̽��ֱ�� of Cambridge - Breeding

Breeder meerkats age faster, but their subordinates still die younger

fpjl2 — Fri, 31 Aug 2018 11:05:36 +0000

In many cooperative species, the dominant breeders live longest despite the wear-and-tear of leadership and reproduction.

It has even been suggested these breeders hold the secret of immunity to age-related diseases. Some social insects, such as bees, do have breeders with genetic profiles that delay ageing – but this has never been documented in our fellow mammals.

Scientists from the ̽��ֱ�� of Cambridge have now investigated the lifespans of meerkats: a highly social mammal that lives in groups of up to fifty, where a single dominant couple produce around 90% of the pups.

̽��ֱ��researchers found that the DNA of dominant breeders actually shows signs of accelerated ageing – yet they still consistently outlive the non-breeding subordinates in the group. Their study shows that dominants live an average of 4.4 years compared to subordinates 2.8 years.

This is because meerkat underlings are forced to take the often-fatal risk of leaving the safety of the group to find breeding opportunities, say scientists. Dominants rarely tolerate rival breeders, and violently eject subordinates from the group if they feel threatened.

On reaching the top of the social pecking order, however, meerkats remain ensconced within the group. ̽��ֱ��study shows an average subordinate spends more than six days each year in the wilderness, with this figure rising year-on-year. Dominant breeders are typically absent for under two hours per year.

“Dominant meerkats typically die due to internal stresses on their bodies, resulting in gradual, predictable declines until death. In humans we might describe this as ‘natural causes’,” said Dr Dominic Cram from Cambridge’s Department of Zoology, lead author of the study published today in Current Biology.

“Subordinate meerkats die due to sudden, unpredictable circumstances such as exposure to predators, killing them instantly. A meerkat’s place within the social group shapes the mortality risks it faces,” he said.

“ ̽��ֱ��secret of long life for meerkats is not to battle the inevitable declines of ageing, but to be the ruler of your community, profiting from social support and cracking down on would-be rivals.”

Cram conducted the research as part of the Kalahari Meerkat Project: a long-term study of social behavior and ecology, run for over twenty years at the ̽��ֱ�� of Cambridge by Professor Tim Clutton-Brock – a leading figure in the study of mammal societies.

̽��ֱ��project has helped train generations of zoologists through the observation of generations of meerkats, resulting in a wide range of data on the life histories of over 3000 meerkat individuals in over 100 groups.

̽��ֱ��team collected blood samples from the meerkats, and measured DNA sections called telomeres that help protect DNA from damage – much like the plastic caps on shoe-laces. As they erode over time, the chance of unravelling increases, so the length of telomeres can be used to estimate “biological age”.

While the telomeres of subordinate meerkats remained stable, dominant telomeres shrunk by a third in just 18 months – suggesting accelerated ageing caused by the toils of raising young and fending off rivals.

Yet the dominant meerkats still lived an average of 60% longer than subordinates, as the lower ranking meerkats were increasingly forced to risk more and more time outside the group as they grew older.

“Each year the subordinates spend over triple the amount of time outside the group as the previous year, reaching a peak of 35 days per year, or 10% of their time, outside the social group,” said Cram.

For subordinate males, all females in the group are their sisters or mother, so they must court females away from the group to avoid inbreeding. Subordinate females are bullied and chased away by the dominant when they become a reproductive rival.

Of all those that leave, some return – or try to – after a few days or weeks. A lucky few start their own group and become dominant breeders. Many are never seen again.

“Within a group, a sentinel always keeps look-out and sounds the alarm, allowing the meerkats to flee into burrows or bolt-holes. Each meerkat takes a turn on sentinel duty,” said Cram.

“Away from the group there is no early warning system, and meerkats are easy prey for eagles, goshawks and caracal. Letting down their guard to dig for food is too risky, so many starve for fear of being eaten.”

“Lone meerkats have even been known to be torn apart by members of a rival group. It’s a dangerous world for a solo meerkat.”

