( ( ( Two species ) ( of frogs ) ) ( occasionally ( ( ( mate ( in ( the wild ) ) ) ( to ( produce ( hybrid offspring ) ) ) ) . ) ) )
(ROOT (S (NP (NP (CD Two) (NNS species)) (PP (IN of) (NP (NNS frogs)))) (ADVP (RB occasionally)) (VP (VB mate) (PP (IN in) (NP (DT the) (JJ wild))) (S (VP (TO to) (VP (VB produce) (NP (JJ hybrid) (NN offspring)))))) (. .)))
Two species of frogs occasionally mate in the wild to produce hybrid offspring.
(ROOT (S (SBAR (IN If) (S (NP (CD two) (NNS populations)) (VP (VBP do) (RB not) (VP (VB mate) (CC and) (VB produce) (NP (ADJP (JJ fertile)) (NN offspring)))))) (, ,) (NP (JJ separate) (NNS species)) (VP (VBP result)) (. .)))