Loss of Sexual Reproduction and Dwarfing in a Small Metazoan

Asexuality has major theoretical advantages over sexual reproduction, yet newly formed asexual lineages rarely endure. The success, or failure, of such lineages is affected by their mechanism of origin, because it determines their initial genetic makeup and variability. Most previously described mechanisms imply that asexual lineages are randomly frozen subsamples of a sexual population.We found that transitions to obligate parthenogenesis (OP) in the rotifer Brachionus calyciflorus, a small freshwater invertebrate which normally reproduces by cyclical parthenogenesis, were controlled by a simple Mendelian inheritance. Pedigree analysis suggested that obligate parthenogens were homozygous for a recessive allele, which caused inability to respond to the chemical signals that normally induce sexual reproduction in this species. Alternative mechanisms, such as ploidy changes, could be ruled out on the basis of flow cytometric measurements and genetic marker analysis. Interestingly, obligate parthenogens were also dwarfs (approximately 50% smaller than cyclical parthenogens), indicating pleiotropy or linkage with genes that strongly affect body size. We found no adverse effects of OP on survival or fecundity.This mechanism of inheritance implies that genes causing OP may evolve within sexual populations and remain undetected in the heterozygous state long before they get frequent enough to actually cause a transition to asexual reproduction. In this process, genetic variation at other loci might become linked to OP genes, leading to non-random associations between asexuality and other phenotypic traits

Genome size evolution at the speciation level: The cryptic species complex Brachionus plicatilis (Rotifera)

<p>Abstract</p> <p>Background</p> <p>Studies on genome size variation in animals are rarely done at lower taxonomic levels, e.g., slightly above/below the species level. Yet, such variation might provide important clues on the tempo and mode of genome size evolution. In this study we used the flow-cytometry method to study the evolution of genome size in the rotifer <it>Brachionus plicatilis</it>, a cryptic species complex consisting of at least 14 closely related species.</p> <p>Results</p> <p>We found an unexpectedly high variation in this species complex, with genome sizes ranging approximately seven-fold (haploid '1C' genome sizes: 0.056-0.416 pg). Most of this variation (67%) could be ascribed to the major clades of the species complex, i.e. clades that are well separated according to most species definitions. However, we also found substantial variation (32%) at lower taxonomic levels - within and among genealogical species - and, interestingly, among species pairs that are not completely reproductively isolated. In one genealogical species, called <it>B</it>. 'Austria', we found greatly enlarged genome sizes that could roughly be approximated as multiples of the genomes of its closest relatives, which suggests that whole-genome duplications have occurred early during separation of this lineage. Overall, genome size was significantly correlated to egg size and body size, even though the latter became non-significant after controlling for phylogenetic non-independence.</p> <p>Conclusions</p> <p>Our study suggests that substantial genome size variation can build up early during speciation, potentially even among isolated populations. An alternative, but not mutually exclusive interpretation might be that reproductive isolation tends to build up unusually slow in this species complex.</p

Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy

Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis, which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size)

MPF2-Like-A MADS-box genes control the inflated syndrome in Withania (Solanaceae): roles of Darwinia Selection

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Perturbed development of striatal dopamine transporters in fatty versus lean Zucker rats: a follow-up small animal PET study

Purpose Post-synaptic dopamine D2/3 receptors are reduced in animal models of obesity, and in obese humans, concordant with similar findings in habitual drug users. However, corresponding pre-synaptic changes in brain dopamine are less documented in obesity models. Therefore, we used positron emission tomography (PET) with the dopamine transporter (DAT) ligand N-(3-[18F]fluoropropyl)-2-β-carbomethoxy-3-β-(4′-methylphenyl) tropane ([18F]FP-CMT) to test the hypothesis that DAT availability is attenuated in adult fatty Zucker (FZ) rats versus lean littermates (LZ). Procedures Groups of nine FZ and LZ rats were examined by [18F]FP-CMT PET at approximately 6 weeks and at 6 months of age. Results The baseline mean striatal binding potential (BPND) of [18F]FP-CMT did not differ between groups (LZ 2.4; FZ 2.5), although FZ rats already had higher body weight and elevated blood triglycerides, cholesterol, and insulin. At follow-up, a mixed effects multiple regression model showed that the maturation of DAT availability was attenuated in FZ rats, such that the mean BPND in striatum was 17 % lower (LZ 4.0; FZ 3.3; p = 0.01). Body weight was twofold higher in the adult FZ rats, and triglycerides fourfold increased, but glucose remained normal despite doubling of insulin levels. Conclusions Maturation of the striatal dopamine innervation is impaired in this model of obesity/hyperlipidaemia without diabetes, implying an acquired trait of reduced dopamine reuptake capacity