THE INFLUENCE OF FEEDING THE ANTERIOR LOBE OF THE HYPOPHYSIS ON THE SIZE OF AMBYSTOMA TIGRINUM

1. Animals of the species Ambystoma tigrinum when fed anterior lobe can reach a size far in excess of that of animals fed earthworms and presumably also of that of liver-fed animals. 2. Liver produces a rate of growth as high as that resulting from anterior lobe-feeding, but maintains growth only, until the animals reach a definite size far below that of anterior lobe-fed animals.     

THE ANTAGONISM BETWEEN THYROID AND PARATHYROID GLANDS

From the facts stated in this paper it is evident that the thymus gland of mammals contains a substance which is capable of producing tetany when fed to the larvæ of certain species of salamanders (Ambystoma opacum and Ambystoma maculatum). As long as the larvæ have not developed their own thymus glands, they are able, by means of some mechanism, to counterbalance the tetanic action of the thymus substance introduced in their food. When, however, the secretion from their own thymus glands is added to the thymus material introduced with the food, this mechanism of preventing tetany becomes inadequate and tetany ensues. In the larva of a third species of salamander, Ambystoma tigrinum, this mechanism will prevent tetany even when the larvæ are fed on thymus. In mammals the parathyroids are known to prevent tetany and are supposed either to absorb the tetany-producing substance and thus prevent its action or to change it into another non-toxic substance. It is at least probable that in the amphibians the parathyroids play the same rôle. Larvæ of anuran amphibians, which develop their parathyroids soon after hatching, never show tetanic convulsions if they are fed on thymus, but in certain species of salamanders, whose parathyroids develop only during metamorphosis, the larvæ invariably have tetanic convulsions upon thymus feeding, while the metamorphosed animals never show tetany. But in addition to the parathyroids the salamanders must possess still another mechanism which during the larval period inhibits the production of tetany by the animal''s own thymus glands. In the larvæ of Ambystoma opacum and Ambystoma maculatum this mechanism is sufficient only to prevent tetany from the animal''s own thymus, while in the larvæ of Ambystoma tigrinum it is capable of preventing tetany even when the larvæ are fed with thymus. If the thymus is the organ by whose action tetany is produced, we can understand why tetany in human beings occurs far more frequently in children than in adults, since in the latter the thymus gland is replaced, at least to a great extent, by connective tissue. The relation of thymus to tetany may also possibly explain the occurrence of tetany during pregnancy; while the parathyroids of the mother may be sufficient to prevent tetany from her largely atrophied thymus, they may not be sufficient to prevent tetany from the excess of thymus substance furnished by the fetus to the blood of the mother.     

Problems of body structure and size of the hypophysis.

The size of the hypophysis, especially of the anterior lobe, is related to body size while the nervous lobe is related to the brain weight. The anterior lobe of the hypophysis in domestic animals is smaller than that of their ancestors in the wild. The proportions of the body, the distribution of bulk, as they appear in different races--whippets and bulldogs--are related to the size of the anterior lobe. Same body weight implies that the anterior lobe is nearly twice as large in animals with a compact body structure. These intraspecific results can also be shown interspecificly by comparing the species of African Bovidae. Independent of the influence of body size, the subfamilies Alcelaphinae and Hippotraginae possess a larger anterior lobe. A tendency can be shown for a relation to body structure as short-legged species living on marshy grounds (Kobus) or soft sands (Addax) have larger anterior lobes.     

The origin of tiger salamander (Ambystoma tigrinum) populations in California, Oregon, and Nevada: introductions or relicts?

Whether intentionally or accidentally introduced, exotic species have the capacity to dramatically disrupt native communities. In central California, tiger salamanders (Ambystoma tigrinum) have been introduced as a by-product of the sport fishing bait industry. Some of these introductions are relatively well known and have resulted in the formation of hybrids with the imperiled native California tiger salamander (A. californiense). Other populations of A. tigrinum, particularly in the northern and eastern parts of the state, remain poorly characterized and are present in regions where relictual amphibian populations of other species have persisted, suggesting that these might be relictual, native A. tigrinum. We used genetic sequence data to determine the provenance of all known extralimital A. tigrinum populations in California and adjacent Oregon and Nevada through comparison with reference samples from the native range of A. tigrinum. Our results suggest that A. tigrinum have been introduced in Northern California, Southern California and the Sierra Nevada, originating from multiple sources across the Great Plains of the US. Furthermore, two populations near the California-Oregon border are most closely related to A. tigrinum populations from Washington and Oregon and may represent native tiger salamander lineages.     

