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1. Parasite escape mechanisms drive morphological diversification in avian lice

   https://doi.org/10.1098/rspb.2023.2665  

   Kolencik, Stanislav; Stanley, Edward L; Punnath, Aswaj; Grant, Avery R; Doña, Jorge; Johnson, Kevin P; Allen, Julie M (March 2024, Proceedings of the Royal Society B: Biological Sciences)

   Organisms that have repeatedly evolved similar morphologies owing to the same selective pressures provide excellent cases in which to examine specific morphological changes and their relevance to the ecology and evolution of taxa. Hosts of permanent parasites act as an independent evolutionary experiment, as parasites on these hosts are thought to be undergoing similar selective pressures. Parasitic feather lice have repeatedly diversified into convergent ecomorphs in different microhabitats on their avian hosts. We quantified specific morphological characters to determine (i) which traits are associated with each ecomorph, (ii) the quantitative differences between these ecomorphs, and (iii) if there is evidence of displacement among co-occurring lice as might be expected under louse–louse competition on the host. We used nano-computed tomography scan data of 89 specimens, belonging to four repeatedly evolved ecomorphs, to examine their mandibular muscle volume, limb length and three-dimensional head shape data. Here, we find evidence that lice repeatedly evolve similar morphologies as a mechanism to escape host defences, but also diverge into different ecomorphs related to the way they escape these defences. Lice that co-occur with other genera on a host exhibit greater morphological divergence, indicating a potential role of competition in evolutionary divergence. 

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2. Mitochondrial genomes of Columbicola feather lice are highly fragmented, indicating repeated evolution of minicircle-type genomes in parasitic lice

   https://doi.org/10.7717/peerj.8759  

   Sweet, Andrew D.; Johnson, Kevin P.; Cameron, Stephen L. (January 2020, PeerJ)

   null (Ed.)

   Most animals have a conserved mitochondrial genome structure composed of a single chromosome. However, some organisms have their mitochondrial genes separated on several smaller circular or linear chromosomes. Highly fragmented circular chromosomes (“minicircles”) are especially prevalent in parasitic lice (Insecta: Phthiraptera), with 16 species known to have between nine and 20 mitochondrial minicircles per genome. All of these species belong to the same clade (mammalian lice), suggesting a single origin of drastic fragmentation. Nevertheless, other work indicates a lesser degree of fragmentation (2–3 chromosomes/genome) is present in some avian feather lice (Ischnocera: Philopteridae). In this study, we tested for minicircles in four species of the feather louse genus Columbicola (Philopteridae). Using whole genome shotgun sequence data, we applied three different bioinformatic approaches for assembling the Columbicola mitochondrial genome. We further confirmed these approaches by assembling the mitochondrial genome of Pediculus humanus from shotgun sequencing reads, a species known to have minicircles. Columbicola spp. genomes are highly fragmented into 15–17 minicircles between ∼1,100 and ∼3,100 bp in length, with 1–4 genes per minicircle. Subsequent annotation of the minicircles indicated that tRNA arrangements of minicircles varied substantially between species. These mitochondrial minicircles for species of Columbicola represent the first feather lice (Philopteridae) for which minicircles have been found in a full mitochondrial genome assembly. Combined with recent phylogenetic studies of parasitic lice, our results provide strong evidence that highly fragmented mitochondrial genomes, which are otherwise rare across the Tree of Life, evolved multiple times within parasitic lice. 

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3. Genomic Approaches to Uncovering the Coevolutionary History of Parasitic Lice

   https://doi.org/10.3390/life12091442  

   Johnson, Kevin P. (September 2022, Life)

   Next-generation sequencing technologies are revolutionizing the fields of genomics, phylogenetics, and population genetics. These new genomic approaches have been extensively applied to a major group of parasites, the lice (Insecta: Phthiraptera) of birds and mammals. Two louse genomes have been assembled and annotated to date, and these have opened up new resources for the study of louse biology. Whole genome sequencing has been used to assemble large phylogenomic datasets for lice, incorporating sequences of thousands of genes. These datasets have provided highly supported trees at all taxonomic levels, ranging from relationships among the major groups of lice to those among closely related species. Such approaches have also been applied at the population scale in lice, revealing patterns of population subdivision and inbreeding. Finally, whole genome sequence datasets can also be used for additional study beyond that of the louse nuclear genome, such as in the study of mitochondrial genome fragmentation or endosymbiont function. 

