Enemy targeting, trade-offs, and the evolutionary assembly of a tortoise beetle defense arsenal

In response to intense enemy selection, immature folivorous insects have evolved elaborate, multi-trait defense arsenals. How enemies foster trait diversification and arsenal assembly depends on which selective mode they impose: whether different enemies select for the same defense or exert conflicting selection on a prey species. Theory has long supposed that the selective advantage of a defense depends on its efficacy against a broad spectrum of enemies, which implies that predator selection is more diffuse than pairwise. Here, we use the multi-trait defense arsenal of the tortoise beetle, Acromis sparsa, which consists of shields, gregariousness and maternal guarding to test whether: (1) diverse enemies have selected for narrowly targeted defenses in the Acromis lineage; (2) newer traits out-performed older ones or vice versa, and; (3) if selection by different enemies results in positive (escalation) trends in defense effectiveness. Because their defenses could be modified or ablated, individuals were rendered differentially protected, and their survival was quantified in a long-term field study. Exclusion experiments evaluated defense efficacy against particular enemy guilds. Logit regression revealed that: (1)no single trait increased survival against the entire enemy suite; (2)trait efficacy was strongly correlated with a particular enemy, consistent with narrow targeting; (3)traits lacked strong cross-resistance among enemies; (4)traits performed synergistically, consistent with the idea of escalation, and; (5)traits interacted negatively to decrease survival, indicative of performance trade-offs. From collation of the phylogenetic histories of arsenal and enemy community assembly we hypothesize that older traits performed better against older enemies and that patterns of both trait and enemy accumulation are consistent with defense escalation. Trade-offs and lack of cross-resistance among defenses imply that enemy selection has been conflicting at the guild level and that negative functional interactions among defenses have fostered the evolution of a defense arsenal of increasing complexity.     

Demographic trade-offs determine species abundance and diversity

Aims Much recent theory has focused on the role of neutral processes in assembling communities, but the basic assumption that all species are demographically identical has found little empirical support. Here, we show that the framework of the current neutral theory can easily be generalized to incorporate species differences so long as fitness equivalence among individuals is maintained through trade-offs between birth and death.Methods Our theory development is based on a careful reformulation of the Moran model of metacommunity dynamics in terms of a non-linear one-step stochastic process, which is described by a master equation.Important findings We demonstrate how fitness equalization through demographic trade-offs can generate significant macroecological diversity patterns, leading to a very different interpretation of the relation between Fisher's α and Hubbell's fundamental biodiversity number. Our model shows that equal fitness (not equal demographics) significantly promotes species diversity through strong selective sieving of community membership against high-mortality species, resulting in a positive association between species abundance and per capita death rate. An important implication of demographic trade-off is that it can partly explain the excessively high speciation rates predicted by the neutral theory of the stronger symmetry. Fitness equalization through demographic trade-offs generalizes neutral theory by considering heterospecific demographic difference, thus representing a significant step toward integrating the neutral and niche paradigms of biodiversity.     

Environment-dependent trade-offs between ectoparasite resistance and larval competitive ability in the Drosophila-Macrocheles system

Costs of resistance are expected to contribute to the maintenance of genetic variation for resistance in natural host populations. In the present study, we experimentally test for genetic trade-offs between parasite resistance and larval competitive ability expressed under varying levels of crowding and temperature. Artificial selection for increased behavioral resistance was applied against an ectoparasitic mite (Macrocheles subbadius) in replicate lines of the fruit fly Drosophila nigrospiracula. We then measured correlated responses to selection in larval competitive ability by contrasting replicate selected and control (unselected) lines in the absence of parasitism. Experiments were conducted under variable environmental conditions: two temperatures and three levels of larval density. Our results reveal a negative genetic correlation between resistance and larval-adult survival under conditions of moderate and severe intra-specific competition. At both low and high temperature, percent emergence was significantly higher among control lines than selected lines. This divergence in larval competitive ability was magnified under high levels of competition, but only at low temperature. Hence, the interaction between selection treatment and larval density was modified by temperature. As predicted, larvae experiencing medium and high levels of competition exhibited an overall reduction in female body size compared to larvae at low levels of competition. Female flies emerging from selected lines were significantly smaller than those females from control lines, but this effect was only significant under conditions of moderate to severe competition. These results provide evidence of environment-dependent trade-offs between ectoparasite resistance and larval competitive ability, a potential mechanism maintaining genetic polymorphism for resistance.     

Ecological immunology: costly parasite defences and trade-offs in evolutionary ecology

In the face of continuous threats from parasites, hosts have evolved an elaborate series of preventative and controlling measures - the immune system - in order to reduce the fitness costs of parasitism. However, these measures do have associated costs. Viewing an individual's immune response to parasites as being subject to optimization in the face of other demands offers potential insights into mechanisms of life history trade-offs, sexual selection, parasite-mediated selection and population dynamics. We discuss some recent results that have been obtained by practitioners of this approach in natural and semi-natural populations, and suggest some ways in which this field may progress in the near future.     

