Category: Molecular Biology
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The paths of evolutionary change at the molecular level frequently result in convergent solutions. Examples of molecular convergence range from gene regulation and genome structure to critical enzymes and other proteins important in cellular to whole organ structure and function.
Both patterns of gene loss and gene transfer from one organism to another frequently recur. For example, members of the two major animal groups, the deuterostomes and protostomes, have independently lost genes used redundantly in amino acid synthesis, and several parasitic bacteria (e.g. spirochaetes and Mycoplasma genitalium, with its tiny 580kb genome) have lost genes for vital cellular functions that are instead carried out by their host. Massive 'horizontal' gene transfer to host organisms has occurred in many pathogenic, endosymbiotic bacteria, in some parasitic protistans and, interestingly, in groups as different as choanoflagellates and rotifers. In a remarkable example of molecular convergence, the mitochondrial oxidase gene Cox2 of green algae (Chlorophyta) and apicomplexan protists was transferred to the nucleus and subsequently divided into two genes at the same position. In terms of whole genetic regulatory networks, it is clear that at certain levels convergence occurs; one case of this is the reduction in pelvis size of sticklebacks and manatee, caused by identical but independent changes in a shared vertebrate developmental pathway.
Organisms have evolved a number of defence mechanisms to cope with pathogens, including anti-microbial compounds and immune systems. The innate immune systems of animals and plants are convergent, sharing trans-membrane and intracellular defence proteins comparable in structure and function, while the adaptive immune systems of vertebrates finds strongly independent parallels in jawless fish, and even to some extent the limited 'memory' of insect immune systems. Tetrodotoxin (or tetrodoxin) is a lethal defence compound synthesised by symbiotic bacteria and recruited by an unusual range of animals including puffer fish, blue-ringed octopus, two unrelated frogs and the newt Taricha. Saxitoxin is produced by the venus clam Saxidomus (a bivalve), one macroscopic alga and a few octopus, crustacean, fish, cyanobacteria and dinoflagellate species. For both tetrodoxin and saxitoxin, animals protect their nervous systems from toxic effects by specific and convergent amino acid changes in sodium voltage-gated channels (these channels themselves being convergent between animals, a protistan heliozoan known as Actinoryne contractilis and an alkaline-tolerant bacterium). A number of bacteria have converged on molecular adaptations to saline environments, including archeal halobacteria and the eubacterium Salinibacter ruber. In a particularly striking case, eubacteria and certain archael bacteria have also independently evolved flagellar motors, constructing them from similar proteins.
Enzymes are proteins that accelerate biochemical reactions, and they provide many examples of convergence. Identical active site structure may evolve, such as the serine-histidine-aspartate 'triad' in trypsin and subtilisin, or different routes may taken by structurally distinct proteins to catalyse an identical substrate (e.g. β-lactamases can function via serine protease or zinc 'metalloprotease' groups). The enzyme carbonic anhydrase (CA) converts CO2 + H20 ↔ HCO3- (bicarbonate) + H+, which is a reversible reaction critical for processes as diverse as photosynthesis, respiration, biomineralisation and kidney function. Not surprisingly, therefore, CA enzymes are ubiquitous, and yet they appear to have evolved at least five (or six) times independently, and various CA families are known in animals, plants, bacteria and certain algae (e.g. diatoms, haptophytes). Peroxidases are typical anti-microbial enzymes, creating toxic oxidising conditions via generation of highly reactive hydrogen peroxide (H2O2) or organic hydroperoxidases. An array of peroxidases is known to have evolved in animals, plants, fungi and bacteria, variously depending on heme (iron-based) cofactors, active cysteine or selenocysteine to function.
Aside from enzymes a wealth of other proteins critical to life show clear convergences, from respiratory proteins to silks. Astonishingly, the copper-based respiratory protein haemocyanin evolved independently in arthropods and molluscs, while iron-based β-haemoglobins show convergent gene duplication patterns in birds and mammals (as well as between monotreme and therian mammals). Eye lenses are transparent due to the properties of crystallin proteins, independently recruited from microbes many times in animal evolution and co-opted from roles in stress resistance (e.g. heat shock proteins). Interestingly, genes for crystallins made of very different proteins are driven by almost identical promoter regions in the genomes of scallops and vertebrates! Proteins with elastic properties show convergences as various levels, from elastins in the vertebrate and cephalopod aorta to the shared characteristics of resilin, abductin, elastin and even gluten from plant seeds. Bivalves such as the well-known mussels have attachment structures with both elastic and more rigid silk fibroin-like regions, and the 'pen shell' Pinna has a byssus of 'sea-silk' threads, reminiscent of arthropod silk. Silk evolved for various functions at least three times in arachnids (spiders, spider-mites and some pseudoscorpions) and many more times in the insects, especially at larval stages. Among many convergent functions: spiders, spider-mites and caddis fly larvae build webs; silk nests are built by weaver ants, leafhoppers, 'webspinners' and pseudoscorpions; the silk-worm Bombyx makes silk cocoons; a few (brave) spiders and hilarinid flies offer silken 'nuptial gifts', and spiders, spider mites and moth larvae use silk lines for 'ballooning' into the air.
