Evolutionary ecology of clonal-bisexual complexes in spined loaches from genus Cobitis (Pisces, Cobitidae)

Abstract

The objective of this work was to analyze several aspects of evolutionary ecology of the spined loach clonal-bisexual complexes. This analysis demonstrates that the twofold population growth rate in clonal forms compared with bisexual species is not a proper feature of spined loaches, because their clonal forms are polyploids with the larger eggs and correspondingly the lower individual fecundity. Both the larger nutrient stores in eggs and the larger hatchlings provide certain ecological advantages for clonal spined loach triploids at early stages of their ontogeny and possibly ensure the higher fitness in a local environment. The clonal-bisexual spined loach complexes have reduced structure usually including one bisexual species and the only clonal form. This reduction may be caused by several factors: 1) the competition between different forms and subsequent superseding of some of them; 2) a particular manner of colonization of new areas by different bisexual and clonal forms; 3) the absorption of one of parental species for hybrid origins of clonal forms (hypothesis of absorption). The relative numbers of bisexual and unisexual forms in different clonal-bisexual complexes depend on “family ties” between clonal forms and “host” bisexual species; their ratios are subjected to temporal dynamics caused by both external (environmental changes) and internal (automatic fluctuating) factors.