A simple rule governs the evolution and development of hominin tooth size

The variation in molar tooth size in humans and our closest relatives (hominins) has strongly influenced our view of human evolution. The reduction in overall size and disproportionate decrease in third molar size have been noted for over a century, and have been attributed to reduced selection for large dentitions owing to changes in diet or the acquisition of cooking1, 2. The systematic pattern of size variation along the tooth row has been described as a ‘morphogenetic gradient’ in mammal, and more specifically hominin, teeth since Butler3 and Dahlberg4. However, the underlying controls of tooth size have not been well understood, with hypotheses ranging from morphogenetic fields3 to the clone theory5. In this study we address the following question: are there rules that govern how hominin tooth size evolves? Here we propose that the inhibitory cascade, an activator–inhibitor mechanism that affects relative tooth size in mammals6, produces the default pattern of tooth sizes for all lower primary postcanine teeth (deciduous premolars and permanent molars) in hominins. This configuration is also equivalent to a morphogenetic gradient, finally pointing to a mechanism that can generate this gradient. The pattern of tooth size remains constant with absolute size in australopiths (including Ardipithecus, Australopithecus and Paranthropus). However, in species of Homo, including modern humans, there is a tight link between tooth proportions and absolute size such that a single developmental parameter can explain both the relative and absolute sizes of primary postcanine teeth. On the basis of the relationship of inhibitory cascade patterning with size, we can use the size at one tooth position to predict the sizes of the remaining four primary postcanine teeth in the row for hominins. Our study provides a development-based expectation to examine the evolution of the unique proportions of human teeth

Factors associated with diversity, quantity and zoonotic potential of ectoparasites on urban mice and voles

Wild rodents are important hosts for tick larvae but co-infestations with other mites and insects are largely neglected. Small rodents were trapped at four study sites in Berlin, Germany, to quantify their ectoparasite diversity. Host-specific, spatial and temporal occurrence of ectoparasites was determined to assess their influence on direct and indirect zoonotic risk due to mice and voles in an urban agglomeration. Rodent-associated arthropods were diverse, including 63 species observed on six host species with an overall prevalence of 99%. The tick Ixodes ricinus was the most prevalent species, found on 56% of the rodents. The trapping location clearly affected the presence of different rodent species and, therefore, the occurrence of particular host-specific parasites. In Berlin, fewer temporary and periodic parasite species as well as non-parasitic species (fleas, chiggers and nidicolous Gamasina) were detected than reported from rural areas. In addition, abundance of parasites with low host-specificity (ticks, fleas and chiggers) apparently decreased with increasing landscape fragmentation associated with a gradient of urbanisation. In contrast, stationary ectoparasites, closely adapted to the rodent host, such as the fur mites Myobiidae and Listrophoridae, were most abundant at the two urban sites. A direct zoonotic risk of infection for people may only be posed by Nosopsyllus fasciatus fleas, which were prevalent even in the city centre. More importantly, peridomestic rodents clearly supported the life cycle of ticks in the city as hosts for their subadult stages. In addition to trapping location, season, host species, body condition and host sex, infestation with fleas, gamasid Laelapidae mites and prostigmatic Myobiidae mites were associated with significantly altered abundance of I. ricinus larvae on mice and voles. Whether this is caused by predation, grooming behaviour or interaction with the host immune system is unclear. The present study constitutes a basis to identify interactions and vector function of rodent-associated arthropods and their potential impact on zoonotic diseases

VALITEST: Validation of diagnostic tests to support plant health

peer reviewedVALITEST is an EU-funded project built to improve the reliability of diagnostic tests performed in plant health laboratories across the European and Mediterranean region. The project is undertaken by a consortium of 16 partners composed of research institutions, private companies (such as diagnostic kit providers), national plant protection organizations and one intergovernmental organization (EPPO). Current harmonized procedures for the validation and organization of test performance studies will be improved based on the experience gained from the project and by including appropriate statistical approaches, by adapting the process for new promising technologies (e.g. high-throughput sequencing) and by providing new guidelines for the production of reference materials for validation studies. The project will provide a more complete and precise description of the performance of 82 diagnostic tests targeting 11 pests of interest for stakeholders of the region. It will also tackle the need for proficient users by developing a horizontal approach for the evaluation of laboratories’ proficiency and by organizing training activities on the concept of validation. The outcomes of the project will stimulate, optimize and strengthen the interactions between stakeholders in plant health for better diagnostics and lay the foundations for structuring the quality and the commercial offers for plant health diagnostics tools thanks to the creation of a dedicated association and a quality charter