Virus and helper component interactions favour the transmission of recombinant potato virus Y strains

In recent years, several recombinant strains of potato virus Y, notably PVYNTN and PVYN:O have displaced the ordinary strain, PVYO, and emerged as the predominant strains affecting the USA potato crop. Previously we reported that recombinant strains were transmitted more efficiently than PVYO when they were acquired sequentially, regardless of acquisition order. In another recent study, we showed that PVYNTN binds preferentially to the aphid stylet over PVYO when aphids feed on a mixture of PVYO and PVYNTN. To understand the mechanism of this transmission bias as well as preferential virus binding, we separated virus and active helper component proteins (HC), mixed them in homologous and heterologous combinations, and then fed them to aphids using Parafilm sachets. Mixtures of PVYO HC with either PVYN:O or PVYNTN resulted in efficient transmission. PVYN:O HC also facilitated the transmission of PVYO and PVYNTN, albeit with reduced efficiency. PVYNTN HC failed to facilitate transmission of either PVYO or PVYN:O. When PVYO HC or PVYN:O HC was mixed with equal amounts of the two viruses, both viruses in all combinations were transmitted at high efficiencies. In contrast, no transmission occurred when combinations of viruses were mixed with PVYNTN HC. Further study evaluated transmission using serial dilutions of purified virus mixed with HCs. While PVYNTN HC only facilitated the transmission of the homologous virus, the HCs of PVYO and PVYN:O facilitated the transmission of all strains tested. This phenomenon has likely contributed to the increase in the recombinant strains affecting the USA potato crop.

Preferred sound groups of vocal iconicity reflect evolutionary mechanisms of sound stability and first language acquisition: evidence from Eurasia

In speech, the connection between sounds and word meanings is mostly arbitrary. However, among basic concepts of the vocabulary, several words can be shown to exhibit some degree of form–meaning resemblance, a feature labelled vocal iconicity. Vocal iconicity plays a role in first language acquisition and was likely prominent also in pre-historic language. However, an unsolved question is how vocal iconicity survives sound evolution, which is assumed to be inevitable and ‘blind’ to the meaning of words. We analyse the evolution of sound groups on 1016 basic vocabulary concepts in 107 Eurasian languages, building on automated homologue clustering and sound sequence alignment to infer relative stability of sound groups over time. We correlate this result with the occurrence of sound groups in iconic vocabulary, measured on a cross-linguistic dataset of 344 concepts across single-language samples from 245 families. We find that the sound stability of the Eurasian set correlates with iconic occurrence in the global set. Further, we find that sound stability and iconic occurrence of consonants are connected to acquisition order in the first language, indicating that children acquiring language play a role in maintaining vocal iconicity over time. This article is part of the theme issue ‘Reconstructing prehistoric languages'.

Can Frequency Account for the Grammatical Choices of Children and Adults in Nominal Modification Contexts? Evidence from Elicited Production and Child-Directed Speech

There is consensus that languages possess several grammatical variants satisfying the same conversational function. Nevertheless, it is a matter of debate which principles guide the adult speaker’s choice and the child’s acquisition order of these variants. Various proposals have suggested that frequency shapes adult language use and language acquisition. Taking the domain of nominal modification as its testing ground, this paper explores in two studies the role that frequency of structures plays for adults’ and children’s structural choices in German. In Study 1, 133 three- to six-year-old children and 21 adults were tested with an elicited production task prompting participants to identify an agent or a patient referent among a set of alternatives. Study 2 analyzed a corpus of child-directed speech to examine the frequency of passive relative clauses, which children, similar to adults, produced very often in Study 1. Importantly, passive relatives were found to be infrequent in the child input. These two results show that the high production rate of rare structures, such as passive relatives, is difficult to account for with frequency. We claim that the relation between frequency in natural speech and use of a given variant in a specific context is indirect: speakers may opt for the less grammatically complex computation rather than for the variant most frequently used in spontaneous speech.

Subordinate questions in Swedish by 12- and 15- year-old Finnish immersion students

The present study explores how 12- and 15-year-old immersion students (n=75 and n=73) produce subordinate questions in Swedish on a written test. Previous studies are sparse, but they report difficulties with both subject-verb word order and use of the subjunctor om and the subject marker som occurring in these clauses; informants with varying ages and competence levels struggle with similar problems. However, the acquisition order between these two types of constructions, a central theme in this study, has gained less attention. Analyses of the actual data show significant differences with varying effect sizes in accuracy between the different subcategories of subordinate questions and both informant groups. Insertion of grammatical words was mastered by significantly fewer informants than word order. Also, effect sizes were large in these contexts. Older informants do better than the younger ones, but the differences are not always statistically significant, as certain constructions are already mastered at a high level by the younger informants, whereas other constructions are still difficult for the older ones.

Human Simulations of Vocabulary Learning

This paper investigates the generalization that noun learning systematically precedes verb learning. Rather than blame this observation on differences in conceptual content, the authors argue that the information requirements of verb learning crucially determine the acquisition order. Efficient verb learning requires access to structural features of the exposure language and thus cannot take place until a scaffolding of noun knowledge enables the acquisition of clause level syntax. A set of experiments with adult subjects ask about the kinds of information that support learning nouns vs. verbs. The proportion correctly identified and the type of word that is identifiable changes significantly as a function of information type.