Features

Male red jungle fowl can adjust the quality of sperm they produce, depending on how attractive the female fowl is.

The story, reported last week by Discovery Channel online, goes on to explain that males of many promiscuous species in the animal kingdom – including humans – can mate with many females, but they adjust the quality of their sperm to improve chances of fertilization when the female is more attractive.

The Oxford University research published in Proceedings of the Royal Society B involved red jungle fowl, the ancestor of all modern chicken breeds. The team showed that males transfer seminal fluid to matings with attractive females that boosts sperm swimming velocity.

The results provide crucial evidence of what causes variation in sperm quality, which has important implications for fertility and the evolution of sexual strategies.

I caught up with Dr Charlie Cornwallis of the Edward Grey Institute in the Department of Zoology to learn more.

OxSciBlog: Why might cockerels adjust the quality of their sperm when mating with different females?
Charlie Cornwallis: Females vary in their attractiveness with some hens having large fleshy combs on their heads whereas other females are barely ornamented at all. The size of a female’s comb relates to size of the eggs she lays. So by inseminating higher quality sperm into these females males have a greater chance of fertilising eggs that result in superior offspring.

OSB: How do they do it?
CC: They do this by allocating different amounts of seminal fluid to attractive and unattractive females. Sperm cells are the machines that swim, but to do so they need fuel and seminal fluid provides a crucial energy source. By allocating more seminal fluid to ejaculates males are able to increase the performance of their sperm.

OSB: How were you able to find this out?
CC: Since female attractiveness can easily be determined by measuring the size of the fleshy comb on top of their heads, we fitted attractive and unattractive females with a small harness that enabled us to collect sperm. After males had copulated with females we analysed ejaculates using computer aided sperm analysis software attached to a microscope that was originally designed for IVF programs. This software measures the speed at which sperm swim and this relates to how likely they are to fertilise eggs.

OSB: What are the implications of your findings?
CC: It has previously been shown in a number of species, including humans, that males can adjust the quality of sperm they ejaculate, but how they do this has remained a mystery. Our results show in chickens that cockerels do this by allocating more seminal fluid. This takes us one step further to understanding the factors that determine fertilisation success. We now have to assess what it is in the seminal fluid that makes sperm tick and if this is the case for other species.

OSB: What do we know about humans? Do men use similar strategies to chickens and is it even possible to do experiments to find out?
CC: The ability of males to adjust the quality of sperm they allocate to ejaculates has been shown to be extremely widespread. In fact it has been demonstrated in insects, fish, birds and mammals, including humans. However, it is not possible to tell whether males across all these species adjust their sperm quality using seminal fluid without conducting experiments specifically tailored to each species. I know that some colleagues are carrying out some experiments on humans at the moment so hopefully they will be able to answer part of this question soon.

Before OxSciBlog packs its bags and heads off on holiday for the summer there's just time to highlight the work of Oxford geology student David Ferguson.

David is writing regular updates for The Guardian's Science Blog about his mission to the Afar region of Ethiopia.

As he explains, it's a place of awesome seismic and volcanic activity, where the earth is literally tearing itself apart as tectonic plates pull away from each other.

This makes it a fascinating location for earth scientists to study.

In this first post David explains how a satellite image of a plume of gas led to him leaping on a plane for Addis Ababa within 24 hours and once there trying to persuade the Ethiopian military to fly him out of one of the remotest places on Earth.

He'll be posting further updates on the expedition over the following days so be sure to check back with The Guardian Science Blog for news on his progress.

A lot of the time, the tables, figures and graphs included in scientific papers can be pretty impenetrable for those outside that particular area of research. But just occasionally there are figures that can stand alone from a paper, illustrating clearly what the raw data show.

This figure comes close to that ideal. It is very clear that the overall death rate among adults aged 15–54 in Russia is much higher than in Western Europe. The reason? Alcohol.

Most, if not all, of the four-fold difference in risk of death now seen in this age range can be put down to alcohol, and to a lesser extent tobacco.

And while overall death rates in Western Europe have been decreasing, largely as people stop smoking, Russian death rates have fluctuated wildly as alcohol use has altered in the face of political and economic change.

The proportion of deaths in adulthood that can be put down to alcohol in Russia is staggering. A study published in The Lancet and led by the Clinical Trial Service Unit [CTSU] at Oxford University and the Russian Cancer Research Centre in Moscow has found that over half of deaths among people in their 20s, 30s and 40s in Russia are caused by alcohol. This can be from alcohol poisoning, accidents, violence, or through diseases strongly related to alcohol, such as TB, pneumonia, pancreatitis or liver disease.

Professor Sir Richard Peto, who led the statistical analysis of the data at CTSU, said: ‘If current Russian death rates continue, then about 5 per cent of all young women and 2 per cent of all young men will die before age 55 years from the direct or indirect effects of drinking.’

The graph shows Russian death rates dropping when alcohol consumption fell by a quarter in 1985 under President Gorbachev’s 1985–8 anti-alcohol laws. They doubled between 1988 and 1994 when they reached a peak before the Russian economy collapsed. Since then, the death rates have varied but remained high.

