A team led by Manfred Schartl of the Theodor-Boveri Institute for Biosciences
in Wurzburg studied the fish Limia perugiae, a close relative of the guppy.
Females are about 40 millimetres long, while males vary between 20 and 60
millimetres long. The larger the male, the greater his dominance, and the
more intense his colours.

Earlier investigations, by independent groups of researchers, seemed
to show that the dominant male in a group of fish always had more offspring.
But the researchers involved in these studies were not always able to determine
the paternity of the offspring. Because they relied on observing inherited
traits, the experiments could be performed only with small groups consisting
of two males, and either one or two females. Now Schartl and his colleagues
have adapted DNA fingerprinting, or profiling, to carry out paternity tests
on fish.

A person inherits half of their DNA from each parent, so a child’s true
parents can be identified by comparing its DNA profile with those of several
potential parents. By modifying this technique, Schartl’s team studied the
offspring from groups of four male and four female fish, which more closely
resemble social groups found in the wild.

The four male fish behaved as expected: the largest became dominant,
and spent most of its time in courtship display and attacking the other
males. But when Schartl and his colleagues determined the paternity of all
the offspring, a completely different pattern emerged: the dominant male
failed to produce any offspring at all. However, the second dominant male
produced between 65 and 100 per cent of the offspring (Proceedings of the
National Academy of Sciences, vol 90, p 7064).

‘While the large, dominant male was courting and attacking,’ says Schartl,
‘the intermediate-sized male would just use more simple sneaking behaviour
as an alternative mating tactic.’

These results help to explain why there are small, subordinate fish.
If the large males always managed to breed, all their progeny would have
been large as well, eliminating small fish from the species.

Today there are fewer than 20 000 cheetahs living in southern and eastern
Africa. Difficulties in breeding the animals prompted a detailed study,
which revealed that there is very little genetic variation between
individual cheetahs. This can lead to abnormalities in sperm, decreased
fecundity, high cub mortality and sensitivity to disease.

Genetic differences in animals occur when DNA mutates randomly. The almost
complete absence of genetic variation in cheetahs suggested that in the past
almost all cheetahs perished, reducing the variation of genes in the few
surviving animals. Since this ‘genetic bottleneck’, there has been
insufficient time for random mutations to produce much new genetic
variation. But when this ‘near-extinction’ happened was not known. Some
people thought it occurred a few hundred years ago, due to hunting, whereas
others believed it was millions of years ago.

Now Marilyn Menotti-Raymond and Stephen O’Brien from the National Cancer
Institute in Frederick, Maryland, have analysed the DNA from 74 cheetahs and
pinned down the genetic bottleneck (Proceedings of the National Academy of
Sciences, vol 90, p 3172). They assumed that at one time only one litter of
cheetahs survived a near-extinction, so there would have been hardly any
genetic variation. By counting the number of mutations that have occurred
since then in a specific part of the DNA, they could estimate when this
near-extinction happened.

The researchers first added restriction enzymes to the DNA. These cleave DNA
when they recognise a specific sequence of 6 nucleotides. Next, they
determined the length of the fragments that contained the mitochondrial DNA
and ‘minisatellite’ DNA, which accumulates mutations 5 to 10, and 100 to
1000, times faster than most other DNA. When an individual does not produce
a fragment of the expected size, it means that a mutation had changed the
sequence recognised by the restriction enzyme.

The mitochondrial DNA suggested that the hypothetical ancestral litter lived
less than 36 000 years ago. The data from the mini-satellite DNA yielded a
time of 3000 to 13 000 years ago. ‘We are not quite sure when it exactly
happened, because of this range, but it wasn’t 200 or 300 years ago,’ says
O’Brien. ‘We’re comfortable that the cheetah almost became extinct around
the same time all those other large animals did.’

The assumption that only one litter survived may be an oversimplification,
but it could be that the progeny of half a dozen or so animals in one small
area survived.

In healthy people, the immune system tolerates self proteins – the body’s
own proteins. But it attacks foreign bodies such as viruses or bacteria.
In autoimmune diseases such as MS, diabetes or rheumatoid arthritis, the
immune system loses its tolerance for a specific self protein.

Several studies have shown that the immune system can sometimes be induced
to tolerate proteins that it considers to be foreign. In particular, animals
with experimental autoimmune encephalomyelitis (EAE), a disease that is
similar to MS, became tolerant to myelin protein after they received the
protein in their food. This treatment also had the benefit of suppressing
the symptoms of the disease.

Now Howard Weiner and David Hafler and their colleagues at Harvard’s
Medical School and the School of Public Health, Boston, have conducted a
pilot double-blind trial with 30 MS patients (Science, 26 February, p 1321).
Half the patients swallowed capsules containing 300 milligrams of bovine
myelin daily, while the other half received capsules with an unrelated bovine
milk protein.

After a year, significantly fewer myelin-treated patients had major
attacks of multiple sclerosis (6 out of 15) than in the control group (l2
out of 15).

