Animal personalities are not simply a matter of aggressive versus non-aggressive types. There is a substantial diversity in the kinds of behaviours that define a temperament, and attractiveness need not be associated with being tough or being weak.
Female zebra finches (Taeniopygia guttata) appear to choose partners based on their level of exploratory behaviour, as do male great tits (Parus major).
Both these bird species are bi-parental and socially monogamous, meaning there is careful selection by both males and females for potential partners.
In this case, it is not just about the personality of a potential mate but about the personality of the choosing party as well. Female finches and male great tits that are more exploratory themselves often choose mates from within their behavioural type – much as humans seek out like-minded individuals for adventurous activities like skydiving or river-rafting.
A similar pattern has been observed in bridge spiders, where more aggressive males tend to mate with more aggressive females and vice versa. Bridge spiders are a non-sexually -cannibalistic species where males and females are of similar size.
Do Opposites Ever Attract?
Indeed they do. When females and males both display distinctive behavioural types, like-minded individuals do not always make for perfect matches.
In the tangle web spider (Anelosimus studiosus), aggressive males can easily beat out more docile males in male: male contests. However, such combative males are much more likely to be cannibalized by aggressive females, whereas docile males are likely to successfully reproduce with aggressive females, perhaps due to their ability to “quietly” sneak in and copulate with minimum disturbance.
On the other hand, aggressive males have a greater reproductive success than docile males when mating with docile females. This could be explained by the fact that aggressive males have no trouble out-competing their docile counterparts for females that are not threatening to them. In this way, such behavioural variation in populations is self-promoting.
This post is an adapted excerpt from my book “Wild Sex: The Science Behind Mating in the Animal Kingdom“