What does the sex life of a lizard and a human have in common? Plenty, as it turns out. In both cases, males compete intensely for females. Also, in both lizards and humans, there are different costs to reproduction for males and females. That is to say, sperm is a relatively cheap commodity for a male, while females make a large energetic investment in reproduction. This may sound strange when thinking about modern humans, but it must be remembered that we are the product of millions of years of evolution. When the survival of your offspring is at stake, it is critical that he/she have the best possible chance of surviving to one day reproduce. This means choosing a male with good genes.

For male lizards, the best strategy is to mate with as many females as possible because parental care and sperm production are not issues. For females, the act of housing developing eggs/embryos is a big energetic investment and the number of times she may be able to reproduce may be severely limited. Therefore, there is conflict in sex: males want as much as possible, while females want quality!

The Augrabies flat lizard (Platysaurus broadleyi) is a good example of the scenario I have just described. Males are extremely brightly coloured and this colour serves two functions. First, it signals fighting ability/aggressiveness for male to male contests. Second, it is thought to indicate overall male quality to females. This colour comes at a price, however. Bright colour makes males more conspicuous to predators such as kestrels and therefore increases their risk of predation. Females on the other hand, are quite drab. This is because they don't require bright colour to signal mates and may as well be inconspicuous, thereby reducing the threat of predation.



above: Female Augrabies flat lizard
© Martin Whiting



above: Male Augrabies flat lizard
© Martin Whiting

Male rivalry and badges of status

Some of the most spectacular lizard behaviour occurs when rival males meet. The extraordinary concentration of lizards at Augrabies results in frequent male contact. During the breeding season, these interactions stem from aggression related to reproductive behaviour. Aggression and fighting in any animal species may be costly; first, the energy expended can be significant; second, there is an increase in the risk of injury and in extreme cases, death. Finally, while heavily engaged in a fight, males may make themselves more vulnerable to predation. It therefore makes sense to have a mechanism to reduce risky and costly behaviour. Males make use of status signalling badges to signal levels of aggression and/or fighting ability. These badges occur on the lizard's abdomen and are orange, yellow, or a combination of the two. Generally, better fighters have larger badges.

By signalling fighting ability, males can determine the superior fighter in a matter of seconds, without having to engage in a fight. The "loser" can therefore back down without any risk of injury. This behaviour, termed a "ventral display" consists of a male raising his side and thereby exposing his abdominal badge. Occasionally, males are closely matched in fighting ability or dispute a resource of high value, for example territory ownership. Under such circumstances, the badges may be ineffective and the two males may engage in a fight. Besides biting, fights still involve various forms of displays in which males attempt to intimidate their opponents. The degree of male-male competition has also resulted in natural selection for larger male body size such that males have significantly larger heads and bodies than females.



above: Male Augrabies flat lizard signalling his
fighting ability to a rival male
© Martin Whiting

Rogue males

The large number of lizards at Augrabies means that good territories are at a premium. Defending a low quality territory may not be a viable strategy. Consequently, some males adopt a "sneaker" strategy. This is a common phenomenon among territorial animals. Sneaking involves trying to secure matings using alternative means. In flat lizards, sneaker males intercept travelling females. However, compared to territorial males, their treatment of females is far from gentlemanly.

Sexual harassment

Persistent advances on females, physical biting and attempted rape constitute sexual harassment. Sneaker males are the primary perpetrators. Under normal circumstances, males (normally territorial males) court females without physical contact. Compared to territorial males, courtship by sneaker males is brief or dispensed with quickly; they also frequently grab a female by a limb or the neck and attempt copulation. This activity often attracts the attention of other sneaker males that attempt to secure the female for themselves! In high density areas, it is not uncommon to see 2-3 males pulling a female from different directions and climbing on her back.

During such pandemonium, males rarely succeed in mating with the female. Males will also attempt to displace rivals from a female; copulating pairs are sometimes disrupted in this manner. Females can reduce the effect of sexual harassment by spending much of their time in a single male's territory. The territorial male will keep sneaker (and other) males at bay and all the female will have to put up with is his occasional courtship. I suppose this could be likened to the bar room situation where the presence of a large, muscluar male, might dissuade other bothersome males from seeking a date! Humans and lizards may therefore have a lot more in common than meets the eye!