Evo­lu­tion: still very spec­u­la­tive, but extremely exciting

We know only a lit­tle about the evo­lu­tion of the genus Parosphromenus. The strik­ing sim­i­lar­ity of these fish through­out the whole genus in a vast geo­graph­i­cal area, with only two obvi­ous excep­tions, the two slim forms parvu­lus and orni­cau­data, has, for a long time until the dis­cov­ery of sig­nif­i­cantly dif­fer­ent forms, led to the assump­tion that it would only be one sin­gle species (“deissneri”).

This sug­gests to con­sider an evo­lu­tion­ary hypoth­e­sis, which has already been ver­i­fied for a major group of plants, the Cryp­to­co­rynes. This group of plants, play­ing a major role in the aquar­ium hobby, is partly com­ing from the same area. Intense genetic research on these plants shows the devel­op­ment of bio-​diversity through adap­tive radi­a­tion. This means the insu­lat­ing effect of habi­tats, which were for­merly con­nected. If these habi­tats are sep­a­rated, dif­fer­ent genetic devel­op­ments occur in the indi­vid­ual habi­tats, although they have the same start­ing pop­u­la­tion. The orig­i­nally iden­ti­cal species grad­u­ally devel­ops genet­i­cally sep­a­rated pop­u­la­tions and later prob­a­bly sub­species or even dis­tinct species. The river basins of the for­mer Sun­da­land looked dif­fer­ent in for­mer times. Geo­log­i­cal processes (uplift, sur­face sub­si­dence, etc.) have opened or closed cor­ri­dors, the cur­rent pic­ture is a snap­shot of the evo­lu­tion­ary events, which occur some­where in the scenario.

We know this form of species devel­op­ment from the aquar­ium plants Cryp­to­co­ryne, which is dis­trib­uted partly in the same area and occurs in forms with dif­fer­ent genetic dis­tance, either with ongo­ing or with already com­pleted hybridi­s­a­tion. For these plants the adap­tive radi­a­tion has been ver­i­fied by the inves­ti­ga­tion of many gene sequences. For the Licorice Gouramis prob­a­bly the same is true, but we can not prove it. Their strik­ing sim­i­lar vari­ety of forms cer­tainly shows us a snap­shot of a still ongo­ing evo­lu­tion­ary process: a com­plex pic­ture of var­i­ous stages of species development.



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