Aquatic Adaptation Research Articles

Repeated evolution of durophagy during ichthyosaur radiation after mass extinction indicated by hidden dentition

Marine tetrapods quickly diversified and were established as marine top predators after the end-Permian Mass extinction (EPME). Ichthyosaurs were the forerunner of this rapid radiation but the main drivers of the diversification are poorly understood. Cartorhynchus lenticarpus is a basal ichthyosauriform with the least degree of aquatic adaptation, holding a key to identifying such a driver. The unique specimen appeared edentulous based on what was exposed but a CT scanning revealed that the species indeed had rounded teeth that are nearly perpendicular to the jaw rami, and thus completely concealed in lateral view. There are three dental rows per jaw ramus, and the root lacks infoldings of the dentine typical of ichthyopterygians. The well-developed and worn molariform dentition with three tooth rows supports the previous inference that the specimen is not of a juvenile. The premaxilla and the corresponding part of the dentary are edentulous. Molariform dentition evolved three to five times independently within Ichthyosauriformes in the Early and Middle Triassic. Convergent exploitation of hard-shelled invertebrates by different subclades of ichthyosauriforms likely fueled the rapid taxonomic diversification of the group after EPME.

A paradigm for the evolution of human features: Apes trapped on barren volcanic islands

The aquatic ape hypothesis for human evolution can account for all the traits that distinguish humans from chimpanzees. This scientific paradigm has been considered impossible. It would require that human ancestors maintained a semiaquatic lifestyle for millions of years, whereas hominin fossils indicate relatively dry terrestrial environments. Here I propose a marine aquatic evolution that is speculative, but compatible with all the fossil and genetic evidence. In this hypothesis, hominins evolved from chimpanzee-like apes that became stranded on proto-Bioko — new volcanic islands with no terrestrial foods available. The apes were forced to eat shellfish and seaweed. From wading in water on two legs to obtain food, their bodies evolved to become bipedal. Naked skin, blubber, and protruding noses were also aquatic adaptations. Brain-size increase resulted from marine fatty acid DHA. Some of these hominins escaped to mainland Africa and their bipedal descendants are recorded at the famous fossil sites. The volcanic islands grew and evolved into Bioko, and the hominins that remained there evolved into Homo sapiens. They gave up their marine diet and semiaquatic habitat after food became available on the evolving island. Then, during one of the low sea-level stands in the Pleistocene epoch, humans walked to the mainland on the emergent Bioko land bridge. Unlike earlier aquatic ape ideas, the Bioko scenario can be tested by DNA. If the human genome includes a retrovirus that is otherwise only found in endemic animals on Bioko, it would show that our ancestors came from there. Unfortunately, Bioko and west-central Africa are not interesting to traditional paleoanthropologists, because they do not contain fossils.

A Total Evidence Phylogenetic Analysis of Pinniped Phylogeny and the Possibility of Parallel Evolution Within a Monophyletic Framework

In the present study, a series of phylogenetic analyses of morphological, molecular, and combined morphological-molecular datasets were conducted to investigate the relationships of 23 extant and 44 fossil caniforme genera, in order to test the phylogenetic position of putative stem pinniped Puijila within a comprehensive evolutionary framework. With Canis as an outgroup, a Bayesian Inference analysis employing tip-dating of a combined molecular-morphological (i.e., Total Evidence) dataset recovered a topology in which musteloids are the sister group to a monophyletic pinniped clade, to the exclusion of ursids, and recovered Puijila and Potamotherium along the stem of Pinnipedia. A similar topology was recovered in a parsimony analysis of the same dataset. These results suggest the pinniped stem may be expanded to include additional fossil arctoid taxa, including Puijila, Potamotherium, and Kolponomos. The tip-dating analysis suggested a divergence time between pinnipeds and musteloids of ~45.16 million years ago (Ma), though a basal split between otarioids and phocids is not estimated to occur until ~26.52 Ma. These results provide further support for prolonged freshwater and nearshore phases in the evolution of pinnipeds, prior to the evolution of the extreme level of aquatic adaptation displayed by extant taxa. Ancestral character state reconstruction was used to investigate character evolution, to determine the frequency of reversals and parallelisms characterizing the three extant clades within Pinnipedia. Although the phylogenetic analyses did not directly provide any evidence of parallel evolution within the pinniped extant families, it is apparent from the inspection of previously-proposed pinniped synapomorphies, within the context of a molecular-based phylogenetic framework, that many traits shared between extant pinnipeds have arisen independently in the three clades. Notably, those traits relating to homodonty and limb-bone specialization for aquatic locomotion appear to have multiple origins within the crown group, as suggested by the retention of the plesiomorphic conditions in early-diverging fossil members of the three extant families. Thus, while the present analysis identifies a new suite of morphological synapomorphies for Pinnipedia, the frequency of reversals and other homoplasies within the clade limit their diagnostic value.

