Cell-mediated immunity predicts the probability of local recruitment in nestling blue tits

We investigated whether the variation in T-cell-mediated immune function of blue tit nestlings affected their fledgling success and the probability of local survival. We studied the relationship between immune function and survival under two rearing conditions: control, unmanipulated, and experimentally enlarged broods. Brood enlargement had negative effects on nestling immune response. Immune response was positively related to fledgling success and it predicted the probability of local recruitment. However, the relationship between immune response and the probability of recruitment was significantly positive only among control broods and nonsignificant among enlarged broods. The effect of immune response on the recruitment probability was not affected by variation in body mass. Our study suggests that selection for immune responsiveness seems to be weak or even absent under unfavourable rearing conditions as simulated by brood size enlargement. Therefore, year-to-year environmental variation and environmental heterogeneity may constrain evolution towards higher immune responsiveness.     

成年雄性林麝消化道寄生虫群落 对不同扰动策略的响应

人工繁育是当前我国保护野生林麝（Moschus berezovskii）资源的主要手段之一,但在林麝种群复壮的过程中,消化道寄生虫病始终威胁着林麝的健康。为探究林麝消化道寄生虫群落对不同扰动策略的响应,本研究分别使用复合药阿苯达唑伊维菌素粉和单一成分药阿维菌素粉去除林麝体内线虫和绦虫,监测林麝其他寄生虫和群落动态变化。选取60只雄性林麝,随机分为三组,分别为阿苯达唑伊维菌素用药组（20只）、阿维菌素用药组（20只）和未做任何处理的对照组（20只）,并连续采集8周用药组和对照组林麝的新鲜粪便。基于改良的Wisconsin粪便虫卵漂浮计数法检测粪便中的虫卵和卵囊,对实验结果进行Kruskal-Wallis检验、Wilcoxon秩检验、Mann Whitney检验和双因素方差分析。研究结果显示,对照组和阿苯达唑伊维菌素用药组林麝的寄生虫感染均为混合感染,球虫为优势物种,其负载量显著高于线虫和绦虫（P < 0.05),阿维菌素用药组林麝仅感染球虫。药物扰动后,两组用药组的林麝球虫的流行率、平均感染强度均高于对照组,但线虫流行率均低于对照组（27.15%,42.15%）。此外,用药后,阿苯达唑伊维菌素用药组林麝先于阿维菌素用药组再次感染线虫和绦虫。通过比较用药组和对照组林麝寄生虫的群落动态变化,表明林麝消化道寄生虫感染现象较为普遍,多重感染中球虫和蠕虫存在竞争关系,复合药物阿苯达唑伊维菌素粉对林麝寄生虫群落的扰动程度更大,林麝寄生虫群落恢复能力与扰动程度成正比。建议林麝人工繁育基地加强科学性和计划性驱虫,并持续性开展林麝寄生虫感染的监测工作。     

Haematobia irritans parasitism of F1 yak × beef cattle (Bos grunniens × Bos taurus) hybrids

The horn fly Haematobia irritans (Diptera: Muscidae) is a blood obligate ectoparasite of bovids that causes annual losses to the U.S. beef cattle industry of over US$1.75 billion. Climate warming, the anthropogenic dispersion of bovids and the cross‐breeding of beef cattle with other bovid species may facilitate novel horn fly–host interactions. In particular, hybridizing yaks [Bos grunniens (Artiodactyla: Bovidae)] with beef cows (Bos taurus) for heterosis and carcass improvements may increase the exposure of yak × beef hybrids to horn flies. The present paper reports on the collection of digital images of commingled beef heifers (n = 12) and F1 yak × beef hybrid bovids (heifers, n = 7; steers, n = 5) near Laramie, Wyoming (～ 2200 m a.s.l.) in 2018. The total numbers of horn flies on beef heifers and F1 yak × beef heifers [mean ± standard error (SE): 88 ± 13 and 70 ± 17, respectively] did not differ significantly; however, F1 yak × beef steers had greater total horn fly abundance (mean ± SE: 159 ± 39) than female bovids. The present report of this experiment is the first such report in the literature and suggests that F1 yak × beef bovids are as susceptible as cattle to horn fly parasitism. Therefore, similar monitoring and treatment practices should be adopted by veterinarians, entomologists and producers.     

The roles of intramembrane proteases in protozoan parasites

Intramembrane proteolysis is widely conserved throughout different forms of life, with three major types of proteases being known for their ability to cleave peptide bonds directly within the transmembrane domains of their substrates. Although intramembrane proteases have been extensively studied in humans and model organisms, they have only more recently been investigated in protozoan parasites, where they turn out to play important and sometimes unexpected roles. Signal peptide peptidases are involved in endoplasmic reticulum (ER) quality control and signal peptide degradation from exported proteins. Recent studies suggest that repurposing inhibitors developed for blocking presenilins may be useful for inhibiting the growth of Plasmodium, and possibly other protozoan parasites, by blocking signal peptide peptidases. Rhomboid proteases, originally described in the fly, are also widespread in parasites, and are especially expanded in apicomplexans. Their study in parasites has revealed novel roles that expand our understanding of how these proteases function. Within this diverse group of parasites, rhomboid proteases contribute to processing of adhesins involved in attachment, invasion, intracellular replication, phagocytosis, and immune evasion, placing them at the vertex of host–parasite interactions. This article is part of a Special Issue entitled: Intramembrane Proteases.     

