Sometimes You Just Have To Shave Off a Fish’s Genital Claws

Check out the Ed Yong’s summary of my lab mate Lucia’s research! Way to go Kwan!

Sometimes You Just Have To Shave Off a Fish’s Genital Claws.


Genitals of a male guppy. From Kwan et al, 2013. Royal Society.

Sometimes You Just Have To Shave Off a Fish’s Genital Claws

by Ed Yong

Guppies are small freshwater fishes that are popular in aquariums around the world. Unlike many fishes, where males and females squirt sperm and eggs into the surrounding water, guppy males fertilise females by delivering sperm into their bodies. They don’t have a penis, as such. Instead, they have modified a pair of their fins into penetrating organs called gonopodia.

These penis-ish organs are tipped with an unpleasant set of claws, hooks ridges and spines. These features evolve very quickly and they’re sometimes the only way of telling one guppy species from another. What are they for? It’s possible that the claws help males to latch onto females, even those that do not want to mate with them. Alternatively, they might help to hold sperm at the tips of the gonopodia, so they can be more easily implanted into the females.

To test these ideas, Lucia Kwan from the University of Toronto used a scalpel to slice off the claws of several males, leaving the rest of their gonopodia intact. She calls it “phenotypic engineering”. That’s a long way of saying: “a shave”.

She then released individual males into tanks with single females, and watched. It was a straightforward experiment with a clear result. Compared to shaved males, clawed ones transferred  three times more sperm into unreceptive females, but the same amount into those that willingly mated.

This strongly suggests that the claws are a “sexually antagonistic trait”—one that benefits one sex over the other. In this case, they help the males to grasp resistant females. If they were simply for anchoring sperm, the de-clawed males should suffer when mating with all females, rather than just the unreceptive ones.

This is the latest in a small but growing line of phenotypic engineeringgenital-shaving studies, which aim to work out just why animal sex organs are so bizarrely adorned. One group laser-shaved the spikes from a fly’s penis to show that they’re like biological Velcro, allowing males to latch onto females. Another team did the same thing with a seed beetle’s penis to show that its terrifying spikes aren’t anchors—their role seems to be to puncture the female’s genital tract for reasons best known to the seed beetle.

The penises of these insects are just as varied in shape, size and spikiness as those of the guppies, so these experiments suggest that the battle of the sexes has fuelled the evolution of these groups, helping them to diversify into the many species we see today. To understand that process, scientists would need to compare the organs of many different species, but these shaving experiments are certainly a good first step.

Reference: Kwan, Cheng, Rodd & Rowe. 2013. Sexual conflict and the function of genitalic claws in guppies (Poecilia reticulata). Biology Letters

Guppies have been important animals for evolutionary biologists. For more:


Snapshots of Snowbird: Evolution 2013

This was just a few steps away from our hotel at Snowbird.

This year, Evolution 2013 was held at the Snowbird ski resort, near Salt Lake City, Utah. I won’t bother going on about how beautiful it is in Little Cottonwood Canyon: just take a second to scroll through the photos, and see for yourself.

Anna Li and I during our hike the first day we arrived for Evolution 2013.

Anna Li and I during a hike up the mountain at Snowbird. We are excited about mountains.

After riding the tram to the summit, Snowbird, Utah. The elevation here was ~11,000 ft (3350m)

The view after riding the tram to the summit, Snowbird, Utah. The elevation here is ~3350m (11,000 ft) above sea level, and at the base (where the conference was held) is about 2400m. For a reference point, Toronto, Ontario, is about 200m above sea level.

Trying to look cool while the wind strangles me with my Evolution name tag.

Trying to look cool (apparently as a teapot) while the wind strangles me with my Evolution name tag on the summit.

And of course there was lots of science. Clearly I was drawn to talks focusing on behaviour and/or genetics, because that’s my thing.

