Terrestrial Lifestyle Research Articles

The metamorphosis of amphibian myocardium: moving to the heart of the matter.

Amphibians are a classical object for physiological studies, and they are of great value for developmental studies owing to their transition from an aquatic larval form to an adult form with a terrestrial lifestyle. Axolotls (Ambystoma mexicanum) are of special interest for such studies because of their neoteny and facultative pedomorphosis, as in these animals, metamorphosis can be induced and fully controlled in laboratory conditions. It has been suggested that their metamorphosis, associated with gross anatomical changes in the heart, also involves physiological and electrical remodeling of the myocardium. We used whole-cell patch clamp to investigate possible changes caused by metamorphosis in electrical activity and major ionic currents in cardiomyocytes isolated from paedomorphic and metamorphic axolotls. T4-induced metamorphosis caused shortening of atrial and ventricular action potentials (APs), with no changes in resting membrane potential or maximum velocity of AP upstroke, favoring higher heart rate possible in metamorphic animals. Potential-dependent potassium currents in axolotl myocardium were represented by delayed rectifier currents IKr and IKs, and upregulation of IKs caused by metamorphosis probably underlies AP shortening. Metamorphosis was associated with downregulation of inward rectifier current IK1, probably serving to increase the excitability of myocardium in metamorphic animals. Metamorphosis also led to a slight increase in fast sodium current INa with no changes in its steady-state kinetics and to a significant upregulation of ICa in both atrial and ventricular cells, indicating stronger Ca2+ influx for higher cardiac contractility in metamorphic salamanders. Taken together, these changes serve to increase cardiac reserve in metamorphic animals.

On the aquatic phenology of sympatric crested and marbled newts (genus Triturus)

Abstract The large-bodied newts Triturus cristatus and T. marmoratus possess ranges that overlap in western France where they frequently share breeding ponds. I test the hypothesis that the aquatic phenology differs between them, as associated with a more aquatic and terrestrial life style respectively. Total adult population sizes were determined in spring in 13 experiments by the capture-mark-recapture methodology, followed by equivalent experiments in summer. Population sizes dropped by an order of magnitude on average whereas species frequencies changed in favour of T. cristatus, suggesting that T. marmoratus leaves the breeding site earlier than T. cristatus. Interspecies hybrids behaved like T. marmoratus. Descriptions are provided of other features (in ecology, morphology, demography, and colouration pattern) that support the different, aquatic versus terrestrial life styles of T. cristatus and T. marmoratus.

The auronidin flavonoid pigments of the liverwort Marchantia polymorpha form polymers that modify cell wall properties.

Plant adaptation from aquatic to terrestrial environments required modifications to cell wall structure and function to provide tolerance to new abiotic and biotic stressors. Here, we investigate the nature and function of red auronidin pigment accumulation in the cell wall of the liverwort Marchantia polymorpha. Transgenic plants with auronidin production either constitutive or absent were analysed for their cell wall properties, including fractionation of polysaccharide and phenolic components. While small amounts of auronidin and other flavonoids were loosely associated with the cell wall, the majority of the pigments were tightly associated, similar to what is observed in angiosperms for polyphenolics such as lignin. No evidence of covalent binding to a polysaccharide component was found: we propose auronidin is present in the wall as a physically entrapped large molecular weight polymer. The results suggested auronidin is a dual function molecule that can both screen excess light and increase wall strength, hydrophobicity and resistance to enzymatic degradation by pathogens. Thus, liverworts have expanded the core phenylpropanoid toolkit that was present in the ancestor of all land plants, to deliver a lineage-specific solution to some of the environmental stresses faced from a terrestrial lifestyle.

Variation in the sacrum of phytosaurs: New evidence from a partial skeleton of Machaeroprosopus mccauleyi.

