The effect of miniaturized body size on skeletal morphology in frogs

Phylogenetic relationships of sleeper gobies (Eleotridae: Gobiiformes: Gobioidei), with comments on the position of the miniature genus Microphilypnus

Microphilypnus and Leptophilypnion are miniaturized genera within the family Eleotridae. The evolutionary relationships among these taxa are still poorly understood, and molecular analyses are restricted to mitochondrial genes, which have not been conclusive. We compiled both mitochondrial and nuclear genes to study the phylogenetic position of Microphilypnus and the evolutionary history and relationships of eleotrids. We propose that Microphilypnus and Leptophilypnus (a non-miniature genus) are not sister groups as suggested by previous studies, but rather separate lineages that arose in the early Eocene, with Leptophilypnus recovered as a sister group to the other analyzed eleotrids. In fact, Microphilypnus is currently associated with the Neotropical clade Guavina/Dormitator/Gobiomorus. We also identified a well-supported clade that indicated Gobiomorus and Hemieleotris as paraphyletic groups, besides a close relationship among Calumia godeffroyi, Bunaka gyrinoides, Eleotris and Erotelis species. This is the first comprehensive report about the evolutionary relationships in members of the family Eleotridae, including multiloci and multispecies approaches. Therefore, we provided new insights about the phylogenetic position of some taxa absent in previous studies, such as the miniature genus Microphilypnus and a recently described species of Eleotris from South America.

The Pristimantis trachyblepharis species group, a clade of miniaturized frogs: description of four new species and insights into the evolution of body size in the genus

Species richness in the genus Pristimantis is underestimated due to the existence of morphologically cryptic species. This is worsened by the low sampling effort and the lack of studies using genetic markers. Here, we use molecular and morphological data to determine the phylogenetic relationships of a clade of Pristimantis distributed throughout montane tropical forests in the eastern Andes, from central Ecuador to northern Perú. We name this clade the Pristimantis trachyblepharis species group. Our results show that it comprises nine species, of which four are formally described and five are new. Four of these undescribed species are formally described here. The group is composed of miniaturized species, such as Pristimantis nanus sp. nov., currently the smallest known species of the genus and the smallest vertebrate in Ecuador. As a first approach to understanding the evolutionary origin and implications of body-size reduction in Pristimantis, we here study the phylogenetic signal and evolutionary trends of body size within the genus. We also provide the first record of P. aquilonaris in Ecuador and we show, for the first time, the phylogenetic position of P. albujai, P. aquilonaris, P. minimus and P. trachyblepharis, which are also members of the P. trachyblepharis species group.

Evolutionary treasures hidden in the West Indies: Comparative osteology and visceral morphology reveals intricate miniaturization in the insular genera Mitophis Hedges, Adalsteinsson, & Branch, 2009 and Tetracheilostoma Jan, 1861 (Leptotyphlopidae: Epictinae: Tetracheilostomina)

The genera Mitophis and Tetracheilostoma comprise two extant lineages of small-sized threadsnakes that exclusively inhabit several islands of the West Indies. Even though leptotyphlopids are known for their extremely reduced size, miniaturization has only been hypothesized to reflect insular dwarfism for the genus Tetracheilostoma. Herein, we aim to describe the comparative osteology and visceral morphology of both genera, investigating and discussing their several internal morphological simplifications and novelties. Our results indicate that these taxa exhibit several autapomorphies mostly concentrated in the dorsoposterior skull elements and maxillae, as well as in their axial skeleton and viscera. These novelties and simplifications are most likely a result of extreme miniaturization driven by the evolutionary constraints or ecological opportunities possibly imposed by the "island rule." Both Mitophis and Tetracheilostoma distinguish from all other Epictinae in lacking a dentigerous process in the maxillae, by having the prootic fused to the otooccipital, and by the lack (except in comparison to a few Epictia) of a cervical vertebrae intercentrum I. Additionally, Mitophis can be distinguished from other Epictinae by the participation of the unpaired supraoccipital in the dorsal border of the foramen magnum, by the absence of the pleurapophyses in the caudal vertebrae, by a higher number of liver segments, and by the extreme degeneration of the pelvic rudiments. Tetracheilostoma differs from other Epictinae by lacking a distinct supraoccipital, which is fused to the parietal. Thus, our results reinforce that morphological characters are extremely valuable for leptotyphlopid systematics given their extremely conserved external morphology.

Lizards as models to explore the ecological and neuroanatomical correlates of miniaturization

Extreme body size reductions bring about unorthodox anatomical arrangements and novel ways in which animals interact with the environment. Drawing from studies of vertebrates and invertebrates, we provide a theoretical framework for miniaturization to inform hypotheses using lizards as a study system. Through this approach, we demonstrate the repeated evolution of miniaturization across 11 families and a tendency for miniaturized species to occupy terrestrial microhabitats, possibly driven by physiological constraints. Differences in gross brain morphology between two gecko species demonstrate a proportionally larger telencephalon and smaller olfactory bulbs in the miniaturized species, though more data are needed to generalize this trend. Our study brings into light the potential contributions of miniaturized lizards to explain patterns of body size evolution and its impact on ecology and neuroanatomy. In addition, our findings reveal the need to study the natural history of miniaturized species, particularly in relation to their sensory and physiological ecology.

