A team of scientists from the University of Arizona have poured through the literature that has been published so far and found something missing. There wasn’t much data on the time different sexes spent in the larval stages. If there is a difference in the time of growth during the larval stages, chances are that the two sexes would differ in size. The difference is sizes between the sexes of a species is most prominent in arthropods and amphibians, animals that go through various stages during their development.

The team chose to study the hawk moth and found that male and female caterpillars spend have different growth rates during the final larval stages. They found that during the pupal stage, the males and females develop differently. Females were found to start pupate at a later stage than the males and were larger at this time, thus making for larger females as is seen in the species. The scientists also found that there was a lot more physiological variation in the female caterpillars than the males, allowing the females to be more sensitive to the selection pressures in becoming larger.

In birds, there are examples of parasitism within the species (non-obligate parasites) as well as examples of young being raised by a different species (obligate). Non-obligate brood parasites are usually colonial birds or monogamous bird species such as Bank Swallows or African Weavers. Obligate brood parasites lay eggs in nests of other species and have completely lost the ability to construct nests and incubate eggs.  Examples include Brown-headed Cowbirds and European Cuckoos.  About 1% of all known bird species are obligate brood parasites.  Other obligate brood parasites include: all African Honeyguides, about half of the species of cuckoos, the Black-headed Duck in South America, Shiny Cowbirds, Screaming Cowbirds, Bronzed Cowbirds, and Giant Cowbirds.

Brood parasitism has resulted in the development of the evolutionary arms race, where both the host and the parasite has developed ways and means of outdoing the other. Parasites use mimicry and other strategies to make sure their egg is incubate, hatched and the young cared for, thereby reducing the reproductive success of the hosts. On the other hand, hosts have developed strategies of their own that protect their own young.

It is quite hard to imagine that what is obvious to us is not to the birds that get conned into raising some other individual’s young. To us, the differences are there to be seen clearly, but a tiny warbler seems unaware that they are raising a young that way bigger than they are. The latest knowledge of hosts effectively removing foreign offspring comes from an unlikely species as the coot.

The coot is a very common water bird and live in large colonies. The American Coots are very protective of their eggs and their young. Neighbors may often fight over small patches from where they procure their food and some females tend to lay their eggs in another’s nest. American coots have developed a strategy that ensures they do not raise another’s young. Scientists have found that coots have the cognitive ability to count their own eggs and differentiate them from another individual’s eggs. They are able to remove the foreign eggs and are also able to recognize their own chicks from others using imprinting. If any foreign chick does hatch in their nest, they able to immediately recognize the impostor and remove them, often very violently.

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The link above takes you to a picture gallery of some of the animals that have been listed by the Wildlife Conservation Society as being under great threat of going extinct due to climate change. The reasons for extinction are all linked to the effects of climate change, like loss of habitat, loss of food source, temperature variations, and disease. This report was to be presented in Copenhagen this year. But politics may yet come in the way of conservation. To view the interesting slide show, do roll over every picture for more information on the animals.

Female Mandrill with her Baby

Opposites attract! One of the most common sayings in the world. We humans seem to believe so, but do we really know why opposites attract?

Mandrills (Mandrillus sphinx) are the world’s largest species of monkey and very closely related to man. They are best known for their colorful faces and rumps. Male mandrills have red, purple and blue skin on their face, rump and genitalia, distinguishing them from the less colorful females. They are highly social animals, known to live in groups of up to about 800 individuals. Living in such close proximity with high number of individuals means there is usually no dearth of mates. But mating constantly within the group can lead to inbreeding and thus reducing the fitness of the future generations of mandrills.

