Journal Articles

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Male larval experience of cues from adult rivals alters lifetime sperm investment patterns in a sperm heteromorphic moth, Ephestia kuehniella
(Wiley, 11/05/2023) Liu J; He XZ; Wang Q
Male animals may adjust their resource allocations for reproduction and other fitness functions in response to cues from rivals. For instance, adult males increase their investment in sperm for a higher paternity share when they perceive sperm competition risk in their surroundings. In nature, both juveniles and adults may coexist spatially and temporally. Yet, it is not clear how juvenile males of different ages respond to cues from adult rivals and fine-tune their lifetime investment in sperm production and ejaculation in any insect. Here we used the Mediterranean flour moth, Ephestia kuehniella, which produces both fertile eupyrene and infertile apyrene sperm, to explore this question. We demonstrate that the late, but not early, instar larvae are sensitive to adult male cues. As a response, they produce more sperm before emergence and their resultant adults have shorter mating latency and ejaculate more sperm in the first few matings. When the juvenile stage produces more eupyrenes, the adult stops making these sperm, but regardless of the number of apyrenes produced during the juvenile stage, the adult continues to make them. These findings suggest that the number of permatogonia for eupyrenes may be limited and that for apyrenes may be flexible. Our results show that the insect does not trade off survival, mating frequency, body size, or testis size for sperm production in response to adult males during the larval stage. Knowledge created in the present study offers insight into the stage-dependent sensitivity of juvenile males to cues from adult rivals and subsequent lifetime resource allocations.
Larval social cues influence testicular investment in an insect
(Oxford University Press, 11/02/2022) Liu J; He XZ; Zheng X-L; Zhang Y; Wang Q
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.
Juvenile socio-sexual experience determines lifetime sperm expenditure and adult survival in a polygamous moth, Ephestia kuehniella
(Wiley, 8/02/2023) Liu J; He XZ; Zheng X-L; Zhang Y; Wang Q
Male animals often adjust their sperm investment in response to sperm competition environment. To date, only a few studies have investigated how juvenile socio-sexual settings affect sperm production before adulthood and sperm allocation during the first mating. Yet, it is unclear whether juvenile socio-sexual 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 social-sexual environment.

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