, Montenegro, Morocco, Portugal, Slovenia, Spain, Syria, Tunisia, and Turkey). The term “local breeds” does not strictly include “locally adapted breeds” (i.e. “breeds which have been in the country for a sufficient time to be genetically adapted to one or more of traditional production systems or environments in the country” (FAO 2012)) which are the focus of this article; indeed a substantial number of “transboundary breeds” are also adapted to local environments. Hence the information available in DAD-IS leads to an underestimation of the diversity of breeds showing particular suitability for extreme environments (FAO 2012).

7The analysis of the DAD-IS data-base shows that 25.2% of local goat breeds and 27.7% of local sheep breeds recorded in the world are concentrated in the Mediterranean area. Hence it appears that more than a quarter of the worldwide small ruminant diversity can be found in an area corresponding to only a few percent of the worldwide arable land surface (according to the World Bank database of surface of arable land by country (http://data.worldbank.org)). This richness has been shaped by the substantial diversity of the environments found in this area. Indeed, The Mediterranean Basin can be seen as a patchwork of nested habitats, in which various combinations of a range of variables (temperature, rainfall, altitude, topography, geology, ground vegetation, soil nutrients, etc.) are the source of the remarkable diversity encountered. Moreover, the emergence of the wide diversity of small ruminant breeds was largely stimulated by the strategic location of the Mediterranean Basin, at the crossroads of three continents (Europe, Africa and Asia), giving the area a major role in trade and economic exchanges, that largely favored the diffusion of breeds around the Basin.

8The number and risk status of small ruminant local breeds in the Mediterranean area (see Table 1) shows that 42.7% of the local breeds are endangered or extinct while there is no information concerning the risk status for 19.1% of them. This percentage of breeds classified as “unknown” is particularly high in developing countries, with a mean of 45.5% considering North African countries (i.e. Algeria, Libya, Egypt, Morocco and Tunisia). Moreover, it appears that France, Italy and Spain account for 56.2% of Mediterranean local breeds, whereas North African countries represent no more than 11.4% of the Mediterranean livestock. This result is probably due to a lack of information, inducing a biased picture of the Mediterranean livestock. Indeed, Scherf et al. (2008) have raised the issue of the underestimation of breeds in dryland areas, with a significant number not officially reported. This implies that some uncharacterized breeds may have disappeared without being recorded. The situation varies depending on the country considered; Morocco, Egypt and Turkey report quite substantial numbers, whereas Algeria Tunisia and Libya show clear underreporting (accounting for less than 8% of the North African livestock). However even for Morocco, Egypt and Turkey, the good levels of reporting are offset by the limited knowledge of the breeds (with 79.2% of the Moroccan breeds classified as “unknown”, given that most information available in the database dates back to 2007 and has not been updated since).

Table 1. Number and risk status of small ruminant local breeds in the Mediterranean area according to FAO DAD-IS database.

Table 1. Number and risk status of small ruminant local breeds in the Mediterranean area according to FAO DAD-IS database.

*breeds with “Critical”, “Critical Maintained”, “Endangered” or “Endangered Maintained” risk status in DAD-IS (2016) allowing for the fact that most information has not been updated since 2007; Med. Bas.= Mediterranean Basin; loc. breeds=local breeds.

9Hence it can be concluded that one of the main threats to the local breeds of Turkey and North Africa, and more generally to local breeds located in developing countries, is a clear lack of knowledge (with breeds unreported and missing or unreliable data for the reported breeds). Lack of infrastructure, lack of organization for the breed sector, areas of political instability, and a policy of disinvestment, amongst other reasons, are responsible for the lack of knowledge for the local breeds of these areas.