Marlene Zuk’s talk, Same-sex pairing in Laysan albatross: a female alternative reproductive strategy?, had to be one of my favourites. Without fail, Marlene gave a witty, and highly informative talk on a topic that many of us would choose to tiptoe around: same-sex pairings in non-humans. I won’t get into the nitty-gritty details, but briefly, she discussed her observations of albatross from female-biased populations, where some females who were unable to pair bond with a male instead bonded with a female. Note: by bonded, I don’t mean the dirty things you might be thinking of, I mean join forces to provide parental care to the egg. Although you were most likely to survive and successfully rear your offspring if you paired with a male, for those who couldn’t score a male, bonding with another female was a much better strategy than trying to go it alone.

Some of the other highlights for me was talks from the symposium entitled Everything you wanted to know about evolution but never thought to ask, specifically, Kay Holecamp’s long-term studies on intelligence and social complexity and Josh Bongard’s work on evolutionary robotics. Check out his site; you can try your own evolutionary robotics experiment! Oh, and Richard Lenski gave the SSE presidential address on insights from his long-term E.coli experiments. His lab has been growing the same strains of E.coli for over 25 years(!!), which has allowed his team to observe evolutionary dynamics over thousands and thousands of generations.

My labmate, Anna Li, giving her presentation on the 'Negative frequency dependent selection in Trinidadian guppies: the rare male effect, aggression and dispersal'

My labmate, Anna Li, giving her presentation on the ‘Negative frequency dependent selection in Trinidadian guppies: the rare male effect, aggression and dispersal’

Stephen De Lisle, a fellow graduate student, giving his presentation on 'Resource competition, social environment, and the expression of  sexual dimorphism'

Stephen De Lisle, a fellow graduate student, giving his presentation on ‘Resource competition, social environment, and the expression of sexual dimorphism’

There is no picture of my standing faithfully beside the poster that I presented at the meeting (I stood there, I swear). You can check out the poster here.

This is literally called guppy love

Hope you like fish porn! Here are some guppy mating pictures that I’ve photoshopped into a pleasing array. Yes, this is what I do with my time. I’m rather pleased with these photos as it’s surprising difficult to get these guys in focus when they are frantically swimming around. A brief overview: the colourful male guppy is trying to mate with the larger, grey female.

So many different positions!

So many different positions!

Some highlights include the second photo on the left, which depicts a male mid-sigmoid: a guppy courtship display. In the third from the left, this male is employing a more sneaky mating strategy, appropriately called a ‘sneak’. You can see his gonopodium (re: his dick) mid swing, as he swims toward the female in hopes of inseminating her. I didn’t say this would be pretty. Male guppies usually switch between these two mating strategies, being more gentlemany if the female seems interested, and switching to being a sneak when she’s not  (which happens to be most of the time– sorry boys).

Experimental set-up: the Chamber of Guppies


Walls of set-up tanks, prior to addition of my focal fish

To get things started, I’m going to post some photos of the Chamber of guppies. This is the official home of my experimental fish, and the unofficial home of yours truly.

This room is the home of my experimental fishies, and is my prison for the next couple years. Jokes! Not sure if you can call it prison if you are a (semi-) willing occupant… Anyways, the first photo shows a wall of fish tanks; the adjacent wall is also full of tanks, so you can get an idea of the scale. This image was taken just prior to the addition of the experimental fish; at the time, their guppy brethren were occupying the tanks to make the water smell ‘fishy’ (the guppies enjoy it, I swear).


And here are the tanks again, now housing my experimental fish. Green tags represent control individuals, while red are treatment tanks

Guppies from particular lineages (aka the chosen ones) were then assigned to treatments when they were approximately one month old. I wanted to ensure that all focal fish had the same experience growing up, as it is known that early experiences can sometimes cause changes in gene expression that persist into adulthood, so each was housed in their own tank. However, guppies are social fish, and it can be very stressful if they are kept alone; to prevent this, we decided to house each fish with one non-focal juvenile guppy as a friend. It definitely would be much easier to just rear focals with their brood mates, but that would likely create differences between tanks; for example, the sex of individuals brood mates and size of the brood could impact interactions between the fish in any given tank. Also the interactions between individuals in treatment tanks (relative to control tanks) could also be very different, so this was another reason to separate the bros. Additionally, I had to standardize who each fish had as neighbours; for example, if you look at the photo to the right, each tank is placed beside one tank with red tape (treatment) and one with green (control).

Interested in what the treatment is? I’ll get to that in another post. Stay tuned!