Sex combs!

I mentioned sex combs a while back, so I thought I’d clarify a bit — I hope none of you rushed out to buy one for yourself (I don’t think human sex combs exist, but if they do, I don’t need to know.) Sex combs are secondary sexual characteristics found in on the forelegs of only male Drosophilidae. They are small dark patches of bristles on the tarsus of the first leg, and they are not something you’d notice if you saw a fly buzzing in your kitchen — you have to knock them out and carefully scrutinize the limbs with a hand lens or microscope to see them, but they’re important for recognizing the sex of a fly definitively. I tell my genetics students that you can tell the sexes apart by the shape of the abdomen or the pigment patterns, but to be really sure you should check for the presence or absence of the sex combs.

Sex comb in Drosophila melanogaster male: a) front leg with sex comb marked with black arrow; b) sex comb bristles

They don’t look like much, but they also matter to female flies. Mutants or surgically modified male flies with the sex combs reduced suffer with lower reproductive success. The flies use them as gentle grasping tools to separate her wings, grasp her abdomen, and tease open the genitals, so of course they’re subject to selection. Different species of fruit flies exhibit different patterns of sex combs, and we observe natural variation within a species.

Sex comb (SC) diversity. A phylogeny of eight comb-bearing species, assuming that the montium subgroup is a sister-taxon to the
Oriental lineage, as in Kopp (2006). Branch lengths are not to scale. Note the variation in the length, size and orientation of the SCs.

Variation within and between species makes sex combs of great interest to evolutionary biologists. Here’s an illustration of the variation we can see.

Variation in sex comb tooth number and development. (A–C) Exam-
ples of Drosophilidae forelegs with long combs. (D and E) D. melanogaster
forelegs. (F–J) Schematics of foreleg development of the top Drosophila legs.
(K–O) Examples of D. melanogaster perturbations in sex comb tooth number.
(A–C and F–H) Drosophila species with long sex combs achieve vertical orien-
tation by different mechanisms: (i) Teeth initially form in a vertical orientation
(F) (e.g., D. ficusphila t1–t2); (ii) rotation of a long row (G) (e.g., D. guanche t1–t2
and D. rhopaloa t1); (iii) rotation of multiple small rows and posterior fusion
into a long sex comb (H) (e.g., D. rhopaloa t2). (D, E, I, and J) In D. melanogaster, the male sex comb rotates from a horizontal to a vertical position
(diagrammed in D), while TRs remain horizontal. The only exception is the
most distal transverse row (red dotted box in D and I), which bends proximally
close to the top part of the sex comb. In contrast, the female rows of bristles
homologous to the sex comb remain static during development (brackets in E
and J). In order to study the phenotypic and developmental effect of changing
the number of sex comb teeth, this trait was perturbed using artificial selection
(K and L), mutants (M–O), and UAS-Scr RNAi transgenic lines . Gray circles represent sex comb teeth in the initial position and
black circles represent sex comb teeth in the final position. Empty circles represent the TR bristles. Gray arrows indicate movement of individual tooth or
sex comb rows. Red brackets indicate sex combs or homologous female bristles. Red numbers represent the range of sex comb teeth in each line. babPR72, bric à bracPR72; scd, sex combs distal; Scr, sex combs reduced; t1 and t2, first and
second tarsal segment, respectively. Distal is down and posterior is to the right.
Scale bar: 20 μm.

Focus for now on the top panel on the right, which shows a male and a female foreleg. They both have hairy legs, and in the default pattern seen in the females is a series of bristles in transverse rows (TRs) in arrays marching down the leg. The flies specifically use these bristles to groom their eyes — if you look closely, flies are remarkably tidy and neat.

The TRs are illustrated diagrammatically as small open circles in rows, the base pattern. These bristles are also developmentally interesting, because the way you make a sex comb is you express a set of specific genes in the distal two rows, and the whole structure rotates 90° to form a longitudinal comb. This opens up a whole set of informative interactions — the rotation is essential for function, and is subject to constraints imposed by adjacent tissues. I’ve been reading papers for the past week focused on the developmental and evolutionary significance of this tiny, odd, little known structure in flies. You should read some of these papers, too! I’m a sucker for anything evo-devo, and that’s what this little patch of hairs illustrates.