Moderate intensity swimming training on bone mineral density preservation under food restriction in female rats

Abstract Aim: To investigate the effect of moderate-intensity swimming training on bone mineral density under a 20% food restriction (FR) schedule for 12 weeks in female rats. Methods: Forty female Wistar rats were distributed into four groups: control (CG), exercised (EG), food restriction (FRG), and food restriction/exercised (FREG). At 95 days, the animals were subjected to aquatic adaptation and then performed the critical load test to individually determine the critical load intensity (CLi, % of body mass). Exercised groups swam 5 days a week, 30 minutes daily with weekly adjustment of the load equivalent to 80% of the CLi. The FR schedule was 20% in relation to CG and started concomitantly with physical training (PT). After 12 weeks, visceral fat weight was recorded and the femur was collected for biophysical and biomechanical analysis. Results: FR and exercise training promoted visceral fat reduction (p<0.01). FR reduced bone mineral density (p<0.01), while exercise training prevented such reduction. On the other hand, FR and exercise training did not promote significant changes in biomechanical parameters of the femur. Conclusion: Exercise training at moderate intensity was efficient in preserving bone mineral density despite long term of FR at 20%.

The oldest diving anseriform bird from the late Eocene of Kazakhstan and the evolution of aquatic adaptations in the intertarsal joint of waterfowl

The oldest diving anseriform bird from the late Eocene of Kazakhstan and the evolution of aquatic adaptations in the intertarsal joint of waterfowl

Loss of olfaction in sea snakes provides new perspectives on the aquatic adaptation of amniotes.

Marine amniotes, a polyphyletic group, provide an excellent opportunity for studying convergent evolution. Their sense of smell tends to degenerate, but this process has not been explored by comparing fully aquatic species with their amphibious relatives in an evolutionary context. Here, we sequenced the genomes of fully aquatic and amphibious sea snakes and identified repertoires of chemosensory receptor genes involved in olfaction. Snakes possess large numbers of the olfactory receptor (OR) genes and the type-2 vomeronasal receptor (V2R) genes, and expression profiling in the olfactory tissues suggests that snakes use the ORs in the main olfactory system (MOS) and the V2Rs in the vomeronasal system (VNS). The number of OR genes has decreased in sea snakes, and fully aquatic species lost MOS which is responsible for detecting airborne odours. By contrast, sea snakes including fully aquatic species retain a number of V2R genes and a well-developed VNS for smelling underwater. This study suggests that the sense of smell also degenerated in sea snakes, particularly in fully aquatic species, but their residual olfactory capability is distinct from that of other fully aquatic amniotes. Amphibious species show an intermediate status between terrestrial and fully aquatic snakes, implying their importance in understanding the process of aquatic adaptation.

Genes lost during the transition from land to water in cetaceans highlight genomic changes associated with aquatic adaptations.

