Some female dolphins have evolved a secret weapon in their sexual arms race with males: vaginas that protect them from fertilisation by unwelcome partners.

Penises come in a wide variety of shapes and sizes, especially in dolphins and other cetaceans. That seems to imply a similar diversity in vaginas, but of Dalhousie University, Canada, says there is 鈥渁 huge lag鈥� in our understanding of female genitalia.

That is partly because it is tricky to visualise vaginal structure. To overcome this problem, Orbach has created silicone moulds of cetaceans鈥� vaginas, revealing complex folds and spirals.

鈥淭here鈥檚 this unparalleled level of vaginal diversity that we had no idea existed before,鈥� Orbach says.

Similarly complex vaginal structures are found in several species of duck. Orbach鈥檚 collaborator of Mount Holyoke College, Massachusetts, has previously found evidence that duck vaginas have evolved to make it harder for males to force copulation. So Orbach wondered if female cetaceans鈥� unusual vaginas had also evolved to keep out unwanted sperm.

Orbach, Brennan and their colleagues obtained genitals from marine mammals that had died of natural causes: and dolphins, and . They inflated the males鈥� penises with saline to see how they looked when they were erect, and compared them with the vaginal moulds. They also took CT scans of penises inserted into the corresponding vaginas, to determine whether they fitted in easily and the best positions.

Take back control

The vaginas of the common dolphin and common seal seemed amenable to penetration, suggesting their genitalia had evolved to allow males access. But the common porpoise and bottlenose dolphin had extensive vaginal folds that obstructed penis entry.

Male bottlenose dolphins form alliances two to four strong to keep competitors away from females. When confronted by such an alliance, a female has little choice in who mates with her, and may mate with everyone.

However, vaginal folds could grant her some agency, says of Georgetown University in Washington DC. 鈥淪he may not choose who she mates with, but might be able to choose which male or, more precisely, which sperm, fertilises her egg.鈥�

In all four species studied, the ideal position for successful fertilisation appeared to be the male on top with his penis hooked underneath the female. Any deviation from this tended to result in unsuccessful penetration. That is consistent with Orbach and Mann鈥檚 observations of wild porpoises and dolphins mating.

This combination of precise positioning and complex vaginal structures means that subtle mid-copulation movements by females could send the penis the wrong way in their vaginas, preventing fertilisation.

鈥淚t might appear behaviourally that females are very passive,鈥� says Orbach. 鈥淏ut looking at the reproductive anatomy, we鈥檙e learning that they have all sorts of cryptic ways to control paternity.鈥�

Journal reference: Proceedings of the Royal Society B, DOI:

It鈥檚 the aquatic battle royale. A previously overlooked conflict between alligators and sharks has been going on for centuries at least, and it seems the alligators are winning.

at Kansas State University has studied American alligators in marine habitats for the past decade. A keen fisherman, Nifong noticed he was catching a lot of sharks in alligator country, and wondered whether the two predators ever interacted. 鈥淎lligators are opportunistic,鈥� he says. 鈥淭hey鈥檙e not going to pass up a big chunk of protein that鈥檚 swimming by.鈥�

However, the only previous evidence of alligators eating elasmobranchs 鈥� the group to which sharks and rays belong 鈥� was an individual with stingray spines in its jaw.

Nifong searched the scientific and historical literature, and consulted experts on alligators and sharks. He found confirmed instances of alligators eating , and sharks, as well as an . He says sharks and other elasmobranch fish could be a significant but underappreciated food source for alligators.

鈥淕ators will eat almost anything that will fit in their mouths,鈥� agrees at the Northwestern State University of Louisiana. But he has analysed the contents of many alligator stomachs and never found shark remains.

Gabrey听says that might be because the听alligators lived in marshes far from salt water, so were less likely to encounter sharks. Alligators also have highly acidic stomachs, which could dissolve the cartilaginous skeletons of sharks with little trace.

Sharks bite back

The only previous accounts of sharks attacking alligators come from credulous late 19th-century newspaper articles. One described hundreds of alligators and sharks assembling in an inlet and 鈥渇ight[ing] like dogs鈥�.

