101-528: Tragelaphus angasii Tragelaphus buxtoni Tragelaphus eurycerus Tragelaphus imberbis Tragelaphus scriptus Tragelaphus spekii Tragelaphus strepsiceros Tragelaphus sylvaticus Tragelaphus is a genus of medium-to-large-sized spiral- horned antelopes . It contains several species of bovines , all of which are relatively antelope-like. Species in this genus tend to be large in size and lightly built, and have long necks and considerable sexual dimorphism . Elands , including
202-414: A Cooperia rotundispiculum race, Gaigeria pachyscelis , a Gongylonema species, Haemonchus vegliai , Impalaia tuberculata , an Oesophagostomum species, a Setaria species, Trichostrongylus deflexus , Trichostrongylus falculatus , the larval stage of a Taenia species, a Thysaniezia species and Schistosoma mattheei . Ostertagia harrisi and C. rotundispiculum were
303-471: A trypanosome was isolated from a nyala, wild-caught in Mozambique, which was diagnosed and found as akin to Trypanosoma vivax , based on biological, morphological and molecular data. The nyala can also suffer from myopathy . In between January 1973 and June 1981, 21 nyalas succumbed to the disease. The main symptoms were stiffness, inability to rise, and failure to suckle in newborns. Necrosis (that is,
404-501: A bird's lifetime. Activational hormones occur during puberty and adulthood and serve to 'activate' certain behaviors when appropriate, such as territoriality during breeding season. Organizational hormones occur only during a critical period early in development, either just before or just after hatching in most birds, and determine patterns of behavior for the rest of the bird's life. Such behavioral differences can cause disproportionate sensitivities to anthropogenic pressures. Females of
505-459: A diverse array of sexually dimorphic traits. Aggressive utility traits such as "battle" teeth and blunt heads reinforced as battering rams are used as weapons in aggressive interactions between rivals. Passive displays such as ornamental feathering or song-calling have also evolved mainly through sexual selection. These differences may be subtle or exaggerated and may be subjected to sexual selection and natural selection . The opposite of dimorphism
606-402: A group of danger. This feature is mainly used by females. They also react to the alarm calls of impala , baboon and kudu. The impala has been found to react to the calls of the nyala as well. The main predators of nyala are lion , leopard , cheetah , spotted hyena , African wild dog and nile crocodile while baboons and raptorial birds are predators of juveniles. As a herbivore ,
707-553: A large role in the changing of sex by the fish. It is often seen that a fish will change its sex when there is a lack of a dominant male within the social hierarchy. The females that change sex are often those who attain and preserve an initial size advantage early in life. In either case, females which change sex to males are larger and often prove to be a good example of dimorphism. In other cases with fish, males will go through noticeable changes in body size, and females will go through morphological changes that can only be seen inside of
808-1007: A less bright or less exaggerated color during the off-breeding season. This occurs because the species is more focused on survival than on reproduction, causing a shift into a less ornate state. Consequently, sexual dimorphism has important ramifications for conservation. However, sexual dimorphism is not only found in birds and is thus important to the conservation of many animals. Such differences in form and behavior can lead to sexual segregation , defined as sex differences in space and resource use. Most sexual segregation research has been done on ungulates, but such research extends to bats , kangaroos , and birds. Sex-specific conservation plans have even been suggested for species with pronounced sexual segregation. The term sesquimorphism (the Latin numeral prefix sesqui - means one-and-one-half, so halfway between mono - (one) and di - (two)) has been proposed for bird species in which "both sexes have basically
909-557: A louse fly species were recovered in a study of 73 nyalas at Umfolozi, Mkuzi and Ndumu Game Reserves in northeastern KwaZulu-Natal in 1983 and 1984 and an additional six individuals in 1994. It was found that nyalas were hosts to all stages of development in Boophilus decoloratus , Rhipicephalus appendiculatus and R. muehlensi and the immature stages of Amblyomma hebraeum and Rhipicephalus maculatus . Adult males served hosts to more ticks and lice than adult females did. Also,
1010-425: A naturally occurring part of development, for example plumage. In addition, the strong hormonal influence on phenotypic differences suggests that the genetic mechanism and genetic basis of these sexually dimorphic traits may involve transcription factors or cofactors rather than regulatory sequences. Sexual dimorphism may also influence differences in parental investment during times of food scarcity. For example, in
1111-414: A significant role in male reproductive success. Males have a propensity to be larger than females of a comparable age but it is unclear whether the size increase is due to a growth spurt at the time of the sexual transition or due to the history of faster growth in sex changing individuals. Larger males are able to stifle the growth of females and control environmental resources. Social organization plays
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#17328478307211212-537: A speciation phenomenon if the variation becomes strongly drastic and favorable towards two different outcomes. Sexual dimorphism is maintained by the counteracting pressures of natural selection and sexual selection. For example, sexual dimorphism in coloration increases the vulnerability of bird species to predation by European sparrowhawks in Denmark. Presumably, increased sexual dimorphism means males are brighter and more conspicuous, leading to increased predation. Moreover,
1313-421: A white chevron between their eyes, and a 40–55 cm (16–22 in) long bushy tail white underside. Both sexes have a dorsal crest of hair running right from the back of the head to the end of the tail. Males have another line of hair along the midline of their chest and belly. Only the males have horns. Horns are 60–83 cm (24–33 in) long and yellow-tipped. There are one or two twists. The spoor
