ENT104 - Monarch Butterfly Migration (L22)

What plants are all monarch butterfly populations associated with?

Milkweeds (common worldwide)

Where are monarch butterflies found?

Almost worldwide

Migratory species are limited to North America

(True/False)

All monarch butterflies are migratory

False

How many populations of monarchs are in North America?

Two (one east, one west)

Where do western monarch populations migrate?

From the west of the rocky mountains to the pacific coast

Where do eastern monarch populations migrate?

From the Northeastern US and Canada to Mexico

Where do nonmigratory monarch populations in the US live?

Florida

Where do eastern monarchs overwinter?

Mexico

Where do eastern monarchs move in the spring?

Northeast

Over several generations, eastern monarchs move _____

Northeast

Where does the final generation of eastern monarchs go? When?

Mexico

Leave in the fall, arrive in Mexico in the winter

When do migratory monarchs return up North?

Spring

Why do monarch butterflies migrate to Mexico?

To overwinter (avoid cold temperatures)

What is threatening monarch overwintering sites?

Logging

How many monarch overwintering sites are in Mexico? Where?

About 12 regions near Mexico city

(True/False)

Migratory monarch species are limited (more or less) to North America

True

(Eastern / Western) Monarchs make short migrations to the pacific coast and have not been studied much

Western

What are the two main threats to eastern monarch populations?

1. Extensive farming in the Midwest removing much of the monarch's habitat

2. Forestry (logging) in Mexico destroying overwintering sites

Briefly describe the eastern monarch's migration patterns

Overwinter in Mexico -> Migrate North in spring -> Move Northeast over several generations -> Final generation (one generation) returns to Mexico in fall -> cycle repeats

Simplified:

Mexico (winter) -> Up North (spring) -> Up Northeast over many generations (spring) -> Down South to Mexico (fall)

Approximately where in Mexico are eastern monarch overwintering sites located? How many are there?

In pine forests high in the mountains near Mexico City

12 regions close in proximity to each other

What is reproductive diapause?

A period of suspended reproductive physiology

What physiological changes occurs in eastern monarchs during the fall?

Eastern monarchs develop into migratory butterflies during the fall and enter reproductive diapause

Migratory butterflies are long-lived (migrating to Mexico takes months)

How long does it take for eastern monarchs to migrate from the Northeast to Mexico?

Many months

What hormone regulates reproductive diapause in migratory eastern monarchs?

Juvenile hormone

When were eastern monarch overwintering sites discovered?

in the 1970s with the help of citizens (search lasted from 1950s-1970s)

What do juvenile hormones respond to?

Photoperiods (lengths of day and night cycles), temperature, other environmental factors

How long do reproductive monarchs live?

A month or so

(Migratory / Reproductive) eastern monarchs migrate North in the spring

Reproductive

How do migratory monarchs differ from non-migratory monarchs (reproductive monarchs)?

Migratory monarchs are better fliers and have larger, differently-shaped wings

What are GMOs?

Genetically Modified Organisms (such as crops modified for agriculture)

How do GMOs threaten monarchs?

Increased use of herbicides (Roundup) eliminates milkweeds, which monarchs depend on for food

What are the three main threats to migratory monarch populations (in general)?

Less Milkweed due to farming

Deforestation

Climate Change

What are roundup ready crops?

Plants that resist roundup, an herbicide that kills weeds (such as milkweed)

Why do animals migrate?

To avoid adverse seasons (cold/hot weather)

What must animals be able to do to perform long-distance migrations?

Navigate

Why do whales and sea turtles navigate during migrations?

To track food abundance

What do animals use to navigate?

Landmarks

Path integration

The sun

The stars

Magnetic reception

Olfaction (smell)

Why do ablation experiments often fail in studies of animal navigation?

Different animals can use many different methods of navigation, which can also vary depending on the migratory distance

Getting rid of some methods through ablation does not narrow down the options effectively

Some methods cannot be completely removed/ablated

Monarch navigation mechanisms are _____

Genetic

What two mechanisms do monarchs use to navigate when migrating?

Time-compensated sun compass

Magnetic sense

How did researchers find out that monarchs use a sun compass?

Monarchs change flight orientation based on the sun's position (in a lab, sun's position = presence or absence of light)

What two organs do monarchs use as "clocks" for sensing UV polarized light (sunlight)?

Brain and antennae

The (brain / antennae) act(s) as a migratory clock

Antennae

How do monarchs use the sun as a compass?

The sun rises in the east and sets in the west

Monarchs orient themselves relative to the sun while also taking into account the movement of the sun throughout the day when navigating (using antennae as a clock)

Angles change as the day progresses (sun changes position in the sky), and monarchs adjust their orientation accordingly

Putting a monarch's clock out of phase by 25% results in a ______-degree error in orientation

90-degree error

How do monarchs infer the position of the sun on a cloudy day (when the sun might get blocked at times)?

Monarchs use patterns of polarized light (detected by the dorsal rim above the eyes) to infer the position of the sun

How do monarchs infer the position of the sun on a completely overcast day (sunlight cannot be detected)?

Using magnetic sense

How do monarchs use magnetic sense to navigate?

Monarchs can sense the Earth's magnetic field, allowing them to orient themselves to the south

Why don't monarchs always use magnetic sense for navigation?

Magnetic sense is less accurate than the sun compass

(True/False)

Magnetic sense is only used by monarchs during completely overcast days

True

Monarchs, turtles, and homing pigeons can use ______ to navigate

Magnetic sense/Magnetic compass

Why are monarchs better than birds as model systems for animal navigation?

Many experiments that cannot be done in birds can be done in monarchs

Monarchs are relatively simple model systems