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Competition and the evolution of imperfect mimicry

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Current Zoology 2012年第4期58卷 608-619页

作者： david W. pfennig david W. KIKUCHI Department of Biology University of North Carolina Chapel Hill NC 27599-3280 USA

Mimicry is widely used to exemplify natural selection＇s power in promoting adaptation. Nonetheless, it has become increasingly clear that mimicry is frequently imprecise. Indeed, the phenotypic match is often poor between mimics and models in many Batesian mimicry complexes and among co-mimics in many Mtillerian mimicry complexes. Here, we consider whether such imperfect mimicry represents an evolutionary compromise between predator-mediated selection favoring mimetic conver- gence on the one hand and competitively mediated selection favoring divergence on the other hand. Specifically, for mimicry to be effective, mimics and their models/co-mimics should occur together. Yet, co-occurring species that are phenotypically similar often compete for resources, successful reproduction, or both. As an adaptive response to minimize such costly interactions, in-teracting species may diverge phenotypically through an evolutionary process known as character displacement. Such divergence between mimics and their models/co-mimics may thereby result in imperfect mimicry. We review the various ways in which character displacement could promote imprecise mimicry, describe the conditions under which this process may be especially likely to produce imperfect mimicry, examine a possible case study, and discuss avenues for future research. Generally, character displacement may play an underappreciated role in fostering inexact mimicry .

关键词： Batesian mimicry Character displacement Hybridization MtUlerian mimicry Reproductive interference Selectivetrade-off

Inducible competitors and adaptive diversification

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Current Zoology 2013年第4期59卷 537-552页

作者： Beren W. ROBINSON david W. pfennig Department of Integrative Biology University of Guelph Guelph Ontario N 1G 2W 1 Canada Department of Biology University of North Carolina Chapel Hill NC 27599 USA

Identifying the causes of diversification is central to evolutionary biology. The ecological theory of adaptive diversi- fication holds that the evolution of phenotypic differences between populations and species--and the formation of new spe- cies-stems from divergent natural selection, often arising from competitive interactions. Although increasing evidence suggests that phenotypic plasticity can facilitate this process, it is not generally appreciated that competitively mediated selection often also provides ideal conditions for phenotypic plasticity to evolve in the first place. Here, we discuss how competition plays at least two key roles in adaptive diversification depending on its pattern. First, heterogenous competition initially generates heterogeneity in resource use that favors adaptive plasticity in the form of ＂inducible competitors＂. Second, once such competitively induced plas- ticity evolves, its capacity to rapidly generate phenotypic variation and expose phenotypes to alternate selective regimes allows populations to respond readily to selection favoring diversification, as may occur when competition generates steady diversifying selection that permanently drives the evolutionary divergence of populations that use different resources. Thus, competition plays two important roles in adaptive diversification---one well-known and the other only now emerging--mediated through its effect on the evolution ofphenotypic plasticity

关键词： Phenotypic plasticity Competition Adaptive radiation Character displacement Genetic assimilation Resourcepolymorphism

More than mimicry？ Evaluating scope for flicker-fusion as a defensive strategy in coral snake mimics

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Current Zoology 2014年第1期60卷 123-130页

作者： Georgia C. TITCOMB david W. KIKUCHI david W. pfennig Department of Biology University of North Carolina at Chapel Hill Chapel Hill NC 27599-3280

Coral snakes and their mimics often have brightly colored banded patterns, generally associated with warning colora- tion or mimicry. However, such color patterns have also been hypothesized to aid snakes in escaping predators through a ＂flicker-fusion＂ effect. According to this hypothesis, banded color patterns confuse potential predators when a snake transitions from resting to moving because its bands blur together to form a different color. To produce this motion blur, a moving snake＇s bands must transition faster than the critical flicker-fusion rate at which a predator＇s photoreceptors can refresh. It is unknown if coral snakes or their mimics meet this requirement. We tested this hypothesis by measuring the movement speed and color pat- terns of two coral snake mimics, Lampropeltis triangulum campbelli and L. elapsoides, and comparing the frequency of color transitions to the photoreceptor activity of the avian eye. We found that snakes often produced a motion blur, but moving snakes created a blurring effect more often in darker conditions, such as sunrise, sunset, and nighttime when these snakes are often active. Thus, at least two species of coral snake mimics are capable of achieving flicker-fusion, indicating that their color patterns may confer an additional defense aside from mimicry

关键词： Coral snake mimicry Flicker-fusion effect CFF Kingsnake Defensive strategy

Reinforcement as an initiator of population Jivergence and speciation

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Current Zoology 2016年第2期62卷 145-154页

作者： Karin S. pfennig Department of Biology University of North Carolina Chapel Hill NC 27599-3280 USA

When hybridization results in reduced fitness, natural selection is expected to favor the evolution of traits that minimize the likelihood of hybridizing in the first place. This process, termed reinforcement （or, more generally, reproductive character displacement）, thereby contributes to the evolution of enhanced reproductive isolation between hybridizing groups. By enhancing reproductive isolation in this way, reinforcement plays an important role in the final stages of speciation. However, reinforcement can also contribute to the early stages of speciation. Specifically, because selection to avoid hybridization occurs only in sympatric populations, the unfolding of reinforcement can lead to the evolution of traits in sympatric populations that reduce reproduction between conspecifics in sympatry versus those in allopatry. Thus, reinforcement between species can lead to reproductive isolation--and possibly speciation-between populations in sympatry versus those in allopatry or among different sympatric populations. Here, I describe how this process can occur, the conditions under which it is most likely to occur, and the empirical data needed to evaluate the hypothesis that reinforcement can initiate speciation.

