Just in time: Circadian defense patterns and the optimal defense hypothesis

The optimal defense hypothesis (ODH) provides a functional explanation for the inhomogeneous distribution of defensive structures and defense metabolites throughout a plant’s body: tissues that are most valuable in terms of fitness and have the highest probability of attack are generally the best defended. In a previous review,¹ we argue that ontogenically-controlled accumulations of defense metabolites are likely regulated through an integration of developmental and defense signaling pathways. In this addendum, we extend the discussion of ODH patterns by including the recent discoveries of circadian clock-controlled defenses in plants.     

Modes of cooperation during territorial defense by African lions

Cooperation during territorial defense allows social groups of African lions to defend access to resources necessary for individual reproductive success. Some forms of cooperation will be dependent upon cognition: reciprocity places greater cognitive demands on participants than does kinship or mutualism. Lions have well-developed cognitive abilities that enable individuals to recognize and interact with others in ways that seem to enhance their inclusive fitness. Male lions appear to cooperate unconditionally, consistently responding to roaring intruders regardless of their male companions’ kinship or behavior. Female lions, however, do keep track of the past behavior of their female companions, apparently using the reliability of a companion as one means of assessing the risks posed by approaching intruders. Some “laggard” females may exploit the cooperative tendencies of “leaders” during territorial encounters. Although leader females clearly recognize laggards as such, the costs of tolerating laggards may be less than the benefits leaders gain through territorial defense behavior. Thus, although lions clearly have the cognitive ability to base cooperation on reciprocity, territorial defense cooperation appears instead to be based primarily on mutual benefits to participants for both male and female lions.     

The importance of species identification and location on interspecific territorial defense by the damselfish,Stegastes fasciolatus

Synopsis The Hawaiian damselfish, Stegastes fasciolatus, defends an all-purpose territory on shallow-water reefs. By conceptually dividing each territory into 3 horizontal and 2 vertical zones, each intruder into the territory was recorded by species, zones violated, and reaction of the resident. Intruders included 3 herbivorous, 7 omnivorous, and 2 carnivorous species. A BMDP 4F analysis for multiway tables was applied to examine the relationships between the proximate causal factors eliciting the chase response by a resident. Species of intruder and their position in the territory had an additive effect on the chase response, with position in the territory as the less important factor. Distance from the bottom was not indicated as an important factor. The ecological implications of these results are discussed.Senior author     

The large genome constraint hypothesis: evolution, ecology and phenotype

BACKGROUND AND AIMS: If large genomes are truly saturated with unnecessary 'junk' DNA, it would seem natural that there would be costs associated ith accumulation and replication of this excess DNA. Here we examine the available evidence to support this hypothesis, which we term the 'large genome constraint'. We examine the large genome constraint at three scales: evolution, ecology, and the plant phenotype. SCOPE: In evolution, we tested the hypothesis that plant lineages with large genomes are diversifying more slowly. We found that genera with large genomes are less likely to be highly specious -- suggesting a large genome constraint on speciation. In ecology, we found that species with large genomes are under-represented in extreme environments -- again suggesting a large genome constraint for the distribution and abundance of species. Ultimately, if these ecological and evolutionary constraints are real, the genome size effect must be expressed in the phenotype and confer selective disadvantages. Therefore, in phenotype, we review data on the physiological correlates of genome size, and present new analyses involving maximum photosynthetic rate and specific leaf area. Most notably, we found that species with large genomes have reduced maximum photosynthetic rates - again suggesting a large genome constraint on plant performance. Finally, we discuss whether these phenotypic correlations may help explain why species with large genomes are trimmed from the evolutionary tree and have restricted ecological distributions. CONCLUSION: Our review tentatively supports the large genome constraint hypothesis.     

Behavioral ecology of disturbed landscapes: the response of territorial animals to relocation

Intraspecific territorial interactions are common for a largevariety of wildlife species. This often results in high-qualityhabitat being occupied by dominant individuals, with subordinatesrelegated to lower quality habitat. The role that these territorialinteractions play in influencing the redistribution of animalsthat have been evicted from their native home ranges remainsunclear. My goals were to determine (1) how the density of conspecificsin the new habitats impacts resettlement patterns and (2) towhat extent prior dominance status is maintained when an animalis forced to relocate. I relocated white-footed mice (Peromyscusleucopus) from high-quality, oak-dominated hardwood and lowerquality, white pine forests to novel sites and released themalong the ecotone of these two habitat types. I relocated micefirst in the presence and then in the absence of a natural densityof resident mice. Habitat selection and resource acquisitionof relocated mice were assessed via mark-recapture livetrappingand passive integrated transponder tagging. Relocated mice selectedhigh-quality habitat significantly more often when residentmice were absent, illustrating the importance of territorialinteractions for determining resettlement patterns of relocatedindividuals. Data on resource acquisition also reflected thecompetitive influence of resident mice—relocated micewere significantly more successful accessing food resourcesin the treatment without residents. The habitat of origin didnot significantly impact habitat selection or resource acquisition,indicating that all relocated individuals were at a disadvantagecompared to residents.     

