Comparison of local and systemic responsiveness of lymphocytes in vitro to Bovicola ovis antigen and Concanavalin A in B. ovis-infested and naive lambs

The in vitro proliferation assay was used to determine lymphocyte responsiveness to soluble antigen of B. ovis and to Concanavalin A (Con A) in peripheral blood, spleen and various lymph nodes from B. ovis-infested and naive lambs. From March to July, an assay of monthly blood samples showed generally higher proliferative responses to antigen and Con A in B. ovis-infested than naive lambs. The proliferative response of cells from the skin-draining prescapular lymph nodes to B. ovis antigen was significantly higher in B. ovis-infested than naive lambs. Responses of cells from the medial iliac, mediastinal and mesenteric lymph nodes (which do not receive lymph from the skin) and spleen showed no significant differences between groups. Within the B. ovis-infested lambs, the response of cells from the prescapular lymph node was significantly higher than that from any other lymphoid organ examined. Responsiveness of the prescapular, medial iliac and mesenteric lymph node and spleen cells to Con A was not significantly different between groups, while mediastinal lymph node cells showed a significantly higher response in B. ovis-infested lambs. The data indicate that the antigen-specific cellular immune response is operating mainly locally, at the level of the skin and draining lymph nodes. Responses to the T cell mitogen Con A did not support non-specific immunodepression as reported in other ectoparasite/host systems.     

Susceptibility of British head lice, Pediculus capitis, to imidacloprid and fipronil

The head louse, Pediculus capitis De Geer (Phthiraptera: Pediculidae) has developed resistance to organochlorines, the organophosphate malathion and to pyrethroids in the U.K. Therefore, headlice from Bristol school children were bioassayed against two new insecticides, fipronil and imidacloprid. Pediculus capitis was fully susceptible to imidacloprid, but it required a relatively high dose and acted slowly. Fipronil acted faster at lower dose, but seemed to be affected by cross-resistance in a small proportion of P. capitis.     

Cophylogenetic relationships between penguins and their chewing lice

It is generally thought that the evolution of obligate parasites should be linked intimately to the evolution of their hosts and that speciation by the hosts should cause speciation of their parasites. The penguins and their chewing lice present a rare opportunity to examine codivergence between a complete host order and its parasitic lice. We estimated a phylogeny for all 15 species of lice parasitising all 17 species of penguins from the third domain of the mitochondrial 12S ribosomal rRNA gene, a portion of the mitochondrial cytochrome oxidase subunit 1 gene and 55 morphological characters. We found no evidence of extensive cospeciation between penguins and their chewing lice using TreeMap 2.02beta. Despite the paucity of cospeciation, there is support for significant congruence between the louse and penguin phylogenies due to possible failure to speciate events (parasites not speciating in response to their hosts speciating).     

New microsporidia parasitizing bark lice (Insecta: Psocoptera)

Two species of bark lice, Xanthocaecilius sommermanae Mockford and Polypsocus corruptus Hagen, collected in a canopy Malaise trap placed in Great Smoky Mountains National Park as part of a survey of the park’s fauna, were found to be infected with microsporidia. Diagnosis was originally based on light microscopy, and was confirmed by PCR amplification and electron microscopy. This is the first record of microsporidia infection in the insect order Psocoptera. Four morphological spore types corresponded to four original SSUrDNA sequences (Genbank accession no. FJ865221-24), suggesting infection with four microsporidia species. Two of those species were examined by electron microscopy. We describe here one new genus and two new species based on morphological and sequence data: Antonospora psocopterae sp. n. with elongated diplokaryotic spores, 4.4 ± 0.05 × 1.9 ± 0.03 μm and Mockfordia xanthocaeciliae gen. n. sp. n. with ovocylindrical monokaryotic spores, 2.5 ± 0.10 × 1.4 ± 0.02 μm. A. psocopterae displayed high sequence (95%) and structural similarity with Antonospora scoticae, fell within a well supported dichotomy with A. scoticae inside the Antonospora-Paranosema clade in phylogenetic analyses by NJ, PS and ML. M. xanthocaeciliae did not exhibit much sequence or structural similarity with any of known microsporidia species, except Encephalitozoon spp. M. xanthocaeciliae fell within one clade with Encephalitozoon spp. in phylogenies and shared with encephalitozoons structural resemblance and about 80% of SSUrDNA sequence identity. The other two species were not described and provisionally were placed to the collective genus Microsporidium as Microsporidium sp. 1 and Microsporidium sp. 4 from bark lice because of insufficient morphological data. The finding that samples fixed and stored for months in propylene glycol (“antifreeze”) are good enough for DNA sequence analysis and can be used for morphological analyses (if no better fixation alternatives are available), is promising for future surveys for microsporidia.     

