29 research outputs found
Experimental evidence for predator learning and Müllerian mimicry in Peruvian poison frogs (Ranitomeya, Dendrobatidae)
Poison frogs are characterized by bright coloration, striking patterns, and toxicity; they have thus become a classic example of aposematism. Ranitomeya imitator mimics three congeneric model species (R. fantastica, R. summersi, and two morphs of R. variabilis), creating geographically distinct populations of the species, including four allopatric mimetic morphs. These complexes are thought to represent a case of Müllerian mimicry, but no empirical data exist on learned avoidance by predators to support this claim. In this study we used young chickens (Gallus domesticus) as naïve predators to determine if a mimetic morph of R. imitator and R. variabilis contribute to reciprocal learned avoidance by predators--a key component of Müllerian mimicry. Chickens exposed to either stimulus species demonstrated learned avoidance of both species; thus our results indicate that this complex functions as a Müllerian mimicry system. Our study shows no difference between learned avoidance in stimuli frogs and a "novel" morph of R. imitator which differed in both colour and pattern--indicating that predator learned avoidance may be generalized in this system. This study provides empirical evidence demonstrating the first known case of Müllerian mimicry in anurans. Further, it demonstrates generalized learning which provides a plausible mechanism for the maintenance of both polymorphic mimicry and the maintenance of intrapopulation phenotypic heterogeneity.M.S
The Effect of Riparian Buffer Zones of Macroinvertebrate Biodiversity and Stream Health
Riparian buffer zones are the forested areas between a stream and the surrounding land. They help preserve stream quality, and in doing so, help preserve biodiversity. Riparian buffer zones have an affect on a vast array of stream attributes, macroinvertebrate biodiversity, and the health of stream ecosystems; it is for this reason that they are important.
Macroinvertebrates are often considered an indicator of ecosystem health and therefore the way that buffer zones affect macroinvertebrate species richness and abundance are often indicative of how they affect the rest of the ecosystem. The purpose of this project was to collect macroinvertebrates to test for differences between riparian and non-riparian zones. The data were collected once during each of the calendar seasons (twice during the fall) in the Yellow Breeches Creek in Cumberland County, Pennsylvania. Richness and abundance are not greater in riparian zones. However, the Shannon index and Becks scales are statistically greater in riparian zones; indicating greater biodiversity in riparian zones
Dodge, Duck, Dip, Dive & Dependence: Using Dodgeball to Explore Frequency Dependent Selection
The term frequency dependence describes scenarios in which the likelihood
of an event occurring is strongly tied to how common a particular trait is.
Understanding frequency dependence is key to understanding numerous
biological processes relevant to evolution by natural selection, such as predation,
mimicry, disease, and effective vaccinations. We use dodgeball to demonstrate
frequency dependent selection in a hypothetical predator–prey community, and
provide possible extensions into other topics. This activity can be used with
biology students in high school through upper-level undergraduate courses
An Empirical Test Indicates Only Qualitatively Honest Aposematic Signaling Within a Population of Vertebrates
Signaling is an important part of intraspecific and interspecific interactions. Theoretical work examining honest signaling in aposematic species (e.g., those with conspicuous colors and secondary defenses) has focused primarily on discerning the patterns between conspicuousness and defense within populations. Most empirical work, however, has investigated these patterns across populations or species. Here, we test for honest signaling across individuals within a population of the aposematic poison frog, Ranitomeya imitator. We find no evidence that increasing levels of the aposematic signal are correlated with increasing levels of defense in this species, indicating that our study population does not signal in a quantitatively honest manner, but rather that the signal is qualitatively honest. Additionally, we found no evidence that frogs with higher levels of defense behave more boldly as a result of the presumed increased ecological release from predation, an expected outcome in a qualitatively honest system. We discuss our findings in light of the ecology and evolution of R. imitator, and suggest mechanisms that may explain the absence of a relationship between toxicity and the aposematic signal