Microgeographic adaptations of spotted salamander morphological defenses in response to a predaceous salamander and beetle

Spatial heterogeneity in the selection imposed by different predator species could promote the adaptive diversification of local prey populations. However, high gene flow might swamp local adaptations at limited spatial scales or generalized phenotypic plasticity might evolve in place of local diversification. Spotted salamander larvae Ambystoma maculatum face strongly varying risks from gape‐limited marbled salamander larvae Ambystoma opacum and gape‐unconstrained diving beetle larvae Dytiscus spp. across natural landscapes. To evaluate if A. maculatum adapts to these predation risk across micro‐geographic scales, I measured selection gradients in response to the two focal predators and then assayed the defensive morphologies of ten populations in a common garden experiment. I found that A. opacum induced selection on A. maculatum for larger tailfins and bodies whereas beetles induced selection for larger tail muscles and smaller bodies. In accordance with the local adaptation hypothesis, A. maculatum populations inhabiting ponds with high beetle densities grew larger tail muscles relative to other populations when raised in a common environment. However, populations exposed to strong A. opacum selection did not evolve larger tailfins as predicted. High gene flow or morphological plasticity could explain the absence of this morphological response to A. opacum. Overall, results suggest that populations can sometimes evolve adaptive traits in response to locally variable selection regimes even across the very limited distances that separate populations in this study. If prey populations often differ in their defenses against local predators, then this variation could affect the outcome of species interactions in local communities.     

Co-habiting amphibian species harbor unique skin bacterial communities in wild populations

Although all plant and animal species harbor microbial symbionts, we know surprisingly little about the specificity of microbial communities to their hosts. Few studies have compared the microbiomes of different species of animals, and fewer still have examined animals in the wild. We sampled four pond habitats in Colorado, USA, where multiple amphibian species were present. In total, 32 amphibian individuals were sampled from three different species including northern leopard frogs (Lithobates pipiens), western chorus frogs (Pseudacris triseriata) and tiger salamanders (Ambystoma tigrinum). We compared the diversity and composition of the bacterial communities on the skin of the collected individuals via barcoded pyrosequencing of the 16S rRNA gene. Dominant bacterial phyla included Acidobacteria, Actinobacteria, Bacteriodetes, Cyanobacteria, Firmicutes and Proteobacteria. In total, we found members of 18 bacterial phyla, comparable to the taxonomic diversity typically found on human skin. Levels of bacterial diversity varied strongly across species: L. pipiens had the highest diversity; A. tigrinum the lowest. Host species was a highly significant predictor of bacterial community similarity, and co-habitation within the same pond was not significant, highlighting that the skin-associated bacterial communities do not simply reflect those bacterial communities found in their surrounding environments. Innate species differences thus appear to regulate the structure of skin bacterial communities on amphibians. In light of recent discoveries that some bacteria on amphibian skin have antifungal activity, our finding suggests that host-specific bacteria may have a role in the species-specific resistance to fungal pathogens.     

SOME ASPECTS OF THE ECOLOGY OF THE FRESHWATER CRAB (POTAMONAUTES PERLATUS MILNE EDWARDS) IN THE UPPER REACHES OF THE BUFFALO RIVER,EASTERN CAPE PROVINCE,SOUTH AFRICA.

Summary

Freshwater crabs (Potamonautes perlatus) are the largest naturally occurring invertebrates in southern African rivers. The ecology of these animals in South African riverine ecosystems is little understood. This study investigates some aspects of the population and feeding ecology of P. perlatus in the upper reaches of the Buffalo River. The densities of crabs (carapace width larger than 25 mm) at two sites in the river ranged between 1.72 and 5.25 crabs m², higher than previously recorded for freshwater crabs in rivers in southern Africa and southern Italy. Twenty-four hour observations revealed that P. perlatus has a nocturnal habit. The diet of P. perlatus was established by examination of the contents of the fore-gut. Crabs with a carapace width smaller than 40 mm fed predominantly on aquatic invertebrates while larger crabs fed on allochthanous material (leaf litter), detritus and algae. Through feeding, crabs reduced the surface area of leaves in the stream by 99.95%.     

