In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
Host–parasite coevolution is a special case of coevolution, the reciprocal adaptive genetic change of a host and a parasite through reciprocal selective pressures. It is characterized by reciprocal genetic change and thus changes in allele frequencies within populations; these are determined by three main types of selection dynamics: negative frequency-dependent selection when a rare allele has a selective advantage. Theories of host–parasite coevolution include the geographic mosaic theory, which assumes a selection mosaic, coevolutionary hotspots, geographic mixing. Model systems include the nematode Caenorhabditis elegans with the bacterium Bacillus thuringiensis. Hosts and parasites exert reciprocal selective pressures on each other, which may lead to rapid reciprocal adaptation. For organisms with short generation times, host–parasite coevolution can be observed in comparatively small time periods, making it possible to study evolutionary change in real-time under both field and laboratory conditions.
These interactions may thus serve as a counter-example to the common notion that evolution can only be detected across extended time. The dynamics of these interactions are summarized in the Red Queen hypothesis, namely that both host and parasite have to change continuously to keep up with each other's adaptations. Host–parasite coevolution is ubiquitous and of potential importance to all living organisms, including humans, domesticated animals and crops. Major diseases such as malaria, AIDS and influenza are caused by coevolving parasites. Better understanding of coevolutionary adaptations between parasite attack strategies and host immune systems may assist in the development of novel medications and vaccines. Host–parasite coevolution is characterized by reciprocal genetic change and thus changes in allele frequencies within populations; these changes may be determined by three main types of selection dynamics. An allele is subject to negative frequency dependent selection if a rare allelic variant has a selective advantage.
For example, the parasite should adapt to the most common host genotype, because it can infect a large number of hosts. In turn, a rare host genotype may be favored by selection, its frequency will increase and it becomes common. Subsequently, the parasite should adapt to the former infrequent genotype. Coevolution determined by negative frequency dependent selection is rapid occurring across few generations, it maintains high genetic diversity by favoring uncommon alleles. This selection mode is expected for multicellular hosts, because adaptations can occur without the need for novel advantageous mutations, which are less to be frequent in these hosts because of small population sizes and long generation times. Overdominance occurs. One example is sickle cell anemia, it is due to a mutation in the hemoglobin gene leading to sickle shape formation of red blood cells, causing clotting in blood vessels, restricted blood flow, reduced oxygen transport. At the same time, the mutation confers resistance to malaria, caused by Plasmodium parasites, which are passed off in red blood cells after transmission to humans by mosquitoes.
Hence and heterozygote genotypes for the sickle-cell disease allele show malaria resistance, while the homozygote suffers from severe disease phenotype. The alternative homozygote, which does not carry the sickle cell disease allele, is susceptible to infection by Plasmodium; as a consequence, the heterozygote genotype is selectively favored in areas with a high incidence of malaria. If an allele provides a fitness benefit, its frequency will increase within a population – selection is directional or positive. Selective sweeps are one form of directional selection, where the increase in frequency will lead to the fixation of the advantageous allele; the process is considered to be slower in comparison to negative frequency dependent selection. It may produce an "arms race", consisting of the repeated origin and fixation of new parasite virulence and host defence traits; this mode of selection is to occur in interactions between unicellular organisms and viruses due to large population sizes, short generation times haploid genomes and horizontal gene transfer, which increase the probability of beneficial mutations arising and spreading through populations.
John N. Thompson's geographic mosaic theory of coevolution hypothesizes spatially divergent coevolutionary selection, producing genetic differentiation across populations; the model assumes three elements that jointly fuel coevolution: 1) a selection mosaic among populations Natural selection on interspecific interactions differs among populations. Thus genotype-by-genotype-by-environment interactions affect fitness of the antagonists. In other words, the specific environmental conditions determine how any genotype of one species influences the fitness of another species.2) coevolutionary hotspots Coevolutionary hotspots are communities in which selection on the interaction is reciprocal. These hotspots are intermixed with so-called coldspots in which only one or neither species adapts to the antagonist.3) geographic mixing of traits Between the communiti
Rabbits in Australia
European rabbits were introduced to Australia in the 18th century with the First Fleet and became widespread. Such wild rabbit populations are a serious mammalian pest and invasive species in Australia causing millions of dollars of damage to crops, their spread was enhanced through the emergence of strong crossbreeds. Various methods in the 20th century have been attempted to control the Australian rabbit population. Conventional methods include shooting rabbits and destroying their warrens, but these had only limited success. In 1907, a rabbit-proof fence was built in Western Australia in an unsuccessful attempt to contain the rabbits; the myxoma virus, which causes myxomatosis, was introduced into the rabbit population in the 1950s and had the effect of reducing the rabbit population. However, the survivors have since adapted and recovered their previous numbers. Rabbits were introduced to Australia by the First Fleet in 1788, they were bred as food animals in cages. In the first decades, they do not appear to have been numerous, judging from their absence from archaeological collections of early colonial food remains.