Genetic erosion of locally adapted breeds

10A productivity-only objective often appears to be detrimental for locally adapted breeds. Indeed, most of these breeds are poorly productive, and the economic pressure leads farmers to carry out unsupervised cross-breeding (i.e. not in the framework of selection plans) hoping to increase animal conformity, and/or to replace native breeds by exotic ones or by a reduced numbers of local breeds among the most productive. In Algeria for example, one native sheep breed, Ouled-Djellal, which is considered more productive, accounts for more than 63% of the Algerian sheep population. Crosses between Ouled-Djellal and local Algerian breeds are a current practice by farmers, so that four breeds have been found to be highly genetically admixed with the Ouled-Djellal (Rembi, Taâdmit (Gaouar et al. 2015), Barbarine and Berber (Gaouar et al. 2016)). The Berber is considered to be the most ancient and primitive sheep breed of the Maghreb and the genetic dilution of this breed represents a great loss for the worldwide livestock genetic heritage. The other local breeds of Algeria are under high risk of disappearance (Iniguez 2005) because they are largely abandoned and suffer from high census contraction.

11Admixture can also be reported among Egyptian goats (Elbeltagy et al. 2016), Turkish sheep (Yilmaz et al. 2015) and among Tunisian sheep (Kdidi et al. 2015). The situation appears different in Morocco, where a national strategy entitled “Plan Moutonnier” (sheep plan) implemented in 1980 (MAMVA 1980) provided substantial support to preserve most local sheep breeds, allowing the identification of breeding areas and monitoring performance. The plan also defined a very limited number of areas where it was allowed to introduce exotic breeds. The current high genetic diversity of Moroccan sheep compared to industrial and indigenous sheep from other countries shows the effectiveness of this strategy in preserving small ruminant genetic resources of Morocco (Benjelloun 2015).

12Hence genetic erosion, via indiscriminate cross-breeding and breed replacement, is a major threat for local breeds of North Africa and Turkey, leading to the homogenization of this unique reservoir and to the loss of allelic combinations of potential interest in a climate change context.

Genetic uniqueness of locally adapted breeds

13Local breeds are largely shaped by natural selection and are hence highly connected or “locally adapted” to their natural environment. Local adaptation could come either from the standing genetic variation (existing variation in a population) or from novel mutations bringing new alleles that are advantageous and thus become selected in a given environment. Current findings suggest that most local adaptations stem from standing variation, rather than from new mutations (Savolainen et al. 2013). Selection (natural and artificial) has left its footprint in the genome, a process known as “selection signature”. Indeed, positive selection favoring local adaptation is expected to increase the frequency of an allele, and in the same time, the length of the haplotype (extent of DNA segment) associated with the selected allele, relative to those that are not under selection. Today, given the availability of dense marker panels, scientists have the possibility to track these selection signatures and hence to identify allele of primary importance in adaptation to harsh environments.

14Recent studies within the EU-funded “NextGen” project (2010-2014) have used whole genome sequences (WGS) to assess genetic resources in various domestic (Moroccan and Iranian indigenous breeds and a worldwide panel of cosmopolitan breeds) and wild populations (bezoars and Asiatic mouflons). Iranian domestic breeds and wild populations were sampled from the presumed domestication centre (Fertile Crescent) with the assumption that genetic diversity in these individuals is at its highest level and would decrease regularly along the migratory routes as described by Bruford et al. (2003). As expected, the NextGen studies identified a very high variation in Iranian domestic populations and in wild populations (Fig. 1); more surprisingly Moroccan breeds were also found to be highly diversified (in numbers comparable to Iranian breeds, Fig. 1) in spite of the fact that Morocco represents the end of a migratory route and hence was expected to show lower variability.

Figure 1
Venn diagrams showing the number of exclusive and shared alleles (in million) in various sheep and goat populations. Source: Benjelloun 2015. Mouflons=Asiatic mouflons (wild populations), Aegagres=Bezoars (wild populations), Iraniens=Iranian domestic breeds, Marocains=Moroccan domestic breeds, Industriels=Cosmopolitan sheep breeds.