Though undoubtedly exaggerated, such stories are not wholly incredible, says Nifong. Both sharks and alligators gather in large numbers to feed, and alligators were far more numerous in the 19th century than today. 鈥淭hat increases the probability these feeding congregations would commingle,鈥� Nifong says.

Nifong also scoured the literature for accounts of sharks clashing with other crocodilians. He found plenty. But in many cases the crocodilians were the prey, from great white sharks preying on American crocodiles in Colombia, to tiger sharks eating estuarine crocodiles in Australia.

There are even , suggesting this conflict is truly ancient.

Conservationists should bear the crocodilian-shark conflict in mind, says Nifong, as both groups contain endangered species. A study published in April found that many Australian sawfish 鈥� another shark relative 鈥� . Similarly, the US nursery grounds of the endangered smalltooth sawfish are known to harbour alligators. 鈥淚f there are alligators in the area, survival of those juveniles is going to go down,鈥� says Nifong.

Journal reference: Southeastern Naturalist,

A newly discovered species of prehistoric 鈥渉ell ant鈥� had anatomy that lived up to its demonic name, including a lethal feeding apparatus reinforced with metal.

Hell ants are an extinct lineage from the Cretaceous Period. Instead of regular mouthparts, they had upward-facing blades.

No living species have such facial anatomy. However, the hairs around hell ants鈥� mouths are reminiscent of hairs on modern trap-jaw ants that cause their mouths to snap shut when triggered. This has led to speculation that the hell ants鈥� mouthparts worked in a similar way.

Some also had a horn-like appendage that jutted out over their tusk-like mandibles. This includes the new species, Linguamyrmex vladi, which at the New Jersey Institute of Technology in Newark and his colleagues found preserved in 98-million-year-old amber.

Springing the trap

It may be that when another insect brushed the trigger hairs, the blade-like mandibles flipped up and impaled the prey against the horn, punching through its outer layer. 鈥淵ou have this sort of stopping plate, made to accommodate the mandibles closing and capturing prey,鈥� says Barden.

That鈥檚 not all. CT scans revealed that L. vladi鈥檚 horn was reinforced with metal.

鈥淧robably the metal helps to keep the horn undamaged,鈥� says at the University of Rennes 1 in France. In 2016, he of another horned hell ant, which he called a 鈥渦nicorn ant鈥�.

鈥淚t makes sense to reinforce that [appendage],鈥� agrees Barden, since the horn must have had to withstand repeated impacts from the mandibles. Some modern insects reduce wear and tear in a similar way, by .

Metal vampires

As well as being a metal-reinforced unicorn, L. vladi may have been a vampire. When their mandibles moved upwards, they formed a 鈥済utter鈥�. 鈥淭hat might be something that developed to funnel haemolymph 鈥� insect blood 鈥� down through the mouthparts,鈥� says Barden.

Next to the ant, Barden鈥檚 team found a preserved beetle grub 鈥� exactly the kind of 鈥渟quishy, haemolymph-laden insect鈥� that could support a vampiric lifestyle. Perhaps it was next on the menu.

But the metal-reinforced horn suggests that the ants鈥� jaws moved with enough power to penetrate the tougher cuticles of adult insects as well.

鈥淯ntil we find a specimen with the prey item trapped, which is probably a matter of time, we鈥檙e left to speculate,鈥� says Barden. However, the Myanmar amber deposits where he found his specimen are so rich that more detailed observations are likely to emerge.

Journal reference: Systematic Entomology, DOI:

The hallucinogenic effects of magic mushrooms are well documented. But nobody knows what psilocybin, the chemical responsible, does for the mushrooms themselves.

Now, one of the first genomic analyses of hallucinogenic fungi has deciphered psilocybin production, and even suggested a function for it. By messing with insect neurochemistry, psilocybin may act as a psychedelic repellent.

A team of researchers led by at Ohio State University compared the genomes of three hallucinogenic fungi with three non-hallucinogenic relatives. By doing so, they identified the cluster of genes responsible for making psilocybin ().

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The gene cluster is found in several distantly related groups, suggesting that the fungi swapped genes in a process called horizontal gene transfer. This is uncommon in mushrooms: it is the first time genes for a compound that is not necessary for the fungi鈥檚 survival听鈥撎� called a secondary metabolite听鈥� have been found moving between mushroom lineages.

