Ontogenetic Variation Research Articles

Three New Species of Deep-Sea Wood-Associated Sea Stars (Asteroidea: Caymanostellidae) from the Eastern Pacific

Caymanostellidae is a group of rarely collected and morphologically unusual sea stars that have been exclusively encountered on wood falls in the deep sea. There are currently three genera and seven species described, occurring in the Atlantic, Pacific and Indian Oceans with a depth range between 418 and 6780 m. Three new species are here described from specimens collected from wood falls in multiple localities across the Pacific margin of Costa Rica and near the Gulf of California (Mexico): Caymanostella scrippscognaticausa sp. nov., Caymanostella davidalani sp. nov. and Caymanostella loresae sp. nov. These records expand the known geographical distribution of caymanostellids and constitute their first report from wood falls found at methane seeps. This study also includes the first descriptions of early-stage juvenile caymanostellids and reveals that traits previously considered useful for diagnosis might represent intraspecific and ontogenetic variability, with important consequences for caymanostellid taxonomy.

Multiple Paths to a Larger Mouth: Morphological Divergence in Two Island Populations of Australian Tiger Snakes (Notechis scutatus)

AbstractWe studied ontogenetic variation in skull morphology in tiger snakes sampled from mainland South Australia (Coffin Bay), mainland Western Australia (Herdsman Lake), Franklin Island, and Hopkins Island. The snakes from the two islands were selected because of their unusually large absolute body and head size, likely attained as a result of dietary constraints and strong selective pressure during thousands of years of isolation on islands. We performed geometric morphometric analysis of the skulls from these snakes to identify and precisely quantify morphological differences. Island snakes are born larger (trunk length) than mainland snakes, and consequently also tend to have larger absolute head size at birth. The heads of island snakes also show a faster relative growth rate (positive allometry) compared to those of mainland snakes, likely to cope with the large prey items found on these islands. However, the snakes from the two islands differ from each other in terms of morphological change associated with ontogeny, especially with regard to a palatal bone (ectopterygoid), which, compared to mainland snakes, is relatively longer in the snakes from Hopkins Island but shorter in the snakes from Franklin Island. Some morphological traits potentially associated with promoting a larger gape were also observed in one of the mainland populations (Herdsman Lake), consistent with standing variability for selection. Our results reveal that discernible changes in morphology and allometry in skull bones have evolved in island populations of tiger snakes in less than 10 000 years, and suggest that the large heads of island tiger snakes might develop via slightly different paths through morphospace on different islands.

A small sauropod trackway from the Upper Cretaceous Jindong Formation (Cenomanian), Goseong County, South Korea

In 2000, a small sauropod trackway was discovered in the Upper Cretaceous Jindong Formation (Cenomanian) at Eosin-ri, Goseong County, South Korea. This quadrupedal trackway consists of 34 very small sauropod footprints, with an average manus width of 10.0 cm and pes length of 12.8 cm, showing low heteropody (mean IPS/IMS: 1.38). The manus tracks are oval to kidney-shaped, while the pes tracks are generally subcircular to V-shaped, lacking distinct claw marks. The trackway shows a medium to wide gauge (mean PTR: 38.8%; WAP/PL: 1.18). The small footprint size and estimated trackmaker body size suggest that the trackmaker was an early juvenile titanosauriform sauropod based on the contemporaneous sauropod taxa of East Asia. Sauropod trackways reported from the Jindong Formation, including the Eosin-ri trackway, exhibit a tendency for narrower trackway gauges as pes length increases. This negative correlation between trackmaker size and trackway gauge may imply ontogenetic or behavioral variations within the same clade of sauropods or differences in gait or body plan amongst different sauropod taxa.

Palaeohistology of Macrospondylus bollensis (Crocodylomorpha: Thalattosuchia: Teleosauroidea) from the Posidonienschiefer Formation (Toarcian) of Germany, with insights into life history and ecology.