However, by 1827 in Tasmania, a newspaper article noted "...the common rabbit is becoming so numerous throughout the colony, that they are running about on some large estates by thousands. We understand, that there are no rabbits whatever in the elder colony" i.e. New South Wales; this shows a localised rabbit population explosion was underway in Tasmania in the early 19th century. At the same time in NSW, Cunningham noted, "... rabbits are bred around houses, but we have yet no wild ones in enclosures..." He noted the scrubby, sandy rubble between Sydney and Botany Bay would be ideal for farming rabbits. Enclosures appear to mean more extensive rabbit-farming warrens, rather than cages; the first of these, in Sydney at least, was one built by Alexander Macleay at Elizabeth Bay House, "a preserve or rabbit-warren, surrounded by a substantial stone wall, well stocked with that choice game." In the 1840s, rabbit-keeping became more common, with examples of the theft of rabbits from ordinary peoples' houses appearing in court records and rabbits entering the diets of ordinary people.
In 1857–1858 Alexander Buchanan, overseer for F. H. Dutton's Anlaby Estate in the Mid-North of South Australia, released a number of rabbits for hunting sport, their population remained stable until around 1866, presumed to have been kept in check by native carnivores and were protected by an Act of Parliament, but by 1867 was out of control. The population explosion was ascribed to the disappearance of native predators, but is explained by the emergence of a hardier breed by natural selection; the current infestation appears to have originated with the release of 24 wild rabbits by Thomas Austin for hunting purposes in October 1859, on his property, Barwon Park, near Winchelsea, Victoria. While living in England, Austin had been an avid hunter dedicating his weekends to rabbit shooting. Upon arriving in Australia, which had no native rabbit population, Austin asked his nephew William Austin in England to send him twelve grey rabbits, five hares, seventy-two partridges and some sparrows so he could continue his hobby in Australia by creating a local population of the species.
William could not source enough grey rabbits to meet his uncle's order, so he topped it up by buying domestic rabbits. One theory as to why the Barwon Park rabbits adapted so well to Australia is that the hybrid rabbits that resulted from the interbreeding of the two distinct types were much more suited to Australian conditions. Many other farms released their rabbits into the wild after Austin. At the time he had stated, "The introduction of a few rabbits could do little harm and might provide a touch of home, in addition to a spot of hunting", a prediction which has not aged well; the rabbits were prolific creatures and spread across the southern parts of the country. Australia had ideal conditions for a rabbit population explosion. With mild winters, rabbits were able to breed the entire year. With widespread farming, areas that might otherwise have been scrub or woodlands were instead turned into vast areas with low vegetation, creating ideal habitats for rabbits. In a classic example of unintended consequences, rabbits had become so prevalent within ten years of their introduction in 1859 that two million could be shot or trapped annually without having any noticeable effect on the population.
It was the fastest spread recorded of any mammal anywhere in the world. Today, rabbits are entrenched in the southern and central areas of the country, with scattered populations in the northern deserts. Although the rabbit is a notorious pest, it proved useful to many people during the depressions of the 1890s and 1930s and during wartime. Trapping rabbits helped farmers and stationhands by providing food and extra income, in some cases helped pay off farming debts. Rabbits were boiled to be fed to poultry. Frozen rabbit carcasses were traded locally and exported. Pelts, were used in the fur trade and are still used in the felt-hat industry. Since their introduction from Europe in the 19th century, the effect of rabbits on the ecology of Australia has been devastating, they are suspected of being the most significant known factor in species loss in Australia. Rabbits are believed to have had an immense impact on the abundance of natural resource availability concerning overgrazing; the rabbits would first deplete the natural pasture vegetation, would resort to consuming woody vegetation, which included small shrubs, the leaves and bark of trees.
