Cryptic species in the zooplankton hindering our understanding of ecological processes

Species identification for most ecological and applied purposes (e.g. biological monitoring, environmental assessment, etc.) is performed through the analysis of morphological features of the organisms collected in the wild and sorted individually. There are growing evidences that several complexes of cryptic species (i.e. species that cannot be identified from morphology) exist in the zooplankton, and that different cryptic species within a single morphological species may respond differently to environmental drivers, because they represent different evolutionary entities with different ecological adaptations. Such differences can represent serious hindrances to our understanding of biological drivers and correlates of biodiversity if the species complexes are not solved. I will report few examples from on-going analyses on aquatic and limno-terrestrial rotifers to support such scenario and provide suggestions on how molecular tools could provide useful avenues to get pass such impasse

Geography, climate, and patterns of genetic diversity in a bdelloid rotifer

The interplay between climate (current and past) and geography is known to be associated with spatial biodiversity patterns. Here we analyze genetic diversity in a bdelloid rotifer species complex along a latitudinal transect in Europe from ~40?N, Sardinia, to ~80?N, Svalbard. Contrary to what is described for larger organisms, none of the analyzed patterns of diversity correlates with climate, and a strange relationship with geographical distances is present

Solving complexes of cryptic species by using detailed analyses on jaw morphology in asexual rotifers

Jaws in rotifers, called trophi, are among the most important hard structure used for taxonomy and systematics. Selection on feeding ecology acts on these features and produced a wide array of shapes and adaptations, including filtering, piercing, grasping, pumping, etc. Bdelloid rotifers are completely asexual and morphological diversification in their trophi happened without the potentials offered by sexual recombination. I will review the approaches that have been used to couple studies on molecular evolution, mostly through phylogenetic approaches, and studies on morphological diversification of trophi, mostly through geometric morphometrics. Such studies cover both macroevolutionary scenarios and microevolutionary detailed analyses of differences between cryptic species and comparisons between populations. Evolution in the absence of sexual recombination in animals is an intriguing topic, and I will suggest further ways to use rotifer jaws as an invaluable window to explore evolutionary changes

At least some protist species are not ubiquitous

Body size is one of the main regulators of the ecological characteristics of living organisms, including their biogeography. The \u27ubiquity hypothesis\u27 for microorganisms states that they are widely distributed, if not cosmopolitan, due to their small size that allows passive dispersal, in contrast to large organisms that are limited by geographical barriers in their active dispersal. Such idea, summarized in the tenet \u27Everything is everywhere, but the environment selects\u27, has driven most of the research in biogeography for microscopic organisms in the last decades, spurring a debate on whether there are fundamental differences in the biogeography of small and large organisms or not (Fenchel & Finlay 2004; Foissner 2008; Hortal 2011). The strong focus on the ubiquity hypothesis may have been often abused to provide a rationale for otherwise descriptive work on the spatial distribution of microscopic organisms; nevertheless, such focus also provides a framework to understand the mechanisms originating and maintaining biodiversity in space. The reliability of the analyses on unknown and understudied organisms is improving, and Heger et al. (2013) is a splendid example on small unicellular eukaryotes of what should be done to overcome the major problems and ambiguities that heated the debate on the ubiquity hypothesis

Evidence for Inefficient Selection Against Deleterious Mutations in Cytochrome Oxidase I of Asexual Bdelloid Rotifers

Evolutionary theory predicts that natural selection should be less efficient in asexually than in sexually reproducing organisms. Obligate asexuals are expected to adapt slowly to changing environments and to accumulate mildly deleterious mutations to their genomes, potentially explaining their typically short evolutionary lifespans. One group of animals that appear to challenge these ideas is the bdelloid rotifers, a large and ancient clade of obligate asexuals. Previous work has found no evidence for inefficient selection against deleterious mutations in protein-coding genes of bdelloids. However, these studies relied mostly on between-species comparisons and were therefore unable to detect mildly deleterious mutations that persist within populations but are removed by selection over longer time periods. Here, we test for inefficient purifying selection acting on the cytochrome oxidase I (cox1) mitochondrial gene in 3 clades of bdelloids. Patterns of variation are compared to those of two facultatively sexual clades: a monogonont rotifer (Brachionus) and a branchiopod crustacean (Daphnia). As predicted due to the strict linkage between mitochondrial and nuclear genomes, bdelloids exhibit higher frequencies of putatively deleterious amino acid polymorphism within populations than the two facultatively sexual clades. While the monophyly and age of bdelloids makes it hard to rule out other explanations for the observed differences, several possible confounding factors, such as differences in effective population size or patterns of codon usage, are shown not to explain the observed differences. We therefore conclude that bdelloid mitochondrial DNA variation does display the signature of inefficient selection expected of obligate asexuals