Female mandrills seemed to have found a unique solution to the inbreeding problem – mate with males that are genetically most different from them. Determining the genetic difference of an individual from oneself is no easy task. But it is known that a lot of female mammals follow their noses to the potential father of their offspring. Odor plays a very important role in mating. Female mandrills know their own body odor, and body odor is also determined partly by genetic make-up of an individual. This means that any male with a different body odor will be genetically different from them. How this process works is still a mystery, but scientists have theorized that finding mates whose body odor is completely different from their own, helps females determine the extent of genetic difference of the male. Thus ensuring that the next generation of mandrills have higher fitness (are able to pass on their genes successfully). Male mandrills have external glands on their chests which they rub against trees and females pick up these scents. During courtship, the female mandrill follows the male around, and if the male is interested then he mounts her. Following a male with as different a body odor is the female’s way of ensuring she’s doing the best for her offspring.

Humans and mandrills are both anthropoid monkeys. Being so closely related to each other, it may be safe to theorize that humans, too, look for genetic diversity in their mates as well. It may be part of the sub-conscious or genetically coded into women, but how this works is something of an enigma.

Posted in Ecology Tagged: body odor, fitness, genetic diversity, mandrills ]]> http://colobine.wordpress.com/2009/11/26/opposites-attract-to-maintain-genetic-diversity/feed/ 0 colobine Female Mandrill with her Baby http://colobine.wordpress.com/2009/11/19/size-does-matter/ http://colobine.wordpress.com/2009/11/19/size-does-matter/#comments Thu, 19 Nov 2009 11:52:40 +0000 Sharmishta http://colobine.wordpress.com/?p=158 ]]> Most women would agree, size does matter!

In the animal kingdom, too, we have been convinced that size is good. The bigger and stronger males are known to sire stronger offspring ensuring their survival and fitness. In the case of mammals and birds, especially, it has been seen that the females choose males that can contribute to the overall fitness of the offspring. But in studies in the recent years, it has been discovered that there may be a downside to this. There may be advantages for females to go for the smaller males – size does matter, but not necessarily be biased towards the bigger males. Being big and strong, may no longer be the norm in the animal kingdom.

In mountain goats, it is always an advantage to be big and strong, and of course, possess a good coat of fur for warmth. The big males are essentially bullies, shoving the smaller ones to get the females. It has been reported that the bigger and stronger males do produce male offsprings that have high fitness, but the female offspring are smaller and weaker than those sired by smaller males. If this is true for mountain goats, then there is a strong possibility it may hold true for other species as well. This puts the onus on the females to chose well and may well begin a selection for the smaller males. If the sex ratio in the population gets skewed, the species may well die out. To maintain this balance, females are endowed with a genetic quirk that enable them to chose smaller males when the population is biased towards the males.

Female birds are known to be very choosy as to who they mate with, and this is true for the female mammals as well. If it comes down to ensuring that their offspring are fit and survive to pass on the genes, then size will matter, and not necessarily favor the bigger and stronger males.

This year, more than 17000 species of plants and animals have been identified as extinct or going extinct. About 47677 species were surveyed across the globe, of which 17291 species in the “endangered” category are at the risk of extinction. There are many more species that are yet to be surveyed, so there is a strong possibility that there are more species that are at the risk of being lost for good. This year’s survey included 2800 more species than last year, and it has been estimated that one on five of all known mammals, about 70% of all known plant species and about a quarter of all reptiles are under threat. 37% of freshwater fish, 35% of invertebrates and about 12% of all known birds are also looking at extinction.

A species of tree frog (Rabb’s fringe-toed tree frog) in Panama that was discovered only 4 years ago is on the list, as is a rodent from Madagascar and two lizards found only in the Philippines (Panay monitor lizard and the sail-fin water lizard). Both lizards are hunted for food. 1147 fresh water fish, out of a total of 3120 surveyed, are threatened with extinction, one of which is the brown mudfish in New Zealand, whose wetland habitat has virtually been destroyed due to drainage, irrigation and land development. The Kihansi spray toad of Tanzania is now considered extinct in the wild due to a dam construction on the Kihansi river and fungal infections.

And to think these numbers are only the tip of the iceberg. Who knows how many more species are yet to be classified as being under the threat of extinction.

