Less parental care leads to an increased stress response in the nestlings.
Parents have a profound impact on the development of their offspring. In birds, the mother directly influences the condition of the offspring by adding particular hormones to the egg. Also, the location of the nest and the incubation schedules of the parents impact consequent egg development. Once the chicks crawl out of the egg, the feeding behavior of the parents determines the amount of stress the young birds experience. Not only will they have to compete with their siblings, they might also experience anxiety when left alone for too long. All in all, the parents cause a certain amount of stress on their offspring which affects their future development. A recent study in the journal Molecular Ecology investigated the effect of parental behavior on the stress experienced by young White-throated Sparrows (Zonotrichia albicollis).
The researchers choose White-throated Sparrows for a reason: these passerines show peculiar behavioral differences due to a genetic phenomenon. White-throated Sparrows come in two morphs: tan and white. These morphs are determined by a large super-gene (an inversion to be more specific, you can read more about it in this blog post). Tan morphs have the same version of the super-gene (i.e. they are homozygous) whereas white morphs have two different versions (i.e. they are heterozygous).
This super-gene contains more than 1000 genes that influence the morphology and behavior of the birds. White-morph males are promiscuous and provide little parental care. Tan-morph males, however, are great partners: they defend their nest and take care of their offspring. Compared to the male morphs, females typically provide intermediate care.
Interestingly, birds tend to prefer the opposite morph. This results in two pair types in terms of parental care. A white-morph male and a tan-morph female (W x T) will provide female-biased care. A tan-morph male and a white-morph female (T x W) will provide biparental care. Are you still with me?
Daniel Newhouse and his colleagues took advantage of this situation to explore the effects of differential parental care on the offspring. They focused on patterns of gene expression in 32 nestlings. The analyses revealed 881 genes that were differentially expressed between the pair types. Detailed analyses of these genes revealed that nestlings raised by W x T pairs (female-biased care) expressed more stress-related genes than nestlings raised by T x W pairs (biparental care).
This finding raises another question: which mechanism is responsible for the differences in genes expression? Do females of different morphs deposit different amounts of hormones in the eggs? Or does the parental care influence gene expression? The authors argue that “the difference in parental provisioning is the most plausible explanation.” But – as always – more research is needed to confirm this idea.
Campagna, L. (2016). Supergenes: the genomic architecture of a bird with four sexes. Current Biology, 26(3): R105-R107.
Newhouse, D. J., Barcelo-Serra, M., Tuttle, E. M., Gonser, R. A., & Balakrishnan, C. N. (2019). Parent and offspring genotypes influence gene expression in early life. Molecular Ecology, 28: 4166-4180.