Lesbian Lizards that will survive the apocalypse

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Does that sound like the name of a hardcore metal grrrl band to anyone else? No? Well, when I tell you that there are multiple species of lizard in Mexico and the US Southwest that are all female and that no male members of these species exist, I am not kidding (nor am I writing a science fiction novel). It’s a real thing, kids. A species of animal that needs only one sex to reproduce is called parthenogenetic, and surprisingly, it happens in over 70 species of vertebrates. Some species of snail, some pythons, hammerhead sharks and Komodo dragons are parthenogenetic (or will occasionally revert to parthenogenesis, depending on the circumstances). Also, just as a fun fact, the name itself comes from the Greek words parthenos or “virgin” and genesis or “creation”.

Parthenogenesis usually evolves in species that are extremely isolated–from other groups of similar organisms, from members of the opposite sex, or both. These lizards, hanging out in the baking deserts on the border between North and South America, fit the bill.  Until recently, scientists were stumped as to how these lizards could produce fully formed offspring: in ‘normal’ sexual reproduction, the female contributes half the chromosomes in her egg while the male donates the other half through his sperm, and the two mix in different creative ways to generate genetic diversity within the population (not that DNA can get ‘creative’ per se, but you get my drift). So if there are no males involved in this process, how are the offspring getting the full complement of genes? As it turns out, the mother provides both sets of chromosomes all on her own.

These resourceful mamas start out the reproductive process with eggs that have twice the number of chromosomes as sexually reproducing females, meaning their offspring will be genetically identical, excluding the random mutation that is bound to occur. They also undergo some pretty fab-tastic genetic recombination with sister chromosomes to make sure the genes stay heterozygous. Although their method of reproduction can decrease the genetic diversity of the population and thus make the individuals more susceptible to disease and predation, it also means that a single lizard could explore and inhabit a new territory and populate it all on her own! (Think about how handy this would be if you were the only woman standing after the zombie apocalypse…)

Even though these lady lizards do not need a male partner to fertilize their eggs, (got it covered, bro, thanks!) they still need to engage in a copulatory act. This means that two female lizards, even though neither can (or needs to) fertilize the other, will perform the movements of traditional copulation. This sends the trigger to their brains that allows them to lay their eggs. The fact that mamas still need faux-copulation as a mechanism to signal egg-laying indicates that males were once an essential part of the species, and though the male population has been lost, the copulation trigger has been conserved as what animal behaviorists call a ‘fixed action pattern’ within the species. (below, two lady lizards helping each other out).

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The BBC, as always, has some pretty awesome videos on the subject of parthenogenesis, as well as some commentary on the whiptail lizards themselves, so check it out! Revel in the fact that there are species on Earth that will produce countless virgin births in the years to come–someone tell the Pope.

 

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Do Your Genes Code for Monogamy?

Image(Above, Prairie voles gettin’ cozy)

Sex and relationships are tough, but luckily we’ve got behavioral psychologists, molecular geneticists, and evo-devo people working on that. In our world today, when communication is instant and the number and diversity of people one meets in a given moment would astound someone from a few decades back, relationships are nothing if not more complicated than they were, say….200,000 years ago. There are obviously huge social differences between us and our hunting-and-gathering ancestors but biologically, we’re pretty much the same. So–can we use our biology to help us understand our behavior…even when it comes to staying faithful to a partner?

There are currently some pretty heated debates about the nature of human relationships and whether or not humans, as animals, are biologically meant to be mated for life. Ryan and Jethá’s New York Times bestselling book Sex at Dawn: The Prehistoric Origins of Modern Sexuality discusses the evolutionary psychology of monogamy. They argue that many human physiological traits, such as copulatory vocalization (uh, sex noises), testicle size, and sexual dimorphism indicate that monogamy was not a common practice in our more primitive ancestors. Evolutionarily speaking, most animals are polygynous—for females, mating with multiple males usually means there’s a greater chance that offspring will be fathered by the most fit individual while for males, the more females he mates with, there’s a greater chance that he will father a greater number of offspring. Perhaps it is only modern bias, in which monogamy is the only really socially acceptable relationship choice, which has resulted in a misinterpretation of our ancestors’ sexual mores.

So why is it that human beings form life-long pair bonds? (Or at least…we try our best). It’s much more likely that sexual behavior shifted from a ‘promiscuous’ system in the hunter-gatherer stage toward long-term pair bonding with the development of agriculture, accumulation of wealth, and a different social structure. The authors of the book argue that the shift toward monogamy is fundamentally at odds with our animal nature.  While carefully staying away from any moral pronouncement about what may be ‘right’ or ‘wrong’, the authors simply take the position that people should be more informed about the behavioral history of our species and go into relationships with a more complete picture of the choices they can make.

But what if a quick peek into our brains could tell us even more about the evolution of our species’ relationships? There are very few animal species who practice monogamy, mostly because usually, it’s more evolutionarily advantageous to mate with diverse members of the opposite sex. One of the lesser known monogamous species is, surprisingly, the prairie vole. Why surprising? Being rodents, voles reproduce fast and often, usually trying to gain an advantage by mixing up their mates. Prairie voles are one of the only species of rodent who mate with one specific individual, and scientists are just beginning to understand why—the answer lies in the structure of their brain.

When male prairie voles mate with same female a number of times in succession, their brain releases the hormone vasopressin, giving them a pleasurable feeling in the reward center of their brain. (They’re really cute too—they like to spend lots of time ‘cuddling’ with their chosen mate. Very scientific stuff, cuddling voles). This reward system makes the voles want to keep mating with the same female. These voles have probably developed a different kind of evolutionary advantage—when a male mates with just the one female, there is a higher chance that he will be the only father of all of her offspring. This behavior can also be explained physiologically: Prairie voles, unlike most other branches of their species, have a high number of vasopressin receptors in their brain, making this feedback loop powerful for them. Polygynous voles are lacking or have reduced version of the gene that codes for vasopressin receptors and so are unable to feel (or feel a greatly reduced version of) the positive sensation the results from monogamous mating.

But wait! It gets even better. Further experiments have shown that females can tell when males have increased levels of this receptor and will always pick them over males that have decreased vasopressin receptor levels. The hypothesis here is that males who mate monogamously are more likely to stick around to help take care of the kids (a much better choice of mate for the ladies). Larry Young and his lab at Emory University have even gone so far as injecting the gene that codes for vasopressin receptors into non-monogamous voles. The result? Voles who like to play the field suddenly became….monogamous. Adorable snuggle time with one specific mate ensued.

Could human brain chemistry give us more insight into the nature of our relationships? Could we genetically alter our mates to make them more faithful? Or is it not quite that simple? As always, social and cultural variables play a role in relationships and unfortunately, not everything is as black and white as science can make it seem. Humans are messy, and it takes a lot more than neurobiology to figure out why we behave the way we do. Let’s keep poking around in rodent brains and see what turns up.