eclosion

An entomological term; the emergence of an adult insect from its pupal case -or- the hatching of a larva from its egg.

electrophoresis

Electrophoresis uses an electrical current to separate different molecules or particles. Based on their size, shape, and chemical composition, particles move through a substance at different rates. In genetic analyses, biologists put the molecules (such as proteins or DNA) from several individuals into a substrate called a gel, apply electricity, and then see how far the molecules move. After applying the electrical current, the scientists adds chemicals that stain the molecules to show where they are. They can then compare "maps" of the gels that show the location of molecules from different individuals. If two maps are the same, it suggests that the individuals have the same alleles, while if they are different, the individuals have different alleles. By comparing many individuals, a researcher can begin to see the variation that exists in the population.

 

environmental conditions

Events in nature often play an important role in structuring and limiting butterfly populations. Weather is one of the most important of these. Unexpected cold snaps, either in normally warm climates or in colder climates after spring has already arrived, can kill larvae and adults because butterflies cannot generate their own heat internally. Severe weather (storms, high wind, heavy rain) can also kill butterflies. For example, Hurricane Andrew in Florida wiped out almost all of the Schaus' Swallowtail butterflies, which lived on islands hard-hit by the storm. (Luckily, a researcher had 100 eggs to breed in Gainesville as part of an experiment, and the descendants of those butterflies now populate the islands again.) Similarly, big snowstorms killed huge numbers of monarch butterflies in the Mexican overwintering sites in 1991-92 and 1995-96. Cold wet springs and summers have also reduced monarch populations in previous years. Drought may lead to butterfly deaths if the plants they eat as larvae or visit as adults die back or don't flower.

Butterfly populations may also be limited by food. If the population of a plant that serves as a food source for either adults or larvae is reduced, butterflies may not find enough food to reproduce, or even to live. Sometimes plant populations decrease for natural reasons, such as drought, herbivory, or weather. Human actions can also reduce plant populations, especially when people develop land into houses, roads, offices, or highly maintained parks.

Habitat destruction may also decrease the amount of space available for butterflies to live in. Butterflies require plants, water, and refuge from the elements and predators. These resources may disappear when people build on once-natural land.

 

exoskeleton

a hard skeleton located on the outside of an invertebrate's body (in contrast to the internal skeleton of vertebrates) that protects it and serves as a point for muscle attachment. Arthropods and mollusks have exoskeletons. Arthropod exoskeletons are made of a substance called chitin, similar to fingernails, while mollusk exoskeletons are made of the mineral calcium carbonate.

 

frass

the waste product of the larvae, called caterpillar poop by most students. Monarch larvae produce a lot of this, especially in their later instars.

 

fungi

Fungi are a kingdom of eukaryotics organisms (see bacteria for a definition of eukaryotic cells) that digest their food outside their bodies and then absorb the nutrients. The most familiar fungal structure is the mushroom. Typically, fungi have a net-like mass of strands or filaments, called hypae, that look like tiny hairs without a microscope. Hyphae grow into whatever the fungus is eating, excrete digestive fluids, and absorb the nutrients. Fungi can grow incredibly fast; they can add up to a kilometer of hyphae in a single day! Mushrooms are dense collections of hyphae that serve as the reproductive structure of a fungus. Mushrooms are connected to a much-larger network of hyphae below the surface of whatever they grow on. Fungi can grow in soil, in dead organic material such as tree stumps, or in combination with living organisms. Sometimes fungi live in other organisms in a mutually beneficial way, including when algae and fungi live together in the structure called lichen. Other times, fungi are parasitic. About one-third of known fungi are parasitic, mostly in or on plants. Examples of fungal diseases include Dutch elm disease, smuts, rusts, and ergots on grains, and athlete's foot in humans.

 

genetic drift

Genetic drift is the change in a population's gene pool that is due to chance. This is especially important in small populations. Any accidents that prevent an individual in a small population from reproducing will have a dramatic effect on the gene frequency of the whole group. Say, for example, an endangered plant has only 10 individuals left and only two of those individuals have a copy of the allele r (the rest of the plants are RR). If a rabbit eats those two plants, there will be no copies of r remaining in the population; chance removed that allele. Genetic drift is most important in populations of 100 or less, although it cannot be ruled out unless a population is very large. See Bottleneck.

 

habituation - (huh-BIT-u-A-shun)

a learned response in which an animal stops responding to a repeated stimulus (such as sound or touch) that normally evokes a reaction.

 

hemolymph - (HEE-muh-lim(p)f)

the name for the blood of insects.

 

heterozygous

 

homozygous

 

Hardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium is named for the two scientists who derived it in 1908. It states that the shuffling of genes that happens during sexual reproduction does not change the overall frequency of genes in a population. If you are interested in the details of how to apply this principle to genes in populations, look in a biology textbook, such as the one listed below. These books will lay out examples and go through the math that proves the principle.

 

Campbell, N.A., L.G. Mitchell, and J.B. Reece. 1994. Biology: Concepts and Connections. The Benjamin/Cummings Publishing Company, Inc.: Redwood City, Calif.