Since these genes have survived in multiple species, Slot thinks psilocybin must be useful to the fungi. 鈥淪trong selection could be the reason this gene cluster was able to overcome the barriers to horizontal gene transfer,鈥� he says.

Hallucinogenic mushrooms often inhabit areas rich in fungi-eating insects, so Slot suggests psilocybin might protect the fungi, or repel insects from a shared food source, by somehow influencing their behaviour.

The specific purpose of many secondary metabolites is unknown, says at the University of Bremen, Germany. But that鈥檚 not to say they don鈥檛 have a use. 鈥淪econdary metabolites are not just produced for fun,鈥� he says.

However, while psilocybin has been shown to affect the brains of mammals including mice, there is little evidence that it affects insects or other invertebrates听鈥� barring a famous 1962 study showing that it changes the way spiders build webs.

That said, other fungi use similar substances to influence insects, 鈥渇or example the zombie ant fungus,鈥� says Slot. And insects have nervous system receptors similar to those affected by the psilocybin successor molecule psilocin in humans.

In a second study, a group led by Dirk Hoffmeister at Friedrich Schiller University Jena in Germany was able to go one step further. After obtaining a legal permit, they have developed a way to make psilocybin using enzymes ().

This has never been done before and could set the stage for commercial production. In recent years there has been a revival of interest in psilocybin鈥檚 potential as a therapeutic drug, an area of research that had stalled due to tough 1970s drug laws.

Hundreds of marine species are known to eat plastic 鈥� including those that regularly end up on our dinner plates. But why? It now seems that ocean-borne plastic has a smell that marine animals find appealing.

at the NOAA Southwest Fisheries Science Center in Monterey, California, explored the dietary preferences of marine life while he was a researcher at the University of California, Davis. He and his colleagues exposed schools of anchovies to seawater that contained odours from plastic. To make this, they left plastic beads in the ocean for three weeks, then stirred the beads into seawater samples before filtering them out 鈥� leaving just the associated odour chemicals.

In the ocean, plastic quickly becomes covered with a layer of algae that releases smelly sulphur compounds. Foraging fish such as anchovies, which feed on algae-munching marine crustaceans called krill, are thought to use these compounds to help them locate their prey.

When analysing videos of the anchovies, the researchers noticed that the fish reacted to the fouled plastic solutions as if they were their crustacean prey. The decision to use solutions that smelled of plastic rather than actual pieces of plastic meant the fish weren鈥檛 responding to visual cues; the fish must have smelled the odours. They did not respond to clean plastic.

The work builds on Savoca鈥檚 earlier research, which suggested that similar sulphurous odours lure tube-nosed seabirds 鈥� which are also krill-feeders 鈥� into eating plastic.

Fish aren鈥檛 stupid

鈥淭his problem of animals eating plastic has not been investigated as completely as it should have been,鈥� says Savoca. Seabirds and fish aren鈥檛 stupid, he says, and generally they are good at locating the correct prey. Savoca thinks we might have overlooked the role of odour because we are such visual animals. 鈥淭hat鈥檚 how we perceive the world most readily.鈥�

This explains why, for example, it is often suggested that marine animals mistake plastic bags for jellyfish, or plastic pellets for fish eggs. 鈥淭his is mostly anecdotal,鈥� says at the University of Toronto. She thinks Savoca鈥檚 experiments provide the most rigorous explanation yet for the high frequency of plastic consumption among marine species.

This dietary confusion is a problem for fish, but it could also be an issue for animals higher up the food chain, including us.

鈥淭here鈥檚 no doubt that we eat microplastics when we eat seafood,鈥� says Rochman. What we don鈥檛 know, she says, is how much of the chemicals leaching out of the plastic then enter our systems 鈥� and whether it matters if they do.

An released last week highlights how much we don鈥檛 know about plastic consumption by animals and the possible impact on human health. While Savoca鈥檚 work doesn鈥檛 provide solutions, he feels it is important to establish why animals are eating plastics in the first place.

鈥淔or any problem, if you want to effectively mitigate it or solve it in any way, you have to fully understand what鈥檚 going on,鈥� he says.

