Of Brobdingnag and Lilliput, or how the area of an island may determine the size of the bodies and genomes that inhabit it, along with their mutation rates

Abstract

Insular gigantism and dwarfism are commonly framed by the island rule, whereby small species become larger and large species smaller. Yet why large species diminish, and why some taxa depart from this rule, remain unclear. Here I propose a neutral null model linking island area to body and genome evolution. Island Biogeography Theory predicts that smaller islands support lower census populations, while Damuths law predicts an inverse relationship between body mass and population density. If effective population size, Ne, declines at a different rate from island area, effective density, De = Ne/area, will also change. Under the drift-barrier hypothesis, variation in Ne may further influence genome size and mutation rate, {micro}. Island area may therefore jointly predict body mass, genome size and {micro}. Analyses of global and datasets and particular species are broadly consistent with this expectation, although the observed associations are generally modest.