Good question. Their last names also end with "ovna". I guess, it's to tell the sex in their first names, Dan. There are a few exceptions, but in Mexico, women's names end with an a and men's names end with an o.
I remember the old Batman series with Adam West and Burt Ward. They had three women that played Catwoman throughout the series. One of them called Batman, "Batushka". It is just now that I realized she was probably Russian. My real name is Ben. My girlfriend calls me Beneshka.
A is the definitive vowel for female in the Russian Language, you would think having a partner who is Russian could explain that. Martin is correct the middle name is taken from the male, though ending with the feminine a. Alexander, would be Alexandrovna for female middle name. Also the difference in Russian an Ukrainian is the womans name usually ends in aya Take the name Chenskaya that's the Russian spelling and pronunciation, the Ukrainian for would be simply Chenska.
A or я is feminine. However, Russian men's first names can be nicknames like Саша, Сашка or Сашенъка. There are no middle names only the patronymic (father's name)
The patronymic is formed from the father's first name by adding -ович or -евмч for males and -овна or -евна for females. So if my father's name is Bill, my middle or patronymic name would be Билович or Billovich.