15These results indicated that each indigenous and wild population constitutes a unique reservoir of millions of alleles (standing variation) making them a potential source of adaptation of sheep and goats in the context of global changes. Moreover, this project studied the whole genomes of hundreds of local sheep and goats representing Morocco-wide diversity in terms of ecology, climate and geographic origin. An approach called “landscape genomic” was used; it involved correlating allele frequencies with several environmental factors in order to identify selected alleles (selection signatures) probably involved in adaptation to harsh environments. This approach was applied jointly with a population genetics analysis. The outcomes highlighted several sets of alleles and genes that probably play a role in local adaptation to extreme altitude, slope, rainfall and temperature; e.g. some alleles within genes involved in respiration and heart function were identified as playing key roles in adaptation to high altitudes (Benjelloun 2015). Candidate genes for adaptation to similar environments were generally different between sheep and goats, suggesting different adaptive mechanisms in both species and even between two breeds in one species (e.g. panting/sweating to adapt to desert environment in two Moroccan goat breeds; Benjelloun et al. 2015).

16Hence, the neutral and adaptive remaining genetic diversity of each local breed could represent a unique treasure that might be needed for the preservation of the species in the current context of environmental changes. Specific strategies should therefore be designed to halt the current loss of autochthonous breeds around the Mediterranean and elsewhere. Moreover, local breed improvement programs have to be planned in order to increase the economic productivity of the local breeds and thus make them more attractive for breeders.

Photo 1
Herds of local sheep and goats, Morocco, High Atlas, Imilchil (altitude: ~ 2300 m). Badr Benjelloun, 2008.

Photo 2
Moroccon local sheep (Timahdite breed), Morocco, Middle Atlas, M’rirt (altitude: ~ 1100 m). Badr Benjelloun, 2007.

Bibliographie

References

Benjelloun B., Alberto F.J., Streeter I., Boyer F., Coissac E. et al., 2015
Characterizing neutral genomic diversity and selection signatures in indigenous populations of moroccan goats (Capra Hircus) Using Wgs Data. Front. Genet., 6:107. Doi: 10.3389/Fgene. 2015.00107

Benjelloun B., 2015
Diversité des génomes et adaptation locale des petits ruminants d’un pays méditerranéen: le Maroc. Thèse de Doctorat. Biodiversité, Ecologie, Environnement. Université Grenoble Alpes. <Nnt: 2015greav011>. <Tel-01280471>. Grenoble, France, 207p.

Bruford M.W., Bradley D.G., Luikart G., 2003
Dna Markers Reveal the complexity of livestock domestication. Nature Reviews Genetics, 4 (11): 900-910.

Elbeltagy A.R., Aboul-Naga A.M., Hassen H., Solouma G.M., Rischkowsky B., Mwacharo J.M., 2016
Genetic diversity and structure of goats within an early livestock dispersal area in Eastern North Africa. Afr. J. Biotechnol., 15(11): 431-441.

FAO, 2015
The Second Report On The State Of The World’s Animal Genetic Resources For Food And Agriculture, Edited By B.D. Scherf & D. Pilling. FAO Commission on Genetic Resources For Food And Agriculture Assessments. Rome (Available At Http://Www.Fao.Org/3/A-I4787e/Index.Html).

FAO, Commission on Genetic Resources for Food and Agriculture, 2012
Report of the Seventh Session of The Intergovernmental Technical Working Group on Animal Genetic Resources for Food and Agriculture, Fao, Rome, Italy.

FAO, Mountain Partnership Secretariat, UNCCD, SDC, CDE, 2011
Highlands And Drylands – Mountains, A Source Of Resilience In Arid Regions. Published by FAO, Unccd, Mountain Partnership, Swiss Agency for Development And Cooperation, and CDE, with the Support of an International Group Of Experts. Rome.

Gaouar S.B.S., Da Silva A., Ciani E., Kdidi S., Aouissat M., Dhimi L., et al., 2015
Admixture and Local Breed Marginalization Threaten Algerian Sheep Diversity. Plos One, 10: E0122667. Doi: 10.1371/Journal.Pone.0122667

Gaouar S.B.S., Lafri M., Djaout A., El-bouyahiaoui R., Bouri A., Bouchatal A., Maftah A., Ciani E., Da Silva A., 2016
Genome-wide analysis highligts genetic dilution in Algerian sheep. Heredity, doi:10.1038/hdy.2016.86.

