3,897 research outputs found
Gut microbiota as a trigger of accelerated directional adaptive evolution. Acquisition of herbivory in the context of extracellular vesicles, microRNAs and inter-kingdom crosstalk
According to a traditional view, the specific diet in vertebrates is one of the key factors
structuring the composition of the gut microbiota. In this interpretation, the microbiota
assumes a subordinate position, where the larger host shapes, through evolution
and its fitness, the taxonomical composition of the hosted microbiota. The present
contribution shows how the evolution of herbivory, framed within the new concept of
holobiont, the possibility of inter-kingdom crosstalk and its epigenetic effects, could
pave the way to a completely reversed interpretation: instead of being passively shaped,
the microbiota can mold and shape the general host body structure to increase its
fitness. Central elements to consider in this context are the inter-kingdom crosstalk, the
possibility of transporting RNAs through nanovesicles in feces from parents to offspring,
and the activation of epigenetic processes passed on vertically from generation to
generation. The new hypothesis is that the gut microbiota could play a great role in
the macroevolutionary dynamics of herbivorous vertebrates, causing directly through
host-microbiota dialog of epigenetic nature (i.e., methylation, histone acetylation, etc.),
major changes in the organisms phenotype. The vertical exchange of the same microbial
communities from parents to offspring, the interaction of these microbes with fairly
uniform genotypes, and the socially restricted groups where these processes take
place, could all explain the reasons why herbivory has appeared several time (and
independently) during the evolution of vertebrates. The new interpretation could also
represent a key factor in understanding the convergent evolution of analogous body
structures in very distant lineages
Does a Cadillac engine need a biological and phylogenetic explanation?
In this text we briefly explore whether ridiculing material objects like a âCadillac engineâ, a âdeskâ, âgold bars
in a vaultâ as reduction ad absurdum in âdialectical duelsâ or as a metaphor for teaching evolution is really
phylogenetically justified, or whether that evidence really needs an explanation in the evolutionary field. The
key of reading is the combination of the definition of semaphorontholomorphy by Willi Hennig, the concept of
Extended Phenotype introduced by Richard Dawkins and the memetic theory by Susan Blackmore. Once these
theoretical elements are considered as a whole and in an integrated way, the logical system of Hennig still shows
its all-encompassing explanatory power, a good opportunity to appreciate the great complexity and elegance of
phylogeny and evolution.
In the perspective presented in this paper, spiders, whales, a desk, the Cadillac engine and the American flag
on the Moon are considered in some way monophyletic, and then require a putative explanation even in the
phylogenetic-evolutionary field
Discrete and continuous character-based disparity analyses converge to the same macroevolutionary signa. A case study from captorhinids
The relationship between diversity and disparity during the evolutionary history of a clade provides
unique insights into evolutionary radiations and the biological response to bottlenecks and to
extinctions. Here we present the first comprehensive comparison of diversity and disparity of
captorhinids, a group of basal amniotes that is important for understanding the early evolution of
high-fiber herbivory. A new fully resolved phylogeny is presented, obtained by the inclusion of 31
morphometric characters. The new dataset is used to calculate diversity and disparity through the
evolutionary history of the clade, using both discrete and continuous characters. Captorhinids do
not show a decoupling between diversity and disparity, and are characterized by a rather symmetric
disparity distribution, with a peak in occupied morphospace at about the midpoint of the cladeâs
evolutionary history (Kungurian). This peak represents a delayed adaptive radiation, identified by the
first appearance of several high-fiber herbivores in the clade, along with numerous omnivorous taxa.
The discrete characters and continuous morphometric characters indicate the same disparity trends.
