Tuesday, October 15, 2013

Although the tapetum

Although the tapetum is considered to be ubiquitous in lemurs, there appear to be exceptions among true lemurs, such as the black lemur and the common brown lemur, as well as the ruffed lemurs.[12][29][86] Since the riboflavins in the tapetum have a tendency to dissolve and vanish when processed for histological investigation, however, the exceptions are still debatable.[12] HP AB0505HX-J0B CPU FAN Lemurs also have a third eyelid known as a nictitating membrane, whereas most other primates have a lesser developed plica semilunaris. The nictitating membrane keeps the cornea moist and clean by sweeping across the eye. Lemurs have low basal metabolic rates (BMR), which helps them to conserve energy during the dry season, when water and food are scarce.[11][65] HP AB5205HB-EBB CPU FAN They can optimize their energy use by lowering their metabolic rate to 20% below the values predicted for mammals of similar body mass.[90] The red-tailed sportive lemur (Lepilemur ruficaudatus), for instance, reportedly has one of the lowest metabolic rates among mammals. Its low metabolic rate may be linked to its generally folivorous diet and relatively small body mass.[65] HP AB5505HX-K0B CPU FAN Lemurs exhibit behavioral adaptations to complement this trait, including sunning behaviors, hunched sitting, group huddling, and nest sharing, in order to reduce heat loss and conserve energy.[90]Dwarf lemurs and mouse lemurs exhibit seasonal cycles of dormancy to conserve energy.[90] Before dry season, they will accumulate fat in white adipose tissuelocated at the base of the tail and hind legs, doubling their weight. HP AB5505HX-OBB CPU FAN At the end of the dry season, their body mass may fall to half of what it was prior to the dry season.[27] Lemurs that do not experience states of dormancy are also able to shut down aspects of their metabolism for energy conservation. Lemur behavior is as variable as lemur morphology. Differences in diet, social systems, activity patterns, locomotion, communication, predator avoidance tactics, breeding systems, and intelligence levels help define lemur taxa and set individual species apart from the rest. HP AB7205HX-GC1 CPU FAN Although trends frequently distinguish the smaller, nocturnal lemurs from the larger, diurnal lemurs, there are often exceptions that help exemplify the unique and diverse nature of these Malagasy primates. Lemur diets are highly variable and demonstrate a high degree of plasticity,[93] although general trends suggest that the smallest species primarily consume fruit and insects (omnivory), while the larger species are more herbivorous, consuming mostly plant material.[35] HP AB7205HX-GC3 CPU FAN As with all primates, hungry lemurs might eat anything that is edible, whether or not the item is one of their preferred foods.[12] For instance, the Ring-tailed Lemur eats insects and small vertebrates when necessary[35][56] and as a result it is commonly viewed as an opportunistic omnivore.[75] Coquerel's giant mouse lemur (Mirza coquereli) is mostly frugivorous, but will consume insect secretions during the dry season.[35] HP AB7805HX-L03 CPU FAN A common assumption in mammalogy is that small mammals cannot subsist entirely on plant material and must have a high-calorie diet in order to survive. As a result, it was thought that the diet of tiny primates must be high in protein-containing insects (insectivory). Research has shown, however, that mouse lemurs, the smallest living primates, consume more fruit than insects, contradicting the popular hypothesis.[12][35] HP CWTT8 CPU FAN Plant material makes up the majority of most lemur diets. Members of at least 109 of all known plant families in Madagascar (55%) are exploited by lemurs. Since lemurs are primarily arboreal, most of these exploited species are woody plants, including trees, shrubs, or lianas. Only the ring-tailed lemur, the bamboo lemurs (genus Hapalemur), and the black-and-white ruffed lemur (Varecia variegata) are known to consume herbs. HP DFS450805M10T CPU FAN While Madagascar is rich in fern diversity, these plants are rarely eaten by lemurs. One possible reason for this is that ferns lack flowers, fruits, and seeds—common food items in lemur diets. They also occur close to the ground, while lemurs spend most of their time in the trees. Lastly, ferns have an unpleasant taste due to the high content of tannins in their fronds. Likewise, mangroves appear to be rarely exploited by lemurs due to their high tannin content.