By Shatakshi Gawade
The prickly, globular sea urchin resides on the hard ocean floor. There are over 900 species of these marine invertebrates, generally 2.5 to 10 cm. in size. The species illustrated above is a Sperosoma grimaldii, first described in 1897 by R. Koehler. The sea urchin’s body is covered with slender sucker-tipped tubular feet, hundreds of movable spines, and small pincers. Its mouth, located on its underside, is equipped with an ‘Aristotle’s lantern’ – five teeth-like plates that close like a beak. The sharp teeth move in different directions to graze on algae, which grows on surfaces such as corals. In the absence of predators such as sea stars, an exploding population of sea urchins could destroy kelp forests.
Photo: Public Domain.
The scuttling crab completely scrambles our understanding of evolution – it is not linear, neat or unidirectional. Unlike humans, who evolved from apes just once, different animals in the same group evolved into crabs not twice, not thrice, but five different times. This march towards the same crabby characteristics is known as carcinisation, which is a type of convergent evolution (it takes place when species adapt in similar ways and occupy the same ecological niche).
The decapod family of crustaceans – to which crabs belong – have five distinct strands that have evolved in this convergent manner to have the crabby body: claws, 10 legs, and a small, flat and sturdy abdomen. Evolutionary paleobiologist Matthew Wills believes such convergence indicates that this particular body shape is well suited to ocean habitats.
Photo: Public Domain.
And to add to the scramble – some crabs have devolved (un-evolved) when changes didn’t seem to work, and also re-evolved when the devolution didn’t prove to be beneficial! An example of decarcinisation can be seen in frog crabs Raninoidea, of which there are 46 living species. Rapid climate change in recent decades has been a trigger for dramatic adaptations in some species such as the hermit crab, enough to qualify the evolved forms as new species. After all, isn’t change the only constant?
While rapid in evolutionary terms can still encompass several decades, the male of the orb-weaving spider does not have so much time to save itself. In fact, it lives on the edge of life and death every time it mates, and is among the few males that can be excused for leaving right after sex.
Female orb-weaving spiders practise sexual cannibalism – the male is captured and eaten instantly after mating. To avoid this unsatisfactory end, the male catapults off the female in a split-second after copulating, using energy stored in its front legs. In human terms, this would translate into a 1.8 m. tall man catapulting 530 m. in less than a second. To achieve this jump, the spider folds the tibia-metatarsus joint of its first leg pair, which exerts tremendous hydraulic pressure and makes the legs expand when released.
The male orb-weaver pulls off the female with an acceleration of 20Gs i.e. 20 times the acceleration felt during free fall, spinning at 175 revolutions per second as it soars to safety. But that isn’t the end of the romp – the male returns to the same female up to six times, repeatedly using a silky strand to climb back up and catapult off. Zhang Shichang, researcher and lead author of this orb-weaver spider study, believes that females of this species judge the quality of a male’s genes by his ability to catapult. She may accept his sperm only after he passes the test, despite having mated before. The female orb spider literally has the male jumping through hoops!
Photo: Public Domain/Biodiversity Hertitage Library.
Here’s a less exhausting tale of courtships in the animal world – a female rock hyrax Procavia capensis, a terrestrial mammal, chooses her mate depending on his musical abilities!
Researchers have surmised that the female connects strong genes and good health with the male rock hyrax’s singing abilities. Males that sing more also seem to have more surviving offspring. The songs the rock hyrax makes have many patterns that are common in human music and language. Their songs also have regional dialects, so individuals living closer together sing more like each other. Researchers also observed that the rock hyrax’s singing has a set structure – the song gets louder as it progresses (as in a crescendo), and the end is more complex, likely to keep its audience’s attention. The sounds in its music occur at regular intervals; this is known as isochronous rhythm. But if the male is not healthy, it is reflected in his singing, which the female can pick up on.
Photo: Public Domain/Biodiversity Hertitage Library.
