The Evolution of Vocal Communication: Inertia and Divergence in Two Closely Related Primates

International Journal of Primatology - Primate vocal repertoires change slowly over evolutionary time, making them good indicators of phylogenetic relatedness. Occasionally, however,...     

The Stability and Persistence of Mutualisms Embedded in Community Interactions

In this paper we argue that two-species models of mutualism may be oversimplifications of the real world that lead to erroneous predictions. We present a four-species model of a pollination mutualism embedded in other types of community interactions. Conclusions derived from two-species models about the destabilizing effect of mutualisms are misleading when applied to the present scenario; although the mutualisms are locally destabilizing, the effect is more than canceled by an increased chance of feasibility. The crucial difference is the interaction of the mutualists with other species in a larger web. Furthermore, community persistence (without unrealistic population explosion), arguably a superior ecological criterion, is greatly enhanced by the presence of mutualisms. Therefore, we predict that mutualisms should be common in the real world, a prediction matching empirial findings and in contrast to the predictions from local stability analysis of basic two-species models. This method of stabilizing a mutualism appears superior in some ways to the often-used method of introducing density dependence in the strength of the mutualism, because it permits obligate mutualisms to exist even at low densities, again matching empirical findings. Lastly, this study is an example of how complex model assemblages can behave qualitatively differently from analogous simpler ones.     

The Role of Off-line Communication in Human Evolution

The existence of embodied communication in humans places them among other living systems and helps to differentiate sign patterns that are common to all bioforms from those that are peculiarly human. Despite the fact that the biological roots of communication have been proven, the understanding of human forms of discourse is still far from being clarified. The main question remains: when and why did humans acquire the ability to exchange messages via speech? My thesis is that it became possible only after humans made a shift from on-line to off-line interaction and learned to communicate in the interpersonal mode via externalized analog codes that constitute the various forms of human culture.     

The Contribution of Ant-Plant Protection Studies to Our Understanding of Mutualism1

One common class of ant-plant mutualism involves ants that defend plants from natural enemies in return for food and sometimes shelter. Studies of these interactions have played a major role in shaping our broad understanding of mutualism. Their central contribution has come via their development of approaches to measuring the benefits, costs, and net outcomes of mutualism, and their explicit consideration of variability in all of these phenomena. Current research on these interactions is suggesting ecological and evolutionary hypotheses that may be applicable to many other forms of mutualism. It is also generating comparative data for testing the few general theories about mutualism that currently exist.     

The Evolution of Cell-to-Cell Communication in a Sporulating Bacterium

Traditionally microorganisms were considered to be autonomous organisms that could be studied in isolation. However, over the last decades cell-to-cell communication has been found to be ubiquitous. By secreting molecular signals in the extracellular environment microorganisms can indirectly assess the cell density and respond in accordance. In one of the best-studied microorganisms, Bacillus subtilis, the differentiation processes into a number of distinct cell types have been shown to depend on cell-to-cell communication. One of these cell types is the spore. Spores are metabolically inactive cells that are highly resistant against environmental stress. The onset of sporulation is dependent on cell-to-cell communication, as well as on a number of other environmental cues. By using individual-based simulations we examine when cell-to-cell communication that is involved in the onset of sporulation can evolve. We show that it evolves when three basic premises are satisfied. First, the population of cells has to affect the nutrient conditions. Second, there should be a time-lag between the moment that a cell decides to sporulate and the moment that it turns into a mature spore. Third, there has to be environmental variation. Cell-to-cell communication is a strategy to cope with environmental variation, by allowing cells to predict future environmental conditions. As a consequence, cells can anticipate environmental stress by initiating sporulation. Furthermore, signal production could be considered a cooperative trait and therefore evolves when it is not too costly to produce signal and when there are recurrent colony bottlenecks, which facilitate assortment. Finally, we also show that cell-to-cell communication can drive ecological diversification. Different ecotypes can evolve and be maintained due to frequency-dependent selection.     