[93] HP DFS531205HC0T CPU FAN Some lemurs appear to have evolved responses against common plant defenses, however, such as tannins and alkaloids.[76] The golden bamboo lemur (Hapalemur aureus), for instance, eats giant bamboo (Cathariostachys madagascariensis), which contains high levels of cyanide. This lemur can consume twelve times the typically lethal dose for most mammals on a daily basis; the physiological mechanisms that protect it from cyanide poisoning are unknown.[11] HP DFS551305MC0T CPU FAN At the Duke Lemur Center (DLC) in the United States, lemurs that roam the outdoor enclosures have been observed eating poison ivy (Taxicodendron radicans), yet have shown no ill effects. Many of the larger lemur species consume leaves (folivory),[93] particularly the indriids.[63] However, some smaller lemurs such assportive lemurs (genus Lepilemur) and woolly lemurs (genus Avahi) also primarily eat leaves, making them the smallest primates that do so.[65] HP F5S6-CW CPU FAN The smallest of the lemurs generally do not eat much leaf matter.[93] Collectively, lemurs have been documented consuming leaves from at least 82 native plant families and 15 alien plant families. Lemurs tend to be selective in their consumption of the part of the leaf or shoot as well as its age. Often, young leaves are preferred over mature leaves.[93] Many lemurs that eat leaves tend to do so during times of fruit scarcity, sometimes suffering weight loss as a result.[94] HP F787 CPU FAN Most lemur species, including most of the smallest lemurs and excluding some of the indriids, predominantly eat fruit (frugivory) when available. Collectively, lemurs have been documented consuming fruit from at least 86 native plant families and 15 alien plant families. As with most tropical fruit eaters, the lemur diet is dominated by fruit from Ficus (fig) species.[93] In many anthropoid primates, fruit is a primary source of vitamin C, HP F9C5 CPU FAN but unlike anthropoid primates, lemurs (and all strepsirrhines) can synthesize their own vitamin C.[95] Historically, captive lemur diets high in vitamin C-rich fruits have been thought to cause hemosiderosis, a type of iron overload disorder, since vitamin C increases iron absorption. Although lemurs in captivity have been shown to be prone to hemosiderosis, the frequency of the disease varies across institutions and may depend on the diet, husbandry protocols, and genetic stock. HP GB0507PGV1-A CPU FAN Assumptions about the problem need to be tested separately for each species.[96] The ring-tailed lemur, for instance, seems to be less prone to the disorder than other lemur species.[97] Only eight species of lemur are known to be seed predators (granivores), but this may be under-reported since most observations only report fruit consumption and do not investigate whether the seeds are consumed as well. HP GC055515VH-A CPU FAN These lemurs include some indriids, such as the diademed sifaka(Propithecus diadema), the golden-crowned sifaka (Propithecus tattersalli), the indri,[11][67] and the aye-aye. The aye-aye, which specializes in structurally defended resources, can chew through Canarium seeds, which are harder than the seeds that New World monkeys are known to break open.[49] At least 36 genera from 23 families of plants are targeted by lemur seed predators.[93] HP GC057015VH-A CPU FAN Inflorescences (clusters of flowers) of at least 60 plant families are eaten by lemurs ranging in size from the tiny mouse lemurs to the relatively large ruffed lemurs. If the flowers are not exploited, sometimes the nectar is consumed (nectarivory) along with the pollen (palynivory). At least 24 native species from 17 plant families are targeted for nectar or pollen consumption.[93] Bark and plant exudates such as tree sap are consumed by a few lemur species. HP GC057514VH-A CPU FAN The exploitation of exudates has been reported in 18 plant species and only in the dry regions in the south and west of Madagascar. Only the Masoala fork-marked lemur (Phaner furcifer) and Coquerel's giant mouse lemur regularly consume tree sap. Bark has never been reported as an important food item in lemur diets, but at least four species eat it: the aye-aye, the red-tailed sportive lemur(Lepilemur ruficaudatus), the common brown lemur (Eulemur fulvus), and Verreaux's sifaka (Propithecus verreauxi). HP KDB0505HB CPU FAN Most bark feeding is directly linked to exudate feeding, except for the aye-aye's bark feeding on Afzelia bijuga (genus Afzelia) at Nosy Mangabe in the northeast.