Oblique Transmission, Conformity, and Preference in the Evolution of Altruism

The evolution of altruism is frequently studied using models of non-random assortment, including kin selection. In genetic kin selection models, under certain assumptions including additive costs and benefits, the criterion for altruism to invade a population is Hamilton's rule. Deviations from Hamilton's rule occur when vertical transmission has cultural and genetic components, or when costs and benefits are combined multiplicatively. Here, we include oblique and vertical cultural transmission and genetic transmission in four models--two forms of parent-to-offspring altruism, sibling-to-sibling altruism, and altruism between offspring that meet assortatively--under additive or multiplicative assumptions. Oblique transmission may be conformist (anti-conformist), where the probability that an individual acquires a more common cultural variant is greater (less) than its frequency. Inclusion of conformist or anti-conformist oblique transmission may reduce or increase the threshold for invasion by altruism relative to Hamilton's rule. Thresholds for invasion by altruism are lower with anti-conformity than with conformity, and lower or the same with additive rather than multiplicative fitness components. Invasion by an allele that increases the preference for altruism does not depend on oblique phenotypic transmission, and with sibling-to-sibling altruism, this allele's invasion threshold can be higher with additive rather than multiplicative fitnesses.

Ontogenetic shifts in microhabitat preference of the temperate reef fish Forsterygion lapillum: implication for population limitation

Quantitative surveys of habitat associations of New Zealand's common triplefin fish Forsterygion lapillum suggest that young settlers disproportionately occur within the fronds of the large brown algae Cystophora retroflexa and C. torulosa (hereafter collectively referred to as Cystophora). This apparent preference is specific to Cystophora (i.e. fish do not appear to respond to structurally similar macroalgal species) and is not exhibited by older juveniles or adults of the species, which suggests that age-specific microhabitat requirements may act as a bottleneck to recruitment. To determine whether the overuse of Cystophora by newly settled F. lapillum could be attributed to a behavioural preference for this specific habitat, we conducted a lab-based choice experiment. Using a purpose-built 'choice chamber' that facilitated assessments of behavioural responses of focal individuals provided with a choice of 4 common habitat types, we determined that newly settled F. lapillum selected chambers containing Cystophora more frequently than predicted by random assortment. To test the ecological consequences of this behavioural preference, we conducted a field experiment (replicated at 2 sites) that manipulated Cystophora cover and examined subsequent patterns of recruitment by F. lapillum. Experimental additions of Cystophora cover enhanced local recruitment of F. lapillum, and the effects of Cystophora additions were most pronounced at the site where Cystophora was naturally rare. Overall, these results suggest that age-specific behavioural preferences may mediate ontogenetic shifts in microhabitat use and limit recruitment in local populations. © Inter-Research 2006.

Ontogenetic shifts in microhabitat preference of the temperate reef fish Forsterygion lapillum: implication for population limitation

Quantitative surveys of habitat associations of New Zealand's common triplefin fish Forsterygion lapillum suggest that young settlers disproportionately occur within the fronds of the large brown algae Cystophora retroflexa and C. torulosa (hereafter collectively referred to as Cystophora). This apparent preference is specific to Cystophora (i.e. fish do not appear to respond to structurally similar macroalgal species) and is not exhibited by older juveniles or adults of the species, which suggests that age-specific microhabitat requirements may act as a bottleneck to recruitment. To determine whether the overuse of Cystophora by newly settled F. lapillum could be attributed to a behavioural preference for this specific habitat, we conducted a lab-based choice experiment. Using a purpose-built 'choice chamber' that facilitated assessments of behavioural responses of focal individuals provided with a choice of 4 common habitat types, we determined that newly settled F. lapillum selected chambers containing Cystophora more frequently than predicted by random assortment. To test the ecological consequences of this behavioural preference, we conducted a field experiment (replicated at 2 sites) that manipulated Cystophora cover and examined subsequent patterns of recruitment by F. lapillum. Experimental additions of Cystophora cover enhanced local recruitment of F. lapillum, and the effects of Cystophora additions were most pronounced at the site where Cystophora was naturally rare. Overall, these results suggest that age-specific behavioural preferences may mediate ontogenetic shifts in microhabitat use and limit recruitment in local populations. © Inter-Research 2006.

