The Princeton Guide to Ecology

Coevolution is reciprocal evolutionary change among interacting species driven by natural selection. It is the evolutionary process by which many predators and prey, parasites and hosts, competitors, and mutualists adapt to each other in the constant struggle for life. It is also a process that can sometimes lead to new species, as different populations of interacting species coevolve in different ways in different geographic regions. Through its effects on adaptation and speciation, coevolution continually reshapes the web of life. Moreover, human society is increasingly altering the coevolutionary process through manipulation of ecological relationships among species within and among ecosystems, alteration of the genetic structure of crop plants, and development of novel strategies for mitigation of human diseases.

coevolution. Reciprocal evolutionary change in interacting species driven by natural selection

coevolutionary cold spot. Geographic regions in which one of a set of interacting species does not occur or in which the interaction, although occurring, does not result in reciprocal evolutionary change

coevolutionary hot spot. Geographic regions in which interactions between two or more interacting species result in reciprocal evolutionary change

local adaptation. Adaptation of populations to the local physical environment or to the local populations of other species with which they interact

Coevolution has been a major part of the process of evolution at least since the beginnings of complex life on Earth. In fact, many of the major events in the history of life are a direct result of the coevolutionary process that has created mutualistic symbioses among species. All complex organisms rely on mitochondria for cellular respiration. Those mitochondria are ancient bacteria that coevolved with their hosts and eventually became obligate organelles within the cells of all eukaryotic life. Every multicellular organism therefore has two genomes, a nuclear genome and a mitochondrial genome, as a direct result of this ancient coevolutionary process. Most animal species harbor one or more other coevolved symbionts that are necessary for their survival and reproduction. Among the most common are gut symbionts that aid digestion and nutrition. In many insect species, for example, coevolved symbionts provide one or more essential amino acids that are missing in the diet.

Plants harbor yet other ancient coevolved partners: obligate symbionts called chloroplasts. These organelles drive photosynthesis, and few plant species can survive without them. Many plants also rely on mycorrhizal fungi that attach to the roots of plants and aid in nutrition. Legumes and a few other plant taxa have coevolved relationships with rhizobial bacteria that convert atmospheric nitrogen into a form usable by the plant. In addition, the leaves of some herbaceous plants and some trees are laced with endophytic fungi, whose coevolved relationships with plants are only now being explored in depth. A majority of plants also rely on animal pollination for reproduction. Hence, survival and reproduction in most plant species require inter

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