Hoffmann I., 2010
Climate Change and the Characterization, Breeding and Conservation of Animal Genetic Resources. Anim Genet., 41 Suppl 1: 32–46. Doi:10.1111/J.1365-2052.2010.02043.X

Iniguez L., 2005
Characterization of Small Ruminant Breeds in West Asia and North Africa. In North Africa (Vol 2), Eds: International Center For Agricultural Research In Dry Areas (Icarda), Aleppo, Syria.

Kdidi S., Calvo J.H., González-Calvo L., Ben Sassi M., Khorchani T., Yahyaoui M.H., 2015
Genetic relationship and admixture in four tunisian sheep breeds revealed by microsatellite markers. Small Ruminant Research, 131: 64–69. Doi:10.1016/J.Smallrumres.2015.08.012

Mamva, 1980
Plan Moutonnier. Ministère De L’agriculture Et De La Mise En Valeur Agricole, Rabat, Maroc.

Savolainen O., Lascoux M., Merila J., 2013
Ecological genomics of local adaptation. Nature Reviews Genetics, 14(11): 807-820.

Scherf B., Rischkowsky B., Hoffmann I., Wieczorek M., Montironi A., Cardellino C. 2008
Livestock genetic diversity in dry rangelands. In The Future Of Drylands, Eds: C. Lee And T. Schaaf, Unesco.

Taberlet P., Valentini A., Rezaei H.R., Naderi S., Pompanon F., Negrini R., et al., 2008
Are cattle, sheep, and goats endangered species? Mol Ecol., 17: 275–284. Doi:10.1111/J.1365-294x.2007.03475.X

Yilmaz O., Cemal I., Karaca O., 2014
Genetic diversity in nine native turkish sheep breeds based on microsatellite analysis. Anim Genet., 45: 604–608. Doi:10.1111/Age.12173

Table des illustrations

Titre Table 1. Number and risk status of small ruminant local breeds in the Mediterranean area according to FAO DAD-IS database.
Légende *breeds with “Critical”, “Critical Maintained”, “Endangered” or “Endangered Maintained” risk status in DAD-IS (2016) allowing for the fact that most information has not been updated since 2007; Med. Bas.= Mediterranean Basin; loc. breeds=local breeds.
URL http://books.openedition.org/irdeditions/docannexe/image/23811/img-1.jpg
Fichier image/jpeg, 226k
Légende Figure 1Venn diagrams showing the number of exclusive and shared alleles (in million) in various sheep and goat populations. Source: Benjelloun 2015. Mouflons=Asiatic mouflons (wild populations), Aegagres=Bezoars (wild populations), Iraniens=Iranian domestic breeds, Marocains=Moroccan domestic breeds, Industriels=Cosmopolitan sheep breeds.
URL http://books.openedition.org/irdeditions/docannexe/image/23811/img-2.jpg
Fichier image/jpeg, 73k
Légende Photo 1Herds of local sheep and goats, Morocco, High Atlas, Imilchil (altitude: ~ 2300 m). Badr Benjelloun, 2008.
URL http://books.openedition.org/irdeditions/docannexe/image/23811/img-3.jpg
Fichier image/jpeg, 250k
Légende Photo 2Moroccon local sheep (Timahdite breed), Morocco, Middle Atlas, M’rirt (altitude: ~ 1100 m). Badr Benjelloun, 2007.
URL http://books.openedition.org/irdeditions/docannexe/image/23811/img-4.jpg
Fichier image/jpeg, 331k

Auteurs

University of Limoges, INRA, France
Geneticist, University of Limoges/INRA, Unité de Génétique Moléculaire Animale, France
anne.blondeau@unilim.fr

University of Grenoble, INRA, Morocco
Geneticist, University of Grenoble/CNRS, Laboratoire d’Écologie Alpine, France INRA Morocco, Centre Régional de Tadla, Beni-Mellal, Morocco
badr.benjelloun@gmail.com

© IRD Éditions, 2016

Conditions d’utilisation : http://www.openedition.org/6540

Lire

Freemium

open access

Offert par L’éditeur de ce site