The most complex and diverse secondary sexual character in Drosophila is the sex comb (SC), an arrangement of modified bristles on the forelegs of a subclade of male fruit flies. We examined SC formation in six representative nonmodel fruit fly species, in an effort to understand how the variation in comb patterning arises. We first compared SC development in two species with relatively small combs, Drosophila takahashii, where the SCs remain approximately transverse, and Drosophila biarmipes, where two rows of SC teeth rotate and move in an anterior direction relative to other bristle landmarks. We then analyzed comb ontogeny in species with prominent extended SCs parallel to the proximodistal axis, including Drosophila ficusphila and species of the montium subgroup. Our study allowed us to identify two general methods of generating longitudinal combs on the tarsus, and we showed that a montium subgroup species (Drosophila nikananu) with a comb convergently similar in size, orientation and position to the model organism Drosophila melanogaster, forms its SC through a different developmental mechanism. We also found that the protein product of the leg patterning gene, dachshund (dac), is strongly reduced in the SC in all species, but not in other bristles. Our results suggest that an apparent constraint on SC position in the adult may be attributable to at least two different lineage-specific developmental processes, although external forces could also play a role.

Atallah J, Liu NH, Dennis P, Hon A, and Larsen EW (2009) Developmental constraints and convergent evolution in Drosophila sex comb formation. Evolution & Development 11(2): 205-218.

Malagón JN, Ahujab A, Sivapatham G, Hung J, Leea J, Muñoz-Gómez SA, Atallah J, Singh RS, and Larsena E (2013) Evolution of Drosophila sex comb length illustrates the inextricable interplay between selection and variation www.pnas.org/cgi/doi/10.1073/pnas.1322342111

Stuffing a gag in the mouth of science

Yet another consequence of the election: scientific meetings are being shut down.

Several meetings of National Institutes of Health study sections, which review applications for fellowships and grants, were canceled without being rescheduled, according to agency notices reviewed by STAT. A Feb. 20-21 meeting of the National Vaccine Advisory Committee, a panel that advises the leadership of the Department of Health and Human Services on vaccine policy, was also canceled. So was a meeting of the Presidential Advisory Council for Combating Antibiotic-Resistant Bacteria that was scheduled for Jan. 28 and 29.

The scope of the cancellations was unclear. It was also unclear whether they were related to the Trump administration’s freeze on external communications until Feb. 1.

Let’s stop all progress on research into vaccines and antibiotics. It’s not as if we’ll ever have another pandemic.

You know, this is going to get depressing fast. Every morning I’ll be getting up first thing in the morning to the latest horrible, evil act executed by this administration. I’m going to have to think of something to break this spiral of doom whirling away in my brain.

Here’s an appropriate comic.

Just change that last word from “January” to “United States of America.”

Putting biology in perspective

This is some nice art illustrating the relative number of species in each clade in a particular environment. Insects, illustrated by a ginormous beetle, are the most diverse group, but spiders and other arthropods make a good showing, with that colorful mite on the left. Tetrapods are relatively insignificant — I suspect part of the reason for that is that we have exterminated so many of our fellow terrestrial vertebrates. Molluscs are surprisingly successful, but I’m not at all surprised at the size of those fungi.

I do not begrudge the insects their dominance, because after all, that’s spider food.

Busy day of making the younguns happy

Think about how you can make young people happy: give them a puppy. I can’t afford to hand out puppies, but today is the day the students will come into my lab and I hand out fruit flies. Swarms of Drosophila! and I’ll tell them they have to feed them and take care of them and love them for the next three months. It will be a joyful afternoon for the student body.

I also have to explain sex to them, which I’m sure is going to be a total surprise to this group of 19-20 year olds.

It’s going to be an enlightening day, especially when all the men in the class look at their own elbows and realize they must be trans because they lack sex combs.

I just got back from setting up the lab in preparation for this big day. It’s like an icebox in there! Temperature regulation must be very complex in this building, because I can go from my office to the hallway to my research lab to the student lab, and the temperature can vary by 5°C in each transition. The student labs are just plain frigid — I’m going to have to send an email announcement to everyone in my class that they need to dress warm, wear a sweater, maybe bring those heating flasks you use when deer hunting or ice fishing, because jesus, at least the flies won’t try to escape their incubator.

Once more unto the breach

I’m preparing to teach genetics again, and as usual, I’m trying to rework some of the lectures, because I don’t care to say the same thing every year. I had one odd thought that I’m probably not going to squeeze into the lectures this year, but thought I’d bounce it off people here.

Evolution and genetics were on parallel tracks in this very interesting period of 1860-1910. While the American Civil War and the Franco-Prussian War and the Boer War might have been distracting most people, biologists had their own obsessions. Charles Darwin published in 1859; Gregor Mendel in 1863. Darwin had immediate popular success, while Mendel was basically ignored and neglected. I was contemplating why the difference was there, and had a random idea.

