The ontogeny of trilobite segmentation: a comparative approach

Paleobiology ◽  
2006 ◽  
Vol 32 (4) ◽  
pp. 602-627 ◽  
Author(s):  
Nigel C. Hughes ◽  
Alessandro Minelli ◽  
Giuseppe Fusco
Keyword(s):  
Direct Development ◽  
Comparative Approach ◽  
Phase Boundaries ◽  
Free Living ◽  
Ancestral Condition ◽  
Morphological Transitions ◽  
Posterior Trunk ◽  
Close Relatives ◽  
Number Of Segments ◽  
Trunk Segments

Ontogenetic stages of trilobites have traditionally been recognized on the basis of the development of exoskeletal segmentation. The established protaspid, meraspid, and holaspid phases relate specifically to the development of articulated joints between exoskeletal elements. Transitions between these phases were marked by the first and last appearances of new trunk segment articulations. Here we propose an additional and complementary ontogenetic scheme based on the generation of new trunk segments. It includes an anamorphic phase during which new trunk segments appeared, and an epimorphic phase during which the number of segments in the trunk remained constant. In some trilobites an ontogenetic boundary can also be recognized at the first appearance of morphologically distinct posterior trunk segments. Comparison of the phase boundaries of these different aspects of segment ontogeny highlights rich variation in the segmentation process among Trilobita. Cases in which the onset of the holaspid phase preceded onset of the epimorphic phase are here termed protarthrous, synchronous onset of both phases is termed synarthromeric, and onset of the epimorphic phase before onset of the holaspid phase is termed protomeric. Although these conditions varied among close relatives and perhaps even intraspecifically in some cases, particular conditions may have been prevalent within some clades.Trilobites displayed hemianamorphic development that was accomplished over an extended series of juvenile and mature free-living instars. Although developmental schedules varied markedly among species, morphological transitions during trilobite development were generally regular, limited in scope, and extended over a large number of instars when compared with those of many living arthropods. Hemianamorphic, direct development with modest change between instars is also seen among basal members of the Crustacea, basal myriapods, pycnogonids, and in some fossil chelicerates. This mode may represent the ancestral condition of euarthropod development.

scholarly journals Nesting strategy shapes territorial aggression but not testosterone: a comparative approach in female and male birds

2020 ◽  
Author(s):  
SE Lipshutz ◽  
KA Rosvall
Keyword(s):  
Tree Swallow ◽  
Comparative Approach ◽  
Female Competition ◽  
American Robin ◽  
Territorial Aggression ◽  
Physical Attack ◽  
Cavity Nesting ◽  
Comparative Framework ◽  
Underlying Mechanisms ◽  
Close Relatives

Our understanding of the proximate and ultimate mechanisms shaping competitive phenotypes primarily stems from research on male-male competition for mates, even though female-female competition is also widespread. Obligate secondary cavity-nesting has evolved repeatedly across avian lineages, providing a useful comparative context to explore how competition over limited nest cavities shapes aggression and its underlying mechanisms across species. Although evidence from one or another cavity-nesting species suggests that territorial aggression is adaptive in both females and males, this has not yet been tested in a comparative framework. We tested the hypothesis that cavity-nesting generates more robust territorial aggression, in comparison to close relatives with less restrictive nesting strategies. Our focal species were two obligate secondary cavity-nesting species and two related species with more flexible nesting strategies in the same avian family: tree swallow (Tachycineta bicolor) vs. barn swallow (Hirundo rustica); Eastern bluebird (Sialia sialis) vs. American robin (Turdus migratorius). We assayed conspecific territorial aggression, and found that cavity-nesting species physically attacked a simulated intruder more often than their close relatives. This pattern held for both females and males. Because territorial aggression is often associated with elevated testosterone, we also hypothesized that cavity-nesting species would exhibit higher testosterone levels in circulation. However, cavity-nesting species did not have higher testosterone in circulation for either sex, despite some correlative evidence that testosterone is associated with higher rates of physical attack in female tree swallows. Our focus on a competitive context that is relevant to both sexes – competition over essential breeding resources – provides a useful comparative framework for co-consideration of proximate and ultimate drivers of reproductive competition in females and males.