Phytosaurs are a group of Upper Triassic semi-aquatic archosauriform reptiles. Their variable skull morphology forms the foundation of our understanding of their relationships and paleoecology, while only a few studies have focused on demonstrating the existence of postcranial variation. The numbers of vertebrae in the sacrum are thought to vary from two, the plesiomorphic condition for archosauriforms, to three, with the addition of a sacralized dorsal (i.e., dorsosacral) vertebra. In this study, we demonstrate the presence of a sacralized first caudal (i.e., caudosacral) vertebra in a sacrum belonging to Machaeroprosopus mccauleyi. We rule out taphonomic distortion or pathology as explanations for the inclusion of this element in the sacrum, suggesting instead that it occurred through modifications of the same developmental processes that likely produced dorsosacral vertebrae in phytosaurs. Additionally, we show that a dorsosacral vertebra is common in phytosaur specimens from the Chinle Formation and Dockum Group of the southwestern United States and suggest that it may be widespread among phytosaurs. The addition of sacral vertebrae potentially aided adaptation to larger body sizes or more terrestrial lifestyles in certain taxa.

Telomere Length Variation in Model Bryophytes.

The ends of linear chromosomes of most eukaryotes consist of protein-bound DNA arrays called telomeres, which play essential roles in protecting genome integrity. Despite general evolutionary conservation in function, telomeric DNA is known to drastically vary in length and sequence between different eukaryotic lineages. Bryophytes are a group of early diverging land plants that include mosses, liverworts, and hornworts. This group of ancient land plants recently emerged as a new model for important discoveries in genomics and evolutionary biology, as well as for understanding plant adaptations to a terrestrial lifestyle. We measured telomere length in different ecotypes of model bryophyte species, including Physcomitrium patens, Marchantia polymorpha, Ceratodon purpureus, and in Sphagnum isolates. Our data indicate that all analyzed moss and liverwort genotypes have relatively short telomeres. Furthermore, all analyzed ecotypes and isolates of model mosses and liverworts display evidence of substantial natural variation in telomere length. Interestingly, telomere length also differs between male and female strains of the dioecious liverwort M. polymorpha and dioecious moss C. purpureus. Given that bryophytes are extraordinarily well adapted to different ecological niches from polar to tropical environments, our data will contribute to understanding the impact of natural telomere length variation on evolutionary adaptations in this ancient land plant lineage.

Paleozoic cave system preserves oldest-known evidence of amniote skin.

The richest and most diverse assemblage of early terrestrial tetrapods is preserved within the infilled cave system of Richards Spur, Oklahoma (289-286 Mya1). Some of the oldest-known terrestrial amniotes2,3 are exquisitely preserved here because of early impregnation and encasement of organic material by oil-seep hydrocarbons within rapidly deposited clay-rich cave sediments under toxic anoxic conditions.4 This phenomenon has also afforded the preservation of exceedingly rare integumentary soft tissues, reported here, providing critical first evidence into the anatomical changes marking the transition from the aquatic and semiaquatic lifestyles of anamniotes to the fully terrestrial lifestyles of early amniotes. This is the first record of a skin-cast fossil (3D carbonization of the skin proper) from the Paleozoic Era and the earliest known occurrence of epidermal integumentary structures. We also report on several compression fossils (carbonized skin impressions), all demonstrating similar external morphologies to extant crocodiles. A variety of previously unknown ossifications, as well as what are likely palpebral ossifications of the deeper dermis layer of the skin, are also documented. These fossils also serve as invaluable references for paleontological reconstructions. Chromatographic analysis of extractable hydrocarbons from bone and cave samples indicates that the source rock is the Devonian age Woodford Shale. Hydrocarbons derived from ancient marine organisms interacting with geologically younger terrestrial vertebrates have therefore resulted in the oldest-known preservation of amniote skin proper.

Convergent Adaptation of True Crabs (Decapoda: Brachyura) to a Gradient of Terrestrial Environments.