Size, microhabitat, and loss of larval feeding drive cranial diversification in frogs

Habitat is one of the most important factors shaping organismal morphology, but it may vary across life history stages. Ontogenetic shifts in ecology may introduce antagonistic selection that constrains adult phenotype, particularly with ecologically distinct developmental phases such as the free-living, feeding larval stage of many frogs (Lissamphibia: Anura). We test the relative influences of developmental and ecological factors on the diversification of adult skull morphology with a detailed analysis of 15 individual cranial regions across 173 anuran species, representing every extant family. Skull size, adult microhabitat, larval feeding, and ossification timing are all significant factors shaping aspects of cranial evolution in frogs, with late-ossifying elements showing the greatest disparity and fastest evolutionary rates. Size and microhabitat show the strongest effects on cranial shape, and we identify a "large size-wide skull" pattern of anuran, and possibly amphibian, evolutionary allometry. Fossorial and aquatic microhabitats occupy distinct regions of morphospace and display fast evolution and high disparity. Taxa with and without feeding larvae do not notably differ in cranial morphology. However, loss of an actively feeding larval stage is associated with higher evolutionary rates and disparity, suggesting that functional pressures experienced earlier in ontogeny significantly impact adult morphological evolution.

Body size miniaturization in a lineage of colubrid snakes: Implications for cranial anatomy

As body size strongly determines the biology of an organism at all levels, it can be expected that miniaturization comes with substantial structural and functional constraints. Dwarf snakes of the genus Eirenis are derived from big, surface-dwelling ancestors, considered to be similar to those of the sister genus Dolichophis. To better understand the structural implications of miniaturization on the feeding apparatus in Eirenis, the morphology of the cranial musculoskeletal system of Dolichophis schmidti was compared with that of the miniature Eirenis punctatolineatus and E. persicus using high-resolution µCT data. The gape index was compared between D. schmidti and 14 Eirenis species. Our results show a relatively increased neurocranium size and decreased maximal jaw muscle force in E. persicus, compared with the D. schmidti, and an intermediate situation in E. punctatolineatus. A significant negative allometry in gape index relative to body size is observed across the transition from the Dolichophis to Pediophis and Eirenis subgenera. However, the gape index relative to head size showed a significant negative allometry only across the transition from the Dolichophis to Pseudocyclophis subgenus. In Dolichophis-Eirenis dwarfing lineages, different structural patterns are observed through miniaturization, indicating that overcoming the challenge of miniaturization has achieved via different adaptations.

Shrinking before our isles: the rapid expression of insular dwarfism in two invasive populations of guttural toad (Sclerophrys gutturalis)

Island ecosystems have traditionally been hailed as natural laboratories for examining phenotypic change, including dramatic shifts in body size. Similarly, biological invasions can drive rapid localized adaptations within modern timeframes. Here, we compare the morphology of two invasive guttural toad (Sclerophrys gutturalis) populations in Mauritius and Réunion with their source population from South Africa. We found that female toads on both islands were significantly smaller than mainland counterparts (33.9% and 25.9% reduction, respectively), as were males in Mauritius (22.4%). We also discovered a significant reduction in the relative hindlimb length of both sexes, on both islands, compared with mainland toads (ranging from 3.4 to 9.0%). If our findings are a result of natural selection, then this would suggest that the dramatic reshaping of an amphibian's morphology-leading to insular dwarfism-can result in less than 100 years; however, further research is required to elucidate the mechanism driving this change (e.g. heritable adaptation, phenotypic plasticity, or an interaction between them).

Miniaturization, Genome Size, and Biological Size in a Diverse Clade of Salamanders

AbstractGenome size (C-value) can affect organismal traits across levels of biological organization from tissue complexity to metabolism. Neotropical salamanders show wide variation in genome and body sizes, including several clades with miniature species. Because miniaturization imposes strong constraints on morphology and development and because genome size is strongly correlated with cell size, we hypothesize that body size has played an important role in the evolution of genome size in bolitoglossine salamanders. If this hypothesis is correct, then genome size and body size should be correlated in this group. Using Feulgen image analysis densitometry, we estimated genome sizes for 60 species of Neotropical salamanders. We also estimated the "biological size" of species by comparing genome size and physical body sizes in a phylogenetic context. We found a significant correlation between C-value and physical body size using optimal regression with an Ornstein-Uhlenbeck model and report the smallest salamander genome found to date. Our index of biological size showed that some salamanders with large physical body size have smaller biological body size than some miniature species and that several clades demonstrate patterns of increased or decreased biological size compared with their physical size. Our results suggest a causal relationship between physical body size and genome size and show the importance of considering the impact of both on the biological size of organisms. Indeed, biological size may be a more appropriate measure than physical size when considering phenotypic consequences of genome size evolution in many groups.

Two-hundred million years of anuran body-size evolution in relation to geography, ecology and life history

Surprisingly, little is known about body-size evolution within the most diverse amphibian order, anurans (frogs and toads), despite known effects of body size on the physiological, ecological and life-history traits of animals more generally. Here, we examined anuran body-size evolution among 2,434 species with over 200 million years of shared evolutionary history. We found clade-specific evolutionary shifts to new body-size optima along with numerous independent transitions to gigantic and miniature body sizes, despite the upper limits of anuran body size remaining quite consistent throughout the fossil record. We found a weak, positive correlation between a species' body size and maximum latitude and elevation, including a dearth of small species at higher elevations and broader latitudinal and elevational ranges in larger anurans. Although we found modest differences in mean anuran body size among microhabitats, there was extensive overlap in the range of body sizes across microhabitats. Finally, we found that larger anurans are more likely to consume vertebrate prey than smaller anurans are and that species with a free-swimming larval phase during development are larger on average than those in which development into a froglet occurs within the egg. Overall, anuran body size does not conform to geographic and ecological patterns observed in other tetrapods but is perhaps more notable for variation in body size within geographic regions, ecologies and life histories. Here, we document this variation and propose target clades for detailed studies aimed at disentangling how and why variation in body size was generated and is maintained in anurans.

