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Abstract Myrsidea Waterston, 1915 (Phthiraptera: Menoponidae) is the most diverse genus of avian chewing lice. Myrsidea has a global distribution, is thought to be highly host-specific, and parasitizes mostly passerine birds. However, the rate of taxonomic studies describing new species is relatively low, and it is thought that much of the diversity of Myrsidea is yet to be discovered. This low rate of taxonomic description for this genus, and many others, may be related to the time-consuming nature of morphological species description and a lack of expertise in louse taxonomy. Furthermore, most of the taxonomic revisions and reviews have focused on specific host families, and no comprehensive review of the morphology and molecular work of Myrsidea has been completed in the last 20 years. Here, we review the taxonomy and systematics of Myrsidea to (i) describe this chewing louse genus and its biological importance; (ii) describe current problems with its taxonomy; (iii) simplify and summarize morphological descriptions; (iv) summarize molecular data; and (v) provide a comprehensive checklist of the Myrsidea species, with all publications and localities of occurrence included. Together, we hope that this information will provide researchers with a single source of information on the genus Myrsidea, making it easier for work to proceed on its taxonomy, systematics, ecology, and evolution. Importantly, our work highlights important gaps in our knowledge of Myrsidea, providing guideposts on where future work on Myrsidea is needed. 

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. 

A new avian chewing louse genus Apomyrsidea gen. nov. is described based on species parasitizing birds in the family Formicariidae. Diagnostic characteristics and phylogenetic analyses were used to evaluate and confirm the generic status and merit its recognition as unique and different from Myrsidea Waterston, 1915. Three species previously belonging to the genus Myrsidea are placed in the new genus Apomyrsidea gen. nov. and are discussed: Apomyrsidea circumsternata (Valim & Weckstein, 2013) gen. et comb. nov., Apomyrsidea isacantha (Valim & Weckstein, 2013) gen. et comb. nov. and Apomyrsidea klimesi (Sychra in Sychra et al., 2006) gen. et comb. nov. 

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.