The transition from land to water in whales and dolphins (cetaceans) was accompanied by remarkable adaptations. To reveal genomic changes that occurred during this transition, we screened for protein-coding genes that were inactivated in the ancestral cetacean lineage. We found 85 gene losses. Some of these were likely beneficial for cetaceans, for example, by reducing the risk of thrombus formation during diving (F12 and KLKB1), erroneous DNA damage repair (POLM), and oxidative stress-induced lung inflammation (MAP3K19). Additional gene losses may reflect other diving-related adaptations, such as enhanced vasoconstriction during the diving response (mediated by SLC6A18) and altered pulmonary surfactant composition (SEC14L3), while loss of SLC4A9 relates to a reduced need for saliva. Last, loss of melatonin synthesis and receptor genes (AANAT, ASMT, and MTNR1A/B) may have been a precondition for adopting unihemispheric sleep. Our findings suggest that some genes lost in ancestral cetaceans were likely involved in adapting to a fully aquatic lifestyle.

Neurovascular anatomy of the protostegid turtle Rhinochelys pulchriceps and comparisons of membranous and endosseous labyrinth shape in an extant turtle

AbstractChelonioid turtles are the only surviving group of reptiles that secondarily evolved marine lifestyles during the Mesozoic Early chelonioid evolution is documented by fossils of their stem group, such as protostegids, which yield insights into the evolution of marine adaptation. Neuroanatomical features are commonly used to infer palaeoecology owing to the functional adaptation of the senses of an organism to its environment. We investigated the neuroanatomy and carotid circulation of the early Late Cretaceous protostegid Rhinochelys pulchriceps based on micro-computed tomography data. We show that the trigeminal foramen of turtles is not homologous to that of other reptiles. The endosseous labyrinth of R. pulchriceps has thick semicircular canals and a high aspect ratio. Comparisons among turtles and other reptiles show that the endosseous labyrinth aspect ratio is not a reliable predictor of the degree of aquatic adaptation, contradicting previous hypotheses. We provide the first models of neuroanatomical soft tissues of an extant turtle. Turtle brain morphology is not reflected by the brain cavity, and the endosseous labyrinth provides an incomplete reflection of membranous semicircular duct morphology. Membranous labyrinth geometry is conserved across gnathostomes, which allows approximate reconstruction of the total membranous labyrinth morphology from the endosseous labyrinth despite their poor reflection of duct morphology.

Comment on: Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurids. 93: 275–284

In a recent paper, the contention that spinosaurine theropods were semi-aquatic was supported by Arden et al., (2019) and they provided a hypothetical sequence of acquisition of traits that had evolved in line with this lifestyle. However, we find that the presented traits were either loosely defined and/or are clearly distinct from those traits seen in extant animals with adaptations to life in water. Some spinosaurs may have spent extensive time in water, but the data to support this is currently insufficient and other hypotheses for their behaviour also fit the available data.

Microstructure of Vertebrae, Ribs, and Gastralia of Triassic Sauropterygians-New Insights into the Microanatomical Processes Involved in Aquatic Adaptations of Marine Reptiles.

Isolated ribs and vertebrae of Middle Triassic sauropterygians are studied. The vertebrae have a well-defined large cavity in their centra, which is a unique feature and is without any modern analogue. The articular facets of vertebrae are made of endochondral bone including calcified as well as uncalcified cartilage. Vertebrae are pachyosteosclerotic in the pachypleurosaurs Neusticosaurus and Serpianosaurus from the Alpine Triassic, and osteosclerotic in the placodont, in the medium-sized Nothosaurus marchicus, and in the pachypleurosaur Anarosaurus. In large Nothosaurus specimens, the vertebrae are cavernous. The ribs of all sampled specimens are osteosclerotic, which resembles the microanatomy of long bones in all studied taxa. The proximal to medial part of ribs mainly consists of a compact periosteal cortex surrounding an inner endosteal territory. Toward the distal end of the ribs, the periosteal thickness decreases whereas the endosteal territory increases. Despite a shift from periosteal versus endosteal tissues, global rib compactness remains relatively constant. Osteosclerosis in ribs and vertebrae is reached by the same processes as in the long bones: by a relative increase in cortex thickness that is coupled by a reduction of the medullary cavity, by the persistence of calcified cartilage, and by an inhibition of remodeling although some resorption may occur but without complete redeposition of bone. Processes differ from those observed in Permian marine reptiles and some mosasaurines, where either extensive remodeling or inhibition of bone resorption leads to osteosclerosis. Besides differences regarding the microanatomy, all studied bones of a taxon are consistent in their bone tissue type. Anat Rec, 302:1770-1791, 2019. © 2019 American Association for Anatomy.