[93] Soil consumption (geophagy) has also been reported and likely helps with digestion, provides minerals and salts, and helps absorb toxins. HP KDB05605HB CPU FAN Sifakas have been observed eating soil from termite mounds, possibly adding beneficial intestinal flora to aid the digestion of cellulose from their folivorous diet. Lemurs are social and live in groups that usually include less than 15 individuals.[11] Observed social organization patterns include "solitary but social", "fission-fusion", "pair bonds", and "multi-male group".[98] HP KSB0605HB CPU FAN Nocturnal lemurs are mostly solitary but social, foraging alone at night but often nesting in groups during the day. The degree of socialization varies by species, gender, location, and season.[26][35] In many nocturnal species, for instance, the females, along with their young, will share nests with other females and possibly one male, whose larger home range happens to overlap one or more female nesting groups. HP KSB06105HA CPU FAN Insportive lemurs and fork-marked lemurs, one or two females may share a home range, possibly with a male. In addition to sharing nests, they will also interact vocally or physically with their range-mate while they forage at night.[35] Diurnal lemurs exhibit many of the social systems seen in monkeys and apes,[11][35]living in relatively permanent and cohesive social groups. Multi-male groups are the most common, just as they are in most anthropoid primates. HP MCF-811AM05 CPU FAN True lemursutilize this social system, often living in groups of ten or less. Ruffed lemurs have been shown to live in fission-fusion societies,[35] and Indri forms pair bonds. Some lemurs exhibit female philopatry, where females stay within their natal range and the males migrate upon reaching maturity, and in other species both sexes will migrate.[11] HP MCF-W13BM05 CPU FAN In some cases, female philopatry may help explain the evolution of female-bonded multi-male groups, such as those of the ring-tailed lemur, Milne-Edwards' sifaka (Propithecus edwardsi), and the Verreaux's sifaka. Their ancestors may have been more solitary, with females that lived in mother-daughter pairs (or dyads). Over time, these dyads may have allied themselves with other neighboring mother-daughter dyads in order to defend more distributed resources in a wide home range. HP 540 CPU FAN If this is true, then multi-male groups in lemurs may differ fundamentally in their internal structure from those incatarrhine primates (Old World monkeys and apes).[99] The presence of female social dominance sets lemurs apart from most other primates and mammals;in most primate societies, males are dominant unless females band together to form coalitions that displace them. However, many Eulemur species are exceptions and the greater bamboo lemur (Prolemur simus) does not exhibit female dominance.[102] HP 550 CPU FAN When females are dominant within a group, the way they maintain dominance varies. Ring-tailed lemur males act submissively with or without signs of female aggression. Male crowned lemurs (Eulemur coronatus), on the other hand, will only act submissively when females act aggressively towards them. Female aggression is often associated with, but not limited to, feeding.[103] HP 6445B Series CPU FAN There have been many hypotheses that have attempted to explain why lemurs exhibit female social dominance while other primates with similar social structures do not,[11][100] but no consensus has been reached after decades of research. The dominant view in the literature states that female dominance is an advantageous trait given the high costs of reproduction and the scarcity of resources available.[100] HP 6520s CPU FAN Indeed, female dominance has been shown to be linked to increased maternal investment.