martes, 22 de enero de 2013

Causas del declive de anfibios en Ecuador


Sapo arlequín Jambato Atelopus ignescens.  Visto por última vez el 30 de Marzo de 1988 © Luis A. Coloma Centro Jambatu












Los científicos Pablo A. Menéndez-Guerrero y Catherine H. Graham acaban de publicar en la revista Ecography un estudio sobre las causas de los declives drásticos de anfibios ocurridos en Ecuador. Su investigación revela que el cambio climático y la quitridiomicosis estarían involucrados en este desastre mientras que la destrucción del habitat no parece ser responsable de estos eventos catastróficos.


Ecography 36: 001–014, 2013
doi: 10.1111/j.1600-0587.2012.07877.x © 2013 The Authors. Ecography © 2013 Nordic Society Oikos Subject Editor: Miguel B. Araújo. Accepted 6 November 2012




Resumen

Los anfibios están disminuyendo en todo el mundo a ritmos alarmantes; sin embargo, las causas de estos declives siguen siendo algo esquivas. Aquí evaluamos tres de las amenazas principales implicadas en la disminución de las poblaciones y la desaparición de los anfibios de Ecuador: chytridiomicosis, cambio climático y pérdida de hábitat. Se evaluaron los patrones espaciales de las principales amenazas para los anfibios ecuatorianos utilizando una base de datos de múltiples especies de ranas endémicas junto con información sobre la distribución del patógeno y los requisitos ambientales, la sensibilidad de las especies al cambio climático (basadas indirectamente en la distribución geográfica de especies y sus requerimientos ecológicos) y la pérdida de hábitat. Nuestros resultados indican que los anfibios muestran un patrón no aleatorio de riesgo de extinción, tanto a nivel geográfico como taxonómico. Además, el cambio climático,  la quitridiomicosis, y sus efectos sinérgicos, es probable que en la actualidad ejercen el mayor impacto sobre los anfibios en el Ecuador, mientras que la pérdida de hábitat no parece ser la causa de la disminución drástica. Las especies más amenazadas en las categorías de riesgo de extinción de la UICN son exactamente aquellas que parecen ser las más afectadas por estas amenazas. Al examinar múltiples causas potenciales según el nivel de amenaza de los anfibios en un marco espacial explícito nuestro estudio proporciona nuevos conocimientos acerca de cual es la combinación de factores más importantes en el declive de anfibios en un “punto caliente” de la diversidad tropical. Además, nuestro enfoque y conclusiones son útiles para estudiar los declives en otras regiones del mundo.


Abstract

Amphibians are declining at alarming rates worldwide; however, the causes of these declines remain somewhat elusive. Here we evaluated three major threats implicated in declines of populations and disappearance of Ecuadorian amphib- ians: chytridiomicosis, climate change, and habitat loss. We assessed spatial patterns of these key threats to Ecuadorian amphibians using a multi-species database of endemic frogs along with information on the pathogen’s distribution and environmental requirements, species sensitivity to climate change (indirectly based on species geographical distribution and ecological properties) and habitat loss. Our results show that amphibians display a non-random pattern of extinction risk, both geographically and taxonomically. Further, climate change, chytridiomicosis, and their synergetic effects, are likely currently exerting the greatest impact on amphibians in Ecuador, while habitat loss does not seem to be causing precipitous declines. The most threatened species under the IUCN extinction risk categories are exactly those that appear to be the most affected by these threats. By examining multiple potential causes of amphibian threat level in a spatially explicit framework our study provides new insights about what combination of factors are most important in amphibian declines in a tropical diversity hotspot. Further, our approach and conclusions are useful for studying declines in other regions of the world.

lunes, 7 de enero de 2013

Insight into the natural variation of frogs of the "Paru morph" Oophaga sylvatica (Anura: Dendrobatidae)


Wild adults of Oophaga sylvatica (Paru morph) of the Otokiki population, Esmeraldas province, Ecuador. Site 1 (70 x 40 m): 734 meters asl, sampled area: 2800 square meters. © Centro Jambatu








































Individuals of the the Paru morph of Oophaga sylvatica (= Dendrobates sylvaticus) exported by Wikiri are the offspring of a parental population from the Otokiki reserve (143 acres of tropical rainforests of northwestern Ecuador). Otokiki reserve is located in the Alto Tambo region (Esmeraldas province) at an altitude of about 700 meters above sea level. 

The amount of color pattern variation within this Otokiki population, which occurs naturally, is perplexing. See figure depicting variation of wild-caught adult individuals at one of the study sites (Site 1) in Otokiki. All individuals found in a preliminary sampling are included, but additional sampling might reveal more individuals and variation.

At Otokiki, similar large variation in colors and patterns is represented in quadrats under management  by Wikiri (three habitat-enriched semiclosed enclosures, one enriched open quadrat), and in one control (not enriched) quadrat.

Also, we have documented a great amount of intrapopulation variation at other sites in Esmeraldas province, for example, towards the east of Alto Tambo at Guadal (near Lita, Esmeraldas province). Less color pattern variation is seen in lowland populations at Durango and Playón de San Francisco, which display more uniform colors.

How to interpret this variation and what are it’s causes?

Underlying causes of this intrapopulation variation of the Paru morph are largely unknown and currently are a matter of speculation. For now, we are reluctant to interpret this variation as the result of hybridization —a phenomenon that can occur between species as a result of primary or secondary contact (after a period of isolation). Underlying factors behind the observed variation probably lie in the evolutionary history of this population. The historical human intervention in the area could have played a role as well, but the variation is not a consequence of Wikiri manipulation.

Understanding the mechanisms that promote intrapopulation divergence (such as the one observed at Otokiki reserve and surrounding areas) and interpopulation divergence (such as the one among populations of O. sylvatica in the pacific lowlands of Ecuador and Colombia), and ultimately speciation, is one of the most challenging and intriguing tasks in evolutionary biology. Geographical barriers, ecological gradients, genetic drift, and sexual selection are the main mechanisms (currently speculative for O. sylvatica populations, as mentioned before) invoked to explain these processes, which are shaping the variation observed.

Centro Jambatu has begun a research program and study projects on the evolution of coloration, morphology and behavior within and among populations of Oophaga sylvatica. The program is a cooperative effort among Ecuadorian and USA researchers. We will be doing field, molecular, and experimental work. The Otokiki population will be critical for our understanding of coloration evolution  because of its huge  variability.

For a better understanding of this variation and its evolution, we need to conduct fine-tuned studies including morphological descriptions in relation to behavior, geography, and molecular population genetic structure. Also, we need to conduct lab controlled experiments to see the consequences of color variation. We will need to set up crosses between color morphs in order to identify color specific SNPs (single nucleotide polymorphisms) and then examine the expression bias of parental alleles in the offspring. We will study behavioral issues and also we will address questions of color determination.

Finally, we think that the hobbyists industry and people who love these frogs should appreciate the unique opportunity and monumental effort done by Wikiri (see also Ecuafrog of Wikiri and the amphibian trade) in providing farm and captive raised frogs from a population that displays such a great intrapopulation variation, which include dull and bright colored individuals, spotted and non-spotted frogs, orange, red, yellow and brown colors. Hopefully this variation can be preserved at the site (Otokiki) and region of Alto Tambo. Backup populations under care of hobbyists are also important as an ex situ tool helping integrative conservation strategies.


Fundación Otonga


Updated: 4 January 2013