World Frogs Research Articles

Peptidomic analysis of the host-defense peptides in skin secretions of the Amazon River frog Lithobates palmipes (Ranidae)

Skin secretions of certain frog species represent a source of host-defense peptides (HDPs) with therapeutic potential and their primary structures provide insight into taxonomic and phylogenetic relationships. Peptidomic analysis was used to characterize the HDPs in norepinephrine-stimulated skin secretions from the Amazon River frog Lithobates palmipes (Ranidae) collected in Trinidad. A total of ten peptides were purified and identified on the basis of amino acid similarity as belonging to the ranatuerin-2 family (ranatuerin-2PMa, -2PMb, -2PMc, and-2PMd), the brevinin-1 family (brevinin-1PMa, -1PMb, -1PMc and des(8–14)brevinin-1PMa) and the temporin family (temporin-PMa in C-terminally amidated and non-amidated forms). Deletion of the sequence VAAKVLP from brevinin-1PMa (FLPLIAGVAAKVLPKIFCAISKKC) in des[(8–14)brevinin-1PMa resulted in a 10-fold decrease in potency against Staphylococcus aureus (MIC = 31 μM compared with 3 μM) and a > 50-fold decrease in hemolytic activity but potency against Echerichia coli was maintained (MIC = 62.5 μM compared with 50 μM). Temporin-PMa (FLPFLGKLLSGIF.NH2) inhibited growth of S. aureus (MIC = 16 μM) but the non-amidated form of the peptide lacked antimicrobial activity. Cladistic analysis based upon the primary structures of ranaturerin-2 peptides supports the division of New World frogs of the family Ranidae into the genera Lithobates and Rana. A sister-group relationship between L. palmipes and Warszewitsch's frog Lithobates warszewitschii is indicated within a clade that includes the Tarahumara frog Lithobates tarahumarae. The study has provided further evidence that peptidomic analysis of HDPs in frog skin secretions is a valuable approach to elucidation of the evolutionary history of species within a particular genus.

Disease surveillance of the amphibian chytrid fungus Batrachochytrium dendrobatidis in Papua New Guinea

AbstractEmerging infectious diseases threaten the persistence of biodiversity globally. The amphibian chytrid fungus, Batrachochytrium dendrobatidis, is one of the most widespread and damaging pathogens to biodiversity. New Guinea hosts 6% of the world's frogs and is the largest landmass where B. dendrobatidis remains undetected despite being largely climatically suitable for its persistence. We surveyed for B. dendrobatidis in Papua New Guinea, by swabbing live frogs in the Gulf Province and Eastern Highlands Province and by examining museum specimens from a range of sites and elevations. Here, we show that over a large geographical range, all 442 samples were negative for B. dendrobatidis. The spread of B. dendrobatidis to Papua New Guinea may have been thus far prevented by the remoteness of New Guinea and the hotter climate in its lowlands, which surrounds a more climatically suitable zone for B. dendrobatidis in the highlands. Alternatively, B. dendrobatidis may be present in isolated patches or at low levels and remain undetected, to date. Papua New Guinea remains at risk and would benefit from a national disease surveillance program for chytrid fungi and pre‐emptive actions, designed to reduce the risk of pathogen transmission. Measures should include improved biosecurity protocols for trade and travel and continued disease surveillance in areas of probable entry and spread.

The influence of anthropogenic noise on the evolution of communication systems

Many species of animals, including man, face the formidable task of communicating in noisy environments. In this talk, I shall discuss the effects of anthropogenic (man-made) noise on the calling behavior of anuran amphibians. Moreover, the role of spectral, temporal, and spatial separation in minimizing masking by background noise will be examined. For example, presenting high-level, periodic (or aperiodic) tones at the males co-note frequency to males of the Puerto Rican treefrog, Eleutherodactylus coqui results in a clear shift in their calling pattern in an attempt to minimize acoustic overlap with the interfering playback stimulus. Amphibians also have a remarkable ability to shift their call timing in response to small intensity shifts in the background noise. Males of E. coqui are capable of reliably detecting a change in interfering tone intensity as small as 2–4 dB. Finally, I shall present behavioral evidence that anthropogenic noise may act as a strong selective force in sculpting the acoustic communication systems of several species of Old World frogs. Some techniques for visualizing sound interference will be discussed. [Supported by grants from the NIDCD (Grant No. DC-00222), and the UCLA Academic Senate (3501).]