The geographical diversification in varanid lizards: the role of mainland versus island in driving species evolution

Monitor lizards (Varanidae) inhabit both the mainland and islands of all geological types and have diversified into an exceptionally wide range of body sizes, thus providing an ideal model for examining the role of mainland versus island in driving species evolution. Here we use phylogenetic comparative methods to examine whether a link exists between body size-driven diversification and body size-frequency distributions in varanid lizards and to test the hypothesis that island lizards differ from mainland species in evolutionary processes, body size, and life-history traits (offspring number and size). We predict that: 1) since body size drives rapid diversification in groups, a link exists between body size-driven diversification and body size-frequency distributions; 2) because of various environments on island, island species will have higher speciation, extinction, and dispersal rates, compared with mainland species; 3) as a response to stronger intraspecific competition, island species will maximize individual ability associated with body size to outcompete closely-related species, and island species will produce smaller clutches of larger eggs to increase offspring quality. Our results confirm that the joint effect of differential macroevolutionary rates shapes the species richness pattern of varanid lizards. There is a link between body size-driven diversification and body size-frequency distributions, and the speciation rate is maximized at medium body sizes. Island species will have higher speciation, equal extinction, and higher dispersal rates compared with mainland species. Smaller clutch size and larger hatchling in the island than in mainland species indicate that offspring quality is more valuable than offspring quantity for island varanids.

Evolution of hyperossification expands skull diversity in frogs

Frogs (Anura) are one of the most diverse vertebrate orders, comprising more than 7,000 species with a worldwide distribution and extensive ecological diversity. In contrast to other tetrapods, frogs have a highly derived body plan and simplified skull. In many lineages of anurans, increased mineralization has led to hyperossified skulls, but the function of this trait and its relationship with other aspects of head morphology are largely unexplored. Using three-dimensional morphological data from 158 species representing all frog families, we assessed wide-scale patterns of shape variation across all major lineages, reconstructed the evolutionary history of cranial hyperossification across the anuran phylogeny, and tested for relationships between ecology, skull shape, and hyperossification. Although many frogs share a conserved skull shape, several extreme forms have repeatedly evolved that commonly are associated with hyperossification, which has evolved independently more than 25 times. Variation in cranial shape is not explained by phylogenetic relatedness but is correlated with shifts in body size and ecology. The species with highly divergent, hyperossified skulls often have a specialized diet or a unique predator defense mechanism. Thus, the evolution of hyperossification has repeatedly facilitated the expansion of the head into multiple new shapes and functions.

Hummingbird-sized dinosaur from the Cretaceous period of Myanmar

Skeletal inclusions in approximately 99-million-year-old amber from northern Myanmar provide unprecedented insights into the soft tissue and skeletal anatomy of minute fauna, which are not typically preserved in other depositional environments^1-3. Among a diversity of vertebrates, seven specimens that preserve the skeletal remains of enantiornithine birds have previously been described^1,4-8, all of which (including at least one seemingly mature specimen) are smaller than specimens recovered from lithic materials. Here we describe an exceptionally well-preserved and diminutive bird-like skull that documents a new species, which we name Oculudentavis khaungraae gen. et sp. nov. The find appears to represent the smallest known dinosaur of the Mesozoic era, rivalling the bee hummingbird (Mellisuga helenae)-the smallest living bird-in size. The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and an autapomorphic ocular morphology⁹ that resembles the eyes of lizards. The conically arranged scleral ossicles define a small pupil, indicative of diurnal activity. Miniaturization most commonly arises in isolated environments, and the diminutive size of Oculudentavis is therefore consistent with previous suggestions that this amber formed on an island within the Trans-Tethyan arc¹⁰. The size and morphology of this species suggest a previously unknown bauplan, and a previously undetected ecology. This discovery highlights the potential of amber deposits to reveal the lowest limits of vertebrate body size.

Historical biogeography and multi-trait evolution in miniature toadlets of the genus Brachycephalus (Anura: Brachycephalidae)

Evolutionary changes towards a miniaturized body plan may directly affect other important phenotypic traits related to the physiology, behaviour and ecology of organisms. The frog genus Brachycephalus is an outstanding example of a radiation of miniaturized species endemic to the Brazilian Atlantic Forest. We inferred ancestral states and historical changes in body size, body colour and hyperossification to test hypotheses about diversification and selective environmental mechanisms leading to the evolution of these specialized traits. The ancestral distribution was associated with high-elevation regions in the northern Serra do Mar mountain range, and diversification in the genus was coincident with important geological and climatic events during the history of the Atlantic Forest. The dynamic historical changes provided an opportunity for multiple lowland lineages and for speciation via dispersal and vicariance in multiple invasions of the highlands. The ancestral Brachycephalus was reconstructed as miniaturized and dull coloured, without hyperossification in the skin, skull or postcranial skeleton. A parallel evolution of phenotypic traits has occurred in northern and southern Atlantic Forest lineages, beginning in the Miocene. Shifts in body size are not related to elevation range or latitude. However, we found a significant correlation between the evolution of hyperossification and aposematism with increasing body size.

