Speciation in Hawaiian Plant hoppers

Scientists are continuously performing experiments testing the validity of hypotheses that derive from the core of evolutionary theory. Oliarus Polyphemus, the subterranean insect lineage that lives in lava tube caves on Hawaii Island, is ideal for studying the effects of natural selection and genetic drift. Known as Hawaiian cave planthoppers, these obligate cavernicoles live in the Hawaiian archipelago, which is subject to frequent volcanism and rapidly changing landscape dynamics. This leads to interconnected systems of lava tube caves and provides for a very unique environment. Hawaiian cave planthoppers are unique in that the different species in this lineage all live in extremely similar environments, but show strong differentiation in behavioral and morphometric characteristics.

Interestingly, Hawaiian cave planthoppers rank among the highest speciation rates among all animal species, which contradicts the prior assumption of the limited evolutionary potential of obligate cavernicoles. Furthermore, the differentiation between the species is random with regard to cave age and geographic distribution. Overall, the Hawaiian cave planthopper system provides an ideal model for testing models of stochastic effects in evolution in a natural system for several reasons. First, the system is simple enough to allow distinction between different factors affecting speciation rates. Also, the system is essentially a series of populations undergoing “natural experiments” of repeated events under similar conditions, which allows for the assessment of relevant factors. The Hawaiian planthoppers seem to directly challenge the Founder-effect concept by Mayr, which hypothesizes a loss of genetic variation that occurs when a new population ...

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...re key factors in the high rate of speciation. These conclusions are derived from the lack of correlation of phenotypic evolution with distance and differences in habitat. Instead, random individual dispersal creates frequent genetic bottlenecks. The observation that phenotypic variability decreases with increasing cave age challenges the traditional founder-effect concept, which claims that genetic variability increases with a growing population. The observation is more consistent with the founder-flush concept. However, the data has led to new questions regarding the factors that play into evolution, specifically the reaction between population density and stochastic events. Further investigation of the role that frequently replicating small founder populations plays in the generation of new species will increase knowledge of the complicated process of speciation.