A dynamic model for the evolution of sabrecat predatory bite mechanics

The ability of sabretoothed felids to achieve sufficiently high bite forces for predation at extreme gape angles has been the subject of decades of debate. Previous studies have indicated that bite forces in derived sabretoothed felids would have been low, but that they were probably augmented by head depressing muscles. However, bite mechanics is a dynamic process, and mechanical properties change with changes in gape angles. In this study, I present the first comprehensive model of bite mechanics, vector angles, and forces about the temporomandibular joint at gape angles from occlusion to maximal inferred gape in sabretoothed felids. Primitive sabrecats (Machairodus, Paramachairodus) appear broadly comparable to extant large felids (Panthera, Puma), but derived sabrecats in the groups Homotherini (Amphimachairodus, Homotherium, Xenosmilus) and Smilodontini (Megantereon, Smilodon) are often substantially different from either of the former. The ability of the mandibular adductors to generate torque changes with gape angle, indicating that previous models fail to capture potentially important differences in bite function. Inferred muscle sizes and the angles of effective torque from individual adductor fibres in derived sabrecats are different from those of primitive sabrecats and extant large felids, but they had evolved a number of compensatory adaptations for maximizing force output at the canine and carnassial, primarily changes in muscle fibre angles and more compact crania. Inferred outforces at the canines and carnassials were comparable amongst all groups at low gape angles, but at extreme gape angles outforces would have been low, supporting previous hypotheses of head flexor contribution during initial stages of the killing bite in sabrecats. Mandibular adduction in extant carnivores is a complicated pattern of differences in twitch tension and electromyographical activity at different gape angles, and inference of maximal isotonic bite forces from reconstructed mandibular adductor sizes in fossils will give estimates primarily suitable for comparative purposes. Potentially, derived sabrecats could have evolved differences from extant felids in adductor histochemistry or pinnation angle of individual fibres. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 220–242.     

Pleistocene Extinctions and the Perceived Morphofunctional Structure of the Neotropical Felid Ensemble

The felid Neotropical ensemble has experienced important changes from the Pleistocene to the present, the extinction of sabertooth cats being the most significant. Assuming that the morphofunctional structure of the Neotropical felid ensemble was maximally expressed when machairodontines were present, we added specimens of Smilodon fatalis and S. populator to a morphological dataset inclusive of all extant species of Neotropical felids to explore the hypothetical effect of extinction of machairodontines on the perceived morphofunctional structure of the ensemble. We studied 321 specimens of 12 extant species of Neotropical felids plus S. populator and S. fatalis by measuring 123 skull and postcranial morphofunctional variables. We used Principal Component Analysis to find morphofunctional patterns of the skull, postcranium, and both combined (with and without correction for size) of both ensembles, past (with Smilodon) and present (with Smilodon lost to extinction). Canonical Phylogenetic Ordination was performed to assess the degree of phylogenetic influence on this morphospace. We also explored the effect of including homotherines in the Pleistocene guild by including specimens of North American Homotherium serum. Size was the principal factor structuring ensembles. Important morphological characters were associated to ecological performance of species. A pattern of bodily proportions was apparent: more stout species with larger skull, longer rostrum, stronger bite force, and longer pectoral crests, versus gracile, jumping species with opposing characters. The felid morphospace shrank after the extinction of Smilodon and Homotherium, but the configuration of the portion of space containing extant felids remained stable. This pattern is associated with deep phylogenetic roots.     

Histopathology of Okra and Ridgeseed Spurge Infected with Meloidodera charis

Histological observations of okra Abelomoschus esculentus ''Clemson Spineless'' and ridgeseed spurge Euphorbia glyptosperma (a common weed) infected with Meloidodera charis Hopper, indicated that the juvenile nematode penetrated the roots intercellularly. Within 5 days after plant emergence the nematode positioned its body in the cortical tissue parallel to the vascular system. By 10 days after plant emergence the juvenile had extended its head into the vascular system and initiated giant cell formation, generally in protophloem tissue. Giant cells were one celled and usually multi-nucleate. Eggs were observed in the female body 30 days after plants emerged and juveniles were found within the female body by 40 days. Nematode development progressed equally in the root system of either host plant. Generally, throughout the nematode''s life cycle its entire body remained inside the cortical tissue of okra. In ridgeseed spurge, however, the posterior portion of the female erupted through the host epidermis as early as 15 days after plant emergence; only the head and neck remained embedded in the host. The nematode caused extensive tissue disruption in the cortical and vascular system of both plant species. Corn, Zea mays, was another host of the nematode.     

