Varying forms of polygyny are observed across many animal groups. In some species, a male defends a group of females from other males, and successful defence leads to greater reproductive success. This is often referred to as harem polygyny and is most observed in mammals. A female-biased sex ratio has been associated with harem polygynous species. In such populations, formation of ‘harems’ may be an inevitable consequence of the relative lack of available males, rather than multiple females actively choosing to mate with a subset of specific males. Although a rare mating system for insects, harem polygyny has been described in several orders, including tree wētā (Orthoptera: Anostostomatidae: Hemideina) in New Zealand. Aggregations of multiple females have been found with a single male in their diurnal roosts. We aimed to determine how the sex ratio and local density of Hemideina thoracica affected the formation of harems in laboratory conditions. ‘Harems’ were observed when the sex ratio was female biased, but no more than would be expected by chance arrangement of individuals, although females preferred to associate with males rather than be alone. Conversely, when the sex ratio was male biased, females preferred to be alone. The number of females associated with each male was lowest when the sex ratio was even and local density was low. However, males and females did not associate randomly: when local density was high aggregations of multiple males with multiple females were observed more often than expected by chance, suggesting that, in contrast to classic ‘harem’ behaviour, males accepted other males being present as long as females were also found in the roost. Additionally, females were more likely to be associated with males than in low-density conditions. Individuals in this study showed much more flexibility in their mating behaviour than what would be expected in a harem polygynous species.

中文翻译：

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从安静的夜晚到派对动物：性别比例和密度影响“后宫”一夫多妻昆虫的雄性/雌性聚集

在许多动物群体中观察到不同形式的一夫多妻制。在某些物种中，雄性保护一群雌性免受其他雄性的侵害，成功的防御会带来更大的繁殖成功。这通常被称为后宫一夫多妻制，在哺乳动物中最为常见。偏向女性的性别比例与后宫一夫多妻的物种有关。在这样的种群中，“后宫”的形成可能是相对缺乏可用雄性的必然结果，而不是多个雌性主动选择与特定雄性的一个子集交配。虽然是昆虫的罕见交配系统，但已在多个目中描述了后宫一夫多妻，包括新西兰的树 wētā（直翅目：Anostomatidae：Hemideina）。在它们的昼夜栖息地中发现了多个雌性的聚集体，其中只有一个雄性。我们旨在确定在实验室条件下 Hemideina thoracica 的性别比例和局部密度如何影响后宫的形成。当性别比例偏向女性时会观察到“后宫”，但不会超过个人偶然安排的预期，尽管女性更喜欢与男性交往而不是独自一人。相反，当性别比例偏向男性时，女性更喜欢独处。当性别比例均匀且局部密度较低时，与每个雄性相关的雌性数量最少。然而，男性和女性并不是随机关联的：当局部密度高时，多个男性和多个女性的聚集比偶然观察到的频率更高，这表明与经典的“后宫”行为相反，只要在栖息地中还发现了雌性，雄性就会接受其他雄性的存在。此外，与低密度条件下相比，女性更有可能与男性联系在一起。本研究中的个体在交配行为方面表现出比后宫一夫多妻物种所预期的更大的灵活性。