60-418: A tenrec ( / ˈ t ɛ n r ɛ k / ) is a mammal belonging to any species within the afrotherian family Tenrecidae , which is endemic to Madagascar . Tenrecs are a very diverse group; as a result of convergent evolution , some resemble hedgehogs , shrews , opossums , rats , and mice . They occupy aquatic , arboreal , terrestrial , and fossorial environments. Some of these species, including
120-414: A spermatangium . Because spermatia cannot swim, they depend on their environment to carry them to the egg cell. Some red algae , such as Polysiphonia , produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar , which attract flies that transfer
180-570: A fully formed but small human. Ejaculated fluids are detected by ultraviolet light , irrespective of the structure or colour of the surface. Sperm heads, e.g. from vaginal swabs, are still detected by microscopy using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining. Sperm cells in algal and many plant gametophytes are produced in male gametangia ( antheridia ) via mitotic division. In flowering plants , sperm nuclei are produced inside pollen . Motile sperm cells typically move via flagella and require
240-399: A neck: During fertilization , the sperm provides three essential parts to the oocyte : (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome ; (3) the centriole, which is responsible for forming the centrosome and microtubule system. The spermatozoa of animals are produced through spermatogenesis inside
300-399: A result of less efficient cell selection (apoptosis) operating during or after spermatogenesis . DNA damages present in sperm cells in the period after meiosis but before fertilization may be repaired in the fertilized egg, but if not repaired, can have serious deleterious effects on fertility and the developing embryo. Human sperm cells are particularly vulnerable to free radical attack and
360-418: A tail, or flagellum, which gives rise to the mature, motile sperm cell. This whole process occurs constantly and takes around 3 months from start to finish. Sperm cells cannot divide and have a limited lifespan, but after fusion with egg cells during fertilization , a new organism begins developing, starting as a totipotent zygote . The human sperm cell is haploid , so that its 23 chromosomes can join
420-553: A water medium in order to swim toward the egg for fertilization. In animals most of the energy for sperm motility is derived from the metabolism of fructose carried in the seminal fluid. This takes place in the mitochondria located in the sperm's midpiece (at the base of the sperm head). These cells cannot swim backwards due to the nature of their propulsion. The uniflagellated sperm cells (with one flagellum) of animals are referred to as spermatozoa , and are known to vary in size. Motile sperm are also produced by many protists and
480-666: Is a vertebrate animal of the class Mammalia ( / m ə ˈ m eɪ l i . ə / ). Mammals are characterized by the presence of milk -producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair , and three middle ear bones . These characteristics distinguish them from reptiles and birds , from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 27 orders . The largest orders of mammals, by number of species , are
540-551: Is borrowed, via French , from the Malagasy word tandraka (variant of trandraka ), which refers to the tailless tenrec ( Tenrec ecaudatus ); it has been speculated that the Malagasy word is related to Malay : landak , lit. ' porcupine '. Tenrecs are believed to have evolved from a single species that colonized Madagascar between 42 and 25 million years ago. The question of how this family reached Madagascar
600-551: Is called a spermatozoan . Sperm cells are carried out of the male body in a fluid known as semen . Human sperm cells can survive within the female reproductive tract for more than 5 days post coitus. Semen is produced in the seminal vesicles , prostate gland and urethral glands . In 2016, scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids from mouse embryonic stem cells artificially. They injected these spermatids into mouse eggs and produced pups. Sperm quantity and quality are
660-484: Is difficult to obtain (as it is not sold in shops or markets) and difficult to prepare correctly. The lesser hedgehog tenrec ( Echinops telfairi ) is one of 16 mammalian species that will have its genome sequenced as part of the Mammalian Genome Project . It is increasingly popular in the pet trade, and in the future may serve as an important model organism in biomedicine, as it is only distantly related to
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#1732855524465720-441: Is negatively affecting tenrec species that inhabit forests. Five of the six threatened Tenrec species are dependent on forest habitats. As of 2022, conservation of the tenrec population is not being prioritized. Because most tenrecs are dependent on forest habitats, conservation efforts would need to include a focus on reduction in deforestation on Madagascar as well as habitat restoration. Current conservation efforts include that of
