Drawing on my work in evolutionary ecology, wilderness ethics, and machine learning, I reflected on the tension between our desire to intervene and our limited ability to forecast long-term ecological outcomes. Using examples like the Chernobyl exclusion zone—where many species are thriving in the absence of people despite nuclear contamination—I argued that ecological recovery is often less about precision intervention and more about restraint. We discussed how machine learning can help us simulate alternative futures and understand potential tradeoffs, but that ultimately, the most powerful conservation tool may be humility. More wilderness, not more control, might be the best way to meet the uncertainties ahead.

Listen to the episode here or wherever you get your podcasts.

I am deep in the Alaskan Arctic,  300 miles from the nearest road system, attempting to conduct the kind of science that usually requires a specialized laboratory. We rowed 30 miles of meandering flatwater today, bringing our total to 200 river miles in 12 days since we landed at a lonely gravel bar on the headwaters of Ambler River in Gates of the Arctic National Park.

Mosquitoes spangle the tent canopy arching over me. Backlit by summer solstice sun, the silhouettes of the insects make an inverted night sky of shifting constellations. The sun never sets on the banks of the Kobuk River this time of year. It hangs high above the horizon even now at 11 p.m., transforming my tent into a solar oven as I, ironically, work to uncover the secrets of a frog that can turn into ice.

… Read the rest of the article here.

During the pandemic, my partner, Bayla, and I began taking daily walks down to Yale’s campus. We often noticed dead birds at the base of the glass walls that wrap the Yale School on Management building when we passed by.

Overlooked casualties of building all-glass buildings. Female and male Ruby-throated hummingbirds with broken beaks, killed by flying into @YaleSOM building. pic.twitter.com/Idl8q0mqWu

— A. Z. Andis Arietta, PhD (@azandisarietta) May 9, 2021

Because we both have working relationships with the Peabody Museum of Natural History, we began saving the bird specimens for the museum’s collection. Through that partnership, we learned that the School of Management building is one of the most lethal pieces of architecture on Yale Campus. We also met Viveca Morris at the Yale Law Ethics and Animals Program who had been helping to organize city-wide bird-strike data collections and spearheading a push to adopt bird-friendly building ordinances in New Haven.

Another @YaleSOM window strike casualty. Yellow warbler.#illustration #watercolour #watercolor #watercolorartist #birdsketch #birdart #deadbird #birdpainting #yellowwarbler #migratorybirds #warblersofinstagram #darkart #baylaart pic.twitter.com/QiX58rc9VX

— Bayla Arietta (@BaylaArt) May 26, 2020

One of the main barriers enacting mitigatory measures at the SOM building was that the lack of hard accounting of the total number of birds killed allowed the administrators of the building to downplay the problem. So, along with Viveca, we began a systematic survey of bird strikes at SOM. I’ll write more about that in a future post.

We also began thinking about the larger picture. How could we get more folks to recognize the magnitude of deaths due to thoughtless architecture? And how could we inspire folks to demand businesses, architects, and municipalities to adopt bird-friend design?

Bayla began painting some of the specimens we found. She posted a painting of five warblers we collected on a single day at SOM. The response was huge. That image seemed to have struck a chord. We realized that art could be a way to simultaneously introduce the topic and inspire emotions toward enacting change.

Bayla contacted Talon and Antler galleries in Portland, Oregon which feature some of our favorite contemporary artists and tend toward natural themes.

They agreed to let us curate a show with us. Over the next few months, Bayla contacted artists whose work fit the theme. In total, 62 artists contributed original pieces to the show titled, “Fractured Aviary”, which hung for the month of June 2022.

If you missed the show, you can see some of my favorites below:

HealingVeronica Steiner watercolor

CrashDarla Jackson plaster, clay, resin, acrylic

Window Strike IBayla Arietta watercolor, gouache, gold leaf

Window Strike IIBayla Arietta watercolor, gouache, gold leaf

Window Strike IIIBayla Arietta watercolor, gouache, gold leaf

The Last Song IIRebecca Reeves hand-beaded ceramic

Yallow WarblersVasilisa Romanenko

Regressive ReincarnationsTeagan White watercolor, gouache, charcoal

The WinoSteve Martinez acrylic, spray paint

In MemoriamMadison Erin Mayfieldgouache

Hollow BonesKatrina Haffner gouache, ink

Caecus VitrumErica Williams ink, gold foil on Bristol

Highway 21 MemorialJay Rasgorshek gouache

Silent DownVeronica Park screen print

Hothouse 3Josie Morway oil, enamel

FracturedBrin Levinson graphite

III of SwordsLauren Marx watercolor, ink, pencil

ImpactMiranda Brandon photo

Fractured Aviary: Ruby-throated Hummingbird-ThroatedHummingbird_04-webJane Kim Kim fabricated this amazing kaleidoscope of glass shards around her hummingbird painting. The dots on the outside represent window glazing patterns to prevent bird strikes.