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4. The reduced genome of a heritable symbiont from an ectoparasitic feather feeding louse

   https://doi.org/10.1186/s12862-021-01840-7  

   Alickovic, Leila; Johnson, Kevin P.; Boyd, Bret M. (December 2021, BMC Ecology and Evolution)

   Abstract Background Feather feeding lice are abundant and diverse ectoparasites that complete their entire life cycle on an avian host. The principal or sole source of nutrition for these lice is feathers. Feathers appear to lack four amino acids that the lice would require to complete development and reproduce. Several insect groups have acquired heritable and intracellular bacteria that can synthesize metabolites absent in an insect’s diet, allowing insects to feed exclusively on nutrient-poor resources. Multiple species of feather feeding lice have been shown to harbor heritable and intracellular bacteria. We expected that these bacteria augment the louse’s diet with amino acids and facilitated the evolution of these diverse and specialized parasites. Heritable symbionts of insects often have small genomes that contain a minimal set of genes needed to maintain essential cell functions and synthesize metabolites absent in the host insect’s diet. Therefore, we expected the genome of a bacterial endosymbiont in feather lice would be small, but encode pathways for biosynthesis of amino acids. Results We sequenced the genome of a bacterial symbiont from a feather feeding louse ( Columbicola wolffhuegeli ) that parasitizes the Pied Imperial Pigeon ( Ducula bicolor ) and used its genome to predict metabolism of amino acids based on the presence or absence of genes. We found that this bacterial symbiont has a small genome, similar to the genomes of heritable symbionts described in other insect groups. However, we failed to identify many of the genes that we expected would support metabolism of amino acids in the symbiont genome. We also evaluated other gene pathways and features of the highly reduced genome of this symbiotic bacterium. Conclusions Based on the data collected in this study, it does not appear that this bacterial symbiont can synthesize amino acids needed to complement the diet of a feather feeding louse. Our results raise additional questions about the biology of feather chewing lice and the roles of symbiotic bacteria in evolution of diverse avian parasites. 

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5. Phylogenetics and host‐specificity of the mega‐diverse louse genus Myrsidea (Amblycera: Menoponidae)

   https://doi.org/10.1111/syen.12536  

   Kolencik, Stanislav; Cacioppo, Joseph A.; Johnson, Kevin P.; Allen, Julie M.; Sychra, Oldrich; Weckstein, Jason D. (January 2022, Systematic Entomology)

   Abstract MyrsideaWaterston is the most diverse genus of chewing lice, primarily parasitizing perching birds (Passeriformes), which is the most speciose avian order.Myrsideaalso parasitize several hosts from non‐passerine groups, including toucans, barbets, woodpeckers (Piciformes) and hummingbirds (Apodiformes). To examine host specificity, host switching and generic limits, we reconstructed a phylogeny of the avian feather louse genusMyrsideausing DNA sequence data from two fragments of the mitochondrial COI gene and a fragment of the nuclear EF‐1α gene for 152Myrsideaspecimens collected from 23 avian host families. Unlike other highly diverse louse genera, only a small proportion ofMyrsideaspecies parasitize more than one host species. We found that host family has significant phylogenetic signal on theMyrsideaphylogeny. These results suggest thatMyrsideais generally highly host‐specific, with some exceptions where host switching is important. We found that there are two separate groups ofMyrsideathat parasitize toucans, and that both are nested withinMyrsideafound on perching birds, suggesting that these toucan ectoparasites may have arisen from two independent host switching events. Lastly, representatives of the genusRamphasticolaCarriker, which was originally described as a distinct genus due to a suite of morphologically unique characters, falls in with a strongly supported clade ofMyrsideaparasitizingRamphastostoucans, and therefore we definitively placeRamphasticolaas a synonym ofMyrsidea. 

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