1414-474: Is Lamprologus callipterus , a type of cichlid fish. In this fish, the males are characterized as being up to 60 times larger than the females. The male's increased size is believed to be advantageous because males collect and defend empty snail shells in each of which a female breeds. Males must be larger and more powerful in order to collect the largest shells. The female's body size must remain small because in order for her to breed, she must lay her eggs inside
1515-537: Is Lasioglossum hemichalceum , which is a species of sweat bee that shows drastic physical dimorphisms between male offspring. Not all dimorphism has to have a drastic difference between the sexes. Andrena agilissima is a mining bee where the females only have a slightly larger head than the males. Weaponry leads to increased fitness by increasing success in male–male competition in many insect species. The beetle horns in Onthophagus taurus are enlarged growths of
1616-463: Is Tragelaphus angasii . The name angasii is attributed to Angas, who said that John Edward Gray had named this species after Angas' father, George Fife Angas of South Australia. According to Article 50.1.1 of the International Code of Zoological Nomenclature and International Commission on Zoological Nomenclature , though, this is insufficient to state Gray as the author. The name "nyala"
1717-627: Is monomorphism , when both biological sexes are phenotypically indistinguishable from each other. Common and easily identified types of dimorphism consist of ornamentation and coloration, though not always apparent. A difference in the coloration of sexes within a given species is called sexual dichromatism, commonly seen in many species of birds and reptiles. Sexual selection leads to exaggerated dimorphic traits that are used predominantly in competition over mates. The increased fitness resulting from ornamentation offsets its cost to produce or maintain, suggesting complex evolutionary implications, but
1818-423: Is a good indicator for females because it shows that they are good at obtaining a food supply from which the carotenoid is obtained. There is a positive correlation between the chromas of the tail and breast feathers and body condition. Carotenoids play an important role in immune function for many animals, so carotenoid dependent signals might indicate health. Frogs constitute another conspicuous illustration of
1919-407: Is a sexually dimorphic trait. Theropoda It has been hypothesized that male theropods possessed a retractable penis, a feature similar to modern day crocodilians . Crocodilian skeletons were examined to determine whether there is a skeletal component that is distinctive between both sexes, to help provide an insight on the physical disparities between male and female theropods. Findings revealed
2020-456: Is a significant increase in corpus luteum in the last third of gestation. Gestation is of seven months. A single calf is born, weighing 5 kg (11 lb). Birth takes place generally away from the sight of predators, in places such as a thicket. The calf remains hidden for up to 18 days, and the mother nurses it at regular intervals. The calf remains with its mother until the birth of the next calf, during which males in rut drive it away from
2121-446: Is about 19 days long. Males will attempt to mate with the female for two days of the cycle, but she allows it for only six hours per cycle. When the male enters a females' herd during mating, he makes a display by raising his white dorsal crest, lowering his horns and moving stiffly. As in many other animals, the males fight over dominance during mating. The kidney fat indices (KFIs) of impalas and nyalas have been studied to understand
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#17328478307212222-423: Is advantageous to both parties because it avoids damaging the developing fruit and wasting the pollinator's effort on unrewarding visits. In effect, the strategy ensures that pollinators can expect a reward every time they visit an appropriately advertising flower. Females of the aquatic plant Vallisneria americana have floating flowers attached by a long flower stalk that are fertilized if they contact one of
2323-587: Is also displayed by dichromatism. In butterfly genera Bicyclus and Junonia , dimorphic wing patterns evolved due to sex-limited expression, which mediates the intralocus sexual conflict and leads to increased fitness in males. The sexual dichromatic nature of Bicyclus anynana is reflected by female selection on the basis of dorsal UV-reflective eyespot pupils. The common brimstone also displays sexual dichromatism; males have yellow and iridescent wings, while female wings are white and non-iridescent. Naturally selected deviation in protective female coloration
2424-673: Is also seen in frog species like P. bibroni i . Male painted dragon lizards, Ctenophorus pictus . are brightly conspicuous in their breeding coloration, but male colour declines with aging . Male coloration appears to reflect innate anti-oxidation capacity that protects against oxidative DNA damage . Male breeding coloration is likely an indicator to females of the underlying level of oxidative DNA damage (a significant component of aging) in potential mates. Possible mechanisms have been proposed to explain macroevolution of sexual size dimorphism in birds. These include sexual selection, selection for fecundity in females, niche divergence between
2525-470: Is believed that this is obtained by the ingestion of green Lepidopteran larvae, which contain large amounts of the carotenoids lutein and zeaxanthin . This diet also affects the sexually dimorphic colours in the human-invisible ultraviolet spectrum. Hence, the male birds, although appearing yellow to humans, actually have a violet-tinted plumage that is seen by females. This plumage is thought to be an indicator of male parental abilities. Perhaps this
