̽��ֱ�� of Cambridge - Mating strategy

Butterflies are genetically wired to choose a mate that looks just like them

ta385 — Fri, 08 Feb 2019 10:35:48 +0000

A team of academics from the ̽��ֱ�� of Cambridge, in collaboration with the Smithsonian Tropical Research Institute in Panama, observed the courtship rituals and sequenced the DNA from nearly 300 butterflies to find out how much of the genome was responsible for their mating behaviour.

̽��ֱ��research, published in PLOS Biology, is one of the first ever genome studies to look at butterfly behaviour and it unlocks the secrets of evolution to help explain how new species are formed. Scientists sequenced the DNA from two different species of Heliconius butterflies which live either side of the Andes mountains in Colombia. Heliconians have evolved to produce their own cyanide which makes them highly poisonous and they have distinct and brightly coloured wings which act as a warning to would-be predators.

Professor Chris Jiggins, one of the lead authors on the paper and a Fellow of St John’s College, said: “There has previously been lots of research done on finding genes for things like colour patterns on the butterfly wing, but it’s been more difficult to locate the genes that underlie changes in behaviour. What we found was surprisingly simple – three regions of the genome explain a lot of their behaviours. There’s a small region of the genome that has some very big effects.”

̽��ֱ��male butterflies were introduced to female butterflies of two species and were scored for their levels of sexual interest directed towards each. ̽��ֱ��scientists rated each session based on the number of minutes of courtship by the male – shown by sustained hovering near or actively chasing the females.

Unlike many butterflies which use scented chemical signals to identify a mate, Heliconians use their long-range vision to locate the females, which is why it’s important each species has distinct wing markings. When a hybrid between the two species was introduced, the male would most commonly show a preference for a mate with similar markings to itself. ̽��ֱ��research showed the same area of the genome that controlled the coloration of the wings was responsible for defining a sexual preference for those same wing patterns.

Dr Richard Merrill, one of the authors of the paper, based at Ludwig-Maximilians-Universität, Munich, said: “It explains why hybrid butterflies are so rare – there is a strong genetic preference for similar partners which mostly stops inter-species breeding. This genetic structure promotes long-term evolution of new species by reducing intermixing with others.”

̽��ֱ��paper is one of two published in PLOS Biology and funded by the European Research Council which brought together ten years of research by Professor Jiggins and his team. ̽��ֱ��second study investigated how factors including mate preference act to prevent genetic mixing between the same two species of butterfly. They discovered that despite the rarity of hybrid butterflies – as a result of their reluctance to mate with one another – a surprisingly large amount of DNA has been shared between the species through hybridisation. There has been ten times more sharing between these butterfly species than occurred between Neanderthals and humans.

Dr Simon Martin, one of the authors of the second paper, from the ̽��ֱ�� of Edinburgh, explained: “Over a million years a very small number of hybrids in a generation is enough to significantly reshape the genomes of the these butterflies.”

Despite this genetic mixing, the distinct appearance and behaviours of the two species remain intact, and have not become blended. ̽��ֱ��researchers found that there are many areas of the genome that define each species, and these are maintained by natural selection, which weeds out the foreign genes. In particular, the part of the genome that defines the sex of the butterflies is protected from the effects of inter-species mating. As with the genetics that control mating behaviour, these genes enable each butterfly type to maintain its distinctiveness and help ensure long-term survival of the species. But can the findings translate into other species including humans?

Professor Jiggins said: “In terms of behaviour, humans are unique in their capacity for learning and cultural changes but our behaviour is also influenced by our genes. Studies of simpler organisms such as butterflies can shed light on how our own behaviour has evolved. Some of the patterns of gene sharing we see between the butterflies have also been documented in comparisons of the human and Neanderthal genomes, so there is another link to our own evolution.”

“Next we would like to know how novel behaviour can arise and what kind of genetic changes you need to alter behaviour. We already know that you can make different wing patterns by editing the genes. These studies suggest that potentially new behaviours could come about by putting different genes together in new combinations.”

References

Martin, S et al. Recombination rate variation shapes barriers to introgression across butterfly genomes. PLOS Biology; 7 Feb 2019; DOI: 10.1371/journal.pbio.2006288

Merrill, R et al. Genetic dissection of assortative mating behavior. PLOS Biology; 7 Feb 2019; DOI: 10.1371/journal.pbio.2005902

Male butterflies have genes which give them a sexual preference for a partner with a similar appearance to themselves, according to new research.

