Nature and significance of intraspecific variation in the early Cambrian oryctocephalid trilobite Oryctocephalites palmeri Sundberg and McCollum, 1997

AbstractOryctocephalid trilobites are seldom abundant and often tectonically deformed, creating problems for robust species delimitation and compromising their utility in biostratigraphic and evolutionary studies. By studying more than 140 specimens recovered from the upper portion of the Combined Metals Member (Pioche Formation, Nevada; Cambrian Stage 4, Series 2), we exploit a rare opportunity to explore how morphological variation among oryctocephalid specimens is partitioned into intraspecific variation versus interspecific disparity. Qualitative and quantitative analyses reveal that two species are represented: Oryctocephalites palmeri Sundberg and McCollum, 1997 and Oryctocephalites sp. A, the latter known from a single cranidium stratigraphically below all occurrences of the former. In contrast to the conclusions of a previous study, there is no evidence of cranidial dimorphism in O. palmeri. However, that species exhibits considerable variation in cranidial shape and pygidial spine arrangement and number. Cranidial shape variation within O. palmeri is approximately one-half of the among-species disparity within the genus. Comparison of cranidial shape between noncompacted and compacted samples reveals that compaction causes significant change in mean shape and an increase in shape variation; such changes are interpretable in terms of observed fracture patterns. Nontaphonomic variation is partitioned into ontogenetic and nonallometric components. Those components share similar structure with each other and with interspecific disparity, suggesting that ontogenetic shape change might be an important source of variation available for selection. This highlights the importance of ontogenetic and taphonomic sources of variation with respect to species delimitation, morphospace occupation, and investigation of evolutionary patterns and processes.

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Ontogeny in the steinmanellines (Bivalvia: Trigoniida): an intra- and interspecific appraisal using the Early Cretaceous faunas from the Neuquén Basin as a case study

Paleobiology ◽

10.1017/pab.2021.32 ◽

2021 ◽

pp. 1-23

Author(s):

Pablo S. Milla Carmona ◽

Dario G. Lazo ◽

Ignacio M. Soto

Keyword(s):

Trajectory Analysis ◽

Sedentary Lifestyle ◽

Shape Change ◽

Shell Shape ◽

Shape Variation ◽

Ontogenetic Changes ◽

Ontogenetic Trajectories ◽

Higher Genus ◽

Gradual Decay

Abstract Despite the paleontological relevance and paleobiological interest of trigoniid bivalves, our knowledge of their ontogeny—an aspect of crucial evolutionary importance—remains limited. Here, we assess the intra- and interspecific ontogenetic variations exhibited by the genus Steinmanella Crickmay (Myophorellidae: Steinmanellinae) during the early Valanginian–late Hauterivian of Argentina and explore some of their implications. The (ontogenetic) allometric trajectories of seven species recognized for this interval were estimated from longitudinal data using 3D geometric morphometrics, segmented regressions, and model selection tools, and then compared using trajectory analysis and allometric spaces. Our results show that within-species shell shape variation describes biphasic ontogenetic trajectories, decoupled from ontogenetic changes shown by sculpture, with a gradual decay in magnitude as ontogeny progresses. The modes of change characterizing each phase (crescentic growth and anteroposterior elongation, respectively) are conserved across species, thus representing a feature of Steinmanella ontogeny; its evolutionary origin is inferred to be a consequence of the rate modification and allometric repatterning of the ancestral ontogeny. Among species, trajectories are more variable during early ontogenetic stages, becoming increasingly conservative at later stages. Trajectories’ general orientation allows recognition of two stratigraphically consecutive groups of species, hinting at a potentially higher genus-level diversity in the studied interval. In terms of functional morphology, juveniles had a morphology more suited for active burrowing than adults, whose features are associated with a sedentary lifestyle. The characteristic disparity of trigoniids could be related to the existence of an ontogenetic period of greater shell malleability betrayed by the presence of crescentic shape change.

