This wild and wonderful list is excerpted from The Modern Bestiary.
“A woman without a man is like a fish without a bicycle” was the 1970s feminist slogan coined by Irina Dunn. But perhaps a better analogy would be that of the all-female mole salamander lineages, Ambystoma, who have made it through for 5 million years without males.
Ambystoma are a genus of salamanders from North America, containing thirty-two species, among them the famous axolotl. Thirty-two species? Well, sort of. While we tend to think of quadrupeds as simple beings in terms of sex lives—a mother, a father, a few children, all sticking to their own kind like a good species should—the mole salamanders spoil it all. They are an absolute nightmare for taxonomists and evolutionary biologists, because the American Great Lakes area is inhabited by a whole female-only lineage.
The first question that pops to mind is: how could they possibly have survived? Sexual reproduction is pretty much ubiquitous across the animal kingdom, and its biggest advantage is genetic recombination—the mixing of different individuals’ genetic material to produce a diverse population. Diversity provides more scope for natural selection, and when a disaster strikes, chances are at least some of the individuals will be able to survive and adapt. That said, there are several species that reproduce outside of the classic, sexual route; some animals, for example, reproduce asexually, creating copies of themselves without any input from another organism. The all-female Ambystoma are not quite that, though—they are unisexual.
Unisexual vertebrates—of which there are eighty or so species—employ one of three reproductive modes. There is parthenogenesis, where eggs develop without fertilization; there is gynogenesis—very similar, but a sperm cell is needed to activate the egg development (though its genetic material is not contributing to the offspring); and hybridogenesis, where an egg is fertilized, but male genes are not passed on to subsequent generations. Unisexual Ambystoma are gynogenetic; they need sperm to kick-start the egg production. To do that, they resort to kleptogenesis: stealing sperm from males of four salamander species living in the same area. Salamander males usually deposit little sperm parcels that are used by females for fertilization—however, the unisexual Ambystoma ladies take the sperm to stimulate their reproduction, and then discard it, preferring to produce clones of themselves. If this weren’t complicated enough, sometimes they will incorporate the genes from the males into the offspring, in a genetic equivalent of pick-and-mix—leading to very complex genomes.
Humans receive two sets of genes, one from the mother, one from the father, making us diploid. But unisexual mole salamanders can be triploid, tetraploid, or even pentaploid. And they can combine genes from several species of neighborhood males in one egg, which is a bit like finding out that your DNA contains the genes from Mom and Dad, but also a gorilla, a chimp and an orangutan. The mix-and-match approach to genomes completely ruins the traditional species concept.
How can we know that all those unisexual salamanders don’t in fact belong to four separate species? The clue is in the mitochondrial DNA, which is only inherited from moms, thus making it possible to neatly determine the maternal lineage. In the case of mole salamanders, the mitochondrial DNA is similar across unisexual Ambystoma, but different from all four “parental” species, which pitched in their genetic material at various points in evolutionary history. Interestingly, the unisexual salamanders are very successful, and outnumber their sexual counterparts by as much as two to one in some populations. Mole salamanders: the original exponents of girl power?
Southern Grasshopper Mouse
This is the story of a Wild West outlaw who roams the desert and prairies of Mexico and the American Southwest. Above all rules, feared by everyone, fearing no one, a true desperado—except it’s the length of a pencil. It’s a mouse.
The southern grasshopper mouse, Onychomys torridus, deserves to be called the baddest mouse in the West; heck, maybe even the world. Unlike the house mouse and most other rodents, it’s almost exclusively carnivorous. It will attack, kill, and eat anything that might cross its path: scorpions, beetles, grasshoppers, and even other mice. Grasshopper mice are incredibly skilled and well-equipped assassins: their jaws deliver a particularly forceful bite, their fingernails are more like talons (Onychomys means “clawed mouse”), and they use a range of techniques for hunting different victims. Fast-moving grasshoppers are executed with a quick chomp to the head. Stink beetles that spray a noxious substance are held with the abdomen against the ground, to block the spread of the defensive secretion. Rodents are killed with a swift bite to the base of the skull, which severs the spinal cord. Yet the most interesting fight is that between a grasshopper mouse and a scorpion.