2626-410: Is displayed in mimetic butterflies. Many arachnid groups exhibit sexual dimorphism, but it is most widely studied in the spiders. In the orb-weaving spider Zygiella x-notata , for example, adult females have a larger body size than adult males. Size dimorphism shows a correlation with sexual cannibalism , which is prominent in spiders (it is also found in insects such as praying mantises ). In
2727-687: Is known in ceratopsids, although there is evidence that the more primitive ceratopsian Protoceratops andrewsi possessed sexes that were distinguishable based on frill and nasal prominence size. This is consistent with other known tetrapod groups where midsized animals tend to exhibit markedly more sexual dimorphism than larger ones. However, it has been proposed that these differences can be better explained by intraspecific and ontogenic variation rather than sexual dimorphism. In addition, many sexually dimorphic traits that may have existed in ceratopsians include soft tissue variations such as coloration or dewlaps , which would be unlikely to have been preserved in
2828-678: Is more prominently selected for in less dimorphic species of spiders, which often selects for larger male size. In the species Maratus volans , the males are known for their characteristic colorful fan which attracts the females during mating. Ray-finned fish are an ancient and diverse class, with the widest degree of sexual dimorphism of any animal class. Fairbairn notes that "females are generally larger than males but males are often larger in species with male–male combat or male paternal care ... [sizes range] from dwarf males to males more than 12 times heavier than females." There are cases where males are substantially larger than females. An example
2929-402: Is of a subdued brown coloration. The plumage of the peacock increases its vulnerability to predators because it is a hindrance in flight, and it renders the bird conspicuous in general. Similar examples are manifold, such as in birds of paradise and argus pheasants . Another example of sexual dichromatism is that of nestling blue tits . Males are chromatically more yellow than females. It
3030-434: Is seen in the bee species Macrotera portalis in which there is a small-headed morph, capable of flight, and large-headed morph, incapable of flight, for males. Anthidium manicatum also displays male-biased sexual dimorphism. The selection for larger size in males rather than females in this species may have resulted due to their aggressive territorial behavior and subsequent differential mating success. Another example
3131-480: Is selected for, which is seen in the family Araneidae . All Argiope species, including Argiope bruennichi , use this method. Some males evolved ornamentation including binding the female with silk, having proportionally longer legs, modifying the female's web, mating while the female is feeding, or providing a nuptial gift in response to sexual cannibalism. Male body size is not under selection due to cannibalism in all spider species such as Nephila pilipes , but
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3232-511: Is similar to that of the bushbuck, but larger. It is 5–6 cm (2.0–2.4 in) long. The feces resemble round to spherical pellets. The nyala has hairy glands on its feet, which leave their scent wherever it walks. The condition of the nyala often varies between the sexes. According to a study, this can be attributed to the differences in their body sizes. It was noted that during nutritional stress, old adults died in more numbers, of which most were males. During an attempt of blood sampling in
3333-473: Is still unknown, but attributed to the photoperiod and the feeding habits of the animal. Females reach sexual maturity at 11 to 12 months of age and males at 18 months (though they are socially immature until five years old), though they begin to show active spermatogenesis at 14 months. Before ovulation, the Graafian follicles reach a length of at least 6.7 cm (2.6 in). A female's estrous cycle
3434-407: Is strong when the factor of environmental selection is also introduced. Environmental selection may support a smaller chick size if those chicks were born in an area that allowed them to grow to a larger size, even though under normal conditions they would not be able to reach this optimal size for migration. When the environment gives advantages and disadvantages of this sort, the strength of selection
3535-661: Is the Tsonga name for this antelope, which is likely the source of the English, along with Zulu inyala . Its first known use was in 1899. The word has a Bantu origin, similar to the Venda word dzì-nyálà (nyala buck). The nyala is the second taxon to branch off from the tragelaphine family tree just after the lesser kudu . As the nyala line has remained separate for a considerable time (over 5 million years), some authorities have placed it in its own monotypic genus Nyala . Nyala
3636-504: Is the dragonet , in which males are considerably larger than females and possess longer fins. Sexual dimorphism also occurs in hermaphroditic fish. These species are known as sequential hermaphrodites . In fish, reproductive histories often include the sex-change from female to male where there is a strong connection between growth, the sex of an individual, and the mating system within which it operates. In protogynous mating systems where males dominate mating with many females, size plays
3737-411: Is weakened and the environmental forces are given greater morphological weight. The sexual dimorphism could also produce a change in timing of migration leading to differences in mating success within the bird population. When the dimorphism produces that large of a variation between the sexes and between the members of the sexes, multiple evolutionary effects can take place. This timing could even lead to
3838-681: The International Union for Conservation of Nature . It generally browses during the day in warm weather and during the night in the rainy season. As a herbivore, the nyala feeds upon foliage, fruits and grasses, and requires sufficient fresh water. A shy animal, it prefers water holes rather than open spaces. The nyala does not show signs of territoriality, and individuals' areas can overlap. They are very cautious creatures. They live in single-sex or mixed family groups of up to ten individuals, but old males live alone. They inhabit thickets within dense and dry savanna woodlands. The principal threats to
