Abstract

Cooperative breeding systems, where individuals other than parents assist in raising offspring, have been documented in insects, fish, birds, and mammals. Still, the factors driving the evolution of such complex systems are not fully understood. Here, we report a new example of cooperative breeding in the obligate shell-brooding cichlid fish Neolamprologus meeli from Lake Tanganyika. Field observations revealed that dominant males were either monogamous or polygynous, with each mating with one to four dominant females. Dominant females maintain nests containing one to ten empty gastropod shells used as breeding substrates and shelters. Up to four immature subordinates of either sex lived in these nests. They assisted with territory defense and nest maintenance, the frequency of which was not different from that of the dominants. Parentage analyses showed that most subordinates were the offspring of at least one of the breeders, suggesting that juveniles delay dispersal and help in raising their relatives. The relatedness of subordinates to the breeders declined with increasing body size and was significantly higher to female than to male breeders. These patterns could be caused by extra-pair paternity, between-group dispersal of helpers, or sex differences in breeder turnover. Male helpers were larger than female helpers, and six out of eight dispersed individuals were females, suggesting female-biased dispersal. Because N. meeli is phylogenetically distinct from other cooperatively breeding cichlids, these results contribute to a better understanding of cooperative breeding in fishes and to understanding of the evolution of complex social systems in general.

Significance statement

Cooperatively breeding cichlid fishes of Lake Tanganyika are an excellent model for studying the evolution of social complexity because cooperative breeding evolved at least 5–6 times independently in a small phylogenetic group. Here, we provide a new example of cooperative breeding in the cichlid Neolamprologus meeli. Field observations revealed that these fish were either monogamous or polygynous. Subordinates remained in the breeders’ nests and helped with territory defense and nest maintenance. Subordinates of both sexes were unlikely to participate in reproduction because of their immature gonads. Parentage analyses showed that most helpers and juveniles were offspring of the dominant breeders, suggesting that N. meeli has a kin-structured cooperative breeding system. As N. meeli is phylogenetically distinct from all other cooperatively breeding cichlids, these results pose a hitherto undescribed independent evolutionary event, leading to a highly complex social system.

中文翻译：

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由于在专性壳育丽鱼科鱼 Neolamprologus meeli 中的有限分散，亲属结构的合作繁殖群

摘要

在昆虫、鱼类、鸟类和哺乳动物中记录了合作育种系统，其中父母以外的个人协助抚养后代。尽管如此，推动此类复杂系统演变的因素仍未完全了解。在这里，我们报告了专性壳育丽鱼科鱼Neolamprologus meeli合作育种的一个新例子来自坦噶尼喀湖。实地观察显示，占优势的雄性要么是一夫一妻制，要么是一夫多妻制，每个都与一到四个优势雌性交配。占优势的雌性保持巢穴，其中包含一到十个用作繁殖基质和庇护所的空腹足动物壳。多达四名不成熟的不成熟的下属生活在这些巢穴中。他们协助进行领土防御和巢穴维护，其频率与统治者的频率没有什么不同。亲子关系分析表明，大多数下属是至少一个饲养员的后代，这表明幼体延迟了分散并帮助抚养他们的亲属。下属与育种者的相关性随着体型的增加而下降，并且与雌性育种者相比显着高于雄性育种者。这些模式可能是由额外的亲子关系引起的，帮手的群体间分散，或饲养员营业额的性别差异。男性佣工比女性佣工大，八分之六的分散个体是女性，这表明有女性偏见的分散。因为N. meeli在系统发育上不同于其他合作繁殖的慈鲷，这些结果有助于更好地理解鱼类的合作繁殖，以及总体上理解复杂社会系统的演变。

意义陈述

坦噶尼喀湖慈鲷的合作繁殖是研究社会复杂性演变的一个很好的模型，因为合作繁殖在一个小的系统发育群体中独立进化了至少 5-6 次。在这里，我们提供了一个在慈鲷 Neolamprologus meeli 中合作繁殖的新例子。实地观察表明，这些鱼要么是一夫一妻制的，要么是一夫多妻制的。下属留在饲养员的巢穴中，并帮助进行领土防御和巢穴维护。由于性腺不成熟，两性的下属都不太可能参与繁殖。亲子关系分析表明，大多数帮手和幼体都是优势育种者的后代，这表明 N. meeli 具有亲属结构的合作育种系统。作为 N。