Research links cancer in birds to clutch size
Scientists suggest this may be an 'evolutionary trade-off' between reproduction and survival.
Research conducted by an international group of scientists has suggested a relationship between birds’ reproductive rates and their risk of cancer.
The study, one of the largest on cancer susceptibility across bird species, discovered that birds which laid more eggs per clutch tended to have higher rates of cancer than those reproducing less.
Although it is investigated in many mammals, cancer in birds has been less extensively studied. The research team from Arizona State University analysed over 5,700 bird necropsies across 108 avian species.
The researchers suggest that the relationship between reproduction and cancer susceptibility could highlight the ‘evolutionary trade-offs’ between reproduction and survival for the birds. They believe that this could be related to energy allocation, as reproducing limits the amount of energy available.
Like all other organisms, birds have limited energy resources that must be allocated across various functions. This means that, when more energy is focused on reproduction, there is less energy available for maintaining health.
Since some birds have high reproductive rates, and invest heavily in raising offspring, they may have less energy available for DNA repair – making them more susceptible to cancer.
These findings may also explain why some long-lived species which have fewer offspring and can invest more in self-maintenance have lower cancer rates. Meanwhile, species with higher reproductive rates and shorter lifespans may focus their energy on reproduction.
In contrast to expectations, the study did not identify a strong correlation between body size or lifespan and cancer risk.
This represents a phenomenon in biology known as ‘Peto’s paradox’. Although larger, longer-lived animals have more cells which could become cancerous, they still display lower cancer rates.
Stefania Kapsetaki, co-first author of the study, said: "It is interesting that depending on the reproductive trait that we focus on, the trade-off between reproduction and bodily maintenance is not always clear.
"For example, investing in a trait linked to increased reproduction does not always mean less investment in a trait linked with bodily maintenance.
"It is important to bear in mind that patterns of avian cancer prevalence are affected by multiple interacting components, some known and others yet to be discovered."
The full study can be found in the journal Evolution, Medicine, and Public Health.
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