The Posidonienschiefer Formation of southern Germany has yielded an array of incredible fossil vertebrates. One of the best represented clades therein is Teleosauroidea, a successful thalattosuchian crocodylomorph group that dominated the coastlines. The most abundant teleosauroid, Macrospondylus bollensis, is known from a wide range of body sizes, making it an ideal taxon for histological and ontogenetic investigations. Previous studies examining thalattosuchian histology provide a basic understanding of bone microstructure in teleosauroids, but lack the taxonomic, stratigraphic, and ontogenetic control required to understand growth and palaeobiology within a species. Here, we examine the bone microstructure of three femora and one tibia from three different-sized M. bollensis individuals. We also perform bone compactness analyses to evaluate for ontogenetic and ecological variation. Our results suggests that (1) the smallest specimen was a young, skeletally immature individual with well-vascularized-parallel-fibered bone and limited remodeling in the midshaft periosteal cortex; (2) the intermediate specimen was skeletally immature at death, with vascularized parallel-fibered bone tissue interrupted by at least 10 LAGs, but no clear external fundamental system (EFS), and rather extensive inner cortical bone remodeling; and (3) the largest specimen was skeletally mature, with parallel-fibered bone tissue interrupted by numerous LAGs, a well-developed EFS, and extensive remodeling in the deep cortex. Macrospondylus bollensis grew relatively regularly until reaching adult size, and global bone compactness values fall within the range reported for modern crocodylians. The lifestyle inference models used suggest that M. bollensis was well adapted for an aquatic environment but also retained some ability to move on land. Finally, both larger specimens display a peculiar, localized area of disorganized bone tissue interpreted as pathological.

Evidence for resource partitioning in weakfishes from a coastal upwelling ecosystem

Resource partitioning plays an important role in supporting species coexistence. In a coastal upwelling ecosystem two weakfish species, Cynoscion guatucupa and C. jamaicensis co-occur and are key commercial species. The present study aimed to provide a comprehensive assessment of the feeding ecology of both species, including to; (i) quantitatively assess diet, (ii) evaluate ontogenetic and seasonal diet variations, and (iii) estimate dietary overlap in the context of competition or resource partitioning, using an integrated approach combining stomach content (SCA) and stable isotope analyses (SIA). Our results revealed that both C. guatucupa and C. jamaicensis prey mainly on pelagic fish and shrimp with ontogenetic and seasonal changes in diet detected. Weakfishes consume a large proportion of similar prey throughout the year and high isotopic niche overlap confirmed the SCA results. Despite the similar use of food resources by both species, the availability and abundance of prey promoted by seasonal upwellings and the possible spatial segregation between C. guatucupa and C. jamaicensis may promote their co-occurrence in an upwelling ecosystem. Due to their commercial value and fisheries importance in the southwestern Atlantic, these results contribute insights to support sustainable fisheries management.

Tiny but Mighty: Vipera ammodytes meridionalis (Eastern Long-Nosed Viper) Ontogenetic Venom Variations in Procoagulant Potency and the Impact on Antivenom Efficacies.

The Eastern Long-Nosed Viper (Vipera ammodytes meridionalis) is considered one of the most venomous snakes in Europe. However, it is unknown whether ontogenetic variation in venom effects occurs in this subspecies and how this may impact antivenom efficacy. In this study, we compared the procoagulant activities of V. a. meridionalis venom on human plasma between neonate and adult venom phenotypes. We also examined the efficacy of three antivenoms-Viperfav, ViperaTAb, and Inoserp Europe-across our neonate and adult venom samples. While both neonate and adult V. a. meridionalis venoms produced procoagulant effects, the effects produced by neonate venom were more potent. Consistent with this, neonate venom was a stronger activator of blood-clotting zymogens, converting them into their active forms, with a rank order of Factor X >> Factor VII > Factor XII. Conversely, the less potent adult venom had a rank order of FXII marginally more activated than Factor VII, and both much more so than Factor X. This adds to the growing body of evidence that activation of factors besides FII (prothrombin) and FX are significant variables in reptile venom-induced coagulopathy. Although all three examined antivenoms displayed effective neutralization of both neonate and adult V. a. meridionalis venoms, they generally showed higher efficacy on adult venom than on neonate venom. The ranking of antivenom efficacy against neonate venom, from the most effective to the least effective, were Viperfav, Inoserp Europe, ViperaTAb; for adult venom, the ranking was Inoserp Europe, Viperfav, ViperaTAb. Our data reveal ontogenetic variation in V. a meridionalis, but this difference may not be of clinical concern as antivenom was effective at neutralizing both adult and neonate venom phenotypes. Regardless, our results highlight a previously undocumented ontogenetic shift, likely driven by the documented difference in prey preference observed for this species across age classes.