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Evolutionary Patterns and Processes in Ferns

American Fern Journal ◽

10.2307/1546907 ◽

1979 ◽

Vol 69 (1) ◽

pp. 16

Author(s):

David B. Lellinger ◽

J. D. Lovis

Keyword(s):

Evolutionary Patterns ◽

Patterns And Processes

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Unravelling the hybrid vigor in domestic equids: the effect of hybridization on bone shape variation and covariation

BMC Evolutionary Biology ◽

10.1186/s12862-019-1520-2 ◽

2019 ◽

Vol 19 (1) ◽

Cited By ~ 4

Author(s):

Pauline Hanot ◽

Anthony Herrel ◽

Claude Guintard ◽

Raphaël Cornette

Keyword(s):

First Generation ◽

Shape Change ◽

Morphological Integration ◽

Hybrid Vigor ◽

F1 Hybrids ◽

Shape Variation ◽

Locomotor System ◽

Domestic Horses ◽

Functional Mechanisms ◽

Underlying Processes

Abstract Background Hybridization has been widely practiced in plant and animal breeding as a means to enhance the quality and fitness of the organisms. In domestic equids, this hybrid vigor takes the form of improved physical and physiological characteristics, notably for strength or endurance. Because the offspring of horse and donkey is generally sterile, this widely recognized vigor is expressed in the first generation (F1). However, in the absence of recombination between the two parental genomes, F1 hybrids can be expected to be phenotypically intermediate between their parents which could potentially restrict the possibilities of an increase in overall fitness. In this study, we examine the morphology of the main limb bones of domestic horses, donkeys and their hybrids to investigate the phenotypic impact of hybridization on the locomotor system. We explore bone shape variation and covariation to gain insights into the morphological and functional expressions of the hybrid vigor commonly described in domestic equids. Results Our data reveal the occurrence of transgressive effects on several bones in the F1 generation. The patterns of morphological integration further demonstrate that the developmental processes producing covariation are not disrupted by hybridization, contrary to functional ones. Conclusions These results suggest that an increase in overall fitness could be related to more flexibility in shape change in hybrids, except for the main forelimb long bones of which the morphology is strongly driven by muscle interactions. More broadly, this study illustrates the interest of investigating not only bone shape variation but also underlying processes, in order to contribute to better understanding how developmental and functional mechanisms are affected by hybridization.

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Redescription of Mastigias papua (Scyphozoa, Rhizostomeae) with designation of a neotype and recognition of two additional species

Zootaxa ◽

10.11646/zootaxa.4457.4.2 ◽

2018 ◽

Vol 4457 (4) ◽

pp. 520 ◽

Cited By ~ 4

Author(s):

MARIANA ROCHA DE SOUZA ◽

MICHAEL N DAWSON

Keyword(s):

Pacific Islands ◽

Parallel Evolution ◽

Morphological Characters ◽

The Philippines ◽

Type Specimens ◽

Additional Species ◽

Evolutionary Patterns ◽

Molecular Analyses ◽

Taxonomic Approach ◽

Patterns And Processes

Mastigias, the ‘golden’ or ‘spotted’ jellyfish, is distributed throughout the Indo-Pacific. Specimens are identified routinely as Mastigias papua, although eight species were described historically, and molecular analyses evince at least three phylogenetic species. Understanding species diversity in Mastigias has become a priority because of its growing relevance in studies of boom-bust dynamics related to environmental change, cryptic species, local adaptation, parallel evolution, and peripatric speciation. However, species delimitation and identification are inhibited by a dearth of type specimens for most species, including M. papua. We address these issues by resampling Mastigias from the type locality in Waigeo, West Papua, as well as in the Philippines, and by comparing cytochrome c oxidase subunit I and up to 34 morphological characters of 268 Mastigias specimens from surrounding regions in the Indo-Pacific. We also gathered data from the historical descriptions of the eight species of Mastigias to estimate the identity of the two other currently revealed clades. Using this integrative taxonomic approach, we re-describe Mastigias papua as endemic to the tropical western Pacific islands (including Papua, Palau, Enewetak) and designate a neotype for the species. Additionally, based on morphological similarity and geographic overlap, we identified a second clade most probably as M. albipunctatus (from Japan, Komodo, Berau and Philippines) and a third clade tentatively as either M. andersoni or M. ocellatus. This study highlights the benefits of combining molecular analyses, samples from type locations, traditional descriptions and statistical analyses of morphological variation in systematic studies, and the concomitant potential of such studies to increase understanding of evolutionary patterns and processes in Scyphozoa.