There’s a small region of the genome that has some very big effects

Chris Jiggins

Heliconius melpomene amaryllis

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‘Believing you’re a winner’ gives men a testosterone boost and promiscuous disposition

fpjl2 — Thu, 09 Aug 2018 08:36:05 +0000

A new study shows that men only have to believe they’ve bested another man in competition to get raised testosterone levels and an inflated sense of their own value as a sexual prospect.

Scientists found that this hormonal and psychological shift made men more inclined to approach new potential partners.

̽��ֱ��research team measured hormone levels, as well as self-perceived attractiveness and confidence in approaching women, in 38 men in their twenties before and after competing in head-to-head battles on rowing machines.

Unbeknownst to participants, the competitions in the study were rigged to randomly declare the winner, regardless of who was the stronger rower.

While previous studies have shown that winning can affect male hormones, it was not known whether this was down to the efforts it takes to win or the belief that one is victorious.

̽��ֱ��latest study, led by biological anthropologists from the ̽��ֱ�� of Cambridge and published today in the journal Human Nature, reveals that just being convinced you have won, or indeed lost, is enough to cause male hormonal fluctuations that can influence sexual behaviour.

Researchers say this is an example of “plasticity”: the body adapting quickly – without altering genetic make-up – to suit a change in circumstance. In this case a perceived change in social status, due to the men believing they have defeated a rival.

̽��ֱ��body attempts to take advantage of this apparent status improvement by inducing chemical and consequently behavioural changes that promote a “short-term” approach to reproductive success, say the researchers. Namely, more sex with new and different partners.

“Much of evolution consists of trade-offs in energy investment,” said study lead author Dr Danny Longman, from Cambridge’s Department of Archaeology.

“A common trade-off for males both across and within species is between mating strategies. One reproductive approach is short-term, investing time and energy in attracting and pursuing many mates, and fighting off competition. Another approach is long-term, investing energy in raising offspring with a single mate.”

“We found that a perceived shift in social status can cause male physiology to adapt by preparing to shift mating strategies to optimise reproductive success.”

Longman points out that in many animal populations, male social hierarchies correspond with reproductive success, and social status is determined by competition between males.

̽��ֱ��study used a simple proxy for social and sexual competition by pitting athletic young men against each other to see who was the most powerful rower.

“Victory in a rowing contest strongly implies the possession of greater physical strength than the opponent, a trait found to be valued by women in our evolutionary past when choosing a mate,” said Longman.

He took saliva samples to test hormone levels before and after the races. A number of psychological questionnaires were also administered, designed to gauge self-esteem, ‘sociosexuality’ (willingness to engage in casual sex), ‘self-perceived mate value’ and mating behaviour (e.g. the likelihood of approaching attractive women). Crucially, Longman and colleagues then manipulated the results of the races.

̽��ֱ��men who believed they had won received an average testosterone increase of 4.92%, while those convinced they had lost dropped by an average of 7.24%. Overall, men who thought they were winners had testosterone levels 14.46% higher their deflated opponents.

̽��ֱ��men who thought they had lost showed no difference in their perceived value as a mate or confidence approaching women. However, the men who felt like winners had a ‘self-perceived mate value’ that was 6.53% higher, on average, than their rivals, and were 11.29% more likely to approach attractive women in an effort to instigate sexual relations.

“ ̽��ֱ��endocrine system that controls hormones is responsive to situational changes. Previous research has shown that testosterone is lower when men are in a committed relationship, or have children, to promote long-term mating strategies,” said Longman.

“Our results show that both testosterone and its corresponding psychological effects can fluctuate quickly and opportunistically, shifting towards short-term mating in response to a perceived change in status that may increase mating value.”

Male social status has less to do with physical strength in many modern societies, and Longman would be curious to see if similar results arise from intellectual challenges more familiar to the office-based culture many men now inhabit. There is always the issue of free will, however.

“Male physiology may shift to take advantage of certain situations, but ultimately a man’s decisions are up to him.”

New findings suggest that the male body tries to “optimise” self-perceived improvements in social status through hormonal shifts that promote “short-term mating”.

Our results show that both testosterone and its corresponding psychological effects can fluctuate quickly and opportunistically

Danny Longman

U.S. Army

U.S. Army World Class Athlete Program wrestler Spc. Jeremiah Davis (right) squares off against Sunkist Kids' Joe Betterman

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Opinion: Mysterious footprint fossils point to dancing dinosaur mating ritual

Anonymous — Fri, 08 Jan 2016 17:00:59 +0000

Studying dinosaurs is a lot like being a detective. Just as Sherlock Holmes was noted for his ability to interpret the behaviour of victims or criminals using footprints, palaeontologists have a similar practice when looking for evidence of dinosaur behaviour known as ichnology.

