SUNSHINE SILVER (BIMETALLIC) SIBERIANS
Many thanks to Silvia Perego, Eleonora Ruggiero and Lesley Morgan for allowing the use of their photographs and information on this page.
Note on Terminology: "Bi-metallic" or "Bimetal" describes a visual effect, while "Sunshine" is the genetic name. In Siberian Cats, the proper term for bimetal is "Sunshine Silver."
For some years, strangely patterned Siberian cats have been turning up. Some are covered in A Torbie Dynasty: A Torbie Dynasty. Caroline Sharp in Germany had several generations of apparently tortoiseshell-tabby male cats. This should be impossible as tortie tomcats are genetically abnormal in some way and even when fertile they should not produce further generations of tortie tomcats. They couldn’t all be chimeras, so there had to be some unidentified mechanism at work.
Other Siberian cats had both silver and golden areas of fur and were dubbed “bimetallic.” This X-colour (mystery colour) looked similar to the partway stages of the amber colour change seen in Norwegian Forest Cats. Siberian breeders had referred to their cats as "golden" but this term clashed with the wide band colour found in Persians, Exotics and British Shorthairs. The official term "sunshine" was adopted to distinguish Siberian golden from "wide band golden".
At birth, Siberian "Sunshine" resembles the early stages of the amber (ee) colour change in Norwegian Forest Cats caused by a non-extension gene. However, the Siberian cats tested negative for the amber gene. There were no genetic tests for Wide-band or for silver inhibitor, let alone for Siberian sunshine, but it can be distinguished visually and by studying pedigrees. Bimetallic colouration has also been seen in the Kurilian Bobtail (a golden colour called "carnelian" and caused by an extension gene mutation known as copal) and in random-bred cats in the Ukraine.
Judge Lesley Morgan come across a number of strangely coloured cats that had been nicknamed “bimetallic” as they displayed a mix of silver tabby and golden tabby in their coats. The effect was beyond the rufousing or breakthrough colouring sometimes seen in silver tabbies and in some cats the golden areas increased as the kittens grew into adulthood. The only link she found was that every bimetallic Siberian she saw had close Polish ancestry. Other Siberians had been registered as black silver tortie tabby, but were more likely to be bimetallics (silver tabby + sunshine).
3 views of "bimetallic" including a close-up of the fur.
In 2013, Silvia Perego of Veselka Siberian Cattery in Italy described more such cats. Her stud male, Yankee, came from Poland and is a black silver tabby with white. When he arrived at her cattery at 4 months old, she noticed that he had a "strange" golden-brown spot on his neck and some little other spots on the back. At first this appeared to be rufism. His first litter included a silver tabby daughter, Lady, who had the same golden-brown spot on her neck. Another litter included a daughter, Lizzy, with the same spot. Then Lady, from the first litter, had her own litter with another silver-and-golden kitten like them. In summer 2013, Yankee had two kittens with the golden-brown patch. Although a judge suggested chimerism, there appeared to be a newly emerging gene at work.
The classic golden colour found in Persian cats is due to the wide-band (Wb) gene. This widens the pale brown area at the base of each agouti (banded) hair and confines the darker colour to the ends of the hairs. The paw-pads are either white (i.e. pink) or match the colour at the hair tip. Combined with the silver inhibitors, this resulted in chinchilla and shaded silver Persians. A golden Persian has wide-band and either has no inhibtor gene or has the recessive form of the inhibitor gene.
Research by Eleonora Ruggiero into the pedigrees of Siberian Cats brought out some intriguing details. For example in “Onix Gloria” lines there are golden tabby Siberians born of non-golden parents. In the pedigrees of “Siberian golden” (provisionally denoted sg), golden offspring are born from two non-golden parents. This means the gene was recessive and only expressed when two copies are inherited. It seems it is not the same as Persian golden (Wb with no inhibitor gene or with homozygous recessive inhibitor). Bimetallic females were often registered as tortoiseshell, but didn't breed as a tortoiseshell as they lacked the red (O) gene (evident when the paw-pads are examined and are never reddish). Their nose leather was dark pink, unlike the nose leather of tabby or genetic tortie cats.
When golden cats started turning up in silver Siberians, it resulted in cats expressing both colours in the coat; something impossible were it the same as Persian golden. The degree and intensity of golden colour (probably influenced by polygenes) rules out rufism or tarnish. These cats were initially referred to as “bi-metal” and later as "sunshine". Siberian sunshine was established in a breeding programme that used much inbreeding to bring out this recessive trait. Early sunshine cats were dismissed as silvers with high degrees of rufism and not bred from. In 2013, all known sunshine Siberians are agouti (tabby markings) and the colour hadn’t been seen in non-agouti (solid) cats. The sunshine gene affects the agouti (ticked) hairs only".
Sunshine silver looks very different from a silver with rufism; the nose leather is pinkish unlike that of a tabby cat. The red colour of a sunshine red tabbies and sunshine torties is brighter and the paws are lighter. The absence of pigment in the sunshine tabbies extends beyond the edges of the nose leather so they have no nose-liner and have whitish fur at the bottom of the nose.
There is a link to one of the Snowknight cats, Joschka, around 7 generations back, so maybe his torbie dynasty continues. The common ancestor from Poland is Snowknight Destiny. Either Destiny or her brother Snowknight Derringer had a very colourful torbie male offspring, but the breeder had him neutered rather than test-mating him. This was carried over from Joschka, who had an extra Chromosome. Caroline Sharp’s torbie male Bogomir Tschudovich of Misinza aka Meli is black-and-white, with a big flame of red over and around his ears and no sex-linked red parentage. Because those cats don't have the inhibitor (silver) gene, they looked even more like tortie-tabbies. However, the sunshine colour is more even across the body, so perhaps Siberians have a variety of unexplored genes.
Emelie Nilsson (2016) has bred a male (Miss Emmi's Iggy Innocent, pictured) which appears to be a combination of the Siberian sunshine (aka "Siberian golden") and the silver gene. She has also bred a sunshine Siberian (Miss Emmi's Leopold Leopard). Both these boys have non-golden parents. To make matters even more complex, there is also a color called "blue golden", which is a combination of the dilution gene and the sunshine gene. Emelie notes "It might well be that some siberians have the "golden-persian-gene", since persians were probably mixed into the breed early on. This might result in a situation where we have two different "golden genes" in the breed, one dominant and one recessive. Of course, this adds to the confusion. I have myself seen brown agouti siberians that are all different shades: from almost golden without the typical pink nose, to an a very dark, more charcoaly color. There may be many modifying genes at play."
For information and genealogies of Sunshine in Siberians and Carnelian in Kurilian Bobtails: Golden Colours in Siberian and Kurilian Cats