Closing the gap: Avian lineage splits at a young,narrow seaway imply a protracted history of mixed population response

The evolutionary significance of spatial habitat gaps has been well recognized since Alfred Russel Wallace compared the faunas of Bali and Lombok. Gaps between islands influence population structuring of some species, and flightless birds are expected to show strong partitioning even where habitat gaps are narrow. We examined the population structure of the most numerous living flightless land bird in New Zealand, Weka (Gallirallus australis). We surveyed Weka and their feather lice in native and introduced populations using genetic data gathered from DNA sequences of mitochondrial genes and nuclear β‐fibrinogen and five microsatellite loci. We found low genetic diversity among extant Weka population samples. Two genetic clusters were evident in the mtDNA from Weka and their lice, but partitioning at nuclear loci was less abrupt. Many formerly recognized subspecies/species were not supported; instead, we infer one subspecies for each of the two main New Zealand islands. Although currently range restricted, North Island Weka have higher mtDNA diversity than the more wide‐ranging southern Weka. Mismatch and neutrality statistics indicate North Island Weka experienced rapid and recent population reduction, while South Island Weka display the signature of recent expansion. Similar haplotype data from a widespread flying relative of Weka and other New Zealand birds revealed instances of North Island—South Island partitioning associated with a narrow habitat gap (Cook Strait). However, contrasting patterns indicate priority effects and other ecological factors have a strong influence on spatial exchange at this scale.     

Dispersal ecology versus host specialization as determinants of ectoparasite distribution in brood parasitic indigobirds and their estrildid finch hosts

Brood parasitic birds offer a unique opportunity to examine the ecological and evolutionary determinants of host associations in avian feather lice (Phthiraptera). Brood parasitic behaviour effectively eliminates vertical transfer of lice between parasitic parents and offspring at the nest, while at the same time providing an opportunity for lice associated with the hosts of brood parasites to colonize the brood parasites as well. Thus, the biology of brood parasitism allows a test of the relative roles of host specialization and dispersal ecology in determining the host-parasite associations of birds and lice. If the opportunity for dispersal is the primary determinant of louse distributions, then brood parasites and their hosts should have similar louse faunas. In contrast, if host-specific adaptations limit colonization ability, lice associated with the hosts of brood parasites may be unable to persist on the brood parasites despite having an opportunity for colonization. We surveyed lice on four brood parasitic finch species (genus Vidua), their estrildid finch host species, and a few ploceid finches. While Brueelia lice were found on both parasitic and estrildid finches, a molecular phylogeny showed that lice infesting the two avian groups belong to two distinct clades within Brueelia. Likewise, distinct louse lineages within the amblyceran genus Myrsidea were found on estrildid finches and the parasitic pin-tailed whydah (Vidua macroura), respectively. Although common on estrildid finches, Myrsidea lice were entirely absent from the brood parasitic indigobirds. The distribution and relationships of louse species on brood parasitic finches and their hosts suggest that host-specific adaptations constrain the ability of lice to colonize new hosts, at least those that are distantly related.     

