Interactive effects of parental age on offspring fitness and age‐assortative mating in a wild bird

Abstract

Variation in parental age can have important consequences for offspring fitness and the structure of populations and disease transmission. However, our understanding of the effects of parental age on offspring in natural populations is limited. Here, we investigate consequences of parental age for offspring fitness and test for age-assortative mating in a short-lived bird, the house wren (Troglodytes aedon). Offspring immunoresponsiveness increased with maternal age and decreased with paternal age, but the strength of these effects varied with the age of one’s mate. Offspring immunoresponsiveness was augmented most with older mothers and younger fathers. Thus, we expected this combination of ages to yield the highest offspring fitness. However, offspring recruitment, longevity, and lifetime reproductive success were greatest when both parents were of above-average age. Consistent with the interactive effects of parental age on offspring fitness, we detected positive age-assortative mating among breeding pairs. Our results suggest that selection favors age-assortative mating, but in different ways depending on how parental ages affect offspring. We suggest that, in this short-lived species, selection for combinations of parental ages that maximize offspring immune responses is likely weaker than selection to produce breeding adults.

Ectoparasite burden of Blue‐footed Booby chicks depends on combined parental ages

“…The pattern mirrors the interacting effect of parental ages on fledgling viability in figure a of Drummond and Rodríguez () and is partially consistent with the effects of parental ages on immune responses of House Wrens shown by Bowers et al . (: S1a), implying that the two phenomena may be linked. Nestlings with one old parent and one young parent may bear the fewest ticks because they are the most immunocompetent and best able to mount an inflammatory response, the main avian defence against blood‐feeding ectoparasites (Owen et al .…”

“…), is greatest in nestlings with an old mother and young father (Bowers et al . ). Might the superior viability of Blue‐footed Booby nestlings with one old parent and one young parent be due to enhanced immunoresponsiveness?…”

“…Although an emergent literature shows that the ages of animal mothers and fathers can affect offspring at all developmental stages from egg to adult, the possibility of parental ages interacting to affect offspring has rarely been explored in any animal species. However, in humans, maternal and paternal ages interact to influence the probability of several birth defects of known or suspected genetic origin (Fisch et al 2003, Bille et al 2005, and in the short-lived House Wren Troglodytes aedon, cutaneous immune responsiveness of neonates, which predicts recruitment, longevity and lifetime fitness (Bowers et al 2014), is greatest in nestlings with an old mother and young father (Bowers et al 2017). Might the superior viability of Blue-footed Booby nestlings with one old parent and one young parent be due to enhanced immunoresponsiveness?…”

Introduction to ecoimmunology: An integrative approach

“…Comparing the effects of freezing and repeated freeze-thaw cycles on plasma in this commonly used ecoimmunological test, between hatchling and adult snapping turtles, Beck et al (2017) found that samples could be frozen for periods of time prior to running the assay, the assay is robust to at least one bout of thawing, but that the assay should be validated for individual species. Phytohemagglutinin (PHA) is a mitogen that can be used in virtually any species to simulate a proinflammatory response that can be measured via swelling of a particular area or tissue (Bowers et al, 2017). Although this assay is most commonly used in birds, Tylan and Langkilde (2017) present results for a validation of PHA use in the green anole.…”

“…Invertebrate species investigated in this current issue are the bumblebee ( Bombus impatiens ), the weevil ( Curculio sp., Coleoptera), the gallfly ( Eurosta solidaginis , Diptera), and larvae of the lepidopteran Pyrrharctia isabella (Czerwinski & Sadd, ; Ferguson & Sinclair, ). Avian species include the house wren ( Troglodytes aedon ), the golden eagle ( Aquila chrysaetos ), the song sparrow ( Melospiza melodia ), the European starling ( Sturnus vulgaris ), and the zebra finch ( Taeniopygia guttata ) (Bowers, Sakaluk, & Thompson, ; Grindstaff & Merrill, ; Kelly et al., ; MacColl et al., ; Pryor & Casto, ). Reptilian species represented in the current issue are the green anole ( Anolis carolinensis ), the gopher tortoise ( Gopherus polyphemus ), and the snapping turtle ( Chelydra serpentina ) (Beck, Thompson, & Hopkins, ; Goessling et al., ; Tylan & Langkilde, ).…”