3939-996: The Ndumo Game Reserve , uMkuze Game Reserve and Hluhluwe-Umfolozi Game Reserve , all in KwaZulu-Natal , as well as in Kruger National Park . As of 1999, 10–15% of nyala occurred on private land. Efforts are being made to retain the populations of nyala in Gorongosa National Park and Banhine National Park in Mozambique. Nyala also thrive in Lengwe National Park in Malawi. Nyala have never been observed showing territoriality . Territories of either sex overlap extensively. The home ranges of males are approximately equal to that of females, about 10 square kilometres (3.9 sq mi) in area. The major threats to
4040-604: The blue-footed booby , the female chicks grow faster than the males, resulting in booby parents producing the smaller sex, the males, during times of food shortage. This then results in the maximization of parental lifetime reproductive success. In Black-tailed Godwits Limosa limosa limosa females are also the larger sex, and the growth rates of female chicks are more susceptible to limited environmental conditions. Sexual dimorphism may also only appear during mating season; some species of birds only show dimorphic traits in seasonal variation. The males of these species will molt into
4141-401: The bushbuck , the large common and giant elands , the greater and lesser kudus , the mountain nyala (of Ethiopia ) and the swamp-dwelling sitatunga , all of which share similar characteristics, such as hornless females, vertical side-stripes and other unique white markings, and the spiraling horns and distinct "beard" or dewlap of males, often with a raised trail of fur extending down
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4242-501: The common eland ( Taurotragus oryx ), are embedded within this genus, meaning that Taurotragus must be subsumed into Tragelaphus to avoid paraphyly. Alternatively, Taurotragus could be maintained as a separate genus, if the nyala and the lesser kudu are relocated to their own monospecific genera, respectively Nyala and Ammelaphus . Other generic synonyms include Strepsiceros (which applies to T. strepsiceros ) and Boocercus (for T. eurycerus ). The name "Tragelaphus" comes from
4343-489: The ovules ). Each pollen grain accordingly may be seen as a male plant in its own right; it produces a sperm cell and is dramatically different from the female plant, the megagametophyte that produces the female gamete. Insects display a wide variety of sexual dimorphism between taxa including size, ornamentation and coloration. The female-biased sexual size dimorphism observed in many taxa evolved despite intense male-male competition for mates. In Osmia rufa , for example,
4444-407: The 'fittest' available male. Sexual dimorphism is a product of both genetics and environmental factors. An example of sexual polymorphism determined by environmental conditions exists in the red-backed fairywren . Red-backed fairywren males can be classified into three categories during breeding season : black breeders, brown breeders, and brown auxiliaries. These differences arise in response to
4545-484: The 14th chromosome, as in other tragelaphids , but no inversion of the Y chromosome occurs. Cranial studies have shown that the mountain nyala and nyala, though sharing a common name, are actually distant relatives. Fossil evidence suggests that the nyala has been a separate species since the end of the Miocene (5.8 million years ago). Genetic evidence suggests that the proto-nyala had some early hybridization with
4646-520: The British Isles", it was noted that spongiform encephalopathy had been diagnosed in one nyala captive in a zoo. The nyala was formerly affected by the disease rinderpest , although the viral disease is considered eradicated now. The nyala is active mainly in the early morning and late afternoon. It browses during the day if temperatures are 20–30 °C (68–86 °F) and during the night in rainy season. These antelopes rest in thick bushes during
4747-458: The back and underside. In 2005, Sandi Willows-Munro (of the University of KwaZulu-Natal ) and colleagues carried out a mitochondrial DNA analysis of the nine Tragelaphus species. Mitochondrial DNA and nuclear DNA data were compared. The results showed the tribe Tragelaphini to be monophyletic , with the lesser kudu ( T. imberbis ) basal in the phylogeny, followed by the nyala. On
4848-413: The basis of mitochondrial data, studies have estimated that the lesser kudu separated from its sister clade around 13.7 million years ago. However, nuclear DNA data shows lesser kudu and nyala forming a clade, which collectively separated from the sister clade 13.8 million years ago. The nyala has 55 male chromosomes and 56 female chromosomes. The Y chromosome has been translocated onto
4949-533: The bird's body condition: if they are healthy they will produce more androgens thus becoming black breeders, while less healthy birds produce less androgens and become brown auxiliaries. The reproductive success of the male is thus determined by his success during each year's non-breeding season, causing reproductive success to vary with each year's environmental conditions. Migratory patterns and behaviors also influence sexual dimorphisms. This aspect also stems back to size dimorphism in species. It has been shown that
5050-995: The body. For example, in sockeye salmon , males develop larger body size at maturity, including an increase in body depth, hump height, and snout length. Females experience minor changes in snout length, but the most noticeable difference is the huge increase in gonad size, which accounts for about 25% of body mass. Sexual selection was observed for female ornamentation in Gobiusculus flavescens , known as two-spotted gobies. Traditional hypotheses suggest that male–male competition drives selection. However, selection for ornamentation within this species suggests that showy female traits can be selected through either female–female competition or male mate choice. Since carotenoid-based ornamentation suggests mate quality, female two-spotted guppies that develop colorful orange bellies during breeding season are considered favorable to males. The males invest heavily in offspring during incubation, which leads to