Read more: Plastic in the food chain: Artificial debris found in fish

Species: A type of mud eel (provisionally: Pythonichthys macrurus)

Habitat: Sea floors off the coast of West Africa

Talk about a crooked character. A small eel appears to have evolved the lopsided look of a flatfish.

Mud eels are seldom caught or studied. Past analysis suggested these fish were adapted for burrowing into sediment, but new specimens hint that some of them have evolved for a more specialised lifestyle.

While sorting through a shipment of fish trawled off the coast of Guinea in West Africa and sent to the American Museum of Natural History in New York, 鈥檚 attention was brought to a pair of these eels. 鈥淎s soon as I picked one up, I knew we had something special,鈥� recalls Martinez, who now works at the University of California, Davis. 鈥淭he connection to flatfishes was immediate.鈥�

The strange anatomy of flatfish is well-documented. These bottom-dwellers lie on their sides, hidden from predators and ready to grab passing prey. Their bodies have adapted by becoming totally asymmetrical, with their features shifted to the upward-facing side.

What first struck Martinez about the mud eels was that, like flatfish, one side was coloured and the other was white. In flatfish, this 鈥渃ountershading鈥� means the exposed side is camouflaged against the sea floor.

Blind-sided

This turned out to be only the most obvious aspect of the mud eels鈥� asymmetry. X-rays and micro-CT imaging of the more asymmetric specimen revealed a whole suite of wonky features. Most notably, the eye on the pallid side had shrunk and almost vanished underneath a thick layer of flesh.

Furthermore, on this 鈥渂lind side鈥� the jaw was flattened and only had a few functioning teeth, and a series of sensory organs running down the eel鈥檚 flank were reduced compared to those on the opposite side. These asymmetric features are also seen in flatfish.

Martinez and his colleague provisionally identified their specimens as Pythonichthys macrurus 鈥� but they don鈥檛 know if these are unusual variants of that already-known species or representatives of a whole new species.

Certainly, nothing as anatomically extreme has been observed before in any mud eel, and the researchers speculate that asymmetric eels could be taking a leaf out of the flatfish鈥檚 book. Instead of burrowing, they may be 鈥渟it-and-wait鈥� ambush predators, with their blind side pressed flat against the ocean floor.

, a researcher at St Lawrence University in Canton, New York, who studies flatfish development, thinks this comparison is accurate. But he points out that the eels have not gone quite as far as flatfish. 鈥淔latfish protect their blind-side eye from sediment damage by shifting it completely to the opposite side, whereas these eels appear to protect it by covering it with skin,鈥� he says.

Schreiber suggests that such asymmetries in the eels could be programmed into their development, as with flatfish, or triggered by physical contact with the seabed when they are juveniles. But to shed more light on this, the growth of these eels would have to be studied in captivity. To do that, researchers will first need to catch a lot more.

Journal reference: Journal of Fish Biology, DOI:

Read more: Why baby flatfish grow into the wonkiest animals in the world

Species: A nest-brooding cichlid (Neolamprologus furcifer)
Habitat: Rocky areas in Lake Tanganyika, East Africa

Appearances can be very deceptive. Look closely at brown striped lake snails and you may spot one that is actually a fish.

Even experts can be fooled. of Osaka City University, Japan, found it hard to keep count of baby cichlid fish when he was studying cichlid reproduction in Lake Tanganyika. 鈥淥ften I confused the fish young with snails,鈥� he says.

The cichlid, Neolamprologus furcifer, raises its brood in rocky nests 鈥� a habitat shared with various snails. Satoh found that the most abundant snail in the nests by far is Reymondia horei. The baby fish sport the same brown and white stripes as these snails, and resemble them in size and shape (see image below).

The cichlid babies appear to be the first known case of fish masquerading as snails. Where the snail is absent, the young of these cichlids don鈥檛 develop the stripes.

So why do they do it? Satoh thought that if he found it hard to tell the fish and snails apart, so too might fish that prey on the young cichlids.

Attacks by mature female cichlids on would-be predators were twice as frequent when Satoh and his colleagues removed the snails. With the snail smokescreen gone, the fish seem to need to work harder to keep their babies alive.

Female cichlids also chase away harmless algae-eating fish as well as predators. The researchers suggest that this could be attracting snails to the nests, by ensuring they have a plentiful supply of algae to eat.