780-536: Is possible to extract sperm through testicular sperm extraction . On the global market, Denmark has a well-developed system of human sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality and, in contrast with the law in the other Nordic countries, gives donors the choice of being either anonymous or non-anonymous to the receiving couple. Furthermore, Nordic sperm donors tend to be tall and highly educated and have altruistic motives for their donations, partly due to
840-572: Is primarily driven by human poaching and habitat destruction , primarily deforestation . Over 70% of mammal species are in the orders Rodentia , Chiroptera , and Eulipotyphla . Mammal classification has been through several revisions since Carl Linnaeus initially defined the class, and at present , no classification system is universally accepted. McKenna & Bell (1997) and Wilson & Reeder (2005) provide useful recent compendiums. Simpson (1945) provides systematics of mammal origins and relationships that had been taught universally until
900-595: Is sperm size, at least in some animals. For instance, the sperm of some species of fruit fly ( Drosophila ) are up to 5.8 cm long—about 20 times as long as the fly itself. Longer sperm cells are better than their shorter counterparts at displacing competitors from the female's seminal receptacle. The benefit to females is that only healthy males carry "good" genes that can produce long sperm in sufficient quantities to outcompete their competitors. Some sperm banks hold up to 170 litres (37 imp gal; 45 US gal) of sperm. In addition to ejaculation , it
960-494: Is still unresolved, but the leading hypothesis suggests a small number of individuals may have found themselves on floating vegetation and crossed the Mozambique Channel , which separates Madagascar from southeastern Africa. The Tenrecidae family is one of only four extant terrestrial mammal lineages to have colonized and diversified on Madagascar. Once established on Madagascar, tenrecs diversified to occupy various niches on
1020-546: Is the male reproductive cell , or gamete , in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum , which are known as spermatozoa , while some red algae and fungi produce non-motile sperm cells, known as spermatia . Flowering plants contain non-motile sperm inside pollen , while some more basal plants like ferns and some gymnosperms have motile sperm. Sperm cells form during
1080-426: Is the viviparous placental mammals , so named for the temporary organ ( placenta ) used by offspring to draw nutrition from the mother during gestation . Most mammals are intelligent , with some possessing large brains, self-awareness , and tool use . Mammals can communicate and vocalize in several ways, including the production of ultrasound , scent marking , alarm signals , singing , echolocation ; and, in
1140-542: Is very different from the route of transmission of Creutzfeldt–Jakob disease . The prevalence of Creutzfeldt–Jakob disease for donors is at most one in a million, and if the donor was a carrier, the infectious proteins would still have to cross the blood-testis barrier to make transmission possible. Sperm were first observed in 1677 by Antonie van Leeuwenhoek using a microscope . He described them as being animalcules (little animals), probably due to his belief in preformationism , which thought that each sperm contained
1200-467: The Cretaceous . The relationships between these three lineages is contentious, and all three possible hypotheses have been proposed with respect to which group is basal . These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Boreoeutheria in turn contains two major lineages— Euarchontoglires and Laurasiatheria . Estimates for
1260-550: The International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List , which counted 5,488 species. According to research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495, including 96 recently extinct. The word " mammal " is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from
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#17328555244651320-547: The Latin mamma ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes ( echidnas and platypuses ) and therian mammals ( marsupials and placentals ) and all descendants of that ancestor. Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from
1380-590: The biological classification scheme used, are the primates : apes , monkeys , and lemurs ; the Cetartiodactyla : whales and even-toed ungulates ; and the Carnivora which includes cats , dogs , weasels , bears , seals , and allies. According to Mammal Species of the World , 5,416 species were identified in 2006. These were grouped into 1,229 genera , 153 families and 29 orders. In 2008,
1440-406: The dominant terrestrial animal group from 66 million years ago to the present. The basic mammalian body type is quadrupedal , with most mammals using four limbs for terrestrial locomotion ; but in some, the limbs are adapted for life at sea , in the air , in trees or underground . The bipeds have adapted to move using only the two lower limbs, while the rear limbs of cetaceans and
1500-493: The greater hedgehog tenrec , can be found in the Madagascar dry deciduous forests . However, the speciation rate in this group has been higher in humid forests . All tenrecs are believed to descend from a common ancestor that lived 29–37 million years ago after rafting over from Africa . The split from their closest relatives, African otter shrews , is estimated to have occurred about 47–53 million years ago. The word tenrec