An examination of multiple factors affecting community structure in an aquatic amphibian community

Summary The potential effects of multiple factors structuring certain larval amphibian communities were studied using a pen experiment in a natural pond. Potential factors (predation and competition from other species) were allowed to act in a stepwise fashion such that their relative importance could be evaluated. Based on a previous study, it was hypothesized that predation by Ambystoma salamander larvae on other larval amphibian species would be the most important factor. Survival of Ambystoma jeffersonianum salamander larvae and Rana sylvatica tadpoles was significantly depressed only by Ambystoma opacum predation. Survival of Ambystoma maculatum salamander larvae was significantly greater in the absence of both A. opacum and A. jeffersonianum predators. The virtual elimination of Hyla chrysoscelis larvae in all treatments also can be largely attributed to Ambystoma predation. Thus, Ambystoma predation was the dominant factor determining larval survival of four amphibian prey species in the experimental communities.     

THE POLYTYPIC SPECIES REVISITED: GENETIC DIFFERENTIATION AND MOLECULAR PHYLOGENETICS OF THE TIGER SALAMANDER AMBYSTOMA TIGRINUM (AMPHIBIA: CAUDATA) COMPLEX

We present a phylogenetic analysis of the Ambystoma tigrinum complex, based on approximately 840 base pairs of mitochondrial-DNA sequence from the rapidly evolving D-loop and an adjacent intron. Our samples include populations of the continentally distributed species, A. tigrinum, plus all described species of Mexican ambystomatids. Sequence divergence is low, ranging from 0–8.5%, and most phylogenetic groupings are weakly supported statistically. We identified eight reasonably well-defined clades from the United States and Mexico, with the geographically isolated A. californiense from California as the probable sister group to the remaining taxa. Our sequence data are not capable of resolving the relationships among these clades, although the pattern of transitional-site evolution suggests that these eight lineages diverged during a period of rapid cladogenesis. We roughly calibrate a molecular clock and identify a few lineages that significantly deviate from the slow, baseline rate of 0.5–0.75% per million years. Our data also suggest that species boundaries for several U.S. and Mexican species need to be altered and that the concept of a continentally distributed, polytypic tiger salamander is not valid.     

Does breeding ecology alter selection on developmental and life history traits? A case study in two Ambystomatid salamanders

Terrestrial breeding with extended incubation has evolved repeatedly in fishes and amphibians but raises challenges for embryos, which must conserve sufficient yolk to continue development until water is available. One means of avoiding premature yolk consumption is for embryos to slow their development such that yolk is consumed more slowly. However slower development is associated with smaller adult body sizes and lower survivorship, particularly in amphibians occupying ephemeral habitats. The variable breeding strategies of Ambystomatid salamanders provide an excellent system in which to examine whether variation in breeding ecology is associated with divergence in embryonic development. Phylogenies of Ambystoma strongly support aquatic egg-laying and winter breeding as ancestral. Early breeding has evolved in three species and terrestrial breeding in two of the three. We propose that early, terrestrial breeding has altered selection on embryonic development. In particular, we propose that the prolonged incubation typically associated with early, terrestrial breeding has selected for longer development times. We compared embryonic development of the terrestrial breeding Ambystoma opacum (Gravenhorst 1807) with the co-occuring, aquatic breeding Ambystoma maculatum (Shaw 1802) under a range of laboratory conditions over two breeding seasons. We found that A. opacum embryos took longer to develop and hatched at a later stage, consistent with the hypothesis that early, terrestrial breeding favors embryos that extend development.     

Predator size and phenology shape prey survival in temporary ponds

Theoretical efforts suggest that the relative sizes of predators and their prey can shape community dynamics, the structure of food webs, and the evolution of life histories. However, much of this work has assumed static predator and prey body sizes. The timing of recruitment and the growth patterns of both predator and prey have the potential to modify the strength of predator–prey interactions. In this study, I examined how predator size dynamics in 40 temporary ponds over a 3-year period affected the survival of spotted salamander (Ambystoma maculatum) larvae. Across communities, gape-limited predator richness, but not size, was correlated with habitat duration (pond permanence). Within communities, mean gape-limited predator size diminished as the growing season progressed. This size reduction occurred because prey individuals grew into a body size refuge and because the largest of the predators left ponds by mid-season. Elevated gape-limited predation risk across time and space was predicted by the occurrence of two large predatory salamanders: marbled salamander larvae (Ambystoma opacum) and red-spotted newt adults (Notophthalmus viridescens). The presence of the largest gape-limited predator, A. opacum, predicted A. maculatum larval survival in the field. The distribution of large predatory salamanders among ponds and across time is expected to lead to differing community dynamics and to generate divergent natural selection on early growth and body size in A. maculatum. In general, a dynamic perspective on predator size often will be necessary to understand the ecology and evolution of species interactions. This will be especially true in frequently disturbed or seasonal habitats where phenology and ontogeny interact to determine body size asymmetries. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Biochemical studies on muscaranic receptors in the salamander olfactory epithelium

