The ultrastructure of the spermatozoa of Epipedobates flavopictus (Amphibia, Anura, Dendrobatidae), with comments on its evolutionary significance

We describe, for the first time, the spermatozoon ultrastructure of a dendrobatid frog, Epipedobates flavopictus. Mature spermatozoa of E. flavopictus are filiform, with a moderately curved head and a proportionally short tail. The acrosomal vesicle is a conical structure that covers the nucleus for a considerable distance. A homogeneous subacrosomal cone lies between the acrosome vesicle and the nucleus. The nucleus contains a nuclear space at its anterior end, and electron-lucent spaces and inclusions. No perforatorium is present. In the midpiece, the proximal centriole is housed inside a deep nuclear fossa. Mitochondria are scattered around the posterior end of the nucleus and inside the undulating membrane in the anterior portion of the tail. In transverse section the tail is formed by an U-shaped axial fiber connected to the axoneme through an axial sheath, which supports the undulating membrane. The juxta-axonemal fiber is absent. The spermatozoon of E. flavopictus has several characteristics not observed before in any anurans, such as a curved axial fiber, absence of a juxta-axonemal fiber, and presence of mitochondria in the typical undulating membrane. Our results endorse the view that, in anurans, the conical perforatorium and subacrosomal cone are homologous and that Dendrobatidae should be grouped within Bufonoidea rather than Ranoidea

Comparative Ontogeny of Cranial Ossification in the Spotted Salamander, Ambystoma Maculatum, and the Tailed Frog, Ascaphus Truei

The ontogenetic sequence of ossification of the cranium, including descriptions of the development of individual elements, from initial appearance of bone through adulthood, is described for two species of amphibian: the Spotted Salamander, Ambystoma maculatum, and the Tailed Frog, Ascaphus truei. This study is based on cleared-and-stained developmental series of 269 specimens of Ambystoma and 325 of Ascaphus. Nine stages of cranial development are defined for Ambystoma maculatum. By metamorphosis, all bones of the skull of Ambystoma except the articular have begun to ossify. The ossification sequence of Ambystoma shows little interindividual variation; only 6 specimens do not follow the modal sequence. Comparisons with other salamanders reveals basic similarities in the developmental pattern of the caudate skull. In Ascaphus truei, geographic variation in the sequence of cranial ossification is greater than previously reported for any species of amphibian. In addition, intraspecific variation within populations is also higher than previously reported. The number of bones present at any developmental stage shows a poor coorelation with external morphology. As many as 13 Gosner stages may pass after initial appearance of a given bone before it appears in all specimens in the sample. Relative to other anurans, ossification of many cranial elements is delayed in Ascaphus. This delay is discussed in terms of larval specialization, and as a possible consequence of heterochrony. Differences in the developmental patterns of ossification in Ambystoma maculatum and Ascaphus truei reflect basic differences in the evolution of larval life histories

A Review on Bradykinin-Related Peptides Isolated from Amphibian Skin Secretion

Amphibian skin secretion has great potential for drug discovery and contributes hundreds of bioactive peptides including bradykinin-related peptides (BRPs). More than 50 BRPs have been reported in the last two decades arising from the skin secretion of amphibian species. They belong to the families Ascaphidae (1 species), Bombinatoridae (3 species), Hylidae (9 speices) and Ranidae (25 species). This paper presents the diversity of structural characteristics of BRPs with N-terminal, C-terminal extension and amino acid substitution. The further comparison of cDNA-encoded prepropeptides between the different species and families demonstrated that there are various forms of kininogen precursors to release BRPs and they constitute important evidence in amphibian evolution. The pharmacological activities of isolated BRPs exhibited unclear structure–function relationships, and therefore the scope for drug discovery and development is limited. However, their diversity shows new insights into biotechnological applications and, as a result, comprehensive and systematic studies of the physiological and pharmacological activities of BRPs from amphibian skin secretion are needed in the future