Despite rapidly ageing, dominant animals live longer because their underlings are driven out of the group – becoming easy targets for predators. ̽��ֱ��secret of a long meerkat life is to be “ruler of your community… cracking down on would-be rivals,” say scientists.

A meerkat’s place within the social group shapes the mortality risks it faces.

Dominic Cram

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No simple way of predicting breathing difficulties in pugs, French bulldogs and bulldogs from external features

sjr81 — Tue, 01 Aug 2017 18:00:17 +0000

̽��ֱ��findings have implications for attempts to ‘breed out’ this potentially life-threatening condition.

Pugs and bulldogs have become popular breeds in recent years – the French bulldog is set to become the UK's most popular canine, according to the Kennel Club. However, a significant proportion are affected by a condition known as Brachycephalic Obstructive Airway Syndrome (BOAS) related to their head structure.

Studies suggest that for over half of such dogs, BOAS may lead to health problems, causing not just snoring but also difficulty exercising and potentially overheating. It can even prove life-threating. But as symptoms often do not arise until after the dog has begun breeding, veterinary scientists have been searching for markers that can predict whether a dog is likely to develop breathing difficulties – and hence potentially help breed out the condition.

A study in 2015 led by researchers at the Royal Veterinary College, ̽��ֱ�� of London, working across many breeds suggested that dogs whose muzzles comprised less than half their cranial lengths and dogs with thicker neck girths were at increased risk of BOAS. However, a new study carried out by researchers at the Department of Veterinary Medicine, ̽��ֱ�� of Cambridge, and published today in the journal PLOS ONE, suggests that these measures applied to individual breeds are not dependable for this purpose.

̽��ֱ��Cambridge researchers took external measurements of features of head and neck shape, and of the external appearance of nostrils, together with measurements of body size and body condition score (an approximation to the degree of fatness/obesity) in just over 600 pugs, bulldogs and French bulldogs, the most numerous breeds that show this problem. Each of the dogs had also been graded objectively for respiratory function.

̽��ֱ��team found that while the external head measurements did have some predictive value for respiratory function, the relationship was not strong, and the measurements that showed the best predictive relationship to BOAS differed between breeds. They were unable to reproduce conclusively the findings from the previous study by the Royal Veterinary College in any breed.

“It can be incredibly difficult to take measurements such as distance between eyes or length of nose accurately, even for experienced vets, as the dogs don’t keep still,” says Dr Jane Ladlow, joint lead author. “This may explain why it is so difficult to replicate the findings of the previous study or find any conclusive markers in our own.”

Neck girth was a slightly more reproducible measurement, and larger neck girth in comparison to chest girth or neck length was associated with disease in the bulldogs and French bulldogs. In male bulldogs, neck girth showed a close enough association with disease to give moderately good predictive accuracy for the presence of clinically significant BOAS.

̽��ֱ��best measure identified by the Cambridge team was the degree of nostril opening, which proved a moderately good predictor of the presence and severity of BOAS in pugs and French bulldogs, and was also a useful marker for disease in bulldogs.

Altogether the variables measured, when combined, gave an 80% accuracy in predicting whether or not dogs will have BOAS, the difficulty of taking some of the measurements accurately, and the need to make multiple measurements and combine them in order to produce a prediction means that the researchers would not recommend using them as a guide to breeding.

Dr Nai-Chieh Liu, first author of the study, says: “Breeding for open nostrils is probably the best simple way to improve these breeds. Dog breeders should also avoid using dogs with extremely short muzzles, wide faces, and thick necks. These traits are all associated with increased risk of having BOAS.”

Joint lead author Dr David Sargan adds “At this moment there is no conclusive way of predicting whether any individual pug or bulldog will develop breathing difficulties, so we are now looking for genetic tests that may help breeders get rid of BOAS more rapidly.

“ ̽��ֱ��best advice we can give to owners of short-nosed dogs is to make sure you get your dog checked annually for any potential difficulties in breathing, even if you have not yourself observed any in your dog, and to keep your dog fit and not let it get fat.”