1560-452: The otter shrews have just two young per litter, the tailless tenrec can have as many as 32, and females possess up to 29 teats , more than any other mammal. Some tenrec species are social, living in multigenerational family groups with over a dozen individuals. In the island nation of Mauritius , and also on the Comoran island of Mayotte , some of the inhabitants eat tenrec meat, although it
1620-424: The otter shrews , and after that other African insectivorous mammals including golden moles and elephant shrews . The common ancestry of these animals, which are classified together in the clade Afrotheria , was not recognized until the late 1990s. Continuing work on the molecular and morphological diversity of afrotherian mammals has provided ever increasing support for their common ancestry. Tenrecs are among
1680-404: The ovule , the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei, which are then discharged through the tube into the ovule for fertilization. In some protists , fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a syncytical antheridium surrounding
1740-428: The rodents , bats , and Eulipotyphla (including hedgehogs , moles and shrews ). The next three are the primates (including humans , monkeys and lemurs ), the even-toed ungulates (including pigs , camels , and whales ), and the Carnivora (including cats , dogs , and seals ). Mammals are the only living members of Synapsida ; this clade , together with Sauropsida (reptiles and birds), constitutes
1800-439: The sea cows are mere internal vestiges . Mammals range in size from the 30–40 millimetres (1.2–1.6 in) bumblebee bat to the 30 metres (98 ft) blue whale —possibly the largest animal to have ever lived. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale . All modern mammals give birth to live young, except the five species of monotremes , which lay eggs. The most species-rich group
1860-455: The 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. In mammals , sperm is stored in the epididymis and released through the penis in semen during ejaculation . The word sperm is derived from the Greek word σπέρμα , sperma , meaning "seed". It is generally accepted that isogamy is the ancestor to sperm and eggs. Because there are no fossil records of
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1920-559: The Madagascar Ankizy Fund, started by a paleontological team from Stony Brook University to improve access to health care and education facilities for villagers in remote areas of Madagascar. A healthy and educated local human population will, in the long term, benefit the Malagasy fauna, such as tenrecs. The three subfamilies, eight genera, and 31 extant species of tenrecs are FAMILY TENRECIDAE Mammal A mammal (from Latin mamma 'breast')
1980-483: The case of humans, complex language . Mammals can organize themselves into fission–fusion societies , harems , and hierarchies —but can also be solitary and territorial . Most mammals are polygynous , but some can be monogamous or polyandrous . Domestication of many types of mammals by humans played a major role in the Neolithic Revolution , and resulted in farming replacing hunting and gathering as
2040-807: The clade originating with the last common ancestor of Sinoconodon and living mammals. The earliest-known synapsid satisfying Kemp's definitions is Tikitherium , dated 225 Ma , so the appearance of mammals in this broader sense can be given this Late Triassic date. However, this animal may have actually evolved during the Neogene. As of the early 21st century, molecular studies based on DNA analysis have suggested new relationships among mammal families. Most of these findings have been independently validated by retrotransposon presence/absence data . Classification systems based on molecular studies reveal three major groups or lineages of placental mammals— Afrotheria , Xenarthra and Boreoeutheria —which diverged in
2100-444: The closest thing to an official classification of mammals, despite its known issues. Most mammals, including the six most species-rich orders , belong to the placental group. The three largest orders in numbers of species are Rodentia : mice , rats , porcupines , beavers , capybaras , and other gnawing mammals; Chiroptera : bats; and Eulipotyphla : shrews , moles , and solenodons . The next three biggest orders, depending on
2160-1332: The divergence times between these three placental groups range from 105 to 120 million years ago, depending on the type of DNA used (such as nuclear or mitochondrial ) and varying interpretations of paleogeographic data. Monotremata Marsupialia Xenarthra Afrotheria Glires Euarchonta [REDACTED] Eulipotyphla Chiroptera Pholidota Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Monotremata [REDACTED] Paucituberculata [REDACTED] Didelphimorphia [REDACTED] Microbiotheria Notoryctemorphia [REDACTED] Peramelemorphia [REDACTED] Dasyuromorphia [REDACTED] Diprotodontia [REDACTED] Cingulata [REDACTED] Pilosa [REDACTED] Hyracoidea [REDACTED] Sirenia [REDACTED] Proboscidea [REDACTED] Tubulidentata [REDACTED] Macroscelidea [REDACTED] Afrosoricida [REDACTED] Eulipotyphla [REDACTED] Chiroptera [REDACTED] Pholidota [REDACTED] Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Scandentia [REDACTED] Lagomorpha [REDACTED] Sperm Sperm ( pl. : sperm or sperms )
