Remember those Short-Tailed Opossum (Monodelphis domestica) neonates from last week?  After some chemical treatments, the specimens were frozen into a cutting compound, and then sectioned into 300 micron (0.01 inch) thick slices on the cryostat.  Here are three slices from the same animal.  The sagittal sections (parallel to the midline that divides the body into right and left halves) show all sorts of wonderful details such as the chain of the vertebral column in white, developing bones of the skull, liver, gut, eye, and tongue.  These sections look amazing, but they are not done yet!  Come back to find out what happens next.  Image credit: Curious Sengi.



A pair of Short-Tailed Opossum (Monodelphis domestica), 14 days postnatal.  Note the presence of hairs and whiskers on the face as well as the bones ossifying in the fore and hindfeet.  Image credit: Curious Sengi.

Greetings, fellow Snurflers!

We have now entered that season during the academic year when many of us are facing great hurdles:  qualifying exams and dissertation defenses.  I will be presenting my research proposal at quals in a few weeks and I wanted to share some of the images from my work with you.

My research on the evolutionary origin and subsequent modifications of facial muscles in mammals involves a lot of comparative morphology:  looking at a wide range of animals (including non-mammals) to piece together a picture of what is old and what is novel, ancestral and derived, conserved and innovative, and what is just plain weird.  I am using techniques and ideas from developmental biology to show the spatiotemporal sequence of how facial muscles grow and differentiate in different embryos, but to also shed light on some key processes behind the question of why muscles grow over the faces of mammals, but not in animals like reptiles.

At the moment, I am working a lot with the embryos and neonates of the Brazilian Short-Tailed Opossum (Monodelphis domestica), a marsupial that is increasingly being used as a model organism in laboratories.  The images here are of young opossums, collected 14 days after birth.  Like all other marsupials, gestation time is short and the babies are born in an extremely underdeveloped state where they are essentially all just forelimbs and a mouth.  Now a few weeks after birth, these little guys are starting to look much more like recognizable animals.

These photographs were taken after the specimens were bleached into a ghostly white.  There are more steps ahead before we can visualize the development of facial muscles.  See what happens next in our following posts!

Image credit: Curious Sengi.

Bunny Surprises

Bunnies are hiding more than just Easter eggs. . . . . . Image credit: Wikimedia Commons.

The ubiquitous presence of rabbits in North America and Europe has percolated this cute, fluffy animal into the Western popular imagination.  Rabbits are carrot-nibbling vegetarians.  They are timid.  And bunnies must be boffing continuously, given their prolific fecundity.

Let’s take a closer look through three vignettes that shed slightly different light on these animals.

Not a bad mom, just a bad day

Rabbits do, in fact, breed like rabbits.  The Common Rabbit (Oryctolagus cuniculus) gives birth to an average of 5 to 6 young after a gestation of about a month.  Though the young are altricial — born with eyes closed, pink, and in need of intensive parental care — the female is ready to mate again a few hours after giving birth.  Under ideal conditions, a female can potentially have anywhere from 5 to 7 litters per year.  However, conditions are rarely ideal.  It is estimated that at least 60% of all O. cuniculus pregnancies are aborted, with the embryos simply resorbing back into the mother’s body (Macmillan Illustrated Animal Encyclopedia 1984; Nowak 1999).

Recently-born rabbits, or kits, peeking out from their fur-lined nest.  Image credit: Ruth : ) via Flickr.

Even under optimal conditions in captivity where there is ready access to nutritious food, water, and nesting material, things do not always go according to plan.  In a study of wild O. cuniculus kept in enclosures, researchers noted that about 13% of all litters experienced neonatal cannibalism, where the mother purposefully killed and consumed her newborns.  (It should be noted that neonatal cannibalism not uncommon amongst mammals.)

The authors of the study concluded that this behavior was most likely triggered by stressful conditions, in this case, placing wild animals into a confined space.  Stress during the time leading up to the birth of the young causes something along the hormonal-neuronal pathway to be disrupted, thus failing to trigger the onset of maternal behavior.  The warning signs were a failure of the mother to construct a proper nest from grasses and especially the lack of nest lining made from the mother’s own belly fur.  Neonatal cannibalism seems to be dependent on specific circumstances.  This behavior destroys an entire litter, but when conditions improve, cannibalistic mothers are perfectly capable of populating the world with their progeny (Gonzalez-Redondo & Zamora-Lozano 2008).

Attack of the “Killer Rabbit”

Back in 1979, the United States was facing another sort of crisis of confidence in its president, Jimmy Carter.  It was a tumultuous time for many people and as the nation looked towards their elected leader for hope, they were hit with a different vision entirely:  the president sitting in a fishing boat on a quiet Georgia lake, flailing an oar at a crazed rabbit swimming towards him (O’Grady 2014).

President v. rabbit, with the President finally gaining the upper hand.  Image credit: Jimmy Carter Library and Museum via WNYC.