The extent of plant species' loss is unknown at this time though it i
Common garter snake
The common garter snake is a species of natricine snake, indigenous to North America and found across the continent. Most common garter snakes have a pattern of yellow stripes on a black, brown or green background, their average total length is about 55 cm, with a maximum total length of about 137 cm; the average body mass is 150 g. Common garter snakes are the state reptile of Massachusetts. Current scientific classification recognizes thirteen subspecies: T. s. sirtalis – eastern garter snake T. s. parietalis – red-sided garter snake T. s. infernalis – California red-sided garter snake T. s. concinnus – red-spotted garter snake T. s. dorsalis – New Mexico garter snake T. s. pickeringii – Puget Sound garter snake T. s. tetrataenia – San Francisco garter snake T. s. semifasciatus – Chicago garter snake T. s. pallidulus Allen, 1899 – Maritime garter snake T. s. annectens B. C. Brown, 1950 – Texas garter snake T. s. fitchi Fox, 1951 – valley garter snake T. s. similis Rossman, 1965 – blue-striped garter snake T. s. lowei W. Tanner, 1988Nota bene: A trinomial authority in parentheses indicates that the subspecies was described in a genus other than Thamnophis.
The subspecific name, fiestchi, is in honor of American herpetologist Henry Sheldon Fitch. The subspecific name, lowei, is in honor of American herpetologist Charles Herbert Lowe; the subspecific name, pickeringii, is in honor of American naturalist Charles E. Pickering. Common garter snakes are thin snakes. Few grow over about 4 ft long, most stay smaller. Most have longitudinal stripes in many different colors. Common garter snakes come in a wide range of colors, including green, yellow, red, orange and black; the common garter snake is a diurnal snake. In summer, it is most active in late afternoon. In warmer southern areas, the snake is active year-round. On warm winter afternoons, some snakes have been observed emerging from their hibernacula to bask in the sun; the saliva of a common garter snake may be toxic to other small animals. Garter snakes were researched and studies show they have a mild venom in their saliva. For humans, a bite is not dangerous, though it may cause slight itching, and/or swelling.
Most common garter snakes secrete a foul-smelling fluid from postanal glands when handled or harmed. Common garter snakes are resistant to found poisons such as that of the American toad and rough-skinned newt, the latter of which can kill a human if ingested. Common garter snakes have the ability to absorb the toxin from the newts into their body, making them poisonous, which can deter potential predators; the common garter snake use toxicity for both defense. On the offensive side, the snake's venom can be toxic to some of its smaller prey, such as mice and other rodents. On the defensive side, the snake uses its resistance to toxicity to provide an important anti-predator capability. A study on the evolutionary development of resistance of tetrodotoxin tested between two populations of Thamnophis and tested inside a population of T. sirtalis. Those who were exposed to and lived in the same environment as the newts that produce tetrodotoxin when eaten were more immune to the toxin. While resistance to tetrodotoxin is beneficial in acquiring newt prey, there are costs associated with it as well.
Consuming the toxin can lead to reduced speed and sometimes no movement for extended periods of time, along with impaired thermoregulation. The anti-predator display that this species uses demonstrates the idea of an "arms race" between different species and their anti-predator displays. Along the entire geographical interaction of T. granulosa and T. sirtalis, there are patches that correspond to strong coevolution as well as weak or absent coevolution. Populations of T. sirtalis that do not live in areas that contain T. granulosa contain the lowest amount of tetrodotoxin resistance, while those that do live in the same area contain the highest levels of tetrodotoxin resistance. In populations where tetrodotoxin is absent in T. granulosa, resistance in T. sirtalis is selected against because the mutation causes lower average population fitness. This helps maintain polymorphism within garter snake populations. In the early part of spring, when snakes are coming out of hibernation the males emerge first to be ready when the females wake up.
