Directionally asymmetric animals generally exhibit no variation in handedness of whole-body architecture. In contrast, reversed chirality in both coil and entire anatomy has frequently evolved in snails. We demonstrate a nonrandom pattern and deterministic process of chiral evolution, as predicted by the following hypothesis. Bimodal shell shapes are associated with discrete mating behaviors in hermaphroditic pulmonates. Flat-shelled species mate reciprocally, face-to-face. This sexual symmetry prevents interchiral mating because genitalia exposed by a sinistral on its left side cannot be joined with those exposed by a dextral on its right. Thus, selection against the chiral minority, resulting from mating disadvantage, stabilizes chiral monomorphism. Tall-shelled species mate nonreciprocally: the 'male' copulates by mounting the 'female's' shell, mutually aligned in the same direction. This sexual asymmetry permits interchiral copulation with small behavioral adjustments. Therefore, the positive frequency-dependent selection is relaxed, and reversal alleles persist longer in populations of tall-shelled species. We verified both the assumption and the prediction of this hypothesis: significantly lower interchiral mating success in a low-spired species and higher chiral evolution rate in high-spired taxa. Sexual asymmetry is the key to understanding the accelerated chiral evolution in high-spired pulmonates.

External asymmetry found in diverse animals bears critical functions to fulfil ecological requirements. Some snail-eating arthropods exhibit directional asymmetry in their feeding apparatus for foraging efficiency because dextral (clockwise) species are overwhelmingly predominant in snails. Here, we show convergence of directional asymmetry in the dentition of snail-eating vertebrates. We found that snakes in the subfamily Pareatinae, except for non-snail-eating specialists, have more teeth on the right mandible than the left. In feeding experiments, a snail-eating specialist Pareas iwasakii completed extracting a dextral soft body faster with fewer mandible retractions than a sinistral body. The snakes failed in holding and dropped sinistral snails more often owing to behavioural asymmetry when striking. Our results demonstrate that symmetry break in dentition is a key innovation that has opened a unique ecological niche for snake predators.

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How speciation genes can spread in a population is poorly understood. In land snails, a single gene for left–right reversal could be responsible for instant speciation, because dextral and sinistral snails have difficulty in mating. However, the traditional two-locus speciation model predicts that a mating disadvantage for the reversal should counteract this speciation. In this study, we show that specialized snake predation of the dextral majority drives prey speciation by reversal. Our experiments demonstrate that sinistral Satsuma snails (Stylommatophora: Camaenidae) survive predation by Pareas iwasakii (Colubroidea: Pareatidae). Worldwide biogeography reveals that stylommatophoran snail speciation by reversal has been accelerated in the range of pareatid snakes, especially in snails that gain stronger anti-snake defense and reproductive isolation from dextrals by sinistrality. Molecular phylogeny of Satsuma snails further provides intriguing evidence of repetitive speciation under snake predation. Our study demonstrates that a speciation gene can be fixed in populations by positive pleiotropic effects on survival.

The unique nature of body handedness, which is distinct from the anteroposterior and dorsoventral polarities, has been attracting growing interest in diverse biological disciplines. Recent research progress on the left-right asymmetry of animal development has focused new attention on the mechanisms underlying the development and evolution of invertebrate handedness. This exploratory review of currently available information illuminates the prospective value of Drosophila and pulmonate snails for innovative new research aimed at elucidating these mechanisms. For example, findings in Drosophila and snails suggest that an actin filament-dependent mechanism may be evolutionarily conserved in protostomes. The polarity conservation of primary asymmetry across most metazoan phyla, which visceral handedness represents, indicates developmental constraint and purifying selection as possible but unexplored mechanisms. Comparative studies using Drosophila and snails, which have the great advantages of using genetic and evolutionary approaches, will accelerate our understanding of the mechanisms governing the conservation and diversity of animal handedness. Developmental Dynamics 237: 3497-3515, 2008.

Diverse animals exhibit left–right asymmetry in development. However, no example of dimorphism for the left–right polarity of development (whole‐body enantiomorphy) is known to persist within natural populations. In snails, whole‐body enantiomorphs have repeatedly evolved as separate species. Within populations, however, snails are not expected to exhibit enantiomorphy, because of selection against the less common morph resulting from mating disadvantage. Here we present a unique example of evolutionarily stable whole‐body enantiomorphy in snails. Our molecular phylogeny of South‐east Asian tree snails in the genus Amphidromus indicates that enantiomorphy has likely persisted as the ancestral state over a million generations. Enantiomorphs have continuously coexisted in every population surveyed spanning a period of 10 years. Our results indicate that whole‐body enantiomorphy is maintained within populations opposing the rule of directional asymmetry in animals. This study implicates the need for explicit approaches to disclosure of a maintenance mechanism and conservation of the genus.

We report a case of severe acute respiratory syndrome coronavirus 2 and Legionella co-infection manifesting as pneumonia with gastrointestinal symptoms. The case highlights the importance of differential diagnosis during the COVID-19 pandemic, so we do not miss the opportunity to diagnose other treatable causes of disease with similar symptoms.

BackgroundIn multidrug regimens, including an intravenous aminoglycoside (e.g. amikacin [AMK]) is recommended for difficult-to-treat non-tuberculous mycobacterial (NTM) lung diseases. We aimed to evaluate the efficacy, safety, and feasibility of inhaled AMK therapy in patients with difficult-to-treat NTM lung diseases in a retrospective chart review.MethodsThe study population consisted of patients with NTM lung diseases who received combination therapy, including inhaled AMK therapy, at Keio University Hospital (Tokyo, Japan), from January 2014 through May 2016. A total of 26 cases, consisting of 23 Mycobacterium avium complex (MAC) and three Mycobacterium abscessus complex (MABC) infections cases, were included in this study. The efficacy, safety, and feasibility of inhaled AMK therapy were retrospectively investigated. The Research Ethics Committee of Keio University Hospital approved this study, and informed consent was obtained from all patients.ResultsAll 26 patients were culture-positive at enrolment. Twenty-three of the 26 patients (88.5%), including 21/23 MAC patients (91.3%) and 2/3 MABC patients (66.7%), were administered inhaled AMK therapy for >3 months. The proportion of patients who had clinical symptoms, including, cough and sputum, declined after inhalation AMK therapy. Ten of the 23 patients (43.5%) who received AMK inhalation, including 8/21 MAC (38.1%) and 2/2 MABC patients (100%), showed sputum conversion, defined as at least three consecutive negative sputum cultures. Seven of the 23 patients, including, 5/21 MAC and 2/2 MABC patients, showed improvements in high-resolution computed tomography imaging of the chest. In addition, the serum AMK trough levels before the second inhalation were <1.2 μg/mL in all 26 patients, with no occurrence of severe adverse events, such as renal toxicity. One patient (3.8%) experienced auditory toxicity, in the form of tinnitus. However, this symptom was reversible, after temporary interruption of AMK, the patient was able to safely resume the therapy.ConclusionsInhaled AMK therapy is an effective and feasible therapy for difficult-to-treat NTM lung disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-017-2665-5) contains supplementary material, which is available to authorized users.