| Topic title | Teaser text | Availability |
|---|---|---|
| Light producing chemicals: how to make bioluminescence | The most remarkable luciferin in terms of its distribution is known as�coelenterazine. This nitrogen-ring based molecule is found in nine separate groups, ranging from radiolarians to fish. | Available |
| Echolocation in bats | How can bats navigate in total darkness amongst trees and branches, but still locate a tiny, fluttering insect with extraordinary acuity? All made possible through echolocation, an astonishing sensory mechanism… | Available |
| Nematode antibacterial proteins and invertebrate defensins | n/a | Unavailable |
| Hermaphroditism in nematodes | n/a | Unavailable |
| Colony specificity and self-recognition in tunicates | n/a | Unavailable |
| Sponge spicules: form, genes and fibre-optics | n/a | Unavailable |
| Horizontal gene transfer in bdelloid rotifers, bacteria and protists | n/a | Unavailable |
| Peroxidases and oxidases | n/a | Unavailable |
| Hydrogenosomes and mitosomes | n/a | Unavailable |
| Mitochondrial genome convergences | Most likely, mitochondria have a single evolutionary origin, but that doesn't mean they are immune to convergence... | Available |
| Mitochondrial TOM proteins | n/a | Unavailable |
| Pufferfish (and inflation) | Pufferfish are some of the most extraordinary fish to have evolved, especially because of their capacity to swallow water and inflate themselves to something like a football. Not only that but some representatives can be deadly to the unwary diner... | Available |
| Water-moulds (oomycetes) | n/a | Unavailable |
| Collagen in animals and bacteria | n/a | Available |
| Flight muscle (arthrin) | n/a | Unavailable |
| Cytoskeleton | n/a | Unavailable |
| Tetrodotoxin | Not many foods served in a restaurant can kill you, but pufferfish is the exception. Tetrodotoxin, the toxin responsible for such culinary fatalities, reveals a fascinating story of convergent evolution... | Available |
| Saxitoxin synthesis: from molluscs to algae | Saxitoxin has a similar molecular structure to tetrodoxin and a wide distribution amongst living organisms, with evidence that is has been recruited independently several times. | Available |
| SNARE protein receptors and the evolution of multicellularity | There is an intriguing correlation with larger numbers of SNAREs and multicellularity, at least in plants and animals. | Unavailable |
| Membrane transport in eukaryotes | Dense core granules (DCGs) are very similar in ciliates and animals, but the systems are clearly convergent, and in particular the recruitment of a key group of proteins (known as dynamins) is independent. | Unavailable |
| Bats: Insights into convergence | Bats show a fascinating array of convergences, from echolocation to flight to nectar feeding. Vampire bats can even detect infrared radiation, while others might be able to see into the ultraviolet end of the spectrum. | Available |
| Echolocation in toothed whales and ground-dwelling mammals | Given the extraordinary powers of echolocation in bats, it is not surprising that this group has received the most attention. However, they are not the only mammals to have evolved echolocation. Who invented sonar millions of years before the Navy? | Available |
| Dandruff, Malassezia and Candida | The presence of Malassezia does not guarantee dandruff, as this fungus is commonly present on healthy skin, but it evidently central to dandruff production if other key factors support it. | Available |
| Extremophiles: Archaea and Bacteria | Surely, no organism can survive in boiling water or brines nine times the salinity of seawater? Wrong - some archaea and bacteria have independently evolved adaptations to such extreme environments... | Available |
| Sodium voltage-gated ion channels | Sodium voltage-gated ion channels are vital to electric signal transmission, but it is less widely appreciated that they are convergent and have evolved at least twice in groups outside the animals. | Unavailable |
| Olfaction: insights into convergence | Although olfaction is very widespread, there is abundant evidence for repeated convergence of key features, strongly suggesting that there really is an optimal solution to detecting smells. | Available |
| Loss of olfactory capacity in primates and cetaceans | It is widely thought that reduced olfactory capacity in apes is linked to the development of acute vision, especially trichromacy. | Available |
| Haptoglobins: convergence of Hp2 allele | One of the allelic forms of haptoglobin, known as Hp2, in the case of humans and cow shows a striking convergence, notably in the so-called complement control protein (CCP) domain. | Unavailable |
