Invasion waves and pinning in the Kirkpatrick–Barton model of evolutionary range dynamics

Journal of Mathematical Biology - The Kirkpatrick–Barton model, well known to invasion biologists, is a pair of reaction–diffusion equations for the joint evolution of population...     

Conservative ecological and evolutionary patterns in liverwort–fungal symbioses

Liverworts, the most ancient group of land plants, form a range of intimate associations with fungi that may be analogous to the mycorrhizas of vascular plants. Most thalloid liverworts contain arbuscular mycorrhizal glomeromycete fungi similar to most vascular plants. In contrast, a range of leafy liverwort genera and one simple thalloid liverwort family (the Aneuraceae) have switched to basidiomycete fungi. These liverwort switches away from glomeromycete fungi may be expected to parallel switches undergone by vascular plants that target diverse lineages of basidiomycete fungi to form ectomycorrhizas. To test this hypothesis, we used a cultivation-independent approach to examine the basidiomycete fungi associated with liverworts in varied worldwide locations by generating fungal DNA sequence data from over 200 field collections of over 30 species. Here we show that eight leafy liverwort genera predominantly and consistently associate with members of the Sebacina vermifera species complex and that Aneuraceae thalloid liverworts associate nearly exclusively with Tulasnella species. Furthermore, within sites where multiple liverwort species co-occur, they almost never share the same fungi. Our analyses reveal a strikingly conservative ecological and evolutionary pattern of liverwort symbioses with basidiomycete fungi that is unlike that of vascular plant mycorrhizas.     

Hunter–Gatherer population structure and the evolution of contingent cooperation

Unlike other vertebrates, humans cooperate in large groups with unrelated individuals. Many authors have argued that the evolution of such cooperation has resulted from reciprocity and other forms of contingent cooperation. This argument is not well supported by existing theory. The theory of contingent cooperation in pairs is well developed: reciprocating strategies are stable when common, and can increase when rare as long as population structure leads to modest levels of relatedness. In larger groups, however, it is not clear whether contingent cooperation can increase when rare. Existing work suggests that contingent strategies cannot increase unless relatedness is high, but depends on unrealistic assumptions about the effects of population structure. Here we develop and analyze a model incorporating a two level population structure that captures important features of human hunter–gatherer societies. This model suggests that previous work underestimates the range of conditions under which contingent cooperation can evolve, but also predicts that cooperation will not evolve unless (1) social groups are small, and (2) the relatedness within ethnolinguistic groups is at the high end of the range of empirical estimates.     

Doomed to die? Predicting extinction risk in the true hawks Accipitridae

One of the most important tasks in conservation biology is identifying species at risk from extinction and establishing the most likely factors influencing this risk. Here, we consider an ecologically well-defined, monophyletic group of organisms, the true hawks of the family Accipitridae, which are not only among the most studied, but also contain some of the rarest bird species in the world. We investigate which intrinsic and extrinsic factors, covering morphology, life history and ecology, covary with International Union for the Conservation of Nature and Natural Resources threat status, as well as global population size and geographic range size. By decomposing threat status into population size and range size, we test whether any factors are generally important: we found that species with less habitat specialization, a larger clutch size and more plumage polymorphism were associated with lower extinction risk and larger population and range sizes. Species with special habitat requirements might be less capable of dealing with habitat transformation and fragmentation, while species with small clutch sizes might not be able to reverse population declines. Plumage polymorphism might indicate the size of the species' gene pool and could be a good marker of extinction risk. The analyses also emphasized that no single factor is likely to be sufficient when predicting the threat of extinction.     

The screening game in plant–pollinator interactions

A central question in the field of plant–pollinator interactions is whether and how can plants choose the optimal pollinators when plants cannot directly assess the quality of floral visitors. To answer this question and to provide a new perspective to this problem, we develop a screening game modeling the plant–pollinator interaction. We propose that some floral traits could be interpreted as an entry barrier with a strategic cost the plants impose on floral visitors. The pollinators decide to further interact with the plant only if the cost is not prohibitive. Therefore, by imposing the right level of costs, the plants may achieve interactions only with high-quality pollinators without a priori knowing the quality of visitors.     