Temporal and spatial dynamics of competitive parapatry in chewing lice

We synthesize observations from 1979 to 2016 of a contact zone involving two subspecies of pocket gophers (Thomomys bottae connectens and T. b. opulentus) and their respective chewing lice (Geomydoecus aurei and G. centralis) along the Río Grande Valley in New Mexico, U.S.A., to test predictions about the dynamics of the zone. Historically, the natural flood cycle of the Rio Grande prevented contact between the two subspecies of pocket gophers. Flood control measures completed in the 1930s permitted contact, thus establishing the hybrid zone between the pocket gophers and the contact zone between their lice (without hybridization). Since that time, the pocket gopher hybrid zone has stabilized, whereas the northern chewing louse species has replaced the southern louse species at a consistent rate of ~150 m/year. The 0.2–0.8 width of the replacement zone has remained constant, reflecting the constant rate of chewing louse species turnover on a single gopher and within a local pocket gopher population. In contrast, the full width of the replacement zone (northernmost G. centralis to southernmost G. aurei) has increased annually. By employing a variety of metrics of the species replacement zone, we are better able to understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts. This research provides an opportunity to observe active species replacement and resulting distributional shifts in a parasitic organism in its natural setting.     

Changes in Atlantic salmon (Salmo salar) epidermal mucus protein composition profiles following infection with sea lice (Lepeophtheirus salmonis)

The mucus protein profile of Atlantic salmon (Salmo salar) and changes due to infection with sea lice (Lepeophtheirus salmonis) were examined. Two-dimensional gel electrophoresis was performed on salmon skin mucus and comparisons between control and infected fish mucus were made. LC MS/MS identified intracellular proteins, calmodulin, actin, and hemopexin and plasma proteins, such as apolipoproteins, lectin, plasminogen and transferrin. Plasma proteins in the mucus may result from either direct expression by epidermal cells, leakage of plasma or via a secondary circulation system. Therefore, RT-PCR was used to measure mRNA of transferrin and lectin in Atlantic salmon skin. Transferrin expression was observed suggesting direct expression by the epidermis. Lectin expression was not detected suggesting another mechanism of entry into mucus, either leakage from plasma or secondary circulation. The lack of observable albumin on 2D gels, suggests that mucus lectin may arise from the secondary circulation route. Interestingly, β-actin was a significant component of Atlantic salmon mucus. Cleaved actin and transferrin fragments were observed and positively correlated with sea lice infection suggestive of proteolytic activity. Increased levels of cleaved transferrin during sea lice infection may activate the nitrous oxide response of salmon macrophages, as part of the fish's immune response to sea lice infection.     

Differences in susceptibility to sea lice infection between a sea run and a freshwater resident population of brown trout

Two experimental groups comprising mixed Norwegian sea run and freshwater resident brown trout Salmo trutta were infected with sea lice Lepeophtheirus salmonis in replicate tanks. Comparison of mean abundance and louse development between the sea run and resident groups revealed highly significant differences in lice abundance. The resident trout had an average abundance ± of 6·3±0·37 and 6·6±0·43 lice whilst the sea trout had an average abundance of 3·5 ±0·25 and 3·3 ±0·28 lice 29 days post infection at 9° C. No differences in development of lice, of either sex, were detected between the groups. As host groups were naive to sea lice at the start of the experiment, this suggests that there was a significant difference in susceptibility to sea lice infection between them, which may be genetically determined.     

Critical thresholds in sea lice epidemics: evidence, sensitivity and subcritical estimation

Host density thresholds are a fundamental component of the population dynamics of pathogens, but empirical evidence and estimates are lacking. We studied host density thresholds in the dynamics of ectoparasitic sea lice (Lepeophtheirus salmonis) on salmon farms. Empirical examples include a 1994 epidemic in Atlantic Canada and a 2001 epidemic in Pacific Canada. A mathematical model suggests dynamics of lice are governed by a stable endemic equilibrium until the critical host density threshold drops owing to environmental change, or is exceeded by stocking, causing epidemics that require rapid harvest or treatment. Sensitivity analysis of the critical threshold suggests variation in dependence on biotic parameters and high sensitivity to temperature and salinity. We provide a method for estimating the critical threshold from parasite abundances at subcritical host densities and estimate the critical threshold and transmission coefficient for the two epidemics. Host density thresholds may be a fundamental component of disease dynamics in coastal seas where salmon farming occurs.