An inventory of British remains of Homotherium (Mammalia,Carnivora, Felidae), with special reference to the material from Kent's Cavern

The genus Homotherium, while wide ranging in Eurasia, has only been considered a sporadic component of the British Pleistocene fauna. The Early Pleistocene Homotherium crenatidens and the Middle to Late Pleistocene Homotherium latidens have however held a prominent position in the annals of the 19th century British geology and the discussion of the antiquity of man. As many of the UK sites containing Homotherium were first investigated over a hundred years ago, the literature is quite confused on the question of what was found and where it was finally curated. An attempt has been made to track down all specimens of British Homotherium mentioned in the literature and to give their current location. As part of this study, I correctly identify for the first time all the Homotherium canines from Kent's Cavern pictured in the famous Plate F of MacEnery. Additionally, a single Homotherium incisor, found by MacEnery, is deduced from the study of his surviving writings and images.     

An almost complete skeleton of Metailurus parvulus (Carnivora, Felidae) from the late Miocene of Kerassia (Northern Euboea, Greece)

We describe a partial skeleton of Metailurus parvulus from the Turolian site of Kerassia 1 (Northern Euboea, Greece). The material, which consists of a mandible, the anterior and posterior limb-bone elements, some sternal bones and some vertebrae, is the most complete known of this species. The dental material is compared to specimens from Pikermi and Chomateri (Greece), and China. The limb-bones available offer us the possibility to discuss the status of some previously described specimens from Pikermi. The limb proportions indicate that M. parvulus had elongated posterior limbs relative to the anterior ones, which reflects developed jumping skills. M. parvulus had moderately developed cursorial abilities, intermediate between open and closed habitat felids, and probably frequented primarily relatively open woodlands.     

Mid-Pliocene Carnivora from the Woranso-Mille Area,Afar Region,Ethiopia

The Woranso-Mille paleontological study area, located in the central Afar region of Ethiopia, is one of the most important Pliocene sites in eastern Africa. Since the Woranso-Mille Research Project began its investigation in 2005, more than 7,500 mammalian fossils, including hominins, have been collected from 80 vertebrate localities. This paper provides a preliminary assessment of the Woranso-Mille carnivoran record, a record that is of great interest given the high level of species richness of African carnivorans during the middle Pliocene. Craniodental and postcranial material of canids, lutrine mustelids, viverrids, herpestids, machairodontine and feline felids, and hyaenids has been recovered. Thus, this diverse fauna includes not only the largest carnivorans from this time period (e.g., Enhydriodon and Homotherium), but also some of the smallest, including mongooses, civets, genets, and felids, some of which represent new species. However, the diversity of small taxa does not yet approach that found in the roughly contemporaneous Upper Laetolil Beds of Tanzania. In contrast, lutrine mustelids are better represented at Woranso-Mille than at Kanapoi (Kenya) or Laetoli (Tanzania), which is to be expected given the diversity of habitats represented at these sites. While more material from these sites and others are necessary to truly understand the increased diversity within the early to middle Pliocene eastern African carnivoran guild, it is clear that the material from Woranso-Mille has the potential to fill many of the gaps in our knowledge of carnivorans during this time period.     

Ecomorphology of the African felid ensemble: The role of the skull and postcranium in determining species segregation and assembling history

Morphology of extant felids is regarded as highly conservative. Most previous studies have focussed on skull morphology, so a vacuum exists about morphofunctional variation in postcranium and its role in structuring ensembles of felids in different continents. The African felid ensemble is particularly rich in ecologically specialized felids. We studied the ecomorphology of this ensemble using 31 cranial and 93 postcranial morphometric variables measured in 49 specimens of all 10 African species. We took a multivariate approach controlling for phylogeny, with and without body size correction. Postcranial and skull + postcranial analyses (but not skull‐only analyses) allowed for a complete segregation of species in morphospace. Morphofunctional factors segregating species included body size, bite force, zeugopodial lengths and osteological features related to parasagittal leg movement. A general gradient of bodily proportions was recovered: lightly built, long‐legged felids with small heads and weak bite forces vs. the opposite. Three loose groups were recognized: small terrestrial felids, mid‐to‐large sized scansorial felids and specialized Acinonyx jubatus and Leptailurus serval. As predicted from a previous study, the assembling of the African felid ensemble during the Plio‐Pleistocene occurred by the arrival of distinct felid lineages that occupied then vacant areas of morphospace, later diversifying in the continent.     