Fractured Aviary: Ruby-throated HummingbirdKim fabricated this amazing kaleidoscope of glass shards around her hummingbird painting. The dots on the outside represent window glazing patterns to prevent bird strikes.

Broken SpellsJake Messing acrylic

I Am LostKate MccGwire feather

Our chapter tells the story of green frogs and the feral condition of their life with suburban human neighbors. We especially highlight the way that the human built-environment of lawns, pavement, sewers, and septic systems is infused into the biology of green frogs (a topic that Max and Dave have studied in depth). As a counter example, I told the story of the wood frog, a species that has escaped a feral fate by clinging to the remnants of wild space away from humans (a topic I study in depth).

I rarely get to write about wood frogs outside of academic articles, so it was a pleasure to contribute to this piece. I think it is some of my best natural history writing. I’ve excerpted my section below (or, read the chapter):

“To better understand why our housing patterns influence frogs, it is worth taking a frog’s-eye-view of suburbanization. Most frogs exhibit distinct life-stages. Like humans, frogs begin development as shell-less and fragile eggs, but while human embryos float within the protection of a womb, frog embryos are buoyed among the vegetation and flotsam of ponds. The embryos have an umbilical relationship to the water that surrounds them. Nutrients and oxygen easily pass through the transparent jelly and are consumed through delicately branching gills. Any contaminants in the water also suffuse the embryos.
Even before their eyes or mouths have formed, the developed embryos hatch as free-swimming larvae not much larger than a grain of rice. Hatchlings are vulnerable. Thus, frogs hedge their bets by producing hundreds of eggs per clutch, hoping that at least a few will win the lottery of life. Some species, like wood frogs, additionally safeguard their offspring by choosing impermanent pools that are devoid of fish as relatively safe nurseries.

Those hatchlings that survive develop into recognizable tadpoles with bulbous bodies and slender tails. A pond’s version of cows, tadpoles graze along the bottom with scraper-like teeth. They consume algae and detritus along with any solid matter that washes into the pond basin. A long digestive tract allows the tadpoles to incorporate nutrients into a growing body. Where ponds neighbor septic systems, this means that human waste makes up a prodigious portion of a tadpole’s body.

The transition from a tadpole to a frog is a remarkable change. It makes the squeaking voice and acne of human puberty seem like a blessing. Every system in the tadpole’s body transforms. The tail gives way to bony limbs. The narrow, disc-shaped mouth morphs into a wide, insect-capturing, gape. The goggle eyes, so fine-tuned to underwater vision, mutate into something much like our own. Even the long and coiled digestive tract shortens and distends. At the end of this metamorphosis, the aquatic vegetarian leaves the water’s edge and becomes a terrestrial carnivore.

Green frogs are parochial and prefer a pond-side life. For a short time as juveniles they might range far and occupy any standing water from lakes and ponds to swimming pools and tire ruts. Upon adulthood though, they settle along freshwater shores where they patiently wait for dragonflies and other insects to approach within range of a lunging gulp. Since green frogs inhabit permanent ponds, they can breed throughout the summer, and without the threat of the pond drying out from beneath them, their tadpoles can be leisurely in development. When snow falls and the pond freezes, both adults and overwintering tadpoles take refuge deep in the insulating layer of pond muck. Because a green frog’s life is so reliant on a pond, they can survive in just about any permanent water with at least a narrow perimeter of vegetation. As long as a homeowner neglects the tufts of grass along the bank, green frogs are more than happy to remain neighbors.

Unlike green frogs, wood frogs become sylvan nomads after metamorphosis. As their home ponds dry up in the summer and fall, they wander the forest floor hunting among the leaves, only briefly returning to recently filled pools in early spring to breed. During the winter months, wood frogs burrow just under the blanket of leaves dropped in fall. This enables them to be the first out of hibernation as the forest thaws in spring. For these reasons, wood frogs rely on leaf-littered landscapes. Manicured lawns where leaves are regularly raked and bagged make inhospitable places for them. Where the balance of forest gives way to lawns, wood frogs disappear…”

Overall, this was a really fun project to work on that gave me a chance to switch up my writing style. It was also a lot of fun to be able to collaborate with my partner, Bayla, who painted the featured image for the chapter.