Mutation and evolutionary rates in adélie penguins from the antarctic

Precise estimations of molecular rates are fundamental to our understanding of the processes of evolution. In principle, mutation and evolutionary rates for neutral regions of the same species are expected to be equal. However, a number of recent studies have shown that mutation rates estimated from pedigree material are much faster than evolutionary rates measured over longer time periods. To resolve this apparent contradiction, we have examined the hypervariable region (HVR I) of the mitochondrial genome using families of Adélie penguins (Pygoscelis adeliae) from the Antarctic. We sequenced 344 bps of the HVR I from penguins comprising 508 families with 915 chicks, together with both their parents. All of the 62 germline heteroplasmies that we detected in mothers were also detected in their offspring, consistent with maternal inheritance. These data give an estimated mutation rate (micro) of 0.55 mutations/site/Myrs (HPD 95% confidence interval of 0.29-0.88 mutations/site/Myrs) after accounting for the persistence of these heteroplasmies and the sensitivity of current detection methods. In comparison, the rate of evolution (k) of the same HVR I region, determined using DNA sequences from 162 known age sub-fossil bones spanning a 37,000-year period, was 0.86 substitutions/site/Myrs (HPD 95% confidence interval of 0.53 and 1.17). Importantly, the latter rate is not statistically different from our estimate of the mutation rate. These results are in contrast to the view that molecular rates are time dependent.     

Bacterial cooperation in the wild and in the clinic: Are pathogen social behaviours relevant outside the laboratory?

Individual bacterial cells can communicate via quorum sensing, cooperate to harvest nutrients from their environment, form multicellular biofilms, compete over resources and even kill one another. When the environment that bacteria inhabit is an animal host, these social behaviours mediate virulence. Over the last decade, much attention has focussed on the ecology, evolution and pathology of bacterial cooperation, and the possibility that it could be exploited or destabilised to treat infections. But how far can we really extrapolate from theoretical predictions and laboratory experiments to make inferences about ‘cooperative’ behaviours in hosts and reservoirs? To determine the likely importance and evolution of cooperation ‘in the wild’, several questions must be addressed. A recent paper that reports the dynamics of bacterial cooperation and virulence in a field experiment provides an excellent nucleus for bringing together key empirical and theoretical results which help us to frame – if not completely to answer – these questions.     

Developmental and evolutionary assumptions in a study about the impact of premature birth and low income on mother–infant interaction

In order to study the impact of premature birth and low income on mother–infant interaction, four Portuguese samples were gathered: full-term, middle-class (n = 99); premature, middle-class (n = 63); full-term, low income (n = 22); and premature, low income (n = 21). Infants were filmed in a free play situation with their mothers, and the results were scored using the CARE Index. By means of multinomial regression analysis, social economic status (SES) was found to be the best predictor of maternal sensitivity and infant cooperative behavior within a set of medical and social factors. Contrary to the expectations of the cumulative risk perspective, two factors of risk (premature birth together with low SES) were as negative for mother–infant interaction as low SES solely. In this study, as previous studies have shown, maternal sensitivity and infant cooperative behavior were highly correlated, as was maternal control with infant compliance. Our results further indicate that, when maternal lack of responsiveness is high, the infant displays passive behavior, whereas when the maternal lack of responsiveness is medium, the infant displays difficult behavior. Indeed, our findings suggest that, in these cases, the link between types of maternal and infant interactive behavior is more dependent on the degree of maternal lack of responsiveness than it is on birth status or SES. The results will be discussed under a developmental and evolutionary reasoning.     

Eutherians experienced elevated evolutionary rates in the immediate aftermath of the Cretaceous–Palaeogene mass extinction

The effect of the Cretaceous–Palaeogene (K–Pg) mass extinction on the evolution of many groups, including placental mammals, has been hotly debated. The fossil record suggests a sudden adaptive radiation of placentals immediately after the event, but several recent quantitative analyses have reconstructed no significant increase in either clade origination rates or rates of character evolution in the Palaeocene. Here we use stochastic methods to date a recent phylogenetic analysis of Cretaceous and Palaeocene mammals and show that Placentalia likely originated in the Late Cretaceous, but that most intraordinal diversification occurred during the earliest Palaeocene. This analysis reconstructs fewer than 10 placental mammal lineages crossing the K–Pg boundary. Moreover, we show that rates of morphological evolution in the 5 Myr interval immediately after the K–Pg mass extinction are three times higher than background rates during the Cretaceous. These results suggest that the K–Pg mass extinction had a marked impact on placental mammal diversification, supporting the view that an evolutionary radiation occurred as placental lineages invaded new ecological niches during the Early Palaeocene.     

