We studied the success of fleas, Synosternus cleopatrae and Xenopsylla ramesis, in switching to a novel host by establishing experimental lines maintained on different hosts for 18 generations. Fleas fed on principal (P-line) or novel hosts, either sympatric with (S-line) or allopatric to (A-line) a flea and its principal host, then we assessed their reproductive performance via the number and size of eggs. We compared reproductive performance between hosts within a line and between lines within a host asking: (a) whether fleas adapt to a novel host species after multiple generations; (b) if yes, whether the pattern of adaptation differs between novel host species sympatric with or allopatric to a flea and its principal host; and (c) adaptation to a novel host is accompanied with a loss of success in exploitation of an original host. Fleas from the S- and A-lines increased their egg production on a novel host (except X. ramesis from the S-line). S. cleopatrae from the S-line but not the A-line increased egg size on a novel host, whereas X. ramesis from the A-line but not the S-line produced larger eggs from a novel host. We found no indication of a loss of reproductive performance on the original host while adapting to a novel host. We conclude that fleas are able to switch rapidly to a new host with the pattern of a switch to either sympatric or an allopatric host depending on the identities of both flea and host species.

我们研究了跳蚤，克氏菌和沙门氏菌的成功，通过建立在不同宿主上维持18代的实验品系来切换到新型宿主。跳蚤以主要（P系）或新型寄主（与（S系）同伴或与（A系）同代跳蚤及其主要寄主）为食，然后通过卵的数量和大小评估它们的繁殖性能。我们比较了一个品系内寄主之间和一个品系内行之间的生殖性能，并询问：（a）跳蚤在多代后是否适应新的寄主物种；（b）如果是，在与跳蚤同住或同种异能的新寄主物种与其主要寄主之间的适应方式是否不同；（c）适应新颖的宿主会伴随着对原始宿主的成功利用的丧失。S系和A系的跳蚤增加了新型寄主的卵产量（除了X.从S线的ramesis）。S. cleopatrae从S-线而不是A线的新型主机上增加鸡蛋大小，而X. ramesis从A线而不是S-线产生更大的鸡蛋从一种新颖的主机。我们没有发现适应新宿主的原始宿主繁殖能力下降的迹象。我们得出的结论是，跳蚤能够根据跳蚤和​​寄主物种的身份，以向同伴或异源寄主的模式快速切换到新寄主。