The online version of the book is a little counter-intuitive to navigate (I think this was intentionally designed as a rhetorical device), but if you can figure it out, it is worth checking out some of the other cool stories of our feral world!

Among other topics, my lab studies the relationship between forest obligate frogs and urbanization. During a seminar, I once heard my advisor mention that Connecticut is the perfect state for us because the state sits a the top of the rankings for both the greatest percentage of tree cover and highest population density.

I’ve been meaning to dig into that statement for a while, so when Storytelling With Data encouraged folks to submit radial graphs for their July #SWDchallenge, I took the opportunity.

I pulled the population data from the US Census Bureau and used “People per sq. mile” from the 2010 census for density estimates. The tree cover data came from Nowak and Greenfield (2012, Tree and impervious cover in the United States. Landscape and Urban Planning).

Here’s how I made the graphic:

library(tidyverse)

TP <- read.csv("C:\\Users\\Andis\\Google Drive\\2019_Summer\\TreePop\\CanopyVsPopDensity.csv", header = TRUE) %>% select(State, Perc.Tree.Cov, Pop.Den.) %>% rename(Trees = Perc.Tree.Cov, Pop = Pop.Den.) %>% filter(State != "AK")

> head(TP)
  State Trees   Pop
1    AL    70  94.4
2    AZ    19  56.3
3    AR    57  56.0
4    CA    36 239.1
5    CO    24  48.5
6    CT    73 738.1
> 

Here is the dataset. First we rename the variables and removed Alaska since it was not included in the tree cover dataset.

ggplot(TP, aes(x = State, y = Trees)) +
  geom_col()

This gives us a column or bar plot of the percent tree cover for each state. Note that we could also use geom_bar(), but geom_col() will be easier to deal with once we start adding more elements to the plot.

Mirrored bar charts are a great way to compare two variables for the same observation point, especially when the variables are in different units. However, we still want to make sure that the scales are at least pretty similar for aesthetic symmetry. In our case, we will actually be asking ggplot to use the same unit scale for both tree cover and population density, so we need to make sure that they are very similar in scale.

The best option would be to standardize both values of tree cover and population density to a common scale by dividing by the respective standard deviation. The problem comes in interpreting the axis because the scale is now in standard deviations and not real-world units.

For this graphic, I’m going to cheat a little. Since we will eventually be removing our y-axis completely, we can get away with our values being approximately congruent. Since tree cover is a percentage up to 100, I decided to simply scale population density to a similar magnitude.

The greatest Population Density is Rhode Island with 1018.1 people per square mile. We can divide by 10 to make this a density in units of “10 people per square miles” which will scale our range of density values down to 0.6 to 101.8, on par with the 0 to 100 range of the tree cover scale.

> max(TP$Pop)
[1] 1018.1
> 

TP <- mutate(TP, Pop.10 = Pop/10)

> range(TP$Pop.10)
[1]   0.58 101.81
>

Now we can add the population density to the figure. To make this a mirror plot, we just need to make the values for population density negative. Also, I gave each variable a different fill color so we could tell them apart.

TP <- mutate(TP, Pop.10 = -Pop.10)

ggplot(TP, aes(x = State)) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_col(aes(y = Pop.10), fill = "#817d79") 

I’ve always loved the vertically oriented mirrored bar plots used so often by FiveThirtyEight. The problem is that these tall charts can’t fit on a wide-format presentation slide. And it is hard to read the horizontally oriented plot above. I realized that if I could wrap a mirrored bar chart into a circle, it can fit in any format. All that we need to do to make this into a circular plot is to add the coord_polar() element.

ggplot(TP, aes(x = State)) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  coord_polar()

Now we have a mirrored, radial bar plot. But, this is super ugly and not very intuitive to read. This first useful adjustment we can make is to order the states to highlight the comparison we are interested in. In this case, we are trying to highlight the states that simultaneously have the greatest tree cover and highest population densities. One easy solution would be to rank order the states by either of those variables. For instance, we can order by tree cover rank.

ggplot(TP, aes(x = reorder(State, Trees))) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  coord_polar()

But that doesn’t really highlight the comparison because having lots of trees doesn’t really correlate with having lots of people.

ggplot(TP, aes(x = Pop, y = Trees)) +
  geom_point(size = 4, alpha = 0.7) +
  theme_minimal()

Instead, we can directly highlight the comparison by computing a new variable that simultaneously accounts for tree cover rank and population density rank. We cannot simply average rankings because that will produce a lot of ties. Also, if a state has a really low rank in one variable, it can discount the higher rank of the other variable. We can deal with this by using the mean of the squared rank orders of each variable (similar to mean squared error in regression). Also, note that since we want the largest values to be rank 1, we need to find the rank of the negative values.