It took no time for the public and Carter’s political detractors to latch onto this story of the “killer rabbit”, pointing out that a leader nearly bested by a little bunny had no place handling serious affairs on the world stage (O’Grady 2014).  But let’s step back for a moment and focus on the biology here.  Carter was most likely accosted by a Swamp Rabbit (Sylvilagus aquaticus), which is found inhabiting marshes and wetlands of the southern U.S.  S. aquaticus is particularly adept at swimming and diving, often taking to the water when pursued by predators or traveling to new feeding areas.  This species is amongst the largest of the cottontail genus, robustly-built and “large-headed” (Macmillan Illustrated Animal Encyclopedia 1984).  The rabbit is generally docile, but it is a territorial animal (Nowak 1999) and confrontation between males can result in vicious fights that leave serious wounds (Macmillan Illustrated Animal Encyclopedia 1984).  Though it is highly unlikely the creature was intentionally going after the President, a swimming rabbit making a chance encounter with one of the most powerful people in the world was just too good to resist.

Expectation:  the killer Rabbit of Caerbannog from “Monty Python and the Holy Grail”.  Reality (at best):  a chance encounter between the Commander-in-Chief and a local Swamp Rabbit doing what Swamp Rabbits do, which is swim and maybe feel a little bit territorial.  Image credit: Wikipedia.

Back to blood

“Are carnivorous rabbits possible, anywhere?  No, this is a theoretical absurdity.”  

(Seddon 1972, quoted in Clauss et al. 2016)

How it’s supposed to be. . . .right?  Image credit: via Pexels.

Rabbits are iconic vegetarians.  It had long been assumed that anything other than herbivory was physiologically impossible.  The lack of carnivorous teeth and a digestive system unadapted to processing meat makes this seem obvious (Clauss et al. 2016).  But we did see instances of neonatal cannibalism in our first vignette.

Clauss et al. 2016 report on two domestic dwarf rabbits that were kept in a mixed-species enclosure at a Swiss raptor rehabilitation center.  Over a 9 month period, these two rabbits shared their home with a variety of kestrels, kites, buzzards, and other birds of prey. . . . as well as a shared taste for meat.  While the rabbits were amply provided with fresh vegetarian fare, the raptors were offered whole mice, rats, and day-old chicks.  The rabbits did not neglect their own food, but were drawn to the meaty offering, even chasing birds away from the food.  The authors noted that the rabbits

. . . used a gnawing ingestion style with the extremities of day-old chicks and rodent tails.  When the caretaker brought the daily prey ration for the raptors, the rabbits immediately ran towards the person and followed him even when the dish was placed on an upper perch, where they had to climb a ladder-like staircase (Clauss et al. 2016).

It is like some kind of Easter gathering gone horribly wrong.  These domestic carnivorous rabbits reportedly had neither a favorite prey item nor seemed to suffer any ill-effects from consuming meat.  Image credit: Clauss et al. 2016.

The question is whether this represents some kind of pathological behavior.  An increasing body of observations of presumably exclusive herbivores consuming carcasses and small animals seems to indicate that this is within the realm of natural activity.  If anything, these instances of carnivory were driven by opportunity.  Under usual circumstances, it is unlikely that a rabbit would remain out in the open, gnawing away at a carcass when it was in danger of meeting the same fate from predators.  But in the safe environment of the enclosure (incidentally, the rehabilitating raptors did not pose a threat) the rabbits were at leisure to engage in some casual carnivory (Clauss et al. 2016).

There is so much more to say about rabbits and their relatives than I have time for right now.  But I hope this little trio of information has sparked your interest in these unassuming, yet utterly surprising animals!


Clauss, Marcus, Andreas Lischke, Heike Botha, & Jean-Michel Hatt.  2016.  “Carcass consumption by domestic rabbits (Oryctolagus cuniculus).”  European Journal of Wildlife Research 62:  143 – 145.

González-Redondo, P. & M. Zamora-Lozano.  2008.  “Neonatal cannibalism in cage-bred wild rabbits (Oryctolagus cuniculus).”  Archivos de Medicina Veterinaria 40:  281 – 287.

Macmillan Illustrated Animal Encyclopedia.  1984.  Philip Whitfield, ed.  New York, NY:  Macmillan Publishing Company.

Nowak, Ronald M.  1999.  Walker’s Mammals of the World, Vol. II.  6th edition.  Baltimore, MD:  The Johns Hopkins University Press.

O’Grady, Jim.  “How Jimmy Carter’s Face-Off with a Rabbit Changed the Presidency.”  WNYC .  New York Public Radio, 17 February 2014.  Web.  Accessed 15 April 2017.

One Year of Curious Sengi

Image credit: Black and Rufous Sengi (Rhynchocyon petersi).  Philadelphia Zoo / Curious Sengi.

Thanks for reading Curious Sengi!

Let’s keep snurfling and discovering all sorts of wonderful things about the living world around us.  I look forward to sharing what I find with you!