Having too many males can be a disadvantage for female lizards. Scientists have found that an excess of males leads to females suffering from violent mating encounters, which decreases their chances of survival and reproduction.
The aggression of males during mating is observed in many species. For instance, the Eastern garter snake often suffocates females during copulation. However, this is the first study to show its impact on population dynamics, according to researcher Xavier Lambin at the University of Aberdeen, Scotland.
Researchers monitored the reproductive processes of two groups of Lacerta vivipara lizards in a field. In one group, 78% of the adults were female, while in the other group, 78% were male. After one year, the group with more females increased from 73 to 118 individuals. In contrast, the male-dominated group saw a decline to just 35 individuals, with an even higher number of males than before. Females in the male-dominated group also experienced mortality rates four times higher than normal and gave birth to 3-4 offspring per year compared to the usual 5.
Researchers speculate that the females may have died from stress caused by constantly accommodating their mates. “Females living with more males will have to endure more violent mating encounters,” explained Jean-François Le Galliard, the lead researcher.
He also noted that male lizards often bite their partners during mating excitement, resulting in the loss of patches of skin on the females’ backs. In the male-dominated group, the surviving females lost three times more skin than those in the other group.
Researchers concluded that an excess of males could ultimately drive the population to extinction. This means that some endangered species with skewed sex ratios will find it increasingly difficult to regain balance when males are not gentle with their partners.
M.T. (Nature)
