How Fish Eat Pointy Food, Finches That Use Cigarettes and Unisexual Salamanders

A quick review of interesting research on living things from the last month.

A tubelip wrasse feeding on coral. Credit: Victor Huertas and David Bellwood

A tubelip wrasse feeding on coral. Credit: Victor Huertas and David Bellwood

How do reef fish eat razor-sharp stinging coral?

Short answer: by drooling. As anyone who has touched live coral with their bare hands knows, the razor sharp surface is covered with stinging polyps. Only 128 species of fish of the 6,000 that live on reefs evolved to live on a punishing diet of coral. By examining the lips of one species – the tubelip wrasse – under an electron microscope, researchers from Australia discovered they are finely-ribbed like the gills of mushrooms. These structures are lined with goblet cells that secrete mucus all the time. Instead of using their teeth to take crunchy bites, the fish “kisses” the coral with its thick pouty lips while the mucus creates a seal around the mouth. It then sucks up chunks of coral mucus and tissue with the sticky saliva protecting their lips from being stung. The fish prefer to focus on damaged parts of coral that produce the most mucus. The yellowtail wrasse that doesn’t eat coral has thin and smooth lips.

How do wasps recognise each other’s faces?

Every golden paper wasp (Polistes fuscatus) of North and Central America has a distinct face. What’s more, they even recognise each other by their looks. The metricus paper wasp (Polistes metricus), a close relation, doesn’t have this talent. After all, every member of its tribe looks alike. But this plain-looking insect can learn to identify patterns.

Researchers trained one group of each species in pattern and facial recognition. Later, by comparing which genes were activated in the brains of the trained wasps, they found differences in 257 genes, including ones that controlled neuron signalling. None of them showed up in the brains of metricus wasps, leading the researchers to think facial recognition isn’t similar to perception of patterns. The answer to golden paper wasps’ extraordinary skill lies in its genes.

Why do house finches weave cigarette butts into their nests?

Urban house finches of Mexico City rip cigarette butts and line their nests with the nicotine-smelling fluffy fibres. Some speculated the fibres resemble feathers and the parent birds can’t tell the difference. Others thought they might use the butts to reduce the load of ticks and mites. Nicotine is a known parasite-killer, but it’s also toxic to the nestlings. By adding ticks, live and dead, replacing cigarette filters with felt, and shaking down the nest afterwards, researchers answered the question of why finches lined their nests with cigarette butts. Parent finches reacted to the addition of live ticks by bringing more nicotine-tainted filters. The researchers speculate the benefits of killing blood-sucking parasites must outweigh the harm nicotine causes. Or the nestlings may imprint on the stink of nicotine in the nest and learn to pick up the butts when they become parents.

A common butterfly’s uncommon sex life

The sex life of cabbage white butterflies is anything but ordinary. When they mate, the males produce spermatophores that are 13% of their body weight. Sperm makes up only 2% of it; the rest is a yummy protein shake garnished with carbohydrates and lipids. A biscuit-hard shell encrusts the gunk. The large spermatophore takes up all the space in the female’s reproductive tract ensuring she cannot mate again until she breaks it down. She wastes no time at the task. Her reproductive organ gushes with digestive enzymes to dissolve it. But it could be a week before she can get through it, giving the sperm ample time to fertilise her eggs. It is in the female’s interest to mate with other males not only for the genetic diversity of her offspring but because the spermatophore replenishes her. To speed up the breakdown, a toothy structure that the researchers jokingly call ‘vagina dentata’ chews on it. Chemical and mechanical action disintegrates the spermatophore within three days, and the female is ready for sex again. She mates two to three times in her lifetime and uses up to 40% of the male’s nutritious care package to produce eggs.

How do spider webs without glue catch prey?

Typical web-spinning spiders have spinnerets that extrude silk with beads of glue to snag their insect prey. Cribellate spiders, however, possess thousands of tiny nozzles that produce extremely fine filaments of silk. Since these woolly-textured nanofibres have no sticky droplets, how do they still ensnare the spiders’ meals? Scientists in Austria and Germany have found the answer by studying cribellate spiders from the Americas, Europe, and Australia.

Insects have a coating of wax on their outer surface. When they touch the cribellate web, the wax melds with the nanofibres, possibly by capillary action. The spiders use the insects’ defences against them. The fine filaments then fuse together to form sturdy threads. The chances of the prey freeing itself from this web are small. The snagging ability of their webs is so successful that the venom glands of this family of spiders have atrophied.

Insects would have to get rid of their waxy coating if they are to escape getting trapped by these spiders. But the wax is crucial to their survival as it reduces water loss. Alternatively, insects can shield the wax layer or increase the viscosity of the wax. They may still fall prey to glue-embedded webs.

A salamander with multiple paternity

The all-female hybrid Ambystoma mates with multiple males and use equal parts of each partner's genetic material in her offspring. Credit: Robert Denton, Ohio State University

The all-female hybrid Ambystoma mates with multiple males and use equal parts of each partner’s genetic material in her offspring. Credit: Robert Denton, Ohio State University

Unisexual salamanders are common throughout the Great Lakes and northeastern America. The hybridisation event occurred about five million years ago, making these salamanders the most ancient unisexual vertebrate known. Since then the all-female offspring mate with the males of three other species.

The unisexual salamander can have five nuclear genomes, a condition called polyploidy. Of nearly 3,000 genes that researchers analysed of one captive hybrid individual, 72% came from males of three species. It retains some of each male’s genes and discards the rest, and it does this equally for all three species. However, such balance is not typical of hybrid plants. The researchers say the unusual level of balance may be the result of high degree of gene exchange between the hybrids and males of other species. The unisexuals may not decide which genes to keep and which ones to discard on an individual basis. They may have struck upon a balanced ratio of genes from the sexual males and maintained it. This stability may be the key to the hybrids’ success.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.

Animals do the most amazing things. Read about them in this series by Janaki Lenin.

Categories: Science