Exposure to a novel male during late pregnancy influences subsequent growth of offspring during lactation

Transitions in paternal social status predict patterns of offspring growth and metabolic transcription

One type of parental effect occurs when changes in parental phenotype or environment trigger changes to offspring phenotype. Such nongenetic parental effects can be precisely triggered in response to an environmental cue in time-locked fashion, or in other cases, persist for multiple generations after the cue has been removed, suggesting multiple timescales of action. For parental effects to serve as reliable signals of current environmental conditions, they should be reversible, such that when cues change, offspring phenotypes change in accordance. Social hierarchy is a prevalent feature of the environment, and current parental social status could signal the environment in which offspring will be born. Here, we sought to address parental effects of social status and their timescale of action in mice. We show that territorial competition in seminatural environments affects offspring growth. Although dominant males are not heavier than nondominant or control males, they produce faster growing offspring, particularly sons. The timing, effect-size, and sex-specificity of this association are modulated by maternal social experience. We show that a change in paternal social status is sufficient to modulate offspring weight: from one breeding cycle to the next, status-ascending males produce heavier sons than before, and status-descending males produce lighter sons than before. Current paternal status is also highly predictive of liver transcription in sons, including molecular pathways controlling oxidative phosphorylation and iron metabolism. These results are consistent with a parental effect of social experience, although alternative explanations are considered. In summary, changes in paternal social status are associated with changes in offspring growth and metabolism.

Male-mediated prenatal loss: Functions and mechanisms

Sexually selected infanticide has been the subject of intense empirical and theoretical study for decades; a related phenomenon, male-mediated prenatal loss, has received much less attention in evolutionary studies. Male-mediated prenatal loss occurs when inseminated or pregnant females terminate reproductive effort following exposure to a nonsire male, either through implantation failure or pregnancy termination. Male-mediated prenatal loss encompasses two sub-phenomena: sexually selected feticide and the Bruce effect. In this review, we provide a framework that explains the relationship between feticide and the Bruce effect and describes what is known about the proximate and ultimate mechanisms involved in each. Using a simple model, we demonstrate that male-mediated prenatal loss can provide greater reproductive benefits to males than infanticide. We therefore suggest that, compared to infanticide, male-mediated prenatal loss may be more prevalent in mammalian species and may have played a greater role in their social evolution than has previously been documented.

The 'Woman in Red' effect: pipefish males curb pregnancies at the sight of an attractive female

In an old Gene Wilder movie, an attractive woman dressed in red devastated a man's current relationship. We have found a similar 'Woman in Red' effect in pipefish, a group of fish where pregnancy occurs in males. We tested for the existence of pregnancy blocks in pregnant male black-striped pipefish (Syngnathus abaster). We allowed pregnant males to see females that were larger and even more attractive than their original high-quality mates and monitored the survival and growth of developing offspring. After exposure to these extremely attractive females, males produced smaller offspring in more heterogeneous broods and showed a higher rate of spontaneous offspring abortion. Although we did not observe a full pregnancy block, our results show that males are able to reduce investment in current broods when faced with prospects of a more successful future reproduction with a potentially better mate. This 'Woman in Red' life-history trade-off between present and future reproduction has similarities to the Bruce effect, and our study represents, to our knowledge, the first documentation of such a phenomenon outside mammals.

The scent of stress: environmental challenge in the peripartum environment of mice affects emotional behaviours of the adult offspring in a sex-specific manner

Early adverse experiences are known to influence the risk of developing psychiatric disorders later. To shed further light on the development of laboratory mice, we systematically examined the influence of a prenatal or postnatal olfactory stressor, namely unfamiliar male mouse faeces, presented to pregnant or nursing mouse dams. Maternal and offspring behaviours were then examined. Maternal behaviours relative to controls revealed changes in nest building by the pregnant dams exposed to the unfamiliar faeces. There were no differences among groups on pup retrieval or exploration by the dams. Behavioural phenotyping of male and female offspring as adults included measures of exploration, anxiety, social and depressive-like behaviours. Additionally, serum corticosterone was assessed as a marker of physiological stress response. Group differences were dependent on the sex of the adult offspring. Males raised by dams that were stressed during pregnancy presented elevated emotionality as indicated by increased numbers of faecal boluses in the open field paradigm. Consistent with the effects of prenatal stress on the males only the prenatally stressed females had higher body weights than their respective controls. Indeed, males in both experimental groups had higher circulating corticosterone levels. By contrast, female offspring of dams exposed to the olfactory stressor after parturition were more anxious in the O-maze as indicated by increased latencies in entering the exposed areas of the maze. These findings emphasize the necessity for researchers to consider the pre- and postnatal environments, even of mice with almost identical genetic backgrounds, in designing experiments and interpreting their data.