The rock hyrax is found in scrub-covered areas, and is native to parts of the Middle East and Africa. It is commonly known as dassie in South Africa. Though it looks like a rodent, its closest living relatives are the elephant and manatee! Its upper incisors grow into two tusks.
While rock hyraxes decide to reproduce based on musical talents, the kãkãpõ – a species of parrot that is flightless – breeds when its favourite fruit tree, the rumi tree, has a bumper crop. This happens only once in four years. This unusual behaviour is partly responsible for the dire condition this species is in. Endemic to some islands of New Zealand, even the ‘critically endangered’ tag given to the kãkãpõ feels blithe, considering there are only 116 mature individuals of the Strigops habroptilus left in the wild. This nocturnal, whiskered, tree-climbing creature seems to take each step after considerable deliberation, as if weighed down by its predicament. New Zealand wildlife officials are hard at work managing this small clutch now. The arrival of humans on the islands is also responsible for its decline as they were hunted for meat, kept in captivity as pets, and killed by predators such as rats and cats, and their habitats were destroyed.
Researchers recently looked at what’s inside the kãkãpõ, and found that its gut microbiome consists almost entirely of the bacterium Escherichia coli. While the jury is still out on whether this is good or bad, such homogeneity may mean that the species cannot carry out all its functions. Studies of other fragmented or small populations have shown similar results – a loss of microbial diversity. Not being in the wilderness, exposure to humans, and change in environment and climate change can all alter an animal’s microbiome, often negatively. Microbiome analysis and engineering is now being used to conserve species, and could come in handy for the slow-breeding kãkãpõ too. Tracking changes in the microbiome profile could help conservationists tailor strategies for it.
Photo: Public Domain.
In Australia, a mysterious creature is spiralling its way into the future – the predatory yellow-spotted goanna Varanus panoptes. Though it occupies a range the size of Europe, it is barely spotted. Goannas have been in Australia for 15 million years; there are currently 27 extant species in the nation, most of which are carnivorous. While these lizards dig holes or burrows for their eggs, the nest of the yellow-spotted goanna is particularly interesting.
Photo: Public Domain.
The female of this 1.5-m.-long monitor lizard digs complex shelters in the shape of a helix, which are as deep as four metres. The expecting mother spends seven to ten days making this crèche for her eggs, ensuring they will be protected from the heat in northern Australia. She remains buried during the entire excavation process. At this depth, the clutch is protected by moist and cool soil for its incubation period of eight months. The newly-hatched babies, however, don’t follow in their mother’s path just yet. They make their way to the surface straight up, punching through the layer of soil.
After the little ones leave, the yellow-spotted goanna’s hard work serves yet another purpose – the eventual collapse of the helical burrow gives rise to a variety of nooks and crannies, which are occupied by other reptiles, frogs and insects. The yellow-spotted goanna thus acts as an unwitting ecosystem engineer.
Speaking of ecosystems, who wouldn’t love the ability to travel through time to experience a recently-discovered, two-million-year-old ecosystem in the farthest northern reaches of Greenland, which reveals what life was like when the Earth was in a warmer period? Today, this region is a harsh polar desert, but back then it was a forested coastline with a river flowing into an estuary. Intriguingly, the species once found here still survive in recent times in the Arctic environment and temperate boreal forests. However, there is no existing parallel for such an ecosystem!
These findings were derived from DNA found in Peary Land, a peninsula in northern Greenland, in a fossil-rich rock formation called Kap København. The temperature then was 11 to 19 degrees higher, and the area was completely dark for nearly half the year. The latest analysis reveals that this bubble of life supported 102 plant genera and nine species of animals such as mastodons, hares and horseshoe crabs. Birch and willow trees dominated this ancient landscape – trees found only in southern Greenland today. Researchers believe the survival of these species in such a climate is testimony to evolutionary adaptation.
Photo: Public Domain/Beth Zaikenjpg.
Wouldn’t it be extraordinary to travel through time and visit these ancient ecosystems and look at the incredible diversity of life there? Nevertheless, we can contend ourselves with our imagination, and take action to prevent ecosystems that exist today from soon becoming a relic.
