Research shows how females choose the 'right' sperm

Main Category: Biology / Biochemistry
Also Included In: Pregnancy / Obstetrics
Article Date: 20 Aug 2013 - 0:00 PDT Current ratings for:
Research shows how females choose the 'right' sperm

University of East Anglia scientists have revealed how females select the 'right' sperm to fertilize their eggs when faced with the risk of being fertilized by wrong sperm from a different species. Researchers investigated salmon and trout, which fertilize externally in river water. The two species occasionally hybridize in the wild, but since hybrid offspring become reproductive dead-ends, females of both species are under selection to avoid hybrid fertilizations, and instead promote external fertilization by their own species' sperm.

Findings published in the journal Evolution show that when eggs from each species are presented with either salmon or trout, they happily allow complete fertilization by either species' sperm. However, if eggs are given a simultaneous choice of both species' sperm, they clearly favour their own species' sperm.

Lead researcher Prof Matt Gage (pictured), from UEA's School of Biological Sciences, said: "The salmon-trout system is ideal for studying sperm-egg compatibilities because we are able to conduct controlled fertilization experiments and measure sperm behaviour under conditions to which the gametes are naturally adapted. Although we found almost 100% interfertility between salmon and trout sperm and eggs, when we mixed equal amounts of sperm from both species together, we found that sperm from their own species won 70 per cent of the fertilizations."

"Since we are conducting in vitro fertilizations without interference or control from males or females, this provides clear evidence that eggs favour the sperm of their own species, but only when given a choice."

The team then went on to investigate what mechanisms allow female eggs to encourage the right sperm to fertilize by examining two key components of reproduction in female fish - the egg, and the ovarian fluid that coats the egg. Ovarian fluid is a protein-rich solution that bathes the eggs and released at spawning - but little has been known about its function.

Prof Gage said: "We ran further sperm competition trials but this time we rinsed eggs of their ovarian fluid and then added back either their own fluid, or that from the other species. Remarkably, we found that the egg itself plays no significant role in promoting fertilization precedence by their own species' sperm. Instead, it is actually the ovarian fluid that controls which species' sperm wins the fertilizations, which was very unexpected. If we put salmon ovarian fluid onto salmon eggs, then salmon sperm win, but if we put trout ovarian fluid onto eggs from that same salmon female, trout sperm now win."

The researchers then used Video Tracking Analysis to analyse how salmon and trout sperm behave in ovarian fluid.

"We found that activating sperm in ovarian fluid makes them live about twice as long as in river water. Importantly, both species' sperm also switch from swimming in tight elliptical circles in river water, to swimming in straightened trajectories in ovarian fluid. This behaviour allows sperm to navigate towards the egg by following a chemical cue."

"So what we're seeing is that ovarian fluid gives a specific chemical signal to the sperm of its own species, causing changes in the way their tails beat, so that they swim in a straighter trajectory, and therefore guided more effectively towards the site of fertilization."

To establish that this was the mechanism which promoted fertilization precedence by their own species' sperm, the research team ran a final experiment in which they measured sperm migration across a membrane permeated with tiny pores mimicking the single entrance into the egg. They found that many more sperm swam through the membrane into their own ovarian fluid, compared with numbers crossing into the other species' ovarian fluid or water.

"These findings allow us to establish that females have indeed evolved mechanisms of 'cryptic choice' at the intimate level of the sperm and egg. The results also give us a valuable insight into why female salmon mate so promiscuously - typically being fertilized by eight, and up to 16, males in one nest. By promoting sperm competition, females provide their eggs with greater choice, allowing ovarian fluid to avoid potentially hybridizing sperm, and instead encourage fertilization by the right sperm."

'Cryptic Choice of Conspecific Sperm Controlled by the Impact of Ovarian Fluid on Sperm Swimming Behaviour' * is published by the journal Evolution.

Article adapted by Medical News Today from original press release. Click 'references' tab above for source.
Visit our biology / biochemistry section for the latest news on this subject.

The research was funded by the Natural Environment Research Council (NERC) and a collaboration between UEA, the Norwegian Institute for Nature Research, and the Institute of Zoology.