Tracing the evolutionary routes of plant–microbiota interactions

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The influence of spatiotemporal conditions and personality on survival in reintroductions–evolutionary implications

Personality exists in non-human animals and can impact fitness. There is, however, a shortage of empirical studies in certain areas within the field, and fundamental evolutionary theory on personality remains largely untested. For example, little is known on how variation in personality is maintained over evolutionary time. Theory suggests that fluctuating selection pressures due to spatiotemporal variation in conditions, e.g. food availability, is a possible mechanism and a few studies have shown that the success of different personality types varies with spatiotemporal conditions. However, it remains unknown whether different mechanisms can maintain personality within a species. Here we use a reintroduction programme for the critically endangered European mink (Mustela lutreola) to test whether multiple personality trait domains (boldness, exploration and sociability) affected survival in two different years and islands. This was done through pre-release personality tests and post-release radio-tracking monitoring. Survival was positively correlated with boldness, whereas the relationship with exploration was either negative or positive depending on year/island. The results show a complex relationship between personality and survival and suggest that exploration can be maintained over evolutionary time via spatiotemporal variation in conditions. However, in contrast to exploration, boldness did not vary spatiotemporally and sociability had no impact on survival. This indicates that different personality trait domains might be maintained by different mechanisms. To date, personality has been studied primarily within behavioural sciences, but through empirical findings we highlight the importance of personality also in ecology and conservation biology.     

A unifying evolutionary theory for the biomass–diversity–fertility relationship

Although a widely accepted ecological theory predicts that more diverse plant communities should be better able to capture resources and turn carbon dioxide into biomass, the most productive communities known are low diversity agricultural ones. This paradox has fuelled a long running controversy in ecology surrounding the nature of the relationship between diversity, productivity and fertility. Here, an evolutionary computer model is used which demonstrates that given the opportunity, species-rich communities may evolve under high fertility conditions. In contrast to low diversity, highly productive agricultural communities are shown to probably be a recent phenomenon. In simulations where fertility was applied to communities that had evolved under lower nutrient conditions, a few species had the ability to become ‘dominant’. These species were responsible for the loss of diversity and for the majority of biomass production. These results are consistent with complementarity theory applying in nature in old co-evolved low nutrient communities, whereas in recently established fertile agricultural communities, dominant species appear to regulate biomass production. Understanding the nature of these ‘dominant’ species throws light on our understanding of phenotypic plasticity and the ecology of invasive species. The appendices files are currently available at .     

Proximity between the sexes in ring doves: Social bonds or surveillance?

Most bird species are monogamous, and in many instances the male provides a substantial contribution to the care of the young. Traditionally, the initial phase of the relationship between the sexes has been characterized in terms of pair formation and an increasing bond between the sexes. But recent formulations emphasize the role of guarding, surveillance, and other behavioural devices that protect the genetic relationship of the male to the offspring for which he cares. Ring doves were studied to determine whether the details of the relationship during the initial period are consistent with this latter view. Experiment 1 reveals that males remain in close proximity to their mates until the first egg is laid and the fertile period of the female ends; social contact then falls to a low level. Experiment 2 shows that when the female is removed during her fertile period, the male searches and calls more vigorously than does a female when her partner is absent. Finally, Experiment 3 demonstrates that it is visual contact rather than simply proximity that the male maintains during the fertile period of the female. These observations are consonant with the view that males maintain surveillance over their mates, but they do not exclude the possibility that the behaviour patterns might provide other benefits as well.     

Leafless autumnal-flowering geophytes in the Mediterranean region — phytogeographical,ecological and evolutionary aspects

Numerous Mediterranean geophytes are hysteranthous, i.e. they flower in a leafless stage during autumn. On the basis of their life cycles and other features two types can be recognized: In the Crocus type flowers with subterranean ovary develop at the start of the new reproductive cycle from an annual storage organ; seed dispersal and germination are delayed to the spring and the next autumn. In the Urginea type, flowers with supraterranean ovary originate from a perennial storage organ at the end of the life cycle; seed dispersal and germination follow flowering immediately. Similar rhythms exist in other seasonal climates. Field observations and some experiments demonstrate flower stimulation by temperature decrease or increase in different geophytes, and relationships between water supply and synanthous versus hysteranthous leaf development. The origin, ecological importance, and horticultural implication of the hysteranthous syndrome is discussed.     

A Mutual Interest? Ethnography in Anthropology and Cultural Studies

Anthropology and cultural studies share a concern with ethnographic method. Cultural studies increasingly uses ethnography in its analyses of popular culture as it seeks to balance earlier preoccupations with text. Where cultural studies diverges from anthropology is in its encompassment within an oppositional paradigm which embeds a political agenda deep in its ethnographic work. This paper uses the area of media to explore the ways in which ethnography has been adopted and developed in cultural studies. Ethnographic focus has shifted interest in media from the text to the reception of media products. At the same time, the oppositional legacy from cultural studies' earliest days has tended to produce rather romanticised findings of a subaltern audience using media products to resist dominant cultural and political structures. It is suggested that anthropology should pay attention to cultural studies use of ethnographic method, first taking seriously the ground of popular culture as a challenge for anthropologists' more extended use of ethnography. But second, we should pay attention to the problem silences in cultural studies' ethnographies—silences like racism in audiences—since these may well have at least part of their basis in the method itself.