Evolutionary anachronism

Evolutionary anachronism is a concept in evolutionary biology named by Connie C. Barlow in her book, ''The Ghosts of Evolution'' (2000). It refers to attributes of living species that are best explained as a result of having been favorably selected in the past due to coevolution with other biological species that have since become extinct. When this context is removed, the natural attributes appear as unexplained energy investments by the living organism, with no apparent benefit, and perhaps are prejudicial to the continued reproduction of the surviving species.

The general theory was formulated by Costa Rican-based American botanist Daniel Janzen and University of Arizona-based geologist Paul S. Martin (a prominent defender of the overkill hypothesis to explain the Quaternary extinction event) in a ''Science'' article published in 1982, titled ''Neotropical Anachronisms: The fruit the gomphotheres ate.'' Previously, in 1977, Stanley Temple had proposed a similar idea to explain the decline of the Mauritius endemic tree tambalacoque following the extinction of the iconic dodo.

Janzen, Martin and Barlow mainly discussed evolutionary anachronisms in the context of seed dispersal and passive defense strategies exhibited by plants that had evolved alongside disappeared megaherbivores, although some examples apply to animal species as relict behavior.

Evolutionary anachronisms are not the same as vestigiality. Though both concepts refer ultimately to organs that evolved in response to environmental pressures not currently present, in the case of anachronisms, the original function of the organ and the capacity of the organism to use it are retained. For example, the present-day absence of avocado-eating gomphotheres does not render avocado pulp vestigial, rudimentary or incapable of its original function in seed nutrition and dispersal ( zoochory) if a new suitable ecological partner were to appear.

Megafauna dispersal syndrome

Dispersal syndromes are complexes of fruit traits that enable plants to disperse seeds. The kind of fruits that birds are attracted to are usually small, with only a thin protective skin, and the colors are red or dark shades of blue or purple. Fruits categorized as mammal syndrome are bigger than bird fruits. They possess a tough rind or husk, emit a strong odor when ripe but retain a dull coloration of brown, burnished yellow, orange or remain green, because most mammals have a powerful sense of smell but poor color vision in general, primates being the most notable exception. The megafauna dispersal syndrome refers to those attributes of fruits that evolved in order to attract megafauna (animals that weigh or weighed more than 44 kilograms) as primary dispersal agents. Since the Holocene extinction, large herbivores have become extinct outside Africa and to a lesser extent Asia, leaving these fruits without a suitable dispersal mechanism in the absence of agriculture.

Common megafaunal dispersal traits

*Large fruit, best suited to be consumed whole by large animals without seed loss.
*Fruit grows on or close to the trunk, or on stout branches.
* Indehiscent fruit that retains its seeds upon ripening.
*Seeds deter or elude being ground up by teeth through having a thick, tough or hard endocarp; or bitter, peppering or nauseating toxins. They are also difficult to separate from the pulp, which is tasty and soft, to deter seed spitting.
*The seeds benefit from—or even require—physical or chemical abrasion to germinate.
*If tropical, the fruit drops on or just before ripening, stopping monkeys from eating them. In colder climates, the fruit stays on the branch for a prolonged time, keeping it away from predation by ineffectual seed dispersers like rodents.
*"Looks, feels, smells, and tastes" like other fruits known to be dispersed by megafauna where megafauna still exists.

Ecological indicators of missing dispersal partners

*The fruit either rots where it falls or is ineffectually disseminated by current dispersal agents.
*The plant is more common where livestock (proxy for megafauna) are present.
*The seeds germinate and grow well in upland habitats where planted, but the species almost exclusively inhabits floodplains (where water flow disperses the seeds) in the wild.
*The geographic range is inexplicably patchy or restricted.

Proposed examples in plants

Afrotropical realm

Madagascar

Australasian realm

New Zealand

Indomalayan realm

Nearctic realm

Neotropical realm

Oceanian realm

Palearctic realm

Proposed examples in animals

In popular culture

The phenomenon was referenced (though not by name) in the 1259 issue "Bee Orchid" of the online comic strip ''xkcd'' by Randall Munroe, published on September 2, 2013. In the comic, it is claimed that the orchid '' Ophrys apifera'' mimics the female of a bee species to attract males and ensure pollination, but that the bee is extinct and the orchid is doomed to follow, only delaying it by resorting to less effective self-pollination. In reality, only the first part is true: the flower mimics a bee, and reproduces exclusively by self-pollination in northern Europe, but it is pollinated successfully by bees of the genus ''Eucera'' in the Mediterranean region.

See also

*Coevolution
*Coextinction
* Evolutionary arms race
*Evolutionary mismatch
* Evolutionary trap
*Holocene extinction
*Keystone species
*Pleistocene extinction
* Pleistocene rewilding

References

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External links

Youtube video "Why are Lemurs Terrified of Predators that don't Exist?"Gourds and squashes (Cucurbita spp.) adapted to megafaunal extinction and ecological anachronism through domestication

Evolutionary biology


Ecology
Habitat