( ( Sexual reproduction ) ( ( ( ( ( is , ) however ) , ) ( ( the more ) ( usual type ) ) ) . ) )
(ROOT (S (NP (JJ Sexual) (NN reproduction)) (VP (VBZ is) (, ,) (ADVP (RB however)) (, ,) (FRAG (X (DT the) (JJR more)) (NP (JJ usual) (NN type)))) (. .)))
Sexual reproduction is, however, the more usual  type.
(ROOT (S (NP (JJ Sexual) (NN reproduction)) (ADVP (RB usually)) (VP (VBP occur) (PP (IN during) (NP (NP (NNS times)) (PP (IN of) (NP (JJ environmental) (NN stress)))))) (. .)))