For much of terrestrial biodiversity, the evolutionary pathways of adaptation from marine ancestors are poorly understood and have usually been viewed as a binary trait. True crabs, the decapod crustacean infraorder Brachyura, comprise over 7600 species representing a striking diversity of morphology and ecology, including repeated adaptation to non-marine habitats. Here, we reconstruct the evolutionary history of Brachyura using new and published sequences of 10 genes for 344 tips spanning 88 of 109 brachyuran families. Using 36 newly vetted fossil calibrations, we infer that brachyurans most likely diverged in the Triassic, with family-level splits in the late Cretaceous and early Paleogene. By contrast, the root age is underestimated with automated sampling of 328 fossil occurrences explicitly incorporated into the tree prior, suggesting such models are a poor fit under heterogeneous fossil preservation. We apply recently defined trait-by-environment associations to classify a gradient of transitions from marine to terrestrial lifestyles. We estimate that crabs left the marine environment at least 7 and up to 17 times convergently, and returned to the sea from non-marine environments at least twice. Although the most highly terrestrial- and many freshwater-adapted crabs are concentrated in Thoracotremata, Bayesian threshold models of ancestral state reconstruction fail to identify shifts to higher terrestrial grades due to the degree of underlying change required. Lineages throughout our tree inhabit intertidal and marginal marine environments, corroborating the inference that the early stages of terrestrial adaptation have a lower threshold to evolve. Our framework and extensive new fossil and natural history datasets will enable future comparisons of non-marine adaptation at the morphological and molecular level. Crabs provide an important window into the early processes of adaptation to novel environments, and different degrees of evolutionary constraint that might help predict these pathways. [Brachyura; convergent evolution; crustaceans; divergence times; fossil calibration; molecular phylogeny; terrestrialization; threshold model.].

Terrestrial Trentepohlia sp. (Ulvophyceae) from alpine and coastal collection sites show strong desiccation tolerance and broad light and temperature adaptation.

For the present study, we collected the Ulvophyceae species Trentepohlia aurea from limestone rock near Berchtesgaden, Germany, and the closely related taxa T. umbrina from Tilia cordata tree bark and T. jolithus from concrete wall both in Rostock, Germany. Freshly sampled material stained with Auramine O, DIOC6, and FM 1-43 showed an intact physiological status. Cell walls were depicted with calcofluor white and Carbotrace. When subjected to three repeated and controlled cycles of desiccation over silica gel (~ 10% relative humidity) followed by rehydration, T. aurea recovered about 50% of the initial photosynthetic yield of photosystem II (YII). In contrast, T. umbrina and T. jolithus recovered to 100% of the initial YII. HPLC and GC analysis of compatible solutes found highest proportions of erythritol in T. umbrina and mannitol/arabitol in T. jolithus. The lowest total compatible solute concentrations were detected in T. aurea, while the C/N ratio was highest in this species, indicative of nitrogen limitation. The prominent orange to red coloration of all Trentepohlia was due to extremely high carotenoid to Chl a ratio (15.9 in T. jolithus, 7.8 in T. aurea, and 6.6. in T. umbrina). Photosynthetic oxygen production was positive up to ~ 1500µmol photons m-2s-1 with the highest Pmax and alpha values in T. aurea. All strains showed a broad temperature tolerance with optima for gross photosynthesis between 20 and 35°C. The presented data suggest that all investigated Trentepohlia species are well adapted to their terrestrial lifestyle on exposed to sunlight on a vertical substrate with little water holding capacity. Nevertheless, the three Trentepohlia species differed concerning their desiccation tolerance and compatible solute concentrations. The lower compatible solute contents in T. aurea explain the incomplete recovery of YII after rehydration.

The virtual brain endocast of Trogosus (Mammalia, Tillodontia) and its relevance in understanding the extinction of archaic placental mammals.

After successfully diversifying during the Paleocene, the descendants of the first wave of mammals that survived the end-Cretaceous mass extinction waned throughout the Eocene. Competition with modern crown clades and intense climate fluctuations may have been part of the factors leading to the extinction of these archaic groups. Why these taxa went extinct has rarely been studied from the perspective of the nervous system. Here, we describe the first virtual endocasts for the archaic order Tillodontia. Three species from the middle Eocene of North America were analyzed: Trogosus hillsii, Trogosus grangeri, and Trogosus castoridens. We made morphological comparisons with the plaster endocast of another tillodont, Tillodon fodiens, as well as groups potentially related to Tillodontia: Pantodonta, Arctocyonidae, and Cimolesta. Trogosus shows very little inter-specific variation with the only potential difference being related to the fusion of the optic canal and sphenorbital fissure. Many ancestral features are displayed by Trogosus, including an exposed midbrain, small neocortex, orbitotemporal canal ventral to rhinal fissure, and a broad circular fissure. Potential characteristics that could unite Tillodontia with Pantodonta, and Arctocyonidae are the posterior position of cranial nerve V3 exit in relation to the cerebrum and the low degree of development of the subarcuate fossa. The presence of large olfactory bulbs and a relatively small neocortex are consistent with a terrestrial lifestyle. A relatively small neocortex may have put Trogosus at risk when competing with artiodactyls for potentially similar resources and avoiding predation from archaic carnivorans, both of which are known to have had larger relative brain and neocortex sizes in the Eocene. These factors may have possibly exacerbated the extinction of Tillodontia, which showed highly specialized morphologies despite the increase in climate fluctuations throughout the Eocene, before disappearing during the middle Eocene.

