Another lab contribution was published this week in the journal Zootaxa, describing a new arboreal species of gymnophthalmid lizard (spectacled lizards). This is a fairly large group of lizards distributed in Central and South America, most species are ground-dwelling and inhabit the forest leaf litter, rocky areas or mosses and grasslands at high elevations, but several species are semi-aquatic and can dive, such as species of Potamites. The new species, named Euspondylus excelsum, however is arboreal and was discovered when the lizard's habitat was flooded by a hydroelectric project in the Amazonian slopes of the Andes in Central Peru. Additional surveys in the area surrounding the flooded area failed to find lizards on the ground; instead all captured lizards were found on leaves and other arboreal microhabitats. Photograph by Lesly Luján.
Doctoral candidate Alex Shepack and collaborators have published a review paper on the salamander-killing fungus, Batrachochytrium salamandrivorans (Bsal) in the journal EcoHealth (available here). The study reviews current research on Bsal, which is currently threatening native salamanders in Europe. This virulent fungus has yet to be detected in the Americas, and multiple efforts are under way to prevent its introduction in North America, which supports one of the most diverse salamander fauna. The article also explains the role of the Bsal Task Force, risks associated with the spread of Bsal, and policy measures proposed or enacted to date.
We are excited to announce that our lab is going tropical! We will be moving next January to Florida International University in Miami. The lab will join the Department of Biological Sciences at the main university campus in Miami (Modesto A. Maidique campus). More updates will be posted soon.
A lab contribution published today explores fungal disease-frog host dynamics in the species-rich frog communities of the eastern slopes of the tropical Andes, near Manu National Park in Peru. We have been studying these communities since 1996, when chytrid disease had not yet caused sharp declines in frog species richness and abundance. Following the epizootic of chytridiomycosis that swept southern Peru in the early 2000s, 19 out of 55 species vanished from the cloud forest (1200-3600 m), as reported previously. Unfortunately most of these species have not been seen since then. But how are the surviving species faring in this environment where chytrid is now established?
Our general approach was to compare species vulnerability to infection by chytrid with observed changes in population abundances for eight common species of frogs. We selected these species to maximize sample size, to provide opportunities for within genus comparisons, and to cover the elevational range where we recorded declines. Our infection experiments were difficult to conduct at the remote Wayqecha Biological Station, but dedication and creativity go a long way towards making things possible. In addition to Vance Vredenburg and Andrea Swei from SFSU, our team was composed by then undergraduate students Emily Foreyt (Gonzaga) and Lauren Wyman (Princeton; shown above), and Jacob Finkle (UC Berkeley), who all co-author our publication.
As shown in the survival curve above and the video below, some "survivors" continue to be susceptible to infection by chytrid. In the example here, Pristimantis toftae quickly succumbs to chytridiomycosis following experimental infection; the videos shows tetanic spasms in a highly infected individual. As pane C shows, most individuals in our "control" group (which was supposed to be negative for disease) were infected at low levels, because our itraconazole baths failed to completely clear infection. Although this limits interpretation of our results, it also suggests that the immunoprotective effect of previous Bd exposure might not be a common response across all amphibian species - in fact we saw little evidence for such effect in our species.
Overall, three out of eight tested species are susceptible to chytridiomycosis. Populations of these three species, and of all other species but one, have somewhat to sharply declined during the decade from 1999 to 2009. Phylogenetic relatedness did not appear to be a good predictor of susceptibility: while two Pristimantis species were susceptible, two other species were not. Among Gastrotheca, one was highly susceptible while the second was not; our previous work suggests that anti-fungal skin bacteria might protect the non-susceptible Gastrotheca excubitor.
Does this mean that more species will vanish? While the results of our experiments suggest trouble for several species, other factors such as transmission risks and environmental exposure to fungal propagules play important roles in driving disease-host dynamics. For example terrestrial-breeding frogs such as Pristimantis are less exposed to infection by the aquatic zoospores of the chytrid fungus, because they generally avoid water bodies. On a positive note, populations of some "surviving" species have recently recovered - hopefully a trend that will continue in the future.
Our lab expeditions over the last few weeks led to the rediscovery of a long-forgotten and rarely seen species, Atractus vertebralis. This species was described by Boulenger in 1904, but as far as we know it has not been collected ever since. Boulenger used material collected by Keays around the "Inca mine" of Santo Domingo, near Bahuaja-Sonene National Park. The discovery will allow a better characterization of the species, as well as molecular analyses to reveal the phylogenetic relationships of these poorly known, fossorial snakes.