As many as a half of all short-nosed dogs such as pugs, French bulldogs and bulldogs experience breathing difficulties related to their facial structure. However, research published today by the ̽��ֱ�� of Cambridge suggests that there is no way to accurately predict from visible features whether an apparently healthy pug or French bulldog will go on to develop breathing difficulties.

Dog breeders should also avoid using dogs with extremely short muzzles, wide faces, and thick necks.

Nai-Chieh Liu

LW Yang

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Cooperation helps mammals survive in tough environments

fpjl2 — Tue, 24 Jan 2017 11:33:11 +0000

Cooperatively breeding mammal species, such as meerkats and naked-mole rats, where non-breeding helpers assist breeding females in raising their offspring, are better able to cope with living in dry areas than related non-cooperative species, new research reveals.

A comparative study of mammals, by ̽��ֱ�� of Cambridge researchers Dieter Lukas and Tim Clutton-Brock, shows that cooperatively breeding species occur in dry areas, yet are absent in tropical climates - even though these are the places on earth with the highest biodiversity.

Researchers have found that most cooperatively breeding mammals live in areas where it might not rain for weeks. While many have long argued that climate and social behaviour are linked, the Cambridge team say these findings provide a detailed understanding of how helping behaviour is connected to the environment individuals live in.

“Rainfall often affects food availability, and cooperatively breeding mammals appear better able to cope with the uncertainties of food availability during periods of drought,” said Lukas, from Cambridge’s Department of Zoology.

In this study, published in the journal Royal Society Open Science, the researchers mapped the global occurrence of mammalian species living in different social systems to determine how averages and variation in rainfall and temperature explain species distributions.

They found that although the presence of non-breeding adults in breeding groups is not associated with contrasts in climate, non-breeders commonly play an important role in raising the offspring of breeders in species living in dry environments.

“Long-term field studies show that helpers improve offspring survival, and our findings highlight that such cooperation is particularly important under harsh conditions,” said Clutton-Brock. Previous studies of birds show that here, too, non-breeding adults often help breeders to raise their young in species living in dry unpredictable environments.

Researchers say the activities of helpers in groups of cooperative mammals may ensure that infants and juveniles born in the group (who are usually closely related to them) are adequately fed, even when resources are scare.

In turn, non-breeders may gain future benefits from helping because it increases their chance that their group will survive adverse years, giving them a chance of inheriting the breeding position.

Groups of cooperative breeders occupy territories year-round. During droughts, mortality can be high, and only the largest groups might persist. “However, females in cooperatively breeding mammals can have very high rates of reproduction as soon as conditions are suitable. Populations can rebound, and dispersers move to fill vacant territories,” said Lukas.

By contrast, he says that many other mammals that live in arid areas are migratory, moving as resources are exhausted, such as the large ungulate herds roaming across the African savannahs.

Researchers say the new study also indicates that cooperation enables cooperative breeders to occupy a wider range of habitats than non-cooperative species which are limited to more favourable habitats.

Cooperative breeders are also twice as likely as non-cooperative mammals to occupy human-modified habitats suggesting that cooperative breeding may make it possible to colonize new environments. “Cooperative breeders may also persist in areas where changes in climate make life increasingly difficult,” said Clutton-Brock.

New research suggests that cooperative breeding makes mammal species such as meerkats better suited to dry, harsh climates.

Cooperative breeders may also persist in areas where changes in climate make life increasingly difficult

Tim Clutton-Brock

graham_alton

Meerkats

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Opinion: How to save inbred, short-faced dogs such as pugs and bulldogs from poor health

Anonymous — Tue, 02 Aug 2016 14:23:06 +0000

Short-faced dogs such as pugs, bulldogs (known as English bulldogs in the US) and French bulldogs are among the cutest pets out there – they’re the very reverse of the wolves they descended from. Over the last few years these breeds have become increasingly common, partly thanks to advertising and their popularity among celebrities. In fact all three breeds are now in Britain’s top ten favourite dogs.