5151-470: The caudal chevrons of male crocodiles, used to anchor the penis muscles, were significantly larger than those of females. There have been criticisms of these findings, but it remains a subject of debate among advocates and adversaries. Ornithopoda Studies of sexual dimorphism in hadrosaurs have generally centered on the distinctive cranial crests , which likely provided a function in sexual display. A biometric study of 36 skulls found sexual dimorphism
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#17328478307215252-400: The costs and evolutionary implications vary from species to species. The peafowl constitute conspicuous illustrations of the principle. The ornate plumage of peacocks, as used in the courting display, attracts peahens . At first sight, one might mistake peacocks and peahens for completely different species because of the vibrant colours and the sheer size of the male's plumage; the peahen
5353-654: The degree of preservation. The availability of well-preserved remains is not a probable outcome as a consequence of decomposition and fossilization . Some paleontologists have looked for sexual dimorphism among dinosaurs using statistics and comparison to ecologically or phylogenetically related modern animals. Apatosaurus and Diplodocus Female Apatosaurus and Diplodocus had interconnected caudal vertebrae that allowed them to keep their tails elevated to aid in copulation. Discovering that this fusion occurred in only 50% of Apatosaurus and Diplodocus skeletons and 25% of Camarasaurus skeletons indicated that this
5454-448: The empty shells. If she grows too large, she will not fit in the shells and will be unable to breed. The female's small body size is also likely beneficial to her chances of finding an unoccupied shell. Larger shells, although preferred by females, are often limited in availability. Hence, the female is limited to the growth of the size of the shell and may actually change her growth rate according to shell size availability. In other words,
5555-454: The end of the Late Miocene . This article about an even-toed ungulate is a stub . You can help Misplaced Pages by expanding it . Tragelaphus angasii The lowland nyala or simply nyala ( Tragelaphus angasii ) is a spiral-horned artiodactyl antelope native to Southern Africa . The species is part of the family Bovidae and the genus Tragelaphus (formerly placed in
5656-510: The estrogen pathway. The sexual dimorphism in lizards is generally attributed to the effects of sexual selection, but other mechanisms including ecological divergence and fecundity selection provide alternative explanations. The development of color dimorphism in lizards is induced by hormonal changes at the onset of sexual maturity, as seen in Psamodromus algirus , Sceloporus gadoviae , and S. undulates erythrocheilus . Sexual dimorphism in size
5757-443: The exhausted anthers after a day or two and perhaps change their colours as well while the pistil matures; specialist pollinators are very much inclined to concentrate on the exact appearance of the flowers they serve, which saves their time and effort and serves the interests of the plant accordingly. Some such plants go even further and change their appearance once fertilized, thereby discouraging further visits from pollinators. This
5858-417: The female is larger/broader than males, with males being 8–10 mm in size and females being 10–12 mm in size. In the hackberry emperor females are similarly larger than males. The reason for the sexual dimorphism is due to provision size mass, in which females consume more pollen than males. In some species, there is evidence of male dimorphism, but it appears to be for distinctions of roles. This
5959-564: The female, which looks different from the males. Various other dioecious exceptions, such as Loxostylis alata have visibly different sexes, with the effect of eliciting the most efficient behavior from pollinators, who then use the most efficient strategy in visiting each gender of flower instead of searching, say, for pollen in a nectar-bearing female flower. Some plants, such as some species of Geranium have what amounts to serial sexual dimorphism. The flowers of such species might, for example, present their anthers on opening, then shed
6060-651: The form of reduced survival. This means that even if the trait causes males to die earlier, the trait is still beneficial so long as males with the trait produce more offspring than males lacking the trait. This balance keeps dimorphism alive in these species and ensures that the next generation of successful males will also display these traits that are attractive to females. Such differences in form and reproductive roles often cause differences in behavior. As previously stated, males and females often have different roles in reproduction. The courtship and mating behavior of males and females are regulated largely by hormones throughout
6161-723: The fossil record. Stegosaurians A 2015 study on specimens of Hesperosaurus mjosi found evidence of sexual dimorphism in the shape of the dermal plates. Two plate morphs were described: one was short, wide, and oval-shaped, the other taller and narrower. In a large proportion of mammal species, males are larger than females. Both genes and hormones affect the formation of many animal brains before " birth " (or hatching ), and also behaviour of adult individuals. Hormones significantly affect human brain formation, and also brain development at puberty. A 2004 review in Nature Reviews Neuroscience observed that "because it
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#17328478307216262-448: The genus Nyala ). It was first described in 1849 by George French Angas and exhibits the highest sexual dimorphism among the spiral-horned antelopes. It is not to be confused with the endangered mountain nyala living in the Bale region of Ethiopia. The nyala's range encompasses much of Southern Africa . As its population is relatively stable, it has been listed as of least concern by