The homology of sarcopterygian gills

Vertebrate gills may be either external (protruding from the body surface) or internal (enclosed in a chamber). Among living amphibians, external gills are found in salamander larvae and neotenes, early frog larvae, and caecilian embryos; internal gills are found only in later-stage frog larvae. Evidence for internal gills has also been found in stem tetrapods, and amphibian-like external gills have been found in some fossil temnospondyls and anthracosaurs. Gill homology among these groups and life stages has long been questioned. To address this, scanning electron microscopy, vascular casting, and paraffin sectioning were utilized to study the morphology of gills and associated vessels of four sarcopterygian species: the basal frog Ascaphus truei, the salamander Dicamptodon tenebrosus, and the lungfishes Lepidosiren paradoxa and Protopterus sp. In all studied species, blood flows from the heart through four pairs of afferent branchial arteries, through the gill lamellae (when present), and drains through efferent branchial arteries into the dorsal aorta. In D. tenebrosus and A. truei no gill lamellae are found on the fourth branchial arch; instead, the afferent branchial artery supplies blood to the lung. In the external gill of D. tenebrosus the afferent arteries travel posterolaterally within an elongation of the interbranchial septum and protrude dorsolaterally from the body, supplying blood to the paired, digit-like lamellae via a single vascular loop per lamella. Ascaphus truei, unlike most anuran larvae, never develops external gills, but only internal gills. These extend directly from the ventral side of the branchial arches. Each unpaired lamella has multiple club-like branches, each housing a vascular loop. Protopterus sp. possesses internal gills on the hyoid arch and branchial arches III-V, with the hyoid and branchial arch V developing unpaired primary lamellae. The lamellae of all arches possess secondary lamellae. No gill lamellae were found in the studied larval Lepidosiren paradoxa. The external gills of Dicamptodon tenebrosus show some remarkable similarities to the internal gills of basal sarcopterygians, possessing paired primary lamellae (though they never develop any secondary lamellae), and provide further evidence that the external gills of amphibians are homologous to the internal gills of fishes. The evolutionary significance of the internal gills of frogs is less clear, but the morphology of the basal Ascaphus truei provides evidence suggesting that the internal gills of frogs are an independently evolved character, rather than a retained ancestral feature. These findings shed light on the morphology and evolution of gills within sarcopterygians

Life history of the coastal tailed frog (Ascaphus truei) across an elevational gradient

The life history of a species is described in terms of its growth, longevity, and reproduction. Unsurprisingly, life history traits are known to vary in many taxa across environmental gradients. In the case of amphibians, species at high elevations and latitudes tend to have shorter breeding seasons, shorter activity periods, longer larval periods, reach sexual maturity at older ages, and produce fewer and larger clutches per year. The Coastal Tailed Frog (Ascaphus truei) is an ideal species for the study of geographic variation in life history because it ranges across most of the Pacific Northwest from northern California into British Columbia, and along its range it varies geographically in larval period and morphology. During a California Department of Fish and Wildlife restoration project in the Trinity Alps Wilderness, I had incidental captures of Coastal Tailed Frog larvae and adults. To date, no population across the species’ range has been described above 2000m. These populations in the Trinity Alps range from 150m to over 2100m in elevation, and those that are in the higher part of the range are likely living at the species’ maximum elevational limit. In this study, I examined size, growth, larval period, size at sexual maturity, and longevity of A. truei across populations along an elevational gradient in the Klamath Mountains of northern California. I calculated growth rates and movement by individually marking tadpoles and post-metamorphic frogs with visual implant elastomer (VIE), then tracking them from May through October of 2018. I described the length of the larval period using length-density histograms to visualize larval cohorts, I determined size at sexual maturity using secondary sexual characteristics of post-metamorphic frogs, and I determined longevity using skeletochronology. I found that the larval period of A. truei in the Klamath Mountains of northern California ranges from two years in low and mid-elevations, to at least three years in high elevations. I also found decreased body size and increased growth rates of tadpoles with increasing elevation. Post-metamorphic frogs grew at similar rates as previously described coastal California populations. There was high site fidelity and significantly greater movement during the months of June and August in post-metamorphic animals. Frogs in the high elevations are capable of great longevity, with a maximum observed age estimated at eight years post-metamorphosis. The high elevation populations described here have the longest larval period documented in California. This study also provides the first field estimates of larval growth rates and the first longevity estimates of post metamorphic frogs in California. Future laboratory experiments will be necessary to separate phenotypic plasticity of life history traits from true genetic differences between A. truei populations in the Klamath Mountains of northern California, as potential explanations for the variation seen

Environmental DNA is an Effective Method to Monitor Species in Various Freshwater Habitats

This research investigated the use of DNA shed from individuals into the environment (eDNA) to monitor three amphibian species and two trout species associated with habitat intersected by Interstate-90 in Snoqualmie Pass, Washington. This included a large catchment area within creeks and nearby wetlands historically affected by I-90, including sites where significant habitat improvements had been made. Species-specific primers were used to detect three focal amphibians of varying local abundance and two focal trout species. This study showed successful detection of species across both lentic and lotic systems throughout the study area through efficient multiplexing (detection of multiple species in one reaction) via quantitative Polymerase Chain Reaction. Results from this study, overall, showed that eDNA methods can produce results that reliably reflect target species’ presence across a large catchment area in an efficient manner