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Morphological evolution of the bivalvePtychomyathrough the Lower Cretaceous of Argentina

Paleobiology ◽

10.1017/pab.2017.32 ◽

2018 ◽

Vol 44 (1) ◽

pp. 101-117

Author(s):

Pablo S. Milla Carmona ◽

Darío G. Lazo ◽

Ignacio M. Soto

Keyword(s):

Time Series ◽

Morphological Variation ◽

Morphological Evolution ◽

The Other ◽

Upward Trend ◽

Shell Size ◽

Evolutionary Patterns ◽

Upper Hauterivian ◽

Patterns And Processes ◽

Early Late

AbstractThe complex morphological evolution of the bivalvePtychomyathroughout the well-studied Agrio Formation in the Neuquén Basin (west-central Argentina, lower/upper Valanginian–lowest Barremian) constitutes an ideal opportunity to study evolutionary patterns and processes occurring at geological timescales. Ptychomyais represented in this unit by four species, the morphological variation of which needs to be temporally assessed to obtain a thorough picture of the evolution of the group. Here we use geometric morphometrics to measure variation in shell outline, ribbing pattern, and shell size in these species. We bracket the ages of our samples using a combination of ammonoid biostratigraphy and absolute ages and study the anagenetic pattern of evolution of each trait by means of paleontological time-series analysis and change tracking. We find that evolution inPtychomyais mostly speciational, as the majority of traits show stasis, with the exceptions of shell size inP. coihuicoensisand shell outline inP. windhauseni, which seem to evolve directionally toward larger and higher shells, respectively.Ptychomyadisplays changes in its average morphology and disparity, which are the result of a mixture of taxonomic turnover and mosaic evolution of traits. Pulses of speciation would have been triggered by ecological opportunity, as they occur during the recovery of shallow-burrowing bivalve faunas after dysoxic events affecting the basin. On the other hand, the presence of directional patterns of evolution inP. coihuicoensisandP. windhauseniseems to be the result of a general shallowing-upward trend observed in the basin during the upper Hauterivian–lowest Barremian, as opposed to the cyclical paleoenvironmental stability inferred for the early/late Valanginian–early Hauterivian, which would have prompted stasis inP. koeneniandP. esbelta.

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Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes

Integrative and Comparative Biology ◽

10.1093/icb/icz033 ◽

2019 ◽

Vol 59 (3) ◽

pp. 616-624 ◽

Cited By ~ 9

Author(s):

Emma Sherratt ◽

Kate L Sanders ◽

Amy Watson ◽

Mark N Hutchinson ◽

Michael S Y Lee ◽

...

Keyword(s):

Morphological Changes ◽

Shape Variation ◽

Micro Computed Tomography ◽

Trophic Specialization ◽

Evolutionary Patterns ◽

Dietary Specialization ◽

Geometric Morphometric ◽

Sea Snakes ◽

Morphometric Methods ◽

Cranial Shape

Abstract Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here we use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes.

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Larval anatomy of Andean tadpoles of Telmatobius (Anura: Ceratophryidae) from Northwestern Argentina

Zootaxa ◽

10.11646/zootaxa.1938.1.3 ◽

2008 ◽

Vol 1938 (1) ◽

pp. 40-60 ◽

Cited By ~ 13

Author(s):

M. FLORENCIA VERA CANDIOTI

Keyword(s):