 

Hymenoptera

There are about 90,000 species of this order of insects, including ants, bees, and wasps. Hymenoptera have two pairs of translucent wings. The hindwings are hooked to the forewings, making the two act as one wing, which improves flight efficiency. Members of this order generally have a narrow waist.

 

instar

a period between larval molts. There are five of these periods in the growth of a Monarch larva.

 

larva - (LAR-vuh), plural, larvae (LAR-vee)

the second stage, after the egg, in metamorphosis. Also known as caterpillar. Monarchs molt five times in their larval state, which lasts about 9-14 days.

 

Lepidoptera - (lep-uh-DOP-ter-uh)

the group or order of insects that is made up of butterflies and moths. This word should be capitalized, but the adjective lepidopteran should not.

 

lepidopterist

Lepidopterists are scientists who study butterflies. Some famous lepidopterists include Vladimir Nabakov and Sir Walter Rothschild. Well-known monarch scientists are Fred Urquhart and Lincoln Brower. Dr. Urquhart led the team that discovered the winter roosts in Mexico during the 1970s, and has been studying monarchs for over 50 years. Dr. Brower did early work on cardenolides and bird predators. He still works on many aspects of monarch biology.

 

mandibles

strong "jaws" on the larval head.

 

maxillary palp

small sensory organs on the larval head, below the mandibles, that may help direct food into the larva's jaws.

 

meconium - (mi-KO-nee-um)

the fluid Monarchs excrete shortly after they emerge from the chrysalis.

 

metamorphosis - (met-uh-MOR-fuh-sis)

the series of developmental stages through which insects go to become adults. Through metamorphosis a butterfly is transformed from an egg, to a larva, to a pupa, to a butterfly.

 

micropyle - (MY-kro-pile)

a funnel-shaped opening in an egg shell through which sperm enter the unfertilized egg.

 

mimicry

Mimicry is the close resemblance of one organism (the mimic) to another (the model). In many cases, predators learn to avoid certain prey items after having a bad experience with them (such as throwing up, being stung, or harmed in another way). Mimics can take advantage of this learning; even if they are not harmful, a predator will avoid them if they look enough like a harmful model. Mimicry is common in butterflies in moths, which may mimic distasteful butterflies and moths, or even unrelated species such as wasps and spiders.

 

mitochondrial DNA

Mitochondrial DNA (mtDNA) is the genetic material of tiny organelles inside each cell that are called mitochondria. Mitochondria are the powerhouses of the body; they convert energy stored in chemicals into energy the body can use. Biologists think that mitochondria were once free-living bacteria that joined with another cell to work together for their mutual benefit (the mitochondria got food and safety, while the cell got an internal efficient mechanism to convert stored energy to usable energy). Mitochondria still have aspects of their free-living life, including their own DNA. mtDNA is especially useful for evolutionary biologists for several reasons:

- mtDNA evolves rapidly because it lacks efficient repair mechanisms. In cellular DNA, these repair mechanisms would change back many alterations since such alterations could be harmful to the cell. The lack of repairs in mtDNA means all mistakes stay in place, which allows scientists to observe them and use them as markers for evolutionary change.

- The way mtDNA changes is through base substitutions in the DNA sequence (the genetic code on DNA is made up of the four bases adenine, guanine, thymine, and cytosine). Unlike cellular DNA, mtDNA does not rearrange during replication, so the overall DNA sequence stays the same over time. Mutation and base substitutions are the only sources of changes in mtDNA's sequence.

- Scientists know a great deal about mtDNA because of the research that has been done. This thorough understanding makes mtDNA a useful tool to study other questions.

- It is easy to isolate mtDNA from the rest of the cellular material. This is critical, since researchers must be able to examine mtDNA alone to use it in studies.

- An organism inherits all its mtDNA from its mother. In sexual reproduction, the egg and sperm combine to form the new individual. The sperm cell is small and contains almost exclusively DNA inside it. The egg brings all the resources to the new individual, including mitochondria and their DNA. Maternal inheritance means that all the genetic information in mtDNA comes from one source, so any similarities between mtDNA of different individuals indicates a common ancestor or shared history.

Researchers have found that the degree of divergence between the mtDNA of individuals from two populations correlates with the length of time the two populations have been isolated. Two populations that had lived in different places for 100 years would have fewer differences in their mtDNA than two populations that had lived apart for 1000 years.

 

molting

the shedding of skin. A monarch larva molts as it grows and becomes too large for its former skin.

 

mutation

A mutation is a change to an organism's DNA, or genetic material. Mutations are usually rare, and often have a negative effect on the organism's fitness. Mutation is the only source of new alleles, though, and is therefore very important in evolution. Many events can cause mutation. Sometimes mistakes are made during DNA replication. Some chemicals and energies can change DNA, including ultraviolet radiation. These are called mutagens. Mutations will only be important to evolution if they happen in the sperm or eggs, since that is the only way the change will pass on to the next generation.