Host sympatry and body size influence parasite straggling rate in a highly connected multihost, multiparasite system

Abstract

Parasite lineages commonly diverge when host lineages diverge. However, when large clades of hosts and parasites are analyzed, some cases suggest host switching as another major diversification mechanism. The first step in host switching is the appearance of a parasite on an atypical host, or “straggling.” We analyze the conditions associated with straggling events. We use five species of colonially nesting seabirds from the Galapagos Archipelago and two genera of highly specific ectoparasitic lice to examine host switching. We use both genetic and morphological identification of lice, together with measurements of spatial distribution of hosts in mixed breeding colonies, to test: (1) effects of local host community composition on straggling parasite identity; (2) effects of relative host density within a mixed colony on straggling frequency and parasite species identity; and (3) how straggling rates are influenced by the specifics of louse attachment. Finally, we determine whether there is evidence of breeding in cases where straggling adult lice were found, which may indicate a shift from straggling to the initial stages of host switching. We analyzed more than 5,000 parasite individuals and found that only ~1% of lice could be considered stragglers, with ~5% of 436 host individuals having straggling parasites. We found that the presence of the typical host and recipient host in the same locality influenced straggling. Additionally, parasites most likely to be found on alternate hosts are those that are smaller than the typical parasite of that host, implying that the ability of lice to attach to the host might limit host switching. Given that lice generally follow Harrison's rule, with larger parasites on larger hosts, parasites infecting the larger host species are less likely to successfully colonize smaller host species. Moreover, our study supports the general perception that successful colonization of a novel host is extremely rare, as we found only one nymph of a straggling species, which may indicate successful reproduction.

Unexpected bird–feather mite associations revealed by DNA metabarcoding uncovers a dynamic ecoevolutionary scenario

“…These symbiont individuals are known as stragglers (Ròzsa ), a term which refers explicitly to individual symbionts that ended up on a different (new) host species. Stragglers rarely survive nor reproduce on the new host, but if they do, and if they eventually succeed spreading within the new host species, they are cataloged as host switches (Clayton et al, ; Rivera‐Parra, Levin, Johnson, & Parker, ; Ròzsa ). This process may lead to genetic differentiation and finally to an event of host‐switching speciation.…”

“…The existence of stragglers has been known for a long time, even long before the relevance of host-switching for symbionts speciation was revealed (Choudhury, Moore, & Marques, 2002;Horak et al, 2006;Kellogg, 1896;Ròzsa 1993;Shepherd & Edmonds, 1976). Rivera-Parra et al (2017) provide a nice recent example. Studying feather lice from Galapagos Islands, they found stragglers in ca.…”

Assessing symbiont extinction risk using cophylogenetic data

“…Straggling (i.e., symbiont dispersal to a novel host) seems to be frequent at an ecological scale, whereas successful host-switches (i.e., not only reaching a new host but also reproducing on the new host) are comparatively rare (Whiteman et al, 2004;Rivera-Parra et al, 2017;Doña et al, 2019bDoña et al, , 2018. Higher straggling and host-switching capabilities might be associated with a higher likelihood of escaping from host extinctions (Agosta et al, 2010;Agosta and Klemens, 2008;Clayton et al, 2015;Engelstädter and Fortuna, 2019).…”