Evolution of the Wild Soay Sheep

Changing Species, Changing Environments: Unit Project The way organisms evolve is a very delicate process, and a number of factors can influence this. A prime example would be the recent evolution of the wild Soay sheep residing on the Scottish island of Hirta. First of all, this changing environment is producing variations to this species in ways that evolutionists would not expect. In addition, the impact of these changes is widespread throughout this population, and will lead to many differences from previous populations of these sheep. Finally, the way the environment is affecting natural evolution of this species is different than many people would suspect. Overall, the changing environment of the wild Soay sheep is giving rise to altered natural selection forces and thereby causing evolutionary processes. Climate change is causing many impacts throughout the world, and the warming climate of Hirta, a Scottish island, is not an exception. The climate of this island and surrounding ones has steadily amplified in warmth since 1985, the year that the study of wild Soay sheep was commenced by Professor Tim Coulson of Imperial College London. This has led to milder, shorter winters with the vegetation being more readily available throughout the year and a reduced competition for food among this species. The change on this species includes a reduction in the average body size and weight by greater than 5% over the time of this study. These warmer temperatures have reduced the need for the young sheep to grow rapidly in size and weight quickly to be able to survive to their first birthday, which ultimately leads to a smaller average phenotypic size for the sheep. As a whole, the ways that the environment has transformed has led to alterations in the evolutionary process of this species. Beyond the simple “paradoxical decrease in size” of these sheep, the changes brought on by this climate change are producing impacts to the species populations as a whole. The gene pool is being affected through the warmer weather causing natural selection to favour the allele for smaller body composition nowadays. In addition, although the small population of 900 to 1500 registered Soay sheep goes through many fluctuations in population size, being a rare case where the species never obtains population equilibrium, more variations of body size phenotypes are able to survive now causing less downward fluctuations. Finally, the “young mum effect” is an impact from the warming climate and an increase in reproductive success as it is understood that younger mothers can now give birth reliably, as the younger the mothers are, the smaller the offspring will be. As the warmer conditions can now support smaller offspring, the mother can start reproducing at a younger age and therefore, produce more over her lifespan. Overall, the warming climate of the wild Soay sheep’s habitat has led to countless impacts in the growth and development of this species’ populations. Throughout the study of these wild Soay sheep, it is evident that the environment plays a big part in the evolutionary trend of a species, especially when one phenotype is studied. It has been proven that this species has been steadily decreasing in size, while natural selection would commonly favour a lager body composition in terms of survivability and reproductive success. This proves the influence of the environment, as this change is causing a greater genetic variation within the size of the sheep than would have been expected. Also, DNA will undergo more mutations in a warmer climate compared to a cooler one, as the germ cells that will eventually turn into the sperm or egg of an individual divide more frequently in warmer condition and therefore, have a greater chance of mutating. This being said, a warmer climate for the Soay sheep will not only create an inflated phenotypic variation of this species, but also at a more rapid rate than previous evolution. As a whole, the amount of gene mutations is multiplied 1.5 times as often in a warmer climate. To conclude, environmental factors can sway the effects of natural selection extensively, allowing one phenotype to have a selective advantage over another, even for a trait that would not have been desired previously. As a conclusion, the warming trend of the environment of the wild Soay sheep on the Scottish island of Hirta has drastically impacted the anatomy and process of natural selection of this species. A warming climate has produced variations of the body composition of this species that is smaller than previously required. As well, this has impacted the growth and development of the population of this species as a whole in terms of numbers and the gene pool. As a final point, it has been proven that these environmental changes have gone on to sway the evolutionary trend of this species and change the course of what would be expected out of this species. It is evident that an environmental change can impact the course of evolution and proves itself a powerful force in the workings of any species in particular, whether detrimental or valuable for the wellbeing of the Earth’s populations.