Acanthocephalan size and sex affect the modification of intermediate host colouration

Abstract

S U M M A R YFor trophically transmitted parasites, transitional larval size is often related to fitness. Larger parasites may have higher establishment success and/or adult fecundity, but prolonged growth in the intermediate host increases the risk of failed transmission via natural host mortality. We investigated the relationship between the larval size of an acanthocephalan (Acanthocephalus lucii) and a trait presumably related to transmission, i.e. altered colouration in the isopod intermediate host. In natural collections, big isopods harboured larger worms and had more modified (darker) abdominal colouration than small hosts. Small isopods infected with a male parasite tended to have darker abdominal pigmentation than those infected with a female, but this difference was absent in larger hosts. Female size increases rapidly with host size, so females may have more to gain than males by remaining in and growing mutually with small hosts. In experimental infections, a large total parasite volume was associated with darker host respiratory operculae, especially when it was distributed among fewer worms. Our results suggest that host pigment alteration increases with parasite size, albeit differently for male and female worms. This may be an adaptive strategy if, as parasites grow, the potential for additional growth decreases and the likelihood of host mortality increases.

Influence of host nutritional condition on post-infection traits in the association between the manipulative acanthocephalan Pomphorhynchus laevis and the amphipod Gammarus pulex

“…An increase in the size of the parasites could also be a result of increased resources, leading to future beneficial effects, such as a better chance of establishment, and higher survival and fecundity in the definitive host [ 59 , 61 – 63 ]. Several studies have shown that parasite size increases with host size [ 13 , 64 , 65 ], supporting a positive effect of higher levels of resources. Here, infection intensity significantly impacted the size of cystacanth larvae, confirming an effect of intra-host competition [ 19 ].…”

The natural history of Echinorhynchus bothniensis Zdzitowiecki and Valtonen, 1987 (Acanthocephala) in a high Arctic lake

“…This probably explains the over-representation of females of E. bothniensis in our fish samples. Alternatively, the manipulation of host phenotype can also differ between male and female cystacanths (Benesh et al 2009), hinting at the possibility of sex-specific transmission rates from intermediate to definitive host. However, the nearly equal sex ratio in larval E. bothniensis is not consistent with females having a substantially higher transmission rate out of mysids and into fish compared to males.…”

Larval size in acanthocephalan parasites: Influence of intraspecific competition and effects on intermediate host behavioural changes

“…Positive relationships between host manipulation and parasite size have been found in few other host-parasite systems [25,39]. In these cases, it was difficult to discriminate between size and age of parasites as the main trigger of this relationship.…”