Comparative tests of evolutionary trade-offs in a palinurid lobster acoustic system

Communication structures vary greatly in size and can be structurally and behaviorally integrated with other systems. In structurally integrated systems, dramatic changes in size may impose trade-offs with the size of neighboring structures. In spiny lobsters (Palinuridae), there is a fivefold difference in size of the antennular plate, on which sound producing apparatus is located, such that the antennular plate reaches 38% carapace length in some sound producers (Stridentes) compared to only 4% carapace length in non-sound producing spiny lobsters (Silentes). We examined whether this major variation in antennular plate size imposes trade-offs with the adjoining antennae, specifically in the context that the signal producing structures and antennae are both used in predator defense. We recorded and analyzed lobster sounds in order to test whether size increases in the acoustic morphology were correlated with production of particular signal features. Antennal and antennular plate structures were measured across the family, including both Stridentes and Silentes. Phylogenetic comparative methods were used to test for correlated evolutionary change among the structures and signal features. We analyzed the phylogenetic relationships of the Palinuridae based on morphological characters and ribosomal DNA evidence (16S, 18S and 28S nuclear and mitochondrial ribosomal RNA gene regions). We found that the number of sound pulses was positively correlated with length of the sound producing apparatus. Opposite to the predicted trade-offs, we found that the size of the antennular plate was positively correlated with size of the surrounding antennae within Stridentes. Nevertheless, when Stridentes were compared to Silentes, the latter had relatively larger antennae for a given antennular plate size than did the sound producing taxa. These results suggest that body size does not limit size increases in acoustic structures within Stridentes, however the presence and associated constructional costs of a sound producing apparatus may impose a trade-off when taxa with and without the apparatus are compared. Alternatively, since both systems are used in predator defense, this pattern may indicate greater selection for antennal force production in Silentes, which lack the additional acoustic mode of predator defense.     

Functional and evolutionary trade-offs co-occur between two consolidated memory phases in Drosophila melanogaster

Memory is a complex and dynamic process that is composed of different phases. Its evolution under natural selection probably depends on a balance between fitness benefits and costs. In Drosophila, two separate forms of consolidated memory phases can be generated experimentally: anaesthesia-resistant memory (ARM) and long-term memory (LTM). In recent years, several studies have focused on the differences between these long-lasting memory types and have found that, at the functional level, ARM and LTM are antagonistic. How this functional relationship will affect their evolutionary dynamics remains unknown. We selected for flies with either improved ARM or improved LTM over several generations, and found that flies selected specifically for improvement of one consolidated memory phase show reduced performance in the other memory phase. We also found that improved LTM was linked to decreased longevity in male flies but not in females. Conversely, males with improved ARM had increased longevity. We found no correlation between either improved ARM or LTM and other phenotypic traits. This is, to our knowledge, the first evidence of a symmetrical evolutionary trade-off between two memory phases for the same learning task. Such trade-offs may have an important impact on the evolution of cognitive capacities. On a neural level, these results support the hypothesis that mechanisms underlying these forms of consolidated memory are, to some degree, antagonistic.     

Predation and the evolutionary dynamics of species ranges

Gene flow that hampers local adaptation can constrain species distributions and slow invasions. Predation as an ecological factor mainly limits prey species ranges, but a richer array of possibilities arises once one accounts for how predation alters the interplay of gene flow and selection. We extend previous single-species theory on the interplay of demography, gene flow, and selection by investigating how predation modifies the coupled demographic-evolutionary dynamics of the range and habitat use of prey. We consider a model for two discrete patches and a complementary model for species along continuous environmental gradients. We show that predation can strongly influence the evolutionary stability of prey habitat specialization and range limits. Predators can permit prey to expand in habitat or geographical range or, conversely, cause range collapses. Transient increases in predation can induce shifts in prey ranges that persist even if the predator itself later becomes extinct. Whether a predator tightens or loosens evolutionary constraints on the invasion speed and ultimate size of a prey range depends on the predator effectiveness, its mobility relative to its prey, and the prey's intraspecific density dependence, as well as the magnitude of environmental heterogeneity. Our results potentially provide a novel explanation for lags and reversals in invasions.     

The recurrent assembly of C4 photosynthesis, an evolutionary tale

Today, plants using C₄ photosynthesis are widespread and important components of major tropical and subtropical biomes, but the events that led to their evolution and success started billions of years ago (bya). A CO₂-fixing enzyme evolved in the early Earth atmosphere with a tendency to confuse CO₂ and O₂ molecules. The descendants of early photosynthetic organisms coped with this property in the geological eras that followed through successive fixes, the latest of which is the addition of complex CO₂-concentrating mechanisms such as C₄ photosynthesis. This trait was assembled from bricks available in C₃ ancestors, which were altered to fulfill their new role in C₄ photosynthesis. The existence of C₄-suitable bricks probably determined the lineages of plants that could make the transition to C₄ photosynthesis, highlighting the power of contingency in evolution. Based on the latest findings in C₄ research, we present the evolutionary tale of C₄ photosynthesis, with a focus on the general evolutionary phenomena that it so wonderfully exemplifies.     