Scorpions defend themselves by delivering a painful sting, used both as a deterrent and a means of buying time to escape. Bark scorpions, which feature on the grasshopper mouse menu, not only inflict intense pain, but are able to kill a human child with their venom. However, while people stung by this scorpion have compared the sensation to being branded with a hot iron, and afflicted house mice will spend a long time licking the throbbing wounds—the grasshopper mouse will groom the sting injury for just a few seconds before pressing on with the attack. They are not put off their meal even when stung in the face, multiple times. In fact, these berserkers evolved a twisted way to harness the scorpion’s venom to their advantage: they use the toxins it contains to block pain transmission, de facto employing one of the world’s most painful stings as a painkiller.
Like all true renegades, grasshopper mice are nocturnal; to make their presence known, adult rodents howl in the moonlight. They find a prominent, elevated area, stand on their hind legs, prop themselves on their tails and emit long, high-pitched calls with their heads high and their mouths wide open. The howls can be heard by humans—and no doubt other mice—up to 100m away; larger individuals have deeper voices. Grasshopper mice have been observed howling in this way prior to a hunt—perhaps making the call a battle cry; alternatively, because most callers were reproductively active males, the “wolf howl” could be a night-time wolf-whistle, a long-distance booty call. The species is not sociable—they will find a mate and breed, but apart from that they are widely spread out, which suggests that their night howling could also be done to mark territories.
Family groups, consisting of a pair and their babies, are tightly knit, and both parents look after the young. Females tend to aggressively exclude their smaller partners from the nest for the first three days after birth, but keen fathers look after their offspring once they are allowed back in, grooming them, huddling over them, and defending them. Perhaps counterintuitively, young grasshopper mice get their aggressive behavior from their doting dads, as single moms produce more docile offspring. Likewise, animals fostered by white footed mice, a meeker species, were found to be much less belligerent. Reckless, violent, and ruthless—all this gangster-mouse is missing is a Colt (and an opposable thumb to hold it).
“Don’t be so picky! When will you settle down?”
Humans aren’t the only ones faced with pressure to find a partner. However, the animal world is perhaps a bit simpler when it comes to who can be choosy.
It all boils down to costs—not financial, but energetic. Each sex bears a cost associated with reproduction, be it due to the production of gametes (sperm or eggs, bigger or smaller, more or fewer), the development of the offspring (carrying or incubating fetuses) or post-natal care (feeding the young, keeping them warm and ensuring their survival). All of these processes require energy, and, depending on the species, one of the sexes is likely to invest more into parenting than the other. But how does this investment link to choosiness?
Parental investment theory, developed by Robert Trivers in 1972, proposes that the sex investing more into parenthood is also the pickier one when it comes to mate selection, and the one investing less must compete with others to access mates. In line with this theory, when females invest more—e.g. through pregnancy, nursing, or producing large eggs—they are the ones that need to be wooed by the males’ dazzling features, gifts, or courtship behavior. These displays may indicate to them how fit a potential partner is, and whether he’s worth the reproductive hassle. Because females are generally the “limiting factor” when it comes to reproduction, they are the choosy sex—and there is a higher selection pressure on males to be more aggressive, impressive, or possessive (see Saiga antelope, page 64, and Guianan cock-of-the-rock, page 184).
While, in most organisms, females invest more in reproduction, there are species, such as the South American wattled jacana, Jacana jacana, where the males bear the brunt of parenting (the giant water bug, page 104, is another such species). Jacanas are wading birds, distinguished by their absurdly long toes. The oversized digits of Edward Scissorfeet distribute their weight over a larger surface, which allows them to walk atop lily pads, gaining them the nickname “Jesus birds.” The jacanas also exhibit sex-role reversal: the females are the bigger and more aggressive sex; their wattles (the flappy skin around their beaks) are a brighter orange-red than the males’, and their wing spurs—keratinous spike-like bits of weaponry that stick out of their wings—are larger. Jacana ladies are polyandrous; they have several partners on the go, and will compete for males and defend their territories. A female lays up to four eggs for each male, and then moves on to her next partner, replacing eggs as needed when they are predated. The eggs are extremely small compared to her body size and only take her about three weeks to produce; in comparison, jacana single dads look after the young for about four months.