Environmental influences on acoustic communication in frogs

Many species of animals, including man, face the formidable task of communicating in naturally noisy environments. The effects of noise on both the calling behavior of frogs and the temporal, and spectral filtering ability of the amphibian auditory pathway are discussed. Moreover, the role of spectral, temporal, and spatial separation in minimizing background noise masking will be examined. Behavioral evidence is presented suggesting that environmental noise may act as a strong selective force in sculpting the communication systems of two species of Old World frogs. One torrent frog (Odorrana tormota) calls frequently from vegetation along fast-flowing mountain streams in Central China. These streams produce high-level, broadband noise spanning the human hearing spectrum. In addition to the high-pitched audible components, the males' calls contain prominent ultrasonic harmonics. Another frog, Huia cavitympanum, lives in a very similar habitat in Borneo. Unlike O. tormota, Huia can modulate its call spectrum to produce purely ultrasonic calls. It is thought that the upward shift of the call frequencies and the upper limit of sensitivity of both O. tormota and H. cavitympanum are responses to the selection pressures from their noisy habitats. [Work supported by NIDCD DC-00222, Paul S. Veneklasen Research Foundation, UCLA Academic Senate (3501).]

EVOLUTIONARY AND BIOGEOGRAPHIC ORIGINS OF HIGH TROPICAL DIVERSITY IN OLD WORLD FROGS (RANIDAE)

Differences in species richness between regions are ultimately explained by patterns of speciation, extinction, and biogeographic dispersal. Yet, few studies have considered the role of all three processes in generating the high biodiversity of tropical regions. A recent study of a speciose group of predominately New World frogs (Hylidae) showed that their low diversity in temperate regions was associated with relatively recent colonization of these regions, rather than latitudinal differences in diversification rates (rates of speciation-extinction). Here, we perform parallel analyses on the most species-rich group of Old World frogs (Ranidae; approximately 1300 species) to determine if similar processes drive the latitudinal diversity gradient. We estimate a time-calibrated phylogeny for 390 ranid species and use this phylogeny to analyze patterns of biogeography and diversification rates. As in hylids, we find a strong relationship between the timing of colonization of each region and its current diversity, with recent colonization of temperate regions from tropical regions. Diversification rates are similar in tropical and temperate clades, suggesting that neither accelerated tropical speciation rates nor greater temperate extinction rates explain high tropical diversity in this group. Instead, these results show the importance of historical biogeography in explaining high species richness in both the New World and Old World tropics.

Predicting susceptibility to future declines in the world's frogs

AbstractThe 2004 Global Amphibian Assessment demonstrated that almost 400 anuran species have recently moved closer to extinction due to a host of threat mechanisms. Of particular concern is the role of the fungal pathogen, Batrachochytrium dendrobatidis (Bd), for which more traditional conservation management is not effective. Determining which biological and environmental factors affect a species' susceptibility to these mechanisms would greatly aid conservation prioritisation and planning. We performed phylogenetic comparative analyses to determine which biological and environmental factors predict species' susceptibility to rapid declines, both generally and in the context of Bd. Our results extend the findings of previous finer scale studies: we find that high‐altitude, restricted‐range, aquatic species with low fecundity are most likely to suffer Bd‐related declines. We use our findings to identify those species most at risk of Bd‐related declines and global extinction in the future, and identify areas where many species are predicted to be susceptible. Identifying susceptible species in advance of their decline is particularly important in setting priorities when, as here, declines are hard to arrest once underway.

Predicting Biomass from Snout–Vent Length in New World Frogs

In this study, we determined how well the snout–vent length (SVL) of anurans estimated their mass for 36 species in the New World. Linear regressions of log-mass on log-SVL were highly significant for all species, explaining more than 75% of the mass variation in most species, and over 50% of the mass variation in all species. We also investigated differences in the mass/SVL relationship within species, comparing juveniles to adults, females to gravid females, and males to females, to determine the importance of developing separate regressions for sex or life-stage classes. Three of six tests between juveniles and adults, and two of nine tests between females and gravid females, indicated statistically significant differences, although these differences had only minor effects on mass estimates. More statistical differences in regression equations occurred between males and females; again, these differences were unimportant for estimates of mass in some cases, but they were important where there was strong sexual size dimorphism within a species. Continued collection of both SVL and mass data in new field studies of anurans will provide broader analyses of mass/SVL regressions. These species regressions along with data on density can be used to determine anuran community biomass.