scholarly journals Diversity of Free-Living and Attached Bacteria in Offshore Western Mediterranean Waters as Depicted by Analysis of Genes Encoding 16S rRNA

1999 ◽  
Vol 65 (2) ◽  
pp. 514-522 ◽  
Author(s):  
Silvia G. Acinas ◽  
Josefa Antón ◽  
Francisco Rodríguez-Valera
Keyword(s):  
16S Rdna ◽  
Restriction Analysis ◽  
Western Mediterranean ◽  
Bacterial Cells ◽  
Free Living ◽  
Attached Bacteria ◽  
Genes Encoding ◽  
Community Fingerprinting ◽  
Close Relatives ◽  
Alteromonas Macleodii

ABSTRACT In a previous study (S. G. Acinas, F. Rodrı́guez-Valera, and C. Pedrós-Alió, FEMS Microbiol. Ecol. 24:27–40, 1997), community fingerprinting by 16S rDNA restriction analysis applied to Mediterranean offshore waters showed that the free-living pelagic bacterial community was very different from the bacterial cells aggregated or attached to particles of more than about 8 μm. Here we have studied both assemblages at three depths (5, 50, and 400 m) by cloning and sequencing the 16S rDNA obtained from the same samples, and we have also studied the samples by scanning electron microscopy to detect morphology patterns. As expected, the sequences retrieved from the assemblages were very different. The subsample of attached bacteria contained very little diversity, with close relatives of a well-known species of marine bacteria, Alteromonas macleodii, representing the vast majority of the clones at every depth. On the other hand, the free-living assemblage was highly diverse and varied with depth. At 400 m, close relatives of cultivated γProteobacteria predominated, but as shown by other authors, near the surface most clones were related to phylotypes described only by sequence, in which the α Proteobacteria of the SAR11 cluster predominated. The new technique of rDNA internal spacer analysis has been utilized, confirming these results. Clones representative of the A. macleodii cluster have been completely sequenced, producing a picture that fits well with the idea that they could represent a genus with at least two species and with a characteristic depth distribution.

scholarly journals Single cell genomics reveals plastid-lacking Picozoa are close relatives of red algae

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Max E. Schön ◽  
Vasily V. Zlatogursky ◽  
Rohan P. Singh ◽  
Camille Poirier ◽  
Susanne Wilken ◽  
...  
Keyword(s):  
Single Cell ◽  
Red Algae ◽  
Free Living ◽  
Plastid Evolution ◽  
Single Cell Genomics ◽  
Close Relatives ◽  
Globally Distributed ◽  
Eukaryotic Supergroup ◽  
Rare Group ◽  
Endosymbiotic Origin

AbstractThe endosymbiotic origin of plastids from cyanobacteria gave eukaryotes photosynthetic capabilities and launched the diversification of countless forms of algae. These primary plastids are found in members of the eukaryotic supergroup Archaeplastida. All known archaeplastids still retain some form of primary plastids, which are widely assumed to have a single origin. Here, we use single-cell genomics from natural samples combined with phylogenomics to infer the evolutionary origin of the phylum Picozoa, a globally distributed but seemingly rare group of marine microbial heterotrophic eukaryotes. Strikingly, the analysis of 43 single-cell genomes shows that Picozoa belong to Archaeplastida, specifically related to red algae and the phagotrophic rhodelphids. These picozoan genomes support the hypothesis that Picozoa lack a plastid, and further reveal no evidence of an early cryptic endosymbiosis with cyanobacteria. These findings change our understanding of plastid evolution as they either represent the first complete plastid loss in a free-living taxon, or indicate that red algae and rhodelphids obtained their plastids independently of other archaeplastids.

scholarly journals Factors mediating plastid dependency and the origins of parasitism in apicomplexans and their close relatives

