MADRID, 09 (SERVIMEDIA)
Female giraffes have proportionally longer necks than males, suggesting that their high nutritional needs may have driven that characteristic.
That is the conclusion of a study carried out by eight researchers belonging to institutions in the United States, Switzerland and Tanzania, and published in the journal ‘Mammalian Biology’.
The predominant hypothesis about the lengthening of the necks of giraffes is that it was influenced by competition between males to court females.
The new study, which explored the body proportions of wild and captive giraffes, indicates that neck length may be a result of females searching for leaves on trees that would otherwise be difficult to reach.
In their classic theories of evolution, both Jean Baptiste Lamarck and Charles Darwin suggested that giraffes’ long necks evolved to help them reach the highest leaves on trees, avoiding competition with other herbivores.
However, a more recent hypothesis suggests that the evolution of long necks was driven by competition between males, who swing their necks at each other to assert dominance, called neck combat. That is, males with longer necks could have been more successful in competition, which would have led to them reproducing and passing their genes on to offspring.
“The sex-neck hypothesis predicted that males would have longer necks than females,” say Doug Cavener, Dorothy Foehr Huck and J. Lloyd Huck of Pennsylvania State University (United States).
These authors add: “Technically they have longer necks, but everything about males is longer; They are 30% to 40% larger than females. “In this study, we analyzed photographs of hundreds of wild and captive Masai giraffes to investigate the relative body proportions of each species and how they might change as the giraffes grow and mature.”
PHOTOGRAPHS
The researchers gathered thousands of photographs of captive Masai giraffes from the publicly accessible photo repositories Flickr and SmugMug, as well as images of wild adult animals that were taken over the past decade.
Because absolute measurements such as total height are difficult to determine from a photograph without a reference point of known length, the researchers focused on measurements relative to each other or on body proportions (for example, neck length in relation to the total body height) of the animal.
They restricted their analysis to images that met strict criteria, such as only using photos of giraffes perpendicular to the camera, so they could take a variety of measurements consistently.
“We can identify individual giraffes by their unique pattern of spots,” says Cavener, adding: “We also have the complete pedigree or family tree of all North American Masai giraffes in zoos and wildlife parks, as well as their birth dates. birth and transfer history.
“By carefully considering this information, when the photo was taken, and the approximate age of the animal, we were able to identify the specific individual in almost every photograph of a captive giraffe. This information was fundamental to understanding when male and female giraffes begin to show size differences and if they grow differently,” he explains.
At birth, male and female giraffes have the same body proportions. The researchers discovered that, although they generally grow faster during the first year, the dimensions are not significantly different until they begin to investigate sexual maturity around three years of age.
ADULTS
Because body proportions change early, the team limited their study of wild animals (whose ages are largely unknown) to fully grown adults.
In adult giraffes, researchers found that females have proportionally longer necks and trunks, or the main section of their body, which does not include the legs or neck or head. Adult males, on the other hand, have longer front legs and a wider neck. This pattern was the same in both captive and wild giraffes.
“Instead of reaching out to eat the leaves on the highest branches, you often see giraffes, especially females, burrowing deep into the trees,” notes Cavener.
This researcher emphasizes: “Giraffes are picky eaters: they only eat the leaves of a few tree species, and their longer necks allow them to reach deeper into the trees to obtain leaves that no one else can. “Once females reach four or five years of age, they are almost always pregnant and nursing, so we believe that the increased nutritional demands of females drove the evolution of giraffes’ long necks.”