6363-700: The head or thorax expressed only in the males. Copris ochus also has distinct sexual and male dimorphism in head horns. Another beetle with a distinct horn-related sexual dimorphism is Allomyrina dichotoma, also known as the Japanese rhinoceros beetle . These structures are impressive because of the exaggerated sizes. There is a direct correlation between male horn lengths and body size and higher access to mates and fitness. In other beetle species, both males and females may have ornamentation such as horns. Generally, insect sexual size dimorphism (SSD) within species increases with body size. Sexual dimorphism within insects
6464-551: The hot hours of the day. The nyala is very shy and cautious in nature, and often remains hidden rather than coming out in the open. Most sightings of the nyala in the wild are at water holes . But in protected areas they become less shy and often come out in view of tourists. Nyala groups are according to sex or mixed. Herds usually browse and drink water together. Each group consists of two to ten individuals. A study in Zinave National Park at Mozambique showed that 67% of
6565-480: The influence of social class and reproduction on them. To determine the KFI, the kidney is removed and weighed with the fat and once again excluding the fat. The resultant difference is the amount of fat on the kidney. The more the fat, the healthier the animal. In rut , male nyalas had lower KFIs, which did not vary much with the season. Pregnant females of both nyala and impala had higher KFIs than non-pregnant ones. There
6666-575: The journal Bulletin des Sciences, par la Société Philomatique in 1816. The name is not of modern scientific invention, but comes from ancient Greek τραγέλαφος ( tragélaphos ), from τράγος ( trágos ), meaning a "male goat", and ἔλαφος ( élaphos ), meaning a "deer". It is generally treated as having eight species, namely:. An alternative classification, supported by genetic data, would recognise 11 species in five groups, which could be treated as subgenera or full genera: (i) Nyala for T. angasii ; (ii) Ammelaphus for T. imberbis ; (iii) Taurotragus for
6767-444: The larger males are better at coping with the difficulties of migration and thus are more successful in reproducing when reaching the breeding destination. When viewing this from an evolutionary standpoint, many theories and explanations come into consideration. If these are the result for every migration and breeding season, the expected results should be a shift towards a larger male population through sexual selection. Sexual selection
6868-508: The male's ability to collect large shells depends on his size. The larger the male, the larger the shells he is able to collect. This then allows for females to be larger in his brooding nest which makes the difference between the sizes of the sexes less substantial. Male–male competition in this fish species also selects for large size in males. There is aggressive competition by males over territory and access to larger shells. Large males win fights and steal shells from competitors. Another example
6969-593: The more ornamented or brightly colored sex. Such differences have been attributed to the unequal reproductive contributions of the sexes. This difference produces a stronger female choice since they have more risk in producing offspring. In some species, the male's contribution to reproduction ends at copulation, while in other species the male becomes the main (or only) caregiver. Plumage polymorphisms have evolved to reflect these differences and other measures of reproductive fitness, such as body condition or survival. The male phenotype sends signals to females who then choose
7070-692: The most common causes for mortality in young fish. Most flowering plants are hermaphroditic but approximately 6% of species have separate males and females ( dioecy ). Sexual dimorphism is common in dioecious plants and dioicous species. Males and females in insect-pollinated species generally look similar to one another because plants provide rewards (e.g. nectar ) that encourage pollinators to visit another similar flower , completing pollination . Catasetum orchids are one interesting exception to this rule. Male Catasetum orchids violently attach pollinia to euglossine bee pollinators. The bees will then avoid other male flowers but may visit
7171-482: The most dominant nematodes in the antelope. Another study of 97 blood samples of South African nyalas revealed the presence of tick -borne hemoparasites (blood parasites). The methods used were polymerase chain reaction (PCR) and reverse line blot (RLB) hybridization. The dominant parasites were Theileria species, T. buffeli , T. bicornis , Ehrlichia species, Anaplasma marginale and A. bovis . Ten tick species, two louse species and
7272-538: The mother. The nyala inhabits dense lowland woodlands and thickets, mainly in southern Malawi, Mozambique, Zimbabwe, and eastern South Africa. It chooses places with good quality grasslands as well as provision of fresh water. It also inhabits lush green river country. The nyala's natural range stretches across southeast Africa from the Lower Shire Valley in Malawi through Mozambique and Zimbabwe to eastern South Africa and Eswatini. The geographic distribution of
7373-423: The mythical tragelaph . Giant eland Common eland Greater kudu Mountain nyala Bongo Sitatunga Cape bushbuck Harnessed bushbuck Lowland nyala Lesser kudu Tragelaphus / t r ə ˈ dʒ ɛ l ə f ə s / is a genus in the tribe Tragelaphini and the family Bovidae . The genus authority is French zoologist Henri Marie Ducrotay de Blainville , who first mentioned it in
7474-399: The nyala is about 19 years. The coat is rusty or rufous brown in females and juveniles. It grows a dark brown or slate grey in adult males, often with a bluish tinge. Females and young males have ten or more white vertical stripes on their sides. Other markings are visible on the face, throat, flanks and thighs. Stripes are very reduced or absent in older males. Both males and females have