Poison frog warning signals: From the rainforest to the genome and back again
Signal communication is pervasive in nature and is used to convey information to both conspecifics and heterospecifics. Aposematic species use warning signals (e.g. bright coloration) to alert predators to the presence of a secondary defense (e.g., spines, toxins, etc). The presence of a conspicuous signal in combination with a secondary defense is thought to increase the efficiency of learned avoidance by predators and may prevent attacks altogether. Aposematism is widespread both geographically and taxonomically, and aposematic species are seen across the tree of life (including nudibranchs, invertebrates, and vertebrates). There are three main requirements for aposematism to function effectively. First, aposematic species must be able to produce a pattern that contrasts the environmental background (typically via chromatophores and pigments). Second, predators must be able to receive and learn to avoid preying upon aposematic individuals based on the signal. And finally, aposematism must confer a fitness benefit to the population of an aposematic species. In this dissertation I examine both the information that aposematic species convey and how the aposematic signal itself is produced. First, I examine whether the aposematic signal conveys detailed information to visual predators regarding an individual's specific level of toxicity--a key, but contentious, hypothesis of aposematic theory. Second, I test whether the aposematic signal is multimodal in vertebrates by determining whether they present non-visual predators with an olfactory cue/signal that contains sufficient information to indicate the possession of toxins and thus decrease the likelihood of attack. Additionally, I use gene expression data across multiple color morphs of an aposematic frog species to look at candidate color genes and how they influence coloration. Finally, I examine gene expression during developmental time periods that correlate with color deposition to examine how candidate color genes influence color production over developmental time and across multiple color morphs
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A histological analysis of coloration in the Peruvian mimic poison frog (Ranitomeya imitator)
Aposematism continues to be a phenomenon of central interest in evolutionary biology. The life history of the mimic poison frog, Ranitomeya imitator, relies heavily on aposematism. In order for aposematic signals to be effective, predators must be able to learn to avoid the associated phenotype. However, in R. imitator, aposematism is associated with four different color phenotypes that mimic a complex of congeneric species occurring across the mimic frog's geographic range. Investigations of the underlying mechanics of color production in these frogs can provide insights into how and why these different morphs evolved. We used histological samples to examine divergence in the color production mechanisms used by R. imitator to produce effective aposematic signals across its geographic range. We measured the coverage of melanophores and xanthophores (the area covered by chromatophores divided by total area of the skin section) in each color morph. We find that morphs that produce orange skin exhibit a higher coverage of xanthophores and lower coverage of melanophores than those that produce yellow skin. In turn, morphs that produce yellow skin exhibit a higher coverage of xanthophores and lower coverage of melanophores than those that produce green skin. Generally, across the morphs, a high ratio of xanthophores to melanophores is associated with colors of brighter spectral reflectance. Together, our results contribute to the understanding of color production in amphibians and document divergence in the histology of a species that is subject to divergent selection associated with aposematism
Alkaloid defenses of co-mimics in a putative Müllerian mimetic radiation
Background
Polytypism in aposematic species is unlikely according to theory, but commonly seen in nature. Ranitomeya imitator is a poison frog species exhibiting polytypic mimicry of three congeneric model species (R. fantastica, R. summersi, and two morphs of R. variabilis) across four allopatric populations (a "mimetic radiation"). In order to investigate chemical defenses in this system, a key prediction of Müllerian mimicry, we analyzed the alkaloids of both models and mimics from four allopatric populations.
Results
In this study we demonstrate distinct differences in alkaloid profiles between co-mimetic species within allopatric populations. We further demonstrate that R. imitator has a greater number of distinct alkaloid types than the model species and more total alkaloids in all but one population.
