Category: animal behavior

Does a split jumping spider, half male and half female, behave as a male, a female, or both?

September 25, 2020 • 9:30 am

Occasionally in some species—mostly insects—we see the phenomenon of gynandromorphs: individuals that, through a genetic or developmental accident, have parts of the body that are male, and other parts that are female. They are patchworks of sex. These are most easily spotted in insects, but may have been missed in other species (alternatively, gynandromorph insects may be more viable than, say, gynandromorph mammals or birds, though I have posted on a gynandromorph cardinal). The various posts I’ve done on gynandromorphs are collected here.

Five years ago Matthew and I wrote a post about how gynandromorphs are formed, something well known genetically in our fruit flies (Drosophila). Using special genetic tools, we can also produce gynandromorphs at will.  This involves a special X chromosome that gets lost easily during cell division. If you put one special X in females (XX), the tissues in which the X gets lost become XO, which happens to be male tissue, though XO males are sterile. The chromosome loss can happen at various stages of development, so you can get flies split straight down the middle (if the X gets lost at the first cell division), or flies with various-sized patches of male and female tissue.

Here are a few examples from flies (white bits are XO male parts and shaded are XX female parts). Note that the upper-left fly is split straight down the middle. I’ve seen a few of these in my time.

Finding gynandromorphs in nature is rarer, as wild insects are small, mobile, and not easily inspected. But the researchers on the paper below, published in The Science of Nature, found a gynandromorph jumping spider whose right half was male and left half was female. This is easily seen (given that the spiders are tiny: 4-6 mm, or 0.15-0.25 inches), for the spiders are sexually dimorphic, with the males having much larger fangs and chelicerae (mouthparts) than females, as well as different pedipalps (“palps”), distal segments of the legs that serve not only for sensory detection, but also for courtship display and sperm transfer in males.

Having a live spider whose right half is male and whose left half is female immediately gives you the chance to answer a question: “Does this weirdo spider behave as a male, as a female, or both?” This is the question that the researchers answered in the paper below.

You might be able to access the article by clicking on the screenshot, as it’s free with the legal UnPaywall app. The pdf is here and the full reference is at the bottom of this post. If you can’t get the pdf, make a judicious inquiry.

The jumping spider Myrmarachne formicaria is palearctic, and has been introduced in the U.S. The authors found one gynandromorph  in Japan in October of 2016, as well as a bunch of normal males and females, which could be used to test the sexual/antagonistic behavior of the gynandromoprph. Here’s what it looked like (see caption below). The very large fangs and chelicerae can be seen on the spider’s right—the male side, as they’re much larger in males than in females. (We don’t know how this individual came about, though I suggest one way below.)

(From paper): External morphology of a Myrmarachne formicaria gynandromorph (a–d) and normal individuals (e, f). a Dorsal view; b ventral view; c enlarged dorsal view of gynandromorphic chelicera; d enlarged ventral view of gynandromorphic chelicera; e enlarged ventral view of normal male chelicera; f enlarged ventral view of normal female chelicera. Scale, 2 mm (a, b); 0.5 mm (c–f)

And the palps were also different on the two sides, for the male palps—the spider equivalent of a penis—differ from those of females. (a) shows the ventral view of the right palp in the gynandromorph, and (b) the ventral right palp of a normal male. As you see, the right palp is male, designed to hold sperm. The left palp of the gynandromorph (c) is identical to a normal female palp (d). Females receive sperm in the genital area (“epigyne”), put there by the male’s palps.

The genitals were also split down the middle, with the gynandromorph having a normal female epigyne (the female genital opening that receives sperm) on the left side (e), with a normal female shown in (f), while the right side of the gynandromorphs (arrow) is screwed up, as males don’t have epigynes.

