viernes, 4 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. 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