Community ecology of helminth parasitism in an insular passerine avifauna.

Three hundred and thirty specimens of 7 species of passerine birds from South Bass Island, Ottawa County, Ohio, were examined for helminth parasites. The total number of helminth specimens collected was 4,333. Forty-one helminth taxa were identified. Ten species of helminths were identified as having foci of infection on the island. An index of association for these 10 species is presented. The low association revealed between helminth species utilizing common species of intermediate hosts indicated that a single intermediate host specimen is likely to harbor infective stages of only one species of parasitic helminth. An index of similarity is presented to express the species importance relationships of the helminth faunas of the 7 species of birds: red-winged blackbirds (Agelaius phoeniceus), blue jays (Cyanocitta cristata), brown-headed cowbirds (Molothrus ater), common grackles (Quiscalus quiscula), house sparrows (Passer domesticus), starlings (Sturnus vulgaris), and robins (Turdus migratorius). The results reveal that competition between these avian species for invertebrate food resources helps to maximize the transmission of those helminth populations which utilize these same invertebrates as intermediate hosts. The aggregation of birds into mixed feeding flocks insures a heavy loading of the feeding grounds with agents infective for the invertebrate populations.     

Interpretation of territorial behaviour in terms of a critical disability hypothesis

The hypothesis is that the great majority of behaviour relating to territorial defence presents difficult anomalies in terms of the normal explanatory mechanism of individual selection. Many, if not all, of the difficulties involved can be solved by using a critical disability hypothesis based upon the principle of group selection. Given this latter model, it is possible to predict the development of (1) highly variable territories, (2) microterritories and (3) macroterritories.     

The defense hypothesis of elemental hyperaccumulation: status,challenges and new directions

Elemental hyperaccumulation may have several functions, including plant defense against natural enemies. A total of 34 studies, including 72 experimental tests, have been conducted to date. At least some tests have demonstrated defense by hyperaccumulated As, Cd, Ni, Se and Zn, but relatively few plant taxa and natural enemies have been investigated. Defense by hyperaccumulated Ni has been shown for most leaf/root chewing herbivores and pathogens tested (20 of 26 tests) but not for herbivores of other feeding modes (1 of 8 tests). Most tests (5 of 6) using Ni concentrations below accumulator levels found no defensive effect, and the single test using plants in the accumulator range also found no effect. For Zn, mixed results have been reported for both hyperaccumulator (3 of 6 tests showed defense) and accumulator levels (3 of 4 tests showed defense). These tests have focused exclusively on leaf chewing/scraping herbivores: no herbivores of other feeding modes, or pathogens, have been tested. Both hyperaccumulator and accumulator concentrations of Se generally have shown defensive effects (12 of 14 tests). Most (75%) of these positive results used plants with accumulator Se concentrations. The three tests of Cd showed defensive effects in two cases, one for hyperaccumulator and one for sub-accumulator Cd concentrations. Arsenic has been tested only once, and was found effective against a leaf-chewing herbivore at a concentration much less than the hyperaccumulator level. Defense studies have used a variety of experimental approaches, including choice and no-choice experiments as well as experiments that use artificial diet or growth media. Investigations of hyperaccumulation as a defense against natural enemies have led to two emerging questions. First, what is the minimum concentration of an element sufficient for defense? Evidence suggests that plants other than hyperaccumulators (such as accumulators) may be defended by elements against some natural enemies. Second, do the effects of an element combine with the effects of organic defensive compounds in plants to produce enhanced joint defensive effects? Recent investigation of this “joint effects hypothesis,” using Ni and secondary plant compounds in artificial insect diet, has demonstrated joint effects. Initial answers to both these questions suggest that defensive effects of elements in plants are more widespread than previously believed. These results also suggest an evolutionary pathway by which elemental hyperaccumulation may have evolved from accumulation. In this “defensive enhancement” scenario, defensive benefits of elevated levels of elements may have led to stepwise increases in element concentrations that further magnified these benefits. This series of steps could have led to increased accumulation, and ultimately hyperaccumulation, of elements by plants.     

