How are bobcats and house cats alike
The feline - a clearly defined basic type
by Nigel Crompton
Summary: On the basis of crossbreeding it had been suspected for a long time that cats were a basic type. So far, however, there has been a dividing gap between large and small cats. A new DNA analysis arranged the ancestry history of the
Cats and canceled this separation. At the same time, new crossbreeding data were reported which, together with the genetic analysis and other data presented here, clearly speak in favor of a clearly defined basic type “feline”.
Cats and their division
The cat family belongs to the carnivores, i.e. the predators. Other carnivorous families include dogs, bears, martens, crawling cats, elephant seals and others. The carnivores are a regulator in the natural balance, they remove weak and diseased herbivores (herbivores) for the benefit of their populations. Many carnivores can run fast, have fangs to catch and kill the prey and the characteristic cutting molars. However, omnivores, such as bears, do not show this formation of the molars.
The cats form a self-contained group of animals, the representatives of which today - a total of 38 species - can be distinguished from other groups of animals with relative certainty, even by laypeople. They have a lithe, muscular, compact, deep-chested body. The teeth (tooth formula 3/3, 1/1, 2-3 / 3, 1/1; see Fig. 1) are used for diagnostic delimitation. The middle ear chambers are enlarged so that they meet in the middle. They are separated by a two-layer septum (the mountain cat, Leopardus jacobita, however, has two separate middle ear chambers). Furthermore, the middle ear chamber is ossified and is therefore also referred to as the middle ear capsule (Fig. 1). The tongue is covered by many horny papillae that point backwards. Cats are toe walkers and they have five toes in the front and four in the back. The sharp and strongly curved claws are usually retractable and well protected in a fleshy sheath. Exceptions are the cheetah, which cannot retract its claws, as well as the fish cat and flat-headed cat, which can only partially retract its claws (Alderton 1993).
A family story or two?
The oldest feline carnivores, the Nimravidae (ancient saber-toothed cats), belong to two lineages that suddenly appeared in fossil form in the jungles of North America in the late Eocene. One line, represented by Hoplophoneus, was equipped with saber teeth; the other line, represented by Dinictus, roughly corresponded in appearance to a modern serval. These fossils are so cat-like that they were named primeval cats (Paleofelidae) and were the first cats to be called (MacDonald 1992). The group of today's cats, the Felidae, contains only the modern cats (Felinae), as well as the new saber-toothed cats (Eng. "Neosabers", Machairodontinae; Martin 1998b). The primeval saber-toothed cats (Nimravidae) are left out, although their skeletal features differ only slightly from modern cats (Felinae). The most striking difference is that the Nimravidae have no bony wall (septum) between the middle ear capsules. Sometimes no middle ear chamber is fossilized at all, from which it can be concluded that this structure consisted of connective tissue (Turner & Anton 1997). For example, the ancient saber-toothed cat Barbourofelis, which lived at the same time as the modern cats (Felidae), had an ossified middle ear chamber; however, there is no evidence of an ossified septum (Martin 1998a). Such morphogenetic differences, however, require only minor microevolutive changes and are therefore insufficient to classify these two groups into two separate families with their help.
The hypothesis of two different families of Nimravidae and Felidae is actually less supported by the observed ossification than by the idea that the modern cats (Felidae) should descend from Proailurus from the Miocene of the Old World (Martin 1998a). Proailurus was about 15cm long and had a body similar to a sneak cat. However, this animal was probably a sole-walker, in contrast to the toe-walking cats today. In the first description of the fossil, it was indeed classified as a stealth cat (Viverridae) (McDonald 1992, Crompton 1998). The problem is that a cat ancestor is “used” within the framework of a general theory of ancestry: Proailurus apparently fills this gap. The tooth formula does not match that of the cats, however, Proailurus has more teeth, which in turn is considered a primitive characteristic of an ancestor. The argument seems questionable, however, since the tooth furrow is in fact more like a sneak cat than that of a real cat. If one takes this questionable hypothesis that the cat ancestor is Proailurus as a basis, then - contrary to what the fossils show (!) - New-worldly saber-tooth cats cannot be cats (because Proailurus is new-worldly and much younger - Miocene - than the old-world Nimravidae the Eocene) and they were therefore either placed in the community of canine carnivores (Flynn & Galiano 1982) or even placed completely outside the carnivores (Neff 1983). A recent extensive cladistic analysis reluctantly incorporated the Nimravidae as an independent sister group to the feline predators (Bryant 1991). It is easy to see how preconceived notions here influenced the genesis of the two-family hypothesis.
