Abstract
Maternal or early life effects may prepare offspring for similar social conditions to those experienced by their mothers. For males, the ability to achieve mating and fertilization success is a key social challenge. Competitive conditions may therefore favour increased body size or ejaculate production in male offspring. We tested this experimentally by comparing reproductive traits of adult male bank voles (Myodes glareolus), whose mothers had experienced contrasting encounter regimes with female conspecifics while breeding. We found that daily sperm production rates and epididymis mass were significantly higher when dams had experienced more frequent encounters with female conspecifics. This response to maternal and early life experience was specific to sperm production and storage, with no evidence for effects on male body mass or the size of testes and accessory reproductive glands. Our findings reveal a potentially adaptive effect of maternal and early life experience on the development of sperm production, which is worthy of wider investigation.
Highlights
The social environment experienced by mothers can have important consequences for the competitive traits of their offspring via maternal and early life effects [1,2]
Our experiment provides evidence that cues of competition in the maternal social environment can lead to increased sperm production by sons
We found no significant difference in the adult body mass of sons produced under contrasting social conditions, or in the mass of their testes and seminal vesicles at sexual maturity
Summary
The social environment experienced by mothers can have important consequences for the competitive traits of their offspring via maternal and early life effects [1,2]. Less well studied than body size in relation to adaptive maternal effects, male ejaculate traits are an important factor predicting male reproductive success across diverse animal taxa [12] This is because females of many species typically mate with multiple partners, resulting in competition between the sperm of different males to fertilize their ova [12,13]. Social conditions experienced by females during pregnancy, including cues of local population density, are likely to predict the level of reproductive competition that their offspring will experience at reproductive maturity, including the intensity of sperm competition, with potential for adaptive maternal effects to influence male competitive traits. Our results demonstrate evidence of increased sperm production in male offspring whose mothers encountered other females more frequently, which is likely to be adaptive under competitive conditions
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