2015 ◽  
Vol 112 (33) ◽  
pp. 10200-10207 ◽  
Author(s):  
Jan Janouškovec ◽  
Denis V. Tikhonenkov ◽  
Fabien Burki ◽  
Alexis T. Howe ◽  
Martin Kolísko ◽  
...  
Keyword(s):  
Plastid Genome ◽  
Sequence Data ◽  
Sister Group ◽  
Molecular Characteristics ◽  
Phylogenomic Analysis ◽  
Free Living ◽  
Plastid Genomes ◽  
Monophyletic Lineage ◽  
Causative Agents ◽  
Close Relatives

Apicomplexans are a major lineage of parasites, including causative agents of malaria and toxoplasmosis. How such highly adapted parasites evolved from free-living ancestors is poorly understood, particularly because they contain nonphotosynthetic plastids with which they have a complex metabolic dependency. Here, we examine the origin of apicomplexan parasitism by resolving the evolutionary distribution of several key characteristics in their closest free-living relatives, photosynthetic chromerids and predatory colpodellids. Using environmental sequence data, we describe the diversity of these apicomplexan-related lineages and select five species that represent this diversity for transcriptome sequencing. Phylogenomic analysis recovered a monophyletic lineage of chromerids and colpodellids as the sister group to apicomplexans, and a complex distribution of retention versus loss for photosynthesis, plastid genomes, and plastid organelles. Reconstructing the evolution of all plastid and cytosolic metabolic pathways related to apicomplexan plastid function revealed an ancient dependency on plastid isoprenoid biosynthesis, predating the divergence of apicomplexan and dinoflagellates. Similarly, plastid genome retention is strongly linked to the retention of two genes in the plastid genome, sufB and clpC, altogether suggesting a relatively simple model for plastid retention and loss. Lastly, we examine the broader distribution of a suite of molecular characteristics previously linked to the origins of apicomplexan parasitism and find that virtually all are present in their free-living relatives. The emergence of parasitism may not be driven by acquisition of novel components, but rather by loss and modification of the existing, conserved traits.

scholarly journals Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia)

2018 ◽  
Author(s):  
Eli Amson ◽  
John A Nyakatura
Keyword(s):  
Bone Structure ◽  
Phylogenetic Signal ◽  
Great Accuracy ◽  
Long Bone ◽  
Comparative Approach ◽  
High Resolution Computed Tomography ◽  
3D Architecture ◽  
Bone Trabeculae ◽  
Close Relatives ◽  
Ground Sloths

ABSTRACTTrabecular architecture (i.e., the main orientation of the bone trabeculae, their number, mean thickness, spacing, etc.) has been shown experimentally to adapt with great accuracy and sensitivity to the loadings applied to the bone during life. However, the potential of trabecular parameters used as a proxy for the mechanical environment of an organism’s organ to help reconstruct the lifestyle of extinct taxa has only recently started to be exploited. Furthermore, these parameters are rarely combined to the long-used mid-diaphyseal parameters to inform such reconstructions. Here we investigate xenarthrans, for which functional and ecological reconstructions of extinct forms are particularly important in order to improve our macroevolutionary understanding of their main constitutive clades, i.e., the Tardigrada (sloths), Vermilingua (anteaters), and Cingulata (armadillos and extinct close relatives). The lifestyles of modern xenarthrans can be classified as fully terrestrial and highly fossorial (armadillos), arboreal (partly to fully) and hook-and-pull digging (anteaters), or suspensory (fully arboreal) and non-fossorial (sloths). The degree of arboreality and fossoriality of some extinct forms, “ground sloths” in particular, is highly debated. We used high-resolution computed tomography to compare the epiphyseal 3D architecture and mid-diaphyseal structure of the forelimb bones of extant and extinct xenarthrans. The comparative approach employed aims at inferring the most probable lifestyle of extinct taxa, using phylogenetically informed discriminant analyses. Several challenges preventing the attribution of one of the extant xenarthran lifestyles to the sampled extinct sloths were identified. Differing from that of the larger “ground sloths”, the bone structure of the small-sized Hapalops (Miocene of Argentina), however, was found as significantly more similar to that of extant sloths, even when accounting for the phylogenetic signal.