Darwin started with a phenomenological and largely descriptive foundation, no significant math anywhere in The Origin. Mendel’s brief paper was little more than a mathematical hypothesis, with limited qualitative description — it was just peas, one model system, and the traits weren’t even particularly interesting, except for the fact that their inheritance was so discrete.

Evolution took off fast, and rather erratically. There were so many bad hypotheses built on the framework of natural selection (for instance, all of Haeckel’s work) that by the end of the 19th century, Darwinism (and in this case, that was an appropriate name for it) was fading, and people were finding flaws and poking holes in the idea. The absence of a quantitative basis for analysis was killing evolutionary theory.

Meanwhile, Mendel’s laws of inheritance weren’t getting any attention, but there was all this foundational qualitative work getting done — cell theory was being established, microscopy was taking off (instruments were reaching the physical limits of optics), Weismann had worked out the limitations of cellular inheritance, Sutton and others were publishing all this tantalizing stuff about chromosomes. When 1900 rolled around and Mendel was rediscovered, everyone was primed for his statistical/probabilistic theory of inheritance. We could do math on it!

Also, evolution was rescued by it’s happy marriage to genetics and in particular, population genetics. We could do math on evolution, too!

Everything is better with mathematics, is my conclusion. Except maybe individual success — before 1900, someone could come up with a hot theory and get it named after themselves. Afterwards, there’s too much detailed quantitative thinking going on for any one person, and eponymous theories went out of style, being regarded with suspicion, even.

Along comes SMBC to correct me:

OK, OK, it’s not just mathematics, it’s thinking precisely. But isn’t that what math is? How do you think precisely without the application of math and statistics and quantitative reasoning?

We’re home at last!

We’re back from our excursion to Madison — a day driving there, two days with Iliana, and a day driving back, but totally worth it. You may recall that I mention the distinct change at the border with Wisconsin (“adult novelty stores, billboards for cheese, and roadkill as far as the eye can see”), but we also saw something in common: so many “Pro Life Across America” billboard spread across both Minnesota and Wisconsin. They’ve gotten more condensed over the years, at least. Nowadays they’re just a photo of a cute, plump 6-month old babies with the words Heartbeat 18 Days. That’s all. Not even grammatical. We’re just supposed to leap to the conclusion they want.

I have a much more interesting statement: Poop 19 Seconds.

That’s from Bethany Brookshire’s Insomniac Academy of brief YouTube shorts with fascinating facts about anatomy. Check it out!

I reaffirm my support for the Freedom From Religion Foundation

Now, both Jerry Coyne and Steven Pinker have announced their resignation from the honorary board at the FFRF. Good. They were a terrible influence, and their departure strengthens the FFRF as a defender of reason.

Their latest post on their website declares Freedom From Religion Foundation supports LGBTQIA-plus rights. They admit that they erred in permitting someone (Coyne, of course) to publish an article in their newsletter that was ignorantly prejudicial against transgender individuals.

However, advocacy is rarely perfect, and progress is not always linear. Recently, we published a guest blog post as part of an effort to provide a forum for various voices within the framework of our mission. Although we included a disclaimer that the viewpoints expressed within the post were not necessarily reflective of the organization, it has wrongfully been perceived as such.
Despite our best efforts to champion reason and equality, we recognize mistakes can happen, and this incident is a reminder of the importance of constant reflection and growth. Publishing this post was an error of judgment, and we have decided to remove it as it does not reflect our values or principles. We regret any distress caused by this post and are committed to ensuring it doesn’t happen again.
Moving forward, we are reviewing our content guidelines and internal processes to ensure our public messaging consistently reflects our values. We are committed to learning from this experience.
We stand firmly with the LGBTQIA-plus community and their allies in advocating for equality, dignity and the freedom to live without fear of religiously motivated discrimination. Our mission to keep religion out of government is inextricably linked to preserving and advancing these fundamental rights.
Together, we will continue to champion a society where all people — no matter their sexual orientation, gender identity, beliefs or nonbeliefs — are treated equally under the law.

That article is currently flooded with comments criticizing the FFRF — many of them seem to be coming from the horde of haters at Coyne’s blog. The gist of many of their comments seems to be that the FFRF is the transphobic one, which is ludicrous and little more than a childish playground taunt. I think we can ignore that nonsense.

Some of them are claiming that Coyne’s claim that sex is totally binary is scientific, and that it is unscientific to argue for a more complex continuum of traits. This is also nonsense. Don’t argue with me, though, take it up with the Society for the Study of Evolution’s position on transgender identity from back in 2018.

