Very occasionally, the tortoiseshell "male" is not male at all. It is genetically a female cat which, due to hormonal problems during embryo development, has developed the external characteristics of a male cat. This is the normal condition in female hyenas where the clitoris is elongated to form a pseudo-phallus and there is also a false scrotum. It is occasionally been reported in other animals which appear to be hermaphrodite, intersex or are masculinised females (genetic females which look like males). Depending on the cause, the false scrotum may contain fatty tissue or ovarian tissue. This may explain those cases of tortoiseshell "males" which act like females - they are genetically female with an external male appearance. These gender anomalies are discussed in more detail in a later section.
The case of Skipper (Hokkaido, northern Japan) was documented by zoologist Jeremy Angel in the 1980s. Skipper originally came from Sapporo. Angel noted that perhaps one in every one or two hundred tortoiseshells is a tomcat and that these were once prized by superstitious boat owners. In 1981, at one year and three months old, Skipper was described as looking un-tomcat-like. In head shape and general conformation, he more closely resembled a female. His genitalia were unambiguously male. He was calico with clearly defined patches of orange and black and unusually for the Japanese cats of the area, he had a straight tail, not a bobtail. His mother was known to be a longhaired calico, but his father was not known. Skipper's character was described as exceptionally calm and friendly and extremely fastidious in toilet habits. He did not spray and did not show any interest when his mother came into oestrus. When introduced to other cats, including full toms, in an enclosed colony, Skipper was curious, nonchalant and non-aggressive - and again, did not spray.
It was noted that other tomcats treated him as a female and attempted to mount him, This was initially thought to be dominance behaviour towards the newcomer. However, Skipper remained attractive to several of the tomcats and had no objection to being mounted. On some occasions he appeared to enjoy this attention and remained crouched and receptive, even after the other tomcat had dismounted. He also adopted the lordosis position and chirruped to attract his suitors. During summer, he was mounted frequently enough that his neck became callused (common in highly active oestrus females). Skipper's attitude to females was very different. By the time he was almost 2 years old, he still did not spray and still showed no interest in mating with females. On occasion he was aggressive towards females and frequently fought with them. Tomcats do not normally fight with females, particularly with oestrus females although females will fight among themselves. In this respect, Skipper's behaviour was female. He was always the instigator of any fight.
In 1982, Skipper showed signs of male behaviour. He stopped picking fights with females and began to show sexual interest in them. He also began to spray. Compared to a normal tomcat, his spraying and his sexual behaviour were half-hearted. Angel isolated Skipper with an oestrus female. Although not an enthusiastic suitor, Skipper mated her three times, but failed to impregnate her. Angel had intended to mate Skipper with other females to determine whether the cat was fertile, but an epidemic of cat flu claimed Skipper as one of its victims. Angel concluded that either Skipper was a slow starter or that he possessed an additional X chromosome which feminized his behaviour, this being the prevalent theory at that time.
Because, at different times, Skipper showed both female and male behaviour, he was possibly an XX/XY chimaera (external male genitalia but some internal structures, including his brain, being genetically female and causing female behaviour). A post mortem, which might have solved the puzzle, was conducted when Skipper died. Although his condition was assumed to be due to an extra X chromosome (XXY, Klinefelter Syndrome), this does not normally result in female behaviour in phenotypical male. However feminisation was once believed to be the norm and in 1997 a cat owner stated "Most calico toms are born infertile with a single testicle. We are currently in the process of having a calico tom checked to see if he is fertile. If he is he will have some sperm 'banked' before being neutered. He is white, tan/orange tabby patches, and light to dark grey spots (and a few stripes)." The only male calico encountered by his/her vet was a long time ago and very obviously a genetic error, since the cat was sterile and had numerous other problems.
In a comparable case, Rachel E Gibson wrote in 1997 of a male calico which only mated with a very sexually aggressive females and which aligned himself with the females more than the males. The other males treated him like a female so he may not have many male hormones. His behaviour corresponded with the theory of the time that XXY made tortie tomcats feminine in their behaviour. Boo, another calico male, was also believed to be sexually confused because of his extra chromosome. He attempted to mate with both females and males and also tried to nurse kittens or carry them around like a mother cat. Boo continued to spray after being neutered and was described as somewhat fat, not uncommon in XXY cats.
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