The origin and significance of diversity Essay
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Ants Formīca are arguably the most successful organisms presently on earth. They evolved from a wasp like common ancestor approximately 150 million years ago(2006 Chuck Lydeard)1. Due to their long ecological dominancy amongst insect and short life span they have undergone a high rate of adaptive radiation. Leading to a reasonably large amount of species and inter- species diversity. There are at least 12000 different species of Formicidae (2008 Edward O. Wilson)2 which have colonised almost every landmass on the planet(Alice S.
This unique dominancy and prevalence means that Ants presently account for an incomparable 15 to 20%(2000 Ted R. Schultz)4,3 of the world’s terrestrial animal biomass. Formīca exhibit eusociality, they have complex rigid social roles and interactions. They form colonies varying form a few hundred to super colonies with billions of individuals. Ant’s prevalence is often over looked due to their size and nature. The time when we most notice their vast numbers is when it starts affecting us; but to put it in perspective there are around 1.7billion ants for every person in Scotland(2006 Edward O. Wilson) 5,6.
History of OriginThe Origin of the Ant stems back even further than we originally thought. A new D.N.A. study which included researchers from Harvard University states that they evolved around 140 to 168 million years ago in the Jurassic or Cretaceous period1. This is significant when we analyze how Ants became so successful and diverse. They evolved from the same common ancestor family as wasps called Vespoidea (1999 Denis J. Brothers)7 the similarity is clear in the family velvet ant (Mutillidae,) [See figure 1] which is actually a wasp but exhibits ant like qualities. They originally evolved in a rain forest type climate living predominantly amongst large herbivores. Indeed this is where we see the greatest number of Formīca and variation in species at present3,4. For a long time Ants were scarce making up only around 1 percent of the insect population(2000 David Grimaldi & and Donat Agosti)8. However around 100 million years ago with the appearance of flowering plants the r-selection species experienced a high rate of evolutionary radiation.
As a result of this period of adaptive radiation, ants ecological dominancy increased: 20-40% of insects found in fossil deposits from the middle of the Tertiary period are ants8. Flowering plants were the key to the ants increased population; they created a much wider range of niches and thus reduced competition amongst insects, which lead to an increase in insects that ants could utilise as a food source(2006 Moreau CS.)9 Over time ants exhibited complex symbiotic relationships. I noted a good example of this in the Edinburgh Botanic Gardens(Ħ). The Acacia sphaerocephala [See figure 2] is tree native to Central and South America it exhibits a symbiotic relationship with an ant species Pseudo myrmex sphaerocephala.
Its thorns are hollow and perfect for the ants to live in protecting them from predators which could disrupt their colonies if on the ground. In turn this mutualistic relationship benefits the tree as the ants guard it from other leaf eating insects. The eusociality social structure exhibited by Formīca is significant to its success. Instinctive genes inherited from its common ancestor Vespoidea give rise to its social colony structure. This is also still seen in most wasps which evolved from the same ancestral family.
Diversity within Formīca-QueensFormīca display a specific, highly organised, affective social colony structure. Diversity within species of Ant is based on the needs of the colony. The colony is even looked at as an organism in itself (a “Super Organism”) for the purpose of some field work. Individuals have specific development pathways which lead to specific roles such as, Soldiers, Workers, Drones, Queens, Foragers and food stores (repletes). The development into these different classes is determined mostly by environmental factors such as nutrition and hormones. Yet in a few studies genetic variation has been found between castes. These genetic changes are small a change in one gene which can, for instance, decide whether a colony has one or multiple queens. However in most cases all ants start with the same genes with the exception of males. Ants generally have 4 development stages, egg, larva, pupa and adult(2002 Myrm)10.
The larvae (see figure 3) are only capable of some minor movement, such as bending their head toward a food source. It is in the larval stage where differing the level of care and nourishment leads to different development pathways. When resources are low most larvae will develop into sterile female workers. Only if the developed colony has an abundant food supply will worker ants map selected larvae using pheromones. These then receive better nourishment than others which triggers select genes to activate(1978 Edward O. Wilson.)11 These larvae develop into, normally winged, sexually mature female ants (See figure 4)which leave to find a male (Drone) and start a new colony. In some colonies for whatever reason there is no queen; in this case a female worker (all ants apart from drones are female) becomes fertile and lays fertile eggs. The Queens main role is to allow gene flow in the gene pool. She mates with one or more males from other colonies before starting her own. This is the only sexual interaction between ants from different colonies. This important role exhibits the significance of variation within a species.
Diversity within Formīca-DronesWorkers generally cannot mate yet because of the “haplodiploid sex-determination system” in most species they have the ability to lay unfertilised eggs that become fully fertile haploid males. This system means that offspring created from the combination of a sperm and an egg develop as a female (Worker or Queen) and an unfertilized egg develops as a male. This results in males having half the number of chromosomes compared to females (males are haploid).