Conclusions
Given that R. imitator is the more abundant species in these populations, R. imitator is likely driving the majority of predator-learned avoidance in these complexes. The success of Ranitomeya imitator as a putative advergent mimic may be a direct result of differences in alkaloid sequestration. Furthermore, we propose that automimicry within co-mimetic species is an important avenue of research
Variation in pigmentation gene expression is associated with distinct aposematic color morphs in the poison frog Dendrobates auratus
Background:
Color and pattern phenotypes have clear implications for survival and reproduction in many species. However, the mechanisms that produce this coloration are still poorly characterized, especially at the genomic level. Here we have taken a transcriptomics-based approach to elucidate the underlying genetic mechanisms affecting color and pattern in a highly polytypic poison frog. We sequenced RNA from the skin from four different color morphs during the final stage of metamorphosis and assembled a de novo transcriptome. We then investigated differential gene expression, with an emphasis on examining candidate color genes from other taxa.
Results:
Overall, we found differential expression of a suite of genes that control melanogenesis, melanocyte differentiation, and melanocyte proliferation (e.g., tyrp1, lef1, leo1, and mitf) as well as several differentially expressed genes involved in purine synthesis and iridophore development (e.g., arfgap1, arfgap2, airc, and gart).
Conclusions:
Our results provide evidence that several gene networks known to affect color and pattern in vertebrates play a role in color and pattern variation in this species of poison frog
Differential gene expression and gene variants drive color and pattern development in divergent color morphs of a mimetic poison frog
Evolutionary biologists have long investigated the ecological contexts, evolutionary forces, and proximate mechanisms that produce the diversity of animal coloration we see in the natural world. In aposematic species, color and pattern is directly tied to survival and thus understanding the origin of the phenotype has been a focus of both theoretical and empirical inquiry. In order to better understand this diversity, we examined gene expression in skin tissue during development in four different color morphs of the aposematic mimic poison frog, Ranitomeya imitator. We identified a suite of candidate color-related genes a priori and identified the pattern of expression in these genes over time, differences in expression of these genes between the mimetic morphs, and genetic variants that differ between color morphs. We identified several candidate color genes that are differentially expressed over time or across populations, as well as a number of color genes with fixed genetic variants between color morphs. Many of the color genes we discovered in our dataset are involved in the canonical Wnt signaling pathway, including several fixed SNPs between color morphs. Further, many genes in this pathway were differentially expressed at different points in development (e.g., lef1, tyr, tyrp1). Importantly, Wnt signaling pathway genes are overrepresented relative to expression in Xenopus tropicalis. Taken together, this provides evidence that the Wnt signaling pathway is contributing to color pattern production in R. imitator, and is an excellent candidate for producing some of the differences in color pattern between morphs. In addition, we found evidence that sepiapterin reductase is likely important in the production of yellow-green coloration in this adaptive radiation. Finally, two iridophore genes (arfap1, gart) draw a strong parallel to previous work in another dendrobatid, indicating that these genes are also strong candidates for differential color production. We have used high throughput sequencing throughout development to examine the evolution of coloration in a rapid mimetic adaptive radiation and found that these divergent color patterns are likely to be affected by a combination of developmental patterns of gene expression, color morph-specific gene expression, and color morph-specific gene variants.Joyner Open Access Publishing Support Fun
Microhabitat use and spatial distribution in Picado’s Bromeliad Treefrog, Isthmohyla picadoi (Anura, Hylidae)
Isthmohyla picadoi is a Neotropical hylid frog found in upper humid montane forests of Costa Rica and Panama. The species is of particular interest because it continues to persist in an area in which the amphibian community has otherwise been decimated by the pathogenic fungus, Batrachochytrium dendrobatidis. Ground search, ladder climbing, and tree climbing techniques were used to locate 32 individuals; including adult males and females, juveniles, andmetamorphosing frogs. The majority of frogs were found in bromeliads, although some individuals were found on plants of the Euphorbiaceae, Musaceae, and Heliconiaceae families. Most frogs were found in larger bromeliads (45 cm or wider). There was a positive correlation between SUL and bromeliad width within the population but not within maturity classes (adult males, adult females, all adults, nonmetamorphosingjuveniles), suggesting that juvenile and adult frogs differ in bromeliad usage. Ranges of SUL and body weight in this particular population are much greater than those reported in previous species accounts