American Dipper, Cinclus mexicanus, Preys Upon Larval Tailed Frogs, Ascaphus truei

The American Dipper (Cinclus mexicanus) is an aquatic songbird that inhabits fast-flowing mountain streams in western North America. Although dippers are known to feed primarily on aquatic invertebrates, they will also eat juvenile fish and salmon eggs when available. In 2002, while monitoring and photographing nesting activities of the American dipper, we observed and photographed adult dippers capturing Tailed Frog (Ascaphus truei) tadpoles and feeding them to their young. This note is intended to document a rarely observed occurrence and identify interactions between two relatively uncommon species

What Limits Tailed Frog Tadpole Density and Distribution in Western Montana Streams?

We explored the possible limitation of temperature and other habitat features on tailed frog tadpole populations in northwestern Montana. We sampled densities and habitat features in two regions with different climatic regimes and in streams with and without tadpoles, expecting larger density and size in the warmer region. We also expected habitat conditons to be more optimal (higher gradient, swifter velocity, and less canopy cover) in streams with tadpoles. Temperature appeared to positively influence tadpole size, though both tadpole size and density were strongly correlated with other variables. Density was correlated with gradient, canopy, depth, and elevation, whereas length was correlated with width and density. Contrary to expectations, we found lower densities in the warmer region. Streams in the warmer region were lower in elevation and gradient than the colder region streams. These lower gradient streams are optimal habitat for sculpin, which prey on tadpoles. The presence of sculpin in these warmer-region lower-gradient streams suggests predation could explain the lower densities. In comparing habitat features of streams with and without tadpoles, only gradient varied significantly, which also supports the idea of predation limiting densities

Faunal assemblages and multi–scale habitat patterns in headwater tributaries of the South Fork Trinity River – an unregulated river embedded within a multiple–use landscape