2220-574: The earlier Triassic , despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and Amphitherium are more closely related to
2280-427: The early Miocene of Kenya show close affinities to living species from Madagascar, such as Geogale aurita . Most species are nocturnal and have poor eyesight. Their other senses are well developed, however and they have especially sensitive whiskers . As with many of their other features, the dental formula of tenrecs varies greatly between species; they can have from 32 to 42 teeth in total. Unusual for mammals,
2340-539: The egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants. Most sperm cells have centrioles in the sperm neck. Sperm of many animals has two typical centrioles, known as the proximal centriole and distal centriole. Some animals (including humans and bovines) have a single typical centriole, the proximal centriole, as well as a second centriole with atypical structure. Mice and rats have no recognizable sperm centrioles. The fruit fly Drosophila melanogaster has
2400-451: The end of the 20th century. However, since 1945, a large amount of new and more detailed information has gradually been found: The paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics . Though fieldwork and lab work progressively outdated Simpson's classification, it remains
2460-412: The evolution of sperm and eggs from isogamy, there is a strong emphasis on mathematical models to understand the evolution of sperm. A widespread hypothesis states that sperm evolved rapidly, but there is no direct evidence that sperm evolved at a fast rate or before other male characteristics. The main sperm function is to reach the ovum and fuse with it to deliver two sub-cellular structures: (i)
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2520-567: The fertilizing sperm cells, and disruption of maternal DNA double-strand break repair pathways increases sperm cell-derived chromosomal aberrations. Treatment of male mice with melphalan , a bifunctional alkylating agent frequently employed in chemotherapy, induces DNA lesions during meiosis that may persist in an unrepaired state as germ cells progress through DNA repair-competent phases of spermatogenic development. Such unrepaired DNA damages in sperm cells, after fertilization, can lead to offspring with various abnormalities. Related to sperm quality
2580-473: The few terrestrial mammals that echolocate . Unusual among placental mammals , the rectum and urogenital tracts of tenrecs share a common opening, or cloaca which is a feature more commonly seen in birds , reptiles , and amphibians . They have a low body temperature , sufficiently low that they do not require a scrotum to cool their sperm as do most other mammals. All species appear to be at least somewhat omnivorous , with invertebrates forming
2640-503: The gametophytes of bryophytes , ferns and some gymnosperms such as cycads and ginkgo . The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and lycophytes , cycads and ginkgo they are multi-flagellated (carrying more than one flagellum). In nematodes , the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell. Non-motile sperm cells called spermatia lack flagella and therefore cannot swim. Spermatia are produced in
2700-399: The generation of oxidative DNA damage, such as that from 8-Oxo-2'-deoxyguanosine . The postmeiotic phase of mouse spermatogenesis is very sensitive to environmental genotoxic agents, because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage. Irradiation of male mice during late spermatogenesis can induce damage that persists for at least 7 days in
2760-547: The island. Many evolved resemblances to familiar but unrelated mammals that are not found on Madagascar. For instance, the two species of hedgehog tenrec possess coats of hardened spines and the ability to roll into a ball when threatened, characteristics similar to those of true hedgehogs . This example, along with others, demonstrates convergent evolution; it has provided evolutionary biologists with opportunities to study adaptation over evolutionary timescales. Tenrecs are small mammals of variable body form. The smallest species are
2820-645: The larger Amniota clade. Early synapsids are referred to as " pelycosaurs ." The more advanced therapsids became dominant during the Guadalupian . Mammals originated from cynodonts , an advanced group of therapsids, during the Late Triassic to Early Jurassic . Mammals achieved their modern diversity in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs , and have been
2880-409: The largest part of their diets. One species, Microgale mergulus , is semiaquatic (similar to the lifestyle of their closest relatives, the otter shrews). All of the species, semiaquatic or not, appear to have evolved from a single, common ancestor with the otter shrews comprising the next, most-closely related mammalian species. While the fossil record of tenrecs is scarce, at least some specimens from