All the patients treated with myelin who had attacks were female, suggesting
that the treatment may work only for men. However, all these female patients
also had a gene known as HLA-DR2, whereas only two out of the eight men
had it. Proteins made by HLA genes are involved in the processing of foreign
proteins, and there are at least 15 varieties of the HLA-DR gene. About
65 per cent of MS patients have the HLA-DR2 variant, so researchers believe
that it is linked to the development of the disease.

The American team acknowledges that because of the small number of patients
involved, it is difficult to demonstrate the benefits of myelin treatment
or the effects of gender or HLA-DR2. They also realise that the dosage used
may not have been optimal. However, David Hafler says: ‘Although these are
only early, non-definitive results, they show that oral tolerisation is
safe and it opens up a new area of investigation for multiple sclerosis
and other autoimmune diseases.’

The classification of whales and dolphins (order Cetacea) should be completely revised, say researchers from the US and Belgium who have analysed the DNA of these animals. According to the new analysis, the sperm whale and the pygmy sperm whale, both of which have teeth, are more closely related to baleen whales than other toothed whales.

Ideally, the classification of a group of animals should reflect how the animals evolved. Fossils can give an indication of this but usually the classification is based on the identification of common characteristics. Whales and dolphins were divided into two suborders. The toothed whales (Odontoceti) have teeth and use echolocation, whereas baleen whales (Mysticeti) have baleens – plates in the mouth – which filter food from the water. Sperm whales were grouped with the Odontoceti because they have teeth in their bottom jaw.

Now Michel Milinkovitch of the Free University of Brussels and his colleagues at the State University of New York have found that this classificaton is not compatible with their DNA analysis of several whales and dolphins.

The researchers studied 16 cetacean species. They determined the DNA sequences of the genes that coded for the mitochondrial 12S and 16S ribosomal RNA, and compared them with the aid of a computer. They found that the DNA sequence of the sperm whale and pygmy sperm whale were more closely related to the baleen whales than to other toothed whales and dolphins. The study also showed that the beaked whale (which has only a few teeth) is only distantly related to any other whale or dolphin (Nature, vol 361, p 346).

To check their results, the researchers obtained from a database the DNA sequences of the myoglobin of 10 whales and dolphins. Myoglobin is the protein that helps muscles to take up and store oxygen. Again, the researchers found that the two sperm whales were more closely related to the baleen whales, and that the beaked whales were distantly related.

The findings have important implications for the evolution of echolocation. According to traditional classification, the ancestor of the toothed whale developed echolocation, while the baleen whales never had the ability (see Figure). But the revised classification implies that the ancestor of all whales used echolocation, and that the baleen whales subsequently lost the ability. The alternative explanation, that both the sperm whales and other toothed whales developed echolocation independently, is unlikely.FIG-mg18612701.GIF

Injecting bacteria into an animal has the advantage that most bacteria
are simple to culture and the dose is easy to measure. But now John Roehrig
and colleagues at the National Center for Infectious Diseases in Fort Collins,
Colorado, have found that an animal’s immune system may respond differ-ently,
depending on the source of the bacterium.

The team focused on the bacterium Borrelia burgdorferi, which is responsible
for Lyme disease, an infection found in people in Europe, North America
and Asia. Its symptoms include arthritis in the knees and elbows, fever,
encephalitis and heart problems. B. burgdorferi is transmitted by bites
of the tick Ixodes dammini.

When people are naturally infected with the bacterium, they quickly
produce antibodies against flagellin, a protein of the bacterium’s tiny
surface ‘hairs’, or flagel-la, which help it tomove. Only later in the infection
does the immune system produce antibodies against two proteins on the bacterium’s
outer surface, OspA and OspB.

In previous studies, hamsters have been used as an animal model for
the disease. By injecting these animals with cultured bacteria, it was found
that antibodies against OspA and OspB as well as flagellin were all produced
shortly after injection, in contrast to what has been found in humans. This
cast doubt on whether hamsters are a suitable model. But Roehrig has found
that when infected ticks are allowed to bite the hamsters, they provoke
an immune response similar to that of people (Journal of Immunology, vol
149, p 3648).

The researchers suggest that cultured bacteria differ from bacteria
present in the ticks in their expression of the OspA and OspB genes. If
the bacteria in the ticks do not need the OspA and OspB proteins, they
will not synthesise them, so no antibodies against these proteins are produced
after a tick infection.

It is well known that bacteria can switch on and off the expression
of certain genes, depending on their environment. Until now, researchers
have largely overlooked the effect of this on immunity. The difference in
the way naturally infected humans and injected animals respond to bacteria
has usually been explained by the differences in their immune systems.

However, these new results indicate that differences may also arise
because cultured bacteria do not necessarily express the same genes as
‘natural’ bacteria. Roehrig concludes: ‘Our results clearly indicate that
the design of both vaccines and of rapid test for Lyme disease must be
guided by the immune response to the natural infection.’