TP <- TP %>% mutate(TreeRank = rank(-Trees), PopRank = rank(-Pop)) %>% mutate(SqRank = (TreeRank^2)+(PopRank^2)/2) %>% mutate(RankOrder = rank(SqRank))

ggplot(TP, aes(x = reorder(State, RankOrder))) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  coord_polar()

Next, we can improve the readability of the plot. Since our y-axis isn’t technically comparable, we can get rid of the axis label and ticks altogether using theme_void(), then we tell ggplot to label all of the states for us and to place the labels at position y = 100.

ggplot(TP, aes(x = reorder(State, RankOrder))) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  geom_text(aes(y = 100, label = State)) +
  coord_polar() +
  theme_void()

This plot is pretty worthless without some numbers to help us interpret what the bar heights represent. We can add those just as we added the state labels. In order to keep the character lengths short, we need to round the values. Also, now that the scale units are independent, I decided to further scale the population density values to 100 people per square mile simply by dividing the density by 100. The values tends to overlap, so we also need to make the font smaller.

ggplot(TP, aes(x = reorder(State, RankOrder))) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_text(aes(y = 10, label = round(Trees, 2)), size = 3)+
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  geom_text(aes(y = -10, label = round(Pop/100, 1)), size = 3)+
  geom_text(aes(y = 100, label = State)) +
  coord_polar() +
  theme_void()

This looks okay, but we can make it look even better. First we can adjust the limits of the y-axis. We can use the negative limit to create a white circle in the center, essentially pushing all of the data towards the outer ring instead of dipping down to the very central point.

Also, it bothers me that the bars cut into the value labels. We can adjust the position of the labels conditionally so that labels too big to fit in the bar are set outside of the bar using an ifelse() statement.

We can use the same type of ifelse() statement to conditionally color the labels so that those inside of the bars are white while those outside of the bars match the colors of the bars. We just need to include the scale_color_identiy() to let ggplot know that we are directly providing the name of the color.

ggplot(TP, aes(x = reorder(State, RankOrder))) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_text(aes(y = ifelse(Trees >= 15, 8, (Trees + 10)), color = ifelse(Trees >= 15, 'white', '#5d8402'), label = round(Trees, 2)), size = 3)+
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  geom_text(aes(y = ifelse(Pop.10 <= -15, -8, (Pop.10 - 10)), color = ifelse(Pop.10 <= -15, 'white', '#817d79'), label = round(Pop/100, 1)), size = 3)+
  geom_text(aes(y = 100, label = State)) +
  coord_polar() +
  scale_y_continuous(limits = c(-150, 130)) +
  scale_color_identity() +
  theme_void()

The way the state labels are so crowded on the right, but not on the left bugs me. We can set a standard distance, like y = 50, but then conditionally bump out the values if they would interfere with the bar.

And finally, ggplot builds in an obnoxious amount of white space around circular plots. We can manually reduce the white area by adjusting the plot margins.

ggplot(TP, aes(x = reorder(State, RankOrder))) +
  geom_col(aes(y = Trees), fill = "#5d8402") +
  geom_text(aes(y = ifelse(Trees >= 15, 8, (Trees + 10)), color = ifelse(Trees >= 15, 'white', '#5d8402'), label = round(Trees, 2)), size = 3)+
  geom_col(aes(y = Pop.10), fill = "#817d79") +
  geom_text(aes(y = ifelse(Pop.10 <= -15, -8, (Pop.10 - 10)), color = ifelse(Pop.10 <= -15, 'white', '#817d79'), label = round(Pop/100, 1)), size = 3)+
  geom_text(aes(y = ifelse(Trees <= 50 , 60, Trees + 15), label = State)) +
  coord_polar() +
  scale_y_continuous(limits = c(-150, 130)) +
  scale_color_identity() +
  theme_void() +
  theme(plot.margin=grid::unit(c(-20,-20,-20,-20), "mm"))

And there we have it. I made some final touches like changing the font and adding a legend in Illustrator.