A similar case is the earlier attempt to classify the small cats and the large cats in separate subfamilies. This distinction was based on the ossification of their hyoid bone and the associated ability to roar (Turner & Anton 1997). In general, the hyoid bone apparatus consists of two chains of seven "bones" each, which are connected to one another at the fifth bone ("central hyoid bone"). This apparatus extends from the middle ear capsule to the larynx, supports the latter and gives the voice its characteristic sound (see Fig. 1). Both the first and the seventh "bone" of the hyoid apparatus consist only of cartilage and connect the middle ear capsule on one side and the cartilaginous larynx on the other. Small cats cannot roar because the third hyoid bone is ossified. In the big cats (= panther-like) this third hyoid bone “bone” is cartilaginous, so they are able to roar deeply. But there are exceptions, such as the snow leopard. Despite a cartilaginous third “bone”, he is unable to roar because he lacks the additional pads on the vocal cords that are necessary for this (Peters & Hast 1994). Of greater taxonomic importance than the actual ossification of these structures are ultimately genetic data and hybridization studies (see below), which show that small cats and large cats belong to the same subfamily, the Felinae.
Large-scale habitat changes as a trigger for radiation
During the Tertiary, gradual cooling and a drying climate caused a significant shift in the dominant groups of organisms (biome shift). Especially during the transition from the Eocene to the Oligocene, the subtropical rainforests were replaced by forest savannahs (Wing 1998). This more open type of landscape resulted in adaptive radiation (splitting into new species) of herbivores such as Oreodontinae (mostly smaller, pig-sized leaf-eaters), three-toed horses (Anchitheres) and small rhinoceroses (Janis et al. 1988). Since these herbivores were the staple food for primeval saber-tooth cats (Nimravidae), this would explain the radiation of primeval saber-tooth cats.
Similarly, during the transition from the Miocene to the Pliocene, the grass savannahs were replaced by partially pure grasslands (Wing 1998). This completely open type of landscape led to the adaptive radiation of groups of herbivores that are capable of rapid locomotion, such as camel-like, forked antelopes (Antilocapridae) and today's horses. Accordingly, this renewed biome change led to the radiation of the Felidae, both saber-toothed cats (Neosabers) and cats as we know them today (Janis et al. 1998). All cats with saber-toothed teeth are without exception extinct today. Only in the clouded leopard (Neofelis nebulosa) are these saber teeth present in rudiments (but together with also elongated lower fangs, which are a rather rare feature in cats). Why these animals no longer occur today remains partly unclear. Animals with saber teeth depend on large prey, their teeth were not suitable for smaller prey. The biome shifts have certainly had a strong influence here.
Fur drawings - a common origin is likely
The evolution of the fur drawings of cats is not yet fully understood, but more recent work has come to interesting results.
Weigel (1961) believed that all contemporary fur drawings originated from a primordial type with simple dark spots. Interestingly, the pigment pattern of the fur in leopards and jaguars changes during their development. Young animals have simple spots, while the adults have rosettes in various forms. Von Werdelin & Olsson (1997) were able to show that simple spots are in fact an original feature in the cat family, which occurs in the most varied of cat lines. A new theoretical study by Liu and co-workers (2006) was able to confirm using mathematical models that in jaguar and leopard both the simple speckle pattern of young animals and the more complex rosettes of adults (including all transitions) use one and the same mathematical function (a so-called Turing model). It can be assumed that during the individual development of the animals as well as in different cat lines, only one parameter adjustment in the "blueprint" for the coat pattern is necessary in order to explain the different patterns. In other words: microevolution is sufficient for the development of various fur markings (at least in spotted cats) as a cause. Other patterns, such as tiger stripes, were not considered by Liu and co-workers (2006), but the same type of modeling is used to simulate the stripes of other animals. Overall, the studies mentioned emphasize the similarities of the basic type "feline".
The radiation of modern cats in the Miocene
The ancestry history of modern cats is complicated and has long been controversial, as speciation occurred very quickly not so long ago. Recently, however, DNA analyzes have largely filled this gap.
DNA analyzes of many different genes or sections on the genome together with modern statistical methods revealed eight groups of cats (Fig. 3):
Despite a coherent overall picture, some ancestry events remain uncertain. This concerns, for example, the position of the mountain cat (L. jacobita) within the ocelot-like, the order of descent of the pipe cat and the black-footed cat within the domestic cat-like, as well as the exact hierarchy of the Panthera species. Within the phylogeny of cats, 21 of 36 ancestral events occurred in just 1 million years, and the seven events that led to the cat groups are on average only 600,000 years (each according to conventional time calculation) apart. Similar radiation events are common for most vertebrate ancestry histories, which is why large sets of genes must always be used for phylogenetic analysis. During their radiation, the cats have repeatedly changed continents and distribution zones through migration. This is best illustrated in Fig. 2 (Johnson et al. 2006).
