The current poultry industry in the developed countries, Sweden included, is dominated by a few commercial breeds. Most of the local breeds in Sweden became threatened by extinction when the commercial breeds became common. At present, there are eleven local chicken breeds originating from different parts of Sweden. Typically only a small number of birds in one or a few locations per breed were left at the time of rescue. Conservation of the Swedish local chicken breeds is coordinated by the Swedish association for local poultry (SLK, Svenska Lanthönsklubben).
Åsbohöna with chicks. Photo taken by Ronny Olsson.
Although these breeds have probably gone through severe bottlenecks, they still express high phenotypic variation, e.g. in body size and plumage colour. Genetic variation and relatedness of the Swedish local chicken breeds had to date not been investigated. Three molecular genetic studies recently shed light on relationships, population structure and genetic diversity within and between these native Swedish chicken breeds. In addition to the scientific interest, such results may be used for the sustainable management of these valuable chicken populations.
Three molecular genetic marker systems were used in these studies: mitochondrial D-loop (mtDNA), microsatellites and single nucleotide polymorphisms (SNP). Mitochondrial DNA is passed only from the mother to offspring, and again only from female offspring to their offspring. Thus, mtDNA follows the maternal line. Microsatellites and SNP markers are autosomal markers and thus are inherited from both parents.
Analysis of mtDNA showed that Ölandshöna were different from the other 8 investigated breeds, and that Swedish local chicken breeds have multiple maternal origins. It was concluded, that in the case of the Swedish local chicken breeds, the D-loop was not very informative for analysing relationships between the breeds, and in future studies autosomal markers should be used.
Genetic diversity, relatedness and population structure of five Swedish chicken breeds were then investigated with 24 microsatellite markers. All the markers used in the study are a part of the 30-microsatellite panel recommended by FAO to study genetic diversity in chickens.
Bohuslän-Dals Svarthöna showed low genetic diversity and a high molecular coancestry. This implies mating of relatives in the past, resulting in inbreeding in this population, which can have severe consequences for the population if not properly managed.
In agreement with the previous study based on mtDNA and a priori knowledge on genealogical origins, the Skånsk blommehöna showed the highest genetic diversity.
In general, the study showed low within breed diversity and highlighted clear genetic separation between the Swedish local chicken breeds. Low diversity is most likely a consequence of a small number of founders at the time point of rescue, followed by un-optimal breeding strategies with little control of within breed coancestry.
The third study looked into the genetic diversity in two Swedish local chicken breeds, Bohuslän-Dals svarthöna and Hedemorahöna, using a 60k SNP chip that gives information on about 60 000 positions in the genome.
The diversity on breed level was higher in Hedemorahöna than in the Bohuslän-Dals svarthöna. Genetic diversity on an individual-level, instead, was lower in samples from Hedemorahöna than in Bohuslän-Svarthöna. High inbreeding was detected in many individuals of Hedemorahöna. This could be due to subpopulations with very little exchange of animals between the subpopulations of Hedemorahöna.
The study confirmed the distinctiveness of these two breeds, and confirmed the within breed population structure in Hedemorahöna.
Proper management and conservation of the existing variation in the local Swedish chicken breeds is of utmost importance. If not properly managed, the diversity of these breeds is further threatened and problems of inbreeding depression will most likely arise. When owners introduce new animals into the flock they should aim at the relatedness to the existing birds being the lowest possible. These local chicken breeds are an important part of the cultural-historical heritage in addition to representing significant genetic diversity. With well managed conservation programs they will exist also for the future generations.
Englund T, Strömstedt L and Johansson A 2014. Relatedness and diversity of nine Swedish local chicken breeds as indicated by the mtDNA-loop. Hereditas 151: 229-233
Abebe AS, Mikko S and Johansson AM 2015. Genetic diversity of five local Swedish chicken breeds detected by microsatellite markers. PLoS ONE 10(4): e0120580. doi:10.1371/journal.pone.0120580
Johansson AM and Nelson RM 2015. Characterization of genetic diversity and gene mapping in two Swedish local chicken breeds. Frontiers in Genetics doi:10.3389/fgene.2015.00044