Reassessment of a theropod ilium from the Kem Kem beds of Morocco and the evolution of ilia in Spinosauridae

A theropod ilium MHNM KK04 from the Kem Kem Beds (Cenomanian) of Morocco was originally described as an abelisaurid. It is here reinterpreted as a spinosaurine spinosaurid. The phylogenetic relationships of MHNM KK04 were analyzed. A thorough and careful comparison between spinosaurids and abelisaurids was made. The Kem Kem ilium was identified as a spinosaurid based on the similarity to the Spinosaurus aegyptiacus neotype and the MSNM V6900 specimen (i.e., the lateral wall of brevis fossa is taller than the medial wall, the ventral margin of the postacetabular blade is straight, and the ventral margin of postacetabular process is posteroventrally oriented). However, MHNM KK04 is slightly different from the ilium of the Spinosaurus aegyptiacus neotype (i.e., the ilium dorsal margin is sub-horizontal to slightly anteriorly inclined, the dorsoventral height of the iliac blade at the postacetabular portion is approximately the same size as the blade height above the acetabulum, and the postacetabulum length is slightly longer than the ischial peduncle length). MHNM KK04, together with previous studies, shows that there were at least two morphotypes of spinosaurines in the Late Cretaceous of Kem Kem beds. Nevertheless, taphonomy, intraspecific or ontogenetic variation cannot be ruled out in the present work. This reclassification adds to the number of juvenile spinosaurines from the Kem Kem beds and provided evidence on the evolution of ilia in spinosaurids.

Green lizards (Squamata, Lacertidae) from ?Pliocene deposits of Węże I in southern Poland, with comments on cranial features for selected lacertids

AbstractI here describe lacertids from the classic Węże I locality in southern Poland (?Pliocene deposits) based on six previously undescribed jaws: an incomplete left maxilla, two dentaries and three mandibles. These jaws collectively provide considerable data on the morphology of the maxilla, dentary, teeth, coronoid, splenial, angular, surangular and prearticular. All six jaws can be unequivocally allocated to Lacertidae and five of those are allocated to European green lizards of the Lacerta viridis group. Currently, La. viridis has regionally extinct or probably extinct status in Poland. The material from Węże I provides evidence that European green lizards had a large geographic distribution in Europe, including Poland during the ?Pliocene. One mandible fragment appears to be slightly different and is allocated to Lacertidae indet. That mandible might point to a higher taxonomic diversity of lacertids in this locality. However, that interpretation needs to be viewed with caution, because based on such limited material, individual and/or ontogenetic variation cannot be ruled out. To reveal the real taxonomic palaeodiversity of lacertids in Węże I, new and more complete cranial material is needed. In addition, this article provides insights into the comparative osteology of skulls and selected cranial elements in lacertids.

Description of newly discovered cranial remains of Decennatherium rex juveniles from Batallones-10 (Late Miocene, Iberian Peninsula)

ABSTRACT The identification of additional Late Miocene (MN10, Late Vallesian) Decennatherium rex cranial remains at Batallones-10 (Torrejón de Velasco, Madrid Basin, Spain) provides valuable insights into the ontogenetic variability of this extinct giraffe. Most recovered specimens are adults, making the discovery of calves significant. The 2022 excavation yielded two juvenile hemimandibles, a maxilla, and a juvenile ossicone, likely from different individuals. The dental material represents one of the youngest specimens in the Batallones complex, with an estimated age of 4 months to 4.5 years, based on molar eruption stages seen in modern giraffes. The ossicone, resembling that of an adult male in shape but much smaller, mirrors the growth patterns in extant giraffes, where juvenile ossicones share adult proportions but are smaller. This ossicone was detached from the skull, typical for juveniles, as ossicones do not fuse with the cranial roof until later. This discovery broadens our understanding of giraffe ontogeny and includes the first giraffe calf ossicone found in the Iberian fossil record.