(From paper): Sexual organs of the gynandromorph (a, c, e) and normal individuals (b, d, f). a, b Ventral view of the right palp; c, d ventral view of the left palp; e, f epigyne. The white arrow indicates the spermatheca at an abnormal position. Scale, 0.1 mm

So we have a spider split straight down the middle, from fore to aft. This may have involved the loss of a chromosome in an original female zygote, as normal female spiders are XX and males X0, lacking a Y chromosome. If an XX female zygote lost one X chromosome at the first cell division, one half of the spider would be female (XX) and the other half male (X0), and it could be split down the middle, as this one is. There are other explanations, but this seems the most likely.

So how did this gynandromorph behave—as a male or a female?

The results can be stated briefly: the spider behaved as a male and was perceived as a male by other males. In the (a) part below, you can see the behavior of normal males, who, when they recognize each other, bend their abdomens, move from side to side, open their legs and raise their chelicerae, and, occasionally, engage in battle, trying to topple each other with their chelicerae. (The numbers show the number of pairs in which different behaviors were seen; the one fight is at the bottom.)

(c) shows the gynandromorph male pitted against other males (four trials).  The red spider is the gynandromorph; the black one a normal male. The same bending of the abdomen and moving from side to side (“pre-fighting behavior”) was seen in both spiders, indicating that the gynandromorph was not only perceived as a male, but itself behaved as a male. The arrow shows that all four antagonistic interactions terminated without a fight.

What about the gyandromorph faced with a female?  Normal male-female courtship behavior is shown in (b). Males approach the female from the front, stretch their legs out to touch the female, and sometimes the female stretches out her legs, too.  Neither of the two regular courtships resulted in a mating, which isn’t surprising. (Females are picky.)

Finally (d) shows the gynandromorph (red) encountering a female (black); there were two trials. The gynandromorph male approached the female and reached out his front legs to touch her, just like “normal” males. In these cases, though, the females ran away when this happened, so we don’t know if the females perceive the gynandromrph as male or as some kind of weirdo.

(From paper): Flow diagrams of the behavioral sequences of agonistic behavior (a, c) and courtship behavior (b, d) performed by non-gynandromorphic individuals (a, b) and among gynandromorphic and normal individuals (c, d). Abbreviations: g, gynandromorph. Numbers within parentheses indicate the observed number of individuals that showed the behavioral elements per total number of observations

The paper also has videos of the mating and antagonistic behavior here.

The upshot: The gynandromorph, though morphologically half male and half female, behaves as a male, both in interactions with other males and with females. Further, it’s perceived as male by other males, while we don’t know how the female perceived its sex (she might even be confused). This shows that although morphology is split down the middle, behavior seems to be male-specific.

Why is this? We don’t know if the brain, presumably the seat of behavioral repertoires, is split down the middle, which might cause muddled behaviors. The inside of the spider might not show the same pattern as the outside. Alternatively, even though the brain might be half male and half female, the hormones and other chemicals that militate behavior might show male dominance, effacing any female behaviors. It’s interesting that the authors list seven other cases of gynandromorphs in spiders and insects, and in six of these the piecemeal individual behaved as male (the exception was a bee that didn’t show male-specific behavior towards a queen).

This experiment needs to be tried with Drosophila, and I don’t think it has been yet. For in flies we have far more sophisticated ways of changing very small parts of the fly from one sex to the other, and it would be better to use those methods than to use the relatively crude method of manipulating the parts of the fly visible only from the outside. With these techniques in flies, we could determine what parts of a fly must be male to show male behaviors, and what parts female to show female behaviors. That’s a really good question but, as Matthew said, “the cool kids aren’t interested in it.”

h/t: Tony

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Suzuki, Y., Kuramitsu, K. & Yokoi, T. 2019. Morphology and sex-specific behavior of a gynandromorphic Myrmarachne formicaria (Araneae: Salticidae) spider. Sci Nat 106, 34.. https://doi.org/10.1007/s00114-019-1625-x

Sashimi breakfast for pet otters

September 11, 2020 • 2:30 pm

It can’t be a picnic living with an otter, but these people have two of them: Kotaro and Hana. I don’t know how these people got Asian Small-Clawed Otters (Aonyx cinareus), but so be it. At least they’re litter-trained and get really fancy food, as you can see from this video.