[101] However, when reproductive costs and extreme seasonality of resources were compared across primates, other primates demonstrated male dominance under conditions that were similar to or more challenging than those faced by lemurs. In 2008, a new hypothesis revised this model using simple game theory. HP 6545B Series CPU FAN It was argued that when two individuals were equally matched in fighting capacity, the one with the most need would win the conflict since it would have the most to lose. Consequently, the female, with higher resource needs for pregnancy, lactation, and maternal care, was more likely to win in resource conflicts with equally sized males. This, however, assumed monomorphism between sexes.[100] The following year, a new hypothesis was proposed to explain monomorphism, HP 6720 CPU FAN stating that because most female lemurs are only sexually receptive for a day or two each year, males can utilize a more passive form of mate guarding: copulatory plugs, which block the female reproductive tract, preventing other males from successfully mating with her, and thus reducing the need for aggression and the evolutionary drive for sexual dimorphism. In general, levels of agonism (or aggression) tend to correlate with relative canine height. HP 6820s CPU FAN The ring-tailed lemur has long, sharp upper canine teeth in both sexes, and it also exhibits high levels of agonism. The Indri, on the other hand, has smaller canines and exhibits lower levels of aggression.[29] When neighboring groups of the same species defend their territories, the conflict can take the form of ritualized defense. In sifakas, these ritualized combats involve staring, growling, scent-marking, and leaping to occupy certain sections of the tree. HP EliteBook 6930P Series CPU FAN The indri defends its home range with ritualized "singing" battles.[11] Like other primates, lemurs groom socially (allogroom) to ease tensions and solidify relationships. They groom in greeting, when waking up, when settling in for sleep, between mother and infant, in juvenile relations, and for sexual advances.[104]Unlike anthropoid primates, who part the fur with the hands and pick out particles with the fingers or mouth, HP EliteBook 8530 Series CPU FAN lemurs groom with their tongue and scraping with their toothcomb. Despite the differences in technique, lemurs groom with the same frequency and for the same reasons as anthropoids. The biological rhythm can vary from nocturnal in smaller lemurs to diurnal in most larger lemurs. Diurnality is not seen in any other prosimian.[26]Cathemerality, where an animal is active sporadically both day and night, occurs among some of the larger lemurs. HP EliteBook 8530p Series CPU FAN Few if any other primates exhibit this sort of activity cycle,[105] either regularly or irregularly under changing environmental conditions.[11] The most heavily studied cathemeral lemurs are the true lemurs.[39][106] Although the mongoose lemur (E. mongoz) is the best-documented example, every species in the genus studied has shown some degree of cathemeral behavior,[69] although night activity is often restricted by light availability and moon periodicity.[12] HP EliteBook 8530w Series CPU FAN This type of behavior was first documented in the 1960s in true lemur species as well as other Lemuridae species, such as ruffed lemurs and bamboo lemurs. Initially described as "crepuscular" (active at dawn and dusk), anthropologist Ian Tattersall stimulated additional research and coined the new term "cathemeral",[105] although many non-anthropologists prefer the terms "circadian" or "diel".[12] DELL Inspiron N3010 Series CPU FAN In order to conserve energy and water in their highly seasonal environment,[90][107] mouse lemurs and dwarf lemurs exhibit seasonal behavioral cycles of dormancywhere the metabolic rate and body temperature are lowered. They are the only primates known to do so.[90] They accumulate fat reserves in their hind legs and the base of their tail before the dry winter season, when food and water are scarce,[27][91] DELL Inspiron N4010 Series CPU FAN can exhibit daily and prolonged torpor during the dry season. Daily torpor constitutes less than 24 hours of dormancy, whereas prolonged torpor averages two weeks in duration and signals hibernation.[90] Mouse lemurs have been observed experiencing torpor that lasts for several consecutive days, but dwarf lemurs are known to hibernate for six to eight months every year,[26][27][92]particularly on the west coast of Madagascar.[107] DELL Latitude 100L CPU FAN

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