Across the animal kingdom, being a parent is hard. But being a single parent is harder! From animal model systems like rodents [1] to humans [2], it is recognized that when there are commonly supposed to be two parents, babies raised by single parents can experience adverse behavioral and/or health outcomes. However, there is a dearth of knowledge in what changes might be occurring in the single parents to contribute and/or cause these adverse outcomes. To address this, Dr. April Booth and team studied the physiological and neurobiological changes that occur in single parents, using pigeons (Columba livia) as their model [3]. 

Pigeons are an ideal model because the same parts of their brains become active when parenting compared to humans. Also, like in humans, both mother and father pigeons can be single parents. This contrasts with mammalian model systems, where typically only single mothers can be studied. Furthermore, it is possible to study both single mothers AND fathers using pigeons because both sexes are capable of “lactating”—technically considered “pseudo-lactating” as pigeons’ milk comes from their crop, whereas in “true lactation”, it comes from a mammary gland as it does in mammals—and producing an energy- and immune-protective- rich substance called “crop milk”. Hormones like prolactin that facilitate lactation in mammals also play a key role in facilitating pseudo-lactation in pigeons. 

In this study, the single parents were the experimental group. The researchers created single mother or single father nests on the first day the chicks hatched by removing one parent from that nest. The single parents were then allowed to parent their chicks for 5 days, during which video data was collected on day 4, and the brain, pituitary (the “master” endocrine gland), and blood plasma from the parents were collected on day 5. The control group consisted of paired parents, and the same type of data was collected on days 4 and 5 as in the experimental group. 

The results show that although single mothers and single fathers spent comparable time feeding their chicks compared to paired mothers and fathers, single parented chicks received less total time being brooded (cuddled) by their single parents and were smaller than paired parented chicks. The researchers also found a difference in expression of one gene in the hypothalamus, a brain region essential to parental care. They specifically found that mothers expressed more receptors for glucocorticoids (these are metabolic hormones that are also involved in the stress response) compared to fathers. The researchers speculate that this difference may assist single mothers in particular to continue to care for their chicks by either altering their response to stress and/or their metabolism. The researchers also found that single mothers and fathers had less expression of prolactin (a hormone associated directly with parental care and lactation) in the pituitary. The researchers propose that this occurred to increase parental care behaviors and to increase crop milk feeding in the long run.  

This study highlights the similarities and differences between how single mothers versus single fathers continue to rear their babies after the loss of a partner. Studies like this have the potential to inspire a deeper understanding of and solutions to real-world issues. One example is determining how to better elicit parental care in captive breeding programs for endangered and threatened species. Another is gaining a better understanding of the neurobiological and physiological effects of adverse childhood experiences that can cause long-term health issues in humans, since being raised in a single-parent household is considered by medical researchers and medical professionals as an adverse childhood experience [4]. The researchers of this study intend to publish two other papers exploring crop milk quality in single mothers and single fathers, and describe the longer-term consequences of single parent care in the future. 

References:

1. Ahern, T.H., Hammock, E.A.D., and Young, L.J., 2011. Parental division of labor, coordination, and the effects of family structure on parenting in monogamous prairie voles (Microtus ochrogaster). 53, 2, 118-131. https://doi.org/10.1002/dev.20498

2. Downey, D.B., Ainsworth-Darnell, J.W., and Dufur M.J., 1998. Sex of parent and children’s well-being in single-parent households. 60, 4, 878-893.  https://doi.org/10.2307/353631

3. Booth, A.M., Viernes, R., Farrar, V.S., Flores, L., Austin, S.H., and Calisi, R.M., 2023. Sex-specific behavioral and physiological changes during single parenting in a biparental species, Columba livia. Hormones and Behavior. 156, 105428. https://doi.org/10.1016/j.yhbeh.2023.105428

4. Burke Harris, N., 2019. The Deepest Well. Mariner Books, New York, New York.

Dr. April Booth is an alumnus of UC Davis (Molecular, Cellular and Integrative Physiology Graduate Group). She has become passionate about science policy and is currently applying for science policy fellowships and government scientist positions. Her hobbies include doing crafts like adult coloring books, reading webcomics, and learning to play the guitar badly. 

ABGG – affiliated authors:

Dr. Rebecca M. Calisi Rodríguez (Professor)

Dr. Victoria Farrar (ABGG alum)

[Edited by Isabelle McDonald]