Some males will assume the role of a female and lead other males away from the burrow, luring them with a fake female pheromone. After such a male has led rivals away, he "turns" back into a male and races back to the den, just as the females emerge, he is the first to mate with all the females he can catch. This method serves to help warm males by tricking other males into surrounding and heating up the male, is useful to species in colder climates. There are far more males than females and, why, during mating season, they form "mating balls," where one or two females will be swamped by ten or more males. Sometimes a male snake will mate with a female before hibernation and the female will store the sperm internally until spring, when she will allow her eggs to be fertilized. If she mates again in the spring, the fall sperm will degenerate, the spring sperm will fertilize her eggs; the females may give birth ovoviviparously to 12 to 40 young from July through
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaiʻi in the south to northernmost Kure Atoll. The group was known to Europeans and Americans as the Sandwich Islands, a name chosen by James Cook in honor of the First Lord of the Admiralty John Montagu, 4th Earl of Sandwich; the contemporary name is derived from the name of Hawaii Island. The U. S. state of Hawaii now occupies the archipelago in its entirety, with the sole exception of Midway Island, which instead separately belongs to the United States as one of its unincorporated territories within the United States Minor Outlying Islands. The Hawaiian Islands are the exposed peaks of a great undersea mountain range known as the Hawaiian–Emperor seamount chain, formed by volcanic activity over a hotspot in the Earth's mantle; the islands are about 1,860 miles from the nearest continent. Captain James Cook visited the islands on January 18, 1778, named them the "Sandwich Islands" in honor of John Montagu, 4th Earl of Sandwich, one of his sponsors as the First Lord of the Admiralty.
This name was in use until the 1840s, when the local name "Hawaii" began to take precedence. The Hawaiian Islands have a total land area of 6,423.4 square miles. Except for Midway, an unincorporated territory of the United States, these islands and islets are administered as Hawaii—the 50th state of the United States; the eight main islands of Hawaii are listed here. All except Kahoolawe are inhabited. Smaller islands and reefs form the Northwestern Hawaiian Islands, or Hawaiian Leeward Islands: Nihoa Necker French Frigate Shoals Gardner Pinnacles Maro Reef Laysan Lisianski Island Pearl and Hermes Atoll Midway Atoll Kure Atoll The state of Hawaii counts 137 "islands" in the Hawaiian chain; this number includes all minor islands and islets, or small islands, offshore of the main islands and individual islets in each atoll. These are just a few: Ford Island Lehua Ka'ula Kaohikaipu Mānana Mōkōlea Rock Nā Mokulua Molokini Mokoliʻi Moku Manu Moku Ola Moku o Loʻe Sand Island Grass Island This chain of islands, or archipelago, developed as the Pacific Plate moved northwestward over a hotspot in the Earth's mantle at a rate of 32 miles per million years.
Thus, the southeast island is volcanically active, whereas the islands on the northwest end of the archipelago are older and smaller, due to longer exposure to erosion. The age of the archipelago has been estimated using potassium-argon dating methods. From this study and others, it is estimated that the northwesternmost island, Kure Atoll, is the oldest at 28 million years; the only active volcanism in the last 200 years has been on the southeastern island, Hawaiʻi, on the submerged but growing volcano to the extreme southeast, Loʻihi. The Hawaiian Volcano Observatory of the USGS documents recent volcanic activity and provides images and interpretations of the volcanism. Kīlauea has been erupting nearly continuously since 1983. All of the magma of the hotspot has the composition of basalt, so the Hawaiian volcanoes are composed entirely of this igneous rock. There is little coarser-grained gabbro and diabase. Nephelinite is exposed on the islands but is rare; the majority of eruptions in Hawaiʻi are Hawaiian-type eruptions because basaltic magma is fluid compared with magmas involved in more explosive eruptions, such as the andesitic magmas that produce some of the spectacular and dangerous eruptions around the margins of the Pacific basin.
Hawaiʻi island is the youngest island in the chain, built from five volcanoes. Mauna Loa, taking up over half of the Big Island, is the largest shield volcano on the Earth; the measurement from sea level to summit is more than 2.5 miles, from sea level to sea floor about 3.1 miles.. The Hawaiian Islands have many earthquakes caused by volcanic activity. Most of the early earthquake monitoring took place in Hilo, by missionaries Titus Coan, Sarah J. Lyman and her family. From 1833 to 1896 4 or 5 earthquakes were reported per year. Hawaii accounted for 7.3% of the United States' reported earthquakes with a magnitude 3.5 or greater from 1974 to 2003, with a total 1533 earthquakes. Hawaii ranked as the state with the third most earthquakes over this time period, after Alaska and California. On October 15, 2006, there was an earthquake with a magnitude of 6.7 off the northwest coast of the island of Hawaii, near the Kona area of the big island. The initial earthquake was followed five minutes by a magnitude 5.7 aftershock.
