Response of an Eleutherodactylus coqui population to hurricane Maria: demography and disease dynamics
Peña-Jiménez, Janelle Alyssa
AdvisorBurrowes, Patricia A.
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Chapter I abstract: The Caribbean region is expected to face an increase in frequency and intensity of climatic disturbances, such as hurricanes. Amphibians and reptiles are especially vulnerable to local abiotic regimes and their response to changes are limited by physiological constraints intrinsic to their evolutionary history. In September of 2017, El Yunque National Forest in Puerto Rico experienced extensive forest damage by the effect of hurricane Maria. In this study, we assessed the effect of hurricane Maria on the abundance, age-specific survivorship, detection probability, and expected gains of a well-studied high-elevation population of Eleutherodactylus coqui. We hypothesize that the population structure would change due to the canopy loss and consequent habitat disturbances caused by the storm blowout. To measure abundance estimates, we used a multi-state N-mixture model to analyze the changes in age-specific demographics on E. coqui population. We found that hurricane Maria had a negative impact on local expected gains and abundance estimates of E. coqui that caused a disruption in the typical demographic pattern as age classes transition through the warm-wet and cool-dry seasons in Puerto Rico. However, no drastic declines were observed. These results point to plasticity in the response of E. coqui to severe environmental events. Recording changes in high-elevation E. coqui population structure may offer insight to how other endangered sympatric species would respond to such phenomena. As stronger and more frequent tropical storms are predicted soon, this study provides baseline data that can help predict, compare, and evaluate future changes to biodiversity in critical areas. Chapter II abstract: Amphibians are declining drastically due, in part, to a pathogenic fungal parasite named Batrachochytrium dendrobatidis (Bd). In addition, extreme climatic events, like hurricanes, are increasing in frequency and intensity and this points to the need to understand the way they influence host-pathogen dynamics. Studies in the Americas have advanced our understanding on how environmental factors affect virulence and dispersion of Bd in wild populations. However, in some amphibian communities where Bd is enzootic, the dynamics of the disease may be driven by pathogen overdispersion. Under these circumstances, it is important to understand how Bd infection intensity and prevalence influences host survival and reproduction because this may explain the underlying mechanisms of persistence or extinction. In this study, we evaluate the effect of severe natural disturbances on the dynamics of Bd infections across seasons in a population of highland Eleutherodactylus coqui in Puerto Rico. We found significant differences in Bd infection intensities in the population of E. coqui after the hurricane, suggesting a hurricane effect on the vulnerability of hosts. In addition, a zero-inflated regression model distinguished the effects of the hurricane, seasons and their interaction on the population-level prevalence of Bd. Our work highlights the value of long-term field studies because they provide time-sensitive data necessary to evaluate population responses to global change. Chapter III abstract: Marking juveniles of terrestrial direct-developing frogs is challenging because of their small size (< 18 mm) and fragility. This difficulty has limited studies on demography or population dynamics where empirical data on the survivorship of juveniles or their recruitment to adulthood are missing. In a controlled laboratory experiment we tested the survivorship of wild caught juvenile Eleutherodactylus coqui Thomas, 1966 to marking with a single colour Visual Internal Elastomer (VIE) in the thigh with and without additional ventral skin-swabbing for disease or microbiome monitoring. Results revealed 100 % survival in all groups, and all juveniles remained unharmed, moved freely, and fed actively during three days after treatments suggesting that this type of manipulation does not cause direct mortality. After 17 months of the experiment, we have recaptured 11 % of the marked juveniles as adults indicating that they can survive to recruitment age. We propose the use of a single VIE colour as a method to mark and follow date-specific cohorts of juvenile direct-developing frogs or young metamorphs until they reach older and larger age classes. This marking method can be used safely together with skin swabbing and provide valuable information for studies on population biology and age-specific response to environmental or disease stressors.