Multi-isotopic analysis reveals the early stem turtle Odontochelys as a nearshore herbivorous forager

IntroductionAfter decades of debate on the origin of turtles, it is now widely accepted that they are diapsid reptiles originating in the Permian from a terrestrial ancestor. It seems that the initial development of the structures that will later form the unique turtle bony shell took place as a response to a fossorial lifestyle. However, the earliest stem turtle with a fully complete plastron, Odontochelys semitestacea from the Late Triassic (lower Carnian) of China, is somewhat controversially interpreted as an aquatic or even a marine form, raising the question of the environment in which the completion of the plastron happened.MethodsHere, we analyzed the stable carbon, oxygen and sulfur isotope compositions (δ13C, δ18O and δ34S) of bones from two specimens of Odontochelys along with bones and teeth of two associated specimens of the marine ichthyosaur Guizhouichthyosaurus tangae.Results and discussionWe first show that δ18O values of Odontochelys are incompatible with a terrestrial lifestyle and imply a semi-aquatic to aquatic lifestyle. Isotopic results also demonstrate that the aquatic environment of Odontochelys was submitted to a strong marine influence, therefore excluding the possibility of a strict freshwater aquatic environment. Additionally, an unusual carbon isotope composition shows that O. semitestacea was herbivorous, probably consuming macrophytic algae in coastal zones like the extant green sea turtle (Chelonia mydas) or the marine iguana (Amblyrhynchus cristatus) do.

Inferring the lifestyles of extinct Crocodyliformes using osteoderm ornamentation.

Osteoderms are bony plates formed within the dermis of diverse vertebrate groups. They are present in all crocodylomorphs but Metriorhynchidae. Most of them show typical bone ornamentation consisting of pits and ridges on their outer surface. The most widely discussed functional hypothesis suggests that the ornamentation of osteoderms influences heat exchange with the environment through the adjacent vascular network, facilitating the absorption of solar radiation. This process allows semiaquatic crocodiles to compensate for heat loss resulting from the high thermal conductivity of surrounding water. In order to test this assertion, we conducted a phylogenetic logistic regression analysis to evaluate the relationship between osteoderm relative area of pits (RAP) and lifestyle (terrestrial versus aquatic) in a sample of crocodyliforms. Our results revealed that lifestyle is significantly explained by RAP: the lower the degree of ornamentation (RAP), the higher the probability of a terrestrial lifestyle. We used this model to infer the lifestyle of two extinct taxa, Peirosaurus torminni and Microsuchus schilleri. We concluded that terrestrial notosuchians may have lost osteoderm ornamentation due to the lower thermal conductivity of air and reduced heat loss in a terrestrial environment compared to what happens in water. Among these notosuchians, we hypothesize that large terrestrial baurusuchids maintained a stable body temperature due to thermal inertia, whereas small notosuchians took advantage of the early morning sun exposure to warm up and stayed in terrestrial burrows during periods of intense solar radiation. Finally, unlike the almost motionless behavior of freshwater crocodiles, fully marine Metriorhynchidae probably lost osteoderms because they constantly swim, generating heat by muscular contraction, so osteoderms with a thermoregulatory function for heat absorption were no longer positively selected.

