Increased Reproductive Output and Telomere Shortening Following Calcium Supplementation in a Wild Songbird

Parental investment comes with increased fitness costs, often expressed as negative effects on survival and future reproduction. We used a novel approach to experimentally alter reproductive investment in a wild bird population and measured telomere length before and after breeding to better understand the costs of reproduction and life history trade-offs. Telomeres are terminal features of chromosomes consisting of highly conserved DNA repeats that shorten with age and stress and whose length is positively correlated with lifespan. We assessed the effects of calcium supplementation on reproductive parameters and telomere length in Tree Swallows (Tachycineta bicolor) in northern Colorado. Measuring telomere length at the beginning and end of each breeding season facilitated evaluation of changes exclusively caused by maternal investment in reproduction. We found that Tree Swallows supplemented with calcium had higher reproductive success and greater telomere shortening compared to control birds. Although mothers supplemented with calcium suffered increased telomere attrition, offspring in calcium supplemented nests had longer telomeres at 12 days old. Thus, Tree Swallow mothers supplemented with calcium had higher reproductive output and offspring with longer telomeres yet these mothers suffered the cost of lower expected maternal lifespan, as indicated by shorter telomeres during the reproductive season.