How Did Seal Lice Turn into the Only Truly Marine Insects?

Insects are the most evolutionarily and ecologically successful group of living animals, being present in almost all possible mainland habitats; however, they are virtually absent in the ocean, which constitutes more than 99% of the Earth’s biosphere. Only a few insect species can be found in the sea but they remain at the surface, in salt marshes, estuaries, or shallow waters. Remarkably, a group of 13 species manages to endure long immersion periods in the open sea, as well as deep dives, i.e., seal lice. Sucking lice (Phthiraptera: Anoplura) are ectoparasites of mammals, living while attached to the hosts’ skin, into their fur, or among their hairs. Among them, the family Echinophthiriidae is peculiar because it infests amphibious hosts, such as pinnipeds and otters, who make deep dives and spend from weeks to months in the open sea. During the evolutionary transition of pinnipeds from land to the ocean, echinophthiriid lice had to manage the gradual change to an amphibian lifestyle along with their hosts, some of which may spend more than 80% of the time submerged and performing extreme dives, some beyond 2000 m under the surface. These obligate and permanent ectoparasites have adapted to cope with hypoxia, high salinity, low temperature, and, in particular, conditions of huge hydrostatic pressures. We will discuss some of these adaptations allowing seal lice to cope with their hosts’ amphibious habits and how they can help us understand why insects are so rare in the ocean.

Frequent tRNA gene translocation towards the boundaries with control regions contributes to the highly dynamic mitochondrial genome organization of the parasitic lice of mammals

Background The typical single-chromosome mitochondrial (mt) genome of animals has fragmented into multiple minichromosomes in the lineage Mitodivisia, which contains most of the parasitic lice of eutherian mammals. These parasitic lice differ from each other even among congeneric species in mt karyotype, i.e. the number of minichromosomes, and the gene content and gene order in each minichromosome, which is in stark contrast to the extremely conserved single-chromosome mt genomes across most animal lineages. How fragmented mt genomes evolved is still poorly understood. We use Polyplax sucking lice as a model to investigate how tRNA gene translocation shapes the dynamic mt karyotypes. Results We sequenced the full mt genome of the Asian grey shrew louse, Polyplax reclinata. We then inferred the ancestral mt karyotype for Polyplax lice and compared it with the mt karyotypes of the three Polyplax species sequenced to date. We found that tRNA genes were entirely responsible for mt karyotype variation among these three species of Polyplax lice. Furthermore, tRNA gene translocation observed in Polyplax lice was only between different types of minichromosomes and towards the boundaries with the control region. A similar pattern of tRNA gene translocation can also been seen in other sucking lice with fragmented mt genomes. Conclusions We conclude that inter-minichromosomal tRNA gene translocation orientated towards the boundaries with the control region is a major contributing factor to the highly dynamic mitochondrial genome organization in the parasitic lice of mammals.

Mechanisms of Survival of Arthropods in the World

The phylum Arthropoda is commonly divided into four subphyla of extant forms: Chelicerate (arachnids), Crustacea (crustaceans), Hexapoda (insects and springtails), and Myriapoda (millipedes and centipedes). Arthropods are classified as [Subclass] Apterygial including: Archaeognatha (Order: Microcoryphia), three-pronged bristletails (Order: Thysanura). [Subclass] Pterygota including : Biting and Sucking lice (Order: Phthiraptera), Booklice and Bark lice (Order: Psocoptera) Cockroaches (Order: Blattodea), Dragonflies and Damselflies (Order: Odonata), Earwigs (Order: Dermaptera), Grasshoppers and Crickets (Order: Orthoptera), Praying Mantids (Order: Mantodea), Mayflies (Order: Ephemeroptera), Stick insects and Leaf insects (Order: Phasmatodea), Stoneflies (Order: Plecoptera), Termites (Previously Order: Isoptera but now part of Order: Blattodea), Thrips (Order: Thysanoptera), True Bugs (Order: Hemiptera), Web-spinners (Order: Embioptera), Zorapterans (Order: Zoraptera), Alderflies, Dobsonflies & Fishflies (Order: Megaloptera), Bees, Wasps and Ants (Order: Hymenoptera), Beetles (Order: Coleoptera), Butterflies and Moths (Order: Lepidoptera), Caddisflies (Order: Trichoptera), Fleas (Order: Siphonaptera), Flies (Order: Diptera), Lacewings, Antlions & Mantidflies (Order: Neuroptera), Scorpionflies (Order: Mecoptera), Snakeflies (Order: Raphidioptera), Strepsipterans (Order: Strepsiptera). Over one million species of insects have been discovered and described but it is estimated that there may be as many as 10 million species on earth. Insects have been around for more than 350 million years, longer than the dinosaurs and flowering plants (Figure. 1).