2940-448: The main parameters in semen quality, which is a measure of the ability of semen to accomplish fertilization . Thus, in humans, it is a measure of fertility in a man . The genetic quality of sperm, as well as its volume and motility, all typically decrease with age . DNA double-strand breaks in sperm increase with age. Also apoptosis decreases with age suggesting that the increase in damaged DNA of sperm as men age occurs partly as
3000-442: The male gonads ( testicles ) via meiotic division. The initial spermatozoon process takes around 70 days to complete. The process starts with the production of spermatogonia from germ cell precursors. These divide and differentiate into spermatocytes , which undergo meiosis to form spermatids . In the spermatid stage, the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it
3060-547: The male pronucleus that contains the genetic material and (ii) the centrioles that are structures that help organize the microtubule cytoskeleton . The nuclear DNA in sperm cells is haploid , that is, they contribute only one copy of each paternal chromosome pair. Mitochondria in human sperm contain no or very little DNA because mtDNA is degraded while sperm cells are maturing, hence they typically do not contribute any genetic material to their offspring. The mammalian sperm cell can be divided in 2 parts connected by
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#17328555244653120-415: The male gametophytes ( pollen grains) are the primary mode of dispersal , for example via wind or insect pollination , eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the stigma of a receptive flower, it germinates and starts growing a pollen tube through the carpel . Before the tube reaches
3180-690: The mice, rats, guinea pigs, and rhesus macaques which comprise the most common research animals. Of the 31 species assessed, 24 (77%) are categorized by the IUCN Red List as Least Concern, 1 species as Data Deficient, 4 species as Vulnerable, and 2 species as Endangered. The conservation status of many tenrec species is of concern due to an increase of threats within the last 50 years. The main threats facing tenrecs include habitat loss due to deforestation , fragmentation and degradation, hunting, incidental capture, and climate change . Slash-and-burn agriculture, as well as commercial logging and mining of metals
3240-427: The permanent dentition in tenrecs tends not to completely erupt until well after adult body size has been reached. This is one of several anatomical features shared by elephants, hyraxes , sengis , and golden moles (but apparently not aardvarks ), consistent with their descent from a common ancestor. Tenrecs have a gestation period of 50 to 64 days, and give birth to a number of relatively undeveloped young. While
3300-716: The primary source of food for humans. This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first civilizations . Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food ( meat and dairy products ), fur , and leather . Mammals are also hunted and raced for sport, kept as pets and working animals of various types, and are used as model organisms in science. Mammals have been depicted in art since Paleolithic times, and appear in literature, film, mythology, and religion. Decline in numbers and extinction of many mammals
3360-475: The process known as spermatogenesis , which in amniotes ( reptiles and mammals ) takes place in the seminiferous tubules of the testicles . This process involves the production of several successive sperm cell precursors, starting with spermatogonia , which differentiate into spermatocytes . The spermatocytes then undergo meiosis , reducing their chromosome number by half, which produces spermatids . The spermatids then mature and, in animals, construct
3420-553: The relatively low monetary compensation in Nordic countries. More than 50 countries worldwide are importers of Danish sperm, including Paraguay , Canada , Kenya , and Hong Kong . However, the Food and Drug Administration (FDA) of the US has banned import of any sperm, motivated by a risk of transmission of Creutzfeldt–Jakob disease , although such a risk is insignificant, since artificial insemination
3480-410: The size of shrews, with a body length of around 4.5 cm (1.8 in), and weighing just 5 g (0.18 oz), while the largest, the common or tailless tenrec , is 25 to 39 cm (9.8 to 15.4 in) in length, and can weigh over 1 kilogram (2.2 lb). Although they may resemble shrews, hedgehogs, or opossums, they are not closely related to any of these groups, their closest relatives being
3540-703: The spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants . Fungal spermatia (also called pycniospores, especially in the Uredinales) may be confused with conidia . Conidia are spores that germinate independently of fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as Neurospora crassa , spermatia are identical to microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization. In almost all embryophytes , including most gymnosperms and all angiosperms ,
3600-537: The therians; as fossils of all three genera are dated about 167 million years ago in the Middle Jurassic , this is a reasonable estimate for the appearance of the crown group. T. S. Kemp has provided a more traditional definition: " Synapsids that possess a dentary – squamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view,
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