Volume 41, Number 2,
June 1995:
The Yucca Plant and
the Yucca Moth

Text-only version

ISSUE HOME PAGE

ABOUT THIS ISSUE
- about KSN
- about the authors

IN THIS ISSUE
- introduction
- mutualism
- coevolution
- a "transparent" system
- yucca moth pollination
- male and female yucca moths
- mark and recapture
- C.V. Riley
- the yucca plant
- yucca flowers
- yucca products
- yucca pods and larval moths
- bailing out of the pods
- old pods
- what we do not know
- what prevents a cheater?
- how did the yucca and yucca moth relationship evolve?
- solving problems
- for additional information

SLIDESHOW
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The Yucca Plant and the Yucca Moth
by Marylee Ramsay and John Richard Schrock

SOLVING PROBLEMS

A. C.V. Riley correctly determined that the yucca plant is not wind pollinated, but requires the yucca moth to fertilize flowers and produce the seed pods. Since you cannot watch flowers 24-hours a day, how would you design an experiment that proved yucca is not wind pollinated?

B. Some of the pods collected in Figure x did not contain moth larvae. Does this prove that pods can develop without pollination by a moth? What are some possible reasons such pods might develop without any larvae?

C. Yuccas are commonly planted to beautify front yards. After the stalk of flowers has withered in June, some homeowners prefer to cut down the "ugly" stalk with pods that remains. What effect will this have on yuccas flowering the next year? Will they set pods again?

D. Yucca plants can be purchased at nurseries and carried home with a ball of soil around their roots, to be planted. Some of these yuccas soon have yucca moths but there are no other yucca plants in the county. Where could the moths come from?

E. You ink-stamp the hands of 50 students entering the stadium to watch a ballgame. Inside, you pick a sample and count that only one out of ten have hand-stamps. How many students are attending the game? How would this estimate be affected if some left early (equal to some dying)? How would this be affected by a migration in of a busload of fans? You can further explore the Lincoln Index in an ecology book.

F. Some of the pods collected in Figure x show six to twelve larvae, enough to decimate all the seeds. If yucca moths "should" only consume a portion of the seeds, what might have "gone wrong" to permit more larvae to develop?

G. You have a cluster of yucca plants that had moths and produced pods, but you accidentally cut and destroyed the stalks and pods before the moths emerged. Since there are no other yuccas in you region, and the moths do not fly far, you do not expect to have any moths or pods next year. Yet, next year both moths and pods appear. Give a possible explanation that does not contradict the above facts.

H. Although it is not possible to go back in time and "rerun evolution", biologists can piece together snapshots of evolution by finding intermediate forms that have survived through to today. What "intermediate forms" would help us understand how the yucca and yucca moth relationship evolved?