But these dogs are the result of an amazing transformation in appearance and temperament caused by selective breeding, which has come at quite a cost to the dogs' health. Around half of them have breathing problems that sometimes lead to overheating, exercise intolerance and sleep apnoea. Their large heads and narrow pelvises also cause problems in giving birth (forcing Caesarean sections for many if not most) and their skin folds can become infected. Their exposed eyes are also vulnerable to damage, with about 15% suffering prolapsed third eyelids and many having other types of eye damage. Quite a number of dogs in several of the breeds also succumb to back or hip problems.

So research geneticists have started to look at ways to reduce the intrinsic health problems of these breeds. A recent investigation of genetic variation in bulldogs showed that all the individuals examined had little genetic diversity in either paternal or maternal lines. ̽��ֱ��same was true for the diversity of some types of immune system genes, so that the ability of these bulldogs to respond to pathogens may be reduced, which may potentially also be connected to common allergies in this breed. ̽��ֱ��authors argued that the breed’s health could only be restored by breeding dogs with other breeds, rather than preserving the breed in its current closed state.

With colleagues including Jane Ladlow, Lajos Kalmar and Nai-chieh Liu, I have been doing both genetic and clinical analyses of bulldogs and other short-faced breeds. Working with breeders of bulldogs, we investigated the respiratory distress that many of these dogs suffer from. We started by developing a computer algorithm to interpret breathing traces taken from dogs at rest, allowing us to objectively identify the disease and quantify variation between individuals. This analysis, together with collection of DNA samples from the studied dogs, opened the way for accurate genetic analyses of the respiratory disease. On the way, we also gained information on the genetic health of the breeds we studied as a whole.

Our findings agree with those of the new study in suggesting that the best way of breeding back to a less extreme skull shape would be to introduce dogs from outside the current breed registers. This is likely to be true of many other aspects of conformation and temperament. And we would agree that the extreme changes in appearance (such as the excessive skin rolls in these breeds) do account for many of their disease problems.

An alternative to outbreeding?

Fortunately not all short-faced dogs suffer from the respiratory disorder and although our research is not yet complete, we now have pretty strong evidence that there are still multiple genetic variations between those that do and those that don’t. But we do not know whether this is also true for other aspects of conformation and appearance-related conditions.

A bulldog being assessed by respiratory trace recording in a barometric chamber. Traces from another dog on the right. Author provided

We believe that the swiftest way to remove these diseases would be to outbreed to a dog type that does not have the features that cause the health problems typical of these breeds.

Over the last few years groups such as the (now disbanded) Advisory Council on the Welfare Aspects of Dog Breeding, the RSPCA, a number of dog welfare charities and the Associate Parliamentary Group on Animal Welfare have offered a lot of advice about the health problems of these dogs in an attempt to reduce their popularity. Yet the kind of expensive advertising campaign that could really reach the public has been lacking.

An additional problem is that most breeders reject the introduction of genes from outside their breed. They fear the breed will “be contaminated”, that new diseases will be introduced and that the breed will lose its character or change in temperament. There appears to be no likelihood of legislation to compel breeders to outbreed on welfare grounds.

But with the help of our research it may be possible to breed for healthier dogs using the existing genetic variation within the breed (in addition to contributions from crosses outside the breed if necessary and if they can be made acceptable to breeders). If within-breed crosses to reduce disease do prove practical, this will probably be a slower route to reduce the disease burden for an individual offspring than an outcross-breed. However, the advantage is that within-breed crosses are likely to be widely accepted by dog breeders and so it may prove a quicker way of moving the whole population forward towards better breed health.

David Sargan, Senior Lecturer in Molecular Pathology at the Department of Veterinary Medicine, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

David Sargan (Department of Veterinary Medicine) discusses the health implications of breeding the perfect pets.

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Female meerkats compete to outgrow their sisters

Anonymous — Thu, 26 May 2016 08:40:26 +0000

Meerkats live in groups of up to 50 individuals, yet a single dominant pair will almost completely monopolise reproduction, while subordinates help to raise offspring through feeding and babysitting. Since only a small minority of individuals ever get to be dominants, competition for the breeding role is intense in both sexes and females are unusually aggressive to each other.

