Two excellent things about the spotted snow skink

Carinascincus ocellatus, the spotted (or ocellated) snow (or cool-) skink is very small and inconspicuous and hangs out on an out-of-the-way island — Tasmania, way down south — but offers two excellent things for us to enjoy:

— the name spotted snow skink, an /s/-alliterative double trochee (SW SW) that lends itself to satisfying repetition as a found mantra

— the occasional individual that’s sexually discordant — of one sex anatomically (and reproductively), but the other sex genetically (for these skinks, anatomically male but genetically female); the change in anatomical sex during incubation (for these skinks, associated with temperature then) is attested in some oviparous (egg-laying) fish, amphibians, and reptiles, but not, until recently, in a viviparous (live-bearing) creature. Most lizards are oviparous, but Carinascincus ocellatus is viviparous, so it’s a new frontier in sexual discordance.

There turns out to be quite a lot to say about this little creature; bear with me as I wander, pretty much aimlessly, over a large intellectual landscape.

Saying it over and over. (There’s a Page on this blog on postings about chants, cheers, mantras, and onomatomania.) Savoring it. The phrase spotted snow skink is a double trochee, SW SW, and therefore well suited to serve as a chant or a mantra through repetition — like (to choose from examples that have previously come up on this blog):

bathtub jet ski – vampire manga – turtle-headed – cosmic catnip – alpine scratcher – goon squad goon squad

On the creatures. We start with skinks in general. From Wikipedia:

Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Skinks are characterized by their smaller legs in comparison to typical lizards and are found in different habitats except arctic and subarctic regions.

And from NOAD:

noun skink: Zoology. Originally: a small lizard, Scincus scincus (family Scincidae), common in northern Africa and the Middle East, and formerly regarded as having medicinal value. In later use (frequently with distinguishing word): any lizard of the large family Scincidae, the members of which occur throughout warm regions of the world and are typically adapted for burrowing, with smooth shiny scales, limbs that are small or absent, and elongated cylindrical bodies with tapering tails.

OED3 (Sept. 2009) on the noun skink supplies the not very illuminating etymology:

< classical Latin scincus (Pliny) < Hellenistic Greek σκίγκος, probably a loanword.

On to the spotted snow skinks (under various common names. Starting with the genus, from Wikipedia:

Carinascincus is a genus of skinks (family Scincidae), commonly called snow skinks or cool-skinks  and residing mainly in Tasmania or Victoria, Australia. … These skinks have adapted to the cooler weather of southern Australia and particularly Tasmania, hence the common names.

NOAD on the carina of Carinascincus:

noun carinamainly Biology a keel-shaped structure.

And going on to the species, first noting this NOAD entry:

adj. ocellated: (of an animal) having eye-like markings. [despite its spots, the ocelot is etymologically irrelevant: ocelot: late 18th century: from French, from Nahuatl tlatlocelotl, literally ‘field tiger’ (NOAD)]

Then, again from Wikipedia:

(photo: Donovan Klein / Alamy)

The spotted skink (Carinascincus ocellatus), sometimes called the ocellated cool-skink or ocellated skink, is a skink endemic to Tasmania, Australia. It is a ground-dwelling, viviparous species [most lizards are oviparous], usually found in rocky habitats, and widespread in the northern and eastern parts of the state, as well as in the eastern Bass Strait islands. It is often found at Arthurs Lake in the Central Highlands of Tasmania.

Spotted skink populations are distributed along an altitudinal gradient, with variations in thermal conditions along the gradient affecting body temperature regulation and reproductive activity. Skinks in low to mid altitudes achieve their optimal body temperature year-round and predominantly undergo vitellogenesis [the process by which a yolk is formed and accumulated in the ovum] and ovulation in spring and gestation in summer, while skinks occupying higher, subalpine altitudes struggle to maintain their preferred temperature in the autumn months, and typically undergo ovulation and parturition [giving birth] one month later than other members of the species.

The Tasmanian government site on wildlife management, about the spotted skink, also notes the altitude variability:

Spotted skinks have a head and body length of 34-74 mm. [ca. 1.3 – 2 in.] Specimens from higher altitudes are as much as a third larger than those from coastal environments.