Here are the YouTube notes:

Hello! We live in Japan with two Asian Small-Clawed Otters.

Kotaro: Male, DOB 11/10/2017 Kotaro has a scar on his tail from being bitten by another otter when he was still a baby.

Hana: Female, DOB 11/24/2018.

They have been toilet trained; they use a special pad that is designed for small dogs.

Since I’m using a translation function, my sentences might come out strange. Please provide me with corrections if anything is translated improperly.

Kotaro and Hana have their own YouTube channel, so you might check it out for some other squee videos. This one’s good, and again they get really fancy food. The fish bill must be astounding.

Standoff: Rooster vs. baby goat

September 1, 2020 • 2:30 pm

Just in: baby goat and rooster go mano a mano. This battle is a mismatch, for the rooster could hurt the goat, even putting out its eye. Fortunately, no mammals or birds were harmed in the making of this video.

The YouTube notes:

Occurred on August 25, 2020 / Cumming, Georgia, USA

“The baby goats [sic] name is Luna, she’s a Nigerian dwarf goat. She is two months old in this video. The rooster’s name is Little Rodney and he’s 3 months old. They are the best of buds most of the time. They are always close to each other. Not sure if the rooster thinks he’s a goat or the goat thinks she’s a rooster. Neither one hurt the other and they do this often.”

 

Toby, the duck-guarding dog

August 24, 2020 • 2:30 pm

Finally—d*gs do something good for waterfowl besides scaring them. Here we have a maremma (technically known as the Maremmano-Abruzzese Sheepdog) who spends his days guarding ducks). These dogs are best known as sheep guardians,  but they do a terrific job with ducks. Or at least Toby does.

From Gold Shaw Farm, we have these terse YouTube notes for a 15-minute video.

Let me tell you the story of our farm dog, Toby. He is a maremma who guards the ducks on our farm.

h/t: Reese

Modeling the huddling behavior of Emperor penguins: everybody gets equal warmth

August 18, 2020 • 9:15 am

Every winter (spring in the Northern Hemisphere), after having produced a chick, female Emperor penguins  (Aptenodytes forsteri) head off to sea for two months to fatten up, while the males stay behind, foodless for over 100 days, to tend the chicks. (The males get their turn to eat later, but often walk about 100 km to get to the water.)  With air temperatures as low as -40° C (same in Fahrenheit), and the winds blowing as hard as 140 kph (90 mph), it gets deadly cold.  And that’s when the penguins huddle together for warmth.

Here’s a short PBS video of penguin huddles.  Note the constant shifting of the birds.

And the huddle really keeps them warm. A 2012 paper in PLOS ONE (screenshot below, pdf here, reference at bottom) reported that the temperature inside the huddle can reach 20°C-37.5°C (68°F-100°F). Individuals outside the huddle, exposed to the air and wind, however, don’t get as warm. As the video shows above, the penguins move constantly, with exterior penguins going into the middle and then being expelled to the margins again. These huddles appear to last only a few hours—during bad storms.

If you click on the screenshot below, you’ll go to a paper in which the three authors, using several simple assumptions, try to predict what shape the huddle will assume, and how it will change over time.  There’s also a shorter but easier-to-understand summary that’s just been published in Quanta Magazine. 

The authors’ assumptions are these:

  1. The penguins form a huddle, and they’re packed in the most efficient way: hexagonally. (This corresponds to how they appear to be packed in nature.)
  2. The huddle is assumed to be on a plane, and the penguins have a uniform size and shape. They encounter wind.
  3. The penguins have an assumed rate of heat loss, with the ones on the outside losing more heat.