| Animal haemoglobins | There is good evidence for convergence in animal haemoglobins because even though the protein itself is ancestral to all animals, during its evolution various episodes of gene duplication have led to a number of different varieties, notably the β-globins. | Unavailable |
| Innate and adaptive immune systems | A vile cough, soaring temperature? When attacked by nasty microbes, our immune system comes in handy. Surprisingly (or not), plants have come up with a very similar solution to dealing with pathogens, but independently... � � | Available |
| Silk production and use in arthropods | Remarkably, fossil silk is known, especially from amber of Cretaceous age. Material includes both silk with trapped insects, possibly from an orb-web, and strands with the characteristic viscid droplets that are the key in trapping prey. | Available |
| Mussel attachment and the Pinna byssus | It is clear that the Pinna byssus has unusual properties in comparison to its equivalent in the bivalve mussel, and is conspicuously different in terms of crystallinity. | Available |
| Biological uses of silk: from webs to ballooning | What material is so versatile that it can be used for capturing prey, building nests, communication and even cleaning? The answer: that most remarkable of biomaterials - silk. | Available |
| Enzymes: convergence on active sites and reaction types | Enzymes make the world go round, each an evolutionary marvel - and convergent. | Available |
| Evolution of insecticide resistance | There are several varieties of insecticide, and each one is designed to knock out some metabolic or physiological capability of the insect, targeting a specific system. | Unavailable |
| Carbonic anhydrase in vertebrates, plants, algae and bacteria | Carbonic anhydrase is extremely convergent and may have evolved as many as six times. The most familiar variants are α, β and γ carbonic anhydrases. | Available |
| Bacterial flagellar motors | The bacterial flagellum has proved to be a cause celebre because of its high-jacking by the “intelligent design” movement who argue that it is “irreducibly complex” and therefore could not have evolved by Darwinian processes. | Unavailable |
| Gene regulation and cell cycles in bacteria and eukaryotes | Regulation of gene networks and cell cycles are of particular importance for convergence because genomic organization in bacteria shows significant differences from the eukaryotes. | Unavailable |
| Butterflies and moths: insights into convergence | Some moths feed on the secretions from the tear-ducts of mammals, and some moths in Madagascar have evolved this independently, but instead of mammals they frequent birds. | Unavailable |
| Plumage in birds | Exampes of convergece in bird plumage are the well-known tendency for different groups of tropical sea-birds to have dark plumage, and what may represent M�llerian mimicry in the pitohuis, which are famous for their convergent use of toxic alkaloids. | Unavailable |
| Developmental genetic pathways to convergence | At first sight there is a fairly simple dichotomy between convergent features that have effectively the same genetic basis, and those where the same feature emerges but the underlying genetics are different. The former, however, is somewhat more complicated... | Available |
| Pheromones in arthropods | Not surprisingly this is a rich area of insights into evolutionary convergence because if an animal, such as a spider, can independently evolve the pheromone then a sexual lure is turned into a metaphorical honey trap. | Unavailable |
| Genome reduction in bacteria and animals | Interestingly, many parasitic bacteria show dramatic and parallel gene reduction independent of each other, although here various vital functions are now undertaken by the host. | Unavailable |
| Haemocyanin in arthropods and molluscs | The degree of similarity between the active sites in arthropod and molluscan haemocyanin has been called “remarkable” and “startling”, but actually suggests that wherever in the universe life employs copper for aerobic respiration it will call upon haemocyanin. | Available |
| Elastic proteins | What do rubber bands and fleas have in common? | Available |
| Crystallins: eye lens proteins | Whereas typically technology demands furnaces, so that the glass for a lens is produced at hundreds of degrees Celsius and then requires most careful grinding, so nature calls upon proteins known as crystallins. | Available |
| Moulting in arthopods, annelids and other animals | Moulting has, however, evolved independently in other groups, including the annelids where some polychaetes shed their jaws. | Unavailable |
