Lizards can evolve penis faster than any other part of its body
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Researchers have found the penises on some species of lizards evolve six times faster than other body parts.
Researchers believe the phenomenon evolved to improve male's chances of mating.
They also say that the size and shape of the organ is key to the lizard - leading to its far quicker shape changing
The researchers measured the length and width of the hemipenes in several specimens of each species, and found they were often very different.
The belief that genitalia evolve more quickly than other body parts in many animals has never been proved - until now.
'Our results provide quantitative support for the common presumption that male genitalia are more variable and evolve more rapidly than nongenital morphological traits,' the researchers wrote in this month's Journal of Zoology.
Harvard researcher Julia Klaczko and her team studied 25 Caribbean Anolis lizard species and compare the evolution of their genitalia, known as a hemipenis compared to other parts of their body.
The lizards' hemipenes are tubular structures with a groove through which semen can flow.
The researchers measured the length and width of the hemipenes in several specimens of each species.
'What we see is, sometimes, very close species have very different hemipenes or genitalia,' Klaczko told Live Science.
Their shape varies from cylindrical tubes to deeply bilobed structures, ornamented with calyces, papillae, flounces, and spines, the team found.
Harvard researcher Julia Klaczko and her team studied 25 Caribbean Anolis lizards (pictured)
In the paper, Klaczko believes the difference could be explained by sexual selection.
There are theories that suggest the female members of some species seek out mates whose genitalia naturally fits better with their own, causing the species to evolve more male species with that size and shape penis.
'The cryptic female choice hypothesis suggests that females favor some males over others, as a result of a better fit with female genitals or more effective stimulation of the female,' the team say.
However, they also believe the change could be part of an 'arms war'
'On the other hand, sexually antagonistic coevolution suggests that the evolution of male genitalia results from an evolutionary arm race between males and females for control over reproduction.'
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