I was only able to stay for the day of my talk and missed the award ceremony on the second day. So it was quite the surprise when I visited the Conference’s website to register for this year and saw that I had won an award for the best speed talk!

Check out the video of my talk below:

Or follow this link to the video.

Speciation starts small. The path of divergence starts with minute change in just a handful of basepairs among the billions of bases in a genome. Overtime, these small differences create feedbacks that propagate further divergence.

That’s the idea of sympatric speciation, the emergence of two species out of one. I’m most interested in the very first steps of this process, but catching this kind of small-scale divergence is hard, because the difference are small and easy to overlook. We call noticeable differences within a species polymorphisms. In most cases, we notice polymorphisms that we can see. For instance, it is hard to miss difference in color morphs of chimpmunks. Many of the classic examples of polymorphisms are visually detectable: industrial melanism in moths, beak size in Galapagos finches, stripe and color pattern in Timema stick insects, etc.

 

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It’s been way too long since I celebrated #TaxidermyTuesday All of these specimens are the same species of Eastern chipmunk (Tamias striatus), but two of them have genetic quirks that make their coats either all black (melanistic) or all white (leucistic). #biology #naturalhistorymuseum #naturalhistory #specimen #taxidermy #chipmunk #zoology

A post shared by Andis A. (@azandis) on Mar 6, 2018 at 3:54am PST

But many polymorphisms cannot be detected visually. For instance, polymorphism in dart frogs is often detected by the chemical composition of their skin toxins. Divergence in birds is often diagnosed by the sound of their calls. I’m in the middle of a collaboration to detect possible divergence in clover populations within and outside of cities via cyanogenesis.
The reliance on our human sight to detect polymorphisms is a problem because human sight, while impressive, is very narrowly limited. There is no reason for us to expect that the most relevant variation (from an ecological or evolutionary perspective) in a population would fall within the range of our senses. For instance, there is a whole vision of the world in the ultra-violet frequency that we cannot see. Flowers that all appear a uniform color to you and me can exhibit huge variation in ultra-violet light. Since birds and bees see ultraviolet, it stands to reason that the strongest selection for divergence would occur in this frequency, completely unknown to us.

All of this led me to think about how we, as eco-evo scientists, can start to shift our paradigm to think about the world through the senses of the organisms we study, which would give us a much better ecological picture of the selection pressures maintaining polymorphisms. The first step, is to take one small step outside of our anthropocentric sense and see the world through the eyes of animals. Thanks to the Yale Center for Teaching and Learning, I was able to design an interactive digital project that helps take those first few steps along a Proustian walk.

Below is an example of a comparison between songbird vision and human vision of the same forest habitat. Songbirds have an extra cone-type that allows them to see in ultraviolet. Also, they have about 240 degrees field of view compared to our 190. But, our range of binocular vision is about 40 degrees, fully twice that of songbirds.

These images were made by stacking two separate panoramas composited from about 75 images each. I took one pano in UV and one in visible spectrum, then layered them for a false-color bird’s-eye-view of the world.

Oh, and here is a sweet gif showing UV verses visible light images.

First, here is the happy mother:

I’m so excited! My Robertus tincs are finally calling!!! I just moved the female in with the confirmed male today, so now we just have to hope for true love! #dartfrog #dendrobates #tinctorius #robertus #frog #poisondartfrog #vivarium #amphibian #proudparent #frogfamily

A post shared by Andis A. (@azandis) on Jan 6, 2018 at 1:42pm PST

Day 1:

Here are the first images of the viable eggs, approximately 36-hours after oviposition and Gosner stage 12. At this stage, the embryo has gone through many cell divisions, but if you look closely, you can still make out the individual cells. For the first period of embryonic development, the zygote (fertilized, single-cell eggs) divides into a mass of multiple cells. Around the developmental period in these photos, the cell are beginning to migrate in order to form specific structures in the embryo. The dark indent on the surface, called the blastopore, is where the outer cells are closing in on themselves, like a deflating basketball that is being inverted. As the cells migrate inward, they create cavities that will form the body cavities of the fully formed animal. The blastopore will eventually become the anus, and the inwardly migrating cells will form the lining of the digestive track.

I also thought it might also be interesting to take a look at some of the non-viable eggs that were beginning to decompose. 

