( ( The ( cave populations ) ) ( ( ( ( have ( retained ( the ( capacity ( to ( ( produce ( fertile offspring ) ) ( with ( surface fish ) ) ) ) ) ) ) ) and ) ( are ( considered ( to ( be ( ( the ( same species ) ) ( -LRB- ( ( ( ( ( Avise and ) Selander ) , ) 1972 ) -RRB- ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ cave) (NNS populations)) (VP (VP (VBP have) (VP (VBN retained) (NP (DT the) (NN capacity) (S (VP (TO to) (VP (VB produce) (NP (ADJP (JJ fertile)) (NN offspring)) (PP (IN with) (NP (NN surface) (NN fish))))))))) (CC and) (VP (VBP are) (VP (VBN considered) (S (VP (TO to) (VP (VB be) (NP (NP (DT the) (JJ same) (NN species)) (PRN (-LRB- -LRB-) (NP (NNP Avise) (CC and) (NNP Selander)) (, ,) (NP (CD 1972)) (-RRB- -RRB-))))))))) (. .)))
The cave populations have retained the capacity to produce fertile offspring with surface fish and are considered to be the same species (Avise and Selander, 1972).
(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)) (. .)))