This is the study of the traces living organisms leave behind including bones, footprints and even bite marks on leaves. Indeed, Sherlock Holmes' creator, Sir Arthur Conan Doyle, was very well aware of the traces of dinosaur footprints that had been discovered in the rocks of the Weald near his home in south-east England.

Now researchers in the US have discovered some very unusual trace fossils they believe could also be footprints. Although it is far from certain, these markings may provide the first clue as to whether dinosaurs performed dance-like mating rituals similar to those of living birds.

Scratching the surface

̽��ֱ��team from the ̽��ֱ�� of Colorado Denver have unearthed some truly extraordinary trace fossils on the bedding surfaces of sedimentary rocks of Cretaceous age in Colorado. ̽��ֱ��bedding surfaces have revealed an irregular array of large scoop-shaped depressions up to 2m in diameter and adjacent hummocks. Many of the scoops also display clear and unequivocal elongate scratch marks.

Given the geological ages of these rocks, the only large, powerful ground-dwelling creatures likely to be able to make such structures would have been dinosaurs. These curious sedimentary structures are not simply a one-off isolated discovery that can be explained as just a weird bit of geology, but have been found in clusters at a number of discrete sites across Colorado. Each site has a rather similar, comparatively dense, cluster of these scoop-like structures.

At first sight it would be perfectly reasonable to consider that such structures were the remnants of ancient dinosaur nests. Dinosaur nest sites, including eggs, shell fragments and even nestling dinosaur remains are comparatively well known. They have been reported from a range of Cretaceous aged sites that have been found in North America, South America and Asia.

Dinosaur detectives. M. Lockley

But these “scoops and hummocks” differ in their detailed structure when compared to definitive dinosaur nests. Dinosaur nests tend to be circular, rather flat-bottomed, usually have traces of egg shell and are typically surrounded by a rim-like perimeter wall.

In fact, these new and distinctive structures show no evidence of what appear to be conventional dinosaur nest structure or scattered egg shell fragments. They are elongate, concave depressions with sediment clearly heaped to one side. In many instances, they display scrape marks that appear to have been made by dragging claws.

These structures are most comparable to the “leks” produced by living ground-nesting birds. Leks are effectively display arenas in which male birds perform a courtship ritual that can include dancing, showing off their feathers and making calls to attract the attention of nearby females.

̽��ֱ��researchers suggest the geological structures were originally created by theropods, the group of dinosaurs most closely related to living birds and which includes Tyrannosaurus Rex. Theropods may well have been very like modern birds in their behaviour and made the scrapes as part of the production of a display arena for courtship. However, it seems likely that if these marks were leks they would have been next to actual breeding/nesting sites, but so far no trace of nests has been discovered.

Tracking down Cinderella

̽��ֱ��frustrating thing about ichnology is that while the tracks and traces left by living creatures can be matched to observations of their actual behaviour, this is rarely the case when it comes to the fossilised traces of dinosaurs. Trying to tie the identity of fossilised tracks to the original track-maker has been a persistent problem for palaeontologists. It’s rather like the hunt for Cinderella: they have to look for animals that lived at the exact time the tracks were formed, with feet bones the right size and shape to precisely fit the shoe of the fossilised footprint.

Fossilised tracks and traces used to be rather disparaged by palaeontologists because the difficulties surrounding the identity of the actual track-maker seemed more or less insurmountable. However, the past few decades has seen a growing appreciation of the information that can be gleaned from such tracks and traces.

This includes the local environmental conditions when the tracks were made, the texture of the sediments that the creature was walking upon, and the details of foot placement, stride length and stride pattern. These can reveal a surprising amount of information about the way the track-maker walked, its posture and even the likely speed at which it was moving – very reminiscent of the skills demonstrated by Conan Doyle’s heroic sleuth.

Just a few years ago the question of bird-dinosaur affinities was also a topic that was very hotly disputed. ̽��ֱ��discovery of feathered theropods in the 1990s finally proved that theropod dinosaurs were ancestral to living birds. Although we can’t yet be sure, the new research suggests some dinosaurs may have been not just anatomically similar to birds but also have shared some mating behaviours. This gives rise to the amusing possibility of a dancing T. Rex trying to impress his potential mate.