Local food availability and nonbreeding carry-over effects affect breeding propensity and success of a tundra-nesting predator, the Long-tailed Jaeger

Abstract Reproduction of long-distance migrants can be affected by local conditions on the breeding grounds as well as those encountered during the nonbreeding season through carry-over effects. We show that this is true in Long-tailed Jaegers (Stercorarius longicaudus) because individuals that spent less time flying at sea during winter had a high breeding propensity and a reduced pre-laying interval, but breeding propensity and nesting success were also positively associated with food abundance at the breeding site. This seabird switches from a marine to a terrestrial lifestyle to breed in summer in the Arctic, where it primarily feeds on lemmings. We monitored jaeger reproduction and lemming densities on Bylot Island in the Canadian Arctic for 16 years, and we used geolocator to study annual movements. We assessed whether movement parameters (travel distance, migration duration, phenology, and number of flying bouts inferred by saltwater immersions) during the nonbreeding season affected the breeding propensity, phenology, and success of individuals. We also examined whether cyclic lemming fluctuations influenced Long-tailed Jaeger reproduction and whether nesting success affected the phenology of their outbound migration. We found that increased time spent flying during winter and early arrival at the breeding site reduced breeding propensity. Moreover, spending less time flying during winter shortened the pre-laying period, and advancing laying date increased nesting success. Birds may thus face a trade-off to minimize the relative costs associated with arriving too early and breeding too late. Local food availability had a strong effect on reproduction because breeding propensity and nesting success increased sharply with lemming abundance. Failed breeders advanced their outbound migration by 10 days on average compared to successful ones, but migration duration was similar. Therefore, the unpredictability of the highly seasonal Arctic environment, especially fluctuating food abundance, appears to be a strong driver of reproduction that can modulate the strength of carry-over effects.

The neuroanatomy and pneumaticity of Hamadasuchus (Crocodylomorpha, Peirosauridae) from the Cretaceous of Morocco and its paleoecological significance for altirostral forms.

We describe the endocranial structures of Hamadasuchus, a peirosaurid crocodylomorph from the late Albian-Cenomanian Kem Kem group of Morocco. The cranial endocast, associated nerves and arteries, endosseous labyrinths, and cranial pneumatization, as well as the bones of the braincase of a new specimen, are reconstructed and compared with extant and fossil crocodylomorphs, which represent different lifestyles. Cranial bones of this specimen are identified as belonging to Hamadasuchus, with close affinities with Rukwasuchus yajabalijekundu, another peirosaurid from the 'middle' Cretaceous of Tanzania. The endocranial structures are comparable to those of R. yajabalijekundu but also to baurusuchids and sebecids (sebecosuchians). Paleobiological traits of Hamadasuchus, such as alert head posture, ecology, and behavior are explored for the first time, using quantitative metrics. The expanded but narrow semi-circular canals and enlarged pneumatization of the skull of Hamadasuchus are linked to a terrestrial lifestyle. Continuing work on the neuroanatomy of supposedly terrestrial crocodylomorphs needs to be broadened to other groups and will allow to characterize whether some internal structures are affected by the lifestyle of these organisms.

A multi-isotopic study reveals the palaeoecology of a sebecid from the Paleocene of Bolivia

Sebecids constitute a family of notosuchian crocodylomorphs of probable terrestrial habits. They are notable for having survived the Cretaceous-Paleogene mass extinction and are known until the Miocene in South America. However, ecological traits that favoured their resilience in continental ecosystems remain unknown. Here, using a multi-isotopic approach, we infer several palaeoecological traits of a sebecid from the locality of Tiupampa (Bolivia), which contains a diverse vertebrate fauna of the Early Paleocene. After having constrained the effects of diagenesis, the study of the oxygen isotope compositions of apatite phosphate allows the identification of water resources for the various studied taxa and to infer an ectothermic thermoregulation strategy for the sebecids. A terrestrial lifestyle is also supported by different oxygen isotope compositions observed between sebecids and aquatic dyrosaurid crocodylomorphs. The radiogenic strontium isotope compositions confirm the continental affinities of this fauna, with no marine input in the palaeoenvironment frequented by the different faunal elements. The calcium and carbon isotope compositions show that the sebecids from Tiupampa were at the top of a C3-based food web. Finally, a local dry environment with tropical temperatures for those specimens is inferred both from oxygen and carbon isotope compositions of their hard tissues.

