Juvenile socio-sexual experience determines lifetime sperm expenditure and adult survival in a polygamous moth, Ephestiakuehniella

Male animals often adjust their sperm investment in response to sperm competition environment.To date,only a few studies have investigated how juvenile sociosexual settings affect sperm production before adulthood and sperm allocation during the first mating.Yet,it is unclear whether juvenile sociosexual experience(1)determines lifetime sperm production and allocation in any animal species;(2)alters the eupyrene:apyrene sperm ratio in lifetime ejaculates of any lepidopteran insects,and(3)influences lifetime ejaculation patterns,number of matings and adult longevity.Here we used a polygamous moth,Ephestia kuehniella,to address these questions.Upon male adult emergence from juveniles reared at different density and sex ratio,we paired each male with a virgin female daily until his death.We dissected each mated female to count the sperm transferred and recorded male longevity and lifetime number of matings.We demonstrate for the first time that males ejaculated significantly more eupyrenes and apyrenes in their lifetime after their young were exposed to juvenile rivals.Adult moths continued to produce eupyrene sperm,contradicting the previous predictions for lepidopterans.The eupyrene:apyrene ratio in the lifetime ejaculates remained unchanged in all treatments,suggesting that the sperm ratio is critical for reproductive success.Male juvenile exposure to other juveniles regardless of sex ratio caused significantly shorter adult longevity and faster decline in sperm ejaculation over successive matings.However,males from all treatments achieved similar number of matings in their lifetime.This study provides insight into adaptive resource allocation by males in response to juvenile sociosexual environment.

Larval social cues influence testicular investment in an insect

Socio-sexual environment can have critical impacts on reproduction and survival of animals.Consequently,they need to prepare themselves by allocating more resources to competitive traits that give them advantages in the particular social setting they have been perceiving.Evidence shows that a male usually raises his investment in sperm after he detects the current or future increase of sperm competition because relative sperm numbers can determine his paternity share.This leads to the wide use of testis size as an index of the sperm competition level,yet testis size does not always reflect sperm production.To date,it is not clear whether male animals fine-tune their resource allocation to sperm production and other traits as a response to social cues during their growth and development.Using a polygamous insect Ephestia kuehniella,we tested whether and how larval social environment affected sperm production,testis size,and body weight.We exposed the male larvae to different juvenile socio-sexual cues and measured these traits.We demonstrate that regardless of sex ratio,group-reared males produced more eupyrenes(fertile and nucleate sperm)but smaller testes than singly reared ones,and that body weight and apyrene(infertile and anucleate sperm)numbers remained the same across treatments.We conclude that the presence of larval social,but not sexual cues is responsible for the increase of eupyrene production and decrease of testis size.We suggest that male larvae increase investment in fertile sperm cells and reduce investment in other testicular tissues in the presence of conspecific juvenile cues.