Intraspecific Variation ◽

Characteristic Pattern ◽

Species Discrimination ◽

Shape Variation ◽

Geometric Morphometric ◽

Northwestern Argentina ◽

Preliminary Results ◽

Internal Morphology ◽

Morphometric Methods ◽

Interspecific And Intraspecific Variation

In this paper I study the oral, buccopharyngeal, and musculoskeletal configuration in tadpoles of nine Telmatobius species from Northwestern Argentina (T. atacamensis, T. ceiorum, T. laticeps, T. oxycephalus, T. pinguiculus, T. pisanoi, T. cf. schreiteri, T. scrocchii, and T. stephani; N = 30, Gosner stages 31–36). Specimens were prepared according to standard clearing and staining protocols; additionally, I applied landmark and outline-based geometric morphometric methods in order to quantify shape variation in chondrocrania, hyobranchial skeletons, and suprarostral cartilages. Although preliminary, results show a marked morphological uniformity on the analyzed levels, and overlapping interspecific and intraspecific variation, which renders species discrimination difficult. Some distinctive traits for the genus are bicuspidate buccal spurs, peculiar arrangement of buccal roof and floor papillae, tetrapartite suprarostral, adrostral cartilages, a lateral slip of the m. subarcualis rectus II-IV invading branchial septum IV, and a characteristic pattern of muscles inserted on the diaphragm. The conservative larval internal morphology in this genus could be explained by a recent speciation and a development possibly characterized by the postmetamorphic appearance of specific features.En este trabajo estudio la morfología oral, bucofaríngea y musculoesquelética de larvas de nueve especies de Telmatobius del Noroeste argentino (T. atacamensis, T. ceiorum, T. laticeps, T. oxycephalus, T. pinguiculus, T. pisanoi, T. cf. schreiteri, T. scrocchii y T. stephani; N = 30, estadios de Gosner 31–36). Los especímenes se prepararon siguiendo protocolos clásicos de transparentación y coloración diferencial; adicionalmente, apliqué métodos de morfometría geométrica basada en landmarks y contornos para cuantificar la variación de formas en condrocráneos, esqueletos hiobranquiales y cartílagos suprarostrales. Aunque de carácter preliminar, los resultados muestran una notable uniformidad morfológica en los niveles analizados, y una variación intraespecífica que se superpone con la interespecífica, dificultando la distinción entre especies. Algunos rasgos distintivos del género son un par de espolones bucales bífidos, un arreglo particular de las papilas del techo y piso bucales, suprarostral tetrapartito, adrostrales, un haz del m. subarcualis rectus II-IV invadiendo el septo branquial IV, y un patrón aparentemente característico de los músculos insertos en el diafragma. La morfología larval interna conservadora en el género podría explicarse por una especiación reciente y un desarrollo posiblemente caracterizado por la aparición postmetamórfica de los rasgos específicos.

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Universal rules of life: metabolic rates, biological times and the equal fitness paradigm

10.22541/au.161226628.83797509/v1 ◽

2021 ◽

Author(s):

Joseph Burger ◽

Chen Hou ◽

Charles Hall ◽

James Brown

Keyword(s):

Structure And Function ◽

The Other ◽

Metabolic Rates ◽

Synthetic Theory ◽

Evolutionary Patterns ◽

Single Origin ◽

The One ◽

Patterns And Processes ◽

And Function ◽

Dynamics Of Populations

Here we review and extend the equal fitness paradigm (EFP) as an important step in developing and testing a synthetic theory of ecology and evolution based on energy and metabolism. The EFP states that all organisms are equally fit at steady state, because they allocate the same quantity of energy, ~22.4 kJ/g/generation to production of offspring. On the one hand, the EFP may seem tautological, because equal fitness is necessary for the origin and persistence of biodiversity. On the other hand, the EFP reflects universal laws of life: how biological metabolism – the uptake, transformation and allocation of energy – links ecological and evolutionary patterns and processes across levels of organization from: i) structure and function of individual organisms, ii) life history and dynamics of populations, iii) interactions and coevolution of species in ecosystems. The physics and biology of metabolism have facilitated the evolution of millions of species with idiosyncratic anatomy, physiology, behavior and ecology but also with many shared traits and tradeoffs that reflect the single origin and universal rules of life.

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A review of the taxonomy of spiny-backed orb-weaving spiders of the subfamily Gasteracanthinae (Araneae, Araneidae) in Thailand

ZooKeys ◽

10.3897/zookeys.1032.62001 ◽

2021 ◽

Vol 1032 ◽

pp. 17-62

Author(s):

Kongkit Macharoenboon ◽

Warut Siriwut ◽

Ekgachai Jeratthitikul

Keyword(s):