David Norman, Reader in Paleobiology, Curator of Palaeontology, Sedgwick Museum of Earth Sciences, ̽��ֱ�� 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 Norman (Sedgwick Museum of Earth Sciences) discusses how palaeontologists can interpret fossil footprints to find clues as to whether dinosaurs performed dance-like mating rituals.

Xing Lida and Yujiang Han

Tyrannosaurus tango

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Opinion: ̽��ֱ��biggest sperm come in the smallest packages – and other odd facts about male sex cells

Anonymous — Thu, 19 Nov 2015 14:32:59 +0000

Most people probably think of sperm as the microscopic tadpole-like things wriggling around in human semen. But there is an astonishing amount of diversity in the size, shape and number of sperm produced by male animals. In fact, despite performing the very same function in all animal species (fertilising eggs), sperm are the most diverse cells found among animals.

This diversity is a product of evolution. Every animal’s sperm has evolved to meet the needs of the individual animal that produces it. For example, new research published in Proceedings of the Royal Society B shows that the number and size of sperm produced by a mammal depends on the size of the female reproductive tract. Studying these kinds of adaptations helps us to better understand the incredible diversity we see in sperm across animal species.

Tiny animals can have massive sperm

Sperm length varies by several orders of magnitude across species, from the tiny sperm of the porcupine (0.0003 cm) to the gigantic sperm of the fruit fly (6 cm), which is more than 20 times the length of the fly. ̽��ֱ��fruit fly’s sperm looks like a wound-up ball of string that unravels once inside the female’s even longer reproductive tract.

̽��ֱ��number of sperm produced by different animals also varies enormously. Humans produce approximately 100 million sperm per ejaculate, while rams can produce 100 billion. Groups of sperm can even work together. Sperm in some species are known to team up and form a “train” that swims faster than individual sperm.

Promiscuous females mean more sperm

Much of the variation we see in the size, shape and number of sperm produced by different species is thought to be the product of competition for fertilisation among the sperm of different males. This is a type of sexual selection, only relatively recently described, known as “sperm competition”. In species whose females mate most promiscuously, there is strong pressure on males to invest more heavily in sperm, to ensure that one of their own little soldiers is the one that wins the battle for fertilisation.

This has led to an extraordinary array of different warfare tactics. These species, in general, produce more sperm, as more soldiers on the ground gives you a numerical advantage. It may also be advantageous to produce bigger sperm, which are faster and able to outcompete the sperm of other males in the race to the eggs.

Bigger females mean smaller sperm

Sperm can also vary depending on the size and shape of the female body. To accommodate this, sperm have to be able to swim far and fast enough, to successfully reach the eggs. In general, bigger sperm swim faster, so males should produce numerous, large sperm. But males only have finite resources to allocate to sperm production and may face trade-offs.

This means that evolutionary pressure to increase sperm size will inevitably lead to a reduction in number, and vice versa. As mentioned, recent research found that among mammals, males of smaller bodied species tend to invest in fewer, larger sperm, while males of larger species tend to invest in more, smaller sperm. This is because the females of larger species have bigger reproductive tracts and so more (but smaller) sperm can spread across the greater space and have more chance of encountering an egg.

Manlier males have lower quality sperm

As sperm can be costly for the body to produce and resources are limited, males can also face trade-offs between producing sperm and other characteristics useful for reproduction. For example, species in which males invest more in big bodies and horns, or deep voices have been shown to produce less sperm.

In humans, men with more attractive voices have been shown to have worse quality sperm. It seems that males are faced with a trade-off between investing in traits that are useful for competing with rivals, or those that increase the chance of fertilising an egg. They can’t have everything.

Males can control sperm quantities

Amazingly, males seem to be able to control the amount of sperm they produce. There is evidence that males vary the amount of sperm in ejaculates, depending on the quality of the female, or the risk of sperm competition. In humans, men looking at explicit images of two males and one female (“sperm competition images”) have been shown to produce more mobile sperm than those looking at explicit images of three females.

Female animals who mate with more than one partner are also thought to have some control over the sperm that fertilises their eggs. So-called, “cryptic female choice” occurs when females use physical or chemical mechanisms to control each male’s chances of fertilisation. This is well described in a number of animal species, providing a mechanism by which females can bias the outcome of reproduction. For example, in some species, females will mate with several males and then selectively fertilise eggs with only the largest sperm or sperm from males with more compatible immune system genes.

Jacob C Dunn, Lecturer in Human Biology, ̽��ֱ�� 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.

Jacob Dunn (Division of Biological Anthropology) discusses why sperm are the most diverse cells found among animals.

Joyce Harper, UCL, Wellcome Images

Sperm cells

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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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