ECOLOGY AND EVOLUTION

To Clone or Not to Clone

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Science  26 May 2000:
Vol. 288, Issue 5470, pp. 1301
DOI: 10.1126/science.288.5470.1301d

Most plant species have the capacity to reproduce both by seed and by vegetative means. Seed production is usually, but not always, the result of sexual fertilization; vegetative reproduction is always asexual and can involve specialized structures such as bulbils, or simply new shoots sprouting from roots, standing trunks, or fallen trees. How do plants balance sexual and asexual propagation, and is one mode favored by particular environmental circumstances?

In herbaceous plants that can produce both sexual and asexual seed, reproduction is usually all sexual or all asexual (apomictic). On the other hand, sexual reproduction can coexist more happily with other forms of asexual propagation, even when these forms are very seedlike. Bengtsson and Ceplitis have used an evolutionary model to show that the two forms of reproduction can coexist in a balanced fashion when the relative fitness of the sexual and asexual propagules varies, as is often the case with seeds and nonseeds; whereas, when there is little relative variation in fitness, the system tends to evolve to domination by only one form of reproduction.

Bellingham and Sparrow model the trade-offs between seeding and vegetative resprouting in woody species. Their scheme entails the relative allocation to seeding and resprouting according to frequency and severity of disturbance; in an advance over earlier models, they also scale disturbance regimes according to ecosystem productivity. Their model suggests that allocation to resprouting will be greatest at low levels of severity of disturbance and intermediate frequency of disturbance.—AMS

J. Evol. Biol.13, 415 (2000); Oikos89, 409 (2000).

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