Hybridization studies within the feline
Cats are popular zoo and domestic pets. Therefore, some hybridization studies in cats are available (Fig. 3; Gray 1972, Alderton 1993), meanwhile seven of the eight have been carried out by Johanson et al. (2006) defined main groups of cats connected to one another via crossbreeding events. The golden cats are not linked to any other group via hybridizations, but are extremely close to the next group, the desert lynx, and are also included in the analysis by Johanson et al. (2006) Sister Groups. Otherwise there are also many known hybrids within groups, as Alderton (1993) reports on a successful mating of a hybrid of jaguar and leopard with lions. Even if the hybridization data do not completely include all cats, the data available show that there is a single group of animals, each of which can have mutually fertile offspring. There are only three species of hybrids between the groups: F. catus (house cat), L. rufus (bobcat), and P. concolor (puma). The hybrids within the lynx group always include the bobcat (L. rufus; see Fig. 3).
Hybrids between species are often given a new name made up of the names of their parents. The first part is borrowed from the father, the last part of the name from the mother. Examples are P. leo x P. tigris (Löger or Tiwe), P. leo x P. pardus (Löpard or Leowe), P. tigris x P. pardus (Tigard), P. onca x P. pardus (Jaguleop or Leopjag ), P. onca x P. leo (hunting lion), P. concolor x P. pardus (Pumapard), C. serval x C. caracal (Servical or Caraval), L. wiedii x L. pardalis (Marlot). Female hybrids are fertile and can reproduce (e.g. Lö-Lögers, Lö-Tiwes, Ti-Lögers, Ti-Tiwes) and are easy to breed from female Lögers or Tiwes.
In terms of taxonomic interest, the hybrids outside the panther-like group are more interesting. The crossing of P. concolor x L. pardalis (Puma x Ozelot) ultimately forms the bridge from cats of small body size to cats with large bodies (Dubost & Royere 1992). Because the puma P. concolor also crosses with the big cats leopard and jaguar (P. pardus or P. onca), while the ocelot (L. pardalis) continues with the long-tailed cat (L. wiedii) via an intergeneric hybrid Domestic cat (F. catus) crosses. Furthermore, seven documented hybrid steps connect the largest cat (tiger, P. tigris), starting from the massive Löger (> 400 kg), with the smallest cat (black-footed cat, F. nigripes): P. tigris (110-320 kg) x P. leo (120-250 kg) x P. pardus (30-85 kg) x P. concolor (35-100 kg) x L. pardalis (11-16 kg) x L. wiedii (3-9 kg) x F. catus (3-7 kg) x F. nigripes (1.5-2.5 kg). Five other cat hybrids are bred commercially as pets: F. chaus x F. silvestris, L. rufus x F. chaus, L. rufus x F. catus, F. catus x P. bengalensis and (F. catus x P. bengalensis) x F. chaus.
Viruses are tiny particles that can only multiply with the help of host cells. Outside the host cell, they are lifeless and motionless. Viruses must first dock on certain cell structures in the host before they can attack its cells. Some viruses can attack a large number of very different hosts; the flu viruses are currently the best known. They easily jump over the basic type boundaries of birds, pigs, other animals and humans. This virus attaches to a cell structure that is obviously found in many warm-blooded animals. Other viruses, on the other hand, show a constant specificity for only a certain group of hosts.
Feline Infectious Peritonitis is a deadly viral disease that only affects cats of all types and is caused by the Feline Coronavirus (FCoV). Although the mutation rate is high (approx. 3 mutations / virus genome in each generation) and the FCoV is very similar to the virus responsible for the human respiratory disease SARS, no host switch (i.e. infection outside of the Cat family) observed. Of course, such a process cannot be ruled out in the future, but so far it has been the case that the FCoV "reliably" only affects the basic type of feline, from domestic cats to lions, with leopards apparently being particularly endangered. The immune status of the individual animal is responsible for whether the disease breaks out or not. Even if the host specificity of FCoV can of course only be an indication, this also suggests that cats are of a basic type, because all cats are equally at risk from this viral disease, while other basic types are not attacked (see www.wikipedia .de "Feline Infectious Peritonitis", Version September 27, 2006).
The criterion of crossability is one of the most important characteristics for belonging to the same basic type according to Scherer (1993). In the case of fossil forms, however, this criterion is not applicable. However, the available skeletal data, hybridizations, molecular biological sequence data and other supplementary data such as common coat drawings or certain virus specificities show that cats are a basic type. It can be assumed that the cats have gone through a microevolutive radiation starting from a single ancestor, which shows a range of possibilities (programmed variability).
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