Within groups, subordinate females are ranked in a hierarchy based on age and weight, forming a “reproductive queue”. When dominant females die, they are usually replaced by their oldest and heaviest daughter, though younger sisters sometimes outgrow their older sisters and can replace them in breeding queues.

̽��ֱ�� of Cambridge scientists working on wild Kalahari meerkats identified pairs of sisters and artificially increased the growth of the younger member of each pair by feeding them three times a day with hard-boiled egg.

̽��ֱ��scientists weighed them and their (unfed) older sisters daily for three months. ̽��ֱ��results, published today in the journal Nature, show that the increased growth of younger females stimulated their older sisters to increase their daily food intake and weight gain in an attempt to outgrow their rivals.

Tellingly, the extent to which the older sister increased her weight was greater when her younger sister’s weight gain was relatively large than when it was slight.

These results suggest that subordinate meerkats are continually keeping tabs on those nearest them in the breeding queue, and make concerted efforts to ensure they are not overtaken in size and social status by younger and heavier upstarts.

But competitive growth does not stop there. If a female meerkat gets to be a dominant breeder, her period in the role (and her total breeding success) is longer if she is substantially heavier than the heaviest subordinate in her group.

During the three months after acquiring their new status, dominant females gain further weight to reduce the risk of being usurped. Regular weighing sessions of newly established dominants showed that that, even if they were already adult, they increased in weight during the first three months after acquiring the dominant position – and that the magnitude of their weight increase was greater if the heaviest subordinate of the same sex in their group was close to them in weight.

This is the first evidence for competitive growth in mammals. ̽��ֱ��study’s authors suggest that other social mammals such as domestic animals, primates and even humans might also adjust their growth rates to those of competitors, though these responses may be particularly well developed in meerkats as a result of the unusual intensity of competition for breeding positions.

“Size really does matter and it is important to stay on top,” said senior author Professor Tim Clutton-Brock, who published the first major overview of research on mammalian social evolution this month in the book Mammal Societies (Wiley).

“Our findings suggest that subordinates may track changes in the growth and size of potential competitors through frequent interactions, and changes in growth rate may also be associated with olfactory cues that rivals can pick up,” Clutton-Brock said.

“Meerkats are intensely social and all group members engage in bouts of wrestling, chasing and play fighting, though juveniles and adolescents play more than adults. Since they live together in such close proximity and interact many times each day, it is unsurprising that individual meerkats are able to monitor each other’s strength, weight and growth.”

Male meerkats leave the group of their birth around the age of sexual maturity and attempt to displace males in other groups, and here, too, the heaviest male often becomes dominant. ̽��ֱ��researchers found a similar strategy of competitive weight-gain in subordinate males.

̽��ֱ��data was collected over the course of twenty years and encompassed more than forty meerkat groups, as part of the long-term study of wild meerkats in the Southern Kalaharu at the Kuruman River Reserve, South Africa, which Clutton-Brock began in 1993. In the course of the study, the team have followed the careers of several thousand individually-recognisable meerkats – some of which starred in the award winning docu-soap Meerkat Manor, filmed by Oxford Scientific Films.

̽��ֱ��meerkats were habituated to humans and individually recognisable due to dye marks. Most individuals were trained to climb onto electronic scales for their weigh-ins, which occurred at dawn, midday and dusk, on ten days of every month throughout their lives. This is the first time it has been feasible to weigh large numbers of wild mammals on a daily basis.

Weighing meerkats. Image credit: Tim Clutton-Brock

Latest research shows subordinate meerkat siblings grow competitively, boosting their chance of becoming a dominant breeder when a vacancy opens up by making sure that younger siblings don’t outgrow them.

Size really does matter and it is important to stay on top

Tim Clutton-Brock

Russell Venn

Sub-adult meerkats playing.

