Kin selection and the Evolution of Mutualisms between Species

Hamilton's theory of kin selection has revolutionized and inspired fifty years of additional theories and experiments on social evolution. Whereas Hamilton's broader intent was to explain the evolutionary stability of cooperation, his focus on shared genetic history appears to have limited the application of his theory to populations within a single species rather than across interacting species. The evolutionary mechanisms for cooperation between species require both spatial and temporal correlations among interacting partners for the benefits to be not only predictable but of sufficient duration to be reliably delivered. As a consequence when the benefits returned by mutualistic partners are redirected to individuals other than the original donor, cooperation usually becomes unstable and parasitism may evolve. However, theoretically, such redirection of mutualistic benefits may actually reinforce, rather than undermine, mutualisms between species when the recipients of these redirected benefits are genetically related to the original donor. Here, I review the few mathematical models that have used Hamilton's theory of kin selection to predict the evolution of mutualisms between species. I go on to examine the applicability of these models to the most well‐studied case of mutualism, pollinating seed predators, where the role of kin selection may have been previously overlooked. Future detailed studies of the direct, and indirect, benefits of mutualism are likely to reveal additional possibilities for applying Hamilton's theory of kin selection to mutualisms between species.     

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.     

Species-Specific Seed Dispersal in an Obligate Ant-Plant Mutualism

Throughout lowland Amazonia, arboreal ants collect seeds of specific plants and cultivate them in nutrient-rich nests, forming diverse yet obligate and species-specific symbioses called Neotropical ant-gardens (AGs). The ants depend on their symbiotic plants for nest stability, and the plants depend on AGs for substrate and nutrients. Although the AGs are limited to specific participants, it is unknown at what stage specificity arises, and seed fate pathways in AG epiphytes are undocumented. Here we examine the specificity of the ant-seed interaction by comparing the ant community observed at general food baits to ants attracted to and removing seeds of the AG plant Peperomia macrostachya. We also compare seed removal rates under treatments that excluded vertebrates, arthropods, or both. In the bait study, only three of 70 ant species collected P. macrostachya seeds, and 84% of observed seed removal by ants was attributed to the AG ant Camponotus femoratus. In the exclusion experiment, arthropod exclusion significantly reduced seed removal rates, but vertebrate exclusion did not. We provide the most extensive empirical evidence of species specificity in the AG mutualism and begin to quantify factors that affect seed fate in order to understand conditions that favor its departure from the typical diffuse model of plant-animal mutualism.     

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.     

Mutualisms in a changing world: an evolutionary perspective

Ecology Letters (2010) 13: 1459-1474 ABSTRACT: There is growing concern that rapid environmental degradation threatens mutualistic interactions. Because mutualisms can bind species to a common fate, mutualism breakdown has the potential to expand and accelerate effects of global change on biodiversity loss and ecosystem disruption. The current focus on the ecological dynamics of mutualism under global change has skirted fundamental evolutionary issues. Here, we develop an evolutionary perspective on mutualism breakdown to complement the ecological perspective, by focusing on three processes: (1) shifts from mutualism to antagonism, (2) switches to novel partners and (3) mutualism abandonment. We then identify the evolutionary factors that may make particular classes of mutualisms especially susceptible or resistant to breakdown and discuss how communities harbouring mutualisms may be affected by these evolutionary responses. We propose a template for evolutionary research on mutualism resilience and identify conservation approaches that may help conserve targeted mutualisms in the face of environmental change.     

Spatial and Temporal Variation in the Ant Occupants of a Facultative Ant-Plant1

Striking variation in ant occupation of a facultative ant-plant, Conostegia setosa (Melastomataceae), was found at three scales: local spatial, geographic, and temporal. C. setosa provides housing for ants and grows in groups of stems (clones). The ant occupants of 14 C. setosa clones were censused four times over a 14-mo period at the La Selva Biological Station, Costa Rica, and twice over a 9-mo period at the Nusagandi Station, Panama. Twelve facultative ant species occupied C. setosa stems at La Selva, compared to six facultative and one obligate species at Nusagandi. Occupancy (as % of stems ever occupied/clone) was higher at Nusagandi (median = 89%) compared to La Selva (65%). Occupancy varied among clones at La Selva but not at Nusagandi. C. setosa clones differed between sites, with larger clones and more small stems/clone at La Selva. Occupancy was influenced by clone structure; larger clones contained more ant species at both sites and had lower occupancy at La Selva. Occupancy was highest in larger stems and lowest in small stems at both sites. Temporally, percent occupation/clone did not differ among censuses at either site, but overall occupancy was lower in the dry season at La Selva. Turnover in ant occupants was higher at La Selva than at Nusagandi. The variation observed in this study is likely due to a number of factors, including differences between sites in plant population structure and history, differences between and within sites in ant faunas and their nesting requirements, and changes over space and time in microclimatic variables. Such high variation at multiple scales draws attention to the importance of long-term comparative studies of facultative animal-plant interactions.     

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.     

The Genomes of Two Billfishes Provide Insights into the Evolution of Endothermy in Teleosts

Endothermy is a typical convergent phenomenon which has evolved independently at least eight times in vertebrates, and is of significant advantage to organisms in extending their niches. However, how vertebrates other than mammals or birds, especially teleosts, achieve endothermy has not previously been fully understood. In this study, we sequenced the genomes of two billfishes (swordfish and sailfish), members of a representative lineage of endothermic teleosts. Convergent amino acid replacements were observed in proteins related to heat production and the visual system in two endothermic teleost lineages, billfishes and tunas. The billfish-specific genetic innovations were found to be associated with heat exchange, thermoregulation, and the specialized morphology, including elongated bill, enlarged dorsal fin in sailfish and loss of the pelvic fin in swordfish.     

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。