The sugar code: letters and vocabulary, writers, editors and readers and biosignificance of functional glycan–lectin pairing

Ubiquitous occurrence in Nature, abundant presence at strategically important places such as the cell surface and dynamic shifts in their profile by diverse molecular switches qualifies the glycans to serve as versatile biochemical signals. However, their exceptional structural complexity often prevents one noting how simple the rules of objective-driven assembly of glycan-encoded messages are. This review is intended to provide a tutorial for a broad readership. The principles of why carbohydrates meet all demands to be the coding section of an information transfer system, and this at unsurpassed high density, are explained. Despite appearing to be a random assortment of sugars and their substitutions, seemingly subtle structural variations in glycan chains by a sophisticated enzymatic machinery have emerged to account for their specific biological meaning. Acting as ‘readers’ of glycan-encoded information, carbohydrate-specific receptors (lectins) are a means to turn the glycans’ potential to serve as signals into a multitude of (patho)physiologically relevant responses. Once the far-reaching significance of this type of functional pairing has become clear, the various modes of spatial presentation of glycans and of carbohydrate recognition domains in lectins can be explored and rationalized. These discoveries are continuously revealing the intricacies of mutually adaptable routes to achieve essential selectivity and specificity. Equipped with these insights, readers will gain a fundamental understanding why carbohydrates form the third alphabet of life, joining the ranks of nucleotides and amino acids, and will also become aware of the importance of cellular communication via glycan–lectin recognition.

Intra-urban patterns of neighborhood-level social capital: a pilot study

Background: Social capital is a construct of interaction and social trust in one’s fellow community members. These interactions can provide a safety net for individuals in terms of information, social support, and adherence to social norms. While a number of studies have previously examined the relationship between social capital and health outcomes, few have examined the theparallel relationship of social capital and geographic "place" with respect to health outcomes. Methods: Considering social capital as facilitated by specific structures, we evaluate the relationship between neighborhood-level social capital and disability rates in a major Southern US city. Disability rates were collected through neighborhood-level data via the AmericanCommunity Survey (ACS) and compared to a geocoded map of neighborhood-level social capital measures during spring, 2016. Results: Higher social capital within a neighborhood coincided with lower disability rates in that neighborhood (r=-0.14, P=0.016) when compared to random assortment models. Conclusion: Findings from this research add evidence to the value of the built environment, not only providing resources and shaping choices, but for facilitating important social relationships.

Non-random associations of maternally transmitted symbionts in insects: The roles of drift versus co-transmission and selection

Virtually all higher organisms form holobionts with associated microbiota. To understand the biology of holobionts we need to know how species assemble and interact. Controlled experiments are suited to study interactions between particular symbionts, but they can only inform about a tiny portion of the diversity within each species. Alternatively, interactions can be inferred from associations among symbionts in the field that are more or less frequent than expected under random assortment. However, random assortment may not be a valid null hypothesis for maternally transmitted symbionts in finite populations, where drift alone can result in associations. Here we report results from a European field survey of endosymbionts in the pea aphid (Acyrthosiphon pisum), and we develop a model to study the effect of drift on symbiont associations under different population sizes, considering varying rates of horizontal and maternal transmission. The model showed that even though horizontal transmissions and maternal transmission failures tend to randomise symbiont associations, drift can induce significant departures from random assortment, at least in moderate-sized populations. Based on these results, we carefully interpret our field survey and we re-visit the association between Spiroplasma and Wolbachia in Drosophila neotestacea reported by Jaenike et al. (2010). For this and for several significant associations between symbionts in European pea aphids we conclude that under reasonable assumptions of effective population size, they are indeed likely to be maintained by biased co-transmission or selection. Our study shows that formulating appropriate null expectations can strengthen the biological inference from co-occurrence patterns in the field.

