Final answer:
Rats most commonly use a) monogamy and polygyny as mating systems, with monogamous pairs remaining together for a mating season and in polygyny one male mating with several females.
Step-by-step explanation:
The two mating systems commonly used with rats are monogamy and polygyny. In a monogamous mating system, one male mates with one female and they often remain together for at least one mating season. This system can provide an advantage in the way of having both parents available to protect and feed the offspring, increasing their chances of survival. On the other hand, a polygynous mating system is one where one male mates with many females. The greater sage grouse is an example of an animal that uses this mating system. Polyandry, which is a system where one female mates with many males, is less commonly observed in rats. This system is considered rare overall in animal populations due to various biological and evolutionary pressures. Considering the Greek roots of the term 'polyandry', where 'poly' means many and 'andry' relates to males, it can be defined as the mating system where one female mates with multiple males, opposite to polygyny.