Evolution, Parallel

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Evolution, Parallel

Parallel evolution occurs when unrelated organisms develop the same characteristics or adaptive mechanisms due to the nature of their environmental

KEY TERMS

Morphological— relates to the study of differences in shape or structure

Natural selection— The process of differential reproduction, in which some phenotypes are better suited to life in the current environment.

Speciation— The divergence of evolutionary lineages, and creation of new species.

Tympanum— The eardrum.

conditions. Stated differently, parallel evolution occurs when similar environments produce similar adaptations. The morphologies (or structural form) of two or more lineages evolve together in a similar manner in parallel evolution, rather than diverging or converging at a particular point in time.

Parallel evolution is exemplified in the case of the tympanal and atympanal mouth-ears in hawkmoths, or Sphingidae species. These insects have developed a tympanum, or eardrum, similar to humans as a means to communicate through sound. Sounds induce vibrations of a membrane that covers the tympanum, known as the tympanic membrane. These vibrations are detected by small proteins at the surface of the tympanic membrane called auditory receptors. Within the Sphingidae species, two differing subgroups acquired hearing capability by developing alterations in their mouthparts by a distinctly independent evolutionary pathway.

Investigating the biomechanics of the auditory system reveals that only one of these subgroups has a tympanum. The other subgroup has developed a different mouth-ear structure that does not have a typanum, but has a mouth-ear with functional characteristics essentially the same as the subgroup with the tympanum. The evolutionary significance of how hearing capabilities developed in parallel in two different subgroups of a species reveals that distinct mechanisms can exist leading to similar functional capabilities with differing means for acquiring the same functional attribute. For both subgroups, hearing must have been an important characteristic for the species to survive given the environmental conditions.

Parallel speciation is a type of parallel evolution in which reproductive incompatibility in closely related populations is determined by traits that independently evolve due to adaptation to differing environments. These distinct populations are reproductively incompatible and only populations that live in similar environmental conditions are less likely to become reproductively isolated. In this way, parallel speciation suggests that there is good evidence for natural selective pressures leading to speciation, especially since reproductive incompatibility between to related populations is correlated with differing environmental conditions rather than geographical or genetic distances.