Adaptive divergence and post-zygotic barriers to gene flow between sympatric populations of a herbivorous mite

Plant-herbivore interactions promote the generation and maintenance of both plant and herbivore biodiversity. The antagonistic interactions between plants and herbivores lead to host race formation: the evolution of herbivore types specializing on different plant species, with restricted gene flow between them. Understanding how ecological specialization promotes host race formation usually depends on artificial approaches, using laboratory experiments on populations associated with agricultural crops. However, evidence on how host races are formed and maintained in a natural setting remains scarce. Here, we take a multidisciplinary approach to understand whether populations of the generalist spider mite Tetranychus urticae form host races in nature. We demonstrate that a host race co-occurs among generalist conspecifics in the dune ecosystem of The Netherlands. Extensive field sampling and genotyping of individuals over three consecutive years showed a clear pattern of host associations. Genome-wide differences between the host race and generalist conspecifics were found using a dense set of SNPs on field-derived iso-female lines and previously sequenced genomes of T. urticae. Hybridization between lines of the host race and sympatric generalist lines is restricted by post-zygotic breakdown, and selection negatively impacts the survival of generalists on the native host of the host race. Our description of a host race among conspecifics with a larger diet breadth shows how ecological and reproductive isolation aid in maintaining intra-specific variation in sympatry, despite the opportunity for homogenization through gene flow. Our findings highlight the importance of explicitly considering the spatial and temporal scale on which plant-herbivore interactions occur in order to identify herbivore populations associated with different plant species in nature. This system can be used to study the underlying genetic architecture and mechanisms that facilitate the use of a large range of host plant taxa by extreme generalist herbivores. In addition, it offers the chance to investigate the prevalence and mechanisms of ecological specialization in nature.

Virulence and diversity of Puccinia striiformis in South Russia

Puccinia striiformis causes wheat yield losses in all countries where wheat is cultivated. Virulence and diversity of the P. striiformis were assessed in 2013–2018 in South Russia, and this showed that the North Caucasian population of the pathogen was diverse. One hundred and eighty two virulence phenotypes were identified in 186 P. striiformis isolates. Among isolates collected in 2014, 2015, and 2018, all phenotypes were unique. In the 2013 and 2017 populations, phenotypes with few (one to eight) virulence alleles prevailed. In the 2014, 2015, and 2018 populations, most of the phenotypes contained greater numbers (nine to 19) of virulence alleles. Over the 5 years of research, the pathogen population lacked isolates virulent to the host Yr resistance genes 3, 5, 26, and Sp. Single (from 1 to 5%) occurrences of isolates virulent to host lines with Yr genes 3a, 17, 24, 3b + 4a + H46, and 3c + Min were identified. Differences in frequencies of virulence alleles between years in the P. striiformis populations (Ney indices, N) were generally non-significant (N = 0.11 to 0.23), with the exception of the populations in 2013 and 2017 (N = 0.37). The minimum N values was found for the populations of 2015 and 2018 (N = 0.10). Over the five years of this study, the dynamics of the virulence of the population and jumps in the frequency of isolates with respect to many Yr genes were identified. This feature of the P. striiformis populations in South Russia, combined with high phenotypic diversity, indicates the ability for rapid race formation and morphogenesis in response to changes in biotic and abiotic factors.

Racial belonging of broomrape (Orobanche cumana Wallr.) seeds, collected on the fields of different regions of the Russian Federation in 2019

Relevance. Broomrape (Orobanche cumana Wallr.) is one of the major limitations in sunflower production in most countries, cultivating it.Results. The analysis of the racial belonging of broomrape seeds collected in 2019 from different fields of the Rostov, Voronezh, Belgorod regions and the Krasnodar Territory of the Russian Federation showed their marked heterogeneity in virulence. In these regions, there are still fields where race E dominates, but with an admixture of highly virulent biotype G. There are fields with domination race F or G. Of the 7 samples of broomrape seeds collected in the Rostov region, three showed the presence of race H, as well as all samples from the Voronezh region and one from the Krasnodar Territory. n the samples of seeds from the Belgorod region, race H was not detected. Monitoring of the racial belonging of broomrape seeds from different fields is still relevant for their use in sunflower breeding for immunity and proper placement of a cultivated assortment that can slow down the race formation in a particular field.

“I Am Already Annexed”: Ramon Reyes Lala and the Crafting of “Philippine” Advocacy for American Empire

This article reconstructs the American career of the Manila-born author Ramon Reyes Lala. Lala became a naturalized United States citizen shortly before the War of 1898 garnered public interest in the history and geography of the Philippines. He capitalized on this interest by fashioning himself into an Oxford-educated nationalist exiled in the United States for his anti-Spanish activism, all the while hiding a South Asian background. Lala's spirited defense of American annexation and war earned him the political patronage of the Republican Party. Yet though Lala offered himself as a ‘model’ Philippine-American citizen, his patrons offered Lala as evidence of U.S. benevolence and Philippine civilization potential shorn of citizenship. His embodied contradictions, then, extended to his position as a producer of colonial knowledge, a racialized commodity, and a representative Filipino in the United States when many in the archipelago would not recognize him as such. Lala's advocacy for American Empire, I contend, reflected an understanding of nationality born of diasporic merchant communities, while his precarious success in the middle-class economy of print and public speaking depended on his deft maneuvering between modalities of power hardening in terms of race. His career speaks more broadly to the entwined and contradictory processes of commerce, race formation, and colonial knowledge production.

Incipient sympatric speciation via host race formation in Phengaris arion (Lepidoptera: Lycaenidae)

The plausibility of sympatric speciation is still debated despite increasing evidence, such as host races in insects. This speciation process may be occurring in the case of the two phenological forms of the obligatorily myrmecophilous Phengaris arion. The main goal of our research was to study the nature and causes of difference between these forms focusing primarily on the incipient speciation via host races. Molecular analyses based on highly variable microsatellites together with Wolbachia screening, male genitalia morphometrics and host ant studies were carried out on four syntopic sample pairs. Our results show that the two phenological forms of P. arion may meet the criteria for host plant races. They coexist in sympatry in certain parts of the species range which is allowed by the adaptation to the distinct phenology of the host plants. Negative selection acts against the intermediate individuals which are on the wing in the inappropriate time frame. Thus, disruptive selection affects and produces bimodal distributions of phenotypes. However, the phenology of food plants is not entirely distinct and fluctuates year by year. Therefore, the two forms can exchange genes occasionally depending on the length of the time slot when they can meet with each other. Consequently, the reproductive isolation could not be completed and the existence of the two arion forms may represent only an incipient stage of sympatric speciation. It is also clear that Wolbachia is likely not a driver of sympatric speciation in this case.