Non-invasive methods unveil the trophic transmission of the tapeworm
Ligula intestinalis in Gull-billed Terns
Abstract
Recent developments in microscopic and molecular tools have opened new
avenues for assessing parasitic infections in wildlife populations. This
is particularly important for the noninvasive detection and
quantification of endoparasites in live animals. Here, we combined
copromicroscopic (Mini-FLOTAC) and molecular (qPCR) techniques to detect
the infection of the macroparasite Ligula intestinalis (Cestoda,
Pseudophyllidea) in fresh droppings of Gull-billed Terns Gelochelidon
nilotica (Charadriiformes, Laridae) breeding in southwestern Spain.
Additionally, we sequenced the cytochrome b gene in parasite isolates
from Gull-billed Terns (definitive host) and Common Bleak Alburnus
alburnus (second intermediate host) sampled around tern colonies to
explore potential genetic differences between the isolates. The qPCR
test showed a higher prevalence (18%; in 13/73 samples) than
Mini-FLOTAC (8%; in 7/87 samples), indicating that qPCR is more
sensitive for diagnostic purposes than fecal flotation alone. Although
the agreement between both techniques was substantial (84.2%) mainly
due to the large number of uninfected samples, only Mini-FLOTAC allowed
us to quantify parasite loads. When combining techniques, prevalence of
infection did not differ between adults and chicks, suggesting frequent
trophic transmission from parents to their offspring via food
provisioning. Phylogenetic analyses identified four haplotypes in the
isolates from Gull-billed Terns and Bleak, all of which were placed
within a European clade composed of tapeworms recovered exclusively from
phylogenetically derived cyprinid fish. This, combined with the short
lifespan of mature tapeworms, suggests that Gull-billed Terns became
infected after consuming infected fish around their breeding colonies
rather than on their West African wintering grounds. Altogether, our
results represent the first record of L. intestinalis in Gull-billed
Terns and the first molecular characterization of the parasite for the
Iberian Peninsula. This integrative copro-diagnostic protocol can be
applied to other host–parasite systems, allowing researchers to study
helminth infections in wild populations in a noninvasive manner.