Niente sesso, siamo bdelloidei

La possibilità che specie possano evolvere, formarsi, e persistere come entità evolutivamente indipendenti in assenza di ricombinazione sessuale in organismi come animali e piante è stata spesso messa in dubbio. Tuttavia, ci sono organismi che sono notiper essere asessuati e che si sono diversificati in più specie, riconosciute in maniera coerente dai naturalisti. Questi organismi sono stati additati come paradossi evolutivi. In questa nota esploreremo tre ipotesi alternative per tentare di risolvere l'apparente paradosso, concentrandosi sui rotiferi bdelloidei, il gruppo più studiato in cui tutte le specie sono considerate asessuate. (1) Gli bdelloidei possono avere una qualche forma nascosta di sesso. (2) Le specie non rappresentano entità biologiche negli bdelloideima sono semplicemente nomi di convenienza. (3) Nel caso in cui le due ipotesi precedentirisultino non supportate, ma i rotiferi bdelloidei siano davvero asessuati e con specie morfologicamente e geneticamente riconoscibili, la logica conseguenza è che i meccanismi di ricombinazione sessuale che producono isolamento riproduttivo non siano un requisito assolutamente necessario per la speciazione. Questo terzo scenario sembrerebbe essere quello che meglio descrive la realtà, anche se studi recenti potrebbero portare una nuova ottica per cambiare ulteriormente la nostra comprensione delle specie e dei processi di speciazione

Stress and fitness in parthenogens: is dormancy a key feature for bdelloid rotifers?

Background: Bdelloid rotifers are the most common and abundant group of animals that reproduce by ameiotic parthenogenesis, only. They are common in temporally ephemeral habitats, and it is unclear if they dwell in unstable habitats because are excluded from better conditions by stronger competitors, or because they need unstable conditions for their success. We tested the hypothesis that bdelloids 'require' stressful conditions for their persistence by comparing fitness-related traits of stressed ( desiccated, D) and unstressed ( hydrated, H) lines of two species, Adineta ricciae and Macrotrachela quadricornifera. Results: For both bdelloid species, fecundity was significantly lower in H than in parallel D line. Fitness components decreased with time progressively in the H line but not in the D line. Recovery rates of D lines were recorded after every desiccation and did not reveal any trend in time, suggesting that no selection was operating. Conclusion: Stress in the form of reiterated desiccations seemed to help both bdelloid species to keep fitness stable; in contrast under stable conditions, like permanent hydration, these bdelloid species had poorer performances. Bdelloids, although aquatic animals, are not only efficient in tolerating desiccation, but seem somehow dependent on anhydrobiosis, a circumstance that might represent a key event in their life cycle. If this is true, life in unpredictable habitats should not be seen as the result of competitive exclusion from 'easier' habitats, but a requirement for long-term survival of these parthenogenetic animals

Tassonomia molecolare per razionalizzare il monitoraggio biologico

Species identification for most ecological and applied purposes (e.g. biological monitoring, environmental assessment, etc.) is performed through the analysis of morphological features of the organisms collected in the wild and sorted individually. There are growing evidences that several complexes of cryptic species (i.e. species that cannot be identified from morphology) exist in the zooplankton, and that different cryptic species within a single morphological species may respond differently to environmental drivers, because they represent different evolutionary entities with different ecological adaptations. Such differences can represent serious hindrances to our understanding of biological drivers and correlates of biodiversity if the species complexes are not solved. I will report few examples from on-going analyses on aquatic and limno-terrestrial rotifers to support such scenario and provide suggestions on how molecular tools could provide useful avenues to get pass such impasse

Does a barcoding gap exist in Prokaryotes? Evidences from species delimitation in Cyanobacteria

The amount of information that is available on 16S rRNA sequences for prokaryotes thanks to high-throughput sequencing could allow a better understanding of diversity. Nevertheless, the application of predetermined threshold in genetic distances to identify units of diversity (Operative Taxonomic Units, OTUs) may provide biased results. Here we tests for the existence of a barcoding gap in several groups of Cyanobacteria, defining units of diversity according to clear differences between within-species and among-species genetic distances in 16S rRNA. The application of a tool developed for animal DNA taxonomy, the Automatic Barcode Gap Detector (ABGD), revealed that a barcoding gap could actually be found in almost half of the datasets that we tested. The identification of units of diversity through this method provided results that were not compatible with those obtained with the identification of OTUs with threshold of similarity in genetic distances of 97% or 99%. The main message of our results is a call for caution in the estimate of diversity from 16S sequences only, given that different subjective choices in the method to delimit units could provide different results

La Cigogne noire Ciconia nigra en Italie du Nord : de quel environnement cette espèce a-t-elle besoin pour nicher ?

La Cigogne noire Ciconia nigra en Italie du Nord: de quel environnement cette espèce a-t-elle besoin pour nicher? - Il existe un besoin général de traiter le peu de données disponibles sur les espèces rares et menacées pour obtenir des indications significatives en vue de décisions politiques les concernant. Nous présentons ici une analyse de quelques données disponibles sur les besoins écologiques de la Cigogne noire dans le nord de l'Italie, en utilisant des analyses statistiques permettant d'extraire des informations significatives sur les préférences de l'espèce. La Cigogne noire recolonise l'Italie après plus d'un demi millénaire; nous analysons les données sur l'utilisation de l'habitat et le choix du site de nid de trois couples suivis de 1994 à 2001. Il apparaît que ces couples ne requièrent pas surtout des forêts humides et de vieux grands arbres comme cela est souvent signalé mais préfèrent (1) des grandes surfaces collinéennes boisées, (2) des zones boisées non fragmentées, (3) un riche réseau hydrographique avec beaucoup de petits cours d'eau, (4) la présence de petites zones avec de fortes pentes, comme des petites falaises et ressauts rocheux. Les nids étaient toujours situés dans les zones avec le plus dense réseau hydrographique, dans lequel les adultes ne vont pas mais où les jeunes apprennent à rechercher leur nourriture sans avoir à aller loin du nid