Otolith morphology of mesopelagic fishes collected from the Irminger Sea, North Atlantic Ocean

A large series of otoliths of 16 mesopelagic teleost fish species from the Irminger Sea, North Atlantic Ocean, are described morphologically to investigate the ontogenetic and intraspecific variation. The results show that the surface morphology of the otoliths between young and adult specimens is variable, especially in the alepocephaliform (Normichthys operosus, Sagamichthys schnakenbecki, Xenodermichthys copei) and astronesthine (Borostomias antarcticus) species. The diagnostic features of the otoliths can be used to confirm the identity of the species, especially in myctophids, where confusion between Benthosema glaciale and Myctophum punctatum may be possible. A SEM-based iconography of the otoliths of all studied species is presented.

Ontogenetic variation in metabolic rate-temperature relationships during larval development.

Predictive models of ectotherm responses to environmental change often rely on thermal performance data from the literature. For insects, the majority of these data focus on two traits, development rate and thermal tolerance limits. Data are also often limited to the adult stage. Consequently, predictions based on these data generally ignore other measures of thermal performance and do not account for the role of ontogenetic variation in thermal physiology across the complex insect life cycle. Theoretical syntheses for predicting metabolic rate also make similar assumptions despite the strong influence of body size as well as temperature on metabolic rate. The aim of this study was to understand the influence of ontogenetic variation on ectotherm physiology and its potential impact on predictive modeling. To do this, we examined metabolic rate-temperature (MR-T) relationships across the larval stage in a laboratory strain of the spongy moth (Lymantria dispar dispar). Routine metabolic rates (RMRs) of larvae were assayed at eight temperatures across the first five instars of the larval stage. After accounting for differences in body mass, larval instars showed significant variation in MR-T. Both the temperature sensitivity and allometry of RMR increased and peaked during the third instar, then declined in the fourth and fifth instar. Generally, these results show that insect thermal physiology does not remain static during larval ontogeny and suggest that ontogenetic variation should be an important consideration when modeling thermal performance.

The skull of the Turks and Caicos rock iguana, Cyclura carinata (Squamata: Iguanidae).

We provide a detailed and first description of the skull, hyoid apparatus, and trachea of the Turks and Caicos rock iguana, Cyclura carinata (Squamata: Iguanidae). Cyclura is a radiation of iguanas restricted to islands of the Caribbean Sea. Species of Cyclura have high rates of endemism, and all species are severely threatened with extinction. Our anatomical description of this threatened iguana is based on high-resolution computed tomography scans of one adult, one putative adult or near adult, and one juvenile specimen, and includes three-dimensional segmented renderings and visualizations. We discuss some observations of intraspecific and ontogenetic variation, and provide a brief comparison with specimens of another species of Cyclura and published descriptions of other iguanas. Our study provides a cranial osteological framework for Cyclura and augments the body of knowledge on iguana anatomy generally. Finally, we posit that our description and future studies may facilitate identification of fossil Cyclura, which could help understand the paleobiogeography of the genus.

Ontogenetic variation in the marine foraging of Atlantic salmon functionally links genomic diversity with a major life history polymorphism.

The ecological role of heritable phenotypic variation in free-living populations remains largely unknown. Knowledge of the genetic basis of functional ecological processes can link genomic and phenotypic diversity, providing insight into polymorphism evolution and how populations respond to environmental changes. By quantifying the marine diet of Atlantic salmon, we assessed how foraging behaviour changes along the ontogeny, and in relation to genetic variation in two loci with major effects on age at maturity (six6 and vgll3). We used a two-component, zero-inflated negative binomial model to simultaneously quantify foraging frequency and foraging outcome, separately for fish and crustaceans diets. We found that older salmon forage for both prey types more actively (as evidenced by increased foraging frequency), but with a decreased efficiency (as evidenced by fewer prey in the diet), suggesting an age-dependent shift in foraging dynamics. The vgll3 locus was linked to age-dependent changes in foraging behaviour: Younger salmon with vgll3LL (the genotype associated with late maturation) tended to forage crustaceans more often than those with vgll3EE (the genotype associated with early maturation), whereas the pattern was reversed in older salmon. Vgll3 LL genotype was also linked to a marginal increase in fish acquisition, especially in younger salmon, while six6 was not a factor explaining the diet variation. Our results suggest a functional role for marine feeding behaviour linking genomic diversity at vgll3 with age at maturity among salmon, with potential age-dependent trade-offs maintaining the genetic variation. A shared genetic basis between dietary ecology and age at maturity likely subjects Atlantic salmon populations to evolution induced by bottom-up changes in marine productivity.

Ontogenetic variation in isotopic niche positions of aquatic consumers in boreal lakes

Ontogenetic variation in isotopic niche positions of aquatic consumers in boreal lakes

Prevalence, intensity, and attachment sites of larval mites (Acari: Erythraeidae) infesting Erginulus clavotibialis, a Neotropical harvestman (Opiliones: Cosmetidae) from Belize

Larval erythraeid mites of the genus Leptus Latreille, 1796 are common ectoparasites of terrestrial arthropods, including harvestmen (Order Opiliones). In this study, we investigated sexual, ontogenetic, and geographic variation in infestations of the Neotropical cosmetid harvestmen Erginulus clavotibialis (Cambridge, 1904) by larval mites across multiple sampling locations in Belize. We did not observe any significant differences in the prevalence or intensity of mite infestation with respect to sex of the host or between juveniles and adults. However, there was significant variation in the prevalence of infestation between field sites, varying from 18-71%. The overall mean intensity of infestation was 3.2 mites/host. Larval mites exhibited a non-random distribution with respect to attachment sites, with significantly more mites occurring on femur IV. Larval mites were absent from the tarsi of the walking legs and were rarely observed attached to the pedipalps or chelicerae of the harvestmen. Of the ten mites attached to hosts that were examined with SEM, six larvae were found in close association to abandoned attachment cones.

Differentially expressed morphological characters depend on sex and ontogenetic stage in the crab Goniopsis cruentata (Crustacea: Grapsidae)

The hypothesis of this study was that significant variations in the growth rates of Goniopsis cruentata are related to intersexual and age-related characteristics, particularly in areas identified as secondary sexual (pleon, carapace and chelipeds). From February 2019 to January 2020, a total of 713 individuals were captured, 378 males and 335 females, with a carapace width ranging from 0.42 to 6.59 cm. Males and females showed negative allometry (β0<1) for all linear morphometric relationships, with an ontogenetic difference (p=0.0001) for all comparisons. In geometric morphometry, the dorsal view showed a significant difference in sexual comparisons (p=0.0001), in which males were wider in the posterior region than females. Furthermore, there was a significant difference in the abdominal region between young and adult females (p=0.0001), with the young ones being triangular and the adults oval, a characteristic brachyuran behaviour. We observed morphological separation in cheliped shape in sexual comparison (F×M) and laterality (R×L) (p=0.0001), with no ontogenetic variations (A×J). Goniopsis cruentata showed a noteworthy ontogenetic and sexual dimorphism. In addition, the discovery of cheliped variation was recorded for arboreal species that do not show a high degree of heterochely. Understanding these ontogenetic variations is crucial for effective conservation strategies because it allows specific life stages and their corresponding needs to be identified.

The Undescribed Juvenile Maxilla from Contrebandiers Cave, Morocco—A Study on Middle Stone Age Facial Growth

In 2009, renewed excavations at the Middle Stone Age (MSA) site of Contrebandiers Cave, Morocco, yielded a skull and partial skeleton of a child dated to Marine Isotope Stage 5. While much of the cranium was found shattered, the midface remained largely intact. In this study, we virtually reconstructed the maxilla and quantified its shape using three-dimensional geometric morphometric methods and compared it to an extensive sample of non-adult and adult Eurasian Neanderthals and Homo sapiens spanning the Middle Pleistocene to Holocene. We used developmental simulations to predict the adult shape of the Contrebandiers maxilla by simulating development along three ontogenetic trajectories: Neanderthal, African, and Levantine early H. sapiens and Holocene H. sapiens. Our results confirm the H. sapiens-like morphology of the Contrebandiers fossil. Both shape and size align it with other North African MSA fossils and Late Pleistocene humans from Qafzeh, Israel. Interestingly, the evaluation of the ontogenetic trajectories suggests that during late ontogeny the facial growth pattern of the Contrebandiers and the Qafzeh children is more similar to that of Neanderthals than it is to recent humans. This suggests that the unique facial growth pattern of Homo sapiens post-dated the MSA. This study is an important step in addressing ontogenetic variability in the African MSA, a period characterized by the origins, emergence, and dispersal of our species, but poorly understood because of the fragmentary and scant human fossil record.

Comparative morphology of the oropharyngeal denticles in the order Rhinopristiformes and its functional implications (Chondrichthyes: Batoidea).

