Breeding relations in the family line

At the end of March, when the winter gradually receded from the New York periphery, the mind of a spotted salamander pointed towards love. After the early spring rains soaked the forest where the salamanders live, thousands of these small creatures landed in spring lakes to find their partners.

Kelly Zamudio, Cornell University ecologist, studied the five-day ritual and said, 'It's almost a frenzy. All males compete with each other, fight each other and try to launch crystals as quickly as possible. '

The spotted salamander sex turned out to be a revolutionary Easter egg hunt. Males release a lot of sperm bags on leaves and branches scattered on the lake surface, while females cling to the semen to fertilize eggs. These sperm pouches - called spermatophores - look like tiny football trophies 'but look like jelly.' A female usually collects more than a dozen of these bags left by the males. Then 'he turned his back away from the males who were frantically launching the sperm. It has everything it needs. "

Zamudio and former student Chris Chandler want to know which males have been the most successful breeders. Because spotted salamanders do not copulate, females have no way of directly assessing potential fathers for their children. So scientists analyzed the DNA samples collected at the scene of males, females and larvae to a surprising discovery.

In the spring, the spotted salamanders (Ambystoma maculatum) descend on lakes in the northeast to breed in just a few days.Many of these mates mate with relatives.(Photo: HH Greene)

Zamudio said, 'Females seem to fertilize eggs with animal gametes quite close to it.' In other words, the salamanders are mating in the clan . In fact, many animals favor mating with siblings and other relatives. Even people can like to kiss a cousin. Zamudio and Chandler published their results in Molecular Ecology. Other researchers have discovered the same trend in fish, birds and beetles.

Mating in clan is sometimes expensive. The birth defects have long affected the children of close relatives. Humans and other species have two versions for most genes - one from father and one from mother. Mating in the clan increases the likelihood that a child will have to inherit both versions of a disease-causing gene . The son of the first relative, French artist Henri de Toulouse - Lautrec suffered from a form of congenital osteoarthritis that caused the artist to have short legs and weak bones. The love of blood between royal families in 19th century Europe caused a high rate of haemophilia. Queen Victoria of England also suffered from the disease and hemophilia had destroyed the royal families of Spain and Russia.

But according to Patrick Bateson, a biologist at Cambridge University, England, mating in the clan also has its advantages. He said that many organisms have genetic optimizations or adaptation to living conditions, and that too much genetic mixing with the outside can wreak havoc on the adaptation. For example, some plants self-pollinate to preserve genes that help them fight insects. 'What we witness is almost a bid between racial mating and outside mating. It is not beneficial to mate in such a clan. It is the balance between clan mating and outside mating that matters. '

Zamudio's analysis of the mating process of spotted salamanders shows a compromise. Comparing the DNA of spotted salamanders, parents and larvae, she and Chandler found the average ratio of mating in the family of first cousins. Although children have hundreds of choices, they usually fertilize their eggs with sperm of male relatives that have blood ties. The females did not choose random sperms, and they certainly did not avoid relatives.

One question Zamudio hopes to find is how female salamanders can distinguish relatives' sperms between hundreds of other bundles. She said the females could trace out some of the gene pheromones that decided to mark sperm odor. Another possibility is that sperm from relatives of males easily defeat sperm of offspring during fertilization of eggs.

She also did not know why the spotted salamanders seemed to like mating in the clan. Amphibians can use mating in families to retain some genetic adaptations. 'If the male moves from one lake to the next, it can carry harmful genes for the lake where the children live - just a little - so the children will benefit from choosing him. he lives with the lake because this guy is the most suitable person. ' Zamudio has paid attention to the subtle DNA differences between animals in different lakes.

When you are better than outsiders

Although spotted salamanders often mate in the lineage, Zamudio has not yet tested whether their descendants pay the price. However, Ambrosia beetles obviously benefit from mating. These tiny Asian insects invaded Europe in the early 1950s and captured new fallen trees in early summer. The female chiseled the trunk into chambers, where they developed mushroom gardens to nourish their children. Often siblings mate with each other, but the males occasionally skip to another chamber on the same trunk.

