Origin Of Variation Between Species
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Published: Wed, 17 May 2017
All forms of life on planet earth vary from each other. Some are more closely related compared to others, resulting to the formation of a species. Remarkably all the different species that exist today on earth are said to originate from a common universal ancestor.
This essay aims to explore, the origin and significance of the diversity within a population of different species, and how that contributes to a greater chance of survival of successful individuals, as well as the source and importance of variation between species, which eventually results into the formation of different species that make up the total diversity on Earth. Examples from the Leporid family will be used for illustration purposes.
All members of the Leporidae family are called leporids. Leporids are part of the order Lagomorpha and the class Mammalia. Leporids are strictly herbivorous mammals and are widely distributed over most continents of the world, including Africa, America, Asia and Europe except Oceania where they have been introduced.
Origin of variation between species
Speciation is defined as the process by which, a group of organisms becomes isolated from original population, eventually resulting into the formation of new species. The new species may arise either through sympatric or allopatric speciation (Raven et al., 2008)
In the case of allopatric speciation, populations split due to geographical barriers, and the gene flow between them is restricted. Since different environments are occupied by each group of organisms, the selection pressures in each environment vary, causing a change in the allele frequency because of natural selection and genetic drift (Reece et al., 2011).
On the contrary, sympatric speciation is the genesis of new species, when populations are found within the same environment, though reproductively isolated from each other.
Significance of variation between species
When two or more species are found occupying the same ecological niche; only the individual best adapted to their environment, tend to survive and transmit their genetic characteristics to increasing numbers in successive generations. The less adapted eventually become extinct.
Significance of variation within species
When a radical change occurs in the environment, adaptation of the organism to the new conditions is crucial to its survival. The factors that determine, whether an organism has the potential to adapt to those new conditions include; the strength of the selection pressure, the reproductive rate of the organism and the gene pool size.
The capacity of an organism to survive and thrive to the extreme conditions (strong selection pressure), is maximized, if the genetic diversity within a population is great (large gene pool size), and the reproduction reproductive rate is relatively fast. Adaptation is eventually achieved through the course of natural selection.
Origin of variation within species
The variation within a species originates from three primary sources: mutation, sexual reproduction and gene flow.
Mutation; is the random, spontaneous change in the DNA, that might provide new genetic capabilities to a population. Only germline mutations are passed on the offspring, while any acquired characteristics are not consider heritable (Hartl and Jones, 2005).
Sexual reproduction is also factor that contributes to genetic variation within a species. Specifically, during sexual reproduction, gametes (haploid) formed by meiosis, whereby the homologous chromosomes exchange DNA (chiasmata formation) during prophase (new alleles maybe formed) and independently assort during telophase. Eventually, the gametes fuse together to form the zygote (diploid), therefore giving rise to diversity. In leporids the chromosome number varies from 38 to 52 (Robinson and Matthee, 2005; Robinson et al., 1938a; Holden and Eabry, 1970), therefore the potential variation of gametes resulting from meiosis will be 219 to 226 (Reece et al., 2011)
Gene flow is the transfer of genes between populations or within the same species. If the characteristics of a newcomer vary from the individuals, already in the new environment and is well adapted, then it has the potential to survive and reproduce successively. As an outcome, the gene pool composition of the recipient population changes. Moreover, genetic drift can affect the frequency of alleles within a population, in the case of isolated population it may lead into the amplification of certain alleles, favouring the rise of extreme phenotypes (Founders effect) or even the loss of alleles in large populations.
Fit off springs are generally produced when inbreeding is avoided.
In general, evolution is described as the gradual change in the rage of organisms, which ensures continuation of life. When a change in the environment occurs, individuals that possess favourable alleles (selective advantage) either by chance mutation or natural variation adapt, survive over time and reproduce, while other do not. On the contrary, selection pressures to which an organism adapts over the course of natural selection are not always associated with environmental factors. For example, a strong selection pressure is inferred due to human intervention, specifically in the Italy, where restocking procedures foreign specimens for hunting with foreign specimens, have resulted into almost complete disappearance of the Lepus europaeus meridiei due to hybridisation and the decrease in the population of Lepus corsicanus, possible because of interspecific competition (Angelici and Luiselli, 2007; Angelici, 1995; Angelici and Luiselli, 2001). Furthermore, as a consequence, the inbreeding rates within the two species has increased significantly(less common under normal circumstances about two thirds of juvenile males as soon as they reach adulthood they leave the parental environment, to avoid inbreeding), causing decrease in the genetic diversity.
In general, the greater the diversity within and between species, the greater the potential, the organisms have to adapt to most changing conditions, and thus survive and thirve.
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