探花直播 of Cambridge - Dieter Lukas

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 探花直播 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.

鈥淩ainfall often affects food availability, and cooperatively breeding mammals appear better able to cope with the uncertainties of food availability during periods of drought,鈥� said Lukas, from Cambridge鈥檚 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.

鈥淟ong-term field studies show that helpers improve offspring survival, and our findings highlight that such cooperation is particularly important under harsh conditions,鈥� said聽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. 鈥淗owever, 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,鈥� said聽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. 聽

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. 鈥淐ooperative breeders may also persist in areas where changes in climate make life increasingly difficult,鈥� said聽Clutton-Brock.聽

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

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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Females protect offspring from infanticide by forcing males to compete through sperm instead of violence

fpjl2 — Thu, 13 Nov 2014 19:08:52 +0000

Previous research has shown that infanticide by males is widespread in many mammal species, but most commonly occurs in those species where females live in social groups dominated by one or a few males.

Outsiders will fight dominant males for access to females. When a rival male takes over a group, they will kill the infants of previously dominant males to render the females 鈥榮exually receptive鈥� again, so that they can sire their own offspring. This may be the main cause of infant mortality in some species, such as Chacma baboons.

Now, a new study published today in the journal Science shows that these brutal acts are strategic; males may only have a short time in charge before they themselves are deposed, and want to ensure the maternal investment of females is directed towards their own future offspring for the longest time possible.聽聽聽聽聽

However, the females of some species - such as the mouse lemur - have evolved a highly-effective counter-strategy to stop males from killing their offspring: by having as many mates as possible in a short amount of time. By confusing the paternity of the infants, known as 鈥榩aternity dilution鈥�, any male act of infanticide risks the possibility of killing his own offspring.

In such species, reproductive competition shifts to after copulation, not before - so that the most successful male is the one whose sperm outcompetes those of the others. This leads to males producing ever larger quantities of sperm, leading in turn to increases in testis size. 探花直播testes of male mouse lemurs swell 5-10 times larger during the breeding season.

鈥淚n species in which infanticide occurs, testis size increases over generations, suggesting that females are more and more promiscuous to confuse paternity,鈥� said lead author Dr Dieter Lukas, from 探花直播 of Cambridge鈥檚 Department of Zoology.

鈥淥nce sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears - since males face the risk of killing their own offspring, and might not get the benefit of siring the next offspring.鈥�

Closely related species that differ in infanticide and testes size include chimpanzees (males commit infanticide) versus bonobos (males have not been observed to kill offspring). Bonobos have testes that are roughly 15% larger than those of chimpanzees.

Male Canadian Townsend voles don鈥檛 commit infanticide, and have 50% larger testes compared to infanticidal males of close relatives the North American meadow voles, says Lukas.

He conducted the research with colleague Dr Elise Huchard, who is now based at the CNRS Centre d鈥橢cologie Fonctionnelle et Evolutive in Montpellier.

Fifty years ago, observations of wild Hanuman langurs shattered previous depictions of monkey groups as peaceful, supportive societies, says Lukas, as new males that had just taken control of a group of females frequently killed all juveniles.

Subsequent observations have accumulated over the years on various mammals to show that infanticide by males is a widespread phenomenon, occurring in species from house mice to lions and gorillas. In some species, he says, the biggest risk faced by infants might not actually be predators or diseases, but the adult males of their own species.

In the latest study, Lukas and Huchard compiled and compared detailed field observations for 260 mammalian species to show that male infanticide occurs in species where sexual conflict is most intense, and reproduction is monopolised by a minority of males. 探花直播researchers鈥� findings indicate that infanticide is a manifestation of sexual conflict in mammalian social systems.

鈥淲hile it had previously been suggested that infanticide might be an evolutionary driver in mammalian societies - leading to females allying themselves with other females or forming bonds with a specific male in order to defend their offspring - we鈥檝e now shown that this isn鈥檛 the case: male infanticide is a consequence of variation in sociality, most commonly occurring in species where both sexes live together in stable groups,鈥� said Lukas.聽

探花直播researchers say the new study supports the idea that infanticide isn鈥檛 a general trait present in all species, but is strategic and occurs only when it is advantageous to males. 探花直播study reveals the reversible nature of male infanticide, and that it is successfully prevented by the 鈥榩aternity dilution鈥� strategy of female sexual promiscuity.

Added Huchard: 鈥淢ale infanticide appears and disappears over evolutionary times according to the state of the evolutionary arms race between the sexes. Although infanticide may not have contributed to shape the diversity of mammalian social systems, it has deeply influenced the evolution of sexual behaviour and sex roles.

鈥淭his study also highlights that some of the greatest challenges faced by mammals during their lifetime come from others of their own species.鈥�

Inset images: A male mouse lemur with large testes (credit: Cornelia Kraus). A Chacma baboon with dead infant (credit: Alice Baniel)

Latest research shows the females of some mammal species will have many mates to ensure unclear paternity, so that males can鈥檛 resort to killing their rival鈥檚 offspring for fear of killing their own. This forces males to evolve to compete through sperm quantity, leading to ever-larger testicles. Scientists find that as testis size increases, infanticide disappears.

Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears

Dieter Lukas

Elise Huchard

Baboon fight

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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.

探花直播comparative study, by 探花直播 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. 探花直播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.聽

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. 探花直播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."

探花直播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, 探花直播 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

探花直播socially monogamous dik-dik, a small antelope that lives in Africa.

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