Evolutionary ecology of senescence: a case study using Tree Swallows, Tachycineta bicolor

Abstract

Tree Swallows, Tachycineta bicolor, have been studied at nest box colonies at sites throughout North America. They can be easily aged, captured, repeatedly sampled, and their physiology and reproductive success measured across their lifetime. These traits have made Tree Swallows an important model species for many ecological and evolutionary studies. We have studied aging in freeliving Tree Swallows colonies located in Iowa and New York, USA, for several years, and here we review what these studies are revealing about physiological attributes of senescence and their ecological and evolutionary consequences. Telomeres, the DNA ''caps'' on each chromosome, shorten with age, which may contribute to the senescing phenotype, and birds with longer telomeres at 1 year of age have a significantly longer predicted life span than birds with shorter telomeres. Tree Swallows display decreased cell-mediated immune function with age, but other components of the immune system do not decline with age. Older, nesting females who display immunosenescence also show exaggerated sickness behavior compared to younger birds in response to a simulated bacterial infection. Sickness behavior in old birds leads to loss of body condition and decreased parental behavior, suggesting that immunosenescence carries fitness costs in the wild.We are also carrying out an experimental test of the leading theory for aging-oxidative stress. Preliminary data from metabolically-handicapped Tree Swallows carrying an extra 5% of their body mass suggest birds may suffer increased oxidative damage and telomere shortening, reduced immune function, and lower reproductive success. Continued cross-sectional and longitudinal studying of Tree Swallows will enable us to distinguish between intrinsic change with age common to all birds and the results of selection on traits that affect survivorship and differ between individuals. Our results suggest continued work with Tree Swallows holds great promise to understand the evolutionary ecology of senescence in birds and other animals.

Measuring the immune system of the three‐spined stickleback – investigating natural variation by quantifying immune expression in the laboratory and the wild

“…3), with larger individuals having higher expression in 0+ aged fish, whilst the reverse pattern was seen in 1+ fish. Changes in Th2 and FoxP3a expression levels could be the result of a decline in immune potential with age, a pattern of growing interest in immunological research (Aw et al 2007;Vleck et al 2011). This pattern could also represent the transition from a resistant to tolerant immune strategy, as has been observed in wild populations of field voles (Jackson et al 2014) and Soay sheep (Hayward et al 2014).…”

“…; Vleck et al . ). This pattern could also represent the transition from a resistant to tolerant immune strategy, as has been observed in wild populations of field voles (Jackson et al .…”

Telomere length and dynamics predict mortality in a wild longitudinal study

“…It has been shown that artificially increasing the mass of free‐living tree swallows ( Tachycineta bicolour ), increases telomere attrition (Vleck et al . ) and increased fat mass is related to telomere shortening in humans (Nordfjäll et al . ).…”

A longitudinal study of age‐related changes inHaemoproteusinfection in a passerine bird

“…This pattern could be explained because hosts could be increasingly exposed to vectors that transmit infections as they aged (Bennett and Fallis , Greiner , Valkiūnas ). Alternatively, the increase in infection with age could be a consequence of age‐related decline in immune function (Haussmann et al , Møller and Haussy , Palacios et al , Vleck et al ). We also observed a dramatic increase in prevalence of infection right after fledgling, while smaller change occur after the first breeding effort.…”