Variation of shell ornamentation with latitude and water depth-A case study using living brachiopods

As a potential anti-predatory defensive structure, the shell ornamentation of marine calcifiers is usually used to understand the macro coevolution of the interactions between predators and preys. Marine calcifiers' shell ornamentation complexity is generally believed to vary negatively with latitude and water depth. In this paper, we explored the association between shell ornamentation and latitude/bathymetry using the latest global database of living brachiopods. We found that (1) ~59% of living brachiopods species are characterized by smooth shells and that (2) there is no statistically significant linear trend, either positive or negative, between the ornamentation index and latitudes nor with water depths. Both findings are puzzling for living brachiopods as they are sharply contrasted to the patterns of fossil brachiopods whereby the latter, especially Paleozoic brachiopods, are known to exhibit (1) a much greater ornamentation diversity and (2) (at least for the geological periods that have been studied) a linear latitudinal gradient of ornamentation complexity existed. The reasons why living brachiopods have such a high proportion of smooth or weakly ornamented shells and fail to demonstrate an unequivocal linear latitudinal ornamentation gradient were explored and are linked to a multitude of potential factors rather than uniquely only to the predation pressure. Among these, the most plausible factor seems to be the cryptic (refuge-type) habitats (e.g., deep waters, cold polar regions, and submarine rock caves) that living brachiopods have been adapted to due to their low metabolism, where predation pressure is low, allowing brachiopods to enact the predator avoidance strategy rather than having to manufacture robust shell ornamentation to survive in an otherwise highly engaged predator-prey global marine ecosystem.

Evolutionary Challenges to Humanity Caused by Uncontrolled Carbon Emissions: The Stockholm Paradigm

This review paper discusses the Stockholm Paradigm (SP) as a theoretical framework and practical computational instrument for studying and assessing the risk of emerging infectious diseases (EIDs) as a result of climate change. The SP resolves the long-standing parasite paradox and explains how carbon emissions in the atmosphere increase parasites' generalization and intensify host switches from animals to humans. The SP argues that the growing rate of novel EID occurrence caused by mutated zoonotic pathogens is related to the following factors brought together as a unified issue of humanity: (a) carbon emissions and consequent climate change; (b) resettlement/migration of people with hyper-urbanization; (c) overpopulation; and (d) human-induced distortion of the biosphere. The SP demonstrates that, in an evolutionary way, humans now play a role migratory birds once played in spreading parasite pathogens between the three Earth megabiotopes (northern coniferous forest belt; tropical/equatorial rainforest areas; and hot/cold deserts), i.e., the role of "super-spreaders" of parasitic viruses, bacteria, fungi and protozoa. This makes humans extremely vulnerable to the EID threat. The SP sees the +1.0-+1.2 °C limit as the optimal target for the slow, yet feasible curbing of the EID hazard to public health (150-200 years). Reaching merely the +2.0 °C level will obviously be an EID catastrophe, as it may cause two or three pandemics each year. We think it useful and advisable to include the SP-based research in the scientific repository of the Intergovernmental Panel on Climate Change, since EID appearance and spread are indirect but extremely dangerous consequences of climate change.

Exploring abnormal Cambrian-aged trilobites in the Smithsonian collection

Biomineralised trilobite exoskeletons provide a 250 million year record of abnormalities in one of the most diverse arthropod groups in history. One type of abnormality-repaired injuries-have allowed palaeobiologists to document records of Paleozoic predation, accidental damage, and complications in moulting experienced by the group. Although Cambrian trilobite injuries are fairly well documented, the illustration of new injured specimens will produce a more complete understanding of Cambrian prey items. To align with this perspective, nine new abnormal specimens displaying healed injuries from the Smithsonian National Museum of Natural History collection are documented. The injury pattern conforms to the suggestion of lateralised prey defence or predator preference, but it is highlighted that the root cause for such patterns is obscured by the lumping of data across different palaeoecological and environmental conditions. Further studies of Cambrian trilobites with injuries represent a key direction for uncovering evidence for the Cambrian escalation event.

The Fossil Record of Predator-Prey Arms Races: Coevolution and Escalation Hypotheses

Arms races between predators and prey may be driven by two related processes—escalation and coevolution. Escalation is enemy-driven evolution. In this top-down view of an arms race, the role of prey (with the exception of dangerous prey) is downplayed. In coevolution, two or more species change reciprocally in response to one another; prey are thought to drive the evolution of their predator, and vice versa. In the fossil record, the two processes are most reliably distinguished when the predator-prey system is viewed within the context of the other species that may influence the interaction, thus allowing for a relative ranking of the importance of selective agents. Detailed documentation of the natural history of living predator-prey systems is recommended in order to distinguish the processes in some fossil systems. A geographic view of species interactions and the processes driving their evolution may lead to a more diverse array of testable hypotheses on how predator-prey systems evolve and what constraints interactions impose on the evolution of organisms. Scale is important in evaluating the role of escalation and coevolution in the evolution of species interactions. If short-term reciprocal adaptation (via phenotypic plasticity or selection mosaics among populations) between predator and prey is a common process, then prey are likely to exert some selective pressure over their predators over the short term (on ecological time scales), but in the long run predators may still exert primary “top-down” control in directing evolution. On the scale of evolutionary time, predators of large effect likely control the overall directionality of evolution due to the inequalities of predator and prey in control of resources.