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Opinion: There’s a reason why Africa’s migratory songbirds sing out of season

Anonymous — Mon, 09 May 2016 11:15:42 +0000

Bird song has fascinated scientists for decades. Songs can be intricate, loud and, as it turns out, very important for reproductive success. In many species the males with the most complex songs secure the highest quality breeding territories and mates, and end up producing the most young. For species that spend their summers in Europe, almost every hour of daylight is crammed full with energetic and often very loud song.

For songbirds that have migrated to Africa at the end of the breeding season, singing shouldn’t be on their to-do list. Singing requires a big energetic investment and increases vulnerability to predators. ̽��ֱ��only time males should be willing to pay these costs is when there is a good chance of attracting females as mates, and that is not going to happen in Africa outside of the breeding season.

Despite this, several species of migratory songbirds, from Wood Warblers to Nightingales, are known to sing a great deal in Africa. This prompted us to ask: what is the purpose of singing in Africa, when the breeding grounds are thousands of kilometres away? To answer this question, we focused on a drab-looking but raucous singer, the Great Reed Warbler. This species breeds in Europe and spends the northern winter in the wet grasslands and savannahs of sub-Saharan Africa.

Testing a long-held hypothesis

We began by testing a long-held hypothesis for the persistence of singing in Africa. Perhaps singing is being used as a means to defend individual winter-feeding territories. It might be acting as a “keep out” sign to other individuals encroaching on the territory holder’s space.

In territorial systems, distinct boundaries are expected between the spaces used by each individual in combination with an aggressive reaction when that territorial boundary is breached. We used radio transmitters to track bird movements through the tall grasses of the study site in Zambia, and used models of Great Reed Warblers with recorded song to simulate territory intrusions. We found no support for the expectations of territoriality. Great Reed Warblers overlapped widely in their use of space, and individuals were unperturbed by other birds in their space.

Radio transmitters were used to track bird movements Jason Boyce

Given that Great Reed Warblers did not have a territorial system, this long-held hypothesis of singing for territorial protection didn’t hold up.

Singing for song improvement

Next, we tackled an intriguing but yet untested hypothesis. Perhaps, given the importance of song quality for males during breeding, they were using their downtime in Africa to improve the quality of their songs.

To find out, we combed through the literature and spoke to other researchers in Africa to determine which of the 57 migratory songbird species that migrate from Europe sing while in Africa and, importantly, how much. If this hypothesis is true, the benefits of singing in Africa should be most important for species in which song is especially valued when choosing a mate. Those should be species with the most complex songs, but conversely with the dullest appearance. So, when males are drab, females are expected to pay more attention to flashy song rather than flashy plumage.

Sure enough, we found that species with more complex songs, and those with drab plumage colouration, sing most often when in Africa. We argue that the costs associated with practice are probably well worth the investment for those species that stand to benefit most from producing the highest-quality songs.

A final piece of evidence comes from the Great Reed Warblers themselves. If songs function to defend territories, then they should sing the short territorial warnings they use to defend their breeding territories. But instead, recordings from Zambia showed that African songs are much more like those sung during mate attraction on the breeding grounds, when attracting a female is paramount. But there are a couple of important differences.

In Africa, songs are much longer and with many more switches between syllables than those sung in Europe. Given that songs in Africa are sung without a female receiver in mind, this may be the best way to practice. In Europe, when songs are mixed amongst the racket from competing males, repeating complex syllables up to five times is important to ensure that they are received loud and clear by females.

With the evidence tallied, both from Great Reed Warblers and across the dozens of songbird species that migrate between Africa and Europe, this puzzling non-breeding singing behaviour appears best explained as a rehearsal period before the big show the following spring.

To conclusively test this hypothesis, researchers would need to follow individual birds between their breeding and non-breeding grounds and monitor changes to their song and their breeding success. But this is close to impossible given the current tracking devices available. For now, this study points towards an intriguing new explanation for this previously unstudied behaviour. It also offers insight into the lives of migratory songbirds during the lengthy, but little-known part of their lives spent in Africa.

