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Societal Impact Statement: Given the rapidly increasing drought and temperature stresses associated with climate change, innovative approaches for food security are imperative. One understudied opportunity is using feral crops—plants that have escaped and persisted without cultivation—as a source of genetic diversity, which could build resilience in domesticated conspecifics. In some cases, however, feral plants vigorously compete with crops as weeds, challenging food security. By bridging historically siloed ecological, agronomic, and evolutionary lines of inquiry into feral crops, there is the opportunity to improve food security and understand this relatively understudied anthropogenic phenomenon. Summary: The phenomenon of feral crops, that is, free‐living populations that have established outside cultivation, is understudied. Some researchers focus on the negative consequences of domestication, whereas others assert that feral populations may serve as useful pools of genetic diversity for future crop improvement. Although research on feral crops and the process of feralization has advanced rapidly in the last two decades, generalizable insights have been limited by a lack of comparative research across crop species and other factors. To improve international coordination of research on this topic, we summarize the current state of feralization research and chart a course for future study by consolidating outstanding questions in the field. These questions, which emerged from the colloquium "Darwins' reversals: What we now know about Feralization and Crop Wild Relatives" at the BOTANY 2021 conference, fall into seven categories that span both basic and applied research: (1) definitions and drivers of ferality, (2) genetic architecture and pathway, (3) evolutionary history and biogeography, (4) agronomy and breeding, (5) fundamental and applied ecology, (6) collecting and conservation, and (7) taxonomy and best practices. These questions serve as a basis for ferality researchers to coordinate research in these areas, potentially resulting in major contributions to food security in the face of climate change. [ABSTRACT FROM AUTHOR]

In our rapidly changing world, where human activities have profound effects on nearly all forms of life, understanding the dynamics of organismal adaptation to human-induced environmental changes is of paramount importance. This paper delves into the concept of domestication as an early manifestation of the Anthropocene, shedding light on how animal populations respond to domestication selection provides valuable insights into the intricate interplay between plastic responses and evolutionary changes. By examining this relationship, we gain a deeper understanding of the fate of wild vertebrates as they navigate a human-altered world. Through a comprehensive analysis, intentional breeding, managed hunting, and extermination emerge as interconnected elements within a continuum of anthropogenic agents driving ecological selection. Moreover, we identify shared targets of selection that extend beyond domestication, encompassing a broader range of human-induced selection pressures. Remarkably, many traits that facilitate successful domestication also equip wild animals with the adaptive capacity to thrive in humandominated environments, highlighting their importance in understanding the larger context of adaptation. Additionally, domestic animals serve as a source for feral lineages and genetic exchange with their wild counterparts. This exchange, coupled with shared ecological constraints and gene flow, contributes to convergent or congruent changes across various responses to human influence. By recognizing domestication as another source of anthropogenic selection, we unlock valuable insights for conservation efforts and present a promising avenue for unraveling the mechanisms underlying behavioral adaptation. In summary, this review emphasizes the urgent need to comprehend how organisms adapt or fail to adapt to human-induced environmental changes. By elucidating the intricate relationships between domestication, human-induced selection pressures, and adaptation, we deepen our understanding of the complex dynamics within the Anthropocene and pave the way for effective conservation strategies while shedding light on the mechanisms that drive behavioral adaptation. [ABSTRACT FROM AUTHOR]

Simple Summary: Understanding the impact of urbanization on biodiversity is a crucial task of our time. Here, we reflect on the importance of feralization in the relationship between ongoing urbanization and the worsening biodiversity crisis. Feralization is often viewed as the exact opposite of a domestication process—a perception that we argue is too simplistic. The interrelations between domestication, feralization, and the adaptation of taxa to novel, human-made environments such as cities are complex. Given their unique traits, feral(izing) taxa can play key roles in sustainability, sometimes problematic (i.e., invasive species) but at other times, improving human well-being in urban settings. Domestication describes a range of changes to wild species as they are increasingly brought under human selection and husbandry. Feralization is the process whereby a species leaves the human sphere and undergoes increasing natural selection in a wild context, which may or may not be geographically adjacent to where the originator wild species evolved prior to domestication. Distinguishing between domestic, feral, and wild species can be difficult, since some populations of so-called "wild species" are at least partly descended from domesticated "populations" (e.g., junglefowl, European wild sheep) and because transitions in both directions are gradual rather than abrupt. In urban settings, prior selection for coexistence with humans provides particular benefit for a domestic organism that undergoes feralization. One risk is that such taxa can become invasive not just at the site of release/escape but far away. As humanity becomes increasingly urban and pristine environments rapidly diminish, we believe that feralized populations also hold conservation value. [ABSTRACT FROM AUTHOR]

