Yolk mass variation in White-Rumped Swallows (Tachycineta leucorrhoa)

Abstract

Egg mass production is costly, but hatching from heavier eggs could be beneficial for the nestling's phenotype and fitness. Egg mass could be influenced by proximate causes, like food abundance, female condition, environmental conditions, and/or by ultimate causes, such as females depositing resources differentially within a clutch to increase the biological fitness of some eggs. Yolk mass, although poorly studied, is the source of nutrients for the embryo, so its mass should be more influential for the nestlings than total egg mass. We used a technique that allowed us to measure yolk size without destroying the eggs. We studied yolk mass in 212 eggs of White-rumped Swallows (Tachycineta leucorrhoa) and found that yolk mass was influenced by laying order, with last laid eggs having heavier yolks than first laid eggs, and the pattern was consistent with egg mass variation. Food abundance also affected yolk mass: when insect availability was high the yolks were heavier. We conclude that embryos in the last laid eggs have more resources from which to develop, and excluding food abundance, neither environmental conditions nor female's condition affected yolk mass. We encourage other researchers to study yolk mass given that multiple variables affected total egg mass.

Maternal adjustment or constraint: differential effects of food availability on maternal deposition of macro‐nutrients, steroids and thyroid hormones in rock pigeon eggs

“…In accordance with our expectation, the eggs laid under the poor food condition were significantly lighter in egg and yolk mass. The results are consistent with previous studies, suggesting that these egg characteristics are to a certain extent constrained by maternal nutrient and energy ingestion prior to or during egg-laying (Ruuskanen et al in press;Williams 1996;De Neve et al 2004;Ardia et al 2006;Karell et al 2008;Barrionuevo et al 2014). Food restriction did not Yolk mass (g) Figure 1.…”

“…; Barrionuevo et al. ). Food restriction did not disproportionally affect the yolk mass after controlling for egg mass, probably because during egg formation, yolk is formed before albumen and eggshell are wrapped up, and yolk mass is probably the determinant of albumen mass instead of the other way around (Williams ).…”

Trade-offs in the early development of tree swallows (Tachycineta bicolor): offspring characteristics, offspring quality, and parental care

“…Like egg mass, yolk mass also increased with order of laying within clutches, as observed in previous studies of tree swallows (Ardia et al 2006), white-rumped swallows (Tachycineta leucorrhoa; Barrionuevo et al 2014), and red-winged blackbirds (Agelaius phoeniceus; Newbrey et al 2015), but in contrast to Chilean swallows (Tachycineta meyeni) for which size of yolk did not vary with laying order (Liljesthrom et al 2012). Since both egg mass and yolk mass increased with laying order in my study, it appears that nestlings hatching from later-laid eggs could benefit from both increased albumen proteins and increased yolk lipids.…”

“…Additionally, females that begin laying eggs earlier in the season are often older birds which lay heavier eggs than younger females, although yolk mass does not appear to differ between ages (Ardia et al 2006). Previous studies of tree swallows and other swallow species have found that both egg and yolk masses increase with increasing flying insect abundance (Ardia et al 2006;Whittingham et al 2007;Barrionuevo et al 2014), while yolk mass increases throughout the season and total egg mass is unrelated to when an egg is laid (Ardia et al 2006;Whittingham et al 2007;Liljesthrom et al 2012).…”

“…Alternatively, heavier eggs with heavier yolks are laid after warmer temperatures because females are less constrained by thermoregulatory energetic concerns and are able to allocate more energy to egg production (Ojanen 1983;Barrionuevo et al 2014). Interestingly, I found that eggs were heavier in clutches that were initiated earlier in the season, while yolks were heavier in clutches that were initiated later in the season.…”