Functional trait assembly through ecological and evolutionary time

A classic community assembly hypothesis is that all guilds must be represented before additional species from any given guild enter the community. We conceptually extend this hypothesis to continuous functional traits, refine the hypothesis with an eco-evolutionary model of interaction network community assembly, and compare the resultant continuous trait assembly rule to empirical data. Our extension of the “guild assembly rule” to continuous functional traits was rejected, in part, because the eco-evolutionary model predicted trait assembly to be characterized by the expansion of trait space and trait/species sorting within trait space. Hence, the guild rule may not be broadly applicable. A “revised” assembly rule did, however, emerge from the eco-evolutionary model: as communities assemble, the range in trait values will increase to a maximum and then remain relatively constant irrespective of further changes in species richness. This rule makes the corollary prediction that the trait range will, on average, be a saturating function of species richness. To determine if the assembly rule is at work in natural communities, we compared this corollary prediction to empirical data. Consistent with our assembly rule, trait “space” (broadly defined) commonly saturates with species richness. Our assembly rule may thus represent a general constraint placed on community assembly. In addition, taxonomic scale similarly influences the predicted and empirically observed relationship between trait “space” and richness. Empirical support for the model’s predictions suggests that studying continuous functional traits in the context of eco-evolutionary models is a powerful approach for elucidating general processes of community assembly.     

Local orientation and the evolution of foraging: changes in decision making can eliminate evolutionary trade-offs

Information processing is a major aspect of the evolution of animal behavior. In foraging, responsiveness to local feeding opportunities can generate patterns of behavior which reflect or "recognize patterns" in the environment beyond the perception of individuals. Theory on the evolution of behavior generally neglects such opportunity-based adaptation. Using a spatial individual-based model we study the role of opportunity-based adaptation in the evolution of foraging, and how it depends on local decision making. We compare two model variants which differ in the individual decision making that can evolve (restricted and extended model), and study the evolution of simple foraging behavior in environments where food is distributed either uniformly or in patches. We find that opportunity-based adaptation and the pattern recognition it generates, plays an important role in foraging success, particularly in patchy environments where one of the main challenges is "staying in patches". In the restricted model this is achieved by genetic adaptation of move and search behavior, in light of a trade-off on within- and between-patch behavior. In the extended model this trade-off does not arise because decision making capabilities allow for differentiated behavioral patterns. As a consequence, it becomes possible for properties of movement to be specialized for detection of patches with more food, a larger scale information processing not present in the restricted model. Our results show that changes in decision making abilities can alter what kinds of pattern recognition are possible, eliminate an evolutionary trade-off and change the adaptive landscape.     

The evolutionary trade-offs in phage-resistant Klebsiella pneumoniae entail cross-phage sensitization and loss of multidrug resistance

Bacteriophage therapy is currently being evaluated as a critical complement to traditional antibiotic treatment. However, the emergence of phage resistance is perceived as a major hurdle to the sustainable implementation of this antimicrobial strategy. By combining comprehensive genomics and microbiological assessment, we show that the receptor-modification resistance to capsule-targeting phages involves either escape mutation(s) in the capsule biosynthesis cluster or qualitative changes in exopolysaccharides, converting clones to mucoid variants. These variants introduce cross-resistance to phages specific to the same receptor yet sensitize to phages utilizing alternative ones. The loss/modification of capsule, the main Klebsiella pneumoniae virulence factor, did not dramatically impact population fitness, nor the ability to protect bacteria against the innate immune response. Nevertheless, the introduction of phage drives bacteria to expel multidrug resistance clusters, as observed by the large deletion in K. pneumoniae 77 plasmid containing bla_CTX-M, ant(3″), sul2, folA, mph(E)/mph(G) genes. The emerging bacterial resistance to viral infection steers evolution towards desired population attributes and highlights the synergistic potential for combined antibiotic-phage therapy against K. pneumoniae.     

Taxonomic, evolutionary and ecological implications of the leaf anatomy of rhizomatous Iris species

The leaf anatomy of the rhizomatous Iris species with ensiform leaves and the related genera Pardanthopsis and Belamcanda is described. Their isobilateral leaves may or may not have a pseudo-dorsiventral structure. Variable characters of their leaf blades include: outline in transverse section, height and shape of papillae, form and structure of stomata, transverse section outline of marginal fibre strands and sclerenchy matous inner bundle sheath at phloem and xylem poles, forms of mesophyll arrangement, mesophyll structure and air canals, vascular bundle arrangement and the detailed structure of the larger vascular bundles, distribution of tannin, size and distribution of crystals. The taxonomic and ecological significance of these characters has been evaluated.
The anatomical characteristics of 25 supraspecific taxa in three genera are presented and compared in tables. The relationships and evolutionary position of these taxa are discussed. Each of the three subgroups within Iris appears to be correlated with a syndrome of anatomical characters. Some species currently of uncertain taxonomic position are discussed, and their classification based on anatomical data is suggested.
Some characters related to xeromorphy or helomorphy are mentioned.