Phylogenetic Tree ◽

Cryptic Species ◽

Species Identification ◽

Intraspecific Variation ◽

Molecular Species ◽

Species Delimitation ◽

Coi Gene ◽

Nominal Species ◽

Model Species ◽

And Behavior

Spiny-backed orb-weaving spiders of the subfamily Gasteracanthinae are broadly distributed in the Old World. Despite their use as a model species in biology, evolution, and behavior because of their extraordinary characteristics, the systematics of this group of spiders are still poorly understood. This study elucidates the systematics of Gasteracanthinae in Thailand based on morphological and molecular-based analyses. In total, seven species from three genera, namely Gasteracantha, Macracantha, and Thelacantha, were recorded in Thailand. Shape of abdominal spines, pattern of sigilla, and female genitalia are significant characters for species identification. In contrast, coloration shows highly intraspecific variation in most species within Gasteracanthinae. A phylogenetic tree based on partial sequences of COI, 16S, and H3 genes recovered Gasteracanthinae as a monophyletic group and supports the existence of three clades. Gasteracantha hasselti is placed as a sister taxon to Macracantha arcuata. Hence, we propose to transfer G. hasselti to Macracantha. Moreover, molecular species delimitation analyses (ABGD, bPTP, and GMYC) using 675 bp of COI gene support all nominal species, with evidence of possible additional cryptic species.

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The systematic relationships and biogeographic history of ornithischian dinosaurs

PeerJ ◽

10.7717/peerj.1523 ◽

2015 ◽

Vol 3 ◽

pp. e1523 ◽

Cited By ~ 47

Author(s):

Clint A. Boyd

Keyword(s):

North America ◽

South America ◽

Wide Distribution ◽

Sister Taxon ◽

Evolutionary Patterns ◽

Biogeographic History ◽

Early Diversification ◽

Systematic Relationships ◽

Patterns And Processes ◽

Comprehensive Framework

The systematic relationships of taxa traditionally referred to as ‘basal ornithopods’ or ‘hypsilophodontids’ remain poorly resolved since it was discovered that these taxa are not a monophyletic group, but rather a paraphyletic set of neornithischian taxa. Thus, even as the known diversity of these taxa has dramatically increased over the past two decades, our knowledge of their placement relative to each other and the major ornithischian subclades remained incomplete. This study employs the largest phylogenetic dataset yet compiled to assess basal ornithischian relationships (255 characters for 65 species level terminal taxa). The resulting strict consensus tree is the most well-resolved, stratigraphically consistent hypothesis of basal ornithischian relationships yet hypothesized. The only non-iguanodontian ornithopod (=basal ornithopod) recovered in this analysis isHypsilophodon foxii. The majority of former ‘hypsilophodontid’ taxa are recovered within a single clade (Parksosauridae) that is situated as the sister-taxon to Cerapoda. The Parksosauridae is divided between two subclades, the Orodrominae and the Thescelosaurinae. This study does not recover a clade consisting of the Asian taxaChangchunsaurus,Haya, andJeholosaurus(=Jeholosauridae). Rather, the former two taxa are recovered as basal members of Thescelosaurinae, while the latter taxon is recovered in a clade withYueosaurusnear the base of Neornithischia.The endemic South American clade Elasmaria is recovered within the Thescelosaurinae as the sister taxon toThescelosaurus. This study supports the origination of Dinosauria and the early diversification of Ornithischia within Gondwana. Neornithischia first arose in Africa by the Early Jurassic before dispersing to Asia before the late Middle Jurassic, where much of the diversification among non-cerapodan neornithischians occurred. Under the simplest scenario the Parksosauridae originated in North America, with at least two later dispersals to Asia and one to South America. However, when ghost lineages are considered, an alternate dispersal hypothesis has thescelosaurines dispersing from Asia into South America (via North America) during the Early Cretaceous, then back into North America in the latest Cretaceous. The latter hypothesis may explain the dominance of orodromine taxa prior to the Maastrichtian in North America and the sudden appearance and wide distribution of thescelosaurines in North America beginning in the early Maastrichtian. While the diversity of parksosaurids has greatly increased over the last fifteen years, a ghost lineage of over 40 myr is present between the base of Parksosauridae and Cerapoda, indicating that much of the early history and diversity of this clade is yet to be discovered. This new phylogenetic hypothesis provides a comprehensive framework for testing further hypotheses regarding evolutionary patterns and processes within Ornithischia.

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