Queens College, City University of New York, New York, United States
Background/Question/Methods
Species introduced by humans into new habitats, if they become invasive, can cause widespread ecological changes, and can also result in evolution of the introduced species itself. The novel habitats can thus create “natural experiments” for evolutionary ecology. The small Indian mongoose (Urva auropunctata) has been introduced from South Asia to several tropical islands throughout the world. These islands release the mongoose from predation and competition and provide high resources, facilitating rapid population growth to densities that are 30-120 times higher than that in the ancestral range. We predicted, based on sexual selection theory, that the high resources and high population densities of the islands of introduction would result in evolutionary changes in two features of the mongoose. First, since chemical communication is only important when organisms do not regularly meet face to face, we predicted a decay of the mongoose’s scent glands in terms of both their size and condition dependence. Secondly, since an increase in population size will increase the encounter rate and thus (for this promiscuous species) sperm competition among males, we predicted an increase in testis size in the islands of introduction.
Results/Conclusions
We found that the small Indian mongoose has markedly reduced anal scent gland pad size on four areas of introduction (Mauritius, St. Croix, Hawaii, and Jamaica), compared to a native population in Uttarakhand, India. Moreover, the anal pads of individuals on these islands have a reduced condition-dependence, as predicted for a trait that has lost functionality. Finally, the testes in the introduced populations are larger than in the ancestral population. Some of these effects are more dramatic with greater time since introduction. These results demonstrate that the ecological conditions of novel habitats can be dramatic enough to cause striking morphological changes in an introduced vertebrate species in just 150 years.