Sentence:  The best way to determine the correct figure ( in captives ) is by direct observation of pairs isolated from birth , a method that produced surprising results : maturing of a male Indian python in less than two years , his <WSD>mate</WSD> in less than three ; data on the boa constrictor about match this . 
Meaning of the word marked with <WSD> tags:  the partner of an animal (especially a sexual partner)