Group-structured genetic models in analyses of the population and behavioral ecology of poikilothermic vertebrates

Estimates of gene correlations among individuals within and among populations are frequently derived from statistical analyses of genetic data (e.g., F statistics). These measures can be important tools in molecular ecology and conservation, and offer important insights into population breeding structure. Using recently derived theory developed for group-structured populations, we show that fixation indices, when combined with basic population ecological and demographic data can be used to investigate population mating systems and to predict dispersal rates, trajectories and asymptotic levels of fixation indices, and effective population size. Four case studies of poikilothermic vertebrates are used to demonstrate the broad utility of evolutionary and ecological inferences afforded by group-structured models.     

Tracking ecology over geological time: evolution within guilds of vertebrates

Community structure, stability and change can be observed in the fossil record over timescales that far exceed what is possible in the present. Recent quantitative studies on ecological structure withion ancient guilds of various vertebrate predators, inlcuding birds, mammals and reptiles, have revealed a common pattern of iterative replacement of feeding ecomorphs over time, despite large differences in phylogenetic composition. As a result, patterns of resource division among sympatric carnivores remain stable over many millions of years and probably reflect interspecific competition and aspects of the food resource.     

The chemical defense ecology of marine unicellular plankton: constraints, mechanisms, and impacts

The activities of unicellular microbes dominate the ecology of the marine environment, but the chemical signals that determine behavioral interactions are poorly known. In particular, chemical signals between microbial predators and prey contribute to food selection or avoidance and to defense, factors that probably affect trophic structure and such large-scale features as algal blooms. Using defense as an example, I consider physical constraints on the transmission of chemical information, and strategies and mechanisms that microbes might use to send chemical signals. Chemical signals in a low Re, viscosity-dominated physical environment are transferred by molecular diffusion and laminar advection, and may be perceived at nanomolar levels or lower. Events that occur on small temporal and physical scales in the "near-field" of prey are likely to play a role in cell-cell interactions. On the basis of cost-benefit optimization and the need for rapid activation, I suggest that microbial defense system strategies might be highly dynamic. These strategies include compartmented and activated reactions, utilizing both pulsed release of dissolved signals and contact-activated signals at the cell surface. Bioluminescence and extrusome discharge are two visible manifestations of rapidly activated microbial defenses that may serve as models for other chemical reactions as yet undetected due to the technical problems of measuring transient chemical gradients around single cells. As an example, I detail an algal dimethylsulfoniopropionate (DMSP) cleavage reaction that appears to deter protozoan feeding and explore it as a possible model for a rapidly activated, short-range chemical defense system. Although the exploration of chemical interactions among planktonic microbes is in its infancy, ecological models from macroorganisms provide useful hints of the complexity likely to be found.     

The ecology of communities of related animal species (research approaches and methods exemplified by terrestrial vertebrates)]

The review is dedicated to some old and modern problems in studying of the assemblages of phylogenetically related species among terrestrial vertebrates. The classical approach by Robert Mac-Arthur, discussed elsewhere summarized briefly. Although an explanative potential of competition theory seems exhausted there is no new paradigm that can simply explain species diversity in natural communities. From the beginning of 90's community ecology became very complex and controversial discipline. At the same time it is still a pioneering science. We have not enough comparative data on geo2 graphically distinct communities studied under the unified methods of data collection and analysis. Some recent results of intercontinental comparisons signify to the high degree of individualism in structure of geographically isolated communities. This makes doubtful any extrapolation from one region to another. Examination and explanation of processes is still the most contradictory field in community ecology. Confusion of causes and effects is continuing to be serious methodological problem. Much of attention was paid recently to the macroecological approach. A desire for reconsideration of some "old rules" of biodiversity is explained by advances in paleozoology, biogeography and systematic, as well as by some unsatisfactory explanations within the framework of competition theory.     

Analysis of the phylogenetic distribution of isochores in vertebrates and a test of the thermal stability hypothesis

Warm-blooded vertebrates show large-scale variation in G + C content along their chromosomes, a pattern which appears to be largely absent from cold-blooded vertebrates. However, compositional variation in poikilotherms has generally been studied by ultracentrifugation rather than sequence analysis. In this paper, we investigate the compositional properties of coding sequences from a broad range of vertebrate poikilotherms using DNA sequence analysis. We find that on average poikilotherms have lower third-codon position GC contents (GC3) than homeotherms but that some poikilotherms have higher mean GC3 values. We find that most poikilotherms have lower variation in GC3 than homeotherms but that there is a correlation between GC12 and GC3 for some species, indicating that there is systematic variation in base composition across their genomes. We also demonstrate that the GC3 of genes in the zebrafish, Danio rerio, is correlated with that in humans, suggesting that vertebrates share a basic isochore structure. However, we find no correlation between either the mean GC3 or the standard deviation in GC3 and body temperature.     

