Sex and reproduction
edyong | June 25, 2009You've got to feel sorry for the female seed beetle. Whenever she mates with a male, she has to contend with his spiked, nightmarish penis (remember this picture?). And despite the damage that it inflicts, one liaison just isn't enough; female seed beetles typically mate with many males before they lay their eggs. Surely, she must benefit in some way?
The most likely idea is that she somehow ensures that her eggs are fertilised by sperm from males with the "best" genes - those that either make for particularly fit and healthy young, or that are a compatible match for the female's own genes.…
edyong | June 5, 2009For humans, sex is a simple matter of chromosomes: two Xs and we become female; one X and a Y and we develop into males. But things aren't so straightforward for many lizards - many studies have found that the temperature of the nest also has a say, even overriding the influence of the chromosomes. But the full story of how the lizard got its sex is even more complicated. For at least one species, the size of its egg also plays a role, with larger eggs producing females, and smaller ones yielding males.
The discovery comes from Richard Shine's group at the University of Sydney. In earlier…
edyong | April 28, 2009The courtship rituals of the spider Harpactea sadistica start innocently enough, with a dance and a hug. The male spider taps the female gently with his front legs and embraces her. But from that point onwards, things for the female go rapidly downhill. The male bites her and she becomes passive, allowing him to manoeuvre her into position. Like all spiders, his genitals are found next to his head, on a pair of appendages called the pedipalps. But unusually, his penis ends in a needle-sharp tip called an embolus.
The embolus sits at the end of a loop called the conductor. The male hooks one…
edyong | April 10, 2009We get a lot of information from watching other people. We read reviews, we follow links to recommended websites and we listen when our friends vouch for strangers. The opinions of strangers may even be a better guide to the things that make us happy than our own predictions. But humans aren't the only species to make decisions based on information gleaned from our peers - even animals as supposedly simple as flies can do the same.
Frederic Mery from LEGS (the Laboratory of Evolution, Genomes and Speciation) studied the fly Drosophila melanogaster and found that females have a tendency to…
edyong | April 8, 2009Many men think of little else besides sex and meat, but male chimpanzees will sometimes exchange one for the other. Chimps are mostly vegetarian but they will occasionally supplement their diet by hunting other animals, especially monkeys. Males do most of the hunting, but they don't eat their spoils alone - often, they will share the fresh meat with females, even those who are unrelated to them. Some scientists have suggested that this apparently selfless act is a trade - the males are giving up their nutritious catch in exchange for sex.
Cristina Gomes and Christophe Boesch from the Max…
edyong | March 27, 2009Termite colonies are families - millions of individual workers all descended from one king and one queen. But the colony itself tends to outlast this initial royal couple. When they die, new kings and queens rise to take their place. These secondary royals are a common feature of some families of termites, and they will often mate with each other for many generations. But there is more to this system than meets the eye.
Kenji Matsuura from Okayama University has found that the secondary queens are all genetically identical clones of the original. There are many copies, and they have no…
edyong | March 1, 2009If you've ever complained about having bad sex, you really have no idea. Human women may have to complain about poor stamina or incompetent technique but the female seed beetle (or bean weevil; Callosobruchus maculatus) has to contend with her partner's nightmarish penis - an organ covered in hard, sharp spikes. Just see if you can look at the picture on the right without wincing.
It's no surprise then that females sustain heavy injuries during sex. But why have male beetles evolved such hellish genitals? What benefits do they gain by physically harming their partners?
It's possible that…
edyong | February 15, 2009
A child in the womb is not just some hapless creature waiting to be born into a world of experience. It is preparing. Through its mother, it senses the conditions of the world outside and its body plans its growth accordingly.
There is strong evidence that people who are under-nourished as embryos grow up to have higher risks of heart disease and other chronic illnesses. For example, people born to women during the Dutch Famine of 1945 had higher risks of coronary heart disease as adults.
We might nod our heads at this as if it were expected news, but it's actually quite a strange result…
edyong | February 3, 2009Our health isn't just affected by the things we do after we're born - the conditions we face inside our mother's womb can have a lasting impact on our wellbeing, much later in life. This message comes from a growing number of studies that compare a mother's behaviour during pregnancy to the subsequent health of her child.
But all of these studies have a problem. Mothers also pass on half of their genes to their children, and it's very difficult to say which aspects of the child's health are affected by conditions in the womb, and which are influenced by mum's genetic legacy.
Take the case…
edyong | January 9, 2009To our ears, the buzz of a mosquito is intensely irritating and a sign of itchiness to come, but to theirs, it's a lover's serenade. The high-pitched drone of a female is a siren's song that attracts male mosquitoes. And a new study shows that when the two love-bugs meet, they perform a duet, matching each other's buzzing frequency with careful precision.
The female Aedes aegypti mosquito (the carrier of both dengue and yellow fever) beats her wings with a fundamental frequency of about 400Hz, producing a pitch just slightly lower than concert A. Males on the other hand, have a fundamental…
edyong | January 7, 2009
For humans and other mammals, sex is neatly determined by the X and Y chromosomes. If you have a Y you are male, and without it you are female. Reptiles however, use a variety of strategies, and the mammalian X/Y system is just one of them.