The hot Tasmanian news of 2022: sexual discordance. From New Scientist issue 3390, “Lizard can switch from female to male before birth, but not vice versa: Some offspring of the spotted snow skink, a lizard found in Tasmania, are born anatomically male but are genetically female” by Christ Lesté-Lasserre, on-line on 6/1/22; “Sex change seen in live-birth animal”, in print in the 6/11/22 issue:

A lizard from Tasmania is the first non-egg-laying animal known to sometimes switch sexes before birth, depending on the surrounding temperatures.

Some egg-laying fish, frogs and reptiles hatch with male sex organs and female chromosomes, or vice versa, when the eggs are exposed to environments that are particularly warm or cool, indicating that their sex changed during incubation.

Now Peta Hill at the University of Tasmania and her colleagues have found the same is true of the spotted snow skink (Carinascincus ocellatus), a lizard found in Tasmania that gives birth to live young.

The researchers trapped 100 newly pregnant female spotted snow skinks at different altitudes in Tasmania and placed them in individual terrariums in their laboratory.

Two groups of 20 skinks had access to a heat lamp over part of the terrarium for either 4 or 12 hours a day, creating temperature zones ranging from 20 to 37°C and falling to around 10°C when the lamp was off. The remaining three groups lived in controlled temperatures of either 33°C, 29.5°C or 26°C for eight hours a day and 10°C for the other 16 hours.

The researchers sexed each newborn skink by examining its sex organs in the first month of life. They also assigned genetic sexes by sequencing DNA taken from the animals’ tails.

All the skinks with female sex organs had XX chromosomes – meaning there were no male-to-female changes. However, 7 per cent of the 423 newborn skinks had male sex organs and XX chromosomes.

These skinks were mostly found in litters in the cooler terrariums and born to females from lower altitudes. Specifically, 20 per cent of the offspring with male sex organs and XX chromosomes were born to females from low altitudes that were in the 26°C terrariums or offered only four hours of heat lamp per day. That was the case for only 2 per cent of the offspring born to females from low altitudes kept in warmer conditions.

The findings are “striking” not only because they are seen in a live-bearing reptile, but also because the phenomenon is so one-sided, says Benjamin Geffroy at the French Institute for the Exploitation of the Sea in Montpellier, who wasn’t involved in the study.

Even so, that might be explained by a generation effect, says Geffroy. Skinks with male sex organs and XX chromosomes – “XX males” – can grow up as functional adult males and might mate with XX females, he says. But because they lack a Y chromosome, all the pair’s offspring would be XX.

“I find it really interesting that we can explain the… bias toward females in warm conditions, if we consider that some XX males reproduce with XX females, leading to more genetic females in the second generation,” he says. A longer study over multiple generations could help support the theory, says Geffroy.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2022.0689

The SGO world, and “sex at birth”. From my 6/19/22 posting “Extended cisgender”, about the the SGO properties (sexual identity, gender identity, sexual orientation):

— sexual identity, or SEX for short (sometimes, alas, referred to as gender): the primary subcategories of SEX are FEMALE and MALE

— gender identity, or GENDER for short: the primary subcategories of GENDER are FEMININE and MASCULINE

— sexuality, or sexual orientation, ORIENTATION for short: the primary subcategories of the category ORIENTATION are SAME-SEX and OTHER-SEX

The default settings:

— default SEX aligns with birth sex; cis(gender) means ‘having default SEX’

— default GENDER aligns with SEX (FEMININE with FEMALE, MASCULINE with MALE)

— ORIENTATION is, by default, OTHER-SEX

All of this apparently concerns psychological or cultural constructs (but see below), but the midst of this discussion appears: “default SEX aligns with birth sex”. And now we know that “birth sex” for human beings is a complex matter, both anatomically and genetically. A variety of types of genitally intersex infants have been observed (and the history of their treatment has many sorry chapters). At the same time, we now know there’s a variety of genetic types, not just XX and XY (and these don’t align well with the anatomical variants). And then we need to face up to the evidence that some of the SGO categories too have an epigenetic or genetic substrate and should probably just be treated as stable minority variants.

But in viviparous creatures like human beings, it’s generally assumed that all this variation in kinds of sex follows from random genetic and epigenetic variation — that in particular there are no systematic associations between aspects of the prenatal environment and this variation in sex, though such associations are common in oviparous creatures. Now comes the spotted snow skink of Tasmania to make us wonder about all of it.


2 Responses to “Two excellent things about the spotted snow skink”

  1. Robert Coren Says:

    Now I want to see Zippy chanting “Spotted snow skink” over and over.

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