RESUMEN
Symbiotic bacterial communities are crucial to combating infections and contribute to host health. The amphibian skin microbiome plays an important role in protecting their hosts against pathogens such as Batrachochytrium dendrobatidis (Bd), one of the causative agents of chytridiomycosis, which is responsible for dramatic amphibian population declines worldwide. Although symbiotic skin bacteria are known to inhibit Bd growth, an understanding of the relationship between Bd genetic variability, environmental conditions, and skin bacterial communities is limited. Therefore, we examined the associations between Bd infection load, Bd genetic diversity and skin bacterial communities in five populations of Hyliola regilla (hypochondriaca) from environmentally contrasting sites in Baja California, Mexico. We observed differences in Bd genetics and infection load among sites and environments. Genetic analysis of Bd isolates revealed patterns of spatial structure corresponding to the five sites sampled. Amphibian skin bacterial diversity and community structure differed among environments and sites. Bacterial community composition was correlated with Bd genetic differences and infection load, with specific bacterial taxa enriched on infected and un-infected frogs. Our results indicate that skin-associated bacteria and Bd strains likely interact on the host skin, with consequences for microbial community structure and Bd infection intensity.
Asunto(s)
Quitridiomicetos , Animales , Anuros/microbiología , Bacterias , Batrachochytrium , Quitridiomicetos/genética , Variación Genética , México , Piel/microbiologíaRESUMEN
Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), is a devastating infectious disease of amphibians. Retrospective studies using museum vouchers and genetic samples supported the hypothesis that Bd colonized Mexico from North America and then continued to spread into Central and South America, where it led to dramatic losses in tropical amphibian biodiversity (the epizootic wave hypothesis). While these studies suggest that Bd has been in Mexico since the 1970s, information regarding the historical and contemporary occurrence of different pathogen genetic lineages across the country is limited. In the current study, we investigated the historical and contemporary patterns of Bd in Mexico. We combined the swabbing of historical museum vouchers and sampling of wild amphibians with a custom Bd genotyping assay to assess the presence, prevalence, and genetic diversity of Bd over time in Mexico. We found Bd-positive museum specimens from the late 1800s, far earlier than previous records and well before recent amphibian declines. With Bd genotypes from samples collected between 1975-2019, we observed a contemporary dominance of the global panzootic lineage in Mexico and report four genetic subpopulations and potential for admixture among these populations. The observed genetic variation did not have a clear geographic signature or provide clear support for the epizootic wave hypothesis. These results provide a framework for testing new questions regarding Bd invasions and their temporal relationship to observed amphibian declines in the Americas.
Asunto(s)
Quitridiomicetos , Anfibios , Animales , Batrachochytrium , Quitridiomicetos/genética , México , América del Norte , Estudios Retrospectivos , América del SurRESUMEN
AbstractIncreases in consumer abundance following a resource pulse can be driven by diet shifts, aggregation, and reproductive responses, with combined responses expected to result in faster response times and larger numerical increases. Previous work in plots on large Bahamian islands has shown that lizards (Anolis sagrei) increased in abundance following pulses of seaweed deposition, which provide additional prey (i.e., seaweed detritivores). Numerical responses were associated with rapid diet shifts and aggregation, followed by increased reproduction. These dynamics are likely different on isolated small islands, where lizards cannot readily immigrate or emigrate. To test this, we manipulated the frequency and magnitude of seaweed resource pulses on whole small islands and in plots within large islands, and we monitored lizard diet and numerical responses over 4 years. We found that seaweed addition caused persistent increases in lizard abundance on small islands regardless of pulse frequency or magnitude. Increased abundance may have occurred because the initial pulse facilitated population establishment, possibly via enhanced overwinter survival. In contrast with a previous experiment, we did not detect numerical responses in plots on large islands, despite lizards consuming more marine resources in subsidized plots. This lack of a numerical response may be due to rapid aggregation followed by disaggregation or to stronger suppression of A. sagrei by their predators on the large islands in this study. Our results highlight the importance of habitat connectivity in governing ecological responses to resource pulses and suggest that disaggregation and changes in survivorship may be underappreciated drivers of pulse-associated dynamics.
