( ( Circannual rhythm ) ( in ( natural killer ) ) )
(ROOT (S (VP (VB Circannual) (NP (NN rhythm)) (PP (IN in) (NP (JJ natural) (NN killer))))))
Circannual rhythm in natural killer
(ROOT (S (NP (JJ Circannual) (JJ behavioral) (NNS rhythms)) (VP (VBP are) (VP (VBN linked) (PP (TO to) (NP (NP (DT the) (JJ yearly) (NN cycle)) (PP (IN of) (NP (NNS seasons))))))) (. .)))