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Abstract Parasitic lice (Psocodea: Phthiraptera) are small, wingless parasites of birds and mammals that have been at the forefront of coevolutionary studies since the 1990s, and at the forefront of human–insect interactions since the dawn of humankind. Despite this, an unfortunate overreliance on a co-radiation model of evolution between lice and their hosts (“Fahrenholz’s Rule”) has left a muddled legacy in their classification and taxonomy. In recent decades, the classifications of lice at the order, suborder, family, genus, and species levels have all been examined by a mixture of morphological, genetic, and genomic data, which have challenged many traditional taxon limits and relationships. Here, we discuss the traditional classification of parasitic lice, the data that challenged it, and our current understanding of the group. We give an overview of the morphological characters that identify the major radiations of lice, and point out a number of areas that need further work. 

Abstract A major challenge faced by living organisms is adaptation to novel environments. This process is poorly understood because monitoring genetic changes in natural populations is difficult. One way to simplify the task is to focus on organisms that can be studied in captivity under conditions that remain largely natural. Feather lice (Insecta, Phthiraptera, Ischnocera) are host-specific parasites of birds that live, feed, and breed solely on feathers. Birds defend themselves against lice, which damage feathers, by killing them with their beaks during bouts of preening. In response, feather lice have evolved background-matching cryptic coloration to help them avoid preening. We experimentally manipulated the color backgrounds of host-specific pigeon lice (Columbicola columbae) by confining them to different colored breeds of rock pigeon (Columba livia) over a period of 4 years (ca. 60 louse generations). Over the course of the experiment, we sampled lice from pigeons every 6 months for genomic resequencing and then calculated allele frequency differences and trajectories to identify putative genomic sites under selection. We documented many loci that changed in response to selection for color. Most loci putatively under selection were unshared among replicate populations of lice, indicating that independent adaptation of distinct lineages to the same novel environment resulted in similar phenotypes driven by different genotypes. 

Abstract Evolution results from the interaction of stochastic and deterministic processes that create a web of historical contingency, shaping gene content and organismal function. To understand the scope of this interaction, we examine the relative contributions of stochasticity, determinism, and contingency in shaping gene inactivation in 34 lineages of endosymbiotic bacteria,Sodalis, found in parasitic lice,Columbicola, that are independently undergoing genome degeneration. Here we show that the process of genome degeneration in this system is largely deterministic: genes involved in amino acid biosynthesis are lost while those involved in providing B-vitamins to the host are retained. In contrast, many genes encoding redundant functions, including components of the respiratory chain and DNA repair pathways, are subject to stochastic loss, yielding historical contingencies that constrain subsequent losses. Thus, while selection results in functional convergence between symbiont lineages, stochastic mutations initiate distinct evolutionary trajectories, generating diverse gene inventories that lack the functional redundancy typically found in free-living relatives. 

Abstract Environmental factors such as temperature and humidity influence the distribution of free‐living organisms. As climates change, the distributions of these organisms change along with their associated parasites, mutualists and commensals. Less studied, however, is the possibility that environmental conditions may directly influence the distribution of these symbionts even if the hosts are able to persist in altered environments. Here, we investigate the diversity of parasitic lice (Insecta: Phthiraptera) on birds in arid Utah compared to the humid Bahamas. We quantified the parasite loads of 500 birds. We found that the prevalence, abundance and richness of lice was considerably lower among birds in Utah, compared to the Bahamas, despite sampling greater host taxonomic richness in Utah. Our data suggest that as climates change, birds in arid regions will have less diverse louse communities over time, potentially relieving birds of some of the cost of controlling these ectoparasites. Conversely, birds in more humid regions will see an increase in louse diversity, which may require them to invest more time and energy in anti‐parasite defense. Additional research with other ectoparasites of birds and mammals across different environmental conditions is needed to more fully understand how climate change may reshape parasite communities, and how these changes could influence their hosts. 

