Worksheet for the Video: Joshua Trees and Evolution

This worksheet accompanies the video “Joshua Trees and Evolution”, which is available for free on YouTube. (https://youtu.be/mibrOhcuqDM)

1. Joshua trees (Yucca brevifolia) belong to the group of monocotyledons (monocots). Complete the comparison of monocots and dicots in the following table.

flowering plants

Monocotyledons (Monocots) Dicotyledons (Dicots) # of species living today approximately 60 000 species approximately 200 000 species multiple groups evolved independently at up to 150 million years Age different times seedlings possess one embryonic leaf seedlings possess two embryonic leaves Characteristics (cotyledon) (cotyledons)

Monocot Seedling (onion) Dicot Seedling (tomato)

Examples: lilies, tulips, orchids, grasses, Joshua tomatoes, roses, sun flowers,

trees, … peas, …

Notes/Vocabulary:

………………………………………………………………………………………………

2. While Joshua trees inhabited a significantly larger area in the past, today they can only be found in small patches in the southwestern US. Explain which factors contributed to the shrinkage of the assumed distribution of Joshua Joshua tree habitat. trees during Pleistocene

………………………………………………………………………………………………The climate in the southwestern United States has ………………………………………………………………………………………………changed since the Pleistocene. The previously much more ………………………………………………………………………………………………humid climate allowed the Joshua trees to grow in places ………………………………………………………………………………………………where they can no longer occur due to the lack of water. ………………………………………………………………………………………………In addition, increasing competition is another reason why ………………………………………………………………………………………………the distribution of the Joshua trees has shrunk occurrence of Joshua ………………………………………………………………………………………………considerably. A number of plant species that compete with trees today ………………………………………………………………………………………………the Joshua trees today didn’t exist in the Pleistocene, or ………………………………………………………………………………………………they weren’t as numerous as they are today. ………………………………………………………………………………………………

……………………………………………………………………………………………… Distribution of Joshua Trees

……………………………………………………………………………………………… Picture altered from: https://commons.wikimedia.org/wiki/File:US_map_-_states-ca.png public domain

3. Give a description of what the term ‘coevolution’ refers to.

Coevolution is a process during which two or more species undergo interlinked evolutionary change. These changes or ………………………………………………………………………………………………....……………………………………………………………………………………

adaptations causes these species to become more specialized in their mutual interactions. ………………………………………………………………………………………………....……………………………………………………………………………………

………………………………………………………………………………………………....……………………………………………………………………………………

4. At the time signature 3:30, the video „Joshua Trees and Evolution“ contains a brief intermission. It asks you to pause the video for a few minutes to work on this task: Form a hypothesis on how the relationship between Yucca moths and Joshua trees might have evolved.

[different answers possible] ………………………………………………………………………………………………....……………………………………………………………………………………

Notes/Vocabulary:

5. Describe and explain the hypothesis on the course of coevolution between Yucca moths and Joshua trees presented in the video.

The hypothesis presented in the video assumes that there was a time when the flowers of the ancestors of our Joshua ………………………………………………………………………………………………....……………………………………………………………………………………

trees today were less specialized than they are today. This enabled them to be pollinated by a number of different ………………………………………………………………………………………………....…………………………………………………………………………………… insects, which placed their eggs into the flowers of the Joshua trees. Just like the larvae of the yucca moth, the larvae ………………………………………………………………………………………………....……………………………………………………………………………………

of these other insects fed on the seeds of the Joshua trees. ………………………………………………………………………………………………....…………………………………………………………………………………… Joshua trees that had somewhat narrower flowers than others had an evolutionary advantage, as their flowers were ………………………………………………………………………………………………....……………………………………………………………………………………

accessible to fewer insects due to their narrower structure. With fewer eggs deposited into their flowers, a smaller ………………………………………………………………………………………………....…………………………………………………………………………………… number of their seeds got eaten by insect larvae. As a result, they had more offspring and could pass on the ………………………………………………………………………………………………....……………………………………………………………………………………

characteristic of the tighter flower structure to the next generation more often. ………………………………………………………………………………………………....…………………………………………………………………………………… At the same time, the insects competed with each other for flowers to lay eggs into. The ancestors of today's Yucca ………………………………………………………………………………………………....……………………………………………………………………………………

moths that were able to use flowers that were inaccessible to other insects due to their narrow structure had an ………………………………………………………………………………………………....…………………………………………………………………………………… evolutionary advantage. Features such as a lean body shape or a longer ovipositor (organ for laying eggs) increased the ………………………………………………………………………………………………....……………………………………………………………………………………

fitness of these individuals because they increased the likelihood of successful reproduction. ………………………………………………………………………………………………....…………………………………………………………………………………… In successive generations, the ancestors of today's yucca moths had the advantage that their physical characteristics ………………………………………………………………………………………………....……………………………………………………………………………………

gave them exclusive access to Joshua tree flowers to deposit their eggs into. ………………………………………………………………………………………………....…………………………………………………………………………………… In summary, the ancestors of today's Yucca moths and Joshua trees changed in adaptation to each other creating an ………………………………………………………………………………………………....……………………………………………………………………………………

exclusive relationship between them. ………………………………………………………………………………………………....……………………………………………………………………………………

………………………………………………………………………………………………....……………………………………………………………………………… …… Notes/Vocabulary:

6. Give reasons why the exclusive relationship between Yucca moths and Joshua trees also poses risks for their survival.

………………………………………………………………………………………………....…………………………………………………………………………The specialization of these two species on one another that arose from their coevolution poses a risk, because …………

both species are now dependent on one another. Neither species can reproduce without the other. The Joshua ………………………………………………………………………………………………....…………………………………………………………………………………… ………………………………………………………………………………………………....………………………………………………………………………………tree can only be pollinated by the Yucca moths, and the larvae of the Yucca moth need the seeds of the Joshua ……

tree for feeding. ………………………………………………………………………………………………....…………………………………………………………………………………… If one of the two species goes extinct, the other species can no longer reproduce and will, therefore, perish too. ………………………………………………………………………………………………....……………………………………………………………………………………

………………………………………………………………………………………………....…………………………………………………………………………………… ………………………………………………………………………………………………....……………………………………………………………………………………

Notes/Vocabulary: