Evolutionary Plasticity of Mating-Type Determination Mechanisms in Paramecium aurelia Sibling Species.

The Paramecium aurelia complex, a group of morphologically similar but sexually incompatible sibling species, is a unique example of the evolutionary plasticity of mating-type systems. Each species has two mating types, O (Odd) and E (Even). Although O and E types are homologous in all species, three different modes of determination and inheritance have been described: genetic determination by Mendelian alleles, stochastic developmental determination, and maternally inherited developmental determination. Previous work in three species of the latter kind has revealed the key roles of the E-specific transmembrane protein mtA and its highly specific transcription factor mtB: type O clones are produced by maternally inherited genome rearrangements that inactivate either mtA or mtB during development. Here we show, through transcriptome analyses in five additional species representing the three determination systems, that mtA expression specifies type E in all cases. We further show that the Mendelian system depends on functional and nonfunctional mtA alleles, and identify novel developmental rearrangements in mtA and mtB which now explain all cases of maternally inherited mating-type determination. Epistasis between these genes likely evolved from less specific interactions between paralogs in the P. aurelia common ancestor, after a whole-genome duplication, but the mtB gene was subsequently lost in three P. aurelia species which appear to have returned to an ancestral regulation mechanism. These results suggest a model accounting for evolutionary transitions between determination systems, and highlight the diversity of molecular solutions explored among sibling species to maintain an essential mating-type polymorphism in cell populations.

First Descriptions of Larva and Pupa of Bagous claudicans Boheman, 1845 (Curculionidae, Bagoinae) and Systematic Position of the Species Based on Molecular and Morphological Data.

In this paper, the mature larva and pupa of Bagous claudicans are described and illustrated for the first time. Measurements of younger larval instars are also given. The biology of the species is discussed in association with larval morphology and feeding habits. Overall larval and pupal morphological characters of the genus Bagous are presented. Confirmation of the larva identification as Bagous claudicans species was conducted by cytochrome oxidase I (COI) sequencing. DNA barcoding was useful for specimen identification of larval stages. The systematic position of the species within the Bagous collignensis-group, based on morphological and molecular results, is also discussed.

Genetic data of museum specimens allow for inferring evolutionary history of the cosmopolitan genus Sirthenea (Heteroptera: Reduviidae).

Among the 30 known genera within subfamily Peiratinae, only the genus Sirthenea has a cosmopolitan distribution. The results of our studies are the first comprehensive analysis concerning one of the representatives of mentioned subfamily based on joint phylogenetic analyses of molecular and morphological data as well as molecular dating. A total of 32 species were included into the dataset with all known species of the genus Sirthenea. Material of over 400 dry specimens was examined for the morphological part of this study. The cosmopolitan distribution of Sirthenea and the inaccessibility of specimens preserved in alcohol required the extraction of DNA from the dried skeletal muscles of specimens deposited in 24 entomological collections. The oldest specimens used for the successful extraction and sequencing were collected more than 120 years ago in India. We performed Bayesian Inference analyses of molecular and morphological data separately, as well as combined analysis. The molecular and morphological data obtained during our research verify the correlation of the divergence dates of all known Sirthenea species. Results of the relaxed molecular clock analysis of the molecular data show that, the genus Sirthenea started diverging in the Late Cretaceous into two clades, which subsequently began to branch off in the Paleocene. Our results of phylogenetic analyses suggest that the fossula spongiosa and its development could be one of the most important morphological characters in the evolution of the genus, most likely associated with the ecological niche inhabited by Sirthenea representatives. Confirmation of the results obtained in our studies is the reconciliation of the evolutionary history of Sirthenea with the biogeographical processes that have shaped current global distribution of the genus.