A <=> B (quality of sperm depends on your intelligence), B <=> A (and vice versa, intelligence depends on your quality of sperm)
<=> is a connector wich means "A is true if and only if B is true". Therefore, you have a good sperm if and only if you are intelligent, wich is the logical twin of "you are intelligent if and only if you have a good sperm". It is a tautology because the 2 expressions are equivalent and the meaning of the first is included in the second.
Even if it sounds superfluous, this kind of exercice actually helps you to spot the weakness of this study, because it logically excludes any other parameter than intelligence to determine successfuly the quality of sperm (depends can be translated to "is a function of"). <=> is a very strong connector. In their study, men with low intelligence and a good quality of sperm don't exist, neither do highly intelligent men wich poor sperm, then they draw conclusions. Wich is convenient, but dumb.
It is unfortunate that an article talking about intelligence starts with a tautology.