关键词： character displacement ecological speciation gene flow hybridization population divergence reinforcement cascades reproductive isolation sexual selection speciation cascades.

Heterospecific interactions and the proliferation of sexually dimorphic traits

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Current Zoology 2012年第3期58卷 453-462页

作者： Karin S. pfennig Allen H. HURLBERT Department of Biology University of North Carolina Chapel Hill Chapel Hill NC 27599-3280

Sexual selection is expected to promote speciation by fostering the evolution of sexual traits that minimize reproductive interactions among existing or incipient species. In species that compete for access to, or attention of, females, sexual selec- tion fosters more elaborate traits in males compared to females. If these traits also minimize reproductive interactions with het- erospecifics, then species with enhanced risk of interactions between species might display greater numbers of these sexually di- morphic characters. We tested this prediction in eight families of North American birds. In particular, we evaluated whether the number of sexually dimorphic traits was positively associated with species richness at a given site or with degree of sympatry with congeners. We found no strong evidence of enhanced sexual dimorphism with increasing confamilial species richness at a given site. We also found no overall relationship between the number of sexually dimorphic traits and overlap with congeners across these eight families. However, we found patterns consistent with our prediction within Anatidae （ducks, geese and swans） and, to a lesser degree, Parulidae （New World warblers）. Our results suggest that sexually selected plumage traits in these groups potentially play a role in reproductive isolation [Current Zoology 58 （3）： 453--462, 2012].

关键词： Speciation Reproductive character displacement Sexual selection species recognition Reinforcement

A Batesian mimic and its model share color production mechanisms

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Current Zoology 2012年第4期58卷 658-667页

作者： david W. KIKUCHI david W. pfennig Department of Biology University of North Carolina at Chapel Hill Chapel Hill NC 27599-3280 USA

Batesian mimics are harmless prey species that resemble dangerous ones （models）, and thus receive protection from predators. How such adaptive resemblances evolve is a classical problem in evolutionary biology. Mimicry is typically thought to be difficult to evolve, especially if the model and mimic produce the convergent phenotype through different proximate mecha- nisms. However, mimicry may evolve more readily if mimic and model share similar pathways for producing the convergent phenotype. In such cases, these pathways can be co-opted in ancestral mimic populations to produce high-fidelity mimicry with- out the need for major evolutionary innovations. Here, we show that a Batesian mimic, the scarlet kingsnake Larnpropeltis elap-soides, produces its coloration using the same physiological mechanisms as does its model, the eastern coral snake Micrurus fulvius. Therefore, precise color mimicry may have been able to evolve easily in this system. Generally, we know relatively little about the proximate mechanisms underlying mimicry .

关键词： Adaptation Coloration Convergent evolution Pteridine Pigment

The influence of HDL and purified apoprotein E on platelet activation induced by serotonin

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Chinese Medical Journal 1998年第1期111卷 91-91页

作者： Olaf pfennig, Bing Liu and R.Dierichs Platelet Research Unit Institute of Anatomy University of Münster Germany Institute of Physiology Ruhr-University Bochum Bochum Germany

Elevated plasma levels of high density lipoprotein (HDL) are recognized as having a beneficial influence on the progression of atherosclerosis. As platelets are closely involved in atherosclerogenesis, it is difficult to evaluate if the protective effect of HDL is associated with its ability to affect platelet structure and function. Previous studies give conflicting reports concerning the HDL platelet interaction. In our in vitro experiments, washed human blood platelets were preincubated with HDL (100 800 μg/ml) and then stimulated by serotonin (5 Hydroxytryptamine, 1 5 μM), a potent agonist and mediator in the process of atherosclerosis. Aggregatory studies and electron microscopy revealed that HDL could not prevent morphological alterations of blood platelets treated with serotonin. Furthermore, high dosages of HDL led to platelet activation. These findings indicate that HDL may not inhibit agonist induced platelet activation. As HDL is a heterogeneous group of different subclasses with opposite effects on platelet function, it Platelet Research Unit, Institute of Anatomy, University of Münster, Germany (pfennig O and Dierichs R) Institute of Physiology, Ruhr University Bochum, Bochum, Germany (Liu B) can be concluded that HDL platelet interaction reflects relative concentrations of the particular sample. Our findings suggest that the protective influence of HDL may not be associated with decreased platelet function. Apoprotein E rich subclasses of HDL (HDL 2), particularly HDL enriched apoprotein E (HDL E), inhibit agonist induced platelet activation. In order to enlighten the role of apo E in this process, platelets in suspensions were preincubated with purified apoprotein E (50 400 μg/ml) and then stimulated by serotonin (5 μM). Apoprotein E of 300 μg/ml prevented morphological alterations of blood platelets and suppressed serotonin induced activation. Lower concentrated apoprotein E showed no clear effects. There is evid

关键词： HDL The influence of HDL and purified apoprotein E on platelet activation induced by serotonin