Then the authors then do their simulation, which involves one chilly penguin moving at a time to get warmer. Here are the steps they simulate:

  1. Generate a huddle and determine the huddle boundary.
  2. Compute the wind flow around the huddle.
  3. Compute the temperature profile around the huddle.
  4. Compute the local rate of heat loss for each penguin.
  5. Add random variations to the rate of heat loss (optional).
  6. Identify the penguin with the highest rate of heat loss (the “mover”) and move it to a location on the boundary where heat loss is minimal.
  7. Determine the new huddle boundary.
  8. Repeat over the desired number of iterations by going back to Step 2.

Quanta shows a diagram of how the simulation works:

Samuel Velasco/Susan D’Agostino/Quanta Magazine; based on: Modeling Huddling Penguins

You’ll notice immediately that some of these assumptions are oversimplified—especially that the coldest penguin is the one that moves, and he (it’s a male) moves to the warmest spot on the periphery, not to just a warmer spot. The video of the huddle above doesn’t seem to show only one penguin moving at a time, nor does it seem realistic that the mover can find the warmest possible spot. Note, though, that as the coldest penguin (on the windward side, of course) moves, an interior penguin becomes an exterior penguin, and that generates a new mover, and so on and so on. Eventually, the shape of the huddle changes.

As the diagram from the paper shows below, the model shows the huddle changing from irregular to roughly rectangular, with one small side of the rectangle facing the wind. (The short faces of the rectangle are actually rounded, not straight.) After about 50 iterations of the model, the steady-state shape begins to emerge. Here’s a diagram from the paper showing the shape change over time (iterations) with the wind coming from the left.

 

 

One interesting outcome of the model is that, in the end, all penguins have experienced about the same loss of heat and have had roughly equal access to the warmth inside the huddle. This is an example of a selfish behavior acting to produce heat equity for all. The authors also note that the model does not produce the least heat loss for the colony as a whole, which I think would come from a sphere. (I’m just guessing here.)

Now the value of this simulation is only as good as its predictive power. Do penguin huddles really assume these shapes over time? The answer appears to be, well, not really: they are not elongated rectangles but are more irregular in shape. (One prediction that was confirmed previously, though, is that in the huddle the penguins are packed hexagonally.)

The authors tweaked the model by allowing random variations in the heat loss of individual penguins, which generate more irregular shapes that, say the authors, produce a shape of the huddle “qualitatively similar to that of real huddles.” They point to a figure that supposedly shows the qualitative similarity (Fig. 5a), but it doesn’t show that: it shows that huddles become more irregular in shape as the degree of random perturbation increases.  It would have been better had they shown some real shapes of huddles evolving over time.

The Quanta article links to studies of heat loss and penguin movement in progress that may eventually yield this data, but it doesn’t exist now. But the data do show that, as predicted, individuals tend to move from the windward to the leeward side of the huddle, and that this movement is more pronounced when wind speed is stronger.

A lot remains to be done, including observations of colonies to see how individuals move. But that’s very hard given the terrible weather conditions and the problems of putting researchers on the site near these fragile colonies (One of the cited papers describes a remote-controlled observatory.) And of course, if the assumptions of the model prove to be wrong, as a couple seem to be, then the model needs to be severely refined. But at least the authors have singled out a cool problem that may eventually have a fairly simple solution. But I think that solution will have to involve more than one penguin moving at a time!

h/t: Paul

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Article: A. Waters, F. Blanchette F, and A. D. Kim. (2012) Modeling huddling penguins. PLOS ONE 7(11): e50277. https://doi.org/10.1371/journal.pone.0050277

Caterpillar makes a tent out of its dinner to hide itself

August 6, 2020 • 1:30 pm

Reader Paul sent in this video of a caterpillar who hides itself in a leaf tent to remain undetected by predators while eating the leaf. It works only because the beast eats only one layer of the leaf. But look at the sophistication of this behavior! I particularly like the way it makes the “hinge” and then pulls the semicircle of leaf over itself.

This is a new video, and I have no identification of the insect, but perhaps readers can help.