Pollination decays in biodiversity hotspots

As pollinators decline globally, competition for their services is expected to intensify, and this antagonism may be most severe where the number of plant species is the greatest. Using meta-analysis and comparative phylogenetic analysis, we provide a global-scale test of whether reproduction becomes more limited by pollen receipt (pollen limitation) as the number of coexisting plant species increases. As predicted, we find a significant positive relationship between pollen limitation and species richness. In addition, this pattern is particularly strong for species that are obligately outcrossing and for trees relative to herbs or shrubs. We suggest that plants occurring in species-rich communities may be more prone to pollen limitation because of interspecific competition for pollinators. As a consequence, plants in biodiversity hotspots may have a higher risk of extinction and/or experience increased selection pressure to specialize on certain pollinators or diversify into different phenological niches. The combination of higher pollen limitation and habitat destruction represents a dual risk to tropical plant species that has not been previously identified.

Uniform vertical transmission and selection in a host–symbiont system. Non-random symbiont distribution generates apparent differential selection

We investigate the survival, prevalence, and distribution of a symbiont in its host population when the forces of vertical transmission (beta) and symbiont-induced selection (s) are uniform (invariant across host genotypes). We use host-symbiont disequilibria to quantify the role played by non-random associations between host genotypes and the symbiont in altering host genetic structure. Results show a larger part of the parameter space permits symbiont survival under mutualism (beta>/=0.25) than parasitism (beta>0.5). The nonlinear interaction between beta and s determines symbiont survival and prevalence at equilibrium; initial symbiont prevalence is a factor only in a small number of parameter combinations. The symbiont's non-random distribution generates apparent differential selection, when selective differences across host genotypes and alleles exist under uniform selection. The direction of change in host allele frequencies is determined exclusively by the signs of s and the allelic disequilibrium. Disequilibria cannot be created or maintained, and heterozygote disequilibrium changes sign in a greater number of runs and at higher magnitudes than homozygote disequilibria. This investigation increases our understanding of the interactions between vertical transmission and selection, and their effect on the coevolutionary dynamics and final states of interacting species under different selection regimes.

The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts

The "geographic mosaic" approach to understanding coevolution is predicated on the existence of variable selection across the landscape of an interaction between species. A range of ecological factors, from differences in resource availability to differences in community composition, can generate such a mosaic of selection among populations, and thereby differences in the strength of coevolution. The result is a mixture of hotspots, where reciprocal selection is strong, and coldspots, where reciprocal selection is weak or absent, throughout the ranges of species. Population subdivision further provides the opportunity for nonadaptive forces, including gene flow, drift, and metapopulation dynamics, to influence the coevolutionary interaction between species. Some predicted results of this geographic mosaic of coevolution include maladapted or mismatched phenotypes, maintenance of high levels of polymorphism, and prevention of stable equilibrium trait combinations. To evaluate the potential for the geographic mosaic to influence predator-prey coevolution, we investigated the geographic pattern of genetically determined TTX resistance in the garter snake Thamnophis sirtalis over much of the range of its ecological interaction with toxic newts of genus Taricha. We assayed TTX resistance in over 2900 garter snakes representing 333 families from 40 populations throughout western North America. Our results provide dramatic evidence that geographic structure is an important component in coevolutionary interactions between predators and prey. Resistance levels vary substantially (over three orders of magnitude) among populations and over short distances. The spatial array of variation is consistent with two areas of intense evolutionary response by predators ("hotspots") surrounded by clines of decreasing resistance. Some general predictions of the geographic mosaic process are supported, including clinal variation in phenotypes, polymorphism in some populations, and divergent outcomes of the interaction between predator and prey. Conversely, our data provide little support for one of the major predictions, mismatched values of interacting traits. Two lines of evidence suggest selection is paramount in determining population variation in resistance. First, phylogenetic information indicates that two hotspots of TTX resistance have evolved independently. Second, in the one region that TTX levels in prey have been quantified, resistance and toxicity levels match almost perfectly over a wide phenotypic and geographic range. However, these results do not preclude the role the nonadaptive forces in generating the overall geographic mosaic of TTX resistance. Much work remains to fill in the geographic pattern of variation among prey populations and, just as importantly, to explore the variation in the ecology of the interaction that occurs within populations.

Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels

Populations of the garter snake Thamnophis sirtalis have evolved geographically variable resistance to tetrodotoxin (TTX) in a coevolutionary arms race with their toxic prey, newts of the genus Taricha. Here, we identify a physiological mechanism, the expression of TTX-resistant sodium channels in skeletal muscle, responsible for adaptive diversification in whole-animal resistance. Both individual and population differences in the ability of skeletal muscle fibers to function in the presence of TTX correlate closely with whole-animal measures of TTX resistance. Demonstration of individual variation in an essential physiological function responsible for the adaptive differences among populations is a step toward linking the selective consequences of coevolutionary interactions to geographic and phylogenetic patterns of diversity.

Symbiont survival and host-symbiont disequilibria under differential vertical transmission

Interspecific genetic interactions in host-symbiont systems raise intriguing coevolutionary questions and may influence the effectiveness of public health and management policies. Here we present an analytical and numerical investigation of the effects of host genetic heterogeneity in the rate of vertical transmission of a symbiont. We consider the baseline case with a monomorphic symbiont and a single diallelic locus in its diploid host, where vertical transmission is the sole force. Our analysis introduces interspecific disequilibria to quantify nonrandom associations between host genotypes and alleles and symbiont presence/absence. The transient and equilibrium behavior is examined in simulations with randomly generated initial conditions and transmission parameters. Compared to the case where vertical transmission rates are uniform across host genotypes, differential transmission (i) increases average symbiont survival from 50% to almost 60%, (ii) dramatically reduces the minimum average transmission rate for symbiont survival from 0.5 to 0.008, and (iii) readily creates permanent host-symbiont disequilibria de novo, whereas uniform transmission can neither create nor maintain such associations. On average, heterozygotes are slightly more likely to carry and maintain the symbiont in the population and are more randomly associated with the symbiont. Results show that simple evolutionary forces can create substantial nonrandom associations between two species.