The origin of blinking in both mudskippers and tetrapods is linked to life on land

Blinking, the transient occlusion of the eye by one or more membranes, serves several functions including wetting, protecting, and cleaning the eye. This behavior is seen in nearly all living tetrapods and absent in other extant sarcopterygian lineages suggesting that it might have arisen during the water-to-land transition. Unfortunately, our understanding of the origin of blinking has been limited by a lack of known anatomical correlates of the behavior in the fossil record and a paucity of comparative functional studies. To understand how and why blinking originates, we leverage mudskippers (Oxudercinae), a clade of amphibious fishes that have convergently evolved blinking. Using microcomputed tomography and histology, we analyzed two mudskipper species, Periophthalmus barbarus and Periophthalmodon septemradiatus, and compared them to the fully aquatic round goby, Neogobius melanostomus. Study of gross anatomy and epithelial microstructure shows that mudskippers have not evolved novel musculature or glands to blink. Behavioral analyses show the blinks of mudskippers are functionally convergent with those of tetrapods: P.barbarus blinks more often under high-evaporation conditions to wet the eye, a blink reflex protects the eye from physical insult, and a single blink can fully clean the cornea of particulates. Thus, eye retraction in concert with a passive occlusal membrane can achieve functions associated with life on land. Osteological correlates of eye retraction are present in the earliest limbed vertebrates, suggesting blinking capability. In both mudskippers and tetrapods, therefore, the origin of this multifunctional innovation is likely explained by selection for increasingly terrestrial lifestyles.

Functional and Behavioral Trade-Offs between Terrestrial and Aquatic Locomotion in the Amphibious Fish Kryptolebias marmoratus.

The mangrove rivulus (Kryptolebias marmoratus) is a phenotypically plastic teleost fish that can spend considerable time on land and traverse the terrestrial realm through a behavior termed the tail-flip jump. The tail-flip jump is a transitional stage between fully aquatic and terrestrial lifestyles. Therefore, understanding this behavior can provide insight into how organisms adapt to new environments over evolutionary time. Studies of K. marmoratus show that terrestrial acclimation and exercise improve tail-flip jumping performance due to muscle remodeling, but the implications of these muscular changes on aquatic locomotion are unknown. In the present study, we hypothesized that (1) terrestrial acclimation and exercise lead to physiological changes, such as changes to muscle fiber type, muscle mass distribution, or body shape, that optimize tail-flip jump distance and endurance while negatively impacting swimming performance in K. marmoratus, and (2) plasticity of the brain (which has been demonstrated in response to a variety of stimuli in K. marmoratus) allows terrestrial emersion and exercise to cause behavioral changes that promote survival and long-term reproductive success. To test these hypotheses, we measured the critical swimming speed (Ucrit), tail-flip jump distance, terrestrial endurance, and undisturbed aquatic behavior of age- and size-matched K. marmoratus before and after a terrestrial exercise period. This period consisted of six 3-min exercise sessions spread over 12 days, during which the fish were prompted to jump continuously. To isolate the effects of air exposure, a separate group was exposed to air for an equivalent period but not allowed to jump. Air exposure improved maximum jump distance but negatively affected swimming performance (Ucrit). Terrestrial endurance (number of jumps) improved in the exercised group, but Ucrit showed no significant change. Contrary to our first hypothesis, a trade-off exists between jump distance and Ucrit but not between jump endurance and Ucrit. Exercised individuals were more active following exercise, resulting either from the onset of dispersion behavior or a heightened stress response.

A new tanystropheid (Diapsida: Archosauromorpha) from the Middle Triassic of SW China and the biogeographical origin of Tanystropheidae

Tanystropheidae is a clade of early archosauromorphs with high morphological disparity and a wide geographical distribution. The origin and early radiation of Tanystropheidae are still incompletely understood. Here we report Luxisaurus terrestris gen. et sp. nov., a new archosauromorph collected from the marine Upper Member of Guanling Formation (Pelsonian substage, Anisian, Middle Triassic) in Luxi County, Yunnan Province, China, and phylogenetically recovered as a tanystropheid. The morphology of Luxisaurus is consistent with a terrestrial lifestyle. This is the first occurrence of a tanystropheid found from the Anisian Guanling Formation in SW China and also the earliest tanystropheid from the eastern Tethys. Phylogenetic analysis shows that Dinocephalosauridae forms the sister group of Tanystropheidae, Fuyuansaurus occupies the most basal position in Tanystropheidae, and Luxisaurus forms the sister group to a clade consisting of all other tanystropheids. Considering that Fuyuansaurus and Luxisaurus are found exclusively in South China, we hypothesize that Tanystropheidae originated in the Early Triassic of South China and then dispersed globally. The discovery of Early Triassic tanystropheids in South China is needed to further support this hypothesis. The discovery of Luxisaurus expands the stratigraphical and geographical distribution of Tanystropheidae, and provides new insights into the origin and early radiation of the clade. http://zoobank.org/urn:lsid:zoobank.org:pub:07DE12AC-8AE7-48F0-8BAD-0B73F04C0858