Ants on an Acacia in Uganda

Plant-animal interactions are very common, and a very obvious relationship in nature. Everybody, at some point or the other, would have seen insects pollinating flowers in return for the nectar, the most popular example of plant-animal interactions. There are many examples of symbiotic relationships between plant and animal, another common example being seed dispersal in forests. There is a strong possibility that most people would have seen ants crawling around tree trunks, scampering into holes they use as nests. It would seem that this would harm the tree as the ants would bore into the wood and cause damage to the plant. On the contrary, the numerous ants provide services to the tree in return for a place to raise their young and tend their queen and also in some cases, in return for food as well.

Plants that harbor colonies of ants are called myrmecophytes, and they have evolved hollow bulges, stems, roots or thorny structures that give ample room for a colony of ants to set up home. In return for the being allowed to live on a particular tree, ants provide security to the plant they live on. They keep away herbivores and other insects as well that would feed on the leaves and also cause extensive damage to neighboring plants trying to establish themselves that may be a competitor for the resources available, like soil nutrients and sunlight.

There are many species of trees that are associated with their own guardian species of ant. The most common examples if ant-tree symbiosis is found between the Acacia trees and some species of ants. Some species of swollen thorn acacias do not have chemical defenses, like alkaloids, in their leaves and shoots to protect them from being grazed by insects and herbivores. The bullhorn acacia, found in Mexico and other part of Central America, houses a stinging ant (Pseudomyrmex ferruginea) that protects it and in return the tree provides the ants with protein-lipid Beltian bodies and carbohydrate rich nectar. The whistling thorn acacia of Kenya has bulbous thorns that harbor another stinging ant species of the genus Crematogaster. The ants hollow out the interior of the thorns to make room for living quarters. These ants deter any browsing by giraffes and other herbivores. Another type of tree that has mutualistic relationships with ants is the Cecropia tree, a member of mulberry family. The stems are usually soft and hollow allowing the Azteca ants to burrow in. The ants also feed on some of the insects that browse on the leaves of the Cercopia.

Ants are known to be excellent engineers, they excavate the bulbs and thorns in such a way as to not leave scars called galls. But in the Amazonian rainforests, it has recently been discovered that if ants run out of room on the host tree, they are burrowing into neighboring non-myrmecophytes. By doing so, they are scarring the trees, leaving large galls or scars.

A group of scientists in China are quite stumped as to why fruit bats would perform fellatio. Considering they could not find any evolutionary theory to explain it, they concluded that it was beneficial to the female as it resulted in longer copulations, ensuring fertilization perhaps. They watched a number of females bend and lick the penis of the male. The news article comes with a short video produced by the scientists of a pair of bats copulating and the female performing fellatio, which can be watched here as well.

Females are known to choose the males that are supposedly more “persistent”. This may be an indication of the fitness of the male, and hence can be assumed that the offspring of this male will be able to inherit the high degree of fitness, ensuring it’s survival. But in a new study using Adzuki beetles, scientists have found that there is no correlation between the females wanting “good genes” and female resistance to males. In the Adzuki beetles, females ward off unwanted suitors by vigorously kicking their hind legs. In the study, scientists increased the fitness of some females by fitting them with prongs that would impede copulations by the males. In some others, they reduced the size of the hind legs. The results showed that there was increased resistance to males had nothing to do with sons being born or females offspring with increased fertility being born. According to this study, there is a good reason to believe that being fussy has nothing much to do with sexual selection, but is a strategy of the females to benefit themselves.

The peacock has been used as an example for years to explain sexual selection. It has been made popular that peahens choose males with the biggest, brightest tails with the most number of ocelli (the “eyes” on the tail of the peacock). But how is the number of ocelli on a tail important, or reflect the fitness the male? But in a study that was conducted a few years ago by researchers in Paris, it was found that females chose males with shorter tails, even though males with longer tails were more dominant. There is a possibility that females chose males with shorter tails as the density of ocelli on shorter tails seem higher than on a longer one. Another theory that came from this study was that males with longer tails will lower their fitness levels due to the weight of the tails. Displays will become less persistent and males will give up easily. Male behavior, thus, also determines who gets to copulate with a female. More persistent males are the ones who can handle the weight of the tails.