New World direct-developing frogs (Anura: Terrarana): Molecular phylogeny, classification, biogeography, and conservation

New World frogs recently placed in a single, enormous family (Brachycephalidae) have direct development and reproduce on land, often far away from water. DNA sequences from mitochondrial and nuclear genes of 344 species were analyzed to estimate their relationships. The molecular phylogeny in turn was used as the basis for a revised classification of the group. The 882 described species are placed in a new taxon, Terrarana, and allocated to four families, four subfamilies, 24 genera, 11 subgenera, 33 species series, 56 species groups, and 11 species subgroups. Systematic accounts are provided for all taxa above the species level. Two families (Craugastoridae and Strabomantidae), three subfamilies (Holoadeninae, Phyzelaphryninae, and Strabomantinae), six genera (Bryophryne, Diasporus, Haddadus, Isodactylus, Lynchius, and Psychrophrynella), and two subgenera (Campbellius and Schwartzius) are proposed and named as new taxa, 13 subspecies are considered to be distinct species, and 613 new combinations are formed. Most of the 100 informal groups (species series, species groups, and species subgroups) are new or newly defined. Brachycephalus and Ischnocnema are placed in Brachycephalidae, a relatively small clade restricted primarily to southeastern Brazil. Eleutherodactylidae includes two subfamilies, four genera, and five subgenera and is centered in the Caribbean region. Craugastoridae contains two genera and three subgenera and is distributed mainly in Middle America. Strabomantidae is distributed primarily in the Andes of northwestern South America and includes two subfamilies, 16 genera, and three subgenera. Images and distribution maps are presented for taxa above the species level and a complete list of species is provided. Aspects of the evolution, biogeography, and conservation of Terrarana are discussed.

Call generation strategy in an Old World frog

Old World treefrogs in the family Rhacophoridae have complex vocalizations. The vocal repertoire of a population of endemic males, Boophis madagascariensis, was studied in the animals’ natural habitat in Ranomafana National Park in eastern Madagascar. Twenty-eight calls and variations were recorded. This represents the largest call repertoire of any frog reported to date. Playback studies demonstrated the strong tendency for males to respond in kind. Moreover, one sequence of call notes tended to stimulate calling, another inhibited calling, and a third had little effect on the calling behavior of males. Applying permutation tests to 100 calls produced by a single male revealed no predictable pattern to the call production sequence. This implies a call generation scheme for Boophis (and perhaps other Rhacophiorids) that differs fundamentally from New World frogs. [Work supported by NIH and a Guggenheim Fellowship to PMN.]

Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui.

Direct development is a common reproductive mode in living amphibians characterized by absence of the free-living, aquatic larval stage. In Eleutherodactylus, a species-rich genus of New World frogs, evolution of direct development from the ancestral biphasic ontogeny is correlated with a comprehensive modification in embryonic cranial patterning, including the loss of many larval-specific components and the precocious formation of many adult (postmetamorphic) structures. We use scanning electron microscopy (SEM) to examine the emergence and early migration of cranial neural crest cells in Eleutherodactylus coqui to begin to assess the possible role of the neural crest in mediating these evolutionary changes. As in metamorphosing frogs, cranial crest cells emerge prior to neural fold closure and assemble into three streams: rostral otic, and caudal otic. These streams contribute to the face and first visceral (mandibular) arch, to the second (hyoid) arch, and to posterior (branchial) arches, respectively. Rostrocaudal position, morphology, and/or migration patterns distinguish subpopulations of cells within the rostral stream and caudal otic stream. With the possible exception of the small size of the rostral otic caudal otic streams, evolution of direct development in E. coqui has not altered basic patterns of neural crest emergence or early migration as assessed by SEM. If observed evolutionary changes in embryonic cranial patterning are mediated by the neural crest, then they likely involve later aspects of crest migration or more subtle features related to pattern formation such as cell behavior and commitment, or gene expression.