Fur loss syndrome and lice infestations observed on arctic foxes in central Nunavut, Canada.

As temperatures in the circumpolar north continue to warm, shifts in species distribution and the breakdown of environmental barriers for arthropods may impact the diversity and distribution of ectoparasites in Arctic ecosystems. In May 2019, fur loss over the neck and shoulders was observed on arctic foxes in a terrestrial arctic ecosystem (Karrak Lake) in central Nunavut, Canada. This was inconsistent with normal patterns of shedding winter fur and had not been observed on arctic foxes in this population over the previous 19 years of live-trapping. Operculated eggs attached to hair shafts were collected from one affected fox. Conventional PCR using universal louse primers targeting conserved regions of mitochondrial 12S and 16S rDNA confirmed that the eggs belonged to the order Phthiraptera. Sequencing results were inconclusive at the species level. Further investigation revealed a single unpublished report of an arctic fox with similar fur loss trapped on mainland Nunavut, in 1997. Adult lice collected from this fox were identified as sucking lice (potentially from the genus Linognathus). Our findings emphasize the need for further monitoring and have significant implications for trappers and wildlife management, as infestations negatively impact the pelt quality of these important furbearers.

The first description of the nymphal stages of Hoplopleura longula (Psocodea: Anoplura: Hoplopleuridae) from the harvest mouse Micromys minutus (Rodentia: Muridae)

Despite the widespread belief that an extensive body of knowledge exists for the sucking lice (Anoplura), some of their common, Eurasian or even cosmopolitan species still lack complete taxonomic descriptions, especially those for their nymphal stages. This applies especially to the most common rodent parasites: the lice of the genus Hoplopleura. In Europe, only two of the five most common Hoplopleura species have full taxonomic characteristics with a description of the nymphal stages. This study enriches the current state of knowledge for another species, Hoplopleura longula and presents the first description of its nymphal stages. The study includes five rare louse specimens (two nymphs I, one nymph II, two nymphs III) of H. longula collected from 63 Eurasian harvest mice Micromys minutus. The collected lice were fixed and preserved in 70% ethyl alcohol solution and then placed in polyvinyl-lactophenol to form total preparations. Only two of the five species found in Eurasia (H. acanthopus, H. affinis, H. captiosa, H. edentula and H. longula) have been given full taxonomic descriptions, including immature stages. This paper presents a description of the nymphal stages of H. longula (described for the first time).

Two New Species of Sucking Lice (Psocodea: Phthiraptera: Hoplopleuridae) from Chestnut Mice, Pseudomys gracilicaudatus and Pseudomys nanus (Rodentia: Muridae), in Australia

We describe two new species of sucking lice in the genus Hoplopleura Enderlein, 1904 (Psocodea: Phthiraptera: Hoplopleuridae) from Australia: Hoplopleura gracilicaudatusa n. sp. from the eastern chestnut mouse Pseudomys gracilicaudatus (Gould) (Rodentia: Muridae), and Hoplopleura nanusa n. sp. from the western chestnut mouse Pseudomys nanus (Gould) (Rodentia: Muridae). Pseudomys Gray is the most speciose genus of rodents endemic to Australia with 24 species; however, only two Pseudomys species have been reported previously to be hosts of sucking lice. The description of the new species in the present study doubles the number of sucking louse species known to parasitize Pseudomys mice and increases the total number of sucking louse species known from endemic Australian rodents from 21 to 23. Pseudomys gracilicaudatus and P. nanus are closely related murines that diverged ~1 MYA with distinct and widely separated extant geographic distributions. The two new Hoplopleura species described in the present study share some morphological characters and likely co-evolved and co-speciated with their chestnut mouse hosts.