Directional selection in the evolution of elongated upper canines in clouded leopards and sabre‐toothed cats

Extremely developed or specialized traits such as the elongated upper canines of extinct sabre‐toothed cats are often not analogous to those of any extant species, which limits our understanding of their evolutionary cause. However, an extant species may have undergone directional selection for a similar extreme phenotype. Among living felids, the clouded leopard, Neofelis nebulosa, has exceptionally long upper canines for its body size. We hypothesized that directional selection generated the elongated upper canines of clouded leopards in a manner similar to the process in extinct sabre‐toothed cats. To test this, we developed an approach that compared the effect of directional selection among lineages in a phylogeny using a simulation of trait evolution and approximate Bayesian computation. This approach was applied to analyse the evolution of upper canine length in the Felidae phylogeny. Our analyses consistently showed directional selection favouring longer upper canines in the clouded leopard lineage and a lineage leading to the sabre‐toothed cat with the longest upper canines, Smilodon. Most of our analyses detected an effect of directional selection for longer upper canines in the lineage leading to another sabre‐toothed cat, Homotherium, although this selection may have occurred exclusively in the primitive species. In all the analyses, the clouded leopard and Smilodon lineages showed comparable directional selection. This implies that clouded leopards share a selection advantage with sabre‐toothed cats in having elongated upper canines.     

The Tribolium ortholog of knirps and knirps-related is crucial for head segmentation but plays a minor role during abdominal patterning

Segment formation in the long germ insect Drosophila is dominated by overlapping gap gene domains in the syncytial blastoderm. In the short germ beetle Tribolium castaneum abdominal segments arise from a cellular growth zone, implying different patterning mechanisms. We describe here the single Tribolium ortholog of the Drosophila genes knirps and knirps-related (called Tc-knirps). Tc-knirps expression is conserved during head patterning and at later stages. However, posterior Tc-knirps expression in the ectoderm is limited to a stripe in A1, instead of a broad abdominal domain covering segment primordia A2-A5 as in Drosophila. Tc-knirps RNAi yields only mild defects in the abdomen, at a position posterior to the abdominal Tc-knirps domain. In addition, Tc-knirps RNAi larvae lack the antennal and mandibular segments. These defects are much more severe than the head defects caused by combined inactivation of Dm-knirps and Dm-knirps-related. Our findings support the notion that the role of gap gene homologs in abdominal segmentation differs fundamentally in long and short germ insects. Moreover, the pivotal role of Tc-knirps in the head suggests an ancestral role for knirps as head patterning gene. Based on this RNAi analysis, Tc-knirps functions neither in the head nor the abdomen as a canonical gap gene.     

β-catenin plays a central role in setting up the head organizer in hydra

In an adult hydra the head organizer, located in the hypostome, is constantly active in maintaining the structure of the animal in the context of its steady state tissue dynamics. Several Wnt genes, TCF, and elevated levels of β-catenin are expressed in the hypostome as well as during the formation of a new organizer region in developing buds suggesting they play a role in the organizer. Transgenic hydra were generated in which a modified hydra β-catenin gene driven by an actin promoter is continuously expressed at a high level throughout the animal. These animals formed heads and secondary axes in multiple locations along the body column. Transplantation experiments indicate they have a high and stable level of head organizer activity throughout the body columns. However, none of the Wnt genes are expressed in the body columns of these transgenic animals. Further, in alsterpaullone-treated animals, which results in a transient rise in head organizer activity throughout the body column, the time of expression of the Wnt genes is much shorter than the time of the elevated level of head inducing activity. These results for the first time provide direct functional evidence that β-catenin plays a crucial role in the maintenance and activity of the head organizer and suggest that Wnt ligands may be required only for the initiation but not in maintenance of the organizer in Hydra.     