* CRYPTIC CHOICE OF CONSPECIFIC SPERM CONTROLLED BY THE IMPACT OF OVARIAN FLUID ON SPERM SWIMMING BEHAVIOR

Article first published online: 12 AUG 2013; DOI: 10.1111/evo.12208

University of East Anglia

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When prescribing antibiotics, doctors most often choose strongest types of drugs

Main Category: MRSA / Drug Resistance
Also Included In: Primary Care / General Practice
Article Date: 05 Aug 2013 - 0:00 PDT Current ratings for:
When prescribing antibiotics, doctors most often choose strongest types of drugs

When U.S. physicians prescribe antibiotics, more than 60 percent of the time they choose some of the strongest types of antibiotics, referred to as "broad spectrum," which are capable of killing multiple kinds of bacteria, University of Utah researchers show in a new study.

Unfortunately, in more than 25 percent of such prescriptions are useless because the infection stems from a virus, which cannot be treated with antibiotics. This overuse of antibiotics has a number of downsides, including that these types of drugs kill more of the "good" bacteria found in our bodies - which may lead to more side effects - and also contribute to the growth of antibiotic-resistant bacteria, according to Adam L. Hersh, M.D., Ph.D., an infectious disease expert, assistant professor of pediatrics at the University of Utah School of Medicine and senior author on a study published July 29, 2013, in the Journal of Antimicrobial Chemotherapy.

Discerning whether an infection is viral or bacterial can be tricky, according to Hersh, which probably accounts for much of the overuse of antibiotics. "It seems that the natural bias, when there is uncertainty about an infection's cause, is to err on the side of prescribing antibiotics," he says. "Our study found that the majority of prescriptions are for antibiotics that kill a wider range of bacteria, and that they are most likely to be given when they're not needed, such as in cases of viral infections."

The types of illnesses where doctors seem to choose stronger antibiotics include respiratory problems, skin infections and urinary tract infections, which in many cases would be better treated by other antibiotics that are less likely to cause resistance.

Hersh, Andrew T. Pavia, M.D., also an infectious disease expert and professor of pediatrics at the University of Utah, Lauri A. Hicks, D.O., a medical epidemiologist at the U.S. Centers for Disease Control and Prevention, and University of California, San Francisco, medical student Daniel J. Shapiro, conducted the study using a public database with information on ambulatory care visits at physician offices and hospital-based outpatient and emergency departments nationwide. Studying data from between 2007-2009, they identified a sample of 238,624 visits by patients 18 and older at those medical facilities and found that 61 percent of antibiotic prescriptions were for broad-spectrum drugs, such as Levaquin®. Narrow-spectrum antibiotics, such as amoxicillin and doxycycline, comprised the remaining 39 percent of antibiotic prescriptions.

Based on the sample of 238,000-plus visits, the researchers estimate there was an average of 985 million annual ambulatory care visits for the 2007-2009 period, with antibiotics being prescribed in an estimated 101 million of those visits each year - 62 million in which broad-spectrum antibiotics were prescribed and 39 million that resulted in narrow-spectrum antibiotics prescriptions.

While this study looked only at adult ambulatory care visits, the prescription pattern for children is similar, according to Hersh. "Many antibiotics prescribed for children are unnecessary, particularly for conditions caused by viruses, where antibiotics don't help at all," he says. "Even when an antibiotic is indicated, such as for strep throat or some ear infection, physicians often prescribe and antibiotic such as a Z-Pak, which can be less effective than amoxicillin."

Hicks emphasizes that antibiotic overuse among children and adults is a serious problem and a threat to everyone's health. "The biggest problem with using antibiotics when they're not needed is the development of antibiotic resistance, which is when bacteria survive by outsmarting the antibiotic," she says. "Common infections become difficult to treat, and when you really need an antibiotic, it may not work."

Uncertainty about the cause of an infection is one factor in the overuse of broad-spectrum antibiotics, but there are other influences too, according to Hersh. This includes a misperception by physicians that their patients expect an antibiotic if they take the time to see the doctor. But Hersh believes this second factor is changing, due in part to major efforts to educate people about the problems associated with overuse of antibiotics, such as CDC's "Get Smart: Know When Antibiotics Work" program.

"The public is increasingly aware of the downside and side effects of antibiotics," Hersh says. "Actually, when they see their doctor, most patients just want an explanation as to what's wrong and are open to considering why an antibiotic wouldn't be helpful."

He urges patients to play a larger role by asking their doctor two questions: Do I really need this antibiotic? And, is this antibiotic the best choice for my infection?

"Both doctors and patients have a role in ensuring the effectiveness of antibiotics is preserved by using them only when needed," Pavia says.

Article adapted by Medical News Today from original press release. Click 'references' tab above for source.
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