( ( Among vertebrates ) ( , ( ( ( ( ( however ( , ( it ( ( occurs only ) ( in reptiles ) ) ) ) ) , ) and ) ( ( all ( such ( unisexual species ) ) ) ( originate ( from ( ( hybridisation ( between two ) ) ( sexually ( reproducing species ) ) ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN Among) (NP (NNS vertebrates))) (, ,) (S (ADVP (RB however)) (, ,) (NP (PRP it)) (VP (VBZ occurs) (ADVP (RB only)) (PP (IN in) (NP (NNS reptiles))))) (, ,) (CC and) (S (NP (DT all) (JJ such) (JJ unisexual) (NNS species)) (VP (VB originate) (PP (IN from) (S (NP (NP (NN hybridisation)) (PP (IN between) (NP (CD two)))) (ADVP (RB sexually)) (VP (VBG reproducing) (NP (NNS species))))))) (. .)))
Among vertebrates, however, it occurs only in reptiles, and all such unisexual species originate from hybridisation between two sexually reproducing species.
(ROOT (S (NP (NNS Vertebrates)) (VP (VB reproduce) (ADVP (RB sexually))) (. .)))