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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. 

Two new species of the genusMelinirmusMey, 2017, are described from Australian honeyeaters (Meliphagidae). These are:Melinirmus coromandelican. sp. exPtilotula penicillatus penicillatus(Gould, 1837) andMelinirmus palmain. sp. exAnthochaera carunculata(Shaw, 1790). A checklist of all known species ofBrueelia-complex chewing lice known from the Meliphagidae is provided. 

Birds have a diverse community of “permanent” arthropods that complete their entire life cycle on the body of the host. Because some of these arthropods are parasites that reduce host fitness, birds control them by grooming, which consists of preening with the beak and scratching with the feet. Although preening is the primary component of grooming, scratching is essential for controlling arthropods on the head and neck, which cannot be preened. Several unrelated groups of birds have evolved comb-like pectinate claws on the middle toenail of each foot. We tested the role of these claws in the control of arthropods by experimentally removing teeth from the claws of captive western cattle egrets (Bubulcus ibis) infested with chewing lice (Insecta: Phthiraptera), feather mites (Acari: Sarcoptiformes), and nasal mites (Acari: Mesostigmata). After a period of 4 mo, we compared the abundance of arthropods on experimental birds to that of control birds with intact teeth. We used video to quantify the grooming rates of the captive birds, which groomed twice as much as wild birds. Experimental and control birds did not differ significantly in grooming time. Both groups virtually eradicated the chewing lice, but not feather mites or nasal mites. We found no support for the hypothesis that pectinate claws increase the efficiency of arthropod control by grooming. Experiments with wild birds are needed to test the hypothesis further under conditions in which birds devote less time to grooming. 

RESUMEN. - We describe a new species of chewing louse, Motmotnirmus danielalfonsoi n. sp., from the Turquoise-Browed Motmot (Eumomota superciliosa). It differs from congeneric species in several characters, including the head shape, the abdominal chaetotaxy of the male, and in the characters of the male genitalia. Females differ from congeneric species primarily in the head shape and the shape and size of abdominal plates. Additionally, we suggest that the true host of Motmotnirmus guatemalensis is the Lesson’s Momot (Momotus lessonii), which is also a new host record. Such suggestion is based on examinations of museum specimens of lice from various motmot species. We also provide a key to the species of Motmotnirmus and an updated checklist of the genus Motmotnirmus. 

We present a protocol to establish a synthetic symbiosis between the mCherry-expressing Sodalis praecaptivus and the grain weevil host, Sitophilus zeamais. We describe steps to isolate grain weevil eggs, followed by microinjecting the bacterial symbiont into insect eggs using a modified Drosophila injection protocol, which leads to localization of bacteria in female insect ovaries. We then detail larval transplantation and visualization of bacteria in live insects using a fluorescence dissection microscope to assess the transgenerational transmission to offspring in weevils. For complete details on the use and execution of this protocol, please refer to Su et al. (2022).1 

Fourteen new species of chewing lice in the Brueelia-complex are described, from hosts in the Campephagidae. In addition, Malardifax a new subgenus of Guimaraesiella Eichler, 1949 is described for the species occurring on minivets (Campephagidae: Pericrocotus). The new species and their hosts are: Guimaraesiella (Guimaraesiella) nouankaoensis n. sp. from Coracina caledonica seiuncta Mayr & Ripley, 1941 and C. caledonica thilenii (Neumann, 1915); Guimaraesiella (Guimaraesiella) sphagmotica n. sp. from Coracina caeruleogrisea strenua (Schlegel, 1871) and C. caeruleogrisea adamsoni Mayr & Rand, 1936; Indoceoplanetes (Capnodella) kamphaengphetensis n. sp. from Lalage melaschistos avensis (Blyth, 1852); Indoceoplanetes (Capnodella) saucia n. sp. from Edolisoma montanum montanum (Meyer, 1874); Indoceoplanetes (Capnodella) subarcens n. sp. from Edolisoma melas melas (Lesson, 1828); Indoceoplanetes (Indoceoplanetes) cinitemnina n. sp. from Edolisoma melas melas (Lesson, 1828); Indoceoplanetes (Indoceoplanetes) ephippiformis n. sp. from Edolisoma montanum montanum (Meyer, 1874); Indoceoplanetes (Indoceoplanetes) fodincana n. sp. from Coracina papuensis oriomo Mayr & Rand, 1936, C. papuensis angustifrons (Salvadori, 1876), and C. papuensis elegans (Ramsay, 1881); Indoceoplanetes (Indoceoplanetes) incisoma n. sp. from Coracina macei siamensis (Baker, 1918) and C. macei rexpineti (Swinhoe, 1863); Indoceoplanetes (Indoceoplanetes) microgenitalis n. sp. from Coracina caeruleogrisea strenua (Schlegel, 1871); Indoceoplanetes (Indoceoplanetes) pterophora n. sp. from Coracina macei nipalensis (Hodgson, 1836); Indoceoplanetes (Indoceoplanetes) saburrata n. sp. from Coracina lineata ombriosa (Rothschild & Hartert, 1905); Indoceoplanetes (Indoceoplanetes) wandoensis n. sp. from Coracina novaehollandiae melanops (Latham, 1802); and Indoceoplanetes (Indoceoplanetes) zambica n. sp. from Coracina pectoralis (Jardine & Selby, 1828). Checklists and keys to the louse species of the Brueelia-complex parasitic on campephagid hosts are provided.