In order to observe whether the same blood couples have produced less healthy children - a phenomenon called mating crisis - Katharina Peer and Michael Taborsky of the University of Bern, Switzerland, have Breeding beetles with relatives and no relatives (Xylosandrus germanus) in specially designed experimental rooms, cultured in fungi grown in laboratories. After the pairs laid eggs, the group allowed some to hatch and eventually breed, giving scientists two generations of insects to look for the disease effects of mating.

The mating beetles in them result in no worse than those mating with the outside and the eggs of the siblings are more likely to hatch than those of unrelated couples. Researchers do not understand why siblings have more descendants but mating in families may help create new species. Ambrosia beetles are one of 1,200 species - close and mating in families - that can overcome minor genetic differences between insects.

Animals can benefit from mating relationships in the clan . A few years ago, Harald Kullmann, an ecologist at the University of Bonn, Germany, was studying how to choose a mate of the bright-colored fish Pelvicachromis taeniatus of the cichlid genus. The fish live in small streams and rivers in Nigeria and Cameroon with only one mate and both parents take care of their children. Males often protect small caves, feeding places, before predators.

For cichlids in small streams in West Africa, siblings are ideal parents.(Photo: iStockphoto)

Kullman hopes that visual features such as color and size can help determine the choice of a partner. His team recreated the caves to test the idea and found that the fish liked to mate with their brother or sister. They also found that broods in brothers and sisters spend an average time protecting the cave higher and both parents tend to pay more attention to the children than non-parent parents. This finding suggests that mating in the lineage can promote the parenting role of this cichlid breed.

'Siblings are more cooperative in the process of taking care of their children. In these fish, both males and females are with their children for several weeks and protect the children. Brothers and sisters also have less disagreement. '

Experiments such as Kullman's gave the necessary control to check whether animals like to mate with relatives. But, with beetles, mating in the clan may be a necessity, not a choice. The same thing happens with small groups of isolated animals. With no other choice, animals will be happy to find siblings, cousins ​​and even parents. Surprisingly, there are species that choose relatives while they are fully accessible outside in the wild.

A large nest of birds in the French Frigate Shoals near Hawaii could be an example. These 2m wingspan can roam to 2,000km to find food. In 2004, ecologists discovered that tropical birds tend to mate with relatives. The average warfare couple has a higher level of intimacy than the second relative. These birds can choose one of countless partners and scientists think they actively choose their relatives.

Marriage in ethnic family

Everyone knows that people also have this marriage relationship. Charles Darwin married his first cousin Emma Wedgewood. More recently, a 1997 study by Pakistani hospitals found that three-fifths of marriages were between first cousins, while another in a South Indian city discovered 1 / 5 marriages take place between you / your uncle and your niece and 1/3 is between the first row.

But mating in the clan may cost people a high price. Zamudio said 'First cousins, when they have children, just like in textbooks describe higher mortality rates.' In contrast, scientists know very little about the effect of marriage among clans between distant couples - from the third row on. But the survey of Icelandic people shows that family love can be a good thing.

A group of researchers at an Icelandic company deciphered the gene passed down from generation to generation during 165 years of data of 160,000 pairs. Couples with the same grandparents - ie the third brother - tend to have more children and grandchildren than non-bloody couples. For example, women born between 1925 and 1949 married a third relative with 3.3 children and 6.6 grandchildren on average. Women who married eighth cousins ​​had 2.5 children and 4.9 grandchildren. But the work published in the February 8 issue of Science also shows that the closest relatives - the first or second row - have fewer children and these babies die younger.

According to Bateson, who in the 1970s proved that Japanese quail preferred first cousins ​​over siblings and unfriendly birds.'This is a great affirmation of what humans have done with other animals.' He and other researchers emphasize that wildlife in the wild must balance the limitations and benefits of marriage within and outside the clan to bring out the best for their children.

Based on this evolutionary calculation, some scientists wonder if biologists should put a new name for this phenomenon. Zamudio said, half jokingly, 'We should not call it mating in clan. This phrase includes things that are not very good - for example, 3-eyed people. ' She suggested the name: the genetic supplement.