Sexual Dimorphism

Sexual Dimorphism is when males and females exhibit different characteristics. These usually involve, color, size, behavior, and other appendages. 

In the animal kingdom, males are typically brighter and more colorful. The males are trying to prove to the ladies that they have good genes, they are disease free, and they can escape predators. 

Larger males can win contests against other males also proving their good genes. Though the males show off, it is the female's choice when she ultimately makes a decision. It is possible for a female to reject all males and choose none. 

Differences in size and coloration indicate that there is female choice, the female will choose a male to fertilize her eggs and in most cases, his job is done, and she leaves to finish the baby-forming process. All she wanted was his genes. 

When a large group of organisms all spawn at the same time, the organisms rely on luck and statistical chance for genetic variation. Males and females will look similar because there is no choice involved.

When males and females work together and take an equal role in raising young or protecting eggs, the males and females tend to look more similar. They look similar because of their equal roles and because the choice is longer-lasting. She is looking for more than just a pretty face (and pretty faces in the animal world do not indicate good egg care or being able to provide nesting materials, food, etc).

Differences in size between males and females varies widely. There is no set rule for who will be bigger, but there is usually a clear reason as to why one of them is bigger. Males can be bigger because they fight other males, because they have to guard eggs, or other reasons. Females can be bigger because they have to carry and nourish a fetus, carry and develop eggs, protect babies, or other reasons. To know why a male is bigger or a female is bigger the biology and reproductive strategies have to be understood.

Keystone Species

We talked about keystone species. Keystone species are important members of the food web because they help maintain biodiversity and keep everything in balance. An example is a sea otter. Sea otters eat sea urchins and keep their population in check.

When the sea otters are removed (like when they used to be hunted for their fur), the sea urchin populations go crazy, eat all the kelp (as in many many 300 foot tall plants), and the loss of kelp leads to a drop in biodiversity because there is less food and habitat for the many other species that like to live in and on and among the kelp.

Expanding your Horizons: Squid Skin

As an introduction to cephalopods, we watched a video that showcased the awesome camouflaging abilities of cephalopods. Cephalopods include the well known octopus and squid, but also the cuttlefish and a creature called a chambered nautilus.

These molluscs are able to control their color by rapidly changing the chromatophores in their skin.

This week, students will need to watch two videos, answer some questions, and then think about what they would use this ability for.

Video1 - Deep Look - Squid Skin

Video2 - Richard Hammond - Can a Cuttlefish camouflage to a living room?

Optional Video2 - Science Friday  Where's the Cuttlefish?

Intro to Color in the Sea

We talked about fish coloration and camouflage. Some of the tricks these fish have up their fins to blend in or advertise or trick predators are quite ingenious. 

One of my favorite organisms is the nudibranch - basically a slug that lives in the ocean. These soft squishy slimy critters would make excellent snacks, but they are all poisonous! They have warning coloration to let would-be predators know that they would not taste good at all. You can click here for a National Geographic Article about nudibranchs.

Parrotfish

Parrotfish are part of the nekton because they swim. They are omnivores because they eat coral (animal) and algae (plants). This fish is a male because it is more colorful than its female counterpart. Some may consider this warning coloration because it will chomp on things that try to mess with it.

An odd part of their niche is that the coral they digest is where most of the white sand in tropical locations comes from.

Bioluminescence

Different colors of light travel different lengths. Blue travels the farthest, but red, orange and yellow do not travel far. Because red does not travel far, these organisms appear black.

After discussing bioluminescence (organisms that can produce their own light) we looked at a TED talk by David Gallo . Gallo's talk showed the organisms in accurate color and in motion. His talk also showed some amazing footage of cephalopods like cuttlefish and octopus performing magical feats of mimicry and camouflage. You should definitely follow the link and watch this video stream.

His talk was based on research by Dr. Widder. We looked at some of her photos and you can learn more about her work and see her presentation here.

When it comes to deep sea creatures - some bioluminesce and some don't. People are fascinated with the gulper eel, a four foot long eel that has a HUGE jaw. It has such a big mouth so that it can eat anything it comes in contact with because in the deep ocean, meals may be far and few between. More information about the gulper eel and other deep sea creatures can be found at Sea & Sky's Website.

You can watch a this one found on YouTube.  This creature to the right is a Firefly Squid; it has amazing lighting capabilities.

For more information check out
The Bioluminescence Web Page
How Stuff Works
Or Sea and Sky's page about Bioluminescence.

Adaptation

Today we also discussed evolution and slow change over time. We discussed that evolution is not debated (the mechanism for evolution is) and that we have even seen change in humans in the last two to three hundred years.

Typically humans are getting taller and have bigger feet than their parents and grandparents. We think this is because of better nutrition.


We talked about the fossil record and how evidence shows whales changing from land mammals to sea mammals over millions of years and how you can observe the small changes in skeletal structure changing over time.