Patterns ofClinostomum marginatuminfection in fishes and amphibians: integration of field, genetic, and experimental approaches

Digenetic trematodes of the genusClinostomumare cosmopolitan parasites infecting fishes, amphibians, reptiles, and snails as intermediate hosts. Despite the broad geographical distribution of this genus, debate about the number of species and how they vary in host use has persisted. To better understand patterns of infection among host species and across life stages, we used large-scale field surveys and molecular tools to examine five species of amphibians and seven species of fishes from 125 California ponds. Among the 12,360 examined hosts, infection was rare, with an overall prevalence of 1.7% in amphibians and 9.2% in fishes. Molecular evidence indicated that both groups were infected withClinostomum marginatum. Using generalized linear mixed effects models, host species identity and host life stage had a strong influence on infection status, such thatLepomis cyanellus(green sunfish) (49.3%) andTaricha granulosa(rough skinned newt) (9.2%) supported the highest overall prevalence values, whereas adult amphibians tended to have a higher prevalence of infection relative to juveniles (13.3% and 2.5%, respectively). Experimentally, we tested the susceptibility of two amphibian hosts (Pseudacris regilla[Pacific chorus frog] andAnaxyrus boreas[western toad]) to varying levels of cercariae exposure and measured metacercariae growth over time.Pseudacris regillawas 1.3× more susceptible to infection, while infection success increased with cercariae exposure dose for both species. On average, metacarcariae size increased by 650% over 20 days. Our study highlights the importance of integrating field surveys, genetic tools, and experimental approaches to better understand the ecology of host–parasite interactions.

Tooth row variation in tadpoles of Dendropsophus labialis (Anura: Hylidae: Dendropsophini) and the evolution of oral morphology in the genus

Labial tooth row variation was assessed in Dendropsophus labialis tadpoles from the Cordillera Oriental in Colombia. The presence of a second anterior labial tooth row was detected, showing thus a labial tooth row formula of 2/2. This second anterior tooth row was present in a substantial number of individuals, suggesting that the observed variation is not unusual. This variation contradicts earlier reports about the number of labial tooth rows in this species, whose labial tooth row formula has been reported as 1/2 without variation. A novel ontogenetic pattern of tooth row addition was detected, differing from earlier observations made on Pseudacris regilla tadpoles in terms of tooth row appearance order. The taxonomic implications for these data are discussed along with the evolution of oral morphologies in the genus.

WETLAND OCCUPANCY OF POND-BREEDING AMPHIBIANS IN YOSEMITE NATIONAL PARK, USA

We estimated wetland occupancy and population trends for three species of pond-breeding anurans in Yosemite National Park from 2007 – 2011. We used a double survey technique in which two observers independently surveyed each site on the same day. Double surveys allowed us to calculate detectability for the three most common anurans within the park: Rana sierrae, Anaxyrus canorus, and Pseudacris regilla. Annual estimates of detectability were generally high; mean detectability ranged from 73.7% + 0.6 (SE) for any life history stage of A. canorus to 86.7% + 0.7 for sites with P. regilla reproduction (eggs or larvae present). Detectability was most variable for Anaxyrus canorus, which ranged from 45.9% to 99.7%. The probability of occupancy for R. sierrae was highest in larger, low-elevation wetlands that lacked fish. Anaxyrus canorus were more common in shallow high-elevation ponds; their occurrence was minimally impacted by the presence of fish. Finally, occurrence of P. regilla was largely unrelated to wetland size and elevation, but like R. sierrae, they were less likely to occupy sites with fish. Occupancy showed no trend over the five years of our study for R. sierrae or A. canorus when considering either sites with any life stage or only sites with reproduction. However, P. regilla showed a modest downward trend for sites with any life stage and sites with reproduction. Our results for R. sierrae run counter to expectations given recent concern about the decline of this species, while our findings for P. regilla raise concerns for this widespread and generally common species.