In some species, the female is the one with different chromosomes, in this case Z and W, and the male has two Zs. And some reptiles ignore sex chromosomes altogether. For them, an individual's sex is determined by the temperature that their eggs were incubated at.
Scientists had long believed that these strategies were mutually exclusive with each…
edyong | December 18, 2008In 1995, a palaeontologist called Mark Norrell reported an amazing discovery - the fossilised remains of a dinosaur called Troodon, sitting on top of a large clutch of eggs. The fossil was so well-preserved and its posture so unmistakeable that it provided strong proof that some dinosaurs incubated their eggs just as modern birds do. And since then, two other small predatory species - Oviraptor and Citipati - have been found in brooding positions on top of egg clutches.
But a subtler look at these fossils reveal much more about dinosaur parenting than the simple fact that it existed. To…
edyong | November 18, 2008There's a glut of awesome science coming out towards the end of this week and not much at the start, so I'm sticking the Revisited post up early (it's usually on a Saturday) to clear the schedule later.
Imagine you are a man who has just learned, through a genetic test, that your son carried your brother's genes instead of your own. You might well have some stern words to exchange with your partner. But if you were a marmoset, this would all be part and parcel of life.
In a striking new study, scientists from the University of Nebraska have shown that marmosets inherit genes not only…
edyong | October 7, 2008
It is the instinct of every mother to protect their children as they grow up, shielding them from the dangers of the outside world. Right from birth, life can be a difficult experience. Within a few hours, the child is sent from a safe, warm, constantly-nourished cocoon into a bright, noisy and threatening world. This stressful transition poses a serious threat to the newborn's vulnerable and still-developing mind. But new research has shown that even in these first vital hours, mothers are already inadvertently protecting their children - by shutting down their brain cells.
In…
edyong | October 3, 2008
According to Christian lore, Mary gave birth to baby Jesus without ever having had sex with Joseph. A biologist might describe this as 'parthenogenesis', the Greek version of the more familiar phrase 'virgin birth'('parthenos' means virgin, and 'genesis' means birth). The New Testament aside, shunning fertilisation and giving birth to young through parthenogenesis is rare among higher animals, occurring in only one in every thousand species. Nonetheless, two Christmases ago, eight virgin births took place in the English town of Chester. The mother's name was Flora and she was a komodo…
edyong | September 15, 2008We like to idolise fearlessness and we equate it to bravery but there is a fine line between that and stupidity. Immunity to the pangs of fear would leave someone unable to assess threats to themselves and to other people, which means that fear not only has consequences for an individual but for their entire social circle. Guillaume Martel and colleagues from Rutgers University demonstrated these far-reaching consequences by examining a special group of mice which had been genetically engineered to be fearless.
Martel's team focused their attention on the amygdalae, a pair of almond-shaped…
edyong | September 2, 2008
Love is all around us and love is in the air, and if I know my mainstream science reporters, today they will have you believe that love is in our genes too. A new report suggests that variation in a gene called AVPR1A has a small but evident influence on the strength of a relationship, the likelihood of tying the knot and the risk of divorce. It's news for humans, but it's well-known that the gene's rodent counterpart affects the bonds between pairs of voles. The story really starts with these small rodents and it's them that I now turn to.
Voles make unexpectedly good animals to study if…
edyong | August 19, 2008
Strip away the trendy clothes, the shiny ornaments and the cosmetically enhanced body parts and consider the naked human body. Free of decorations and distractions, what makes one body more attractive than another? According to one group of scientists, symmetry is part of the answer. William Brown and colleagues at Brunel University found that both men and women fancied symmetrical bodies over asymmetrical ones.
Many animals naturally develop asymmetric body parts; just look at the massive claw of the fiddler crab or the distorted Picasso-like face of the flatfish. But most mismatches…
edyong | July 31, 2008They say that all's fair in love and war, and that certainly seems to be the case of Atlantic mollies (Poecilia mexicana). These freshwater fish are small and unassuming, but in their quest to find the best mates, they rely on and Machiavellian misdirection.
The males always prefer larger females but not if they are being watched. Under the voyeuristic gaze of a rival male, Atlantic mollies will either feign disinterest or direct their attentions toward a smaller, less attractive female.
Deception is par for the course in the animal kingdom. Plovers will try to lure predators away from…
edyong | May 17, 2008As far as humans are concerned, sexually-transmitted infections are things to avoid. But imagine if these infections didn't cause death and disease, but gave you superpowers instead. It may sound like a bizarre fantasy, but it's just part of life for aphids.
Aphids mostly reproduce without sex, giving rise to many all-female generations that are exact copies (clones) of their parents. They only have sex once in autumn, the only time when mothers give birth to males. Asexual reproduction makes sense for aphid mothers since they pass on all of their genes to their daughters. If they…