The relative costs and benefits of territorial defense and the two conditional male mating tactics in the Comanche Springs pupfish (Cyprinodon elegans)

We examined the aggressive costs and reproductive benefits of territorial defense and its alternatives in a population of the Comanche Springs pupfish (Cyprinodon elegans). The breeding system was characterized by three different male mating tactics: territorial defense, satellite positioning, and sneak spawning. The mating tactic adopted by males reflected the males' sizes. Territorial residents were the largest, satellites were medium-sized, and sneakers were the smallest adult males observed. Consistent with the hypothesis that primary mating tactics are relatively high-cost, high-benefit strategies, we found that territorial males engaged in a number of aggressive encounters but had higher reproductive successes than any other males. However, our observations did not support the premise that conditionally breeding males engage in relatively low-benefit, low-cost tactics. Medium satellites and small sneakers acquired fewer spawns than did territorial males, but both satellites and sneakers were involved in as much aggression as territorials. That is, the data supported the prediction that satellite or sneaker males with the inability to compete for territories would attempt to accrue some reproductive opportunities in the presence of territorial males despite the high costs of spending time on the breeding grounds. Adopting conditional tactics appeared to allow satellites and sneakers to make the best of a bad situation. During a subsequent breeding season, large males were absent from the population, and medium-sized males established territories. The aggressive behavior exhibited by medium residents was similar to the previous year, but these males did not acquire higher reproductive successes than medium satellites had. The implications of switching tactics and the influence of operational sex ratios on the costs and benefits of the male tactics are briefly addressed. Electronic Publication     

Testing the low latitude/high defense hypothesis for broad-leaved tree species

We tested the hypothesis that leaves of broad-leaved tree species are more highly defended at low latitudes than at high latitudes. We used canonical discriminant analysis to compare tree species from Panama (9°N, 39 species), Missouri, USA (38°N, 37 species), and southern Ontario, Canada (44°N, 34 species) with respect to two structural and five nutritional traits, taking into account each species' tolerance to shade. Trees from the three locations differed significantly, with Panamanian species the most distinct. Defenses of shade-tolerant species were significantly greater than those of shade-intolerant species, but only for the Panamanian sample, which is consistent with the low latitude/high defense hypothesis. Because we sampled many of the same tree species from Missouri and southern Ontario, and many tree species in the same taxonomic families in Missouri and Panama, we were able to control for the potential confounding effects of phylogeny. Overall defense levels, calculated by summing the z-scores for individual traits in each location, were significantly higher for Panama compared to Missouri, and marginally so for Missouri compared to southern Ontario, again consistent with the low latitude/high defense hypothesis. Traits contributing to these differences were mostly structural factors (e.g., fiber) and to a lesser degree nutritional traits, while secondary compounds made no independent contribution to differences in overall defense levels (four traits compared between Panama and Missouri). Contrary to our expectation, the number and types of secondary compounds per species reported in the literature for our species did not differ between temperate and tropical locations, while the diversity of these compounds was greater for the temperate species. Overall, our results provide some support for the hypothesis that leaf defenses against herbivory are better developed in tropical than in temperate trees, but the differences were due to structural and nutritional factors rather than secondary compounds.     

Habitat selection and territorial defense behaviors in juvenile cortez angelfish,Pomacanthus zonipectus (gill)

Scuba diving observations in the Gulf of California (Mexico) on juvenile Cortez angelfishes, Pomacanthus zonipectus (Gill), indicate that these fish select and defend territories centered about a rock crevice. By day, they make brief feeding excursions, venturing even over open sandy areas near the rocks. They are substrate feeders, and will remove ectoparasites from other fishes, even attempting to clean human divers. At night they remain in their rock crevices. Laboratory experiments, conducted to quantify habitat-selection and territorial-defense behaviors in juvenile P. zonipectus, revealed that they spend 75% of their time during the day near rocks and 25% over sand in a divided experimental tank. The frequency of attacks on a mirror image increased as the mirror was moved closer to the rock crevice which was the territorial focus.