Entomophagous insects – an introduction

This special issue contains papers presented at the 6th International Entomophagous Insects Conference. Entomophagous insects consume other insects. They are a fundamental component of ecosystems and are extensively used as biocontrol agents. The first article reviews the role of ladybirds in biological control and the second reviews the biological control of stink bugs. The following nine research articles cover the rearing, behavior, life history, and ecology of parasitoid and predator species.     

Colonization of Pacific islands by parasites of low dispersal ability: phylogeography of two monogenean species parasitizing butterflyfishes in the South Pacific Ocean

Aim To investigate the phylogeographical patterns of two poorly dispersing but widely distributed monogenean species, Haliotrema aurigae and Euryhaliotrematoides grandis, gill parasites of coral reef fishes from the family Chaetodontidae. Location South Pacific Ocean (SPO). Methods Sequence data from the mitochondrial cytochrome oxidase subunit I (COI) gene were obtained from samples from five localities of the SPO (Heron Island, Lizard Island, Moorea, Palau and Wallis) for the two parasite species. Phylogenetic and genetic diversity analyses were used to reconstruct phylogeographical patterns, and dates of cladogenetic events were estimated. Results Overall, 50 individuals of 17 Haliotrema aurigae and 33 of Euryhaliotrematoides grandis were sequenced from five localities of the SPO for COI mtDNA (798 bp). Our results revealed a deep phylogeographical structure in the species Euryhaliotrematoides grandis. The molecular divergence between individuals from Moorea and individuals from the remaining localities (7.7%) may be related to Pleistocene sea‐level fluctuations. In contrast, Haliotrema aurigae shows no phylogeographical patterns with the presence of most of the mitochondrial haplotypes in every locality sampled. Main conclusions Our study shows contrasting phylogeographical patterns of the two monogenean parasite species studied, despite many shared characteristics. Both parasites are found on the same host family, share the same geographical range and ecology, and are phylogenetically close. We propose two hypotheses that may help explain the diparity: the hypotheses involve differences in the evolutionary age of the parasite species and their dispersal capabilities. Additionally, the lack of phylogeographical structure in Haliotrema aurigae contrasts with its apparently restricted dispersion, which is likely to occur during the egg stage of the life cycle, inducing a passive dispersal mechanism in butterflyfish monogeneans.     

Eastward Ho: phylogeographical perspectives on colonization of hosts and parasites across the Beringian nexus

The response of Arctic organisms and their parasites to dramatic fluctuations in climate during the Pleistocene has direct implications for predicting the impact of current climate change in the North. An increasing number of phylogeographical studies in the Arctic have laid a framework for testing hypotheses concerning the impact of shifting environmental conditions on transcontinental movement. We review 35 phylogeographical studies of trans-Beringian terrestrial and freshwater taxa, both hosts and parasites, to identify generalized patterns regarding the number, direction and timing of trans-continental colonizations. We found that colonization across Beringia was primarily from Asia to North America, with many events occurring in the Quaternary period. The 35 molecular studies of trans-Beringian organisms we examined focused primarily on the role of glacial cycles and refugia in promoting diversification. We address the value of establishing testable hypotheses related to high-latitude biogeography. We then discuss future prospects in Beringia related to coalescent theory, palaeoecology, ancient DNA and synthetic studies of arctic host–parasite assemblages highlighting their cryptic diversity, biogeography and response to climate variation.     

Rapid evolution and ecological host-parasite dynamics

Traditionally, the termination of parasite epidemics has been attributed to ecological causes: namely, the depletion of susceptible hosts as a result of mortality or acquired immunity. Here, we suggest that epidemics can also end because of rapid host evolution. Focusing on a particular host–parasite system, Daphnia dentifera and its parasite Metschnikowia bicuspidata , we show that Daphnia from lakes with recent epidemics were more resistant to infection and had less variance in susceptibility than Daphnia from lakes without recent epidemics. However, our studies revealed little evidence for genetic variation in infectivity or virulence in Metschnikowia . Incorporating the observed genetic variation in host susceptibility into an epidemiological model parameterized for this system reveals that rapid evolution can explain the termination of epidemics on time scales matching what occurs in lake populations. Thus, not only does our study provide rare evidence for parasite-mediated selection in natural populations, it also suggests that rapid evolution has important effects on short-term host–parasite dynamics.     

Parasites, sex, and clonal diversity in natural snail populations

Under the Red Queen hypothesis, host-parasite coevolution selects against common host genotypes. Although this mechanism might underlie the persistence of sexual reproduction, it might also maintain high clonal diversity. Alternatively, clonal diversity might be maintained by multiple origins of parthenogens from conspecific sexuals, a feature in many animal groups. Herein, we addressed the maintenance of overall genetic diversity by coevolving parasites, as predicted by the Red Queen hypothesis. We specifically examined the contribution of parasites to host clonal diversity and the frequency of sexually reproducing individuals in natural stream populations of Potamopyrgus antipodarum snails. We also tested the alternative hypothesis that clonal diversity is maintained by the input of clones by mutation from sympatric sexuals. Clonal diversity and the frequency of sexual individuals were both positively related to infection frequency. Surprisingly, although clones are derived by mutation from sexual snails, parasites explained more of the genotypic variation among parthenogenetic subpopulations. Our findings thus highlight the importance of parasites as drivers of clonal diversity, as well as sex.