Mode of miniaturisation influences body shape evolution in New World anchovies (Engraulidae)

We explored the macroevolutionary dynamics of miniaturisation in New World anchovies by integrating a time-calibrated phylogeny, geometric morphometrics and phylogenetic comparative methods. We found that the paedomorphic species Amazonsprattus scintilla occupies a novel region of shape space, while the dwarf species Anchoviella manamensis has an overall shape consistent with other anchovies. We found that miniaturisation did not increase overall clade disparity in size or shape beyond the expectations of Brownian motion, nor were there differences in rates of size or shape evolution among clades. Overall, our study shows that while the mode of miniaturisation influences shape evolution, the phenotypic novelty produced by the evolution of miniaturisation did not seem to alter macroevolutionary dynamics.

Phylogenomic species delimitation in microendemic frogs of the Brazilian Atlantic Forest

The advent of next-generation sequencing allows researchers to use large-scale datasets for species delimitation analyses, yet one can envision an inflection point where the added accuracy of including more loci does not offset the increased computational burden. One alternative to including all loci could be to prioritize the analysis of loci for which there is an expectation of high informativeness. Here, we explore the issue of species delimitation and locus selection with montane species from two anuran genera that have been isolated in sky islands across the southern Brazilian Atlantic Forest: Melanophryniscus (Bufonidae) and Brachycephalus (Brachycephalidae). To delimit species, we obtained genetic data using target enrichment of ultraconserved elements from 32 populations (13 for Melanophryniscus and 19 for Brachycephalus), and we were able to create datasets that included over 800 loci with no missing data. We ranked loci according to their number of parsimony-informative sites, and we performed species delimitation analyses using BPP with the most informative 10, 20, 40, 80, 160, 320, and 640 loci. We identified three types of phylogenetic node: nodes with either consistently high or low support regardless of the number of loci or their informativeness and nodes that were initially poorly supported where support became stronger as we included more data. When viewed across all sensitivity analyses, our results suggest that the current species richness in both genera is likely underestimated. In addition, our results show the effects of different sampling strategies on species delimitation using phylogenomic datasets.

Conservation Status of Brachycephalus Toadlets (Anura: Brachycephalidae) from the Brazilian Atlantic Rainforest

The number of described anurans has increased continuously, with many newly described species determined to be at risk. Most of these new species inhabit hotspots and are under threat of habitat loss, such as Brachycephalus, a genus of small toadlets that inhabits the litter of the Brazilian Atlantic Rainforest. Of 36 known species, 22 were described in the last decade, but only 11 have been assessed according to the IUCN Red List categories, with just one currently listed as Critically Endangered. All available data on occurrence, distribution, density, and threats to Brachycephalus were reviewed. The species extent of occurrence was estimated using the Minimum Convex Polygon method for species with three or more records and by delimiting continuous areas within the altitudinal range of species with up to two records. These data were integrated to assess the conservation status according to the IUCN criteria. Six species have been evaluated as Critically Endangered, five as Endangered, 10 as Vulnerable, five as Least Concern, and 10 as Data Deficient. Deforestation was the most common threat to imperiled Brachycephalus species. The official recognition of these categories might be more readily adopted if the microendemic nature of their geographical distribution is taken into account.

Morphological evolution of the skull roof in temnospondyl amphibians mirrors conservative ontogenetic patterns

Addressing the patterns of ontogenetic allometry is relevant to understand morphological diversification because allometry might constrain evolution to specific directions of change in shape but also facilitate phenotypic differentiation along lines of least evolutionary resistance. Temnospondyl amphibians are a suitable group to address these issues from a deep-time perspective because different growth stages are known for numerous Palaeozoic and Mesozoic species. Herein we examine the patterns of ontogenetic allometry in the skull roof of 15 temponspondyl species and their relationship with adult morphological evolution. Using geometric morphometrics, we assessed ontogenetic and evolutionary allometries of this cranial part and the distribution of adult shapes in the morphospace to investigate whether these patterns relate to each other and/or to lifestyle and phylogeny. We found conspicuous stereotyped ontogenetic changes of the skull roof which are mirrored at the evolutionary level and consistency of the adult shape with phylogeny rather than lifestyle. These results suggest that the evolution of adult cranial shape was significantly biased by development towards pathways patterned by ontogenetic change in shape. The retrieved conserved patterns agree with a widespread evolutionary craniofacial trend found in amniotes, suggesting that they might have originated early in tetrapod evolutionary history or even earlier.

Postmetamorphic ontogenetic allometry and the evolution of skull shape in Nest-building frogs Leptodactylus (Anura: Leptodactylidae)

Allometry constitutes an important source of morphological variation. However, its influence in head development in anurans has been poorly explored. By using geometric morphometrics followed by statistical and comparative methods we analyzed patterns of allometric change during cranial postmetamorphic ontogeny in species of Nest-building frogs Leptodactylus (Leptodactylidae). We found that the anuran skull is not a static structure, and allometry plays an important role in defining its shape in this group. Similar to other groups with biphasic life-cycle, and following a general trend in vertebrates, ontogenetic changes mostly involve rearrangement in rostral, otoccipital, and suspensorium regions. Ontogenetic transformations are paralleled by shape changes associated with evolutionary change in size, such that the skulls of species of different intrageneric groups are scaled to each other, and small and large species show patterns of paedomorphic/peramorphic features, respectively. Allometric trajectories producing those phenotypes are highly evolvable though, with shape change direction and magnitude varying widely among clades, and irrespective of changes in absolute body size. These results reinforce the importance of large-scale comparisons of growth patterns to understand the plasticity, evolution, and polarity of morphological changes in different clades.