Functional analysis of Scr during embryonic and post-embryonic development in the cockroach, Periplaneta americana

The cockroach, Periplaneta americana represents a basal insect lineage that undergoes the ancestral hemimetabolous mode of development. Here, we examine the embryonic and post-embryonic functions of the hox gene Scr in Periplaneta as a way of better understanding the roles of this gene in the evolution of insect body plans. During embryogenesis, Scr function is strictly limited to the head with no role in the prothorax. This indicates that the ancestral embryonic function of Scr was likely restricted to the head, and that the posterior expansion of expression in the T1 legs may have preceded any apparent gain of function during evolution. In addition, Scr plays a pivotal role in the formation of the dorsal ridge, a structure that separates the head and thorax in all insects. This is evidenced by the presence of a supernumerary segment that occurs between the labial and T1 segments of RNAiScr first nymphs and is attributed to an alteration in engrailed (en) expression. The fact that similar Scr phenotypes are observed in Tribolium but not in Drosophila or Oncopeltus reveals the presence of lineage-specific variation in the genetic architecture that controls the formation of the dorsal ridge. In direct contrast to the embryonic roles, Scr has no function in the head region during post-embryogenesis in Periplaneta, and instead, strictly acts to provide identity to the T1 segment. Furthermore, the strongest Periplaneta RNAiScr phenotypes develop ectopic wing-like tissue that originates from the posterior region of the prothoracic segment. This finding provides a novel insight into the current debate on the morphological origin of insect wings.     

Divergent and conserved roles of extradenticle in body segmentation and appendage formation, respectively, in the cricket Gryllus bimaculatus

The cricket Gryllus bimaculatus is a typical hemimetabolous intermediate germ insect, in which the processes of segmentation and appendage formation differ from those in Drosophila, a holometabolous long germ insect. In order to compare their developmental mechanisms, we have focused on Gryllus orthologs of the Drosophila developmental regulatory genes and studied their functions. Here, we report a functional analysis of the Gryllus ortholog of extradenticle (Gb′exd) using embryonic and parental RNA interference (RNAi) techniques. We found the following: (1) RNAi suppression of Gb′exd results in the deletion or fusion of body segments. Especially the head was often very severely affected. This gap-like phenotype may be related to reduced expression of the gap genes hunchback and Krüppel in early RNAi germbands. (2) In the appendages, several segments (podomeres) were fused. (3) Head appendages including the antenna were transformed to a leg-like structure consisting of at least one proximal podomere as well as several tarsomeres. The defects in appendages are reminiscent of the phenotype caused by large exd clones in Drosophila antennal discs. These findings led us to the conclusion that (1) Gb′exd is required for segment patterning in the gnathal to abdominal region, acting in a gap gene-like manner in the anterior region. (2) Gb′exd plays important roles in formation of the appendages and the determination of their identities, acting as a regulatory switch that chooses between the fates of head appendages versus the appendage ground state. Although functions of Gb′exd in appendage patterning appear fundamentally conserved between Gryllus and Drosophila, its role in body segmentation may differ from that of Drosophila exd.     

The mitochondrial genome of the chimpanzee louse,Pediculus schaeffi: insights into the process of mitochondrial genome fragmentation in the blood-sucking lice of great apes

Background

Blood-sucking lice in the genera Pediculus and Pthirus are obligate ectoparasites of great apes. Unlike most bilateral animals, which have 37 mitochondrial (mt) genes on a single circular chromosome, the sucking lice of humans have extensively fragmented mt genomes. The head louse, Pediculus capitis, and the body louse, Pe. humanus, have their 37 mt genes on 20 minichromosomes. The pubic louse, Pthirus pubis, has its 34 mt genes known on 14 minichromosomes. To understand the process of mt genome fragmentation in the sucking lice of great apes, we sequenced the mt genome of the chimpanzee louse, Pe. schaeffi, and compared it with the three human lice.

Results

We identified all of the 37 mt genes typical of bilateral animals in the chimpanzee louse; these genes are on 18 types of minichromosomes. Seventeen of the 18 minichromosomes of the chimpanzee louse have the same gene content and gene arrangement as their counterparts in the human head louse and the human body louse. However, five genes, cob, trnS₁, trnN, trnE and trnM, which are on three minichromosomes in the human head louse and the human body louse, are together on one minichromosome in the chimpanzee louse.

