Convergent evolution in the colour polymorphism of Selkirkiella spiders (Theridiidae) from the South American temperate rainforest

Abstract

Convergent evolution tends to lead to similar phenotypic responses to the same selective pressures. However, when the phenotypic response is polymorphic, it is less clear how evolutionary convergence can lead to parallel diversity across species and populations. The present study focuses on South American spiders in the genus Selkirkiella (Theridiidae), which are shown to be polymorphic for colour. We (1) examine the number of morphs and their correspondence across taxa and (2) place the phenomenon in a phylogenetic context to determine whether the colour polymorphism in Selkirkiella albogutatta from the Juan Fernández archipelago represents a case of independent evolution and convergence, or whether there is common ancestry with other colour-polymorphic theridiids. Regarding the latter question, we also examine colour morphs in a related species (Selkirkiella luisi) from continental areas. We show that S. alboguttata and S. luisi have six and two morphs, respectively. The rank-order of morph frequencies in both species is approximately similar to that reported in other polymorphic theridiids. A molecular phylogeny supports previous work and shows that the colour polymorphism in Selkirkiella species appears to be a case of convergent evolution of a diverse colour polymorphism at the family level.