Molecular adaptation mechanism of secondary aquatic life in cetaceans

Cetaceans are a unique group in the history of mammalian evolution owing to a series of evolutionary changes in morphology, anatomy, physiology, biochemistry and other aspects that have been generated during the return to water of their ancestors. Cetaceans therefore are the ideal models for studying the molecular mechanism of adaptation to a new environment. In this paper, the evolutionary genetic mechanisms of secondary aquatic adaptation in cetaceans in recent years are briefly reviewed, including body shape change, osmotic regulation, immune defense, dietary change, sensory system, and hypoxic tolerance. With the development of omics technology and their application, those potential functional regions and sites related to adaptive evolution based on bioinformatics analysis are needed to be tested using cell or animal models. These results will give us new insights into the molecular basis of secondary aquatic adaptation in cetaceans.

Shellfish collection on the westernmost Mediterranean, Bajondillo cave (∼160-35 cal kyr BP): A case of behavioral convergence?

The Middle (MP) and Early Upper Paleolithic (EUP) evidences of shellfish collection on the southern Iberian site of Bajondillo cave are presented and compared with Westernmost Mediterranean archaeological sites. The main feature is stasis for Mytilus galloprovincialis represents the dominant taxon during a ∼120kyr temporal sequence. The second feature is the decrease of the shellfishing signal when site distance to the coast increases. The data reveal that shellfish collection was practiced during Marine Isotopic Stage 4, a poorly documented stage in terms of aquatic adaptations. Striking is also that mollusc assemblages evidence an uninterrupted decreasing trend in terms of remains from the earliest to the latest levels, in particular when H. sapiens replaced H. neanderthalensis. Although taxa of secondary importance are too scarce to make reliable inferences, another difference between the MP and EUP collections is the substantial increase of infaunal bivalves in the latter cultural period. Warm and cold water mollusc records match temperature rises and drops although the scarcity of data do not allow one to proceed beyond qualitative statements. Likewise, the prevalence of fresh and brackish water mollusc hint at a permanent presence of freshwater around the site at all times. When compared with assemblages from the Alboran sea region (Westernmost Mediterranean Sea), the Bajondillo cave collections are remarkable for their abundance of mussels. Comparison between Bajondillo cave and Pinnacle Point reveal that infaunal bivalve abundances in the South African site are far higher than those recorded in the MP levels, though not those from the EUP. Whether this feature hints at subtle differences existing between the collection of shellfish by H. sapiens and H. neanderthalensis, reflects a behavioral convergence between the two hominine lineages or represents an inherited cognitive trait from a common ancestor is an issue in need of further analysis.

Mysticetes to MiniConference to Manuscripts: Introduction to Thematic Issue on Mysticete Anatomy.

This issue of the Anatomical Record is focused on the theme of Mysticete Anatomy. There are six included articles that explore the anatomy of the nasal region (Marquez et al., 2018; Maust-Mohl et al., 2018), larynx (Damien et al., 2018), lungs (Fetherston et al., 2018), sublingual fascia (Werth et al., 2018), and brain (Raghanti et al., 2018). These papers document anatomical features exhibited by mysticetes (baleen whales) and their related cousins (including other whales, and the semiaquatic moose and hippopotamus). This theme stems from a 2-day MiniConference on Mysticete Anatomy, hosted at the Icahn School of Medicine at Mount Sinai in New York City on May 2016. Anatomy is explored in the contexts of function and evolution of aquatic adaptations. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc. Anat Rec, 302:663-666, 2019. © 2019 Wiley Periodicals, Inc.

Introduction to the Special Section on the Aquatic Climate Change Adaptation Services Program

The Aquatic Climate Change Adaptation Services Program (ACCASP) was launched in 2011 by Fisheries and Oceans Canada (DFO). The initial five-year programme was renewed for a further two years in 201...