Simple Summary: Cats (Felis silvestris catus) live with humans as domesticated animals. However, it is not clear how they have evolved from African wildcats (Felis silvestris lybica) through domestication. In this study, we compared the facial morphology of cats and wildcats to determine how the facial morphology of cats has changed in relation to their interactions with humans. Cats kept by humans had a smaller nose length and a lower eye angle compared with wildcats and feral cats, and these changes were found to influence cuteness ratings. The facial morphology of feral cats not living with humans was not significantly different from that of wildcats, suggesting that this change is due to the process of feralization. We aimed to clarify the changes in facial morphology of cats in relation to their interactions with humans. In Study 1, we compared the facial morphology of cats (feral mixed breed, owned domestic mixed breed, and owned domestic purebreds) with that of African wildcats. After collecting 3295 photos, we found that owned domestic cats' noses were significantly shorter than those of African wildcats and feral mixed breed, and there were no significant differences between the latter two. The eye angles were significantly more gradual in owned domestic purebreds than in the other groups. In Study 2, we examined the correlation between facial morphology and years with the owner, and found that the former is not affected by the latter. This suggests that changes in facial morphology are possibly transgenerational changes. The difference in facial morphology between wildcats and owned cats might be caused by domestication, and that between feral cats and owned cats might be due to feralization. In Study 3, we investigated whether cats' facial features affect cuteness ratings. We asked human participants to evaluate the cuteness of cats' face images and found that faces with shorter nose lengths were considered cuter. This suggests that owned domestic cats' facial morphology is preferred by humans. [ABSTRACT FROM AUTHOR]

The release of domesticated conspecifics into the natural environment, whether deliberate or accidental, has the potential to alter the genetic integrity and evolutionary trajectory of wild populations. This widespread challenge is of particular concern for wild Atlantic salmon. By investigating phenotypic differences between the offspring of domesticated, hybrid, and wild Atlantic salmon released into the natural environment, earlier studies have documented the short‐term consequences of introgression from domesticated fish into wild salmon populations. However, few studies have investigated the joined product of introgression and natural selection after several generations. Here, we investigated the phenotypic response of an Atlantic salmon population that has been subjected to an average of 24% genetic admixture by domesticated conspecifics escaping from fish farms over three decades (approximately 6–7 generations). Individual levels of admixture were positively correlated with increased size at the smolt and adult stages for both sexes, a decrease in the age of male smolts, and a decrease in the age at maturity for males. These life history changes are presumably the consequence of the well‐documented directional selection for increased growth in domesticated salmon and are likely maladaptive. However, the most novel result of this study is that admixture was positively linked with delayed date of return to the river, with highly admixed fish arriving up to 26 days later than nonadmixed fish. Potentially, this phenological change provides admixed individuals with a survival advantage in the later phase of the life cycle as it reduces their period of exposure to selection through rod and line angling. We, therefore, conclude that while gene flow from domesticated conspecifics changes life history and phenological traits of wild Atlantic salmon populations, most of which are likely to be maladaptive, when pressured by additional anthropogenic challenges, some changes may confer a fitness advantage for a short part of the life cycle. [ABSTRACT FROM AUTHOR]

Feral populations, those which successfully persist outside of cultivation or husbandry, provide unique opportunities to study the genomic impacts of domestication and local adaptation. We argue that by leveraging genomic resources designed for domestic counterparts, powerful phylogenetic and population genomic data collection and analyses can be designed to disentangle complex demographic processes. [ABSTRACT FROM AUTHOR]

Formerly domesticated organisms and artificially selected genes often escape controlled cultivation, but their subsequent evolution is not well studied. In this review, we examine plant and animal feralization through an evolutionary lens, including how natural selection, artificial selection, and gene flow shape feral genomes, traits, and fitness. Available evidence shows that feralization is not a mere reversal of domestication. Instead, it is shaped by the varied and complex histories of feral populations, and by novel selection pressures. To stimulate further insight we outline several future directions. These include testing how 'domestication genes' act in wild settings, studying the brains and behaviors of feral animals, and comparative analyses of feral populations and taxa. This work offers feasible and exciting research opportunities with both theoretical and practical applications. Feral animals and plants have become ubiquitous worldwide, but their evolution has not been well studied. The process of feralization offers unique and important opportunities to study adaptive evolution, often in model systems inhabiting diverse, novel, and/or changing environments. Recent work shows that feral taxa undergo rapid evolutionary changes at loci controlling an array of fitness-related traits, including morphology, behavior, and development. Gene flow between domesticated and wild populations has important, diverse, and context-dependent effects on fitness in recipient populations. Legacies of domestication are seen in many feral plants and animals. These features can have important and unexpected roles in subsequent adaptation to changing (e.g., feral) environments. [ABSTRACT FROM AUTHOR]

Selection regimes and population structures can be powerfully changed by domestication and feralization, and these changes can modulate animal fitness in both captive and natural environments. In this review, we synthesize recent studies of these two processes and consider their impacts on organismal and population fitness. Domestication and feralization offer multiple windows into the forms and mechanisms of maladaptation. Firstly, domestic and feral organisms that exhibit suboptimal traits or fitness allow us to identify their underlying causes within tractable research systems. This has facilitated significant progress in our general understandings of genotype–phenotype relationships, fitness trade‐offs, and the roles of population structure and artificial selection in shaping domestic and formerly domestic organisms. Additionally, feralization of artificially selected gene variants and organisms can reveal or produce maladaptation in other inhabitants of an invaded biotic community. In these instances, feral animals often show similar fitness advantages to other invasive species, but they are also unique in their capacities to modify natural ecosystems through introductions of artificially selected traits. We conclude with a brief consideration of how emerging technologies such as genome editing could change the tempos, trajectories, and ecological consequences of both domestication and feralization. In addition to providing basic evolutionary insights, our growing understanding of mechanisms through which artificial selection can modulate fitness has diverse and important applications—from enhancing the welfare, sustainability, and efficiency of agroindustry, to mitigating biotic invasions. [ABSTRACT FROM AUTHOR]