Super-Mendelian inheritance mediated by CRISPR/Cas9 in the female mouse germline

A gene drive biases the transmission of a particular allele of a gene such that it is inherited at a greater frequency than by random assortment. Recently, a highly efficient gene drive was developed in insects, which leverages the sequence-targeted DNA cleavage activity of CRISPR/Cas9 and endogenous homology directed repair mechanisms to convert heterozygous genotypes to homozygosity. If implemented in laboratory rodents, this powerful system would enable the rapid assembly of genotypes that involve multiple genes (e.g., to model multigenic human diseases). Such complex genetic models are currently precluded by time, cost, and a requirement for a large number of animals to obtain a few individuals of the desired genotype. However, the efficiency of a CRISPR/Cas9 gene drive system in mammals has not yet been determined. Here, we utilize an active genetic “CopyCat” element embedded in the mouse Tyrosinase gene to detect genotype conversions after Cas9 activity in the embryo and in the germline. Although Cas9 efficiently induces double strand DNA breaks in the early embryo and is therefore highly mutagenic, these breaks are not resolved by homology directed repair. However, when Cas9 expression is limited to the developing female germline, resulting double strand breaks are resolved by homology directed repair that copies the CopyCat allele from the donor to the receiver chromosome and leads to its super-Mendelian inheritance. These results demonstrate that the CRISPR/Cas9 gene drive mechanism can be implemented to simplify complex genetic crosses in laboratory mice and also contribute valuable data to the ongoing debate about applications to combat invasive rodent populations in island communities.

Mythicizing History

This chapter examines how the study of local history as an “act of self-reassurance” has grown in importance as societies have become mobile and people are less tied to a specific location. Historian Helmut Flachenecker writes of modern society that one is no longer the citizen of a location primarily by birth, but rather by history. This is true to an extreme degree of the Polish city of Wroclaw, whose society came into being as the result of a complete population exchange. Societies of this kind typically yearn for tradition just as much as they lack it. Only by identifying collectively with the history of the city could a coherent citizenry develop out of a random assortment of settlers thrown together by the population shifts of postwar Poland.

Abundance distribution of common and rare plant species of Brazilian savannas along a seasonality gradient

We examined the species abundance distribution (SAD) of plant communities in: (1) a wet grassland, waterlogged throughout most of the year; (2) a seasonal savanna, with an annual dry season; and (3) a hyperseasonal savanna, with alternating drought and waterlogging over the year. We searched for differences in the abundance distributions of all species, as well as of the common and rare species. We tested whether the SADs fitted the lognormal, log-series, power fraction, and random assortment models. We found that environmental constraints may reduce the evenness of plant communities and change the SADs in savannas. We observed a lognormal abundance distribution in the wet grassland and a random abundance distribution in the hyperseasonal cerrado. The SAD of the seasonal savanna did not follow any model. The common species in the three communities were better fitted by the lognormal model. The rare species in the wet grassland and the hyperseasonal cerrado were better fitted by the random assortment model. The SAD of the rare species of the seasonal savanna did not follow any model. Seasonality seems to modify the lognormal distribution of the overall plant community, generating abundance distributions indistinguishable from random. However, differential community structuring between common and rare species may not be affected by seasonality. The different signatures of the abundance distributions of common and rare plants indicate that composite models are better predictors for SADs in savannas.

Niche shifts and local competition between two coral reef fishes at their geographic boundary

Competition theory predicts that, when resources are limiting, interacting species should differ more in resource use where they co-occur, compared with where they do not (resource partitioning). The damselfishes Dascyllus aruanus and D. melanurus provide a useful test of this prediction because they exhibit largely allopatric geographic ranges that overlap near Port Moresby, Papua New Guinea. To test whether this species pair exhibited responses in resource use that were consistent with competition theory, the depth distributions, coral substrata and diet of each species at allopatric and sympatric locations were compared. Where sympatric, the frequency of co-occurrence was examined and foraging ranges and diet on corals where the species do and do not co-occur were compared. Contrary to expectations, the species were more similar in depth, habitat use and diet in the sympatric region. Within this location, they sometimes co-existed in the same coral shelters, but much less often than would be expected with random assortment. Where they did co-exist, their diets converged. D. melanurus exhibited restricted foraging ranges and consumed smaller prey in the presence of D. aruanus, but not vice versa. It was concluded that niche shifts along different resource axes at the geographic boundary are explained both by large-scale constraints in resource availability and local-scale competitive interactions.