Muscarinic cholinergic receptors in the olfactory epithelium of the salamander, Ambystoma tigrinum, were studied via binding of 3-[³H]quinuclidinyl benzilate. The receptors are present on the olfactory receptor cells in the epithelium to an amount of 0.08 pmol/mg homogenate protein. Both choline acetyltransferase and acetylcholine esterase are present in the salamander olfactory epithelium.     

Genie Control of Axolotl Metamorphosis

SYNOPSIS. Neoteny in the Mexican axolotl, Ambystoma mexicanum,is caused by homozygosity for a single recessive gene. The dominantallele causing physical metamorphosis is found in the closelyrelated species, Ambystoma tigrinum, with which it can hybridize.Despite the failure of axolotls to undergo physical metamorphosis,they do undergo a cryptic metamorphosis. A larval-to-adult hemoglobinform change, serum protein changes and other physiological eventsusually associated with amphibian metamorphosis occur duringearly larval life at ages comparable to the age at which Ambystomatigrinum undergoes both the cryptic and external metamorphicevents. Axolotl cryptic metamorphosis can be induced precociouslyby immersion of the larvae in low concentrations of thyroxine;physical metamorphosis can be induced with higher thyroxineconcentrations. The site of action of the gene responsible foraxolotl neoteny has not been identified. A change in the sensitivityof external metamorphic processes to thyroxine, or reduced hormonalstimulation by the pituitary or hypothalamus may be responsible.A comparison of these functions in Ambystoma tigrinum and theaxolotl may identify the lesion.     

Evolution mediates the effects of apex predation on aquatic food webs

Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance.     

Arrival sequence and diet mediate interspecific competition in an ant community

The arrival sequence of organisms in a habitat and their diet are two factors that are thought to modulate animal performance, affect the outcome of behavioural interactions, and shape communities. In New Zealand, two species that seldom co-occur in field populations are Prolasius advenus and Monomorium antarcticum. Herein we tested the hypotheses that arrival sequence and diet influence the strength of interactions between these two species. These ant species presented asymmetric responses to arrival sequence and diet variations. When arriving first P. advenus displayed increased aggression and M. antarcticum a defensive reaction. Changes in carbohydrate and protein availability modulated colony activity rates of both species. Colonies of M. antarcticum fed on a high carbohydrate and low protein diet displayed higher activity rates than colonies fed on a low carbohydrate and high protein diet. In contrast, control colonies of P. advenus fed on a high carbohydrate and low protein diet displayed lower activity rates than colonies fed on a low carbohydrate and high protein diet. These results indicate that arrival sequence can modulate the agonistic reaction displayed by interacting species in situations of conflict. This work also demonstrates that species adjust activity rates in response to diet, but different species do so differently. Therefore, arrival sequence and diet could explain species mutually exclusive distribution patterns observed in nature.     

Polymorphic microsatellite loci for tiger salamanders,Ambystoma tigrinum

Microsatellites have been developed for few amphibian species. However, developing genetic markers for population genetic studies in amphibians is critical because amphibians are declining globally. The tiger salamander, Ambystoma tigrinum, is widespread throughout the United States and includes the endangered subspecies, A. t. stebbinsi. We present primers and amplification conditions for 10 polymorphic microsatellite loci that have produced successful results in three subspecies of A. tigrinum. Number of alleles per locus ranged from one to 11 and heterozygosity ranged from 0 to 0.815 depending on the subspecies and locus analysed. These markers should prove useful for future studies of genetic diversity and population subdivision.     