Morphological and ecological convergence at the lower size limit for vertebrates highlighted by five new miniaturised microhylid frog species from three different Madagascan genera

Miniaturised frogs form a fascinating but poorly understood amphibian ecomorph and have been exceptionally prone to taxonomic underestimation. The subfamily Cophylinae (family Microhylidae), endemic to Madagascar, has a particularly large diversity of miniaturised species which have historically been attributed to the single genus Stumpffia largely based on their small size. Recent phylogenetic work has revealed that several independent lineages of cophyline microhylids evolved towards highly miniaturised body sizes, achieving adult snout-vent lengths under 16 mm. Here, we describe five new species belonging to three clades that independently miniaturised and that are all genetically highly divergent from their relatives: (i) a new genus (Mini gen. nov.) with three new species from southern Madagascar, (ii) one species of Rhombophryne, and (iii) one species of Anodonthyla. Mini mum sp. nov. from Manombo in eastern Madagascar is one of the smallest frogs in the world, reaching an adult body size of 9.7 mm in males and 11.3 mm in females. Mini scule sp. nov. from Sainte Luce in southeastern Madagascar is slightly larger and has maxillary teeth. Mini ature sp. nov. from Andohahela in southeast Madagascar is larger than its congeners but is similar in build. Rhombophryne proportionalis sp. nov. from Tsaratanana in northern Madagascar is unique among Madagascar's miniaturised frogs in being a proportional dwarf, exhibiting far less advanced signs of paedomorphism than other species of similar size. Anodonthyla eximia sp. nov. from Ranomafana in eastern Madagascar is distinctly smaller than any of its congeners and is secondarily terrestrial, providing evidence that miniaturisation and terrestriality may be evolutionarily linked. The evolution of body size in Madagascar's microhylids has been more dynamic than previously understood, and future studies will hopefully shed light on the interplay between ecology and evolution of these remarkably diverse frogs.

The earliest equatorial record of frogs from the Late Triassic of Arizona

Crown-group frogs (Anura) originated over 200 Ma according to molecular phylogenetic analyses, though only a few fossils from high latitudes chronicle the first approximately 60 Myr of frog evolution and distribution. We report fossils that represent both the first Late Triassic and the earliest equatorial record of Salientia, the group that includes stem and crown-frogs. These small fossils consist of complete and partial ilia with anteriorly directed, elongate and distally hollow iliac blades. These features of these ilia, including the lack of a prominent dorsal protuberance and a shaft that is much longer than the acetabular region, suggest a closer affinity to crown-group Anura than to Early Triassic stem anurans Triadobatrachus from Madagascar and Czatkobatrachus from Poland, both high-latitude records. The new fossils demonstrate that crown anurans may have been present in the Late Triassic equatorial region of Pangea. Furthermore, the presence of Early Jurassic anurans in the same stratigraphic sequence ( Prosalirus bitis from the Kayenta Formation) suggests that anurans survived the climatic aridification of this region in the early Mesozoic. These fossils highlight the importance of the targeted collection of microfossils and provide further evidence for the presence of crown-group representatives of terrestrial vertebrates prior to the end-Triassic extinction.

A new maximum body size record for the Berry Cave Salamander (Gyrinophilus gulolineatus) and genus Gyrinophilus (Caudata, Plethodontidae) with a comment on body size in plethodontid salamanders

Lungless salamanders in the family Plethodontidae exhibit an impressive array of life history strategies and occur in a diversity of habitats, including caves. However, relationships between life history, habitat, and body size remain largely unresolved. During an ongoing study on the demography and life history of the paedomorphic, cave-obligate Berry Cave Salamander (Gyrinophilusgulolineatus, Brandon 1965), we discovered an exceptionally large individual from the type locality, Berry Cave, Roane County, Tennessee, USA. This salamander measured 145 mm in body length and represents not only the largest G.gulolineatus and Gyrinophilus ever reported, but also the largest plethodontid salamander in the United States. We discuss large body size in G.gulolineatus and compare body size in other large plethodontid salamanders in relation to life history and habitat.

Diversity of miniaturized frogs of the genus Adelophryne (Anura: Eleutherodactylidae): A new species from the Atlantic Forest of northeast Brazil

The number of species of frogs in the South American genus Adelophryne has increased in recent years, and it has become apparent that this group contains a substantial amount of undescribed diversity. Currently the genus contains nine described species and five candidate species. Here we describe the tenth species of the genus Adelophryne from the municipality of Igrapiúna, southern Bahia state, Brazil. The new species is characterized by its small body size, indistinct tympanum, and two phalanges in the finger IV. The species of the genus are distributed in three groups, Northern Amazonia Clade, Northern Atlantic Forest Clade and Southern Atlantic Forest Clade. The new species is phylogenetically related to species of the Northern Atlantic Forest Clade of Adelophryne and restricted to forested habitat, as typical for other Adelophryne. The species is restricted to the pristine forests in the type locality, and we consider its conservation status as Near Threatened. New morphological and molecular data of other Adelophryne species are presented, extending the distribution of Adelophryne sp. 2, Adelophryne sp. 4, Adelophryne mucronata and Adelophryne glandulata. However, a more comprehensive revision of the diversity and phylogenetic position of most Adelophryne species is needed, and the evolutionary relationships of A. meridionalis and A. pachydactyla remain unknown.

