Tosi-Germán Rafael A, Tassino Bettina, Reboreda Juan Carlos
Facultad de Ciencias, Universidad de la República, 11400 Montevideo, Uruguay.
Departamento de Ecología, Genética y Evolución & IEGEBA-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428EGA Buenos Aires, Argentina.
Behav Processes. 2020 Sep;178:104152. doi: 10.1016/j.beproc.2020.104152. Epub 2020 May 27.
Hosts of interspecific brood parasites often evolve antiparasitic defences, like the recognition and rejection of parasite's eggs. Most hosts use differences in coloration and maculation to discriminate between their own and parasitic eggs, but there are a few cases of hosts using the size of eggs as a cue. To recognize parasite eggs, hosts may require the presence of their own eggs and use a discordancy rule or may use a mental template of their own eggs. Females are responsible for egg rejection in hosts in which they incubate alone, but if incubation is shared, males can also reject parasitic eggs. The rufous hornero, Furnarius rufus, a host of the shiny cowbird Molothrus bonariensis, ejects parasite eggs using egg size as a cue. We studied the cognitive mechanism underlying the recognition and ejection of parasitic eggs by this host. We experimentally parasitized hornero nests with eggs of different size, with and without the presence of host eggs and determined which sex was responsible for the ejection. We found that horneros ejected parasitic eggs using the size of the egg as a cue and did not need to compare parasitic eggs with their own eggs, which is consistent with the hypothesis of a mental template. Females and males ejected eggs at similar frequencies. We also found that cowbird eggs laid in hornero nests were longer and wider than those laid in nests of other host in the same area, which is consistent with the hypothesis of host-specific female cowbird lineages evolving larger eggs to deceit horneros from recognizing and ejecting their eggs.
种间巢寄生的宿主通常会进化出抗寄生防御机制，比如识别并拒绝寄生卵。大多数宿主利用颜色和斑纹的差异来区分自己的卵和寄生卵，但也有少数宿主利用卵的大小作为线索。为了识别寄生卵，宿主可能需要自己的卵在场，并使用不一致规则，或者可能使用自己卵的心理模板。在独自孵卵的宿主中，雌性负责拒绝寄生卵，但如果是共同孵卵，雄性也可以拒绝寄生卵。棕灶鸟（Furnarius rufus）是辉拟椋鸟（Molothrus bonariensis）的一种宿主，它以卵的大小为线索排出寄生卵。我们研究了这种宿主识别和排出寄生卵背后的认知机制。我们用不同大小的卵对灶鸟巢进行实验性寄生，有宿主卵在场和没有宿主卵在场的情况都进行了实验，并确定了负责排出寄生卵的是哪种性别。我们发现，灶鸟以卵的大小为线索排出寄生卵，不需要将寄生卵与自己的卵进行比较，这与心理模板假说一致。雌性和雄性排出卵的频率相似。我们还发现，产在灶鸟巢中的拟椋鸟卵比产在同一地区其他宿主巢中的卵更长更宽，这与特定宿主的雌性拟椋鸟谱系进化出更大的卵以欺骗灶鸟识别和排出它们的卵这一假说一致。