Cutaneous Exchange of Ions in Lower Vertebrates

SYNOPSIS. Cutaneous ion transport has long been studied forits role in osmotic and ionic regulation in amphibians. In additionto this role, it is becoming clear that cutaneous ion exchangeinfluences, and is influenced by, a number of other physiologicaland morphological factors. The exchange of Na^$ and Cl^–across the skin of larval Ambystoma tigrinum is clearly involvedin acid-base balance. The animals require NaCl in their bathingmedia in order to compensate for a respiratory acidosis or torecover normally from a metabolic acidosis. Conversely, Na^$influx is stimulated and Cl^– influx is inhibited duringhypercapnia. Cutaneous ion transport in larval A. tigrinum appearsto be at least partially influenced by cutaneous circulationas immersion in isosmotic media to reduce skin blood flow alsoslows Na^$ influx. Allometric analysis of Na^$ influx yieldeda slope of 0.52, which is significantly less than the slopepredicted for surface area. The lower slope for ion transportmay reflect changes in capillary recruitment, skin thicknessor distribution of ion transporters over the skin. In additionto the well known cutaneous ion transport of amphibians, a numberof fish and reptilian species have also been discovered to exchangeions across skin in ways which may have homeostatic consequences.     

Comparative morphometric data on the epiphysis, the subfornical organ, and the anterior pituitary gland in 2 groups of pure strain Wistar female rats, SPF or conventional]

In SPF female rats, the pineal gland is less voluminous and its cell-nuclei are smaller than those of conventionnal female rats. This confirms (with the voluminous adrenals previously reported) the stressing action of the absence of pathogenic germs on these animals. The anterior lobe of the hypophysis is slightly smaller and subfornical organ a little larger than in conventionnal female rats.     

THE EVOLUTION OF TETRAPOD FEEDING BEHAVIOR: KINEMATIC HOMOLOGIES IN PREY TRANSPORT

One of the major features of the aquatic-to-terrestrial transition in vertebrate evolution was the change in the mechanism used to transport prey from the jaws to the throat. Primarily, vertebrates use hydraulic transport, but the transition to terrestrial life was accompanied by modifications of the hyobranchial apparatus that permit tongue-based transport. Despite an extensive data base on amniote feeding systems and mechanisms of intraoral prey transport, few data are available on the mechanism of prey transport in anamniote tetrapods. Transport cycles of four Ambystoma tigrinum (Amphibia) feeding on worms and crickets were filmed at 150 flames per second to produce quantitative profiles of the intraoral transport cycles for the two prey types. During the transport cycle the head and body remain stationary relative to the background: transport in Ambystoma tigrinum thus does not involve inertial movements of the head or body. Prey type had little effect on the kinematics of prey transport. The process of prey transport may be divided into four phases: preparatory, fast opening, closing, and recovery. The preparatory phase itself is divided into two parts: an extended segment that may include slight slow opening and a static phase prior to mouth opening where no change in gape occurs. The kinematic profile of transport in terrestrial salamanders is extremely similar to that used by fishes during hydraulic (aquatic) prey transport. We hypothesize that the distinct recovery and preparatory phases in the transport cycle of anamniote tetrapods are together homologous to the slow opening phases of the amniote cycle, and that during the evolution of terrestrial prey processing systems the primitive extended preparatory phase has become greatly compressed and incorporated into the amniote gape cycle.     

Subterranean Sympatry: An Investigation into Diet Using Stable Isotope Analysis

In the Western Cape three species of mole-rat occur in sympatry, however, little is known about differences in their dietary preferences. Dietary composition of the three species; the common mole-rat (Cryptomys hottentotus hottentotus), the Cape mole-rat (Georychus capensis) and the Cape dune mole-rat (Bathyergus suillus) were examined using stable isotope analysis. Blood, fur and claw samples were collected from 70 mole-rats, in addition to several potential food items, to assess food selection of the three species under natural conditions. Overall there was a significant difference in the isotopic composition (δ¹³C and δ¹⁵N) between all three species and significant differences in their diet composition. There were also significant differences between tissues in all three species suggesting temporal variation in diet. The small size and colonial lifestyle of C. h. hottentotus allows it to feed almost 100% on bulbs, while the solitary and larger species G. capensis and B. suillus fed to a greater extent on other resources such as grasses and clover. B. suillus, the largest of the species, had the most generalized diet. However, overall all species relied most heavily upon geophytes and consumed the same species suggesting competition for resources could exist. We also showed a high level of individual variation in diet choices. This was most pronounced in B. suillus and G. capensis and less so in C. h. hottentotus. We demonstrate that stable isotope analysis can successfully be applied to examine dietary patterns in subterranean mammals and provide insights into foraging patterns and dietary variation at both the inter and intra population level.