Abstract

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.

中文翻译：

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幼虫社会线索影响昆虫睾丸投资

摘要

社会性环境会对动物的繁殖和生存产生重大影响。因此，他们需要通过将更多资源分配给能够在他们所感知的特定社会环境中为他们带来优势的竞争特征来做好准备。有证据表明，男性通常会在检测到当前或未来的精子竞争加剧后增加对精子的投资，因为相对精子数量可以决定他的亲子关系份额。这导致睾丸大小被广泛用作精子竞争水平的指标，但睾丸大小并不总是反映精子的产生。迄今为止，尚不清楚雄性动物是否会微调其对精子生产和其他特征的资源分配，以响应其生长和发育过程中的社会线索。使用一夫多妻制昆虫Ephestia kuehniella，我们测试了幼虫的社会环境是否以及如何影响精子的产生、睾丸大小和体重。我们将雄性幼虫暴露于不同的青少年社会性暗示，并测量了这些特征。我们证明，无论性别比例如何，与单独饲养的雄性相比，群体饲养的雄性产生更多的 eupyrenes（可育和有核精子）但睾丸较小，并且体重和 apyrene（不育和无核精子）数量在治疗期间保持不变。我们得出结论，幼虫社交而非性暗示的存在是导致紫芨生成增加和睾丸大小减小的原因。我们建议雄性幼虫在存在同种幼体线索的情况下增加对可育精子细胞的投资并减少对其他睾丸组织的投资。