In addition to Darwin’s and Wallace’s foundational theories of evolution by natural selection and Ernst Haeckel’s recognition of ecology as a discipline in the mid-19th century (cf. and references therein), later refined by figures such as George Evelyn Hutchinson and Charles Elton in the early to mid-20th century (; ), the next major advance in understanding how nature functions was John Thompson’s treatise on co-evolutionary processes (). These developments have shaped how ecologists and evolutionary biologists conceptualise interactions among species and their environments.
From this perspective, no organism exists as a free ecological agent; rather, all species are defined by their associations with others. Even animals regarded as dietary “generalists” are constrained by factors governing what they can exploit. These include morphological traits (e.g. teeth, jaws, mandibles), behavioural specialisations (e.g. solitary vs. cooperative hunting), chemical and physiological capacities (e.g. pursuit ability, detoxification), spatial overlap with prey, and cost–benefit trade-offs influencing feeding efficiency. These interactions are dynamic, shaped by coevolutionary feedback that continually refines ecological relationships.
In assembling this Research Topic of Frontiers in Ecology & Evolution, we sought contributions illustrating these co-evolved species relationships and underscoring that all organisms—living or extinct—are, in essence, ecological specialists. As the poet John Donne (1572-1631) wrote, “No man is an island, entire of itself; every man is a piece of the continent, a part of the main” (). Similarly, no animal is ecologically independent of its nutritional associations. Each species occupies a unique ecological niche defined by its evolutionary history and resource dependencies.
Habitats are rarely homogeneous but rather heterogeneous across altitudinal, geographical, and environmental gradients. Consequently, a species’ diet may vary across locations and habitats, whether terrestrial or aquatic. Apparent generalism should therefore be interpreted cautiously. Indeed, generalism runs counter to the direction of evolutionary processes—selection, adaptation, and specialisation. If true generalism persisted, evolution itself would stagnate. In reality, most animals are specialists, their niches fine-tuned by natural selection to local conditions.
A related issue is the widespread discovery of morphologically cryptic species within many taxa, such as the complex of tube-nosed bats in the Philippines revealed through combined morphological and molecular approaches (). If cryptic entities exist within what is considered a single “good species,” each with distinct dietary preferences, then our understanding of species ecology and specialisation is necessarily incomplete ().
Among the studies in this Research Topic, the molecular genetic analysis by Nio et al. of the peach–potato aphid Myzus persicae (Sulzer) sensu stricto in France is particularly relevant. This species has long been regarded as a highly polyphagous pest capable of feeding on plants in over 40 families (; ), especially within the Brassicales and sugar beet crops, and is an important vector of plant viruses (). Although the study’s data are geographically restricted, its implications are broad. The dominance of a few superclonal lineages across diverse hosts suggests that successful genotypes can exploit multiple hosts through molecular-based phenotypic plasticity (e.g. ) rather than true genetic generalism.
The study by Rafter and Walter provides compelling support for specialism as the prevailing evolutionary outcome. Revisiting frameworks for understanding insects that exploit multiple hosts, they show that apparent generalism often reflects behavioural and neurological constraints rather than genuine flexibility. Host recognition, mediated by sensory and neurological feedback, determines host choice in the field. Because host searching carries energetic costs and predation risks, insects are selective even when physiologically capable of feeding on several plants. These findings suggest that many “generalists” are, in reality, a collection of host-associated specialists maintained through behavioural canalisation.
Such insights have direct implications for pest management and biological control. Understanding the behavioural ecology and host-recognition mechanisms of pest species is essential for effective integrated pest management (IPM) (e.g. ). Knowledge of host specificity also informs risk assessments when releasing non-native biocontrol agents and helps minimise non-target impacts.
Quicke et al. contribute a monumental 38-year study from the Área de Conservación Guanacaste (ACG) in north-western Costa Rica, documenting caterpillar–host plant associations across habitats. This dataset, complemented by their companion study on tachinid parasitoids (), provides an unparalleled perspective on specialisation and generalism among Lepidoptera. The results reveal a spectrum of feeding strategies, from monophagy to polyphagy, with some groups confined to specific microhabitats or host-plant taxa.
