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
A new lab contribution is available as Early View article today in Ecology & Evolution. The study compares variation in maximum and minimum critical temperatures of more than 20 species of craugastorid frogs in the Amazonian lowland rainforest and contiguous Andean slopes. In this region craugastorid frogs such as the Pristimantis danae female guarding over her hatchlings of the photo have diversified into what is one of the largest vertebrate radiation.
As suggested by previous findings, lowland frogs seem to be at higher risk from climate warming than highland frogs, because lowland frogs are already living at temperatures that are fairly close to the maximum critical temperatures that they could tolerate. This expanded study incorporates the frog's evolutionary history and data on tolerance to cold, and tested whether tolerance to heat and cold exhibit different rates of change, given that critical thermal limits (and their plasticity) may have evolved differently in response to different temperature constraints along the gradient. Our findings indicate great variation in thermal limits, and relatively faster rates of change for tolerance to cold than tolerance to heat. Remarkably, some high-elevation species such as Bryophryne cophites tolerated temperatures as low as 0.4 degrees Celsius.
The study was led by our collaborator Rudolf von May, postdoctoral researcher in the Department of Ecology and Evolutionary Biology at the Univerisity of Michigan, shown here preparing biophysical models to measure temperatures that frogs experience in their microhabitats in the cloud forests and grasslands of Wayqecha Biological Station. See our previous blog post about substantial recent warming in these environments.
I would like to share some online tools that I find very useful when determining whether a species might be new, and during the process of describing new species. This is geared towards amphibians, but many of these resources apply more broadly to other taxa.
Is it new? Tools to compare materials and information
AmphibiaWeb (www.amphibiaweb.org): this comprehensive portal provides information on natural history, population declines and conservation, current taxonomy and amphibian news. Species accounts include links to Amphibian Species of World, Genbank, VertNet and FonoZoo (see below).
Amphibian Species of the World (http://research.amnh.org/vz/herpetology/amphibia): Darrel Frost's taxonomic catalog of all amphibian species, this is the best resource to retrieve past taxonomic changes, and to check current taxonomy.
VertNet (www.vertnet.org): this searchable database aggregates specimen data from hundreds of musem collections across the world. It is an extremely useful tool to discover and locate comparative material and associated data.
Biodiversity Heritage Library (www.biodiversitylibrary.org): this website stores nearly 50 million pages of biodiversity literature, including scanned copies (which can be downloaded as PDFs) of species descriptions from the XIX and XX centuries.
What should I sequence?
PhyLoTa (http://phylota.net): This website returns information about the potential phylogenetic data sets (clusters, or sets of homologous sequences) that can be constructed from the database for taxa of interest. Very useful to choose genes for sequencing by maximizing species sampling.
Describing the species: digital repositories
Zoobank (http://zoobank.org): this is the official registry of zoological nomenclature, and the place to register new nomenclatural acts and papers describing the new taxa, especially useful for journals that do not include nomenclature registration as part of their publication process.
Genbank (https://www.ncbi.nlm.nih.gov/genbank): The NIH genetic sequence database, an annotated collection of all publicly available DNA sequences, including tools to upload and submit newly generated sequences to assign accession numbers for each sequence.
Calphotos (http://calphotos.berkeley.edu): database storing biodiversity and natural history photographs. When uploading photographs of a recently described species, you should email Calphotos first with a copy of the publication to make sure Calphotos will incorporate the new species in their database.
Fonoteca (http://www.fonozoo.com): largest database of anuran calls (>1000 species), including form to submit new recording and have them indexed for publication.
Our lab had a strong presence at the Undergraduate Symposium today with three posters featuring ongoing herpetological research, and first place award for Chris (Rookies category) -- congratulations Chris! Nate (left) presented about the strength of chytrid fungus inhibition by symbiotic skin bacteria of several species of montane tropical frogs in a region where chytrid has caused the collapse of amphibian communities. Joseph (center) worked on identifying each bacterial strain, and additional strains not assayed for inhibitory capacities, through sequencing of 16S rRNA gene. Chris (right) reported on the rediscovery of an enigmatic colubrid snake, appropriately named Erythrolamprus problematicus, and previously known from a single specimen, which does not appear to fit into any previously described genera. Preliminary analyses seem to suggest that this snake is basal to all other Xenodontinae genera.
Our lab has been awarded a Scientific Product Grant by Wildlife Acoustics. We will use the awarded Song Meter acoustic recorders and Kaleidoscope Pro software to collect and analyze frog vocalization data covering six threatened species listed on the IUCN Red list. The results will be used to locate environmental refugia where frogs that are highly susceptible to chytridiomycosis can persist. Discoveries of surviving populations will be shared with governmental and non-governmental organizations to guide future conservation efforts.
Alessandro was invited by the Searle Lab to give a seminar at Purdue on Monday 27 March, "Ecological and physiological filters preventing upslope range shifts in tropical montane frogs". The presentation integrates different ecological and physiological research that our lab and collaborators are conducting on the eastern slopes of the Andes, from reproductive biology to disease ecology and thermal physiology. The host Dr. Catherine Searle is Assistant Professor at Purdue and her lab investigates the community ecology of infectious diseases.
Andrew Rubio (Master student) was awarded a research grant from the Sigma Xi Grants-in-Aid of Research Program for his master thesis project. Andrew will investigate the ecosystem consequences of reduced grazing abilities in stream tadpoles infected by fungal disease. We have known for a while that some organisms can play disproportionate roles in ecosystems, and if their abundances vary in response to variation in prey or predator abundances, cascading effects can occur. Less known is the effect of disease on ecosystem function, and Andrew is proposing to study larval stages of amphibians that, when infected by fungal disease, have reduced grazing ability. This reduced ability in turn influences ecosystem processes such as nutrient cycling and trophic interactions.
Chris Smaga (Freshman) was awarded a research grant from the Chicago Herpetological Society Undergraduate Research in Herpetology program. He will be studying the impact of snake fungal disease (Ophidiomyces ophiodiicola) in Southern Illinois. Although still relatively unknown, this disease could become a substantial threat to native snakes species. Other fungal diseases, such as chytridiomycosis in amphibians and white nose syndrome in bats, have caused dramatic numerical losses, and in some cases local and regional extinction of wildlife. It is thus crucial to understand the potential for snake fungal disease to cause epizootics similar to those associated with these and other emerging fungal diseases. Chris’s proposal is very timely and a necessary first step towards this goal.
Congratulations to Chris and Andrew and best wishes for fun & productive times in the field!
News from the lab