Day 3:

Approximately 72 hours, Gosner stage 12. The eggs are still developing. I took a scale shot to give a sense of their size. They measure 3.034 mm (L) and 3.180 mm (R) in diameter, which I estimate makes them about 14.6 (L) and 16.8 (R) cubic mm in volume. It’s worth remembering that, at this point, the embryo is still the same size as when it was a single-cell zygote after initial fertilization, even though it is now comprised of thousands of cells. The cells are dividing, but not growing. In the high magnification photos you can see that the blastopore indent is deforming and elongating. Inside the embryo, cells are beginning to form the notochord which will eventually become the nervous system. Although it doesn’t look like much, most of the structural components of the major life systems are already in place.

Day 5:

The embryos have elongated, measuring are 4.48 mm and 4.54 mm in length, almost 50% longer than yesterday, but the total mass should be about the same.

Gosner stage 18. The embryos developed a lot in just the last 48 hours. The embryos blew right through the end of gastrulation and into neurulation before I got these photos. So unfortunately, we missed the development of the neural plate, neural folding, and embryo elongation. As an overview, in the last photos the embryos were at the end of gastrulation. The cells had differentiated into cell layers, dividing the embryo into the ecotoderm (outer cell layer, eventually forming the skin, teeth, and most of the nervous system), mesoderm (middle cell layer, eventually forming most of the skeleton, internal organs, and muscles), and the endoderm (inner cell layer, eventually forming the lining of internal body cavities like the digestive track and lungs). So, at the end of gastrulation, the future fate of all cells were set, but the embryos still looked just like a ball of cells. Neurulation follows gastrulation, and as the name suggests, is characterized by the development of the proto neural system. These neural cells begin to migrate outward and develop ridges that will fold in on themselves during creation of the neural tube (which will eventually form the brain and spinal cord). (Since I didn’t capture a photo of the tinctorius eggs at this stage, I’ve include an example of a wood frog embryo at this stage as an example.)

As neurulation continues, the embryo starts to elongate and look more like a tadpole. By the later stages of neurulation (as in the photos today) most of the organ systems are fully established.

You can also see the very large yolk. Unlike bird, mammal, and reptile embryos, amphibian yolks form internally as part of the digestive track. Dendrobates eggs have much larger yolks than other frogs due to their particular larval ecology. In the wild, tinctorius eggs are deposited terrestrially, but the larvae are aquatic after hatching and require water immediately. So, these frogs have evolved a parental care strategy wherein the male attends the eggs, and upon hatching, transports them to a larger pool. The rearing pool can be hundreds of meters away from the egg site, and may take multiple days of transport. The large yolk ensures that the tadpoles will be hardy enough for the trip. Being hardy also helps the tadpoles once they are in the rearing pool since tinctorius larvae are cannibalistic.

You’ll also notice that the membrane around the embryo has expanded and is more pronounced. This called the vitelline membrane and it is analogous to the membrane surrounding the yolk in a chicken egg, the one that keeps a sunny-side-up egg from becoming a scrambled egg. Since tincortius eggs are laid out of the water, this membrane (along with the jelly layer) helps prevent drying.

Day 6:

Gosner stage 19. We have gill buds! Those little nubbin-wings on either side are the sprouts of tiny gills. Up to this point, the cells of the embryo have been able to diffuse oxygen without special structures. But as the cells proliferate and some cells are buried deep within the developing embryo, simple diffusion can’t cut it. Over the next two or three days, the gills and circulatory system will take form and start pumping oxygenated fluid throughout.

Day 7:

Gosner stage 20. The gills are elongating and the simple heart, which is basically just a tube at this point, is pumping blood cells through the limited circulatory system.

Day 8:

Gosner stage 21. The gills have formed almost to their external extent.

Tinctorius eggs are laid in oxygen poor conditions compared to many other frogs. As such, they have developed extremely long and filamentous gills compared to the “average” anuran. The greater the surface area of the gills, the more time there is for Co2 and O2 to diffuse across the lining of the gills to the jelly and, after hatching, to the water. If you look closely in the video, you will see the rhythmic expansion and contraction of the embryo. That’s the heart pumping. In the last portion of the video, you should be able to see individual blood cells flowing through the gills in time with the heartbeat.

Also notable at this point is that the nervous system is developing quickly, both the brain itself and the sensory organs. The proto-eye, while not externally visible, is developing as an outgrowth from the brain.

