Q & A
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Why do so few birds bear weapons?
Birds lack arms in more ways than one. Avian equivalents of antlers, horns, tusks and canine teeth are few and far between – only about two per cent of our feathered friends possess specialised weapons in the form of spurs on their legs and wings. If push comes to shove, claws and beaks are capable of inflicting some damage, but these are built primarily for other purposes.
It’s probably no coincidence that most of the species that do pack dedicated weaponry are ground-feeding fowl – turkeys, chickens, pheasants, peacocks and the like – which don’t fly much, or indeed at all.
For flying animals, weight is critical. A small reduction in payload can save a great deal of energy. Weapons are heavy, so it might be quite literally a matter of fight or flight. Little surprise then that birds tend to settle disputes with displays of colour and song rather than direct combat.
Why do spiders have eight eyes?
Though a few spiders have six eyes, the default number is eight, usually arranged in two approximate rows. Scorpions also have multiple eyes (6-12), but they are less obvious because they are smaller. It seems likely that the original proto-arthropod probably had two eyes (as did the extinct trilobites and giant sea scorpions), and this pair has been maintained in crustaceans (such as woodlice), millipedes and insects.
But as arachnid ancestors evolved, the eyes split into a front portion and a side portion, and then split again.
Spiders then evolved so that rather than the multiple lens facets shown in insect compound eyes, a spider eye is a single lens with multiple receptors beneath for far better resolution of the final visual image.
Do chimps and gorillas ever fight with each other?
No – until recently. Though the two species often coexist in the same areas, interactions of any kind are thought to be rare – those that do happen have been described as relaxed and peaceful. However, a new study has revealed the first known lethal attacks on gorillas by chimpanzees. The researchers observed an encounter between a group of 18 chimps and five gorillas, in which the chimps formed coalitions to attack the family group. While the adults escaped, two infant gorillas were separated during the fray and were killed by the chimpanzees.
It is not yet known whether this was a rare or isolated event, or whether killings between the two species are actually more common than thought, as observing such interactions is not easy.
What is superfetation?
This refers to a second conception during pregnancy, leading to a mother carrying different-aged embryos. It’s rare in most creatures, but well known in Poeciliidae fish. The least killifish, for example, found in freshwater habitats across the south-east of the USA, stores sperm in her ovaries after mating. She sequentially fertilises her eggs, resulting in cohabiting embryos at different stages of development. A female will typically carry three to five litters (though up to seven litters have been found) of different ages, with her placenta providing each with nutrition for about four weeks before she gives birth. The fry are released over a period of 10-14 days, or longer.
It’s thought that this strategy allows her to maintain a relatively sleek physique during pregnancy, which is crucial when needing to evade predators at speed.
Can you ever find rooks in cities?
Yes, but rarely. In west London, I have observed a small annual spring passage of rooks flying overhead from south to north over the years, but none residing.
Rooks were once a common breeding bird in urban areas, even central London. In the mid to late 1800s, several sites in the capital housed rookeries – Lincoln’s Inn Fields was home to up to 35 nests, while Greenwich Park and Kensington Gardens housed even larger colonies. The birds clung on to their patches in London until relatively recently, but were eventually driven out of the country’s capital.
In Eastern Europe, though, it is a different story. Cities such as Kraków and Belgrade still have several inner-city rookeries. The majority of the cities where rooks occur contain a lot of natural woodland, with the cities themselves often on the edge of forests. Perhaps this is why rooks have not survived in British cities.
Being one of the least forested countries in Europe has its consequences.
RECORD BREAKER!
What is the largest mustelid?
This title goes to the strong and solitary wolverine, found in the north of the USA, Canada and Europe, which can grow to more than a metre in length. The wolverine is an omnivore and a scavenger, feeding on anything from birds’ eggs to berries to rodents. They have even been known to take down deer! Catchy monikers include skunk bear and glutton.
FACT.
Frogs do not drink water through their mouths. Instead, they absorb it through a semipermeable area of skin called a drinking patch, located on their belly and under their thighs.
WHAT ON EARTH?
Low profiles
They may look like roadkill on a cycle path, but these colourful splodges are very much alive. Once a female scale insect has plumbed herself into her foodplant of choice and started sucking the sap that flows forth, she has no reason to go anywhere ever again. A life of total immobility requires no functional wings, or even legs, but defences are essential, so these close relatives of aphids secrete a resinous shield for protection. The resin of some species is the source of shellac, once used to make gramophone records and still a component of wood varnish and nail polish. SB
FAST ANSWERS
Why do yellow longnose butterfly fish have such long noses?
