Breeding zebra finches prioritize reproductive bout over self-maintenance under food restriction

Abstract

Reproduction requires high amounts of energy, and challenging environments during breeding can force parents to prioritize their current reproductive bout over self-maintenance or vice versa. However, little is known about how common stressors, such as food restriction, can influence these trade-offs during breeding, and the physiological mechanisms for these trade-off decisions. In this study, adult zebra finches (Taeniopygia castanotis) were subjected to a control diet (ad libitum) or a 40% food restriction while raising nestlings and fledglings, and we measured body mass, furculum fat, plasma corticosterone (CORT) and blood glucose levels of the parents at the time of pairing, when their offspring fledged, and when their offspring reached nutritional independence. We also measured body mass and growth rate in the offspring from hatching until the end of the treatment period. Food-restricted parents had lower body mass when their offspring fledged and reached nutritional independence and higher baseline CORT when their offspring fledged compared to controls. Offspring did not differ in body mass or growth rate between treatment groups. However, there was no effect of food restriction on parents' furculum fat, baseline glucose, the adrenocortical response, or the glucose response. Furthermore, path analysis results suggest that alterations in baseline glucose is the primary driver of changes in body mass in parents and offspring brood mass. Taken together, these results suggest that food restriction during chick rearing in a short-lived passerine drives parents to prioritize their current reproductive bout over self-maintenance, and glucose could potentially be a mechanism for diverting energy toward parental effort.

Keywords: Corticosterone; Glucose; Nutritional stress; Reproduction; Songbirds; Stress.

Fig. 1.

Standardized path coefficients for models in Tables S1 and S2. Significant paths are shown with solid lines with coefficients in bold. Non-significant paths are shown with dashed lines.

Fig. 2.

Body mass and furculum fat score of food-restricted and control parents. Body mass and furculum fat were collected from 11 males and 12 females in food-restricted nests and 11 males and 11 females in control nests at each timepoint. (A) Body mass results from a linear mixed model are plotted at three timepoints; at pairing (treatment: t₈₆=−1.58; P=0.613), at fledging (treatment: t₈₆=−4.28; P=0.001), and nutritional independence (Nut. Ind.; treatment: t₈₆=−3.13; P=0.028). Raw means±s.e.m. are plotted. Asterisk denotes a statistically significant difference between treatment groups at a particular timepoint based on post-hoc tests for each timepoint. (B) Furculum fat results from a cumulative link mixed model shows there is no significant effect of food restriction on furculum fat in parents (z=0.09; P=0.929). This experiment has not been replicated.

Fig. 3.

Body mass and growth rate of food-restricted and control offspring. Body mass and growth rate was collected from the offspring of 12 food-restricted nests and 11 control nests at each timepoint. These results from linear mixed models show that food-restricted offspring do not differ from controls in (A) body mass (treatment at each timepoint: t₂₁≥−3.63; P≥0.065), or (B) growth rate (treatment: F_1,21=3.55; P=0.074). Raw means±s.e.m. are plotted. Offspring were measured for body mass at 0, 5, 10, 16, 25, 45, and 60 dph and tarsus length at 5, 10, 16, 25, and 45 dph. This experiment has not been replicated.

Fig. 4.

CORT results in food-restricted (n=12) and control (n=11) parents. Blood samples to measure CORT were collected from 11 males and 12 females in food-restricted nests and 11 males and 11 females in control nests at each timepoint. (A) Results from a linear mixed model investigating the effect of food restriction on baseline corticosterone (CORT) (treatment: t₇₉=0.69, P=0.982 at pairing; t₇₉=3.41, P=0.013 at fledging; t₇₉=0.23; P=1.000 at nutritional independence). Raw means±s.e.m. are plotted. Asterisk denotes a statistically significant difference between treatment groups at a particular timepoint based on Tukey's post-hoc tests for each timepoint. (B) Linear mixed model shows food restriction does not impact the adrenocortical response (treatment: F_1,76=0.21; P=0.644). Raw means±s.e.m. are plotted. This experiment has not been replicated.

Fig. 5.

Glucose results in food-restricted (n=12) versus control (n=11) parents. Blood samples to measure glucose were collected from 11 males and 12 females in food-restricted nests and 11 males and 11 females in control nests at each timepoint. Parents were measured at three timepoints; at pairing, at fledging, and nutritional independence (Nut. Ind.). (A) Linear mixed model shows food restriction did not impact baseline glucose (treatment: F_1,60=0.01; P=0.906). Raw means±s.e.m. are plotted. (B) Linear mixed model shows there is no effect of food restriction on the glucose response (treatment: F_1,52=0.72; P=0.400). Raw means±s.e.m. are plotted. This experiment has not been replicated.