Sexual selection is a field that has produced numerous theories on female choice. Though Darwin’s origin theory of sexual selection has undergone some changes due to the works of noted biologists like Amotz Zahavi and W.D. Wallace, there are still a lot of conflicting ideas that are floating around. With variations in genetic material come variations in behavior patterns and sexual selection and female choice has caught the imaginations of behavioral biologists across the world. It is, by far, one of the most interesting fields of study in biology.

Lion-tailed macaque (Macaca silenus)Slender loris

The area called Silent Valley in Kerala, India, was declared a National Park on the 15th of Nov 1984. This month, the Kerala Forest Department will celebrate the silver anniversary of the park with a 2-day seminar beginning on the 15th of Nov 2009.

Silent Valley National Park has been under the microscope for years. It began in 1847, when the British decided to explore the area as a watershed. In 1914, the entire area was declared as a Reserve Forest, although by the late 1920s, forestry operations had begun to take place. In 1928, a power project was identified which threatened to damage large areas of the pristine forest, which, it is claimed, has been around for almost 50 million years. But work on the power project did  not begin till 1958. In 1977, the Kerala Forest Research Institute conducted an environment impact survey and requested that Silent Valley be declared a biosphere reserve. In 1986, it was included into the Nilgiri Biosphere Reserve. Today, it is one the most secure and one of the most beautiful tropical moist evergreen forests (rainforest) in the country and is part of the Western Ghats World Heritage Site under the consideration of the United Nations.

Silent Valley National Park is home to the largest population of Lion-tailed macaque (Macaca silenus), an endangered primate species that is endemic (found only in a particular area) to the Western Ghats. It is also home to other endangered and endemic animal species, such as the Nilgiri langur, the Nilgiri tahr, and Malabar giant squirrel. Among the other residents of this area are the tiger, leopard, gaur, elephants, a few species of civets, the ruddy mongoose, striped-neck mongoose, many species of bats, and many species of deer, including the mouse deer and the barking deer. All told, there are about 34 different species of mammals that are found in the Park. About 730 species of insects have been identified so far in the Park, among which are about 128 species of butterflies, 9 are exclusive to the Western Ghats. Amongst the other insects, there is an estimated 400 species of moths, 33 species of crickets and grasshoppers, and about 128 species of beetles. Of these, there are about 20 odd species of insects that have been newly discovered. According to Birdlife International, about 16 species of birds out of the identified 211 are threatened or endangered. Out of the 211, 15 species of birds are endemic to the Western Ghats. It has been estimated that there are about 35 species of reptiles in Silent Valley, 11 of these are not found anywhere else. A couple of new species of amphibians have also been found here.

The flora of the Valley include about a 1000 species of flowering plants, 107 species of orchids, 100 ferns and fern allies, 200 liverworts, 75 lichens and about 200 algae. Of these plants a good majority are endemic to the Western Ghats. There is an outstanding number of orchids in the Valley are well. There are more than a hundred species of orchids there, a lot of which are endangered and exclusive to the area. There is a huge number of plant species within the Silent Valley area that are known to have medicinal value. If looked for, there is a possibility of finding many more medicinal plants here, some which may not be found anywhere else in the world.

There is no human habitation within the core area of the Park, but there are a few indigenous peoples that call the adjacent areas home, the Mudular, Kurumbar and the Irulas are a part of the Valley as much as are the animals to be found there.

Silent Valley National Park is a treasure trove of beauty and nature’s goodness. A naturalist’s paradise. It is an area worth protecting for the generations to come and definitely worth hiking through.

Posted in Places Tagged: biosphere reserve, endemic species, India, Kerala, Lion-tailed macaque, Malabar giant squirrel, Nilgiri langur, Nilgiri tahr, protected area, Silent Valley National Park, tribals, tropical rainforest, Western Ghats, World Heritage Site ]]> http://colobine.wordpress.com/2009/11/05/silent-valley-national-park-25-years-of-conservation/feed/ 0 colobine Lion-tailed macaque