Show those beans - poly paws
I am happy to see the MCPolydactyl webside back online, with information about the polydactyl trait in Maine Coon cats. AND I love the feedback and discussions in the MCPolydactyl group on Facebook. When I bought my first Maine coon, I did not know much about the history of the breed. It evolved through natural selection and developed all the characteristics of a good working cat. They are large, intelligent and skilled hunters, well adapted to survive harsh coastal winter climates. Learning about the polydactyly in Maine coon cats, and FIFe´s banning of showing and registering poly Maine coon cats, triggered my interest. I started reviewing the litterature to find out more about what was known about the genetics behind the polydactyl trait, and if there are any animal welfare reasons not to include them in breeding.
As a dog breeder I am of course familiar with extra toes / dew claws. In the ancient Norwegian Lundehund used for hunting puffins (sea birds), polydactyly is regarded as a signature trait and a selective advantage to the breed (Stronen et al. 2017). One could argue the same for Maine coon cats! According to the breed standard the Lundehund should have at least six toes in both front and hind paws. This breed consequently represents a very interesting model to study polydactyly (Kropatsch et al. 2014). Earlier studies have shown that dew claws are found in many different dog breeds and two distinct single-base changes have been detected so far, in the upstream sequence (pZRS) of the ZRS in the gene LMBR1 (Park et al. 2004; Park et al. 2008). MyDogDNA includes two genetic tests for polydactyly in dogs: LIMBR1 DC-1 (allele associated with hind dewclaws in Asian breeds) and LIMBR1 DC-2 (allele associated with hind dewclaws in western breeds). The genetics underlying polydactyly in cats is also not fully mapped. So far three mutations are known.
Reading up on polydactyly in cats, I was convinced that there is no reason to exclude poly MC from breeding. Polydactyly is a harmless anatomical anomali that pose no treat to the wellbeing of the cat (Lange et al. 2014, Hamelin et al. 2017). It should be considered an innocent phenotypic variant of the breed. The big paws of the poly Maine coon cats are often compared to snowshoes and some argue that they facilitate walking on snow. The large paws are also thought to help the cat climb and hunt more efficiently. The need to widen the gene base of the breed through outcross breeding also speaks against excluding poly Maine coon cats from breeding. Poly Maine coon cats originally contributed to a large proportion of the gene pool (40%). And are consequently part of the pedigree of most of todays Maine coon cats. The trait is inherited as an autosomal dominant trait with high penetrance (Danforth 1947; Lettice et al. 2008, Hamelin 2011), and can thus easily be selected against in breeding. Disqualification from shows sadly led to the exclusion of many polydactyl Maine coons from breeding and hence also narrowing the gene pool.
I decided to leave FIFe and I imported a beautiful F3 poly female from Taschanas Maine coon in Sweden. This December, after two years of planning and dreaming, our two first Maine coon litters were born. Both litters are outcross combinations with new Maine lines through their father, Lynx Luna Inferno PP of Taschanas, bred by Johanna Eli Forssblad / Lynx Luna Maine Coons and owned by Marita R. Sørensen / Taschanas Maine Coon. I feel greatful and really priviliged to have been entrusted with these unique blood lines.
Two out of eight kittens in these two litters have poly paws: Brutus (in the A-litter) and Lucifer (in the B-litter). Below are some early morning photos of the two sleepy boys (Brutus at 5 weeks and 5 days, and Inferno at 5 weeks) and their lovely paws:
Brutus and his brother Ulyssess sound asleep. Brutus to the right is poly. See close up photos of his paws below.
Their mother, Bellona, was tested for the three known poly mutation variants found in cats, and tested positive for the «Hemingway mutation» found in Maine coon cats. She is heterozygous for this singel point mutation (Hw/N). Bellona´s DNA screening results are public and are available online. Bellona is born with two extra toes on each of her front paws and one extra toe on each of her back paws (7-7-5-5), 24 toes in total. Hence, Bellona's Hw effected all four paws and this same pattern of toes is found in her father Elders and her grandmother Bluebell (F1 cat from Maine, US).
Brutus - front paw left side - is a mitten with seven digits: dew, thumb, tiny dew and 4 standard toes.
I hope to see both of these F3 boys continue in breeding - not because of their extra toes - although this is and has always been a natural trait of the breed - but because of their genetics. They are really valuable cats in the work to increase the gene pool resulting from outcross combinations with new Maine blood lines. Just as their non-poly siblings. It would be a shame and a waste to exclude them from breeding just because they are poly.
Danforth CH (1947) Heredity of polydactyly in the cat. J Hered 38: 107-112
Kropatsch R, Melis C, Stronen AV, Jensen H, Epplen JT (2014) Molecular genetics of sex identification, breed ancestry and polydactyly in the Norwegian Lundehund breed. Journal of Heredity 106: 403-406.
Hamelin A (2011) La Polydactylousie du Maine Coon. École Nationale Vétérinaire d’Alfort. Dissertation
Hamelin A, Begon D, Conchou F,Fusellier M, Abitbol M (2017) Clinical characterization of polydactyly in Maine coon cats. Journal of Feline Medicine and Surgery 19: 382-393.
Lange A, Nemeschkal HL, Müller GB (2014) Biased polyphenism in polydactylous cats carrying a single point mutation: the Hemingway model for digit novelty. Evolutionary Biology 41:262–275.
Lettice LA, Hill AE, Devenney PS,Hill RE (2008) Point mutations in a distant sonic hedgehog cis-regulator generate a variable regulatory output responsible for preaxial polydactyly. Human Molecular Genetics 17:978-985
Park K, Kang J, Park S, Ha J, Park C (2004) Linkage of the locus for canine dewclaw to chromosome 16. Genomics 83: 216-224.
Park K, Kang J, Suebedi KP, Ha JH, Park C (2008) Canine polydactyl mutations with heretogenous origin in the conserved intronic sequence of LMBR1. Genetics 179: 2163-2172.
Stronen AV, Salmela E, Bardusóttir BK, Berg P, Espelien IS, Järvi K, Jensen H, Kristensen TN, Melis C, Manenti T, Lohi H, Pertoldi C (2017) Genetic rescue of an endagered domestic animal through outcrossing with closely related breeds: A case study of the Norwegian Lundehund. PLOS ONE 12(6): e0177429.