Histological study on the skin structure in two mudskippers, Periophthalmus waltoni and Boleophthalmus dussumieri in relation to their terrestrial life

Microscopic structure of skin in two amphibious mudskipper fish; Boleophthalmus dussumieri Valenciennes, 1837 (B. dussumeri) and Periophthalmus waltoni Koumans, 1941 (P. waltoni) were investigated in relation to their lifestyle. The general structure of skin is the same among the two species. Epidermis in B. dussumeri was thicker significantly than P. waltoni. The dermal bulges were only well developed in the skin of B. dussumeri. Mucous cells were absent in the epidermis of P. waltoni but present in B. dussumeri. Both B. dussumeri and P. waltoni have well-developed swollen middle cells as a shared epidermal feature. The thickness of the middle cell layer of the epidermis in B. dussumeri was significantly greater than in P. waltoni. Capillaries in the dorsal and ventral parts of the body are more closely distributed to the epidermal surface in P. waltoni than in B. dussumeri. The diffusion distance in the dorsal epidermis of P. waltoni was less than that in the ventral epidermis of B. dussumeri. A comparative examination of the skin of mudskipper species suggests that, due to the more terrestrial lifestyle adopted by P. waltoni, the skin contributes more to respiration.

Restructuring of the Optokinetic Reflex during Metamorphosis in Pelobates fuscus Laur.

The restructuring of the gaze stabilization system in Pelobates fuscus was investigated by quantitative analysis of the optomotor response using video imaging. Gaze stabilization is an important component in the system of neural mechanisms of visual depth perception. It was shown that the optomotor response in aquatic tadpoles of P. fuscus is similar to that of fish (movement of the animal in the direction of the visual background movement and eye nystagmus consisting of a fast and a slow phase). During metamorphosis (transition from the aquatic to the terrestrial lifestyle), froglets of P. fuscus responded to the movement of the visual background by eyes and head movements. One year after metamorphosis, P. fuscus responded to movement of the visual background as adult Anura: only by head movements (a slow and a fast phase), while eye movements were absent. Possible causes of the loss of active eye movements by Anura amphibians in the process of evolution are discussed.

Thrushes (Aves: Passeriformes) as indicators of microplastic pollution in terrestrial environments

Microplastic pollution is one of the leading global conservation issues. The aim of this study was to investigate the occurrence of microplastics in the gastrointestinal tracts of Common Blackbirds Turdus merula (N = 16) and Song Thrushes Turdus philomelos (N = 18), songbirds with exceptionally terrestrial lifestyles and a wide distribution range. We searched for microplastics of over 100 μm in size and assessed whether their contamination differed regarding the age of the birds and the time of year. We used birds that had died as a result of collision with anthropogenic infrastructure, which were sampled during wildlife monitoring of anthropogenic infrastructures and citizen science projects in north-eastern Poland. We found that all the analysed individuals contained microplastic in their gastrointestinal tracts, which were classified as fibers, fragments, films and pellets. A total number of 1073 microplastics were observed, mostly consisting of fibers (84 %) and films (10 %) below 1 mm in size. The dominant colours of microplastics were transparent (75 %) and brown (14 %). The species average microplastic concentration was higher in Song Thrushes (40.1) than Common Blackbirds (21.9), however the difference was not statistically significant. Moreover, we found no seasonal or age-related differences in microplastic ingestion in either species. While our results show a ubiquity of microplastics in terrestrial environments, they also indicate that thrushes have the potential to be used as indicators of microplastic pollution in terrestrial ecosystems.