It's about squid and it's about sperm, and apparently the combination is sexy enough to get this research onto the BBC, MSNBC, Discover, and more. (Not to malign io9--that's actually where I first read about it.)
The particular squid in question is Loligo bleekeri--whoops, I mean Doryteuthis bleekeri--er, I mean Heterololigo bleekeri. Taxonomists*, can we please get this species complex sorted out??
ANYWAY, as is common in loliginid squids, male bleekeri come in two flavors: consorts and sneakers. Consorts are larger and engage in all the classic male mating behaviors: competing with each other for female attention, inserting spermatophores inside the female's body, and guarding her after mating.
Sneaker males are smaller and don't bother with any of that stuff. They're drive-by maters. They jet in, drop spermatophores on the female's skin, and jet off again.
You'll notice I'm using a long fancy word instead of just saying sperm. That's because squids (and octopuses and all other cephalopods) package their sperm up before passing it from male to female. These packages (each of which contains billions of sperm) are called spermatophores, and they break open at the right time, allowing the sperm inside to do their fertilizing duty.
In the case of consort males, who left spermatophores inside the female's body, their sperm springs into action as soon as the female's eggs start oozing out of her oviducts. That's internal fertilization. But in the case of sneaker males, their sperm doesn't get to touch the eggs until they're already outside her body, having passed by the consort's sperm. That's external fertilization. Seems crazy, but apparently they still have a fighting chance, because eggs do get fertilized by both consorts and sneakers.
This curious system raises a lot of questions. Why do both strategies work? Do the sperm from consorts and sneakers compete with each other? And what makes a male a consort or a sneaker, anyway?
You might guess that younger, smaller males act as sneakers until they grow big enough to duke it out, then they switch to being consorts. But the authors of the study that's been causing all the media hullaballo call such a transition "unlikely". (They don't cite a source, however, which seems odd.) Supposing they're right, one has to wonder: Is it genetic--are some squid born consorts and others born sneakers? Or is it environmental? Or simply a personal squid preference?
Whatever it is, it has to be pretty fundamental. As it turns out, consorts and sneakers differ in more than just body size. They also make differently sized spermatophores AND sperm. Wacky!
The difference in spermatophores was discovered back in 2007 by a couple of Japanese squid researchers named Iwata and Sakurai. Consort males, they found, produced larger spermatophores than sneaker males. But although consorts' bodies and spermatophores are bigger, when it comes to sperm--where the rubber meets the road, if you'll pardon the expression--
Sneaker males make bigger sperm.
That was the discovery made by Iwata, and published in BMC Evolutionary Biology four years after his spermatophore paper, which has all the science news sites abuzz. I'm delighted to see something this weird make big headlines, and I think it is legitimately a very cool study, but don't take my word for it. The BMC in the journal title stands for BioMed Central, which is an Open Access Publisher, so you can read the whole article for yourself. Yay open access!
This is the first time that physically different kinds of sperm, associated with different mating tactics (consort and sneaker), have been described within a single species. Plenty of other animals have "alternative mating tactics" in which males employ one of two or several strategies to pass their genes on. But none of these other species has such a difference between sperm.
So--why bleekeri? What makes it special? The authors think that the key lies in where the sperm meets the egg. Although males of other species employ various mating tactics, when it comes to actual fertilization, it always happens in the same place, either internal (for some species) or external (for other species). But in bleekeri, the two different strategies actually result in fertilization in two different places: internal (for the consorts) and external (for the sneakers).
Since the inside of the female's body is a radically different environment than outside in the open ocean, they suspect that it must be better to have small sperm for internal fertilization and large sperm for external fertilization.
But why? (Being a good scientist is basically the same as being a whiny child, repeating "but whyyyyyy?" over and over again.)
The authors have this to say: "At the moment the mechanisms by which sperm polymorphism has evolved remain elusive."
That means: we don't know. Yet. I'm certainly looking forward to the next Iwata paper!
Iwata, Y., Shaw, P., Fujiwara, E., Shiba, K., Kakiuchi, Y.,&Hirohashi, N. (2011). Why small males have big sperm: dimorphic squid sperm linked to alternative mating behaviours BMC Evolutionary Biology, 11 (1) DOI: 10.1186/1471-2148-11-236
* Taxonomists? Hello? Anyone? . . . Oh right, we don't make taxonomists anymore. Sigh.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- Top Secret: On Confidentiality On Scientific Issues, Across The Ring And Across The Bedroom
- The Mystery Of The Red Sea
- Would New Planet X Clear Its Orbit? - And Any Better Name Than "Planet Nine"?
- Stop Using BMI To Determine Health
- Make Sexual Harassment in Federally Funded Institutions a Crime.
- First-semester GPA A Better Predictor Of College Success Than ACT Score
- The Greenhouse Effect Fallacy
- "Hello Vance,yes I know about that model, and about at least two experimental attempts, one with..."
- "No, I am not from the states. It sounds like an astonishing arrangement to have multiple jurisdiction..."
- "Very true. The observation I've made is that in 2001 it was John F. Nash and Alicia DeLarde ..."
- "The male female difference you think is so basic isn't so simple. Consider this bird. http..."
- "It is a matter of jurisdiction. In the USA the federal government can only claim jurisdiction..."
- BMI is Bologna
- Energy Drinks: The Dose Makes the Poison
- California’s Prop 65: Bad For Public Acceptance Of Science, About To Get Worse
- Wear Red Today! It’s Women’s Heart Health Awareness Day
- Can Marijuana Ease NFL Players’ Pain? Claims Are All Over The Field
- Mid-Life Crisis Clusters Found In 4 US Cities
- Cambridge researcher develops smartphone app to map Swiss-German dialects
- Studies link healthy workforces to positive stock market performance
- Pioneering discovery leads to potential preventive treatment for sudden cardiac death
- Online shopping might not be as green as we thought
- Gene family turns cancer cells into aggressive stem cells that keep growing