Therefore, we argue that in the absence of one of these two possible proxies, the disparity obtained
from just one source can be considered robust and representative of a general disparity pattern
Phylogenetic analysis of cyrtocrinid crinoids and its influence on traditional classifications
The cyrtocrinids are a group of mostly Mesozoic articulated crinoids, with rare Cenozoic forms and
only two extant taxa. A careful analysis of previous studies indicates that the systematic arrangement of cyrtocrinids is
very weak and unsatisfactory for several reasons. In particular, most of the original descriptions and diagnosis date from
the past century and are logically influenced by a classical typological philosophy. Not being based on phylogeny, the
currently accepted groups for cyrtocrinids must be putatively regarded as âartificialâ. In addition, an inappropriate use of
characters has been used, typically considered as diagnostic in other groups of crinoids but only marginally applicable to
cyrtocrinids (the latter differently characterized for several highly distinctive and autapomorphic characters). In order to
mitigate these problems and to arrive at the definition of characters and clades based on unambiguous synapomorphies,
we present in this paper a preliminary and exploratory phylogenetic analysis based on parsimony of cyrtocrinids. The
obtained topology showed how the traditionally recognized groups prove to be highly paraphyletic and polyphyletic,
indicating the need for a complete revision of cyrtocrinids taxonomy, based on phylogeny. The gap-weighting method
used for codifying morphometric continuous character, has proved to be a powerful tool to obtain well-resolved and
consistent cladograms, even with a limited number of characters
Detrital events within pelagic deposits of the Umbria-Marche basin (Northern Apennines, Italy). Further evidence of Early Cretaceous tectonics
Re-sedimented deposits characterize different stratigraphical intervals in the pelagic successions of the
Umbria-Marche-Sabina Domain (Central and Northern Apennines, Italy). Three stratigraphic sections of the Maiolica
and Marne a Fucoidi Formations, characterized by breccias and calcarenites embedded in pelagic sediments, were sampled
across the Mt. Primo area (Umbria- Marche Ridge, Northern Apennines). Facies analysis indicates a gravity-driven origin
for the clastic levels, interpreted as debris-flows, or turbidity flows. The massive lensoid-to-tabular levels are composed of
loose shallow-water benthic material, sourced from an unknown carbonate platform, associated with: i) lithoclasts made
of Lower Jurassic and Lower Cretaceous shallow-water carbonates; ii) Jurassic mudstones and wackestones referable to the
pelagic succession; iii) calpionellid/radiolarian-rich soft pebbles (Maiolica-type facies). The compositional features of the
studied detrital deposits imply submarine exposure and dismantling of portions of the stratigraphic succession older than
the Barremian/Aptian, which had to be buried in the late Early Cretaceous. Such evidence led us to refer the investigated
clastic event to an extensional tectonic phase. Our interpretation well fits with data coming from different geological
settings of Italy, strongly suggesting the occurrence of a widespread extensional phase in the late Early Cretaceous
New material of Alierasaurus ronchii (Synapsida, Caseidae) from the Permian of Sardinia (Italy), and its phylogenetic affinities
New characters of the giant caseid Alierasaurus ronchii are described here based
on material recovered from the type locality in the Permian deposits of Cala del Vino
Formation (Sardinia NW) and additional preparation of the previously collected material.
All new described osteological elements are characterized by the same state of
preservation and, given the absence of double elements and the total compatibility in
absolute size, the new material can be attributed without doubt to the holotypic individual
of A. ronchii. Highly diagnostic material includes a caudal neural spine with a broad
bifid distal termination. This represents a synapomorphy characterizing the more
derived caseids, thus fully confirming the attribution of the Sardinian specimen to
Caseidae. Also the other vertebral material and newly collected ribs show a typical
caseid structure, fully consistent with the previously published material. Despite the
highly partial nature of Alierasaurus, the taxon was included in a recent phylogenetic
analysis of caseids to investigate its phylogenetic position within the monophyletic
Caseasauria. Alierasaurus falls as the sister taxon of Cotylorhynchus, and is autapomorphic
in the general construction of MT-IV and proximal phalanx IV-I. The absolute
size of the newly recovered material confirms a gigantic body size for Alierasaurus,
comparable, if not greater, to that of the huge North American species Cotylorhynchus
hancocki (up to 6 m in length). Such gigantic adult body size, closely correlated to its
herbivorous lifestyle, must have been selected during evolution of caseids, leading to
substantial advantages in terms of fitness
Elongated theropod tracks from the Cretaceous Apenninic Carbonate Platform of southern Latium (central Italy)
New dinosaur footprints were recently discovered in southern Latium (Italy). The
tracks all appear slightly differently preserved and are characterized by elongated
metatarsal impressions, recording the complex locomotor behaviour of a medium-sized
theropod. The spatial distribution and the features of the footprints indicate that the
trackmaker adopted a âcrouchedâ position as part of an activity as well as a resting
phase suggested by sub-parallel, calcigrade tracks. These new data once again highlight
the great potential of ichnological evidence in the study of the biology and
behaviour of extinct tetrapods
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