The length of telomeres, the DNA fragments that protect the ends of chromosomes from deterioration, could be an indicator of life expectancy in the southern giant petrel (Macronectes giganteus), an emblematic species of the Antarctic and sub-Antarctic regions, according to an article published in the journal Behavioral Ecology by an international group of researchers including Dr. Jacob González-Solís, from the UB's Department of Animal Biology and the Institute of Research of the Biodiversity (IRBio) at the University of Barcelona.
The project on which the article is based, which is directed by the expert Pat Monhagan (University of Glasgow, UK), also reveals that adult male giant petrels have shorter telomere lengths than females, a genetic difference that had not been documented until now in a scientific study of a bird species.
Telomeres, situated at the terminal end of chromosomes, are key elements in cell division. According to international research studies, telomeres shorten progressively with each cell division, and this reduction in length is associated with cell aging. The 2009 Nobel Prize for Medicine, awarded to Elizabeth H. Blackburn, Carol W. Greider and Jack Szostak, reflects the importance of the biological role of telomeres in cellular and molecular machinery.
The article in Behavioral Ecology focuses on a study of the giant petrel, a large scavenger found in the Arctic and sub-Antarctic regions which displays significant differences between males and females (size, behaviour, diet, etc), carried out in a breeding colony on Bird Island in South Georgia. "The giant petrel is a bird that can live over 50 years, making it ideal for studies of longevity," says Dr. González-Solís, who nevertheless explains that, "It is not easy to study the effects of longevity in wild species. You need to be able to work with communities that have been extensively observed since the mid-part of the 20th century, which is the case of the colony on Bird Island, where we have been able to monitor petrels in different age groups."
Why telomere length is different?
Male telomere length is known to be shorter in humans and in other animal species such as rats. The article in Behavioral Ecology looks at the genetic material of red blood cell samples taken from giant petrels and is the first research study to reveal differences in telomere length between males and females of the same bird species, raising the question of why telomere shortening is more pronounced in males than females. There appears to be no single explanation, although for González-Solís the different lifestyles of males and females may be one, if not the only, explanation: "There is a clear division of roles between males and females, particularly as regards feeding: males compete for the prey of seals and penguins on Antarctic beaches, whereas females feed on marine species including fish, squid or krill." When animals have to compete for food, size is an advantage, and González-Solís explains that, "the specialized feeding strategies of males have led to an increase in body size, which raises the cell division rate and creates greater oxidative stress, hence the telomere shortening observed." As he explains, "this is not consistent with observations in other dimorphic species such as the wandering albatross or the European shag, in which telomere length is similar between sexes."
The difference in telomere length between males and females is also found in chicks, a finding that cannot be accounted for by lifestyle differences, since, as González-Solís explains, "At this stage the birds have not begun to display different behavioural patterns, so the different roles of males and females cannot be the only reason for the disparity in telomere lengths. In the case of chicks, perhaps it is simply that sexual dimorphism imposes different growth rates, which may promote greater telomere shortening in males. At the moment there are a number of theories and more research will be needed to work through them."
Telomere length and bird survival
Another interesting finding of the study is the relationship between telomere length and bird survival, with those that died during the 8-year period after sampling having significantly shorter telomere lengths on average at the time of measurement. This suggests that telomere length may partially determine the life expectancy of giant petrels, independently of age and sex.
The southern giant petrel, a frequent victim of accidental capture by trawlers, is included on the Red List of Threatened Species maintained by the International Union for Conservation of Nature (IUCN). With an adult population that has fallen to 100,000, it is believed that thousands of these birds were killed inadvertently by illegal fishing vessels during the 1990s. In its future work, the team behind the study will focus on population genetics studies of colonies of giant petrels, a species with an extreme life-history strategy combining longevity and a low reproductive rate -- females lay only one egg in each breeding season -- that makes adults highly vulnerable to any type of survival threat.
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