Ancient roaches further exemplify ‘no land return’ in aquatic insects

Among insects, 236 families in 18 of 44 orders independently invaded water. We report living amphibiotic cockroaches from tropical streams of UNESCO BR Sumaco, Ecuador. We also describe the first fossil aquatic roach larvae (6 spp.; n = 44, 1, 1, 1, 1, 1) from the most diverse tropical Mesozoic sediments (Middle Jurassic Bakhar Fm in Mongolia, Kimmeridgian Karabastau Fm in Kazakhstan; Aptian Crato Fm in Brazil), and the Barremian Lebanese and Cenomanian Myanmar ambers. Tropic-limited occurrences are trophic- (biomass/litter-fall), structural- (diversity) and also abiotic-factor-dependent (high temperatures). Diverse Paleozoic aquatic eoblattids are here (re)described from the lower Permian sediments of Elmo, U.S.A. and Chekarda, Russia. They competed with true cockroaches to reach water prior to the Mesozoic. Due to different evolutionary rates or periodical changes in water characteristics, non-adapted terrestrial insects repeatedly invaded the aquatic realm with well adapted hydrobionts. Obscurely, most aquatic lineages still survive. In contrast with Crustacea, aquatic-terrestrial reversal is absent. A single principal lineage, namely of moths, ancestral to butterflies (origination of modern insects from ephemerans and dragonflies is questioned), possibly evolved from insects with aquatic immature stages, and none from aquatic adults. The rest of the orders are terrestrial-derived. The proposed reason for the lack of land return is the character of numerous aquatic adaptations related to reductions, which are unlikely to be resuppressed. The aquatic insect family/terrestrial insect family ratio over time reveals a sharp rise from the Late Carboniferous to Late Triassic followed by lasting stability. Diversification of aquatic insects seems consistent with a 62.05 ± 0.02 Ma periodicity.

The bony labyrinth of Platecarpus (Squamata: Mosasauria) and aquatic adaptations in squamate reptiles

Mosasaurs were among the last marine reptiles that lived before the Cretacesous–Paleogene extinction. Little is known about the sensory evolution of mosasaurs in relation to their aquatic lifestyle. In this study, the braincase of Platecarpus was CT-scanned and virtual models were constructed showing the bony labyrinth — or the inner ear — a sensory apparatus for balance and hearing. The virtual inner ear consists of the semicircular canals, vestibule, and cochlea. Compared with extant squamates, Platecarpus resembles sea snakes in having a small vestibule with a flat dorsal surface, but it differs from non-mosasaurian squamates in having rounded semicircular canals. Phylogenetic linear regression analysis supports a linear relationship, independent from phylogeny, between the length of the three semicircular canals and the length of the skull. The semicircular canals of Platecarpus are shorter than predicted, but the fossil data fell within the 95% prediction interval calculated from the extant data and the skull length of Platecarpus. Although size reduction of the bony labyrinth has been associated with aquatic adaptions in mammals, our results suggest that in squamates, semicircular canal size is related to skull size rather than habitat preference.

A Comparison of Common Hippopotamus (Artiodactyla) and Mysticete (Cetacea) Nostrils: An Open and Shut Case

Hippos are considered the closest living relatives to cetaceans and they have some similar adaptations for aquatic living, such as a modified respiratory tract. Behavioral observations of male and female common hippos (Hippopotamus amphibius) at Disney's Animal Kingdom® and the Adventure Aquarium were conducted to describe and examine movements of the nostrils during respiration (inspiration, expiration, and inter-breath interval). The hippo nostril is a crescent shaped opening with lateral and medial aspects that are mobile and can be adducted and abducted to regulate the nostril opening. Notably, the default (resting) position of the nostrils is closed during the inter-breath interval, even when hippos are resting in water and their heads are not submerged. Similar to cetaceans, this aquatic adaptation protects the respiratory tract from an accidental incursion of water that can occur even when the nostrils are above water. Dissection of a deceased captive common hippo suggests there are separate muscles that pull the medial and lateral aspects for abduction. The internal nasal passage has a nasal plug that is similar in shape but less pronounced than the nasal plugs of two baleen whale species studied (minke whale Balaenoptera acutorostrata, fin whale Balaenoptera physalus). Examination of the musculature suggests fibers attach from the premaxillae and extend caudally to retract the plug to open the nasal passage. We discuss similarities and differences of the nostrils/blowholes of fully aquatic, semi-aquatic, and terrestrial species to assess adaptations related to environmental conditions that may be convergent or derived from a common ancestor. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:693-702, 2019. © 2018 Wiley Periodicals, Inc.

