Within-year differences in reproductive investment in laboratory zebra finches (Taeniopygia guttata), an opportunistically breeding bird

Manipulation of Heat Dissipation Capacity Affects Avian Reproductive Performance and Output

Animal life requires hard work but the ability to endure such workload appears to be limited. Heat dissipation limit (HDL) hypothesis proposes that the capacity to dissipate the excess of body heat during hard work may limit sustained energy use. Experimental facilitations of heat loss rate via feather-clipping in free-living birds seem to support HDL hypothesis but testing of HDL through laboratory experiments under controlled conditions is not reported. We employed a two-factorial experimental design to test HDL hypothesis by manipulating the capacity to dissipate heat through exposure of captive zebra finches (Taeniopygia guttata) to a cold and warm ambient temperature (14°C and 25°C), and through manipulation of the insulating layer of feathers around the brood patch in females (clipped and unclipped). To simulate foraging costs encountered in the wild we induced foraging effort by employing a feeding system that necessitated hovering to access food, which increased energetic costs of reproduction despite ad libitum conditions in captivity. We quantified the outcome of reproductive performance at the level of both parents, females, and offspring. Thermal limitations due to warm temperature appeared at the beginning of reproduction for both parents with lower egg-laying success, smaller clutch size and lower egg mass, compared to the cold. After hatching, females with an enhanced ability to dissipate heat through feather-clipping revealed higher body mass compared to unclipped females, and these clipped females also raised heavier and bigger nestlings. Higher levels for oxidative stress in plasma of females were detected prior to reproduction in warm conditions than in the cold. However, oxidative stress biomarkers of mothers were neither affected by temperature nor by feather-clipping during the reproductive activities. We document upregulation of antioxidant capacity during reproduction that seems to prevent increased levels of oxidative stress possibly due to the cost of female body condition and offspring growth. Our study on reproduction under laboratory-controlled conditions corroborates evidence in line with the HDL hypothesis. The link between temperature-constrained sustained performance and reproductive output in terms of quality and quantity is of particular interest in light of the current climate change, and illustrates the emerging risks to avian populations.

Pregnancy intervals after stillbirth, neonatal death and spontaneous abortion and the risk of an adverse outcome in the next pregnancy in rural Bangladesh

BACKGROUND

Studies have revealed associations between preceding short and long birth-to-birth or birth-to-pregnancy intervals and poor pregnancy outcomes. Most of these studies, however, have examined the effect of intervals that began with live births. Using data from Bangladesh, we examined the effect of inter-outcome intervals (IOI) starting with a non-live birth or neonatal death, on outcomes in the next pregnancy. Pregnancy spacing behaviors in rural northeast Bangladesh have changed little since 2004.

METHODS

We analyzed pregnancy histories for married women aged 15-49 years who had outcomes between 2000 and 2006 in Sylhet, Bangladesh. We examined the effects of the preceding outcome and the IOI length on the risk of stillbirth, neonatal death and spontaneous abortion using multinomial logistic regression models.

RESULTS

Data included 64,897 pregnancy outcomes from 33,495 mothers. Inter-outcome intervals of 27-50 months and live births were baseline comparators. Stillbirths followed by IOI's <=6 months, 7-14 months or overall <=14 months had increased risks for spontaneous abortion with adjusted relative risk ratios (aRRR) and 95% confidence intervals = 29.6 (8.09, 108.26), 1.84 (0.84, 4.02) and 2.53 (1.19, 5.36), respectively. Stillbirths followed by IOIs 7-14 months had aRRR 2.00 (1.39, 2.88) for stillbirths. Neonatal deaths followed by IOIs <=6 months had aRRR 28.2 (8.59, 92.63) for spontaneous abortion. Neonatal deaths followed by IOIs 7-14 and 15-26 months had aRRRs 3.08 (1.82, 5.22) and 2.32 (1.38, 3.91), respectively, for stillbirths; and aRRRs 2.81 (2.06, 3.84) and 1.70 (1.24, 3.84), respectively, for neonatal deaths. Spontaneous abortions followed by IOIs <=6 months and 7-14 months had, respectively, aRRRs 23.21 (10.34, 52.13) and 1.80 (0.98, 3.33) for spontaneous abortion.

CONCLUSION

In rural northeast Bangladesh, short inter-outcome intervals after stillbirth, neonatal death and spontaneous abortion were associated with a high risk of a similar outcome in the next pregnancy. These findings are aligned with other studies from Bangladesh. Two studies from similar settings have found benefits of waiting six months before conceiving again, suggesting that incorporating this advice into programs should be considered. Further research is warranted to confirm these findings.

Dietary antioxidants and flight exercise in female birds affect allocation of nutrients to eggs: how carry-over effects work

Physiological challenges during one part of the annual cycle can carry over and affect performance at a subsequent phase, and antioxidants could be one mediator of trade-offs between phases. We performed a controlled experiment with zebra finches to examine how songbirds use nutrition to manage trade-offs in antioxidant allocation between endurance flight and subsequent reproduction. Our treatment groups included (1) a non-supplemented, non-exercised group (control group) fed a standard diet with no exercise beyond that experienced during normal activity in an aviary; (2) a supplemented non-exercised group fed a water- and lipid-soluble antioxidant-supplemented diet with no exercise; (3) a non-supplemented exercised group fed a standard diet and trained to perform daily endurance flight for 6 weeks; and (4) a supplemented exercised group fed an antioxidant-supplemented diet and trained to perform daily flight for 6 weeks. After flight training, birds were paired within treatment groups for breeding. We analyzed eggs for lutein and vitamin E concentrations and the plasma of parents throughout the experiment for non-enzymatic antioxidant capacity and oxidative damage. Exercised birds had higher oxidative damage levels than non-exercised birds after flight training, despite supplementation with dietary antioxidants. Supplementation with water-soluble antioxidants decreased the deposition of lipid-soluble antioxidants into eggs and decreased yolk size. Flight exercise also lowered deposition of lutein, but not vitamin E, to eggs. These findings have important implications for future studies of wild birds during migration and other oxidative challenges.

Rapid and reliable sedation induced by diazepam and antagonized by flumazenil in zebra finches (Taeniopygia guttata)

Songbirds have emerged as attractive model systems in many areas of biological research. Notably, songbirds are used in studies of the neurobiological and neuroendocrine mechanisms that shape vocal communication, and zebra finches (Taeniopygia guttata) are the most commonly studied species. In these studies, some form of chemical restraint is often needed to facilitate procedures and to minimize the risk of injury during handling. To determine the minimum dose of the benzodiazepine diazepam that is adequate to achieve deep sedation across individual birds, a low dose (5 mg/kg) and a high dose (10 mg/kg) was administered intramuscularly to 20 zebra finches. Results showed that a 10 mg/kg dose of diazepam resulted in deep sedation, defined by dorsal recumbency, which was achieved in minutes and lasted for several hours. Sedation was induced without complication, because no birds displayed signs of distress during sedation or lethargy after recovery, and was adequate to permit minimally invasive surgical procedures. In addition, the duration of sedation was dose dependent, which provides additional information for researchers who seek to match the depth of sedation to their experimental requirements. Finally, complete recovery from the deeply sedated state was induced by a 0.3 mg/kg dose of the antagonist flumazenil, which enabled birds to more rapidly resume homeostatic behaviors to promote well-being and survival. Together, these results indicate that diazepam is a safe and reliable sedative for use in zebra finches and support specific recommendations to achieve rapid and reliable sedation and recovery.