Stay tuned! The embryos are developing quickly and could hatch any time in the next few days!

Day 9:

The gills continue to branch and elongate. By this point, I think the heart has developed into two chambers, a huge architectural achievement from its origin as a single tube.

A caveat: it is worth mentioning at this point that my descriptions of developmental timing of internal organs are based on “average” anuran development. Not a lot of research has been conducted on dendrobatids, so most of these descriptions reflect ranid development. This is most clear in my attempts to assign Gosner stages to the embryos, as the ranid timing doesn’t sync entirely. Where research has been carried out, I try to give the specific description. 

Day 10:

The gills are still growing, but should be reaching about their maximum extent. Soon, the gills will begin to atrophy and the animal will switch to internal respiration.

The eyes are just beginning to appear.

The embryonic eye forms as an extension of the developing nervous system that grows outward from the neural tube. As it reaches the surface of the embryo, the optic stalk differentiates into the component cell types of the eye. At this stage, the tip of the optic stalk at the skin surface is forming into a cup-like shape. In the coming stages, that cup deepens and widens. At the same time, the lens begins to form across the “rim” of the cup from the ectoderm. As the eye progresses, the lens becomes more “lens shaped” and the skin covering the eye becomes the cornea. If you are interested in learning more about the development of the anuran eye, I would suggest checking out Thomas Reh’s lab webpage.

Day 11:

Today the eyes are well-along in development and obvious.

I outlined the formation of the eye yesterday, but I thought it would be good to also include a diagram of the formation.

To give you a sense of where the embryos’ eyes are heading, below is a close photo of a fully formed larval wood frog eye.

Day 12:

One of the embryos hatched today! The vitelline membrane is ruptured; however, the hatchling remains in the jelly and has not fully liberated itself. In the photo above, the animal on the right is the hatchling.

You’ll notice that the gills have begun to atrophy and shrink. As the heart becomes more efficient and the circulatory system grows, the distribution of oxygen to the body systems requires less surface area for gas exchange with the water. Also around this time, the primitive red blood cells of the early embryo transition into more efficient larval type red blood cells. Interestingly, there are a total of four generations of blood cells from embryo to adult. The cells change in shape, size, and even blood-type over the course of development. Even the organs producing blood cells shifts from kidneys, to the liver, and on to the spleen and bone marrow in adults.

Day 13:

Both of the embryos have hatched out of the vitelline membrane, but remain in the egg jelly. They are very active and respond to movement and light. The gills have diminished quite a bit as the respiratory system switches to internal respiration. The eyes, while still covered by the outer skin layer, look much like a completed larval eye.

Day 14:

One of the hatchlings was deceased when I checked on it this morning. The tissue still looked pretty good; so I fixed it in a formalin solution to preserve its form.

The cornea is almost entirely transparent and the gills have almost complete atrophied. From this point on, the larva will assume the classic tadpole/pollywog body plan that is most familiar of anuran larvae.

References:

Hill, R. W., Wyse, G. A., and Anderson, M. (2016). Animal Physiology. 4 edition. Oxford University Press.

McDiarmid, R. W., and Altig, R. (2000). Tadpoles: the biology of anuran larvae. University of Chicago Press.

Rojas, B. (2014). Strange parental decisions: Fathers of the dyeing poison frog deposit their tadpoles in pools occupied by large cannibals. Behav. Ecol. Sociobiol. 68, 551–559.

Vences, M., Kosuch, J., Lötters, S., Widmer, A., Jungfer, K. H., Köhler, J., et al. (2000). Phylogeny and classification of poison frogs (Amphibia: dendrobatidae), based on mitochondrial 16S and 12S ribosomal RNA gene sequences. Mol. Phylogenet. Evol. 15, 34–40.

Vitt, L., Vitt, L., and Caldwell, J. (2013). Herpetology: an introductory biology of amphibians and reptiles. 4th ed. Academic Press.

Wells, K. D. (2010). The Ecology and Behavior of Amphibians. University of Chicago Press.

Weygoldt, P. (1987). Evolution of parental care in dart poison frogs (Amphibia: Anura: Dendrobatidae). J. Zoolog. Syst. Evol. Res. 25, 51–67.

An article I wrote along with Lisa Ronald and Bob Dvorak about perspectives on the future of Wilderness stewardship is out in the International Journal of Wilderness. This piece is a sort of wrap-up for the Millenial track at the 2016 National Wilderness Workshop that I helped to organize.