Effects of the temperature during embryonic development on adult reproduction and the phenotype of the second generation in zebra finches

Across taxa, the temperature experienced by individuals early in life can have large effects on their development. However, comparatively little is known about whether the effects of this thermal developmental environment can be long-lasting or transgenerational. In birds, one important aspect of the developmental environment is incubation and, in general, eggs incubated at low temperatures produce offspring with smaller morphology, suboptimal physiology, and even lower long-term survival. Yet, little is known about whether incubation temperature may affect avian reproduction in adulthood, and nothing is known about whether the effects of avian incubation temperature may be transgenerational. To investigate this, we incubated zebra finch (Taeniopygia guttata) eggs at two different temperatures: 37.5 degrees C ('control') and 36.3 degrees C ('low'), raised nestlings until adulthood, and allowed same-temperature treatment pairs to reproduce. We found that F-1 individuals incubated at the low temperature had shorter beaks at the start of reproduction than those incubated at the control temperature. Further, compared to those from control parents, F-2 offspring from parents incubated at the low temperature had lighter body masses at 5 days-old and had shorter beaks at 30 days-old. However, we found little evidence that incubation temperature affected other aspects of reproduction, with no effect on latency to lay, clutch size, egg mass, incubation period, hatching success/asynchrony, fledging, or the number of offspring that ultimately survived until independence. Overall, we found some evidence that a difference in the early thermal developmental environment can have lasting morphological effects into the next generation. However, future work is needed to determine whether the incubation temperature that birds experience as embryos may influence parental care behaviors or lifetime reproductive success.