First case of parthenogenesis in ladybirds (Coleoptera: Coccinellidae) suggests new mechanisms for the evolution of asexual reproduction

Parthenogenesis, the development of unfertilized eggs resulting in the exclusive production of female offspring, is rare in animals relative to sexual reproduction and is mainly reported in invertebrates. It has been hypothesized that polyploidy, hybridization and endosymbiont infections are its major causal events but the mechanisms triggering asexual reproduction remain unclear. Here, we study the proximate causes at the origin of parthenogenesis in the first reported case of asexuality in the Coccinellidae (Coleoptera). The asexual populations were found in the Azores and the Mascarene archipelagos, and were identified as Nephus voeltzkowi Weise, a bisexual species widespread in sub-Saharan Africa. The specimens from both populations are diploid but present different karyotypes and heterozygosities that evoke hybrid origins, commonly associated with parthenogenesis in Coleoptera. However, the close proximity of their genomes (99.8% homology for the complete mitochondrial genome and 99.9% for the complete nuclear ribosomal cluster) together with the congruence between the mtDNA tree and the nuclear tree, and the low heterozygosity levels, suggests that the two populations are not hybrid. We propose that they belong to a single chromosomally polymorphic species undergoing Robertsonian fusions. Furthermore, specimens from both populations are infected with Wolbachia (supergroup B strain), contrary to sympatric bisexual species of the same genus. Although Wolbachia has been shown to induce parthenogenesis in haplodiploid organisms, it has been recently suggested that it could also induce parthenogenesis in hosts with other sex determination systems. Whether chromosome rearrangements and/or Wolbachia infections are post-parthenogenetic events or are at the origin of parthenogenesis still needs to be determined.     

Investigation of cellular morphology and proliferation on patterned electrospun PLA-gelatin mats

Journal of Biological Physics - The morphology and proliferation of eukaryotic cells depend on their microenvironment. When electrospun mats are used as tissue engineering scaffolds, the local...     

The role of corals on the abundance of a fish ectoparasite in the Great Barrier Reef

Coral Reefs - Gnathiid isopods, common fish ectoparasites, can affect fish physiology, behaviour and survival. Gnathiid juveniles emerge from the benthos to feed on fish blood. In the Caribbean,...     

Impacts of zebra mussels (Dreissena polymorpha) on isotopic niche size and niche overlap among fish species in a mesotrophic lake

Zebra mussels (Dreissena polymorpha) filter feed phytoplankton and reduce available pelagic energy, potentially driving fish to use littoral energy sources in lakes. However, changes in food webs and energy flow in complex fish communities after zebra mussel establishment are poorly known. We assessed impacts of zebra mussels on fish littoral carbon use, trophic position, isotopic niche size, and isotopic niche overlap among individual fish species using δ¹³C and δ¹⁵N data collected before (2014) and after (2019) zebra mussel establishment in Lake Ida, MN. Isotope data were collected from 11 fish species, and from zooplankton and littoral invertebrates to estimate baseline isotope values. Mixing models were used to convert fish δ¹³C and δ¹⁵N into estimates of littoral carbon and trophic position, respectively. We tested whether trophic position, littoral carbon use, isotopic niche size, and isotopic niche overlap changed from 2014 to 2019 for each fish species. We found few effects on fish trophic position, but 10 out of 11 fish species increased littoral carbon use after zebra mussel establishment, with mean littoral carbon increasing from 43% before to 67% after establishment. Average isotopic niche size of individual species increased significantly (2.1-fold) post zebra mussels, and pairwise-niche overlap between species increased significantly (1.2-fold). These results indicate zebra mussels increase littoral energy dependence in the fish community, resulting in larger individual isotopic niches and increased isotopic niche overlap. These effects may increase interspecific competition among fish species and could ultimately result in reduced abundance of species less able to utilize littoral energy sources.

     

DNA mutagenesis in 2- and 20-yr-old Panax ginseng cell cultures

Previously, Panax ginseng var. Mimaki C.A. Meyer had been shown to accumulate genetic mutations during long-term propagation of a callus culture over a period of 20 yr. In this study, we analyzed the mutation types and frequency in a 2-yr-old P. ginseng callus culture and compared it with the 20-yr-old callus culture, and leaves of cultivated plants. We analyzed the sequence variability between the Actin genes, which are a family of housekeeping genes; phenylalanine ammonia-lyase (PAL) and dammarenediol synthase (DDS), which actively participate in the biosynthesis of ginsenosides; and the somatic embryogenesis receptor kinases (SERK), which control plant development. The frequency of point mutations in the Actin, PAL, DDS, and SERK genes in the 2-yr-old P. ginseng callus culture was markedly higher than in cultivated plants, but lower than in the 20-yr-old callus culture. Most of the mutations in the 2-yr-old P. ginseng calli were A?G and T?C transitions, as in the 20-yr-old calli and intact P. ginseng plants. The number of nonsynonymous mutations was higher in the 2- and 20-yr-old callus cultures than the number of nonsynonymous mutations in cultivated P. ginseng. Interestingly, the total number of N→G or N→C substitutions in the analyzed genes was 1.6 times higher than the total number of N→A or N→T substitutions. Using a methylation-sensitive DNA fragmentation assay, we showed the level of methylcytosine to be higher in the DNA of the 20-yr-old P. ginseng calli that than in the DNA of the 2-yr-old cultures.