The Effect of Health Status on Urban Adaptation of the Rural Elderly after Migration

As urbanization accelerates in China, more and more rural elders are moving to cities to live with their children. However, they face challenges in overcoming cultural, social, and economic disparities and maintaining health in urban life, and health is important human capital that may have a significant impact on the urban adaptation of rural elderly migrants (REMs). Based on the 2018 China Health and Retirement Longitudinal Study (CHARLS), this paper constructs an indicator system to measure the level of urban adaptation of REMs. The health level and urban adaptation of REMs are studied in depth, and how to better help them adapt to urban life in order to provide a healthy living environment and a good lifestyle is explored. The empirical analysis finds the following: (1) good health helps REMs achieve a better level of urban adaptation. (2) REMs with good health status are more likely to go to community clubs for activities and do physical activities and thus improve their urban adaptation level. (3) There are significant differences in the effects of health status on urban adaptation among REMs with different characteristics. REMs with better health status in the central and western regions have significantly higher levels of urban adaptation than those in the eastern regions, and men have higher levels of urban adaptation than women. Therefore, the government should construct classification measures according to the differentiated characteristics of rural elderly migrants' urban adaptation, and guide and support their stratified and orderly adaptation to urban society.

Consistent signatures of urban adaptation in a native, urban invader ant Tapinoma sessile

Biological invasions are becoming more prevalent due to the rise of global trade and expansion of urban areas. Ants are among the most prolific invaders with many exhibiting a multiqueen colony structure, dependent colony foundation and reduced internest aggression. Although these characteristics are generally associated with the invasions of exotic ants, they may also facilitate the spread of native ants into novel habitats. Native to diverse habitats across North America, the odorous house ant Tapinoma sessile has become abundant in urban environments throughout the United States. Natural colonies typically have a small workforce, inhabit a single nest, and are headed by a single queen, whereas urban colonies tend to be several orders of magnitude larger, inhabit multiple nests (i.e., polydomy) and are headed by multiple queens (i.e., polygyny). Here, we explore and compare the population genetic and breeding structure of T. sessile within and between urban and natural environments in several localities across its distribution range. We found the social structure of a colony to be a plastic trait in both habitats, although extreme polygyny was confined to urban habitats. Additionally, polydomous colonies were only present in urban habitats, suggesting T. sessile can only achieve supercoloniality within urbanized areas. Finally, we identified strong differentiation between urban and natural populations in each locality and continent-wide, indicating cities may restrict gene flow and exert intense selection pressure. Overall, our study highlights urbanization's influence in charting the evolutionary course for species.

Urban evolution comes into its own: Emerging themes and future directions of a burgeoning field

Urbanization has recently emerged as an exciting new direction for evolutionary research founded on our growing understanding of rapid evolution paired with the expansion of novel urban habitats. Urbanization can influence adaptive and nonadaptive evolution in urban-dwelling species, but generalized patterns and the predictability of urban evolutionary responses within populations remain unclear. This editorial introduces the special feature "Evolution in Urban Environments" and addresses four major emerging themes, which include: (a) adaptive evolution and phenotypic plasticity via physiological responses to urban climate, (b) adaptive evolution via phenotype-environment relationships in urban habitats, (c) population connectivity and genetic drift in urban landscapes, and (d) human-wildlife interactions in urban spaces. Here, we present the 16 articles (12 empirical, 3 review, 1 capstone) within this issue and how they represent each of these four emerging themes in urban evolutionary biology. Finally, we discuss how these articles address previous questions and have now raised new ones, highlighting important new directions for the field.

Experimental evidence that matching habitat choice drives local adaptation in a wild population

Matching habitat choice is a unique, flexible form of habitat choice based on self-assessment of local performance. This mechanism is thought to play an important role in adaptation and population persistence in variable environments. Nevertheless, the operation of matching habitat choice in natural populations remains to be unequivocally demonstrated. We investigated the association between body colour and substrate use by ground-perching grasshoppers (Sphingonotus azurescens) in an urban mosaic of dark and pale pavements, and then performed a colour manipulation experiment to test for matching habitat choice based on camouflage through background matching. Naturally, dark and pale grasshoppers occurred mostly on pavements that provided matching backgrounds. Colour-manipulated individuals recapitulated this pattern, such that black-painted and white-painted grasshoppers recaptured after the treatment aggregated together on the dark asphalt and pale pavement, respectively. Our study demonstrates that grasshoppers adjust their movement patterns to choose the substrate that confers an apparent improvement in camouflage given their individual-specific colour. More generally, our study provides unique experimental evidence of matching habitat choice as a driver of phenotype-environment correlations in natural populations and, furthermore, suggests that performance-based habitat choice might act as a mechanism of adaptation to changing environments, including human-modified (urban) landscapes.

