Karel Janko, Peter Mikulíček, Roman Hobza, Ingo Schlupp

In a world of metazoans, where sexual reproduction vastly predominates, asexual organisms are nonetheless very important. The aim of this review is to show that asexuals can have general effects on other species, ecosystems and biological networks via mechanisms that deserve more attention. These include 1) impact on the genepool of coexisting sexual species by either restricting their population sizes or by providing bridges for interspecific gene-flow whose type and consequences substantially differ from gene flow mechanisms expected under sexual reproduction; 2) impact on diversification rate, either direct by serving as stepping-stones in speciation or indirect by promoting the formation of pre- and postzygotic reproduction barriers among nascent species; and 3) impact on spatial effects, via direct or indirect (apparent) types of competition and Allee effects. We specifically point to these important mechanisms, provide empirical examples how asexuals impact the evolution of sexual species and ecosystems, and, finally, show that these broad effects may last beyond the tenure of the individual asexual lineages causing them. We also propose new research directions to incorporate the aforementioned impacts of asexual organisms which will ultimately enhance the understanding of evolution of genomes and ecosystems in general.