For feeding. This extra-long appendage enables the fish to access tiny food items lurking in nooks and crannies in the coral, giving it an advantage over its peers. The species also feeds by using its powerful teeth to rip into bristleworms and sea urchins. Viewed from the front, its snout resembles a pair of forceps, leading to its alternate name of forceps fish. SM
Why do male and female tree sparrows look alike?
We’re still not sure!
Of all the sparrow species in the world, the tree sparrow is the only one in which the sexes are similar. That they evolved without sexual dimorphism has puzzled many a scientist. But there is one potential way to tell them apart: when the male uses his slightly larger black throat patch to display to potential mates. DL
Why is crack willow so named?
This large willow species, a common sight along our waterways, is so named because its trunk often bears the scars of cracks and splits –a result of the speed at which it grows.
Crack willow is also known for its brittle twigs, which snap readily at the base – probably not a species for exposed or windy areas. SM
INSTANT EXPERT
Does the tree of life reflect evolution?
NATURALISTS ONCE PUT LIVING things on a scale of progress from primitive to advanced, with man as the pinnacle of creation, inspired by the Scala Naturae or Great Chain of Being conceived by Aristotle in about 350BCE. That ‘ladder of life’ was later replaced by the idea of putting all species – past and present – on one tree to represent evolutionary history. But does that ‘tree of life’ accurately reflect the relationships between everything that has ever lived?
Where did the metaphor come from?
Charles Darwin published On the Origin of Species in 1859. His book contains a single abstract diagram to illustrate ‘descent with modification’ (evolution), a V-shaped tree with groups of organisms as branches, leading to species as twigs. In 1866, Ernst Haeckel drew the first annotated ‘tree of life’, with three major branches: animals, plants and ‘protists’. The third group originally included anything that wasn’t fauna or flora, including microscopic organisms.
How are species put on branches?
Similar species are grouped together based on shared characteristics that are assumed to have existed further back along their branch, in a common ancestor. While the characteristics can be physical features such as anatomy – the only option for extinct species that have left fossils behind – living things are now typically grouped by genetic similarity.
The practice of putting species into groups or clades (from klados, Greek for branch) is called cladistics and reconstructing evolutionary trees is phylogenetics (meaning origin of races).
Has the tree changed over time?
Yes. Old textbooks split life into five kingdoms: animals, plants, fungi and protists, plus ‘monera’ – single-celled organisms without a nucleus, now known as prokaryotes. But that changed in about 1977, after microbiologist Carl Woese discovered differences in the gene for producing 16S rRNA (a part of a cell’s protein-making machinery) among prokaryotes, suggesting they actually consist of two groups – namely bacteria and archaea – which are as distinct from one another as they are from the other kingdoms combined. Along with eukaryotes, whose cells have a nucleus, that gave three major branches on the tree of life.
Is the metaphor right?
Not entirely, as trees capture only a partial picture of evolution. A tree can only show how genes and their associated characteristics are inherited along a vertical route via a branch – how they’re passed down from one generation to the next (‘up’ the tree), from parent to offspring, ancestors to descendants.
But genetic material can be transferred between two species on separate branches too. Such ‘horizontal gene transfer’ is rare in multicellular eukaryotes because a foreign gene would need to overcome two barriers before it could be inherited – entering a reproductive cell (sperm or egg) and then crossing into the nucleus.
Why does gene transfer matter?
It matters because horizontal transfer can offer new abilities that enable a species to adapt to its environment, such as providing superbugs with genes that confer antibiotic resistance. While rare in complex life, swapping genes is common among microbes. A comparison of distantly-related groups revealed that, on average, 40 per cent of a microbe’s genome (its complete set of genes) comes from ancient transfers.
If you draw those gene transfers as connections between branches on the tree of life, the tidy structure ends up looking like a messy web or ‘network of life’.
So was Darwin wrong about the tree?
No, but its structure is hazy. The tree of life is really a ‘tree of cells’ whose evergrowing branches divide to reproduce. Like multicellular life, single-celled microbes also reproduce by dividing so, despite horizontal transfer, it should be possible to detect an underlying pattern of branches. In fact, scientists have studied networks of genomes and found ‘genetic worlds’ of eukaryotes, archaea, bacteria and viruses – which are connected by thin webs of gene transfer yet remain broadly discrete. If you draw those ‘worlds’ as branches of life, you see a backbone of evolution that (if you squint) still looks roughly tree-shaped.
BBC WILDLIFE EXPERTS
