Widespread decoupling of mtDNA variation and species integrity in Grammia tiger moths (Lepidoptera: Noctuidae)

Abstract. We investigate the diversity of the North American tiger moth genus Grammia Rambur (Lepidoptera: Noctuidae) by comparing mitochondrial DNA (mtDNA) ‘barcode’ fragments of cytochrome oxidase I with non‐molecular characters such as morphology, ecology, behaviour and distribution. Mitochondrial DNA genealogy is strikingly at odds with morpho‐species taxonomy for most of the 28 sampled species, as haplotypic polyphyly not only is taxonomically widespread, but involves multiple shared haplotypes among two to four species. Morpho‐ecological traits show that those species sharing haplotypes are often not closely related. Furthermore, high mtDNA divergences occur within species. Haplotypic variation is highly discordant with species taxonomy, but variation at a continental scale reveals significant geographic structuring of haplogroups, transcending morpho‐species boundaries. A nested clade analysis and comparison of non‐molecular with mtDNA data indicate that most discordance between mtDNA and taxonomy in Grammia is explained best by taxonomically and geographically widespread ongoing hybridization events resulting in mtDNA introgression. We hypothesize that broad areas of sympatry, interspecifically compatible genitalic structure, and species overlap in pheromone components facilitate hybridization, with disparate interspecies abundances promoting mitochondrial introgression. The molecular evolution of Grammia challenges the view that interspecific gene exchange occurs rarely and is restricted to recently diverged species. These results show the value of mtDNA in detecting cryptic hybridization, while highlighting the inherent dangers of drawing taxonomic conclusions based solely on mtDNA.     

The α- and β-Tubulin Genes of Euplotes octocarinatus

ABSTRACT. The α- and the β-tubulin genes of the hypotrichous ciliate Euplotes octocarinatus were isolated from a size-selected macronuclear DNA library. The α-tubulin gene is located on a 1,587 bp macronuclear DNA molecule and the β-tubulin gene on a 1,524 bp macronuclear DNA molecule. Sequencing revealed that all the cysteine residues of the two genes are encoded by the common cysteine codons UGU and UGC and none by an UGA codon. This is in contrast to the genes of E. octocarinatus sequenced so far, where some of the cysteines are encoded by the opal codon UGA. The tubulin genes end like other Euplotes genes with a TAA. They do not contain introns. The last codon for an amino acid in the α-tubulin gene is a GAA which codes for glutamic acid. This is in contrast to what has been reported for most α-tubulin genes, but it supports findings for other hypotrichous ciliates. No evidence for the existence of more than one type of α- and one type of β-tubulin genes could be obtained.     

APPLICATION OF A DOUBLE TUBE SYSTEM FOR ENUMERATION OF CLOSTRIDIUM TYROBUTYRICUM

Clostridium tyrobutyricum, a spore-forming, gram-positive, anaerobic bacterium, is considered to be the main organisms responsible for the late spoilage of cheese by gas formation. Most methods for detecting C. tyrobutyricum are based on spore germination and vegetative growth and take 4–7 days plus an identification step for confirmation. The purpose of this study was to develop a faster detection method using a Double Tube System. Because no selective medium is available for detection of C. tyrobutyricum, three media (Reinforced Clostridial, AC, and Tomato Juice) were compared using two strains of C. tyrobutyricum and one strain of C. sporogenes. Each 4 day-old test strain was inoculated on duplicated plates of each agar that were then placed in anaerobic jars or in the double-tube systems for 2–4 days at 30 or 37C. All three agars consistently supported growth of the test strains. Counts did not differ with incubation at 30 or 37C and were comparable using the conventional anaerobic jar or a Double Tube System. However, in the Double Tube System, colonies could be counted accurately at least 6 h earlier than on the plates in anaerobic jars.