Evolution and Function of Drumming as Communication in Mammals

An amazing variety of mammals produce seismic vibrations bydrumming a part of their body on a substrate. The drumming cancommunicate multiple messages to conspecifics about territorialownership, competitive superiority, submission, readiness tomate, or presence of predators. Drumming also functions in interspecificcommunication when prey animals drum to communicate to predatorsthat they are too alert for a successful ambush. The diversityof mammals that drum in varied contexts suggest independentevolution in different lineages. Footdrumming, as with othersignals, probably originated by ritualization of older formsof behavior not associated with communication such as runningand digging. Footdrumming patterns are species specific andrange from single thumps to individual footdrum signatures.Although mammals communicate above ground with airborne drummingsignals, they can also transmit sound seismically into the burrowwhere the signals become airborne and are received with earsespecially adapted to hear low-frequency sound. Footdrumminghas been studied the most extensively in kangaroo rats, Dipodomys.A comparison of species of different body mass shows that smallersized, non-territorial species have no ritualized footdrumming;medium-sized species drum a simple pattern in limited contexts;while larger-sized species communicate territorial ownershipwith complex patterns. Future studies should examine the mechanicsand energy requirements of drumming to test hypotheses aboutbody size limitations on the evolution of footdrumming. Ourunderstanding of drumming as communication is limited untilinvestigators conduct field tests of responses to drumming signalsin the contexts in which the signals are generated.     

Evolution of Resistance in the Presence of Two Insecticides

A two-locus model is used to analyze the effectiveness of a mixture of insecticides in delaying resistance, compared to the use of the insecticides singly. The effects of factors such as recombination, effective dominance, initial value of allele frequencies and initial value of linkage disequilibrium are considered. It is shown that the use of mixtures is always more effective in delaying the onset of resistance, often by many orders of magnitude. It is shown that there exists a threshold value of recombination fraction, above which the evolution of resistance is extremely slow. Resistance evolves very rapidly for values of recombination fraction below the threshold. Finally, the relevance of these results on resistance management is discussed.     

乙型流行性感冒病毒两大谱系的起源及其演变特征

测定1972－2000年间在中国分离并保存的乙型流行性感冒（流感）病毒一些毒株的HA1区核苷酸序列,结合GenBank中其它毒株的相关序列以及流行病学资料进行分析。结果提示,当前在世界上流行的乙型流感病毒两大谱系起源于20世纪70年代中期,而不是以前推测的60年代末,并且其中一个谱系起源于中国。结果还提示,乙型流感病毒的演变同时受到很强的正选择与负选择的作用,而以前人们认为选择对乙型流感病毒的演变作用甚微。还修正了乙型流感病毒变异速率的计算方法。     

The Cultural Evolution of Human Communication Systems in Different Sized Populations: Usability Trumps Learnability

This study examines the intergenerational transfer of human communication systems. It tests if human communication systems evolve to be easy to learn or easy to use (or both), and how population size affects learnability and usability. Using an experimental-semiotic task, we find that human communication systems evolve to be easier to use (production efficiency and reproduction fidelity), but harder to learn (identification accuracy) for a second generation of naïve participants. Thus, usability trumps learnability. In addition, the communication systems that evolve in larger populations exhibit distinct advantages over those that evolve in smaller populations: the learnability loss (from the Initial signs) is more muted and the usability benefits are more pronounced. The usability benefits for human communication systems that evolve in a small and large population is explained through guided variation reducing sign complexity. The enhanced performance of the communication systems that evolve in larger populations is explained by the operation of a content bias acting on the larger pool of competing signs. The content bias selects for information-efficient iconic signs that aid learnability and enhance usability.     

Geographical and Seasonal Variation in the Richness of Ant-Plant Interactions in México1