These findings illustrate a long-standing evolutionary arms race between plants and herbivores. Plants, unable to flee, rely on anatomical and chemical defences, while herbivores evolve counteradaptations to exploit them. This interaction dates back hundreds of millions of years to the emergence of terrestrial insects (~480 MYA). Chemical defences such as jasmonate not only deter herbivory but also signal to nearby plants and attract predators of herbivores (; ; ; ).
As Quicke et al. emphasise, insect host range is tightly linked to biochemical detoxification mechanisms, particularly broad-spectrum enzymes such as carboxyl esterases and cytochrome P450s. Evolving and maintaining such systems is metabolically costly, possibly explaining why true polyphagy is rare. Although a broad diet can buffer species against local food shortages, long-term evolutionary trade-offs may favour specialisation (Loxdale and Balog).
Quicke et al.’s study also highlights the challenge of identifying morphologically cryptic species without molecular tools. Only with high-resolution markers—mitochondrial DNA, microsatellites, or genome sequencing—can we accurately assess genetic uniformity across populations. This Research Topic has been underscored by , who revealed numerous cryptic parasitoid complexes through DNA barcoding. Such findings reinforce that ecological specialisation is mirrored at the molecular level, where genetic divergence tracks ecological divergence.
Finally, the study by Sipos et al. compares two hornet species in Hungary—the native Vespa crabro and the invasive Asian hornet, Vespa velutina nigrithorax, both predators of honey bees, Apis mellifera—using digital microscopy and micro-CT imaging. They found V. velutina to be darker, smaller, and more agile, with longer legs and greater wing surface area relative to body mass. These traits confer superior flight performance, manoeuvrability, and bee-hunting efficiency, providing a competitive advantage where the two species co-occur. Such morphological and behavioural differences exemplify how ecological specialisation drives invasion success.
Collectively, the papers in this Research Topic underscore the prevalence and importance of ecological specialisation. Even studies not directly focused on diet breadth illuminate the complex, co-evolved interactions that structure ecosystems. Together, they affirm that specialisation—not generalism—is the dominant mode of life, fundamental to both evolutionary process and ecological balance.
Statements
Author contributions
HL: Writing – review & editing, Project administration, Writing – original draft, Conceptualization. AB: Project administration, Conceptualization, Writing – original draft, Writing – review & editing.
Acknowledgments
We most sincerely thank all the referees for their expert services in reviewing this collection of papers, without whose efforts the production of the Research Topic would have been impossible.
Conflict of interest
The authors declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.
Publisher’s note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
References
1
BlackmanR. L. (2010). “ Aphids – Aphidinae (Macrosiphini),” in Handbooks for the identification of British insects, vol. 2. ( Royal Entomological Society, Field Studies Council, Shrewsbury, U.K).
2
BlackmanR. L.EastopV. F. (2000). Aphids on the World’s crops: an identification and information guide. 2nd Edn (Chichester, U.K: John Wiley & Sons Ltd).
