Spring 2020

Decided to record some of the lovely spring that is taking place in the northeastern US (mostly in Prospect Park and Park Slope).  

April 2020

The Importance of Being Warm

The darker side of pronghorn life: sibling rivalry in the womb

One pronghorn embryo piercing another

On Mother's Day, Montana Public Radio aired my field note on siblicide among pronghorn embryos in utero, and I was on the Rocky Mountain front near Choteau, watching a pronghorn that had just given birth to one fawn.

The umbilical chord was still dangling from both, and we watched for over an hour as the fawn struggled to stand and suckle for the first time.

The mother seemed quite uneasy about all the traffic on Bellview Rd and after lying down and getting back up several times, led her first fawn away from the road, probably to find a more private spot to deliver number two. We left her in peace so didn't watch the second little horror arrive.

The very next day, on the same road, we saw a female pronghorn with two young fawns.

A week later, on the National Bison Range, the pronghorn there are no newborn pronghorn in sight, as their mothers have probably hidden them among the brilliant yellow arrowleaf balsamroot.

Yearling and adult female pronghorn among the arrowleaf balsamroot

Ellie

Our new dog, a rescue. Named after Eleanor from Sense and Sensibility, though after knowing her for two weeks, Marianne might have been more appropriate.

Cheyanne

Reference illustrations for a book on evolution

Cuckoo hosts

 

Primate phylogeny pictures

 

Birds and mammals of Montana

Gyrfalcon at Deer Lodge

  

Red-shafted flickrs

American three-toed woodpecker seen on Lolo

Male spruce grouse on Lolo

Sperm and chromosomes competing

The mouse Y chromosome has recently been revealed, and its content is strikingly different from the handful of other mammalian sex chromosomes sequenced so far. I have written about how the many recently acquired, repetitive DNA sequences in the mouse Y are signatures of a evolutionary arms race with the X chromosome. In short, both the Y and X chromosomes in the house mouse genus have 50-100 copies of the same three sets of genes, because the copies on the X are "drivers" that exclude Y chromosomes from the next generation, while copies on the Y are "suppressors" that defend the Y chromosome.

This is a classic instance of one of my favourite evolutionary phenomena with the unfortunate, clumsy names, "meiotic drive" and "segregation distortion". The reason drive is so compelling is that it is the archetypal result of selfish genes in action, and the perfect example to trot out when explaining that selection does not act "for the good of the species", or sometimes, for the good of the individual.

From the viewpoint of a driving allele (a particular version of a gene) on the X chromosome, genes on the Y chromosome are a waste of space. A good way to double its fitness, would be to make sure none of the Y chromosomes get into sperm, so all the offspring of a male with this driving allele will be daughters (because he would only make sperm with X chromosomes). This is no good for the Y chromosome, and it seems to have solved the problem by acquiring genes that resemble the driving X copies enough to suppress them. An arms race of more driving X copies and more defending Y ensues.

The other cost of a driving allele, whether it is on the X or some other chromosome, is that the male carrying this allele will be making much less sperm than males without the rogue gene. Essentially, his sperm making efficiency is being compromised by these selfish genes because sperm that don't carry them don't make it to the next generation.

If all males had exclusive access to their mates, this wouldn't be much of a problem, since even half their sperm would be more than enough to fertilise eggs. However, most female mice are likely to mate with more than one male, so sperm competition would select for males without driving alleles because they would have more sperm than males handicapped by internal genomic conflicts.

One prediction that arises from this, is that one should see more signs of an arms race between genes on the X and Y chromosomes in species with less sperm competition. In other words, more repeated copies of the driver and suppressor alleles on both sex chromosomes -- a phenomenon known as co-amplification. The sex chromosomes of three mouse species in the Y chromosome paper do indeed vary in composition and size, but it isn't clear how much sperm competition varies in these species. Furthermore, mating systems are notoriously variable and evolve rapidly, so they might not generate a steady enough selection pressure to detect clear differences in co-amplification between conflicting sex chromosomes.

References:

Soh, Y. Q. S., Alföldi, J., Pyntikova, T., Brown, L. G., Graves, T., Minx, P. J., … Page, D. C. (2014). Sequencing the Mouse Y Chromosome Reveals Convergent Gene Acquisition and Amplification on Both Sex Chromosomes. Cell, 159(4), 800–813. doi:10.1016/j.cell.2014.09.052

Inspired by Beatrix Potter

The Morgan Library in New York is currently showing some fabulous letters and art by one of my greatest heros, Beatrix Potter. Potter was especially fond of rabbits, and two of her pets, Peter and Benjamin are the inspiration for her most famous story, "The Tale of Peter Rabbit".

As a testament to the power of artificial selection, rabbits like the Flemish giant can weigh up to 20kg (about 50 pounds).

Flemish Giant Rabbit

Beach mice are subspecies of oldfield mouse (Peromyscus polionotus) that have evolved pale fur to match the pale sand they live on. Hopi Hoekstra and her lab have worked out exactly which mutations in which genes are responsible for this adaptive colouration.

Choctawhatchee beach mouse (Peromyscus polionotus allophrys)

As a Victorian, Potter wouldn't have seen these North American mice in the genus Peromyscus, but I think she would have liked them, with their enormous eyes and relatively infantile proportions.

Animal Acknowledgements

To all who helped, directly and indirectly in producing Dr. Tong, THANK YOU!

A subset of people are depicted below, sans surnames: