Yes, lizards have biological sexes. Like most animal species, they exhibit distinct male and female individuals, fundamental for their reproduction. While the presence of sexes is straightforward, the methods of sex determination and identification vary considerably across diverse lizard species.
Basic Principles of Lizard Sex
The existence of two distinct sexes in lizards is tied to sexual reproduction. This process involves the fusion of male and female gametes (sperm and eggs) to create offspring. Male lizards typically have testes that produce sperm, and paired hemipenes for sperm transfer during mating. Female lizards, conversely, have ovaries that produce eggs and oviducts where eggs develop and are fertilized. These reproductive roles are fundamental to their biological sex.
Identifying Male and Female Lizards
Distinguishing male and female lizards often relies on sexual dimorphism, physical differences between the sexes. Males in many species exhibit brighter coloration, especially during breeding seasons, for attracting mates or warding off rivals. Some male lizards also have pronounced physical decorations like crests, spikes, or dewlaps that are absent or smaller in females. Size differences are common, with males often larger and having more robust heads due to male-male combat, though in some species, females can be the larger sex.
A more specific indicator in many male lizards is the presence of prominent femoral or pre-anal pores, specialized glands on the inner thighs or near the vent that secrete waxy substances involved in scent marking. Additionally, male lizards typically have visible bulges at the tail base, housing their hemipenes. Beyond physical traits, behavioral cues like head bobbing, push-ups, and territorial displays are frequently observed in males.
Diverse Sex Determination in Lizards
Lizard sex determination mechanisms are remarkably diverse.
Genetic Sex Determination (GSD)
One common mechanism is Genetic Sex Determination (GSD), where sex is set at conception by inherited sex chromosomes. Lizards can have various chromosomal systems, such as XX/XY (females XX, males XY) or ZW/ZZ (females ZW, males ZZ).
Temperature-Dependent Sex Determination (TSD)
In contrast, Temperature-Dependent Sex Determination (TSD) occurs in many species, where egg incubation temperature dictates hatchling sex. Different patterns exist: some species produce one sex at cooler temperatures and the other at warmer temperatures, while others produce males at intermediate temperatures and females at extremes. This environmental influence can even override genetic predispositions, as seen in bearded dragons where high temperatures can feminize chromosomally male individuals.
Parthenogenesis
Parthenogenesis, a unique asexual reproductive strategy, is found in some female lizard species. In these species, females produce offspring without male genetic contribution. Resulting offspring are typically genetically identical females, though sterile male offspring can occasionally occur. While these species do not require males for reproduction, their lineage originates from ancestors with distinct sexes.