Minor-to-moderate damage was reported on most of the Big Island. Several major roadways became impassable from rock slides, effects were felt as far away as Honolulu, nearly 150 miles from the epicenter. Power outages lasted for several hours to days. Several water mains ruptured. No deaths or life-threatening injuries were reported. On May 4, 2018 there was a 6.9 earthquake in the zone of volcanic activity from Kīlauea. Earthquakes are monitored by the Hawaiian Volcano Observatory run by the USGS; the Hawaiian Islands are subjec
Antimicrobial resistance is the ability of a microbe to resist the effects of medication that once could treat the microbe. The term antibiotic resistance is a subset of AMR, as it applies only to bacteria becoming resistant to antibiotics. Resistant microbes are more difficult to treat, requiring alternative medications or higher doses of antimicrobials; these approaches both. Microbes resistant to multiple antimicrobials are called multidrug resistant; those considered extensively drug resistant or drug resistant are sometimes called "superbugs". Resistance arises through one of three mechanisms: natural resistance in certain types of bacteria, genetic mutation, or by one species acquiring resistance from another. All classes of microbes can develop resistance. Fungi develop antifungal resistance. Viruses develop antiviral resistance. Protozoa develop antiprotozoal resistance, bacteria develop antibiotic resistance. Resistance can appear spontaneously because of random mutations. However, extended use of antimicrobials appears to encourage selection for mutations which can render antimicrobials ineffective.
Preventive measures include only using antibiotics when needed, thereby stopping misuse of antibiotics or antimicrobials. Narrow-spectrum antibiotics are preferred over broad-spectrum antibiotics when possible, as and targeting specific organisms is less to cause resistance, as well as side effects. For people who take these medications at home, education about proper use is essential. Health care providers can minimize spread of resistant infections by use of proper sanitation and hygiene, including handwashing and disinfecting between patients, should encourage the same of the patient and family members. Rising drug resistance is caused by use of antimicrobials in humans and other animals, spread of resistant strains between the two. Growing resistance has been linked to dumping of inadequately treated effluents from the pharmaceutical industry in countries where bulk drugs are manufactured. Antibiotics increase selective pressure in bacterial populations, causing vulnerable bacteria to die.
At low levels of antibiotic, resistant bacteria can have a growth advantage and grow faster than vulnerable bacteria. With resistance to antibiotics becoming more common there is greater need for alternative treatments. Calls for new antibiotic therapies have been issued. Antimicrobial resistance is increasing globally because of greater access to antibiotic drugs in developing countries. Estimates are that 700,000 to several million deaths result per year; each year in the United States, at least 2 million people become infected with bacteria that are resistant to antibiotics and at least 23,000 people die as a result. There are public calls for global collective action to address the threat that include proposals for international treaties on antimicrobial resistance. Worldwide antibiotic resistance is not identified, but poorer countries with weaker healthcare systems are more affected; the WHO defines antimicrobial resistance as a microorganism's resistance to an antimicrobial drug, once able to treat an infection by that microorganism.
A person cannot become resistant to antibiotics. Resistance is a property of not a person or other organism infected by a microbe. A World Health Organization report released April 2014 stated, "this serious threat is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country. Antibiotic resistance—when bacteria change so antibiotics no longer work in people who need them to treat infections—is now a major threat to public health." The European Centre for Disease Prevention and Control calculated that in 2015 there were 671,689 infections in the EU and European Economic Area caused by antibiotic-resistant bacteria, resulting in 33,110 deaths. Most were acquired in healthcare settings. Bacteria with resistance to antibiotics predate medical use of antibiotics by humans. However, widespread antibiotic use has made more bacteria resistant through the process of evolutionary pressure. Reasons for the widespread use of antibiotics in human medicine include: increasing global availability over time since the 1950s uncontrolled sale in many low or middle income countries, where they can be obtained over the counter without a prescription resulting in antibiotics being used when not indicated.