This system means that a drone (See figure 5) has no father and cannot have sons however he has a grandfather and is able to have grandsons. The Jack Jumper Ant Myrmecia pilosula’s (See figure 6) genome is enclosed on a single pair of chromosomes as males are haploid they only have 1 chromosome, the lowest amount identified for any animal. ( 1986 Michael W. J. Crosland & Ross H. Crozier)12 Interestingly Myrmecia pilosula have a venomous poison and cause more deaths in Tasmania than spiders, snakes, wasps, and sharks combined.(2008 Killer Ants T.V.)13 The only purpose of drones is to mate with a queen so she can start a new colony when this is complete he dies.
Diversity within Formīca-WorkersWorkers carry out every other role in ant society. Depending on their age and a number of environmental conditions, including the state of the colony, workers can be soldiers, nurses, farmers, repletes and more, depending on the species. Ants are the only taxonomic group to evolve into specific eusocialit roles with age. This creates a very clear and significant diversity within species. Soldiers are often older workers which develop powerful mandibles. In contrast to workers soldiers are a lot larger; in the species Pheidologeton diversus the dry mass of a soldier can be 500 times that of a worker. The difference is most prevalent in the army ant genus Dorylus(See figure 7.) Due to seasonal food shortages they leave their temporary ant hill and march in columns of up to 50 million individuals.
Columns are ordered with workers being flanked and protected by the larger soldier ants(1991Bert Hölldobler)14. The soldiers create a defensive moving wall allowing the workers to safely and swiftly move through the corridor (at around 20 meters an hour.) A clear example of the diversity within a species is found in the genus Myrmecocystus. It is literally a living food store, workers feed another worker until its abdomen swells and it gets too large to get out of the chamber it is in. They are termed repletes (See figure 8) and are used by the colony to survive in times of reduced resources such as; food, water and nutrients(1993 Randy C. Morgan)15.
Diversity between different species of FormicaFormica’s ecological dominance has driven diversity between species to reduce competition. To allow successful resource partitioning and acquisition of new resources there are vast differences in the physical abilities of different species. A resent example of this is the study of the species Odontomachus bauri (Trap Jaw Ant) by Andrew Suarez (an ecologist and entomologist at the University of Illinois) in late 2006. Through the use of high speed cameras (about 10,000 times faster than those used to film movies) the speed of the ant jaws closing was able to be measured. It is, by a clear margin, the fastest self perpetuated moment in the animal kingdom with speeds exceeding 144 miles per hour. Even more interesting is the power involved in this movement “the jaws accelerate at 100,000 times the force of gravity.” This results in the movement being completed very quickly, the movement could be repeated approximately 2300 times in the time it takes you to blink: exerting a force up to 500 times the ant’s body mass(2006 Andrew Suarez)16.
This diversity gives the ant a competitive advantage over other species. They use this ability to kill pray, attack predators and to flee from predators. As when the jaws close against the predator or ground the ant gets propelled away. An example of very specific diversity is that of leaf cutter ants Myrmicinae. They farm specific fungi as food sources in their colonies. Gathering specific leaves to feed the fungi and carrying antimicrobial bacteria to stop infection or competition for their specific fungi. However a more unique and resent discovery in Formica diversity is Polyrhachis sokolova (See figure 9) discovered in Australia in 2006 in mangrove swamps it is the only ant found to swim and nest under water. They survive in air pockets and by swimming to the surface to breath (2006 Dr Simon Robson)17. Not much more is known about them and research is ongoing. They clearly demonstrate the level of diversity and its significance in avoiding and reducing competition between ant species.
To conclude Formica are exceedingly diverse both within and between species. They exhibit very specific roles within their colonies so much so that the entre colony can be viewed as a single organism. They have been present on earth for a comparably long time. During this time they have diversified amongst species creating many complex and delicate symbiotic relationships with other organisms. However the impending threat of climate change coupled with deforestation and loss of habitat could threaten ant species. With a body I work with- the IPCC (international panel on climate change) predicting that “Climate change alone is expected to force a further 15%- 37% of species to the brink of extinction within the next 50 years.”(2006 IPCC.)18 There may be a serious impact on the biodiversity of ants due to their many obligate host habitats and specific dependency on other organisms.
1 http://news.bio-medicine.org/biology-news-3/Ancient-ants-arose-140-168-million-years-ago-7286-1/2 http://www.nytimes.com/2008/07/15/science/15wils.html3 http://ngm.nationalgeographic.com/2007/08/ants/did-you-know-learn4 http://www.pnas.org/content/97/26/140285 http://everything2.com/index.pl?node_id=17930206 http://www.gro-scotland.gov.uk/press/2007-news/scotlands-mid-year-population-estimates.html7 “Phylogeny and evolution of wasps, ants and bees” 233- 249.
8 http://www.pnas.org/content/97/25/136789 http://www.ncbi.nlm.nih.gov/pubmed/1660119010 http://www.antnest.co.uk/cycle.html11 “Caste and ecology in the social