There is some hope in these observations. As Professor Peto says, ‘This shows that when people who are at high risk of death from alcohol do change their habits, they immediately avoid most of the risk.’ 

Final preparations are underway for our 3 July event for visitors from the World Conference of Science Journalists (WCSJ 2009).

As our previous post explains the event gives international and UK journalists the chance to meet some of Oxford's top scientists and enjoy drinks and food in the lovely riverside surroundings of Magdalen College.

We've been bowled over by the response from all quarters and the final guest list is bursting at the seams with the sort of people who make Oxford University such an exciting place to do/write about science.

As previously reported Professor Sir Richard Peto, Professor Lionel Tarassenko, Professor Fred Taylor and Dr Ian Goldin are among those attending but the guest list now also includes Professor Sir David Weatherall, Professor Valerie Beral, and Professor Steve Davies - and we also hope to see Lord May.

I'd like to give a special mention to the friends of OxSciBlog who will be there: these include engineer and roboticist Dr Paul Newman, and podcast contributors Professor Irene Tracey and Professor Frances Ashcroft.

Thanks in advance to everyone helping to make this happen. 

It's easy to think of mass extinctions only in terms of the impact on animal species but of course plants suffered too.

Stephen Hesselbo of Oxford's Department of Earth Sciences reports in this week's Science on his research studying fossils to see how plants fared in a major extinction event 200 million years ago.

I asked him about what these plant fossils can tell us about extinctions, biodiversity and climate change.

OxSciBlog: Why are these Greenland fossils of particular interest to those studying climate/biodiversity?
Stephen Hesselbo: The East Greenland fossil plant beds represent a uniquely detailed record of floral change across one of the 'big five' mass extinctions that characterize the history of life over the last 500 million years - that which occurred at the Triassic-Jurassic boundary, 200 million years ago.

The plant beds, which represent a warm temperate community, have been known about for about a hundred years, but have previously been worked on principally from the point of view of taxonomy and evolutionary relationships.

This new study takes advantage of the fact that a series of plant beds leading up to the mass extinction horizon were laid down under similar conditions on the banks of rivers in flood - changes in plant assemblages can therefore be interpreted in terms of changing ecosystems rather than vagaries of plant preservation.

A series of expeditions have shipped back more than a tonne of fossil material and so the statistics of the present study are based on large numbers.

OSB: What do they tell us about interactions between CO2 levels and plant life in the Triassic?
SH: Previous work on the density of stomata [the holes through which CO2 diffuses to the site of photosynthesis] on the fossil leaves  has indicated increases in CO2 over the Triassic-Jurassic boundary interval.  These are estimated to have risen from a starting value of about 600 ppm to a maximum of about 1800 ppm through the extinction event.

One effect of the flux of CO2 into the atmosphere is to leave a record in the carbon-isotope ratios of organic matter formed at the time.

Although the Triassic-Jurassic extinction was dramatic amongst animals, hitherto the effects on plants appear to have been much less intense.  However, the present study provides evidence for very marked collapse in ecosystem diversity in the run up to the extinction.

OSB: What do we think may have caused the sort of dramatic loss of biodiversity seen in this period?
SH: The Triassic-Jurassic boundary coincides with a period of volcanism on a massive scale - think Iceland but scaled up a hundred to a thousand times.  This happened as the super-continent Pangaea broke up (initiating formation of the Atlantic ocean in the process).

As well as directly contributing gasses such as CO2 and SO2 to the atmosphere, it is likely that molten rock baked older deposits of organic-rich sediments and salt to create large fluxes of CO2 and SO2 and other gases such as halocarbons. Other mass extinctions similarly coincided with periods of hugely enhanced volcanic activity.

OSB: Can we draw any lessons from this period about how rising CO2 emissions may affect plant/animal life in the future?
SH: To a certain extent yes - the present day flux rates for carbon are higher than anything that was likely at the Triassic-Jurassic boundary, but the total amount of carbon emitted is considerably less, so far.

Further complications are the unknown quantities and effects of the the additional gases produced during the mass extinction event.

Nevertheless, these so called 'flood basalt eruption' episodes do represent a natural pre-run of exactly the kind of release of fossil carbon, sulphur and other elements that we are currently subjecting the planet to.

OSB: How might further research in this area help us to better understand the impacts of climate change?
SH: This study shows how plant ecosystems responded to environmental change in the interval leading up to a mass extinction. Further work should tackle also the recovery interval, after the peak of the mass extinction, as ecosystems returned to normality.

Additionally we need to better constrain the changes in atmospheric carbon-dioxide that went alongside floral change, and also document similar changes that must have been occurring on different parts of the ancient Earth at the same time.

Finally an improved 'age model' (i.e. chronology of events) would be very useful. With these pieces of information we will be in a better position to describe the deterioration of plant ecosystems in response to greenhouse-gas forcing.

Professor Stephen Hesselbo is based at Oxford University's Department of Earth Sciences. The research was conducted with co-authors Jennifer McElwain of University College Dublin and Peter Wagner of the Smithsonian Institution.