We found these snakes under a thick layer of wet mosses, along with Proctoporus lizards, terrestrial-breeding frogs of the genus Noblella and the Pristimantis platydactylus group, and Pristimantis danae. In the picture, Isabel Diaz and Alex Ttito are searching for herps along the trail -- despite this being our third day of all-day hiking! There is always some energy left for a nice discovery.
We collaborated with Dr. Lily Rodriguez for another exciting discovery from the eastern slopes of the Andes, four new species of Phrynopus from Abiseo National Park in northern Peru. This park protects the entire watershed of the Abiseo river, containing many ecosystems such as cloud and elfin
forest, wet montane grasslands, and puna, as well as archaeological sites such as the Gran Pajatén, all of which forms the Gran Pajatén Peruvian Biosphere Reserve. Shown here is Phrynopus anancites from the southern border of the park at Ventanas.
The new species were discovered during several expeditions organized by APECO starting in the late 1980s, 1990s and early 2000s. The photograph to the right shows one of these expeditions, in July 2000, as a group of researchers descends from the last mountain pass into the upper watershed of the Montecristo river. These grasslands at Pampas del Cuy are inhabited by one of the new species, Phrynopus dumicola.
Three of the four new species are restricted to grassland and elfin forest habitats, but the fourth species Phrynopus personatus shown here lives in the leaf litter of the cloud forest in a narrow elevational range around 3000 m elevation. These forests are also home to the endemic yellow-tailed woolly monkey, a critically endangered species of monkey. With the addition of the four new species, the genus Phrynopus, which is endemic to Peru, now includes 32 species.
The latest lab contribution to amphibian taxonomy is a new species of Peruvian moss frog, Bryophryne phuyuhampatu, which we discovered during our second hike to Ukumari Llakta in June 2016. The discovery came after a morning long, brutal descent from the high Andean grassland down into the cloud forest. That afternoon was very moist and drizzly, as are most afternoons in the Andean cloud forests, but that did not prevent (some of) us from frogging.
Most of the frogs were found just across from our camp site, along the banks of a fast-flowing torrent. The forest grounds were covered by lush green mosses and leaf litter, the perfect habitat for Bryophryne frogs, as their name indicates (from greek, bryo = mosses). And the specific epithet, phuyuhampatu, comes from Quechua meaning frog (hampatu) of the clouds (phuyu). These frogs live under mosses, are small (<1 in), and "freeze" when moss is removed - making them hard to spot.
We found another individual further down the valley, where the torrent grew somewhat larger and became more arduous to cross, as our collaborators and coauthors Isabel Diaz and Alex Ttito soon realized. This new frog is smaller than previously known Bryophryne, and is only known to occur in the Quespillomayo valley within the reserve. All species of this genus are micro-endemics, and 12 out of 13 known species have been described since 2009.
During the last week of May we embarked on a field trip to Reserva Nacional Pampas Galeras, where Andrew is conducting field work for his master thesis. This Reserve was set up, among other reasons, to protect the habitat of vicuñas and to promote their sustainable use. These camelids, which along with guanacos are not domesticated (in contrast with the domesticated llamas and alpacas), produce the finest wool, which is highly prized for luxury clothing.
But the reserve also protects native Telmatobius frogs, which live and breed in streams and torrents, for example the stream in the picture below where young vicuñas are taking a bath, and where Andrew (right, handling an adult frog) is currently doing field work. These populations, like other populations of Telmatobius throughout the Andes have been affected by epizootics of chytridiomycosis. Whereas other species of Telmatobius have been very negatively impacted by this fungal disease, such as the three species previously distributed in Ecuador and most species living in the cloud forests of the eastern slopes of the Andes, the Telmatobius at Pampas Galeras seem to be able to cope with chytridiomycosis. Our collaborator Victor Vargas, in the photo below swabbing an adult female, started monitoring these populations a couple of years ago, and introduced us to the unique ecosystem.
Our collaborator Dr. Sarah Kupferberg, seen in the picture recording the call of the (very rare) males of Telmatobius, joined the team for a week of diatom sampling, tadpole hunting, and other stream ecological studies in the context of Andrew's thesis. Andrew is investigating the ecological consequences of reduced grazing abilities by the very large Telmatobius tadpoles (some weighing up to 25 g). Although chytridiomycosis does not seem to be lethal to tadpoles, it does damage their mouthparts, affecting their diet.
