Sperm priming response to perceived mating opportunities is reduced in male guppies with high baseline sperm production

Producing sperm is costly and males have been selected to strategically adjust their sperm produc- tion and/or expenditure according to the fitness return associated with a specific mating. For exam- ple, males respond to fluctuations in the mating opportunities by adjusting the number of ＂ready＂ sperm. This phenomenon is known as ＂sperm priming＂ and is interpreted as a strategy to econo- mize the investment in sperm. The cost and benefits of the sperm priming response, however, are expected to depend on a male＇s baseline sperm production （BSP） in the absence of females, because of the different risk of sperm depletion and the nonlinearly increasing costs of sperm pro- duction. We tested this prediction in 2 replicated lines of male guppies Poecilia reticulata that were artificially selected for high and low BSP. BSP has a large genetic variance and a high sire heritabil- ity in guppies, and males respond to the perceived mating opportunities by increasing the number of ＂ready＂ sperm. We investigated whether males with a different BSP differed in their sperm pri- ming response. We found that when the perceived mating opportunities increased, males from low-sperm lines had a stronger sperm priming response than those from high-sperm lines. This result suggests that adaptive plasticity in sperm priming has the potential to evolve in response to different levels of BSP. The comparison between guppy populations with different levels of sperm production would allow to test whether the pattern reported here is also observed at the interpopulation level.

Cycloheximide prevents production of arresting,a fraction of 30-50 kDa obtained from seminiferous tubule conditioned medium

Aim: To evaluate the effect of a protein synthesis inhibitor cycloheximide on arresting activity in spermato-genesis and sperm count in male rats. Methods: The study used seminiferous tubule (ST) segments from adult rats cultured in vitro with or without cycloheximide to condition culture media, which have been concentrated, size fractioned (30-50 kDa) and administered 7 days to adult rats by intraperitoneal injections. The effects on testicular and epididymal weights, spermatogenesis and epididymal sperm count were determined. Results: The fraction (30-50 kDa), named arresting, obtained from the culture without cycloheximide decreased testicular and epididymal weights (P<0.01) and reduced the epididymal sperm count significantly. Study of the spermatogenic cycle by transillumination showed spermatogenic arrest at stage VII in rats treated with arresting compared to that observed in controls. The length of stage VII in the group receiving the seminiferous tubules culture media with cycloheximide (30-50 KDa CHX-STCM fraction) was similar to control. Conclusion: The difference in the effect may be the result of the presence or absence of arresting, a protein secreted by the tubules.

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.