scholarly journals Crossover interference and sex-specific genetic maps shape identical by descent sharing in close relatives

2019 ◽  
Author(s):  
Madison Caballero ◽  
Daniel N. Seidman ◽  
Jens Sannerud ◽  
Thomas D. Dyer ◽  
Donna M. Lehman ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Real Data ◽  
Genetic Maps ◽  
Pedigree Data ◽  
Crossover Interference ◽  
Interference Modeling ◽  
Identical By Descent ◽  
Close Relatives ◽  
The Impact ◽  
Number Of Segments

AbstractSimulations of close relatives and identical by descent (IBD) segments are common in genetic studies, yet most past efforts have utilized sex averaged genetic maps and ignored crossover interference, thus omitting features known to affect the breakpoints of IBD segments. We developed Ped-sim, a method for simulating relatives that can utilize either sex-specific or sex averaged genetic maps and also either a model of crossover interference or the traditional Poisson model for inter-crossover distances. To characterize the impact of previously ignored mechanisms, we simulated data for all four combinations of these factors. We found that modeling crossover interference decreases the standard deviation of the IBD proportion by 10.4% on average in full siblings through second cousins. By contrast, sex-specific maps increase this standard deviation by 4.2% on average, and also impact the number of segments relatives share. Most notably, using sex-specific maps, the number of segments half-siblings share is bimodal; and when combined with interference modeling, the probability that sixth cousins have non-zero IBD ranges from 9.0 to 13.1%, depending on the sexes of the individuals through which they are related. We present new analytical results for the distributions of IBD segments under these models and show they match results from simulations. Finally, we compared IBD sharing rates between simulated and real relatives and find that the combination of sex-specific maps and interference modeling most accurately captures IBD rates in real data. Ped-sim is open source and available fromhttps://github.com/williamslab/ped-sim.Author summarySimulations are ubiquitous throughout statistical genetics in order to generate data with known properties, enabling tests of inference methods and analyses of real world processes in settings where experimental data are challenging to collect. Simulating genetic data for relatives in a pedigree requires the synthesis of chromosomes parents transmit to their children. These chromosomes form as a mosaic of a given parent’s two chromosomes, with the location of switches between the two parental chromosomes known as crossovers. Detailed information about crossover generation based on real data from humans now exists, including the fact that men and women have overall different rates (women produce ~1.6 times more crossovers) and that real crossovers are subject tointerference—whereby crossovers are further apart from one another than expected under a model that selects their locations randomly. Our new method, Ped-sim, can simulate pedigree data using these less commonly modeled crossover features, and we used it to evaluate the importance of sex-specific rates and interference in real data. These comparisons show that both factors shape the amount of DNA two relatives share identically, and that their inclusion in models of crossover better fit data from real relatives.

Body size and segmentation patterns in free-living and parasitic polychaetes

2001 ◽  
Vol 79 (5) ◽  
pp. 741-745 ◽  
Author(s):  
Robert Poulin
Keyword(s):  
Life History ◽  
Body Length ◽  
Life History Traits ◽  
The Body ◽  
Free Living ◽  
Body Segments ◽  
The Family ◽  
Body Sizes ◽  
Number Of Segments ◽  
Over Time

Taxa that include both free-living and parasitic lineages present opportunities to examine if and how the life-history traits of parasitic organisms have diverged from those of their free-living relatives. In a comparative analysis the body sizes and numbers of body segments of parasitic polychaetes of the family Oenonidae were compared with those of free-living polychaetes from closely related families. There was no difference in body length between oenonids and free-living polychaetes. However, the parasitic oenonids attain, on average, a much higher number of body segments than their free-living counterparts. The number of segments per unit body length is also much higher in oenonids than in related free-living polychaetes. This suggests that new segments are produced at a higher rate or for longer periods in oenonids than in free-living polychaetes, in which the proliferation of new segments slows down over time to allow for the segments to grow in size. Given that each segment can produce gametes late in the life of the worm, the proliferation of segments in oenonids may be an adaptation to their parasitic life-style.