Urbanization without isolation: the absence of genetic structure among cities and forests in the tiny acorn ant Temnothorax nylanderi

Urban alteration of neutral and adaptive evolutionary processes is still underexplored. Using a genome-wide SNP dataset, we investigated (i) urban-induced modifications of population demography, genetic diversity and population structure and (ii) signature of divergent selection between urban and forest populations in the ant species, Temnothorax nylanderi. Our results did not reveal an impact of urbanization on neutral processes since we observed: (i) analogous genetic diversity among paired urban/forest sites and two control populations; (ii) weak population genetic structure explained neither by habitat (urban versus forest) nor by geography; (iii) a remarkably similar demographic history across populations with an ancestral growth followed by a recent decline, regardless of their current habitat or geographical location. The micro-geographical home range of ants may explain their resilience to urbanization. Finally, we detected 19 candidate loci discriminating urban/forest populations and associated with core cellular components, molecular function or biological process. Two of these loci were associated with a gene ontology term that was previously found to belong to a module of co-expressed genes related to caste phenotype. These results call for transcriptomics analyses to identify genes associated with ant social traits and to infer their potential role in urban adaptation.

Risk Inequality and the Food-Energy-Water (FEW) Nexus: A Study of 43 City Adaptation Plans

Goals aimed at adapting to climate change in sustainable and just ways are embedded in global agreements such as the Sustainable Development Goals and the New Urban Agenda. However, largely unexamined, are the ways that narrative understandings conveyed in adaptation plans consider and attempt to address inequality in climate risk to urban populations and FEW-systems. In this paper, we examine whether and how adaptation plans from C40 member cities address inequality in risk, by planning actions to reduce hazard exposure or tackling the drivers of social vulnerability. C40 is a network of 94 of the world's cities fostering policies to address climate change. We apply a mixed methods approach, including a discourse analysis and meta-analysis of adaptation plans. The discourse analysis helps to unpack framings of urban equity issues as they relate to policy actions, and the meta-analysis seeks to quantitatively investigate patterns of framing and policy across adaptation plans. Our findings suggest that FEW-nexus thinking is not yet embedded in narrative understandings of risk and planned adaptation actions, within the adaptation plans we studied. In the city adaptation plans we analyzed, we found multiple frames coexisting behind the broader adaptation visions (e.g., risk and resilience). Rather than converging, issues, and principles such as those of equality, coexist with economic issues in an imbalance of incongruent political movements and priorities. Techno-infrastructural and economic investments and concerns tend to take precedence over concerns and interests for inequality in climate risks. We discuss some of the institutional factors explaining this. Knowledge integration, for instance, is constrained by the existence of a plurality of sectors, levels of government, power, values, and ways of understanding and managing climate risk. We also suggest that the relatively low importance of equality considerations in the adaptation plans will likely limit the capacity of cities to support broader goals such as those of the New Urban Agenda and the Sustainable Development Goals.

Species interactions limit the occurrence of urban-adapted birds in cities

Urbanization represents an extreme transformation of more natural systems. Populations of most species decline or disappear with urbanization, and yet some species persist and even thrive in cities. What determines which species persist or thrive in urban habitats? Direct competitive interactions among species can influence their distributions and resource use, particularly along gradients of environmental challenge. Given the challenges of urbanization, similar interactions may be important for determining which species persist or thrive in cities; however, their role remains poorly understood. Here, we use a global dataset to test among three alternative hypotheses for how direct competitive interactions and behavioral dominance may influence the breeding occurrence of birds in cities. We find evidence to support the competitive interference hypothesis: behaviorally dominant species were more widespread in urban habitats than closely related subordinate species, but only in taxa that thrive in urban environments (hereafter, urban adapted), and only when dominant and subordinate species overlapped their geographic ranges. This result was evident across diverse phylogenetic groups but varied significantly with a country's level of economic development. Urban-adapted, dominant species were more widespread than closely related subordinate species in cities in developed, but not developing, countries; countries in economic transition showed an intermediate pattern. Our results provide evidence that competitive interactions broadly influence species responses to urbanization, and that these interactions have asymmetric effects on subordinate species that otherwise could be widespread in urban environments. Results further suggest that economic development might accentuate the consequences of competitive interactions, thereby reducing local diversity in cities.

