Abstract
ABSTRACTAvidin is a key egg white antimicrobial protein with strong binding capacity for biotin, an essential growth and immune cell precursor. As such, it is assumed to have a pronounced, though still poorly explored, effect on hatchling phenotype. We tested the effect of experimentally increased egg white avidin concentration (AVIDIN+) on hatching success, chick morphology, post-hatching growth performance and innate immune function in a model bird, Japanese quail (Coturnix japonica). Probability of embryo survival in the late embryonic phase increased with increasing egg weight in control eggs, but not in AVIDIN+ eggs. Chicks hatching from lighter AVIDIN+ eggs had a shorter tarsus than chicks hatching from heavier AVIDIN+ eggs. This suggests that an increase in egg white avidin favours embryo survival in lighter eggs during late embryogenesis, but at the expense of reduced structural body size. Plasma complement activity in 6-day-old AVIDIN+ chicks decreased with increasing body mass and tarsus length; the opposite was observed in control chicks, implying that the later post-hatching innate immune function of larger chicks was compromised by an increase in egg white avidin concentration. Here, we document an important role of egg white antimicrobials in maintenance of embryo viability, avian hatchling morphology and immune phenotype.
Highlights
In birds, parental investments linked with maternal deposition of different substances into the egg during oogenesis are assumed to directly affect brood and offspring quality (Mousseau and Fox, 1998; Gil, 2003; Navara and Mendonca, 2008; Hasselquist and Nilsson, 2009)
Hatching success and post-hatching survival We found no effect of egg white avidin manipulation on overall hatching success or embryo mortality in either early or late developmental stages (Table 1; mean±s.e. probability of hatching=0.65±0.04 and 0.58±0.04, and mean±s.e. probability of surviving early incubation=0.90±0.02 and 0.88±0.03 for AVIDIN+ versus control phosphate buffer saline (PBS)+ eggs, respectively)
Late embryonic phase survival for AVIDIN+ eggs was unaffected by egg weight [Separate generalized linear mixed model (GLMM) for AVIDIN+ eggs: Logit slope±s.e.=0.038±0.178, delta degrees of freedom (Δ D.F.)=1, χ2=0.046, P=0.830], we observed a marked positive association between egg weight and late embryonic survival in the control PBS+ eggs (Separate GLMM for PBS+ eggs: Logit slope± s.e.=0.466±0.197, Δ D.F.=1, χ2=5.963, P=0.015; Fig. 1)
Summary
Parental investments linked with maternal deposition of different substances into the egg during oogenesis are assumed to directly affect brood and offspring quality (Mousseau and Fox, 1998; Gil, 2003; Navara and Mendonca, 2008; Hasselquist and Nilsson, 2009). Egg white proteins are thought to provide an effective defence against microbial trans-shell infection Both the alkaline pH (Grizard et al, 2015) and the presence of antimicrobial proteins (Shawkey et al, 2008; Horrocks et al, 2014) have been shown to significantly reduce the growth of microorganisms (Board and Fuller, 1974) able to penetrate the eggshell and fundamentally affect egg hatchability (Pinowski et al, 1994) and/or offspring phenotype (Javůrková et al, 2014). The binding of these essential molecules to specific proteins prevents their use in the growth and proliferation of many pathogenic microorganisms, their presence is probably more important for proper development of the embryo (Bonisoli-Alquati et al, 2010; Giansanti et al, 2012; Javůrková et al, 2015)
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