Advertisement call of Brachycephalus albolineatus (Anura: Brachycephalidae)

Background

Brachycephalus are among the smallest terrestrial vertebrates in the world. The genus encompasses 34 species endemic to the Brazilian Atlantic Rainforest, occurring mostly in montane forests, with many species showing microendemic distributions to single mountaintops. It includes diurnal species living in the leaf litter and calling during the day, mainly during the warmer months of the year. The natural history of the vast majority of the species is unknown, such as their advertisement call, which has been described only for seven species of the genus. In the present study, we describe the advertisement call of Brachycephalus albolineatus, a recently described microendemic species from Santa Catarina, southern Brazil.

Methods

We analyzed 34 advertisement calls from 20 individuals of B. albolineatus, recorded between 5 and 6 February 2016 in the type locality of the species, Morro Boa Vista, on the border between the municipalities of Jaraguá do Sul and Massaranduba, Santa Catarina, southern Brazil. We collected five individuals as vouchers (they are from the type series of the species). We used the note-centered approach to describe the advertisement calls of the species.

Results

B. albolineatus have a long advertisement call of 40-191 s (mean of 88 s) composed of 8-29 notes (mean of 17 notes) emitted at a rate of 6-18 notes per minute (mean of 11 notes per minute) and at a note dominant frequency of five to seven kHz (mean of six kHz). Advertisement calls are composed of isolated notes and note groups (two notes involved in each particular note group); the former is composed by one to three pulses (mean of 2.0) and the note groups by two or three pulses in each note (mean of 2.7). Most advertisement calls present both isolated notes and note groups, with a few cases showing only the former. Note groups are emitted invariably in the last third of the advertisement call. Most isolated notes escalate their number of pulses along the advertisement call (1-2, 1-3 or 2-3). Note duration of isolated notes varies from 0.002 to 0.037 s (mean of 0.020 s) and duration of note group vary from 0.360 to 0.578 s (mean of 0.465 s).

Discussion

Individuals increase the complexity of their calls as they proceed, incorporating note groups and pulses per note. Intra-individual variation analysis also demonstrated that less structured advertisement calls (i.e., with notes with fewer pulses) are not stereotyped. It is possible that isolated notes and note groups could have distinct functions, perhaps territorial defense and mating, respectively. We argue that using a note-centered approach facilitates comparisons with calls of congeners, as well as underscores the considerable differences in call structure between species in a single group and among species groups.

Ballistic tongue projection in a miniaturized salamander

Miniaturization of body size is often accompanied by peculiarities in morphology that can have functional consequences. We examined the feeding behavior and morphology of the miniaturized plethodontid salamander Thorius, one of the smallest vertebrates, to determine if its performance and biomechanics differ from those of its larger relatives. High-speed imaging and dynamics analysis of feeding at a range of temperatures show that tongue projection in Thorius macdougalli is ballistic and achieves accelerations of up to 600 G with low thermal sensitivity, indicating that tongue projection is powered by an elastic-recoil mechanism. Preceding ballistic projection is an unusual preparatory phase of tongue protrusion, which, like tongue retraction, shows lower performance and higher thermal sensitivity that are indicative of movement being powered directly by muscle shortening. The variability of tongue-projection kinematics and dynamics is comparable to larger ballistic-tongued plethodontids and reveals that Thorius is capable of modulating its tongue movements in response to prey distance. Morphological examination revealed that T. macdougalli possesses a reduced number of myofibers in the tongue muscles, a large projector muscle mass relative to tongue mass, and an unusual folding of the tongue skeleton, compared with larger relatives. Nonetheless, T. macdougalli retains the elaborated collagen aponeuroses in the projector muscle that store elastic energy and a tongue skeleton that is free of direct myofiber insertion, two features that appear to be essential for ballistic tongue projection in salamanders.

Trait independence primes convergent trait loss

The repeated, independent evolution of traits (convergent evolution) is often attributed to shared environmental selection pressures. However, developmental dependencies among traits can limit the phenotypic variation available to selection and bias evolutionary outcomes. Here, we determine how changes in developmentally correlated traits may impact convergent loss of the tympanic middle ear, a highly labile trait within toads that currently lack adaptive explanation. The middle ear's lability could reflect evolutionary trade-offs with other skull features under selection, or the middle ear may evolve independently of the rest of the skull, allowing it to be modified by active or passive processes without pleiotropic trade-offs with other skull features. We compare the skulls of 55 species (39 eared, 16 earless) within the family Bufonidae, spanning six hypothesized independent middle ear transitions. We test whether shared or lineage-specific changes in skull shape distinguish earless species from eared species and whether earless skulls lack other late-forming skull bones. We find no evidence for pleiotropic trade-offs between the middle ear and other skull structures. Instead, middle ear loss in anurans may provide a rare example of developmental independence contributing to evolutionary lability of a sensory system.

Body shape convergence driven by small size optimum in marine angelfishes

Convergent evolution of small body size occurs across many vertebrate clades and may reflect an evolutionary response to shared selective pressures. However it remains unclear if other aspects of phenotype undergo convergent evolution in miniaturized lineages. Here we present a comparative analysis of body size and shape evolution in marine angelfishes (Pomacanthidae), a reef fish family characterized by repeated transitions to small body size. We ask if lineages that evolve small sizes show convergent evolution in body shape. Our results reveal that angelfish lineages evolved three different stable size optima with one corresponding to the group of pygmy angelfishes (Centropyge). Then, we test if the observed shifts in body size are associated with changes to new adaptive peaks in shape. Our data suggest that independent evolution to small size optima have induced repeated convergence upon deeper body and steeper head profile in Centropyge These traits may favour manoeuvrability and visual awareness in these cryptic species living among corals, illustrating that functional demands on small size may be related to habitat specialization and predator avoidance. The absence of shape convergence in large marine angelfishes also suggests that more severe requirements exist for small than for large size optima.

