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33-516: The Mesozoic marine revolution was not the first bout of increased predatory pressure ; that occurred around the end of the Ordovician . There is some evidence of adaptation to durophagy during the Palaeozoic , particularly in crinoids . The Mesozoic marine revolution was driven by the evolution of shell-crushing behaviour among Mesozoic marine predators, particularly marine reptiles , with

66-405: A certain population, causing many individuals from said population to die due to not being adapted to this new pressure. The individuals that are better adapted to this new pressure will survive and reproduce at a higher rate than those who are at a disadvantage. This occurs over many generations until the population as a whole is better adapted to the pressure. This is natural selection at work, but

99-403: A decline in wingspan of living swallow populations, while also noting a decrease in the number of cliff swallows killed by passing cars. Those cliff swallows that were killed by passing cars showed a larger wingspan than the population as a whole. Confounding effects such as road usage, car size, and population size were shown to have no impact on the study. Evolutionary pressure imposed by humans

132-453: A different species (horizontal gene transmission). Because of this, the drug resistance increases over generations. For example, in hospitals, environments are created where pathogens such as C . difficile have developed a resistance to antibiotics. Antibiotic resistance is made worse by the misuse of antibiotics. Antibiotic resistance is encouraged when antibiotics are used to treat non-bacterial diseases, and when antibiotics are not used for

165-471: A separate study also showed behavioral differences, with older females displaying the timid behavior that one would expect from this selection. Since the domestication of dogs , they have evolved alongside humans due to pressure from humans and the environment. This began by humans and wolves sharing the same area, with a pressure to coexist eventually leading to their domestication. Evolutionary pressure from humans led to many different breeds that paralleled

198-538: A threat to patients in hospitals, who are immunocompromised from illness or antibiotic treatment. Virulence factors are the characteristics that the evolved bacteria have developed to increase pathogenicity. One of the virulence factors of C . difficile that largely constitutes its resistance to antibiotics is its toxins: enterotoxin TcdA and cytotoxin TcdB. Toxins produce spores that are difficult to inactivate and remove from

231-431: Is a constant battle for evolutionary advantages in outcompeting each other. The evolutionary arms race between the rapidly evolving virulence factors of the bacteria and the treatment practices of modern medicine requires evolutionary biologists to understand the mechanisms of resistance in these pathogenic bacteria, especially considering the growing number of infected hospitalized patients. The evolved virulence factors pose

264-442: Is a major cause of death by nosocomial infections. When symbiotic gut flora populations are disrupted (e.g., by antibiotics ), one becomes more vulnerable to pathogens. The rapid evolution of antibiotic resistance places an enormous selective pressure on the advantageous alleles of resistance passed down to future generations. The Red Queen hypothesis shows that the evolutionary arms race between pathogenic bacteria and humans

297-414: Is a major health concern, because the condition grants some resistance to this infectious disease. Just as with the development of antibiotic resistance in bacteria, resistance to pesticides and herbicides has begun to appear with commonly used agricultural chemicals . For example: Human activity can lead to unintended changes in the environment. The human activity will have a possible negative effect on

330-477: Is a quantitative description of the amount of change occurring in processes investigated by evolutionary biology , but the formal concept is often extended to other areas of research. In population genetics , selective pressure is usually expressed as a selection coefficient . It has been shown that putting an amino acid bio-synthesizing gene like HIS4 gene under amino acid selective pressure in yeast causes enhancement of expression of adjacent genes which

363-506: Is also seen in elk populations. These studies do not look at morphological differences, but behavioral differences. Faster and more mobile male elk were shown to be more likely to fall prey to hunters. The hunters create an environment where the more active animals are more likely to succumb to predation than less active animals. Female elk who survived past two years, would decrease their activity as each year passed, leaving more shy female elk that were more likely to survive. Female elk in

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396-500: Is commonly attributed to selective pressure by humans, who often kill the snakes when they are discovered. Non-rattling snakes are more likely to go unnoticed, so survive to reproduce offspring that, like themselves, are less likely to rattle. Populations of cliff swallows in Nebraska have displayed morphological changes in their wings after many years of living next to roads. Collecting data for over 30 years, researchers noticed

429-518: Is due to the transcriptional co-regulation of two adjacent genes in Eukaryota . Drug resistance in bacteria is an example of an outcome of natural selection . When a drug is used on a species of bacteria, those that cannot resist die and do not produce offspring, while those that survive potentially pass on the resistance gene to the next generation (vertical gene transmission). The resistance gene can also be passed on to one bacterium by another of

