Animals face stressful environments in the wild. When the going gets rough, parents can prepare their developing offspring for life in a tough world. They can alter gene expression patterns in their young to best ‘match’ their babies’ physical characteristics to their new home. For example, in a habitat with little food, parents may influence gene expression to produce smaller offspring that would require fewer meals and be more likely to survive to adulthood. They may also affect their offspring's characteristics in other ways, including selecting the sex, or even altering behaviour. Together, these parent-induced changes are called parental effects.
But which parent causes these changes? So far, the maternal effects that mothers exert through signalling in their eggs have received the most research attention; but, what about fathers? Might they also signal to their future young about the environment that they are experiencing through sperm cells?
Jonathan Evans and his colleagues from the Centre for Evolutionary Biology at the University of Western Australia wanted to investigate the potential for paternal effects. The research team placed soon-to-be father guppies on an abundant or restricted diet for one month, mimicking the fathers’ experiences of an environment with plentiful or scarce food resources.
Next, Evans and colleagues tested whether the sperm would inform the offspring of the harsh or plentiful conditions that the fathers experienced. To do this, the team artificially inseminated female guppies with sperm from males in either diet treatment (the females were fed normally). The researchers found that the juvenile guppies sired by males on a restricted diet were smaller, while those sired by males on a plentiful diet were larger. The researchers showed that fathers could in fact change their offspring's growth and size through the contribution of sperm alone.
The team underscored the important effects that smaller or larger body size might have on the survival of young guppies in the wild. For instance, larger newly hatched guppies are better at avoiding predators than smaller guppies, and larger juvenile guppies grow faster, out-competing their smaller counterparts in a dense population. The group's tantalizing finding that a father's sperm can influence their offspring's development opens up many exciting avenues for future research. It will be intriguing to understand exactly how sperm transmit their message to developing offspring and also whether sperm signal in other species of the animal kingdom.