Not all snails have the stripes that the baby fish mimic, however, and the team observed female cichlids carrying non-striped snails away from their nests, effectively giving the striped ones more space to colonise.

鈥淭he results strongly suggest the mother fish鈥檚 behaviour enhances the chances that the offspring will be mistaken for inedible snails,鈥� says at Newcastle University, UK, who studies animal disguise. He says it is the first example of an animal altering the efficacy of another鈥檚 masquerade. The mothers collaborate with their young to optimise their disguise, and consequently waste less time and energy fighting off enemies.

The survival of baby fish wasn鈥檛 lower when the snails were removed, but this is because mothers had upped their vigilance.

As the offspring are protected either way, it is the mothers who have the most to gain from the masquerade.

鈥淎ll of the literature on masquerade investigates how individuals benefit from their own disguise,鈥� Skelhorn says. 鈥淭he results of this study seem to suggest that masquerade doesn鈥檛 directly benefit the masquerader, but rather it benefits the third party.鈥�

Species: An undescribed species of Poltys orb web spider

Habitat: Rainforests in south west China and Southeast Asia

I鈥檓 a leaf. Really, I am. A spider found in the Chinese rainforest has gone to unique lengths to convince the world it is a leaf.

of the Slovenian Academy of Sciences and Arts in Ljubljana, stumbled across this novel arachnid while on an expedition in Yunnan province. Shining torch light on strands of spider silk led him and his team to a suspicious looking patch of leaves.
鈥淚t then became apparent that one of those leaves was not really a leaf,鈥� he says. 鈥淚t was a spider.鈥�

The spider鈥檚 back resembled a green, living leaf complete with veins, while its dull, brownish front looked more like a dead leaf (move the slider below to see the difference). It even had an unusual abdominal extension reminiscent of a stalk.

Matja啪 Kuntner

The team dubbed this feat the 鈥渦ltimate leaf masquerade鈥�, but the spider has a lot of competition according to , a researcher at Newcastle University, UK, specialising in animals that masquerade as other things.

鈥淭here are loads of really, really good masqueraders,鈥� he says, listing leaf insects and dead leaf mantises as two supremely adapted leaf mimics. Spiders, on the other hand, are not generally renowned for their masquerading abilities.

However, this spider has unusual behaviour to complement its anatomical adaptations, placing it in the top echelons of mimicry. From the living branch where the team found their first specimen, there were dead leaves hanging on strands of silk 2.5 metres up.

Kuntner thinks these spiders haul leaves up from the ground and hang them up to create daytime hideaways that match their camouflage and protect them from predators. At night they can emerge and build webs to catch prey.

Skelhorn wonders if the addition of dead leaves might even put off herbivores that could otherwise accidentally consume the spider in a mouthful of greenery.

This spider is yet to be formally classified after Kuntner鈥檚 team was unable to find more specimens, except for a single juvenile. Kuntner thinks they are pretty rare, and that the same enigmatic adaptations helping these spiders avoid predation may also be helping them avoid the attention of researchers.

Journal reference: Journal of Arachnology, DOI: http://dx.doi.org/10.1636/JoA-S-16-027.1

听

Species: Dwarf crocodile (Osteolaemus tetraspis)
Habitat: Abanda caves, in the rainforests of Gabon

Caves are scary places 鈥� especially ones filled with crocodiles. 鈥淚 was crawling through the cave and suddenly there were two red eyes,鈥� says explorer . 鈥淚t was frightening!鈥�

In 2010, he was part of an following a tip-off about a population of dwarf crocodiles living there.

While crocs sometimes retreat underground during droughts, this is the first population documented taking up long-term residence in caves.

The team鈥檚 crocodile expert, from the Rare Species Conservatory Foundation, soon realised why they had done so: a bounty of ready-made snacks was falling into the water or lining up to be plucked off the cave walls.

鈥淵ou walk in and there are just bats and crickets everywhere,鈥� he says. 鈥淭he crocodiles are pretty good hunters anyway, but even if they didn鈥檛 have to pull bats off the walls, there are individuals falling to the floor all the time.鈥�

Thanks to a steady diet of bats and other cave critters, the crocs appear to be in better physical condition than their forest counterparts, especially the young ones.

