A major focus of modern evolutionary ecology is the study of coevolution: investigating interactions between organisms in nature and analyzing how interacting pairs of organisms influence one another as they evolve. One of the most remarkable coevolutionary interactions is between various species of i butterflies and various species of Passiflora vines. Heliconius butterflies lay their eggs only on Passiflora vines and select only the newest, most tender shoots for the newly hatched Heliconius caterpillars to feed on. The effect of this parasitism is that caterpillars, either by defoliating a juvenile vine or devouring new shoots on a mature vine, prevent the vine from reproducing. In response, Passiflora vines have developed defenses against Heliconius butterflies.
One of the factors Heliconius butterflies take into account when deciding where to lay eggs is the shape of the leaves of the potential host plant. However, the leaves of some Passiflora species have gradually come to resemble the leaves of several nonhost plants closely, and from seedling to maturity, the shape of Passiflora leaves undergoes dramatic changes. A butterfly's ability to recognize the shape of Passiflora leaves reduces the reproductive potential of the plant, and scientists have hypothesized that varying their leaf shapes is a mechanism that has evolved in Passiflora vines under the pressure of Heliconius parasitism. This has not been an entirely successful strategy for the plants, however, since Heliconius butterflies have developed the ability to recognize other Passiflora characteristics, including leaf chemistry, in locating Passiflora vines, and variations in leaf shape have not been sufficient to deter the butterflies from laying eggs.
Because the caterpillars of some Heliconius species eat the eggs of other Heliconius species, the presence of an egg on a leaf can cause a female to reject a plant as a potential egg-laying site. Recent field studies have discovered further evidence of a possible coevolutionary relationship: some species of Passiflora vines have developed yellow spots identical in color and shape to Heliconius eggs. Subsequent studies of "egg-mimicry" reveal that it has been found in only some two percent of the 500 known Passiflora species, indicating that it probably evolved relatively recently, but where it does occur, it has been a successful deterrent to Heliconius egg-laying.
1. With which of the following statements about the coevolutionary relationship between Passiflora vines and Heliconius butterflies would the author of the passage be most likely to agree?A. It will eventually result in a decrease in the number of
Passiflora species.
B. It has ensured that
Passiflora species will survive longer than
Heliconius species.
C. It will probably end because the development of egg-mimicry by
Passiflora vines will force
Heliconius butterflies to find other host plants.
D. It has been more thoroughly studied than any other coevolutionary relationship in nature.
E. It is a dynamic, continuing process that may produce further variations in the plants and butterflies.
2. Which of the following best describes the function of the third paragraph of the passage?A. To answer a question posed at the beginning of the passage about a coevolutionary relationship between two organisms
B. To sum up the examples given in the passage with a generalization about coevolutionary relationships
C. To provide an additional example of an adaptation that indicates a coevolutionary relationship between two organisms
D. To outline the steps taken in a research project to study coevolutionary relationships
E. To propose further research into the coevolutionary relationships between plants and animals
3. The primary purpose of the passage is toA. explain why
Heliconius butterflies select
Passiflora vines for depositing their eggs
B. describe the manner in which
Heliconius butterflies distinguish
Passiflora vines from other plants
C. explore aspects of the coevolutionary relationship between
Passiflora vines and
Heliconius butterflies
D. give an overview of coevolutionary relationships in plants and animals, using the relationship between
Heliconius butterflies and
Passiflora vines as an example
E. argue that the only species of
Passiflora vines to survive are those that adapt to
Heliconius parasitism
4. Passiflora leaf chemistry is mentioned in the passage as a characteristic thatA. deters
Heliconius butterflies from laying eggs on
Passiflora vines
B. developed relatively recently as a result of coevolution
C. represents a successful adaptive strategy on the part of
Passiflora vines
D. is likely to change over time in response to changes in habitat
E. helps
Heliconius butterflies locate
Passiflora vines