The high-Andean streams where these tadpoles live are dominated by in situ primary producers, mostly epilithic diatoms, which also represent an important source of food for tadpoles. Damage to keratinized mouthparts, as seen in the picture here (upper beak should be entirely black; depigmentation indicates damage), is likely to reduce the tadpole's ability to displace these diatoms from their rocky substrates. In order to study these effects, Andrew is rearing tadpoles in flow-through enclosures. Because of their dominance (along with mayflies) as diatom grazers, disease could then be having important consequences on the functioning of these stream ecosystems by affecting the diet of tadpoles.
As for the question of why adults seemed to have survived epizootics of chytridiomycosis, we won't have an answer for a while, but preliminary surveys indicate that many adults may be protected by one symbiotic bacterium, Janthinobacterium lividum, known to inhibit growth of the fungal disease in co-culture assays, and to protect inoculated amphibians from chytridiomycosis. We isolated this bacterium from most adults, which is unusual for tropical amphibians where this microbe has rarely been recorded. Hopefully these frogs will continue to maintain stable or growing populations in spite of the presence of fungal disease.
A new paper from the Catenazzi lab (Burkart et al. 2017) suggests that bacteria, but not peptides, play an important role in protecting a Peruvian marsupial frog from chytridiomycosis. Controlled susceptibility trials determined that Gastrotheca excubitor is resistant to chytridiomycosis but its congeneric, G. nebulanastes, is susceptible. It was hypothesized that this finding could be explained by interspecific differences in cutaneous defenses since infection by the disease-causing fungus Batrachochytrium dendrobatidis (Bd) is initiated on the skin. Two of these defenses, antimicrobial peptides and symbiotic bacteria, have previously been shown to play roles in providing other frogs with disease resistance.
We collected peptides and bacteria from both species. Growth inhibition assays using whole peptide mixtures and bacterial isolates were conducted to determine if either defense was anti-Bd in vitro. Although neither species’ peptide mixtures differed in anti-Bd ability, 6/15 G. excubitor bacterial isolates inhibited Bd compared to 1/11 from G. nebulanastes. Furthermore, the G. nebulanastes isolate was the weakest of all anti-Bd bacteria. The frogs shared no bacterial species, and a microhabitat analysis suggested that environment may be an important inoculum since G. excubitor is terrestrial and G. nebulanastes is arboreal.
Understanding what contributes to host resistance is important for informing disease mitigation strategies. The application of anti-Bd bacteria to susceptible frogs has been proposed as a method to prevent chytridiomycosis, and our research corroborates the important role bacteria play in providing this protection. Furthermore, the reproductive strategy of these marsupial frogs likely allows for vertical transfer of bacteria from mother to offspring so that probiotics can proliferate through a population. The implications of our research extend beyond the amphibian-Bd disease system, as beneficial bacteria are likely important host defenses for other diseases.
Low flow conditions downstream of dams promote invasion by non-native species, including predators, competitors and sub-optimal food resources for the frogs. However, some populations persist even in spite of unfavorable water flow and temperature conditions. In collaboration with Dr. Sarah Kupferberg, we aimed at understanding the role of plasticity in thermal preference and performance in allowing river fauna to persist under temperature challenging conditions. We monitored water temperature in six river catchments inhabited by Rana boylii, pairing one regulated (i.e., dammed) and unregulated river in each catchment. We also compared thermal preference and performance of tadpoles from these catchments, in field and common-garden rearing experiments.
We found substantial geographic variation in frog population distribution and abundance based on river size combined with water temperature, but overall frogs in regulated rivers bred in colder waters than they did in free-flowing rivers. Sierran rivers were colder during spring (breeding and egg deposition) but became warmer during the summer ( when tadpoles develop) than coastal rivers. Tadpoles from all rivers had a positive linear growth response to temperature, but individuals from inland rivers displayed higher growth rates. Consistent with a counter-gradient model of selection in which the response to temperature change is in the opposite direction of the change, individuals from cooler rivers selected warmer temperatures. When reared under common conditions (photo right), however, tadpoles showed similar temperature (see thermal gradient below) preferences regardless of source river.
Plasticity in thermoregulatory behavior and growth performance may explain how small populations of Rana boylii are able to survive in river where cold water is released from reservoirs downstream of large dams. To further promote the persistence of these small populations, regulated rivers could be managed with a goal to increase the availability of edgewater, shallow habitats where tadpoles can thermoregulate and complete development by the end of summer.
Catenazzi A, Kupferberg SJ. 2017. Variation in thermal niche of a declining river-breeding frog: From counter-gradient responses to population distribution patterns. Freshwater Biol. ##:1–11. https://doi.org/10.1111/fwb.12942
News from the lab