3
EgerJ. L.SedlockJ. L.LimB. K.HeaneyL. R. (2025). Systematics and biogeography of tube-nosed bats, Murina (Mammalia, Chiroptera, Vespertilionidae), from the Philippines with descriptions of six new species. Zootaxa5691, 1–44. doi: 10.11646/zootaxa.5691.1.1
4
Finlay-DoneyM.WalterG. H. (2012). The conceptual and practical implications of interpreting diet breadth mechanistically in generalist predatory insects. Biol. J. Linn. Soc.107, 737–763. doi: 10.1111/j.1095-8312.2012.01991.x
5
JanzenD. H.HallwachsW.BlandinP.BurnsJ. M.CadiouJ.-M.ChaconI.et al. (2009). Integration of DNA barcoding into an ongoing inventory of complex tropical biodiversity. Mol. Ecol. Resour.9, 1–26. doi: 10.1111/j.1755-0998.2009.02628.x
6
LoxdaleH. D. (2010). Setting the scene…meeting up with Darwin and Wallace. Ecol. Entomol.35, 1–9. doi: 10.1111/j.1365-2311.2009.01139.x
7
LoxdaleH. D.DavisB. J.DavisR. A. (2016). Known knowns and unknowns in biology. Biol. J. Linn. Soc.117, 386–398. doi: 10.1111/bij.12646
8
MathersT. C.ChenY.KaithakottilG.LegeaiF.MugfordS. T.Baa-PuyouletP.et al. (2017). Rapid transcriptional plasticity of duplicated gene clusters enables a clonally reproducing aphid to colonise diverse plant species. Genome Biol.18, 20. doi: 10.1186/s13059-016-1145-3
9
PartingtonA. (1992). “ John Donne, (1572–1631),” in The Oxford dictionary of quotations, 4th Edn ( Oxford University Press, Oxford and New York).
10
QuickeD. L. J.FlemingA. J.WoodD. M.WoodleyN. E.ManjunathR.NaikS.et al. (2025). Tachinid flies (Diptera), caterpillar hosts (Lepidoptera) and their food plants, reared in Área de Conservación Guanacaste (ACG), Northwestern Costa Rica: documenting community structure with the aid of DNA barcodes. Diversity17, 658. doi: 10.3390/d17090658
11
RichardsonD. M.PyšekP. (2008). Fifty years of invasion ecology – the legacy of Charles Elton. Divers. Distrib.14, 161–168. doi: 10.1111/j.1472-4642.2007.00464.x
12
SlobodkinL. B.SlackN. G. (1999). George Evelyn Hutchinson: 20th-century ecologist. Endeavour23, 24–30. doi: 10.1016/S0160-9327(99)01182-5
13
StevensM.LacommeC. (2017). “ Transmission of plant viruses,” in Aphids as crop pests, 2nd Edn. Eds. van EmdenH. F.HarringtonR. ( CABI, Wallingford, Oxon, U.K), 323–361.
14
ThalerJ. (1999). Jasmonate-inducible plant defences cause increased parasitism of herbivores. Nature399, 686–688. doi: 10.1038/21420
15
ThalerJ. S.StoutM. J.KarbanR.DuffeyS. S. (2001). Jasmonate-mediated induced plant resistance affects a community of herbivores. Ecol. Entomol.26, 312–324. doi: 10.1046/j.1365-2311.2001.00324.x
16
ThompsonJ. N. (1994). The co-evolutionary process (Chicago, IL: University of Chicago Press).
17
WangJ.WuD.WangY.XieD. (2019). Jasmonate action in plant defense against insects. J. Exp. Bot.70, 3391–3400. doi: 10.1093/jxb/erz174
18
WarA. R.BuhrooA. A.HussainB.AhmadT.NairR. M.SharmaH. C. (2020). “ Plant defense and insect adaptation with reference to secondary metabolites,” in Co-evolution of secondary metabolites. Eds. MérillonJ. M.RamawatK. ( Springer Nature, Cham, Switzerland), 795–822. doi: 10.1007/978-3-319-96397-6_60
Summary
Keywords
specialism, generalism, genetic variation, geographic range, dietary breadth, cryptic speciation
Citation
Loxdale HD and Balog A (2025) Editorial: The paradox of generalism. Front. Ecol. Evol. 13:1754212. doi: 10.3389/fevo.2025.1754212
Received
25 November 2025
Accepted
05 December 2025
Published
12 December 2025
Volume
13 - 2025
Edited and reviewed by
Sasha Raoul Xola Dall, University of Exeter, United Kingdom
Updates
Copyright
© 2025 Loxdale and Balog.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Hugh D. Loxdale, LoxdaleH@cardiff.ac.uk
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.