This may result in emergence of resistance in any remaining bacteria. Other causes include: Antibiotic use in livestock feed at low doses for growth promotion is an accepted practice in many industrialized countries and is known to lead to increased levels of resistance. Releasing large quantities of antibiotics into the environment during pharmaceutical manufacturing through inadequate wastewater treatment increases the risk that antibiotic-resistant strains will develop and spread, it is uncertain whether antibacterials in soaps and other products contribute to antibiotic resistance, but antibacterial soaps are discouraged for other reasons. Antiseptics create AMR to antibiotics and other antiseptics: Antiseptics appear to activate tolerance mechanisms in bacteria, which offer them protection against a range of antiseptics as well as antibiotics. Antiseptics are used in many wound care dressings; these findings may explain the increase in treatment-resistant hospital infections. Exposure to low doses of the antiseptic octenidine allowed several different strains of Pseudomonas aeruginosa to develop
Bats are mammals of the order Chiroptera. Bats are more manoeuvrable than birds, flying with their long spread-out digits covered with a thin membrane or patagium; the smallest bat, arguably the smallest extant mammal, is Kitti's hog-nosed bat, 29–34 mm in length, 15 cm across the wings and 2–2.6 g in mass. The largest bats are the flying foxes and the giant golden-crowned flying fox, Acerodon jubatus, which can weigh 1.6 kg and have a wingspan of 1.7 m. The second largest order of mammals, bats comprise about 20% of all classified mammal species worldwide, with over 1,200 species; these were traditionally divided into two suborders: the fruit-eating megabats, the echolocating microbats. But more recent evidence has supported dividing the order into Yinpterochiroptera and Yangochiroptera, with megabats as members of the former along with several species of microbats. Many bats are insectivores, most of the rest are frugivores. A few species feed on animals other than insects. Most bats are nocturnal, many roost in caves or other refuges.
Bats are present throughout the world, with the exception of cold regions. They are important in their ecosystems for dispersing seeds. Bats provide humans at the cost of some threats. Bat dung has been used as fertiliser. Bats consume insect pests, they are sometimes numerous enough to serve as tourist attractions, are used as food across Asia and the Pacific Rim. They are natural reservoirs such as rabies. In many cultures, bats are popularly associated with darkness, witchcraft and death. An older English name for bats is flittermouse, which matches their name in other Germanic languages, related to the fluttering of wings. Middle English had bakke, most cognate with Old Swedish natbakka, which may have undergone a shift from -k- to -t- influenced by Latin blatta, "moth, nocturnal insect"; the word "bat" was first used in the early 1570s. The name "Chiroptera" derives from Ancient Greek: χείρ – cheir, "hand" and πτερόν – pteron, "wing"; the delicate skeletons of bats do not fossilise well, it is estimated that only 12% of bat genera that lived have been found in the fossil record.
Most of the oldest known bat fossils were very similar to modern microbats, such as Archaeopteropus. The extinct bats Palaeochiropteryx tupaiodon and Hassianycteris kumari are the first fossil mammals whose colouration has been discovered: both were reddish-brown. Bats were grouped in the superorder Archonta, along with the treeshrews and primates. Modern genetic evidence now places bats in the superorder Laurasiatheria, with its sister taxon as Fereuungulata, which includes carnivorans, odd-toed ungulates, even-toed ungulates, cetaceans. One study places Chiroptera as a sister taxon to odd-toed ungulates; the phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision into Megachiroptera and Microchiroptera reflected the view that these groups of bats had evolved independently of each other for a long time, from a common ancestor capable of flight; this hypothesis recognised differences between microbats and megabats and acknowledged that flight has only evolved once in mammals.
Most molecular biological evidence supports the view that bats form a monophyletic group. Genetic evidence indicates that megabats originated during the early Eocene, belong within the four major lines of microbats. Two new suborders have been proposed. Yangochiroptera includes the other families of a conclusion supported by a 2005 DNA study. A 2013 phylogenomic study supported the two new proposed suborders. In the 1980s, a hypothesis based on morphological evidence stated the Megachiroptera evolved flight separately from the Microchiroptera; the flying primate hypothesis proposed that, when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features not shared with Microchiroptera. For example, the brains of megabats have advanced characteristics. Although recent genetic studies support the monophyly of bats, debate continues about the meaning of the genetic and morphological evidence; the 2003 discovery of an early fossil bat from the 52 million year old Green River Formation, Onychonycteris finneyi, indicates that flight evolved before echolocative abilities.
Onychonycteris had claws on all five of its fingers, whereas modern bats have at most two claws on two digits of each hand. It had longer hind legs and shorter forearms, similar to climbing mammals that hang under branches, such as sloths and gibbons; this palm-sized bat had short, broad wings, suggesting that it could not fly as fast or as far as bat species. Instead of flapping its wings continuously while flying, Onychonycteris alternated between flaps and