Little plant, big city: a test of adaptation to urban environments in common ragweed (Ambrosia artemisiifolia)

A full understanding of how cities shape adaptation requires characterizing genetically-based phenotypic and fitness differences between urban and rural populations under field conditions. We used a reciprocal transplant experiment with the native plant common ragweed, (Ambrosia artemisiifolia), and found that urban and rural populations have diverged in flowering time, a trait that strongly affects fitness. Although urban populations flowered earlier than rural populations, plants growing in urban field sites flowered later than plants in rural field sites. This counter-gradient variation is consistent adaptive divergence between urban and rural populations. Also consistent with local adaptation, both urban and rural genotypes experienced stronger net selection in the foreign than in the local habitat, but this pattern was not significant for male fitness. Despite the evidence for local adaptation, rural populations had higher lifetime fitness at all sites, suggesting that selection has been stronger or more uniform in rural than urban populations. We also found that inter-population differences in both flowering time and fitness tended to be greater among urban than rural populations, which is consistent with greater drift or spatial variation in selection within urban environments. In summary, our results are consistent with adaptive divergence of urban and rural populations, but also suggest there may be greater environmental heterogeneity in urban environments which also affects evolution in urban landscapes.

How normative interpretations of climate risk assessment affect local decision-making: an exploratory study at the city scale in Cork, Ireland

Urban areas already suffer substantial losses in both economic and human terms from climate-related disasters. These losses are anticipated to grow substantially, in part as a result of the impacts of climate change. In this paper, we investigate the process of translating climate risk data into action for the city level. We apply a commonly used decision-framework as our backdrop and explore where in this process climate risk assessment and normative political judgements intersect. We use the case of flood risk management in Cork city in Ireland to investigate what is needed for translating risk assessment into action at the local city level. Evidence presented is based on focus group discussions at two stakeholder workshops, and a series of individual meetings and phone-discussions with stakeholders involved in local decision-making related to flood risk management and adaptation to climate change, in Ireland. Respondents were chosen on the basis of their expertise or involvement in the decision-making processes locally and nationally. Representatives of groups affected by flood risk and flood risk management and climate adaptation efforts were also included. The Cork example highlights that, despite ever more accurate data and an increasing range of theoretical approaches available to local decision-makers, it is the normative interpretation of this information that determines what action is taken. The use of risk assessments for decision-making is a process that requires normative decisions, such as setting 'acceptable risk levels' and identifying 'adequate' protection levels, which will not succeed without broader buy-in and stakeholder participation. Identifying and embracing those normative views up-front could strengthen the urban adaptation process-this may, in fact, turn out to be the biggest advantage of climate risk assessment: it offers an opportunity to create a shared understanding of the problem and enables an informed evaluation and discussion of remedial action.This article is part of the theme issue 'Advances in risk assessment for climate change adaptation policy'.

Selection based on the size of the black tie of the great tit may be reversed in urban habitats

A standard approach to model how selection shapes phenotypic traits is the analysis of capture–recapture data relating trait variation to survival. Divergent selection, however, has never been analyzed by the capture–recapture approach. Most reported examples of differences between urban and nonurban animals reflect behavioral plasticity rather than divergent selection. The aim of this paper was to use a capture–recapture approach to test the hypothesis that divergent selection can also drive local adaptation in urban habitats. We focused on the size of the black breast stripe (i.e., tie width) of the great tit (Parus major), a sexual ornament used in mate choice. Urban great tits display smaller tie sizes than forest birds. Because tie size is mostly genetically determined, it could potentially respond to selection. We analyzed capture/recapture data of male great tits in Barcelona city (N = 171) and in a nearby (7 km) forest (N = 324) from 1992 to 2008 using MARK. When modelling recapture rate, we found it to be strongly influenced by tie width, so that both for urban and forest habitats, birds with smaller ties were more trap-shy and more cautious than their larger tied counterparts. When modelling survival, we found that survival prospects in forest great tits increased the larger their tie width (i.e., directional positive selection), but the reverse was found for urban birds, with individuals displaying smaller ties showing higher survival (i.e., directional negative selection). As melanin-based tie size seems to be related to personality, and both are heritable, results may be explained by cautious personalities being favored in urban environments. More importantly, our results show that divergent selection can be an important mechanism in local adaptation to urban habitats and that capture–recapture is a powerful tool to test it.