Predation is an important factor during adaptation to novel environments, and the feralisation of introduced domestic species often involves responding appropriately to allopatric predators despite a background of domestication and inbreeding. Twenty years ago, domestic guppies were introduced to a semi-natural environment at Burgers’ Zoo in the Netherlands, where they have since been exposed to avian predation. We compared predation-linked behaviours in this feral population and in domestic guppies akin to the original founders. We found that both populations responded to a novel predator and to conspecific alarm cues. However, shoaling, an important anti-predator behaviour, was higher among feral guppies both at baseline and when exposed to the novel predator. We did not observe a linked suite of anti-predator behaviours across shoaling, predator inspection, alarm substance sensitivity and boldness, suggesting that these responses may be decoupled from one another depending on local predation regimes. As we compared two populations, we cannot identify the causal factors determining population differences, however, our results do suggest that shoaling is either a particularly consequential anti-predator adaptation or the most labile of the behaviours we tested. Finally, the behavioural adaptability of domestic guppies may help to explain their success as an invasive species. [ABSTRACT FROM AUTHOR]

This study tested the 'silver spoon' hypothesis which posits that individuals that develop under favourable conditions should enjoy a fitness advantage later in life because they are more likely to recognize and settle in high-quality habitats. Atlantic salmon Salmo salar of two age classes (0+ and 1+ years) were reared in environmentally enriched or standard hatchery tanks for a short period (c. 10 weeks), were then released into a natural river and sampled on repeated occasions to test for silver-spoon effects. Compared with controls, enriched fish had a 6·4% higher recapture rate and settled in higher velocity habitats when they were stocked as 0+ year fry, but not when they were stocked as 1+ year parr. The opportunity for selection was generally higher for environmentally enriched fish than for controls, and also higher for 0+ than for 1+ year fish. Selection favoured individuals with high condition factor, extensive fat reserves and longer than average pectoral fins in both age classes but favoured a small body size in 1+ year and a large body size in 0+ year releases. Stomach analysis showed that enriched fish ate more, and adapted quicker to natural prey than controls. These results provide support for silver-spoon effects in fish and indicate that enrichment can improve post-release performance in conservation programmes, but seemingly only if fish are not kept in captivity for too long. [ABSTRACT FROM AUTHOR]

Changes in body shape, fluctuating asymmetry (FA) and crypsis were compared among Atlantic salmon Salmo salar fry kept as controls in captivity and those released and subsequently recaptured in the wild according to a before-after-control-impact (BACI) design. Hatchery fish that survived in the wild became more cryptic and displayed a much lower incidence of fin erosion and of asymmetric individuals than control fish kept in captivity. Significant differences in body shape were also apparent, and survivors had longer heads, thicker caudal peduncles and a more streamlined body shape than hatchery controls as early as 20 days following stocking, most likely as a result of phenotypic plasticity and non-random, selective mortality of maladapted phenotypes. Hatchery-reared fish typically perform poorly in the wild and the results of this study indicate that this may be due to phenotypic mismatch, i.e. because hatcheries generate fish that are phenotypically mismatched to the natural environment. [ABSTRACT FROM AUTHOR]

Allometries of the brain to body size relationship in eutherian mammals are examined in this study as they can be used for comparative analyses concerning encephalization. In contrast with some modern presentations of this issue, an older concept is revived and expanded through this author’s current study. Three allometries with clearly different slopes are valid and lead to reliable results: interspecific, intraspecific, and ontogenetic allometries. Interspecific allometries follow lines with slope values of 0.56 or 0.63 for larger and smaller species, respectively, and characterize different average encephalization plateaus with rodents and lagomorphs generally more strongly encephalized compared to basal insectivores. Artiodactyls, perissodactyls and carnivores as a whole are again on a higher but rather similar plateau. Several species of carnivores have reached different encephalization levels with respect to their average plateau indicating diverse radiations. A phylogenetic brain size increase from fossil to recent radiations is also evident. Intraspecific allometries have slope values of about 0.25. These are of help in comparing brain sizes of ancestral species with their domesticated relatives. Domestication has generally led to a brain size decrease, but species on higher encephalization plateaus show this trend more strongly than species on a lower level of encephalization. Several brain parts and the sense organs also decrease in size during the domestication process, but vary arbitrarily and to different degrees. Ontogenetic growth allometries are species-specific, but are especially different between altricial and precocial mammals. A very steep 1st phase slope of highly encephalized species is particularly useful for understanding evolutionary and adaptive phenomena. Domesticated mammals that have become feral do not show an increase in brain size despite living many generations in wild habitats. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]