An important point is the relative timing of the evolution of the various traits that appear to be part of the coevolution. If the presumed reciprocally induced, sequential traits actually evolved in the plant host before the insect parasite became associated with it, we should not call it coevolution.
See different example figs. There are a variety of different modes of coevolution. In some cases coevolution is quite specific such as those between two cellular functions.
The endosymbiont theory proposes that current day mitochondria and chloroplasts were once free-living unicellular individuals. These cells entered the cytoplasm of other cells, an example of the general phenomenon of endosymbiosis. Current-day mitochondrial and chloroplast genomes are much smaller than the genome sizes of their presumed free-living ancestors. Some of this reduction in genome size is due to the transfer of genes from organelle genomes to the nuclear genome.
Thus, being in the cellular environment has influenced the evolution of organelle genomes. There is evidence that the faster rate of evolution of animal mitochondrial DNA has accelerated the rate of evolution of some of the nuclear genes that function in the mitochondria.
Thus there is some evidence for reciprocal phenomena. Other modes of coevolution involve competitive interaction between two specific species. The Plethodon salamander study is a good example: two species are competing: in the Great Smoky mountains the two species compete strongly as evidenced by the fact that each species will increase population size if the other is removed. Here there is a clear reciprocal interaction between the two populations species , each affecting the other.
There is coevolution because the competitive interactions between resident and invading species of Anolis involve reciprocal responses in the evolution of body size. These affect the structure of the lizard community as evidenced by the general pattern of there being a single species of lizard on each island. Character displacement also provides and example of a pattern we might interpret as the result of coevolution.
Mud snails show pattern of character displacement in sympatry due presumably to competition for food items don't confuse this with reinforcement; the selective agent here is not reduced hybrid fitness. If only one species exhibited character displacement and you were a really picky evolutionist you might not be convinced of a reciprocal response.
Another strong case is the Ant - Acacia mutualism. Each of the participating organisms thus presents an evolutionary "moving target". The relationship between these distantly related taxa is symbiotic in the broad sense that characterizes life and that gives rise to the high degree of complexity and diversity that we perceive in nature.
If the rule in nature is "whatever works," our observations are that many things work, and that what works keeps changing. Our understanding is that each species evolves to its own benefit; in coevolution, these two self-interests collide, and remarkable things happen. For an example, bees appear to be especially adept at perceiving bilateral symmetry and the colors blue and yellow, and at manipulating flower parts.
So plants being pollinated by bees are subject to a strong selective pressure favoring bilateral symmetry and those colors. In turn, the flowers exert pressure on the bees, favoring hairiness, body shape, and behavior that effectively transfer pollen. The resulting specialization can favor a trend toward an exclusive relationship, which may be to the benefit of each participant. The plant gains the constancy of the bee, which majors on the particular species and facilitates pollination of widely spaced, specialized flowers.
The bee gains exclusive access to the nectar. The specialization may contribute to developing isolation, often a component of speciation. A long spur. Coevolution can be complex, involving the interactions of numerous characteristics, or in some cases, it can be simpler, such as when the back and forth pressure favoring longer floral tubes and longer insect tongues or bird beaks can lead to extremes of each. Hummingbird beaks and the long-tubular flowers on some of the plants they pollinate are often used as examples.
Charles Darwin described an interesting case of pollinator-flowering plant coevolution in Madagascar: the star orchid, Angraecum sesquipedale , has foot-long spurs, with the nectary at the tip. In , when Darwin examined this orchid, he predicted that a long-tongued moth would be found that pollinated it; no moth with that extreme length of tongue was known at the time. Then, in , he was proven correct when a long-tongued moth, Xanthopan morganii praedicta was discovered.
It was so-named because its occurrence had been predicted. Wind and water. Among vascular plants, the largest share of diversity, by far, is found among the flowering plants, the most recent plant phylum to evolve.
A handful 30 of these are conifers, and a few more 86 are spore producing plants like ferns and horsetails. The rest are essentially all flowering plants. Some of these flowering plants, like the grasses , sedges , and rushes 63 , are pollinated by the wind, though these families are believed to have been derived from insect-pollinated ancestors.
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