Mountain colonisation, miniaturisation and ecological evolution in a radiation of direct-developing New Guinea Frogs (Choerophryne, Microhylidae)

AIMS

Mountain ranges in the tropics are characterised by high levels of localised endemism, often-aberrant evolutionary trajectories, and some of the world's most diverse regional biotas. Here we investigate the evolution of montane endemism, ecology and body size in a clade of direct-developing frogs (Choerophryne, Microhylidae) from New Guinea.

METHODS

Phylogenetic relationships were estimated from a mitochondrial molecular dataset using Bayesian and maximum likelihood approaches. Ancestral state reconstruction was used to infer the evolution of elevational distribution, ecology (indexed by male calling height), and body size, and phylogenetically corrected regression was employed to examine the relationships between these three traits.

RESULTS

We obtained strong support for a monophyletic lineage comprising the majority of taxa sampled. Within this clade we identified one subclade that appears to have diversified primarily in montane habitats of the Central Cordillera (>1,000 m a.s.l.), with subsequent dispersal to isolated North Papuan Mountains. A second subclade (characterised by moderately to very elongated snouts) appears to have diversified primarily in hill forests (<1,000 m a.s.l.), with inferred independent upwards colonisations of isolated montane habitats, especially in isolated North Papuan Mountains. We found no clear relationship between extremely small body size (adult SVL less than 15 mm) and elevation, but a stronger relationship with ecology-smaller species tend to be more terrestrial.

CONCLUSIONS

Orogeny and climatic oscillations have interacted to generate high montane biodiversity in New Guinea via both localised diversification within montane habitats (centric endemism) and periodic dispersal across lowland regions (eccentric endemism). The correlation between extreme miniaturisation and terrestrial habits reflects a general trend in frogs, suggesting that ecological or physiological constraints limit niche usage by miniaturised frogs, even in extremely wet environments such as tropical mountains.

Geographical and altitudinal distribution of Brachycephalus (Anura: Brachycephalidae) endemic to the Brazilian Atlantic Rainforest

Mountains of the Brazilian Atlantic Forest can act as islands of cold and wet climate, leading to the isolation and speciation of species with low dispersal capacity, such as the toadlet species of the genus Brachycephalus. This genus is composed primarily by diurnal species, with miniaturized body sizes (<2.5 cm), inhabiting microhabitats in the leaf litter of montane forests. Still, little is known about the geographical distribution, altitudinal range, and ecological limits of most Brachycephalus species. In this study, we review the available data on the geographical and altitudinal distribution of Brachycephalus based on occurrence records compiled from literature and museums, both for the genus as a whole and separately for the three recently proposed groups of species (ephippium, didactylus, and pernix). The final ensemble dataset comprised 333 records, 120 localities, 28 described species, and six undescribed ones. Species were recorded in six relief units, the richest of which being the Serra do Mar, with 30 species. When the Serra do Mar is subdivided into three subunits, Northern, Central and Southern Serra do Mar, the number of species increase from north to the south, with records of six, nine, and 16 species, respectively. We were able to estimate the extent of occurrence of nearly half of the described species, and the resulting estimates indicate that many of them show remarkably small ranges, some of which less than 50 ha. Brachycephalus species are present from sea level to roughly 1,900 m a.s.l., with the highest richness being found between 751 and 1,000 m a.s.l. (21 spp.). The species with the broadest altitudinal range were B. didactylus (1,075 m) and Brachycephalus sp. 1 (1,035 m), both in the didactylus group, and B. ephippium (1,050 m), of the ephippium group. The broadest altitudinal amplitude for species of the pernix group was recorded for B. brunneus (535 m). The lowest altitudinal records for the pernix group were at 845 m a.s.l. in the state of Paraná and at 455 m a.s.l. in the state of Santa Catarina. The altitudinal occurrence in the pernixspecies group seems to decrease southward. Syntopy between species is also reviewed.

Genetic diversity, phylogeny and evolution of alkaloid sequestering in Cuban miniaturized frogs of the Eleutherodactylus limbatus group

The miniaturized frogs of the Eleutherodactylus limbatus group, endemic to Cuba, have recently been shown to contain alkaloids in their skin, representing the fifth independent evolutionary origin of alkaloid sequestering in anurans. Based on a comprehensive sampling of all known species of the group we here assess their range-wide phylogeography using DNA sequences of the mitochondrial cytochrome b and the nuclear Rag-1 gene. We found E. etheridgei, E. cubanus, and E. orientalis to be genetically highly distinct, with uncorrected pair-wise distances >12% in the cytochrome b gene and >5% in the 16S rRNA gene, and without haplotype sharing in the Rag-1 gene. On the contrary, E. iberia, E. jaumei, E. limbatus, and one unnamed lineage from Gran Piedra mountains had lower mitochondrial divergences to each other (<6% in cytochrome b; <3% in 16S) and extensive Rag-1 haplotype sharing, suggesting that their species status requires careful revision. All species and lineages of the group occur in the mountain areas of eastern Cuba and only one of them, E. limbatus, colonized central and western Cuba. Populations of this latter lineage are only weakly genetically differentiated, and its range expansion to western Cuba is probably Pleistocenic, demonstrating that also miniaturized frog species are able of considerable range expansions (over hundreds of kilometers) in short time spans. A phylogeny based on about 5 kb of mitochondrial and nuclear genes places, with maximum support, E. etheridgei basalmost in the group, followed by E. cubanus, E. orientalis, and the E. iberia-jaumei-limbatus clade. The screening of skin alkaloids revealed the presence of alkaloids in all lineages of the group, but alkaloids known to be sequestered by other anurans were not found in the basalmost E. etheridgei. Furthermore, individuals of the derived lineages of the E. iberia-jaumei-limbatus clade had a much larger variety of different alkaloid compounds (3-18) than the other three species (0-4). Traces of alkaloids were found in other species only remotely related to the E. limbatus group, i.e., E. caspari, E. goini, E. ricordii, and E. tetajulia. According to these findings, it can be hypothesized that the capacity to sequester dietary alkaloids into the skin evolved first in an ancestral, litter-dwelling and small-sized Cuban Eleutherodactylus, followed by evolution of miniaturization and diurnality in the early representatives of the E. limbatus group, and eventually by increased brightness of color with probable aposematic function and a highly efficient mechanism of alkaloid sequestering.