Marjorie Sorensen, Humboldt Postdoctoral Fellow, Goethe ̽��ֱ�� Frankfurt am Main and Claire Spottiswoode, BBSRC David Phillips Research Fellow and Hans Gadow Lecturer, ̽��ֱ�� of Cambridge

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̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

Claire Spottiswoode (Department of Zoology) and Marjorie Sorensen (Goethe ̽��ֱ�� Frankfurt am Main) discuss why several species of migratory songbirds sing a great deal in Africa when their breeding grounds are thousands of kilometres away.

Son of Groucho

̽��ֱ��African Golden Weaver, Zanzibar

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Monogamy evolved as a mating strategy

gm349 — Mon, 29 Jul 2013 19:00:02 +0000

Social monogamy, where one breeding female and one breeding male are closely associated with each other over several breeding seasons, appears to have evolved as a mating strategy, new research reveals. It was previously suspected that social monogamy resulted from a need for extra parental care by the father.

̽��ֱ��comparative study, by ̽��ֱ�� of Cambridge researchers Dieter Lukas and Tim Clutton-Brock, shows that the ancestral system for all mammalian groups is of females living in separate ranges with males defending overlapping territories, and that monogamy evolved where males were unable to monopolise and defend multiple females. ̽��ֱ��research is published in the journal Science.

For the study, the researchers classified all 2500 mammalian species for which information exists as either solitary, socially monogamous or group-living (several breeding females share a common range and either eat or sleep together). They showed that nine per cent of mammals are socially monogamous, including a few rodents, a number of primates, and some carnivores, like jackals, wolves, and meerkats.

Previously, it had been suggested that monogamy evolved as a result of selection for paternal support in raising offspring (for example, if the female alone could not provide enough food or adequately defend the young). This study shows that paternal care usually evolved after monogamy was already present.

This advance in understanding was, says Lukas of Cambridge's Department of Zoology, due to the volume of information they collected and the availability of genetic information that allowed the researchers to determine the sequence in which different traits evolved.

"Up until now, there have been different ideas about how social monogamy in mammals evolved," says Lukas. "With this study we were able to test all these different hypotheses at once. Paternal care evolves after monogamy is present, and seems to be a consequence rather than a cause of the evolution of monogamy. It appears to occur in about half of all socially monogamous species, and once it does evolve, it provides a clear benefit to the female."

They found convincing support for the hypothesis that monogamy arose as a mating strategy where males could not defend access to more than one female. Monogamy is associated with low density of females, low levels of home-range overlap, and indirectly, with their diets. ̽��ֱ��study showed that monogamy evolves in species that rely on high quality but patchily distributed food sources, such as meat and fruit. In contrast, in herbivores, which rely on more abundant resources, social monogamy is rare.

"Where females are widely dispersed," says Clutton-Brock, "the best strategy for a male is to stick with one female, defend her, and make sure that he sires all her offspring. In short, a male's best strategy is to be monogamous."

̽��ֱ��analysis did not include humans, and the researchers are sceptical that these results tell us much about the evolution of human breeding systems.

Clutton-Brock adds: "It is debatable whether humans should be classified as monogamous. Because all the African apes are polygamous and group living, it is likely that the common ancestor of hominids was also polygamous. One possibility is that the shift to monogamy in humans may be the result in the change of dietary patterns that reduce female density, and another is that slow development of juveniles required extended care by both sexes. However, reliance by humans on cultural adaptations means that it is difficult to extrapolate from ecological relationships in other animals."

For more information about this story, please contact: Genevieve Maul, Office of Communications, ̽��ֱ�� of Cambridge. Email: Genevieve.Maul@admin.cam.ac.uk; Tel: 01223 765542.

New research indicates that social monogamy evolved as a result of competition for females.

Where females are widely dispersed, the best strategy for a male is to stick with one female, defend her, and make sure that he sires all her offspring. In short, a male's best strategy is to be monogamous.

Professor Tim Clutton-Brock

Peter Brotherton

̽��ֱ��socially monogamous dik-dik, a small antelope that lives in Africa.

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