Museum Collections

 When I look at the New York City landscape around me I notice how much of it is covered with cement. It wasn’t always this way. Even now bustling Manhattan used to be rural. It makes me wonder, how has urbanization over the past century changed our environment?

Wouldn’t it be nice if we could go back fifty or a hundred years and scientifically compare their environment to ours now?

It ends up we can do just that.

Well, not exactly. Time travel has not been invented (yet!), but scientists do have a way of preserving pieces of the past for future study. Museums and scientific institutions around the world like the Smithsonian, the American Museum of Natural History, and the Natural History Museum, London, have been collecting specimens of fish, birds, invertebrates, reptiles and amphibians, and mammals for many years. These collections document biodiversity over time and across the globe.

Having these collections is a great asset to science. Let’s say a scientist wants to know how urbanization is effecting different species. The scientist could look at specimens of many different species collected from an area that was once rural but is now urbanized and examine any changes in the specimens and populations they were collected from. Maybe this scientist decides to focus how urbanization has effected one particular species. Then s/he could look a specimens of this species from different areas, and compare populations of this species over both space and time.

Once we know how urbanization has effected a species, we can use this data to predict how further development will continue to effect it in the future. Knowing what happened in the past can help people realize what needs to change if we want to maintain a healthy environment. We can use this information to develop good environmental policies and policies for conservation.

It’s pretty cool that museum collections can be used to study environmental health, but that’s not the only way collections are used. Here are a few more ways we can use species collections:

o   To study evolution. Maybe during urbanization, one population of a particular species became isolated. Using specimens collected from the original population and the isolated one, researchers can see if the populations change enough to be considered different species or different subspecies.

o   To study genetics. DNA can be obtained from tissue samples and from the skins of specimens, as long as they weren’t preserved in formalin. Today we can obtain DNA from specimens collected when people barely even knew what DNA was! Who knows what information old collections will provide scientists in the future.

o   To study disease, contaminates and parasites and how they effect a species.

o   To identify unknown species using DNA or morphology.

o   To study the diet of a species and how it changes.

The interesting thing about collections is that they are always being used in new ways. Early collectors probably had no idea the specimens they collected would be used to study the effects of urbanization. Not too long ago no one thought we would be using DNA from specimens for science, but now that is common practice. Future scientists will probably use specimens we collect today in ways on one could dream of now.

Thanks to Neil Duncan and Nuala Caomhanach at the American Museum of Natural History for helping me research for this post.

Sources.

Attending a Dissection

Whenever I think I know a lot about a subject, something happens that makes me realize how little I actually know. I had a moment like last Tuesday when I went to the American Museum of Natural History to watch William Mauck III, the ornithology-laboratory supervisor at AMNH, dissect, clean and stuff a raven before it entered the collections at the museum. Mauck normally would prepare the bird alone in the lab, but this week he did the work in front of one of AMNH’s afterschool classes and a few guests like myself.

Raven pre-dissection. Photo credit: Sandra Lewocki

Anatomy is one of my favorite subjects, and I know a little about birds, so I expected what I would see during the dissection to be familiar. Mauck skinned the raven and showed us the bird’s now skinless abdomen, and I saw what I expected - large pectoral muscles and some fat stored in the clavicular region. After we all got a good look, Mauck proceeded to cut open the abdomen to get tissue samples and see what the stomach contents were.

First cuts into the raven. Photo credit: Sandra Lewocki

As he sliced open the body, all of us were shocked by what we found.

Raven being skinned. Photo credit: Sandra Lewocki

Six eggs were inside our raven! The eggs were in varying stages of development. The most developed egg had a thin shell around it while the other five did not. Since the bird had been in the freezer for so long, the eggs were hard and we got to see them clearly, which is rare. Even Mauck, who prepares birds all the time, was surprised. He said that normally you don’t see many eggs, and if you do, they tend to pop into a gooey mess right away.

The most developed egg and its shell. Photo credit: Sandra Lewocki

I knew birds laid eggs, of course, but I never thought about how that happened. Mauck explained to us that bird genitalia is completely different than that of mammals. Both male and female birds of most species reproduce, urinate, defecate, and, if female, lay eggs through the same opening called the cloaca.

During mating season, the cloaca swells, and male birds temporarily store sperm in their cloaca. While bird courtship is notoriously long and involved, actual intercourse is short, taking about a minute. During mating, the male bird balances on top of the female, who moves her tail out of the way, allowing the male to briefly touch his sperm-saturated cloaca to hers, just long enough for sperm transfer. (Aquatic bird anatomy and intercourse is slightly different.) The sperm enter the female’s sperm-storage tubules and will then fertilize eggs as ovulation occurs. Birds may mate several times during the season to increase chance of fertilization as only1-2% of sperm that enter the female’s cloaca make it to the sperm-storage tubules.

The raven and its eggs. Photo credit: Sandra Lewocki

Female birds only have one ovary and oviduct, usually the left one, with the exception of raptors which have two. No one knows why they have only one, but it means most birds can only lay one egg per day. Once the females have sperm to fertilize their eggs, eggs develop in an assembly line. First the newly-fertilized egg is released from a follicle of the ovary to the oviduct. In the oviduct, layers of yolk are formed to provide food for the young embryo. Then the egg goes to the isthmus where the shell membranes are formed. Once that’s done, the egg moves to the uterus where the hard calcified shell is made. Colors or patterns are also added in the uterus. Finally the egg travels out the cloaca and is laid.

Egg development in the body is extremely fast, taking about 24 hours per egg. Most of the embryotic development happens outside the mother’s body, after the egg is laid. Laying eggs rather than carrying their young inside the mother’s body works well for birds since it keeps the mother from becoming too weighed down to fly.

Diagram by blog author

The raven we dissected in the AMNH classroom had one large egg with a thin shell and several eggs in earlier stages of development without shells. The raven died at a bird rehab facility near Berkeley, California of a broken wing before it could lay the eggs. The bird’s life ended, but the dissection doesn’t mark the end of the story or the end of our study - the skin and tissue samples will be kept at AMNH for researchers to learn from, both now and in the future.