The richness and seasonal variation of ant-plant interactions were compared in four habitats in México: lowland tropical dry forest (La Mancha, Veracruz), coastal sand dune matorral (San Benito, Yucatán), semiarid highland vegetation (Zapotitlán, Puebla), and lower montane humid forest (Xalapa, Veracruz). The effects of temperature and precipitation on the seasonal distribution of the number of ant-plant interactions differed among habitats. The general linear models fitted to the ant-plant interaction curves explained 78.8 percent of the variation for La Mancha, 80.1 percent for Zapotitlán, 18 percent for San Benito, and 29.5 percent for Xalapa. Even though rainfall is low in Zapotitlán and San Benito, minimum temperature was the most important factor accounting for the seasonal distribution and low number of interactions. At La Mancha, with milder minimum temperatures and higher water availability, temperature alone did not account for the seasonal distribution and number of interactions, whereas the effect of the precipitation × temperature interaction was highly significant. Xalapa exhibits the lowest temperatures and the highest precipitation, but the role of these factors was only marginal. We suggest that the vegetation at Xalapa, a mixture of tropical and temperate floristic elements, constrains ant-plant interactions due to a limited presence of nectaries. Also, ants are less abundant in cool and relatively aseasonal habitats. The other habitats have tropical floristic elements that are abundant and frequently have nectar-producing structures. We report considerable variation among habitats in the number and seasonal distribution of ant-plant interactions, and suggest that it is due to the effect of variation in environmental parameters, the richness of plants with nectaries in the vegetation, and habitat heterogeneity.     

Facultative Ant-Plant Interactions: Nectar Sugar Preferences of Introduced Pest Ant Species in South Florida1

We observed nectar use by native and exotic ant species in nature, garden, and urban situations, and found ants utilizing floral and extrafloral nectar of a variety of flowering plant species. We collected 31 plant nectars (29 floral, 2 extrafloral) and used them in feeding preference tests against standard solutions of sugars (20 percent fructose, glucose, and sucrose, and their mixture), 10 trials for each nectar-ant comparison. We compared time-to-discovery and total ant visits to each droplet using ANOVA, and found that both trial and solution contributed significantly to the variation in most experiments. Seven of the floral nectars tested were significantly more attractive to certain ant species than the sugar solutions. Not only do ants use floral nectar, but it appears that some floral nectars contain compounds that are especially attractive to ants.     

Evolution of Swarm Communication in Eusocial Wasps (Hymenoptera: Vespidae)

Eusocial paper wasps, yellowjackets, and hornets (Vespidae) exhibit two modes of colony foundation, primitively eusocial independent founders and advanced eusocial swarm founders. Unlike independent founders, swarmfounding wasps require a means of social communication to coordinate the movement of colony members between nest sites. We employed a phylogeny of paper wasps, yellowjackets, and hornets to test for patterns of correlated evolution between the mode of colony foundation and the presence of sternal exocrine glands. We also reviewed data on worker actions during swarming to determine whether swarm communication behavior was dependent upon gland possession and whether communicative behavior was shared among swarm-founding species. We did not find evidence for an association of sternal glands with swarm founding. Although sternal gland presence differed among swarm-founding species, worker behavior during swarming showed little variation. Workers of nearly all swarm-founding species rub their gasters on objects along swarm routes, independently of the occurrence of sternal glands. Widespread gastral rubbing indicates the use of swarm emigration trail pheromones from a diversity of glandular sources. Transitions from independent to swarm founding have been achieved via diverse pheromonal mechanisms in the Vespidae, while worker communicative behavior is either highly conserved or convergent.     

Vibrational Communication in Two Sympatric Species of Mantophasmatodea (Heelwalkers)

The communication via percussion of the abdomen on the substrate for species recognition and mate location of males and females of two sympatric species of the recently described insect order Mantophasmatodea (Heelwalkers) was investigated. Each sex produced a single and distinctive call. The female call consisted of repeated single pulses, whereas the more complex male call comprised repeated pulse trains. The calls of males and females of the two species were of similar general structure, but differed in most temporal characters such as pulse and pulse train repetition time. In behavioral playback experiments females reacted to the call of conspecific males by calling and decreasing locomotion. When stimulated with the call of the heterospecific, sympatric male, females showed no reaction. Males exhibited abdominal rubbing, high tapping rates, increased activity (both movement and active searching) as well as characteristic searching behavior at branch nodes, when presented with the conspecific female call. Being stimulated with the playback of the heterospecific female call and the conspecific male call respectively, males responded with less intense locomotor and searching behavior. The drumming behavior in the control situation (no playback) suggests that males sometimes call in the absence of other individuals.