Las cabeceras pueden representar el 80% de los kilómetros de recorrido en una cuenca fluvial y poseen unas propiedades físicas y biológicas únicas, cuya importancia hasta hace poco no se habían reconocido para el sostenimiento de un funcionamiento sano de las redes de cuencas y sus servicios ecológicos. Tomamos muestras de 60 cabeceras de los afluentes del río South Fork Trinity, una cuenca de 2.430 km2, boscosa en su mayor parte y de múltiples usos, situada en el noroeste de California. Nuestros objetivos eran: (1) diferenciar tipos de cabeceras únicos utilizando 69 variables abióticas y vegetales, medidas a tres escalas espaciales, y luego reducirlos a subconjuntos informativos; (2) determinar si distintos biotas ocupaban los distintos tipos de afluentes; (3) determinar las características medioambientales asociadas con la presencia y abundancia de dichas comunidades bióticas; y (4) utilizando una modelización de nichos, determinar los umbrales de los atributos claves para ilustrar cómo estos biotas podrían emplearse para la medición de la integridad del sistema y los servicios ecológicos. Varios taxones fueron suficientemente abundantes y extendidos para utilizarlos como bioindicadores; la presencia y abundancia de la trucha arco iris (Oncorhynchus mykiss), la riqueza en especies de la herpetofauna (reptiles y anfibios) y el cangrejo señal (Pacifastacus leniusculus) representaban diferentes posiciones tróficas, el valor como recursos comerciales (la trucha arco iris), la sensibilidad al estrés ambiental (anfibios), e indicadores de la biodiversidad (riqueza de especies de la herpetofauna). La riqueza de especies de la herpetofauna no difirió, pero la abundancia de la trucha arco iris, del cangrejo señal, la riqueza de anfibios, difirieron significativamente entre los tipos de afluentes. Los modelos de los nichos indicaron que los patrones de distribución y abundancia, tanto en los ambientes acuáticos como en los ribereños, estaban asociados con atributos físicos y estructurales a multiples escalas espaciales, tanto dentro como alrededor de los tramos acuáticos. Los bioindicadores respondieron a series únicas de atributos, reflejando la elevada heterogeneidad ambiental en las cabeceras de los afluentes en toda esta gran cuenca. Dichos atributos de los nichos representaban una amplia gama de ambientes de cabeceras fluviales, indicando respuestas a una serie de condiciones naturales y antropogénicas. Se demostró el valor de utilizar una serie de bioindicadores para elucidar las condiciones de las cabeceras y para examinar las numerosas perturbaciones que pueden influir sobre la integridad ecológica. Palabras clave: Cabeceras de afluentes, Bioindicadores, Multiescala, Integridad ecológica.Las cabeceras pueden representar el 80% de los kilómetros de recorrido en una cuenca fluvial y poseen unas propiedades físicas y biológicas únicas, cuya importancia hasta hace poco no se habían reconocido para el sostenimiento de un funcionamiento sano de las redes de cuencas y sus servicios ecológicos. Tomamos muestras de 60 cabeceras de los afluentes del río South Fork Trinity, una cuenca de 2.430 km2, boscosa en su mayor parte y de múltiples usos, situada en el noroeste de California. Nuestros objetivos eran: (1) diferenciar tipos de cabeceras únicos utilizando 69 variables abióticas y vegetales, medidas a tres escalas espaciales, y luego reducirlos a subconjuntos informativos; (2) determinar si distintos biotas ocupaban los distintos tipos de afluentes; (3) determinar las características medioambientales asociadas con la presencia y abundancia de dichas comunidades bióticas; y (4) utilizando una modelización de nichos, determinar los umbrales de los atributos claves para ilustrar cómo estos biotas podrían emplearse para la medición de la integridad del sistema y los servicios ecológicos. Varios taxones fueron suficientemente abundantes y extendidos para utilizarlos como bioindicadores; la presencia y abundancia de la trucha arco iris (Oncorhynchus mykiss), la riqueza en especies de la herpetofauna (reptiles y anfibios) y el cangrejo señal (Pacifastacus leniusculus) representaban diferentes posiciones tróficas, el valor como recursos comerciales (la trucha arco iris), la sensibilidad al estrés ambiental (anfibios), e indicadores de la biodiversidad (riqueza de especies de la herpetofauna). La riqueza de especies de la herpetofauna no difirió, pero la abundancia de la trucha arco iris, del cangrejo señal, la riqueza de anfibios, difirieron significativamente entre los tipos de afluentes. Los modelos de los nichos indicaron que los patrones de distribución y abundancia, tanto en los ambientes acuáticos como en los ribereños, estaban asociados con atributos físicos y estructurales a multiples escalas espaciales, tanto dentro como alrededor de los tramos acuáticos. Los bioindicadores respondieron a series únicas de atributos, reflejando la elevada heterogeneidad ambiental en las cabeceras de los afluentes en toda esta gran cuenca. Dichos atributos de los nichos representaban una amplia gama de ambientes de cabeceras fluviales, indicando respuestas a una serie de condiciones naturales y antropogénicas. Se demostró el valor de utilizar una serie de bioindicadores para elucidar las condiciones de las cabeceras y para examinar las numerosas perturbaciones que pueden influir sobre la integridad ecológica. Palabras clave: Cabeceras de afluentes, Bioindicadores, Multiescala, Integridad ecológica.Headwaters can represent 80% of stream kilometers in a watershed, and they also have unique physical and biological properties that have only recently been recognized for their importance in sustaining healthy functioning stream networks and their ecological services. We sampled 60 headwater tributaries in the South Fork Trinity River, a 2,430 km2, mostly forested, multiple–use watershed in northwestern California. Our objectives were: (1) to differentiate unique headwater types using 69 abiotic and vegetation variables measured at three spatial scales, and then to reduce these to informative subsets; (2) determine if distinct biota occupied the different tributary types; (3) determine the environmental attributes associated with the presence and abundance of these biotic assemblages; and (4) using niche modeling, determine key attribute thresholds to illustrate how these biota could be employed as metrics of system integrity and ecologi¬cal services. Several taxa were sufficiently abundant and widespread to use as bio–indicators: the presence and abundance of steelhead trout (Oncorhynchus mykiss), herpetofauna (reptile and amphibian) species richness, and signal crayfish (Pacifastacus leniusculus) represented different trophic positions, value as commercial resources (steelhead), sensitivity to environmental stress (amphibians), and indicators of biodiversity (herpetofauna species richness). Herpetofauna species richness did not differ, but abundances of steelhead trout, signal crayfish, and amphibian richness all differed significantly among tributary types. Niche models indicated that distribution and abun¬dance patterns in both riparian and aquatic environments were associated with physical and structural attributes at multiple spatial scales, both within and around reaches. The bio–indicators responded to unique sets of attributes, reflecting the high environmental heterogeneity in headwater tributaries across this large watershed. These niche attributes represented a wide range of headwater environments, indicating responses to a number of natural and anthropogenic conditions, and demonstrated the value of using a suite of bio–indicators to elucidate watershed conditions, and to examine numerous disturbances that may influence ecological integrity. Key words: Headwater tributaries, Bio–indicators, Multi–scale, Ecological integrity