Many insects benefit from ancient nutrient-supplementing endosymbionts. While symbiont losses and replacements occur on evolutionary timescales, their dynamics remain enigmatic due to the lack of experimentally tractable systems. Here, we report on the experimental establishment of the culturable bacterium Sodalis praecaptivus in a grain pest beetle (Oryzaephilus surinamensis) and its effect on the native symbiont Shikimatogenerans silvanidophilus, which produces the tyrosine precursor prephenate. Injection of Sodalis into female beetles led to systemic intracellular infection and efficient transovarial vertical transmission but reduced host survival and reproduction. Interestingly, Sodalis also invaded the host’s bacteriomes, causing irregular morphology and rapid loss of Shikimatogenerans within three beetle generations. Transcriptomics revealed a strong upregulation of host immune effectors upon Sodalis infection, but little reaction from Shikimatogenerans, indicating that the ancient symbiont is incapable of responding adaptively to the introduced competitor. The rapid elimination of the native symbiont in O. surinamensis showcases the fragility of ancient beneficial symbioses and experimentally recapitulates a crucial step towards a functional symbiont replacement. 

Many parasitic insects, including lice, form close relationships with endosymbiotic bacteria that are crucial for their survival. In this study, we used genomic sequencing to investigate the distribution and evolutionary history of the bacterial genusSodalisacross a broad range of feather louse species spanning 140 genera. Phylogenomic analysis revealed significant diversity amongSodalislineages in feather lice and robust evidence for their independent and repeated acquisition by different louse clades throughout their radiation. Among the 1020 louse genomes analysed, at least 22% containedSodalis, distributed across 57 louse genera. Cophylogenetic analyses between theSodalisand feather louse phylogenies indicated considerable mismatch. This phylogenetic incongruence between lice andSodalis, along with the presence of distantly relatedSodalislineages in otherwise closely related louse species, strongly indicates repeated independent acquisition of this endosymbiont. Additionally, evidence of cospeciation among a few closely related louse species, coupled with frequent acquisition of these endosymbionts from free-living bacteria, further highlights the diverse evolutionary processes shapingSodalisendosymbiosis in feather lice. 

Four new species of Brueelia Kéler, 1936, are described from African emberizids: Brueelia anomala sp. nov. from Emberiza striolata striolata (Lichtenstein, 1823); Brueelia kalaharicae sp. nov. from Emberiza flaviventris kalaharica Roberts, 1932; Brueelia saharae sp. nov. from Emberiza sahari Levaillant, 1850; Brueelia semicingulata sp. nov. from Emberiza tahapisi arabica (Lorenz von Liburnau & Hellmayr, 1902). All four species belong to a new species group within Brueelia, here termed the ‘Brueelia anomala species group’, characterized by the presence of a transverse dorsal preantennal suture that does not reach the lateral margins of the head; in three of the four species the gonopore is also modified in a way that is previously unknown within Brueelia. 

Feathers are critical for locomotion, communication, thermoregulation, waterproofing, and protection from UV radiation. To maintain these functions, birds care for their feathers by grooming, which consists of preening with the bill and scratching with the feet. Grooming cleans and arranges feathers, distributes preen oil and powder down, and removes ectoparasites. Birds devote considerable time and energy to grooming, to the exclusion of other activities, such as foraging. All else being equal, birds should aim to minimize their grooming time. Seasonal changes in grooming have been documented, with some species of birds grooming more in summer than winter. The higher rate of summer grooming may be caused by molt; however, the relationship between the dynamics of grooming and molt have been quantified only in captive birds subject to other manipulation, such as induced molt in poultry, or access to mates in zebra finches. We conducted an eight‐month study of wild‐caught feral rock pigeonsColumba liviato compare rates of grooming and molt. We found that the intensity of grooming parallels the intensity of molt throughout the molt cycle. Pigeons more than double their grooming time at peak molt, consistent with patterns observed in wild birds. Our results suggest that molt may be more energetically costly than previously realized, given concomitant increases in grooming. 

We describe Guimaraesiella (Guimaraesiella) inaccessibilis sp. nov. from the Inaccessible Island finch, Nesospiza acunhae Cabanis, 1873 (Passeriformes: Thraupidae), and Guimaraesiella (Guimaraesiella) aedon sp. nov. from the Nightingale Island finch, Nesospiza questi Lowe, 1923. Considering that the conservation status of both host species is “vulnerable”, it can be assumed that G. (G.) inaccessibilis and G. (G.) aedon are also vulnerable.