With at least 5 kilometres of caves to occupy, it鈥檚 difficult to precisely know how many crocs are taking advantage of this banquet. However, based on the team鈥檚 exploration up to 100 metres into the cave system, Shirley reckons there are at least 50, and probably many more.

Orange is the new black

As the team headed further into the caves, they made an unexpected discovery: in the deeper recesses, the older, dark-coloured males had become paler, turning a bright orange. Were they losing unnecessary pigment in a similar way to other cave-dwelling animals, such as Mexican blind cavefish?

Shirley doesn鈥檛 think so. Cave crocs must maintain contact with the outside world for one simple reason. 鈥淭hey cannot reproduce in the caves,鈥� he says. 听鈥淚t鈥檚 a nesting ecology thing: they need big mounds of rotting vegetation to lay their eggs in.鈥�

So while the crocodiles appear to spend the entire dry season in the caves, they emerge during the wet season 鈥� at least to breed. Instead of the colour change marking an early stage of subterranean adaptation, Shirley has a more disgusting explanation.

The water these crocodiles swim through is essentially an alkaline slurry formed from bat droppings. 鈥淭he urea in bat guano makes the water very basic,鈥� he says. 鈥淓ventually that will erode away the skin and change its colour.鈥�

Bizarrely, this is similar to the chemical treatment applied to crocodile skin so it can be turned into belts and wallets.

Dwarf crocs in Gabon are in little danger of becoming belts, but they are hunted extensively for bushmeat.

Thankfully, Shirley thinks the Abanda population avoids this threat, citing the difficulty he had capturing them in narrow, often impassable, tunnels 鈥� 鈥渁nd I consider myself to be fairly good at catching crocodiles鈥�.

Read more: When crocodiles roamed the Arctic; These baboons and lemurs have left the trees to live in caves

While Tyrannosaurus rex was stalking prey some 68 million years ago in what is now North America, down south an unrelated predator was trying out a similar look.

A new dinosaur species, Gualicho shinyae, unearthed in Argentina鈥檚 Huincul formation bears a mosaic of features and looks a bit like an Allosaurus, a subgroup of two-legged, bird-like theropods.听Its most striking feature, however, is its tiny arms that look like those of a T. rex 鈥� even though the two species lived on separate continents.

The Huincul formation is renowned for remarkable dinosaur fossils, including Argentinosaurus 鈥� perhaps the largest dinosaur ever. But nothing quite like Gualicho had ever been found here.

鈥�Gualicho has anatomical traits that you see in very disparate groups of theropod dinosaurs,鈥� says Pete Makovicky of The Field Museum in Chicago, who described this 鈥渕osaic鈥� dinosaur. 鈥淚t appears to be closest to Allosaurus, but it doesn鈥檛 quite fit comfortably.鈥�

Armed and dangerous

The team estimates Gualicho was between 7 and 8 metres long and weighed roughly the same as a polar bear, but its arms were only the size of a human child鈥檚.

The functionality of T. rex鈥檚 tiny arms has long been a source of debate, with theories ranging from grasping onto a partner during mating to holding prey in place to deliver a death blow.听Many experts still think that the arms served no useful function, but the fact that Tyrannosaurus and Gualicho have both independently evolved the same highly reduced forelimbs with two fingers, despite occupying different branches of the dinosaur family tree, suggests otherwise.

鈥淚t seems to be something that鈥檚 adaptive in lineages of dominant predators,鈥� says Makovicky. If a feature appears separately multiple times, it becomes less and less likely that it evolved accidentally.

Thomas Carr of Carthage College, Wisconsin, agrees that these were not useless appendages. 鈥淪ure, they only have short arms and two fingers, but it鈥檚 clear with Tyrannosaurs at least that those arms were powerful,鈥� he says.听For Tyrannosaurus, though, the real power would have been in its听enormous skull, which it probably used to hunt meaning it听didn鈥檛 need big arms.听It鈥檚 possible that Gualicho had a similar hunting strategy, which led to it also having small arms.

Journal reference: PLOS One, DOI: 10.1371/journal.pone.0157793

Read more: Stunning fossils: Dinosaur death match