The strength of the archaeological record is that it provides tangible evidence of the deep history and evolution of resource management over time and across space.
An additional selective agent influencing the evolution of resource polymorphism in this system is interspecific competition for food.
While the experimentally supplied resources are identical across microcosms, the evolution of resource specialists critically depends on the genetic and ecological diversity present in the population.
Moreover, the evolution of resource polymorphism – in which alternative morphs showing differential resource use occur in the same population [4] – may represent a critical, early phase in the formation of a new species [1], [4], [6], [7].
One group of such fishes, the gudgeon Sarcocheilichthys (Family Cyprinidae), provides an ideal opportunity for testing the hypothesis that bottom environmental differences lead to the evolution of resource polymorphism.
Yet, maternal effects may play a key role in the development and evolution of resource polymorphism, especially in species, such as amphibians, where egg provisioning often constitutes the only maternal investment [11], [12], and where a mother's environment can influence the amount (and, possibly, quality) of provision she allocates to each egg [13] [16].
Further, Bonsall and Wright 55 show how cooperation can facilitate the evolution of resource specialisation, presumably limiting within-group competition.
If the allocation towards female function did not change, the only way to have evolved increased earlier self-reproduction was by the evolution of resource allocation towards male function.
We detected phylogenetic under-dispersion in host-species use that is consistent with i) cycles of oligophagy or polyphagy interspersed with repeated colonisations of Acacia over protracted periods before the evolution of resource specialisation; and ii) colonisation of host phenotypes that favour resource use in one environment over the other.
These results, together with those of previous studies [ 18, 21, 46], strongly support the role of disruptive selection in the evolution of resource polymorphism in Spea tadpoles [ 46], and add to the evidence that disruptive selection can be widespread within certain systems [ 22].