We, the Council of the Society for the Study of Evolution, strongly oppose attempts by the Department of Health and Human Services (HHS) to claim that there is a biological basis to defining gender as a strictly binary trait (male/female) determined by genitalia at birth. Variation in biological sex and in gendered expression has been well documented in many species, including humans, through hundreds of scientific articles. Such variation is observed at both the genetic level and at the individual level (including hormone levels, secondary sexual characteristics, as well as genital morphology). Moreover, models predict that variation should exist within the categories that HHS proposes as “male” and “female”, indicating that sex should be more accurately viewed as a continuum.* Indeed, experiments in other organisms have confirmed that variation in traits associated with sex is more extensive than for many other traits. Beyond the false claim that science backs up a simple binary definition of sex or gender, the lived experience of people clearly demonstrates that the genitalia one is born with do not define one’s identity. Diversity is a hallmark of biological species, including humans. As a Society, we welcome this diversity and commit to serving and protecting members regardless of their biological sex, gender identity or expression, or sexual orientation.

*Here we are speaking of the multi-dimensional aspects that underlie male-ness and female-ness, including hormones, physiology, morphology, development, and genetic aspects. We acknowledge that many of these aspects are bimodal. Furthermore, some of these aspects are discrete categories (e.g., XX/XY, SRY presence/absence, gamete size, sperm production vs egg production, presence/absence of certain genitalia), but these categories don’t always align within individuals, are not always binary, and should be irrelevant to the determination of a person’s legal rights and freedoms.

There’s a second letter there, too.

As scientists, we write to express our concerns about the attempt by the Department of Health and Human Services (HHS) to claim that there is a biological basis to defining gender as a strictly binary trait (male/female) determined by genitalia at birth.

Variation in biological sex and in gendered expression has been well documented in many species, including humans, through hundreds of scientific articles. Such variation is observed at both the genetic level and at the individual level (including hormone levels, secondary sexual characteristics, as well as genital morphology). Moreover, models predict that variation should exist within the categories that HHS proposes as “male” and “female”, indicating that sex should be more accurately viewed as a continuum. Indeed, experiments in other organisms have confirmed that variation in traits associated with sex is more extensive than for many other traits. Beyond the incorrect claim that science backs up a simple binary definition of sex or gender, the lived experience of people clearly demonstrates that the genitalia one is born with do not define one’s identity.

Diversity is a hallmark of biological species, including humans. Our three scientific societies represent over 3000 scientists, many of whom are experts on the variability that is found in sexual expression throughout the plant and animal kingdoms. If you wish to speak to one of our experts or receive peer-reviewed papers that explain why there is a continuum of sexual expression, please contact us at president@evolutionsociety.org.

Sincerely,

Dr. Hopi Hoekstra
President, Society for the Study of Evolution
Professor, Harvard University

Dr. Sharon Strauss
President, American Society of Naturalists
Professor, University of California, Davis

Dr. Susana Magallón
President, Society of Systematic Biologists
Professor, Universidad Nacional Autónoma de México

Hmmm. Hoekstra has published with Coyne in the past, so maybe that will have some weight with him.

I look forward to Coyne’s resignation from the SSE, as well. Or maybe he’s waiting and hoping for a purge of all those woke scientists from the Society? He might get his wish, given the ascendancy of the ideology he favors in our government.

Breaking news: Richard Dawkins has also resigned from the FFRF! And there was much rejoicing!

You think spider sex is crazy?

I beg to differ about spider sex — it’s perfectly normally weird, but then I have been spending a fair amount of time trying to encourage spiders to have sex. Mainly what I’m concerned about is that it’s too infrequent, and they seem to have seasonal depression. But OK, it is interesting, as this video demonstrates.

You know what’s kinky, though? The video mentions that “some flies have a female who penetrates the male to collect sperm”. Not spiders, but barklice (Neotrogla), which aren’t flies and aren’t lice, but a kind of true bug, have completely reversed sex roles.

The female has a penis-like protrusion called a gynosome, which is erectile and curved. The male has no such organ; he has an internal chamber instead. When she penetrates him during sex, he delivers sperm into a duct in her gynosome, which leads to a storage organ. He still ejaculates, but he does so inside his own body, not hers.

Neotrogla sex can last for days, so it’s important for the duo to stabilise themselves. The female does it by inflating the base of her gynosome inside the male. It’s covered in patches of tiny spines, which help to anchor her in place for her sexual marathon. You can find similar spines on the penises of many male animals where they provide extra stimulation during sex (as in cats, mice and chimps) or inflict horrendous wounds on the females (as in the seed beetle).