Asunto(s)
Dieta/veterinaria , Ecosistema , Cadena Alimentaria , Lagartos/fisiología , Animales , Bahamas , Femenino , Islas , Masculino , Algas Marinas , Conducta SocialRESUMEN
Understanding processes that may stabilize ecological systems confronted with rapidly changing environmental conditions is a key issue in ecology. We studied a system of highly fluctuating populations, the moth Achyra rantalis feeding on the plant Sesuvium portulacastrum in a group of small subtropical islands of the Bahamas. The plant is a prostrate inhabitant of shorelines, and consequently moths are highly vulnerable to being consumed by the ground-foraging lizard Anolis sagrei. We measured the percent ground cover of Sesuvium and abundance of Achyra on 11 islands with lizards present and 21 islands without lizards annually for 10 consecutive years. Overall abundance of Achyra was 4.6 times higher on no-lizard islands than on lizard islands. The percent cover of Sesuvium exhibited lower temporal variability on lizard islands when the study site was undisturbed by hurricanes, and higher recovery rate on lizard islands following hurricanes. We suggest that both of these stabilizing phenomena are linked to a trophic cascade in which predatory lizards control herbivore populations, thereby suppressing outbreaks and enhancing plant recovery following physical disturbance.
Asunto(s)
Herbivoria , Lagartos , Animales , Bahamas , Tormentas CiclónicasRESUMEN
Flows of energy and materials link ecosystems worldwide and have important consequences for the structure of ecological communities. While these resource subsidies typically enter recipient food webs through multiple channels, most previous studies focussed on a single pathway of resource input. We used path analysis to evaluate multiple pathways connecting chronic marine resource inputs (in the form of seaweed deposits) and herbivory in a shoreline terrestrial ecosystem. We found statistical support for a fertilization effect (seaweed increased foliar nitrogen content, leading to greater herbivory) and a lizard numerical response effect (seaweed increased lizard densities, leading to reduced herbivory), but not for a lizard diet-shift effect (seaweed increased the proportion of marine-derived prey in lizard diets, but lizard diet was not strongly associated with herbivory). Greater seaweed abundance was associated with greater herbivory, and the fertilization effect was larger than the combined lizard effects. Thus, the bottom-up, plant-mediated effect of fertilization on herbivory overshadowed the top-down effects of lizard predators. These results, from unmanipulated shoreline plots with persistent differences in chronic seaweed deposition, differ from those of a previous experimental study of the short-term effects of a pulse of seaweed deposition: while the increase in herbivory in response to chronic seaweed deposition was due to the fertilization effect, the short-term increase in herbivory in response to a pulse of seaweed deposition was due to the lizard diet-shift effect. This contrast highlights the importance of the temporal pattern of resource inputs in determining the mechanism of community response to resource subsidies.
Asunto(s)
Ecosistema , Herbivoria , Lagartos , Algas Marinas , Animales , Bahamas , Dieta , Densidad de Población , Conducta PredatoriaRESUMEN
The effect of environmental change on ecosystems is mediated by species interactions. Environmental change may remove or add species and shift life-history events, altering which species interact at a given time. However, environmental change may also reconfigure multispecies interactions when both species composition and phenology remain intact. In a Caribbean island system, a major manifestation of environmental change is seaweed deposition, which has been linked to eutrophication, overfishing, and hurricanes. Here, we show in a whole-island field experiment that without seaweed two predators--lizards and ants--had a substantially greater-than-additive effect on herbivory. When seaweed was added to mimic deposition by hurricanes, no interactive predator effect occurred. Thus environmental change can substantially restructure food-web interactions, complicating efforts to predict anthropogenic changes in ecosystem processes.
Asunto(s)
Hormigas , Artrópodos , Cadena Alimentaria , Lagartos , Plantas , Conducta Predatoria , Algas Marinas , Animales , Bahamas , Ecosistema , Conducta Alimentaria , Geografía , Estaciones del AñoRESUMEN
Protective ant-plant mutualisms-where plants provide food or shelter to ants and ants protect the plants from herbivores-are a common feature in many ecological communities, but few studies have examined the effect of disturbance on these interactions. Disturbance may affect the relationship between plants and their associated ant mutualists by increasing the plants' susceptibility to herbivores, changing the amount of reward provided for the ants, and altering the abundance of ants and other predators. Pruning was used to simulate the damage to buttonwood mangrove (Conocarpus erectus) caused by hurricanes. Pruned plants grew faster than unpruned plants, produced lower levels of physical anti-herbivore defenses (trichomes, toughness), and higher levels of chemical defenses (tannins) and extrafloral nectaries. Thus, simulated hurricane damage increased plant growth and the amount of reward provided to ant mutualists, but did not have consistent effects on other anti-herbivore defenses. Both herbivores and ants increased in abundance on pruned plants, indicating that the effects of simulated hurricane damage on plant traits were propagated to higher trophic levels. Ant-exclusion led to higher leaf damage on both pruned and upruned plants. The effect of ant-exclusion did not differ between pruned and unpruned plants, despite the fact that pruned plants had higher ant and herbivore densities, produced more extrafloral nectaries, and had fewer physical defenses. Another common predator, clubionid spiders, increased in abundance on pruned plants from which ants had been excluded. I suggest that compensatory predation by these spiders diminished the effect of ant-exclusion on pruned plants.