What you will learn: The absence of fathers might be affecting the social and neural development of women and men differently. However, it is unexpected that the social development of paternally-deprived males would not be adversely affected, but would seem to be enhanced. This is indeed a discrepancy between the two species, if such results are consistent and proven to be true.

Extrapolating behavioral study outcomes from rodents to humans should always be done with the limitations in mind. However, some thought experiments that ignore these limitations tend to be insightful and provide a fresh outlook on some aspects of the human condition.  

In a study led by Zuoxin Wang – of the Department of Psychology and Program in Neuroscience, Florida State University – researchers investigated the effect of father absence on the neuronal and social development of prairie vole offspring. Unlike most rodent species which are polygamous, prairie voles (Microtus ochrogaster) typically raise their offspring in a monogamous bi-parental setting. This presents a very good model for studying parental deprivation (PD) in humans.

To investigate the effect of paternal deprivation, the researchers randomly assigned 3-day old prairie voles to either be left with only the mother (PD), or with both parents (control, CT). The offspring were then allowed to grow with their assigned parents, uninterrupted, for 21 days–which is roughly when they reach sexual maturity. Subsequently, they were weaned, and put in the same cage with prairie voles of the same sex and category i.e. PD males were allowed to live in the same cage with other PD males, CT females were allowed to live in the cage with other CT females as well etc.

Previously, studies have shown that the effects of PD can be detected as early as 60 days after birth. In the wild, natal dispersal (departing from the site of birth to that of first reproduction) occurs after 60 days. For this reason, the current study started experiments after day 70. 

Whereas neonatal handling has been shown to improve cognition in rodents, maternal deprivation has adverse effects on hippocampal development and cognition. The PD offspring in this study had reduced parental contact relative to the control group. The effects of paternal deprivation are not as understood, partly due to the lack of good models of bi-parental monogamous pairing in laboratory mammals. 

In adulthood, the animals were subjected to a variety of behavioral experiments to investigate anxiety levels, social affiliation (SOA), and social recognition (SOR). Interestingly, there was no significant difference in anxiety-like behavior between the CT and PD groups. However, PD males demonstrated increased social contact with a stimulus animal placed in the same cage, demonstrating that the effects of PD experienced in early development last until adulthood. Such increased contact with conspecifics might be due to decreased aggression in the males. This is supported by previous findings of reduced aggression in male prairie voles induced by partner loss. As the authors suggest, increased SOA might be anxiolytic to the animals. The increase in SOA was not found to be due to increase in SOR.

In addition to behavioral assays, the expression of neurochemicals involved in social memory, stress response, and social behaviors was investigated in the hippocampus. There was a considerable elevation in RNA and protein expression of BDNF and TrkB receptors in the hippocampus of the PD group, in both sexes. BDNF increased expression had been previously shown to accompany maternal separation in rats after weaning. This increase in BDNF and TrkB in the hippocampus as a result of stress experienced in early development has been suggested to protect against stress in the future (Daniels et al., 2004, Faure et al., 2007). Furthermore, total histone h3 histone 3 acetylation was increased in a sex specific manner, in the females of the PD group. The functional significance of such acetylation requires additional study, but it hints at a possible role in synaptic plasticity alterations in the adult hippocampus following PD in early development.  

Blogger's thoughts: If PD increases social attachment in these rodents, wouldn’t it follow that humans who have been deprived of either or both parents early in development have increased craving for social attachment? How would this manifest itself in the world? Possibly, adherence to gangs, co-depency in relationships, too much attachment to friendships, emotional abandonment issues? But the PD males also showed decreased aggression. This is in stark contrast to what happens in humans, as it has been shown that early life stress increases aggression in adults, usually men (Virkkunen, 1985, Veenema et al., 2006, Widom, 1989, Chapple et al., 2005). 

As aforementioned, such extrapolations should be done carefully, as human development is far too complex to simply draw simple inferences from rodent studies. Nonetheless, such findings provide good grounds for theorising.  

Journal Reference:

1. Manal Tabbaa,Kelly Lei,Yan Liu,Zuoxin Wang: Paternal deprivation affects social behaviors and neurochemical systems in the offspring of socially monogamous prairie voles. https://doi.org/10.1016/j.neuroscience.2016.12.011

References:  

CHAPPLE, C. L., TYLER, K. A. & BERSANI, B. E. 2005. Child neglect and adolescent violence: examining the effects of self-control and peer rejection. Violence Vict, 20, 39-53.

DANIELS, W. M., PIETERSEN, C. Y., CARSTENS, M. E. & STEIN, D. J. 2004. Maternal separation in rats leads to anxiety-like behavior and a blunted ACTH response and altered neurotransmitter levels in response to a subsequent stressor. Metab Brain Dis, 19, 3-14.

FAURE, J., UYS, J. D., MARAIS, L., STEIN, D. J. & DANIELS, W. M. 2007. Early maternal separation alters the response to traumatization: resulting in increased levels of hippocampal neurotrophic factors. Metab Brain Dis, 22, 183-95.

VEENEMA, A. H., BLUME, A., NIEDERLE, D., BUWALDA, B. & NEUMANN, I. D. 2006. Effects of early life stress on adult male aggression and hypothalamic vasopressin and serotonin. Eur J Neurosci, 24, 1711-20.

VIRKKUNEN, M. 1985. Urinary free cortisol secretion in habitually violent offenders. Acta Psychiatr Scand, 72, 40-4.

WIDOM, C. S. 1989. Child abuse, neglect, and adult behavior: research design and findings on criminality, violence, and child abuse. Am J Orthopsychiatry, 59, 355-67.