In Neotrogla, the spines are such good anchors that it’s impossible to separate a mating pair without killing the male. As Yoshizawa writes, “Pulling apart coupled specimens (N. curvata; n = 1) led to separation of the male abdomen from the thorax without breaking the genital coupling.” In other words: We tried yanking one pair apart; it didn’t work and the male kinda broke.

See? Spiders are perfectly ordinary, mundane, familiar little creatures. No pegging involved.

It’s a wrap

Portrait of the Fall 2024 semester

The grades for all of my classes, Fundamentals of Genetics, Evolution, and Development, and History of Evolutionary Thought, and Cell Biology lab, and Biological Communication II, have been submitted. I am done. This was not my favorite semester of the 50-some semesters I’ve taught here.

Now I’m getting ready for spring semester — or rather, I have been getting ready. I set up fly stocks way back in early November, I have to do one more generation, and then I set up all the flies for our first lab. Bonus: next semester, I have no classes on Fridays. Three day weekends every week! That might make up for all the grading I’ll have to do in the writing class I’ll be teaching.

The journal Intelligence really needs to change its name

That’s a journal I would never trust — after all, they were responsible for publishing Richard Lynn’s hacky paper on the IQ of nations. Now here’s another example of a terrible racist paper from it. It’s an evolutionary psychology paper by Kanazawa, a terrible combination that ought not to ever pass peer review.

On the basis of his theory of the evolution of intelligence (Kanazawa, 2004), Kanazawa (2008) proposed that, during their evolutionary travels away from the relatively stable and hence predictable environment of evolutionary adaptedness (EEA; i.e., the African savanna of the late Pleistocene), the ancestors of Eurasians encountered evolutionarily novel environments that selected for higher intelligence. Therefore, Kanazawa (2008) predicted higher average IQ scores in countries located farther away from the EEA. Kanazawa (2008) tested this hypothesis against data gathered by Lynn and Vanhanen (2006), who estimated so-called “national IQ-scores,” i.e., the average IQ of the inhabitants of nations in terms of western norms. Kanazawa (2008) found a significant negative correlation between countries’ national IQs and their distance from three geographic locations in and around sub-Saharan Africa.

This is from a paper analyzing the problems of peer review, using Kanazawa’s paper as a case study. That evo-psych paper flew through peer review, with reviewers missing a number of deep problems.

We point to a number of indisputable issues that should have precluded publication of the paper as constituted at the time of review. First, Kanazawa’s (2008) computations of geographic distance used Pythagoras’ theorem and so the paper assumed that the earth is flat (Gelade, 2008). Second, these computations imply that ancestors of indigenous populations of, say, South America traveled direct routes across the Atlantic rather than via Eurasia and the Bering Strait. This assumption contradicts the received view on evolutionary population genetics and the main theme of the book (Oppenheimer, 2004) that was cited by Kanazawa (2008) in support of the Out-of-Africa theory. Third, the study is based on the assumption that the IQ of current-day Australians, North Americans, and South Americans is representative of that of the genetically unrelated indigenous populations that inhabited these continents 10,000 years ago (Wicherts et al., 2010b). In related work by others who share Kanazawa’s (2008) views on the nature of race differences in IQ, the latter issue was dealt with by excluding countries with predominantly non-indigenous populations (Templer and Arikawa, 2006). Thus, although Wicherts et al. (2010b) raised additional issues that may the topic of debate (see below), these three problems are beyond dispute.

I am amused that Kanazawa’s methodology assumed that the Earth is flat and that all peoples ignored geographical obstacles, like mountains and oceans, to make a beeline to their modern location. I am horrified that anyone would use Lynn’s deeply racist and wrong paper to make any estimates of a population’s intelligence. I reject the whole notion of IQ as a useful measure of intelligence in the first place.

The authors propose some changes towards a more open peer review process, which sound good to me. My simpler solution is to simply throw out the whole goddamn journal of Intelligence, along with anyone who publishes in it.

Speaking of flat earth follies, I see that YouTube is in a tizzy because someone is doing something called “The Final Experiment” — a group of people are flying to Antarctica to witness the fact that there is a period where the sun never sets, which ought to be impossible if Antarctica is actually a ring of land surrounding the whole planet. It’s ridiculous. No, flat earthers will find a new excuse and will not be persuaded by a “final” experiment — it’s not as if they reached their beliefs by experiment and reason in the first place, or as if all the other evidence that the earth is roughly spherical were insufficient.

Can you imagine someone proposing a “final experiment” to “prove” that life on earth evolved? I can’t. I know the idiots who are creationists far too well to think that.