The male is the sole caregiver—he does all the incubation and shading of the eggs, and, after they hatch, he guards the young, teaches them how to forage, and broods them under his wings. When in danger, wattled jacana chicks employ one of two escape strategies. Upon their dad’s call, they jump into the water and stay there for up to half an hour, using the tip of their beak as a snorkel. Alternatively, if the threat comes from the water, they will hide under their father’s wings—and, what is more unusual, he will use specialized wing bones to pick up the chicks and carry them to safety (while treating onlookers to a freakish display of long toes sticking out from underneath his feathers). The male may also feign injury to distract the predator, or occasionally call on the female to attack the intruder while he escapes with the young ones.
Apart from these sporadic defenses, the mom engages with the young extremely rarely—only when the dad dies, or when she miscalculates her laying and leaves the male to tend to a nest full of eggs and a clutch of mobile chicks at the same time. In such emergency circumstances, the female is able to take over all the necessary parental duties; in all other respects jacana ladies boast a rather enviable free-agent lifestyle.
Old World fruit bats
Megabat sounds like a great name for a new character in the Batman franchise. Still, with a hedonistic lifestyle and the ability to kill en masse, this bat might be better cast as supervillain than caped crusader.
Old World fruit bats are some 200 species of bat belonging to the family Pteropodidae, native to the tropics and subtropics of Africa, Eurasia, and Oceania. Though they are casually known as megabats, about a third of species are, in fact, not very mega at all— the smallest of the lot, the spotted-winged fruit bat, Balionycteris maculata, weighs a mere 13g (about 120 times less than some of the biggest species, collectively called flying foxes). Unlike the rather nightmarish-looking, echolocating, carnivorous microbats, most Old World fruit bats have pleasant, dog-like faces, are vegetarian, and find their way around with their keen eyesight, sense of smell and excellent spatial memory.
Fruit bats play an important role as seed dispersers, especially for plants with smaller seeds. Thanks to their size and a good set of teeth, larger bats can carry fruits at least as big as those swallowed by birds—and, once home, they are able to hang by one foot and use the other to manipulate their bounty. Even though most seeds don’t spend long inside the bat (the rapid digestion of soft fruit prompts an exit within 10–70 minutes of entry), they can still be carried over distances of tens of kilometers. And when considering that social fruit bats can live in colonies of more than a million individuals (each pooping seeds all day, every day), it is no wonder that megabats are able to replant entire forests.
Meanwhile, fifteen or so species of Old World fruit bats are technically nectar bats, being specifically adapted to visiting flowers. Some, such as the Malaysian cave nectar bat, Eonycteris spelaea, travel up to 50km from their roosts for a floral meal. Long-snouted and long-tongued, they land on flowers to slurp up nectar and provide a pollinating service at the same time. Bat-pollinated blossoms are larger and more robust than insect- or bird-pollinated ones, and emit attractive scents at night to lure mammalian visitors.
What megabats also love to eat, apart from fruit and nectar, is each other. There have been reports of oral sex, both fellatio and cunnilingus, across different fruit bat species—before, during, and sometimes after copulation. The longer the foreplay or oral stimulation during sex (yes, they can bend like that), the longer the intercourse—and likely the higher the chance of fertilization. The Bonin flying fox, Pteropus pselaphon, displays fellatio between males— probably used as a means of avoiding conflict within a group.
Another interesting relationship is one with their pathogens. During flight, bat metabolism is very high, and body temperatures can jump to 41oC—which may cause DNA damage. While bats protect their own DNA with enhanced DNA repair pathways, resident viruses are less lucky. If they survive, they can stay—unlike other mammals, bats don’t try to annihilate germs with a full-on inflammatory response, but are happy to let them linger at a low background level, merely limiting viral propagation. Consequently, bats harbor a range of pathogens without showing signs of disease—they are reservoirs of emerging viruses such as SARS, Middle Eastern Respiratory Syndrome and a range of other coronaviruses, as well as Nipah virus, Hendra virus, and, possibly, Ebola; they can also carry rabies.