Conclusions

Using the human pubic louse, Pt. pubis, as an outgroup for comparison, we infer that a single minichromosome has fragmented into three in the lineage leading to the human head louse and the human body louse since this lineage diverged from the chimpanzee louse ~6 million years ago. Our results provide insights into the process of mt genome fragmentation in the sucking lice in a relatively fine evolutionary scale.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1843-3) contains supplementary material, which is available to authorized users.     

Waterborne toxoplasmosis - Recent developments

Humans become infected with Toxoplasma gondii mainly by ingesting uncooked meat containing viable tissue cysts or by ingesting food or water contaminated with oocysts from the feces of infected cats. Circumstantial evidence suggests that oocyst-induced infections in humans are clinically more severe than tissue cyst-acquired infections. Until recently, waterborne transmission of T. gondii was considered uncommon, but a large human outbreak linked to contamination of a municipal water reservoir in Canada by wild felids and the widespread infection of marine mammals in the USA provided reasons to question this view. The present paper examines the possible importance of T. gondii transmission by water.     

Aphelenchoides microstylus n. sp. and Seinura onondagensis n. sp. (Nemata: Aphelenchina) from New York

Aphelenchoides microstylus n. sp. and Seinura onondagensis n. sp., a nematode predator, are described from dead Scots pine (Pinus sylvestris L.) in Onondaga County, New York. Females of A. microstylus are 370 to 485 µm long. The body is slender and tapers posteriorly to an amucronate, pointed terminus. The head is continuous with the body, and lips bear a stylet guide. Diagnostic characters of females are three incisures in the lateral field, a short stylet (6-7.5 µm) with small basal knobs, a single row of oocytes, and a long postuterine sac (25-50 µm). Males are characterized by small spicules (10-11µm); two pairs of post-anal, subventral papillae; and a single row of spermatocytes. A bursa and gubernaculum are absent. Seinura onondagensis females are characterized by a body of moderate length (475-595 µm), finely annulated cuticle, and a slightly set-off head. Diagnostic characters are four incisures in the lateral field, long stylet without basal knobs (17-22 µm), single row of oocytes, and presence of a postuterine sac (14-38 µm). Males are unknown. The monospecific genus Indaphelenchus is proposed as a synonym of Seinura, and S. siddiqii n. comb. is proposed for the only species, I. siddiqii.     

A Case of Diphyllobothrium nihonkaiense Infection as Confirmed by Mitochondrial COX1 Gene Sequence Analysis

Diphyllobothrium nihonkaiense has been reported in Korea as Diphyllobothrium latum because of their close morphologic resemblance. We have identified a human case of D. nihonkaiense infection using the mitochondrial cytochrome c oxidase subunit I (cox1) gene sequence analysis. On 18 February 2012, a patient who had consumed raw fish a month earlier visited our outpatient clinic with a long tapeworm parasite excreted in the feces. The body of the segmented worm was 2 m long and divided into the scolex (head) and proglottids. It was morphologically close to D. nihonkaiense and D. latum. The cox1 gene analysis showed 99.4% (340/342 bp) homology with D. nihonkaiense but only 91.8% (314/342 bp) homology with D. latum. The present study suggested that the Diphyllobothrium spp. infection in Korea should be analyzed with specific DNA sequence for an accurate species identification.     

Definition and review of the lancangjiang species group of the termitophilous genus Orthogonius Macleay, 1825 (Coleoptera,Carabidae, Orthogoniini)

The lancanjiang species group of the termitophilous ground beetle genus Orthogonius Macleay, 1825, is defined and reviewed. This group is characterized by the black and rather elongate body, dense punctation on head and elytra, long and slender appendages, thin fore tibiae, and elytral interval 3 without a subapical setiferous pore. To date, the lancanjiang species group is composed of four species and one subspecies, including three new species and one new subspecies which are described in the present paper: O. macrophthalmus sp. n. (northern Vietnam), O. euthyphallus sp. n. (southern Vietnam), O. euthyphallus bolavenensis ssp. n. (southern Laos) and O. carinatus sp. n. (northern Laos). A distribution map and a key to all species of this group are also provided.