Guitarfishes and sawfishes are included in the order Rhinopristiformes, which currently encompasses five families: Pristidae, Rhinobatidae, Trygonorrhinidae, Rhinidae and Glaucostegidae. Considering the low number of studies focused on oral structures in Rhinopristiformes and the need to better understand their internal morphology, this study aimed to(1) evaluate and describe the morphological variation of the oropharyngeal denticles of guitarfishes and sawfish; (2) evaluate and describe the ontogenetic and sexual variation of the oropharyngeal denticles of Zapteryx brevirostris; (3) propose characters potentially useful for taxonomic and systematic purposes and (4) discuss the possible functions and advantages of these structures. Tissue samples were taken from the oropharyngeal region of specimens preserved in 70% alcohol and then prepared for visualization in scanning electron microscopy. A new method for sampling the pharynx region is proposed herein. Considerable morphological variation between families and genera was observed. However, no variation between conspecifics was found. Regional variations of denticles when examining a single individual were observed in shape, ornamentation, and orientation. In Zapteryx brevirostris, males had a significantly higher density of denticles in the ventral region than females and lower densities were observed in juveniles. The four characters discussed here are based on the presence of keels, number of cusps, distal end elongation and width/length ratio of the oropharyngeal denticles. Among the possible functions and advantages of these structures are the improvement of food adherence, tissue protection against food abrasion and parasitism, and attenuation of hydrodynamic drag in the oropharyngeal cavity during food ingestion.

Ontogenetic Changes in Pigmentation Pattern in Mesanthura miyakoensis (Crustacea: Isopoda: Anthuridae).

Species in the anthurid isopod genus Mesanthura have specific, dorsal dark pigmentation patterning on the body. Though Mesanthura species have traditionally been distinguished mainly by differences in the dorsal pigmentation pattern in females, the stability of the pigmentation pattern within species had not been investigated, and information was lacking on ontogenetic variation in the pattern. Our study showed the following for M. miyakoensis. (1) Mancae begin to show dorsal pigmentation in the marsupium roughly 9 days before their release. (2) The pigmentation pattern in the first-instar mancae (first free-living stage) differs from that in later instars. (3) The pigmentation pattern in females is discrete and stable from putative second-instar mancae through females lacking oostegites, and distorted but recognizable in ovigerious females. (4) The pattern in males is different from and less discrete than that in females; it remains similar through the molt from subadult to adult male but changes markedly with age, leading to heavy pigmentation of the body. (5) The pigmentation pattern in mancae and females remains stable and observable after storage in ethanol for at least 13.7 months. Our results suggest that comparisons of pigmentation pattern across species in Mesanthura taxonomy should be restricted to females in the post-manca or later stages.

THE GENUS PHILOBRYA J.G. COOPER, 1867 (BIVALVIA: PHILOBRYIDAE) IN PATAGONIA AND ADJACENT ANTARCTIC WATERS

The present study provides the first comprehensive revision of the species of Philobrya occurring in the Atlantic and Pacific coasts of Patagonia, the Strait of Magellan, the Beagle Channel, Isla de los Estados, Malvinas/Falkland Islands, Burdwood Bank, the Scotia Arc islands, the Antarctic Peninsula and the Bellingshausen Sea. Based on extensive collections, the identity of all species previously described from these areas is re-evaluated, and species are redescribed and figured, considering their ontogenetic variability. As part of this study, 15 taxa are recognized as valid, including Philobrya delli new species and another possibly new (Philobrya cf. barbata) species. Philobrya crispa Linse is considered a junior synonym of Philobrya blakeana (Melvill & Standen), and Philobrya antarctica (Philippi) is regarded as a nomen dubium. Neotypes for Philobrya sublaevis Pelseneer and Philobrya quadrata (Pfeffer) and a lectotype for Brachidontes (Hormomya) blakeanus are here designated. The clarification of the identity of P. sublaevis allows the revalidation of Philobrya limoides E.A. Smith and Philobrya orbiculata (Hedley), two species regarded as synonyms of P. sublaevis in the last 60 years. Furthermore, the synonymy of Philippiella Pfeffer, Stempelleria Clasing and Stempellia Odhner (non Léger and Hesse) with Philobrya is here confirmed.