Terrestrialization, miniaturization and rates of diversification in African puddle frogs (Anura: Phrynobatrachidae)

Terrestrialization, the evolution of non-aquatic oviposition, and miniaturization, the evolution of tiny adult body size, are recurring trends in amphibian evolution, but the relationships among the traits that characterize these phenomena are not well understood. Furthermore, these traits have been identified as possible "key innovations" that are predicted to increase rates of speciation in those lineages in which they evolve. We examine terrestrialization and miniaturization in sub-Saharan puddle frogs (Phrynobatrachidae) in a phylogenetic context to investigate the relationship between adaptation and diversification through time. We use relative dating techniques to ascertain if character trait shifts are associated with increased diversification rates, and we evaluate the likelihood that a single temporal event can explain the evolution of those traits. Results indicate alternate reproductive modes evolved independently in Phrynobatrachus at least seven times, including terrestrial deposition of eggs and terrestrial, non-feeding larvae. These shifts towards alternate reproductive modes are not linked to a common temporal event. Contrary to the "key innovations" hypothesis, clades that exhibit alternate reproductive modes have lower diversification rates than those that deposit eggs aquatically. Adult habitat, pedal webbing and body size have no effect on diversification rates. Though these traits putatively identified as key innovations for Phrynobatrachus do not seem to be associated with increased speciation rates, they may still provide opportunities to extend into new niches, thus increasing overall diversity.

Body size evolution in extant Oryzomyini rodents: Cope's rule or miniaturization?

At the macroevolutionary level, one of the first and most important hypotheses that proposes an evolutionary tendency in the evolution of body sizes is “Cope's rule". This rule has considerable empirical support in the fossil record and predicts that the size of species within a lineage increases over evolutionary time. Nevertheless, there is also a large amount of evidence indicating the opposite pattern of miniaturization over evolutionary time. A recent analysis using a single phylogenetic tree approach and a Bayesian based model of evolution found no evidence for Cope's rule in extant mammal species. Here we utilize a likelihood-based phylogenetic method, to test the evolutionary trend in body size, which considers phylogenetic uncertainty, to discern between Cope's rule and miniaturization, using extant Oryzomyini rodents as a study model. We evaluated body size trends using two principal predictions: (a) phylogenetically related species are more similar in their body size, than expected by chance; (b) body size increased (Cope's rule)/decreased (miniaturization) over time. Consequently the distribution of forces and/or constraints that affect the tendency are homogenous and generate this directional process from a small/large sized ancestor. Results showed that body size in the Oryzomyini tribe evolved according to phylogenetic relationships, with a positive trend, from a small sized ancestor. Our results support that the high diversity and specialization currently observed in the Oryzomyini tribe is a consequence of the evolutionary trend of increased body size, following and supporting Cope's rule.

Comparative skull morphology of uropeltid snakes (Alethinophidia: Uropeltidae) with special reference to disarticulated elements and variation

Uropeltids form a diverse clade of highly derived, fossorial snakes that, because of their phylogenetic position among other alethinophidian lineages, may play a key role in understanding the early evolution of cranial morphology in snakes. We include detailed osteological descriptions of crania and mandibles for eight uropeltid species from three nominal genera (Uropeltis, Rhinophis, and Brachyophidium) and emphasize disarticulated elements and the impact of intraspecific variation on previously proposed morphological characters used for phylogenetic analysis. Preliminary analysis of phylogenetic relationships strongly supports a clade composed exclusively of species of Plectrurus, Uropeltis, and Rhinophis. However, monophyly of each of those genera and Melanophidium is not upheld. There is moderate support that Sri Lankan species (e.g., Rhinophis and Uropeltis melanogaster) are monophyletic with respect to Indian uropeltids. Previously proposed characters that are phylogenetically informative include the shape of the nasals, length of the occipital condyle, level of development of the posteroventral process of the dentary, and participation of the parietal in the optic foramen. Additionally, thirty new features that may be systematically informative are identified and described, but were not verified for their utility. Such verification must await availability of additional disarticulated cranial material from a larger sample of taxa. All characters require further testing through increased focus on sources and patterns of intraspecific variation, inclusion of broader taxonomic samples in comparative studies, and exploration of skeletal development, sexual dimorphism, and biogeographic patterns. Additionally, trends in the relative enlargement of the sensory capsules, reduction in cranial ossification and dentition, fusion of elements, and the appearance of novel morphological conditions, such as the structure and location of the suspensorium, may be related to fossoriality and miniaturization in some uropeltid taxa, and may complicate analysis of relationships within Uropeltidae and among alethinophidian snakes.