The Tropical Leaf-Cutter, or Attine, ant Provides a Remarkable Example of Complex Symbiosis

Reading Passage Question

The tropical leaf-cutter, or attine, ant provides a remarkable example of complex symbiosis involving several species. The ants cultivate a fungus in underground caverns to serve as a source of food. DNA analysis reveals that the fungi in attine gardens around the world are clones of a single source. The ants do not allow their fungus crop to develop fruiting bodies, the means by which plants engage in sexual reproduction. Instead, a queen ant starting a new nest takes a sample of the fungus from the old nest to start the new garden, spreading the fungus vegetatively, or asexually.

For many years, the phenomenon of sexual reproduction puzzled biologists, as it passes only half of the parents’ genes to the succeeding generation and requires a more complex mechanism than does asexual reproduction. What benefit of sexual reproduction would outweigh these limitations? One likely answer is that it provides a defense against parasitic attack. Simple parasites, such as bacteria or molds, mutate rapidly and pose a challengeto other species developing defense mechanisms. The rapid evolution of the attacking species provides an advantage in this biological arms race. Sexual reproduction allows the more complex species to shuffle its genes between generations and, as a result, evolve quickly enough to match the parasites’ mutations.

A clonal monoculture, such as that of the attine, should be highly susceptible to parasites, yet preliminary research suggested no evidence of such a problem in the ants’ gardens. More comprehensive studies showed that the Escovopsis mold, a parasite related to the “green mold” known to commercial mushroom farmers, is present in the ants’ crops and poses a serious threat to the fungus. However, the attine ants provide the defense mechanism lacking in the fungus’s asexual reproduction by means of a bacterium that grows in patches on their skin. This actinomycete bacterium produces an antibiotic used to control the mold and limit its destructive effects on the ants’ food source.

“The tropical leaf-cutter, or attine, ant provides a remarkable example of complex symbiosis”- is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 4 comprehension questions. The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. The phrase “clonal monoculture” (Highlighted) refers to which of the following?

A)The Escovopsis mold
B)A species of leaf-cutter ant
C)Sexual reproduction
D)A fungus
E)An antibiotic bacterium

2. Which of the following can be most reasonably inferred from the passage?

A)The fruiting bodies found on numerous fungi are a means of vegetative reproduction.
B)Plants that rely on sexual reproduction are highly susceptible to parasitic attack by bacteria and molds.
C)Sexual reproduction is an inefficient method for transmitting a parent’s genes to its offspring.
D)The bacterium found on patches of green mold produces an antibiotic substance used by commercial mushroom farmers.
E)Parasitic bacteria use sexual reproduction as a means to achieve rapid mutation.

3. The author describes the interaction between a parasite and a sexually reproducing organism as an “arms race” (Highlighted) in order to

A)emphasize the aggressive nature of the parasitic organism
B)warn of the dangers of biological weapons
C)underscore the need for the attine ants to defend their gardens
D)point out the devastating effects of the Escovopsis mold
E)depict the result of rapid evolution by both organisms

4. The passage suggests which of the following about the fungus grown by the attine ants?

A)By shuffling its genes, it is able to mutate rapidly in response to parasitic threats.
B)Due to its asexual reproduction, it is susceptible to attack by the actinomycete bacterium.
C)It could potentially engage in sexual reproduction.
D)It is closely related to the crops grown by commercial mushroom farmers.
E)Without the care of the attine ants, it would quickly become extinct.

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