scholarly journals Habitats of native and exotic plants in Colorado shortgrass steppe: a comparative approach

1998 ◽  
Vol 76 (4) ◽  
pp. 664-672 ◽  
Author(s):  
Peter M Kotanen ◽  
Joy Bergelson ◽  
Donald L Hazlett
Keyword(s):  
Geographic Origin ◽  
Habitat Characteristics ◽  
Comparative Approach ◽  
Riparian Zones ◽  
Common Ancestry ◽  
Central Plains ◽  
Invading Species ◽  
Close Relatives ◽  
Grassland Habitats ◽  
The Relationship

Invading species often are close relatives, and therefore share many characteristics as a consequence of their common ancestry. This tends to confound studies of invasions, since many irrelevant characteristics are likely to be correlated with a species' geographic origin (alien or native). We address this problem by using phylogenetically independent comparisons to investigate the habitat characteristics of plants of the Central Plains Experimental Range (Colorado, U.S.A.). We initially show that exotic species are more likely than natives to occur in riparian zones, roadsides, and disturbed sites, and less likely to occur in grassland. The relationship between exotic origins and disturbed sites disappears when phylogenetic dependence is removed from the analyses; in contrast, the other associations persist following phylogenetic detrending, indicating that aliens and their native relatives consistently differ in their ability to exploit riparian, roadside, and grassland habitats. Our results indicate that disturbed sites currently are dominated by only a few groups of related exotic ruderals, while the ability to exploit roadsides and riparian zones has been and may continue to be important for the success of many taxa of invaders.Key words: biological invasions, comparative methods, disturbance, grasslands, phylogeny.

Life history evolution of nematodes: linking epidemiological modelling and comparative tests

Nematology ◽  
2002 ◽  
Vol 4 (5) ◽  
pp. 593-599 ◽  
Author(s):  
Serge Morand
Keyword(s):  
Life History ◽  
Life History Evolution ◽  
Monophyletic Group ◽  
Comparative Approach ◽  
Free Living ◽  
Comparative Tests ◽  
Epidemiological Modelling ◽  
Life Traits ◽  
Evolution Of Life ◽  
Unique Model

AbstractNematodes form a highly diversified, monophyletic group present in all environments as free-living individuals. As parasites they may infect plants, invertebrates and vertebrates. This group is then a unique model for testing evolutionary and ecological consequences of being a parasite. I summarise some recently published studies on the evolution of life traits of nematodes. Some predictions were obtained using the framework of epidemiological modelling and were tested using the comparative approach (and then some comparative methods).

scholarly journals The Role of Gene Duplication in the Divergence of Enzyme Function: A Comparative Approach

2021 ◽  
Vol 12 ◽  
Author(s):  
Alejandro Álvarez-Lugo ◽  
Arturo Becerra
Keyword(s):  
Gene Duplication ◽  
Representative Sample ◽  
High Ratio ◽  
Enzyme Function ◽  
Comparative Approach ◽  
Biochemical Traits ◽  
Free Living ◽  
New Genes ◽  
Enzyme Families

Gene duplication is a crucial process involved in the appearance of new genes and functions. It is thought to have played a major role in the growth of enzyme families and the expansion of metabolism at the biosphere’s dawn and in recent times. Here, we analyzed paralogous enzyme content within each of the seven enzymatic classes for a representative sample of prokaryotes by a comparative approach. We found a high ratio of paralogs for three enzymatic classes: oxidoreductases, isomerases, and translocases, and within each of them, most of the paralogs belong to only a few subclasses. Our results suggest an intricate scenario for the evolution of prokaryotic enzymes, involving different fates for duplicated enzymes fixed in the genome, where around 20–40% of prokaryotic enzymes have paralogs. Intracellular organisms have a lesser ratio of duplicated enzymes, whereas free-living enzymes show the highest ratios. We also found that phylogenetically close phyla and some unrelated but with the same lifestyle share similar genomic and biochemical traits, which ultimately support the idea that gene duplication is associated with environmental adaptation.

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