462-459: Is thought that the break-up of Pangaea and the formation of new oceans throughout the Mesozoic brought together previously isolated marine communities, forcing them to compete and adapt. The increased shelf space caused by sea-level rise and a hyper- greenhouse climate provided more iterations and chances to evolve, resulting in increasing biodiversity . The explosion of angiosperms in

495-548: The Cretaceous also enhanced the hydrological cycling, speeding up rates of weathering and nutrient flow into the oceans, which has been cited as a possible driver of the MMR. Another proposal is the evolution of hermit crabs . These exploit the shells of dead gastropods , effectively doubling the life-span of the shell. This allows durophagous predators nearly twice the prey, making it a viable niche to exploit. The net result of

528-856: The Late Cretaceous. Cidaroids too may have contributed to the downfall of the crinoids. The increases in echinoid predation continued into the Cenozoic. Brachiopods, the dominant benthic organism of the Palaeozoic, suffered badly during the Mesozoic Marine Revolution. Their sessile foot-attached nature made them easy prey to durophagous predators. The fact that they could not re-attach to a substrate if an attack failed meant their chances of survival were slim. Unlike bivalves, brachiopods never adapted to an infaunal habit (excluding lingulids ) and so remained vulnerable throughout

561-473: The Late Triassic to the Late Cretaceous. Three major trends can be associated with this: Major casualties of the Mesozoic marine revolution include: sessile crinoids, gastropods , brachiopods and epifaunal bivalves . The Mesozoic Marine Revolution heavily affected the crinoids, making the majority of their forms extinct. Their sessile nature made them easy prey for durophagous predators since

594-476: The Mesozoic Marine Revolution. Bryozoans exhibited no significant anti-predatory adaptations during the Jurassic, suggesting that they were during this period unaffected by the MMR. Evolutionary pressure Evolutionary pressure , selective pressure or selection pressure is exerted by factors that reduce or increase reproductive success in a portion of a population, driving natural selection . It

627-459: The Mesozoic Marine Revolution. As a result of increased predation pressure on top of heightened competition with bivalves, brachiopods became a minor component of most marine faunas by the Cenozoic despite their incredible diversity and abundance during the Palaeozoic and early Mesozoic. Bivalves adapted more readily than the brachiopods to this ecological transition. Many bivalves adopted an infaunal habit, using their siphons to gather nutrients from

660-539: The Mesozoic marine revolution was a change from the sedentary epifaunal lifestyle of the Palaeozoic evolutionary fauna to the infaunal / planktonic mode of life of the modern fauna. Non-mobile types that failed to re-attach to their substrate (such as brachiopods ) when removed were picked off as easy prey, whereas those that could hide from predation or be mobile enough to escape had an evolutionary advantage. Per capita mean metabolic rates among marine gastropods living in shallow water increased by approximately 150% from

693-486: The Triassic. Survivors (such as the comatulids ) could swim or crawl, behaved nocturnally or had autotomy (the ability to shed limbs in defence). The shift in the range of sessile stalked crinoids during the late Mesozoic from the shallow shelf to habitats further offshore suggests that they were forced by increased predation pressure in shallow water to migrate to a deep water refuge environment where predation pressure

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726-637: The ability to fuse to the substrate made them more difficult to consume for smaller predators. Epifaunal bivalves were preyed on heavily before the Norian but extinction rates diminish after this. Benthic gastropods were heavily preyed upon throughout the Mesozoic Marine Revolution, the weaker shelled types being pushed out of the benthic zone into more isolated habitats. The Palaeozoic archaeogastropods were subsequently replaced by neritaceans, mesogastropods and neogastropods . The former typically have symmetrical, umbilicate shells that are mechanically weaker than

759-840: The body of the producing organisms, whereas gastrolites and cololites are found in situ in their respective organs, but there are rare exceptions (see Seilacher, 2002). Whilst coprolites and regurgitalites are often difficult to tie to a specific producer, all bromalites potentially provide important and sometimes unique evidence concerning diet and other trophic factors. They are thus useful indicators for reconstructing ancient food webs in palaeoecology . Shelton, C. D. (2013). "A new method to determine volume of bromalites: Morphometrics of Lower Permian (Archer City Formation) heteropolar bromalites". Swiss Journal of Palaeontology . 132 (2): 221–238. doi : 10.1007/s13358-013-0057-z . S2CID   129158414 . Aldridge, R. J.; Gabbott, S. E.; Siveter, L. J.; Theron, J. N. (2006). "Bromalites from