7575-609: The nyala may be based on the genetic variation. According to a study of nyala in South Africa, Mozambique, Malawi and Zimbabwe, there was a marked difference in the gene frequencies at three microsatellite loci . Mitochondrial DNA analysis revealed the presence of a unique haplotype in individuals from each location. Thus, the geographic variation in the nyala may be due to a distribution pattern based on habitat specificity. Today nyala are found in South African protected areas in
7676-473: The nyala's diet consists of foliage, fruits, flowers and twigs. During the rainy season they feed upon the fresh grass. They need a regular intake of water, and thus choose places with a water source nearby. However, they are adapted to live in areas with only a seasonal availability of water. A study in Zululand showed that the nyala fed mainly in the early morning and the late afternoon. They feed at night during
7777-459: The nyala, it was found that Vitamin E levels varied during stress. A study of the helminths from 77 nyalas from four game reserves in Natal revealed the presence of ten nematode species and four nematode genera, a trematode species and paramphistomes (members of superfamily Paramphistomoidea ), and two cestode genera. The research discovered new parasites that the nyala was host of - namely
7878-419: The observations were of groups of one to three nyalas, and the rest of the herds consisted of up to 30 nyalas. Herds often broke up and re-formed. Generally adult males remain alone. Females often remain near their mothers when they have their offspring, so the relationships in female herds may be closer than those of males. Alert and wary in nature, the nyala use a sharp, high, dog-like bark to warn others in
7979-436: The plants become sexually mature. Every sexually reproducing extant species of the vascular plant has an alternation of generations; the plants we see about us generally are diploid sporophytes , but their offspring are not the seeds that people commonly recognize as the new generation. The seed actually is the offspring of the haploid generation of microgametophytes ( pollen ) and megagametophytes (the embryo sacs in
8080-870: The population of the nyala are poaching, habitat loss, agriculture and cattle grazing. Rinderpest outbreaks have also contributed in population loss. This species is currently of Least Concern , and the population is considered stable by both the IUCN and CITES . As of 1999, the total population of the nyala was around 32,000 individuals. More recent estimates show that South Africa has at least 30,000 nyalas, with 25,000 in KwaZulu-Natal. There are now more than 1,000 on protected areas and ranches in Eswatini. In Mozambique there are not more than 3,000, in Zimbabwe over 1,000, and numbers in Malawi have fallen from 3,000 to about 1,500. Namibia has
8181-430: The premature death of cells in a living tissue) and mineralization were found in the skeletal muscle after a histological analysis. In the juveniles there was acute necrosis of the cardiac muscle . In adults, there was interstitial fibrosis of the cardiac muscle, along with arteriosclerosis . In a report published in 1994 entitled "Epidemiological observations on spongiform encephalopathies in captive wild animals in
8282-418: The presence of specific sex-related behaviour is common to many lizards; and vocal qualities which are frequently observed in frogs . Anole lizards show prominent size dimorphism with males typically being significantly larger than females. For instance, the average male Anolis sagrei was 53.4 mm vs. 40 mm in females. Different sizes of the heads in anoles have been explained by differences in
8383-410: The principle. There are two types of dichromatism for frog species: ontogenetic and dynamic. Ontogenetic frogs are more common and have permanent color changes in males or females. Ranoidea lesueuri is an example of a dynamic frog with temporary color changes in males during the breeding season. Hyperolius ocellatus is an ontogenetic frog with dramatic differences in both color and pattern between
8484-408: The production of more exaggerated ornaments in males may come at the cost of suppressed immune function. So long as the reproductive benefits of the trait due to sexual selection are greater than the costs imposed by natural selection, then the trait will propagate throughout the population. Reproductive benefits arise in the form of a larger number of offspring, while natural selection imposes costs in
8585-542: The proto-lesser kudu, but the two have remained separate long after this crossing. The nyala is a spiral-horned and middle-sized antelope, between a bushbuck and a kudu . It is considered the most sexually dimorphic antelope. The nyala is typically between 135–195 cm (53–77 in) in head-and-body length. The male stands up to 110 cm (43 in), the female is up to 90 cm (3.0 ft) tall. Males weigh 98–125 kg (216–276 lb), while females weigh 55–68 kg (121–150 lb). Life expectancy of
8686-519: The rainy season. A study in Mkhuze Game Reserve and Ndumu Game Reserve in Natal focused on the dietary habits of the impala and the nyala showed that the amount of dicotyledons in their diets varied seasonally. In the dry season, the nyala's dicotyledon diet content was 83.2% and the impala's 52%. In this season, the diet grew richer in fiber and dietary proteins were less. The reverse occurred in
8787-433: The rainy season. As the rainy season arrived, both species took to a diet of mainly monocotyledons , and the impala consumed more of them. The diet contained more proteins than fiber. Another study was done to find whether the sexual dimorphism in the nyala influenced its foraging habits. Vegetation surveys were conducted with the end of each feeding bout. It was found that females spent equal periods of time foraging in all
8888-585: The same plumage pattern, though the female is clearly distinguishable by reason of her paler or washed-out colour". Examples include Cape sparrow ( Passer melanurus ), rufous sparrow (subspecies P. motinensis motinensis ), and saxaul sparrow ( P. ammodendri ). Examining fossils of non-avian dinosaurs in search of sexually dimorphic characteristics requires the supply of complete and articulated skeletal and tissue remains. As terrestrial organisms, dinosaur carcasses are subject to ecological and geographical influence that inevitably constitutes
