Coelacanth: Living Fossil

Discovering a species previously thought to be extinct sounds like the plot of a Steven Spielberg film however, that’s exactly what happened in 1938 with the discovery of the Coelacanth (Latimeria chalumnae). This species of fish was thought to have last lived on Earth about 65 million years ago. To the surprise of scientists around the world, a fishing vessel accidently captured an adult and it was quickly identified as the long lost Coelacanth. More recently, in 1997, a second species of Coelacanth (Latimeria menadoensis) was identified. These deep sea dwelling fish usually inhabit waters 700 meters below the ocean surface and can grow up to two meters in length and nearly 200 pounds. The fossil record has shown that nearly 90 species were present 360-90 million years ago. However, the question may be asked, what’s so important about Coelacanths?

Coelacanths have both evolutionary as well as anatomical significance. These are some of the earliest bony fishes which are also related to lungfish. Most importantly, Coelacanths are believed to be a precursor to vertebrates. It has been hypothesized that Coelacanths, lungfish, and tetrapods diverged from one another 390 million years ago.

These fish are also unique to be characterized as having a rostral organ, which is electrosensory and used to locate prey; an intracranial joint allows the Coelacanths to open their mouth very wide for prey; a notochord that is hollow and fluid filled; as well as paired lobed fins which move in a tetrapod – like pattern. When observing the fish swimming its fins mimic the pattern of a galloping horse.

I was drawn to this topic following the Assessment Test required for this class. I encountered some difficulty answering questions regarding evolution. In an attempt to improve my knowledge on this content, I came across a National Geographic article about the Coelacanth. I was instantly drawn to this because; although I was familiar with this animal I did not know of its significant role in evolution of tetrapods.

Fruit Flies: One man's nuisance, another man's treasure

The Drosophila melanogaster is an organism commonly known as the fruit fly. It has received this name because it accumulates near ripened or rotten fruit. It is about 3 mm in length, and belongs to the order Diptera, the order in which most common flies belong to, and the family Drosophilidae. The Drosophila melanogaster may be viewed by many as a common household pest, but the Drosophila melanogaster in biology is so much more than that. It is a model organism, extremely valuable to the field of biological research, particularly genetics.

Drosophila have become extremely valuable to biological research for many reasons. First, Drosophila are economically feasible. It costs very little to purchase and maintain Drosophila allowing many to be purchased for very little cost. Second, they have a short generation time allowing Drosophila reproduction to be rapid, providing biologists with a continuous supply with a very little wait period.
The rapid life cycle of Drosophila consists of four stages: egg, larva, pupa, and adult. The life cycle begins with a fertilized egg that has been laid. After the egg has been laid, it takes about one day for the larva to develop. In the larval stage, there are three periods of molting called instars. These instars occur on days 1, 2, and 4 (first, second, and third instars respectively). In the third instar stage a puparium develops, in which metamorphosis occurs. In the puparium, the larva develops wings and is remodeled into an adult form. The adult form is then hatched from the puparium producing an adult Drosophila. This whole process takes about 14 days, with the life span of an adult consisting of several weeks.

Another reason as to why Drosophila are extremely valuable to biology research is because their entire genome has been sequenced. Their sequence contains four pairs of chromosomes consisting of; autosome 2, autosome 3, autosome 4, and a pair of X/Y chromosomes. The sequenced genome has been established to contain around 165 million base pairs and around 14,000 genes. This sequenced genome has proven to be especially beneficial to the study of human diseases, as around 75% of identified human disease genes correlate with a matching gene in the genome of the fruit fly. The human disease genes correlating to matching genes in the Drosophila have been used as a major research tool for many diseases. Some of these disease include but are not limited to Alzheimer's, Parkinson's, and Huntington's, three common neurodegenerative disorders. Drosophila are also being used to study certain diseases and the mechanisms in which they work such as cancer, immunological diseases, and diabetes. Nonetheless, Drosophila melanogaster prove to be beneficial in many ways to the medical field.

Along with being an ideal genetic organism, Drosophila are extremely easy to work with. The sex of the Drosophila is easy to determine visibly due to the female Drosophila melanogaster being slightly larger than males. Along with differences in size, the male Drosophila can be identified due to a darker part on the back of their body, along with a black patch found on their abdomen. They are also very small in size and require very little room for storage, as well as minimal maintenance.

As you can see, the Drosophila melanogaster may be seen as a nuisance to some, but in science they have provided researchers with valuable information and are an ideal organism used time and time again.

References:
http://www.ceolas.org/fly/intro.html
http://animaldiversity.ummz.umich.edu/site/accounts/information/Drosophila_melanogaster.html
http://www.woodrow.org/teachers/bi/1994/life_cycle.html

Who's your momma?: the science behind imprinting

 

   Because I never took an ethology course, I wanted to do a presentation on imprinting. I have an interest in animal behavior, I just never had a chance to take the class. As a kid, I watched movies like Fly Away Home and Fox in the Hound and wondered if I could ever get a wild animal to follow me around (especially a fox). That didn't work out obviously, maybe because I was never in the right place at the right time, or maybe i was focusing on the wrong species.

I would have started my presentation with the history of ethology and imprinting studies. Imprinting is defined by brittanica online as a form of learning in which a young animal fixes its attention the first object it sees, hears or comes in contact with after hatching. This is mostly observed in birds, but hardly ever noted in mammals. Imprinting has been extensively studied in the lab, but in the wild the imprinted object is almost always the hatchlings mother.  Imprinting studies were first done in the lab by Konrad Lorenz (an Austrian naturalist, 1903-1989). He found that chicks don't always follow their mother upon hatching, but they will follow and bond with the first thing they come in contact with (Cardoso and Sabbitini).  

 Next, I think it is important to recognize why imprinting is important to the species. Imprinting is important for birds to learn to recognize others of their species (Terning et al, 2008). This was found by cross-fostering blue tits, Cyanistes caeruleus, with great tits, Parus major. They found that species recognition is irreversible once established in youth ( Terning et al, 2008).  Recognizing those of the same species is important for sexual isolation (Burley, 2006).

In my presentation, I would have discussed thoroughly the proposed mechanisms behind imprinting associations and where those associations are stored in the brain: ie the Hyperstriatum ventrale, Dorso ventricular ridge, and the wust.  (Cardoso and Sabbitini).  Studying imprinting is important for understanding different species behavior that contributes to recognition, selectivity, and survival (Cardoso and Sabbitini). 


 

  Obviously, in a presentation I would have included a lot more detail about Imprinting studies, mechanisms, and in different species.  Most of the research articles I found were outdated, but there are more genomic studies going on currently.  I would be interested in understanding if imprinting is present in mammals, and understanding the difference in imprinting mechanisms in different species.

References

Burley, N. T. (2006). AN EYE FOR DETAIL: SELECTIVE SEXUAL IMPRINTING IN ZEBRA FINCHES. Evolution, 60(5), 1076-1085.

Cardoso, SH and Sabbatini, RME. Learning who is your mother: The behavior of imprinting. Brain & Mind Magazine. 

Hansen, B. T., Johannessen, L. E., , & Slagsvold, T. (2008). Imprinted species recognition lasts for life in free-living great tits and blue tits. Animal Behaviour, 75(3), 921-927.