How Snakes Find Prey Underwater: Sea Snakes Use Visual and Chemical Cues for Foraging.

Fully aquatic adaptation generally leads amniotes to change sensory modalities drastically. Terrestrial snakes rely heavily on chemical cues to locate and recognize prey, but little is known about how sea snakes find prey fishes underwater. Sea snakes of the genus Hydrophis are fish-eating marine elapids which adapted from land to water approximately 5-10 million years ago. Here, using two species of captive Hydrophis snakes, we show that they can recognize and discriminate their preferred fish species solely by using olfactory cues. However, they locate places where their preferred fishes may hide without relying on chemical cues. These findings indicate that Hydrophis snakes find prey in water as follows: they use visual cues to locate a place where their prey fishes are likely to hide, and then use chemical cues to find and attack prey. As is the case for other aquatic amniotes, snakes also modified their sensory modalities upon becoming aquatic.

Molecular footprints of inshore aquatic adaptation in Indo-Pacific humpback dolphin (Sousa chinensis)

The Indo-Pacific humpback dolphin, Sousa chinensis, being a member of cetaceans, had fully adapted to inshore waters. As a threatened marine mammal, little molecular information available for understanding the genetic basis of ecological adaptation. We firstly sequenced and obtained the draft genome map of S. chinensis. Phylogenetic analysis in this study, based on the single copy orthologous genes of the draft genome, is consistent with traditional phylogenetic classification. The comparative genomic analysis indicated that S. chinensis had 494 species-specific gene families, which involved immune, DNA repair and sensory systems associated with the potential adaption mechanism. We also identified the expansion and positive selection genes in S. chinensis lineage to investigate the potential adaptation mechanism. Our study provided the potential insight into the molecular bases of ecological adaptation in Indo-Pacific humpback dolphin and will be also valuable for future understanding the ecological adaptation and evolution of cetaceans at the genomic level.

Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurids

The Spinosauridae is a specialized group of theropod dinosaurs characterised by a long, narrow skull, robust forelimbs with a hooked thumb claw, and tall neural spines forming a dorsal sail. The ecology of these unusual dinosaurs has been debated since the original discovery of Spinosaurus aegyptiacus in 1912. Morphological similarities to crocodilians, including tooth shape and an elongated rostrum, indicate a piscivorous diet, and in the giant Spinosaurus, a long body and short limbs suggest semi-aquatic habits. However, the hypothesized aquatic habits of Spinosaurus have been called into question, and the distribution of aquatic habits within Spinosauridae remain unclear. Here, new spinosaurid specimens from the Kem Kem beds of Morocco reveal aquatic adaptations in the cranium. Elevated orbits and bending of the frontals placed the eyes atop the skull, as in semiaquatic animals such as crocodiles and hippos. Two morphologies are present, a smaller morph characterized by narrow, triangular frontals, and a larger morph characterized by broad, subrectangular frontals overlapping the prefrontals. The two morphs suggest two distinct spinosaurine taxa, and are tentatively referred to the spinosaurines Spinosaurus cf. aegyptiacus and Sigilmassasaurus brevicollis, respectively. Semiaquatic habits were widespread within the Spinosaurinae and at least two distinct aquatic spinosaurines inhabited the Cenomanian of North Africa, challenging previous assumptions that non-avian dinosaurs were solely terrestrial. The appearance of giant semiaquatic dinosaurs may have followed the disappearance of giant pholidosaurid crocodylomorphs, suggesting that the extinction of large crocodylomorphs was associated with the rise of dinosaurs as apex predators in the freshwater ecosystem in North Africa.