8989-479: The sexes, and allometry, but their relative importance is still not fully understood . Sexual dimorphism in birds can be manifested in size or plumage differences between the sexes. Sexual size dimorphism varies among taxa, with males typically being larger, though this is not always the case, e.g. birds of prey , hummingbirds , and some species of flightless birds. Plumage dimorphism, in the form of ornamentation or coloration, also varies, though males are typically
9090-526: The sexes. At sexual maturity, the males display a bright green with white dorsolateral lines. In contrast, the females are rusty red to silver with small spots. The bright coloration in the male population attracts females and is an aposematic sign to potential predators. Females often show a preference for exaggerated male secondary sexual characteristics in mate selection. The sexy son hypothesis explains that females prefer more elaborate males and select against males that are dull in color, independent of
9191-511: The sexual preference in colorful females due to higher egg quality. In amphibians and reptiles, the degree of sexual dimorphism varies widely among taxonomic groups . The sexual dimorphism in amphibians and reptiles may be reflected in any of the following: anatomy; relative length of tail; relative size of head; overall size as in many species of vipers and lizards ; coloration as in many amphibians , snakes , and lizards, as well as in some turtles ; an ornament as in many newts and lizards;
9292-414: The size dimorphic wolf spider Tigrosa helluo , food-limited females cannibalize more frequently. Therefore, there is a high risk of low fitness for males due to pre-copulatory cannibalism, which led to male selection of larger females for two reasons: higher fecundity and lower rates of cannibalism. In addition, female fecundity is positively correlated with female body size and large female body size
9393-731: The smallest population, at about 250. Today over 80% of the total population is protected in national parks and sanctuaries, mostly in South African protected areas. In South Africa there is a high demand for adult males as game trophies. Sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction . The condition occurs in most dioecious species, which consist of most animals and some plants. Differences may include secondary sex characteristics , size, weight, color, markings, or behavioral or cognitive traits. Male-male reproductive competition has evolved
9494-493: The species are illegal poaching and habitat loss resulting from human settlement and livestock grazing. However, the large-horned, impressive males are highly prized as game animals by sport hunters. Giant eland Common eland Greater kudu Mountain nyala Bongo Sitatunga Cape bushbuck Harnessed bushbuck Lowland nyala Lesser kudu The nyala was first described by George French Angas , an English naturalist, in 1849. The scientific name of nyala
9595-567: The species' vision. Similar sexual dimorphism and mating choice are also observed in many fish species. For example, male guppies have colorful spots and ornamentations, while females are generally grey. Female guppies prefer brightly colored males to duller males. In redlip blennies , only the male fish develops an organ at the anal-urogenital region that produces antimicrobial substances. During parental care, males rub their anal-urogenital regions over their nests' internal surfaces, thereby protecting their eggs from microbial infections, one of
9696-537: The thousands of free-floating flowers released by a male. Sexual dimorphism is most often associated with wind-pollination in plants due to selection for efficient pollen dispersal in males vs pollen capture in females, e.g. Leucadendron rubrum . Sexual dimorphism in plants can also be dependent on reproductive development. This can be seen in Cannabis sativa , a type of hemp, which have higher photosynthesis rates in males while growing but higher rates in females once
9797-467: The three habitats, but males preferred sand forest more. More differences were noted, as males ate woody species at a greater average height whereas females fed from the low herbaceous layer . It was concluded that the differences resulted from varying nutritional and energetic demands according to their diverse body sizes and differing reproductive strategies. The nyala breeds throughout the year, but mating peaks in spring and autumn. The reason for this
9898-442: The two elands ( T. oryx and T. derbianus ); (iv) Strepsiceros for T. strepsiceros and (v) Tragelaphus restricted to T. buxtoni , T. spekei , T. scriptus , T. sylvaticus (Imbabala - separated from a polyphyletic T. scriptus ) and T. eurycerus . In terms of divergence time estimates, a 2006 study showed that core Tragelaphus (now known to excude T. angasii and T. imberbis ) diverged from Taurotragus (elands) towards
9999-454: The whinchat in Switzerland breed in intensely managed grasslands. Earlier harvesting of the grasses during the breeding season lead to more female deaths. Populations of many birds are often male-skewed and when sexual differences in behavior increase this ratio, populations decline at a more rapid rate. Also not all male dimorphic traits are due to hormones like testosterone, instead they are
10100-470: Was exhibited in the crest of 3 species of hadrosaurids. The crests could be categorized as full (male) or narrow (female) and may have given some advantage in intrasexual mating-competition. Ceratopsians According to Scott D. Sampson, if ceratopsids were to exhibit sexual dimorphism, modern ecological analogues suggest it would be found in display structures, such as horns and frills. No convincing evidence for sexual dimorphism in body size or mating signals
10201-531: Was proposed in 1912 by American zoologist Edmund Heller , who also proposed Ammelaphus for the lesser kudu, but it was not widely recognized. It was re-erected as a valid genus in 2011 under the classification of Peter Grubb and Colin Groves , but has not been embraced by taxonomic authorities such as the Mammal Diversity Database. Among its closest extant relatives are the forest-inhabiting bongo ,
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