Such tough conditions push the germs to evolve quickly—or perish. Problems start when these super pathogens infect species with less robust immune systems, like humans. Since large fruit bats are hunted for food across their entire geographic range, the risk of infection for people is high—and megabats, already threatened by habitat loss and food shortages, shed more pathogens if they are stressed or malnourished.
While fruit bats look sweet, have a sweet tooth and make sweet love, they are best left at a safe distance—because their revenge can also be sweet.
White butterfly parasite wasp
Are you a screenwriter looking for a plot for a B-movie, perhaps sci-fi or horror? Look no further, nature comes to the rescue. The story opens with the victim—a butterfly. Specifically, the cabbage white butterfly, Pieris rapae, found commonly throughout Europe, Asia, and North Africa. More precisely—its larval form, a caterpillar, enjoying a sunny day of munching Brussels sprouts in a garden. Enter an innocent-looking black wasp, only 3–7mm long, akin to a flying ant. The wasp looks inoffensive, but the music foreshadows a threat. And indeed—the wasp lands on the caterpillar, pierces it with its sharp ovipositor and proceeds to lay a few dozen eggs inside the living, eating, cabbage white. It’s the antagonist: a female white butterfly parasite wasp, Cotesia glomerata—a parasitoid. Unlike parasites, who don’t usually kill their hosts, parasitoids don’t care if their chosen caterpillar lives or dies (spoiler: it dies). The white butterfly parasite wasp is a koinobiont; it does not slay the caterpillar immediately, but lets it live, grow, and even undergo metamorphosis—a sensible move, since a bigger host means more food for young wasps. Two to three weeks later, wasp larvae emerge, killing the caterpillar and building cocoons on its remains, like true body-snatchers. An unparasitised caterpillar turns into a beautiful, white butterfly—a parasitised one disintegrates into a bag of wasp larvae. Parasitoidy is very common among wasps (see Emerald cockroach wasp, page 180), as tens, if not hundreds, of thousands of species employ this reproductive strategy. And, to be fair, the motive is also not uncommon in sci-fi movies (see Ridley Scott’s Alien). But there is more to our plot: once the eggs are laid in the unsuspecting caterpillar, in comes the avenger. It’s another wasp, Lysibia nana, who—you guessed it—lays eggs inside the larvae of the white butterfly parasite wasp. Unlike the original parasitoid wasp, this hyperparasitoid, a parasitoid of parasitoids, is what’s known as an idiobiont: in other words, it paralyzes the host straightaway via venom injection, preventing any further development. It then lays a single egg in an existing wasp larva, creating a rather morbid larval Russian doll. When the egg hatches, the hyperparasitoid wasp larva pierces the skin of its host and sucks out its insides, eventually eating all of it and moving into its cocoon to pupate. Because it takes up all the available space, the adult forms of the hyperparasitoid L. nana and parasitoid C. glomerata are surprisingly similar in size.
Now for the final twist—who orchestrated all of this? Who is the mastermind behind the psychopathic killings? It’s a good one, because nobody saw it coming. The evil genius is . . . the plant. Yes, when chewed on by the cabbage white butterfly caterpillars, that Brussels sprout bush (or, frankly, any cabbage relative could be cast in this role) emits a chemical cry for help. Attacked plants release substances called herbivore-induced plant volatiles, botanical equivalents of a bat-signal. Parasitoid wasps sense these scents and fly over to parasitise the hungry caterpillars. But once parasitised, the caterpillars change; what changes, too, is the composition of their oral secretions. As a consequence, the volatile emissions of the plant chewed up by a parasitised herbivore smell different from those emitted by an unparasitised animal. The difference in smell is enough to inform the hyperparasitoid of the presence of freshly laid wasp eggs. In the end, two winners arise: the plant and the newly emerged hyperparasitoid wasp.
As the camera pans over the beautiful garden landscape, the narrator’s voice (perhaps Morgan Freeman’s?) recites an excerpt from Jonathan Swift’s On Poetry: A Rhapsody:
So, nat’ralists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite ’em;
And so proceed ad infinitum.
Credit roll. The end.
From The Modern Bestiary by Joanna Bagniewska, published by Smithsonian Books, distributed by Penguin Random House Publisher Services.
Illustrations copyright © 2022 Jennifer N. R. Smith