792-470: The environment are necessary practices in health facilities. The virulence of this pathogen is remarkable and may take a radical change at sanitation approaches used in hospitals to control CDI outbreaks. The malaria parasite can exert a selective pressure on human populations. This pressure has led to natural selection for erythrocytes carrying the sickle cell hemoglobin gene mutation ( Hb S)—causing sickle cell anaemia —in areas where malaria

825-509: The environment. This is especially true in hospitals where an infected patient's room may contain spores for up to 20 weeks. Combating the threat of the rapid spread of CDIs is therefore dependent on hospital sanitation practices removing spores from the environment. A study published in the American Journal of Gastroenterology found that to control the spread of CDIs glove use, hand hygiene, disposable thermometers and disinfection of

858-759: The human in a tangible way. An unintended consequence of this selection is that domesticated dogs also tend to have heritable diseases depending on what specific breed they encompass. Bromalite Bromalites are the fossilized remains of material sourced from the digestive system of organisms. As such, they can be broadly considered to be trace fossils . The most well-known types of bromalites are fossilized faeces or coprolites . However, other types are recognised, including: regurgitalites (fossilized remains of vomit or other regurgitated objects such as owl pellets ); cololites (intestinal contents); and gastrolites (stomach contents). Regurgtitalites and coprolites are thus essentially known only after they have left

891-441: The latter. These lack an umbilicus and also developed the ability to modify the interior of their shells, allowing them to develop sculptures on their exterior to act as defence against predators . Another development among Muricidae was the ability to bore through shells and consume prey. These marks (while relatively rare) generally occur on sessile invertebrates, implying that they put pressure on Palaeozoic-type faunas during

924-433: The needs of the time, whether it was a need for protecting livestock or assisting in the hunt. Hunting and herding were a couple of the first reasons for humans artificially selecting for traits they deemed beneficial. This selective breeding does not stop there, but extends to humans selecting for certain traits deemed desirable in their domesticated dogs, such as size and color, even if they are not necessarily beneficial to

957-413: The prescribed amount of time or in the prescribed dose. Antibiotic resistance may arise out of standing genetic variation in a population or de novo mutations in the population. Either pathway could lead to antibiotic resistance, which may be a form of evolutionary rescue . Clostridioides difficile , gram-positive bacteria species that inhabits the gut of mammals, exemplifies one type of bacteria that

990-507: The pressure is coming from man-made activity such as building roads or hunting. This is seen in the below examples of cliff swallows and elk. However, not all human activity that causes an evolutionary pressure happens unintentionally. This is demonstrated in dog domestication and the subsequent selective breeding that resulted in the various breeds known today. In more heavily (human) populated and trafficked areas, reports have been increasing of rattlesnakes that do not rattle. This phenomenon

1023-403: The sediment-water interface while remaining safe. Corbulids developed layers of conchiolin within their shells to better resist predation. Others still, like Pecten , developed the ability to jump a short distance away from predators by contracting their valves. Like brachiopods, epifaunal varieties of bivalves were preyed upon heavily. Among epifaunal types (such as mussels and oysters ),

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1056-716: The technique being perfected in the Late Cretaceous. This forced shelled marine invertebrates to develop defences against such predation or become extinct. The consequences of this can be seen in many invertebrates today. Such predators are thought to include: Triassic placodonts , Triassic ichthyosaurs , Triassic omphalosaurids , Triassic plesiosaurs , Jurassic pliosaurs , Late Cretaceous mosasaurs and Cretaceous ptychodontoid sharks. Many gastropods also evolved to feed on prey with shells. However, because most durophagous predators were generalists, their effect on anti-predator shell architecture has been viewed by some as diffuse and not as extensive as other authors have suggested. It

1089-861: Was lower and their mode of life more viable. This migration was not globally synchronous and delayed in the Southern Hemisphere; it did not occur until the Late Eocene in Australia and Antarctica , and until the Early Miocene in Zealandia . Echinoids do not suffer major predation (save for general infaunalisation) during the Mesozoic Marine Revolution but it is clear from bromalites (fossilised ‘vomit’) that cidaroids were consumed by predators. Echinoids radiate into predatory niches and are thought to have perfected coral grazing in

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