4/26 Evolution - Sex, Treachery, Death

Today we learned about three different aspects of evolution, as seen in birds. The first was the use of treachery in nesting and egg laying. Weaver eggs in the same cluster will have a similar appearance. This is for the purpose of preventing other birds from laying their eggs in the nest and having the mother waste effort on children that aren't hers. Despite this, the cowbird has adapted treacherous techniques to outwit and overpower the weaver and other birds. The cowbirds never make nests of their own, so they must lay their eggs in other birds nests. Due to evolution, they have become extremely successful with this method. Their eggs are more round and thicker, causing beaks meant to pierce the cowbird eggs to deflect and risk breaking the mother's own eggs. If the mother is successful in removing the cowbird's eggs, the cowbird will come mess up the nest and destroy some of the host's eggs. Evolution has led to an increase in the size of the bird's brain, allowing for it to recall all of the nests it has planted its eggs in.

We learned how the number of juveniles is important for learning how climate changes effect the species in question and how invasive species can harm a population. The number of juveniles is set in a ratio with the number of adults in order to compare. Different traits are used to determine the age. An example of this would be the changing color, which is depending on the season, of the marbled murrelet. Determining the age ratios of animals can help us dig deeper and find the reasons for problems that the animal may face. This was seen with the marbled murrelet and their problems with reproduction. After scientists were able to determine the ages of the populations, they learned why the younger birds did not do as well as the older ones. The older male birds were able to set up territory before the younger birds, and as a result could acquire the most plentiful land while the younger birds were forced into the less bountiful mountains.

Sex plays a huge role in evolution and its direction, as it is the most important factor in carrying on the species. In birds, the males tend to be colorful and larger, while the females remain dull colors. This are features that help the male first attract mates and then fight/defend their choice. There is a balance for these features though; if a male bird is too colorful survival will be more difficult and a larger body is harder to feed. This is not always the case, as males are normally smaller when they are the ones that take care of the nest. This is the case with the Jesus Christ Bird, a species where the female attracts multiple males and does the fighting using the sharp spike underneath its wing.

Posted on June 1, 2012 01:58 AM by beardendb