Eight New Species of Sucking Lice (Psocodea: Phthiraptera) From Endemic Murine Rodents in Australia and an Updated Identification Key

Based on a comprehensive study of museum specimens, eight new species of sucking lice of the genus Hoplopleura Enderlein, 1904 (Psocodea: Phthiraptera: Hoplopleuridae), are described from six genera of Australian Old Endemic rodents: Conilurus Ogilby, 1838 (Rodentia: Muridae), Leggadina Thomas, 1910 (Rodentia: Muridae), Leporillus Thomas, 1906 (Rodentia: Muridae), Mesembriomys Palmer, 1906 (Rodentia: Muridae), Pogonomys Milne-Edwards, 1877 (Rodentia: Muridae), and Xeromys Thomas, 1889 (Rodentia: Muridae). The description of these new species increases the number of sucking louse species from endemic Australian rodents from 13 to 21 and extends the records of sucking lice to all of the 14 genera of endemic rodents in Australia. Our results show that sucking lice are much more diverse among rodents in Australia than previously known. Furthermore, the Australian Hoplopleura species are host specific—each Hoplopleura species, including the eight new species described in the present study, parasitizes only a single host species, except Hoplopleura irritans Kuhn and Ludwig, 1967 (Psocodea: Phthiraptera: Hoplopleuridae) and Hoplopleura melomydis Weaver, 2017 (Psocodea: Phthiraptera: Hoplopleuridae), each of which is found on two host species. An updated dichotomous key for identifying Australian Hoplopleura species is included.

Variation of mitochondrial minichromosome composition in Hoplopleura lice (Phthiraptera: Hoplopleuridae) from rats

Background The family Hoplopleuridae contains at least 183 species of blood-sucking lice, which widely parasitize both mice and rats. Fragmented mitochondrial (mt) genomes have been reported in two rat lice (Hoplopleura kitti and H. akanezumi) from this family, but some minichromosomes were unidentified in their mt genomes. Methods We sequenced the mt genome of the rat louse Hoplopleura sp. with an Illumina platform and compared its mt genome organization with H. kitti and H. akanezumi. Results Fragmented mt genome of the rat louse Hoplopleura sp. contains 37 genes which are on 12 circular mt minichromosomes. Each mt minichromosome is 1.8–2.7 kb long and contains 1–5 genes and one large non-coding region. The gene content and arrangement of mt minichromosomes of Hoplopleura sp. (n = 3) and H. kitti (n = 3) are different from those in H. akanezumi (n = 3). Phylogenetic analyses based on the deduced amino acid sequences of the eight protein-coding genes showed that the Hoplopleura sp. was more closely related to H. akanezumi than to H. kitti, and then they formed a monophyletic group. Conclusions Comparison among the three rat lice revealed variation in the composition of mt minichromosomes within the genus Hoplopleura. Hoplopleura sp. is the first species from the family Hoplopleuridae for which a complete fragmented mt genome has been sequenced. The new data provide useful genetic markers for studying the population genetics, molecular systematics and phylogenetics of blood-sucking lice.

Variation of mitochondrial minichromosome composition in Hoplopleura lice (Phthiraptera: Hoplopleuridae) from rats

Background: The family Hoplopleuridae contains at least 183 species of blood-sucking lice, which widely parasitize both mice and rats. Fragmented mitochondrial (mt) genomes have been reported in two rat lice (Hoplopleura kitti and H. akanezumi) from this family, but some minichromosomes were unidentified in their mt genomes.Methods: We sequenced the mt genome of the rat louse Hoplopleura sp. with an Illumina platform and compared its mt genome organization with H. kitti and H. akanezumi.Results: Fragmented mt genome of the rat louse Hoplopleura sp. contains 37 genes which are on 12 circular mt minichromosomes. Each mt minichromosome is 1.8–2.7 kb long and contains 1–5 genes and one large non-coding region. The gene content and arrangement of mt minichromosomes of Hoplopleura sp. (n = 3) and H. kitti (n = 3) are different from those in H. akanezumi (n = 3). Phylogenetic analyses based on the deduced amino acid sequences of the eight protein-coding genes showed that the Hoplopleura sp. was more closely related to H. akanezumi than to H. kitti, and then they formed a monophyletic group.Conclusions: Comparison among the three rat lice revealed variation in the composition of mt minichromosomes within the genus Hoplopleura. Hoplopleura sp. is the first species from the family Hoplopleuridae for which a complete fragmented mt genome has been sequenced. The new data provide useful genetic markers for studying the population genetics, molecular systematics and phylogenetics of blood-sucking lice.