The research, conducted by scientists at Stockholm University, examined over 580 species, encompassing more than 90 percent of all known skates and rays. This comprehensive dataset enabled the team to reconstruct the evolutionary history of these animals’ conspicuous markings in unprecedented detail. Their findings underscore the importance of considering an animal’s entire suite of defenses when trying to understand the evolutionary pressures shaping these visual traits. By integrating ecological context, environmental factors, and other defensive mechanisms, the study reveals why dramatic visual features such as eyespots appear selectively and evolve only under certain conditions.

Unlike previous studies that isolated eyespots as singular evolutionary phenomena, this research examines how these markings coexist and trade off with other anti-predator adaptations. Skates and rays navigate a perilous world inhabited by formidable predators, including sharks, marine mammals, and predatory fishes. Evolutionary biology teaches us that survival tactics rarely rely on a single solution. Some species are equipped with potent mechanical defenses such as venomous spines or electrical organs capable of delivering shocks to potential attackers. These weapons represent a highly effective deterrent that reduces the necessity for conspicuous signaling. By contrast, species lacking such robust physical defenses are more inclined to develop vivid markings as a complementary or alternative strategy.

One of the study’s pivotal revelations is the strong correlation between the density and type of visual markings and the animal’s habitat. Species dwelling in shallow, well-lit waters—typically less than 200 meters in depth—are far more prone to exhibit eyespots or bold spots. Light availability is a crucial factor since the efficacy of visual cues depends directly on the environmental conditions in which they operate. In darker, deeper waters where sunlight penetration is minimal, visual signals lose their utility, and selection pressures favor cryptic coloration and other forms of camouflage, leading to the absence or loss of conspicuous markings. The researchers conclude that in well-illuminated habitats, where vision-based signaling can effectively communicate danger or unpalatability, eyespots provide a valuable addition to the defensive arsenal.

Lead researcher Madicken Åkerman eloquently summarizes the findings: eyespots do not emerge randomly but are tightly linked to ecological and defensive variables that shape their adaptive value. Their presence reflects a trade-off within evolutionary “toolkits” available to a species. If an organism already possesses a strong mechanical or chemical defense, such as a venomous sting or an electrical shock, investing energy and evolutionary resources into visual warning signals offers marginal benefit. In such cases, the exclusivity of potent physical defenses suppresses the need for prominent coloration. In contrast, smaller-bodied skates and rays that lack these formidable features often resort to visual signals as a frontline deterrent, a testament to the multiplicity of evolutionary solutions to predation threats.

The evolutionary pathway leading to the development of eyespots does not follow a straightforward trajectory. Contrary to intuition, these complex concentric-ring markings rarely appear abruptly in evolutionary time. Instead, eyespots typically arise through a gradual refinement of simpler markings—bold spots or other conspicuous dots. Statistical modeling shows that the probability of initially gaining simple markings outstrips that of directly evolving fully formed eyespots by an estimated factor of one hundred. This suggests a stepwise evolutionary process whereby incremental changes in pigmentation patterns accumulate over generations, eventually culminating in the elaborate eyespots that are ecologically advantageous under specific conditions.

Senior co-author John Fitzpatrick emphasizes this gradational evolution as indicative of adaptive fine-tuning. Gradual enhancement of visual signals allows species to balance the costs and benefits associated with conspicuousness over time. Larger, more complex eyespots may offer superior deterrence by mimicking the eyes of predators or by creating illusions that confuse attackers, but they also carry risks. Conspicuous markings increase visibility to predators and may come at an energetic cost. Thus, natural selection carefully mediates their appearance, favoring eyespots only when the benefits in predator deterrence outweigh the risks inherent in being more visible.

Furthermore, the study highlights that these conspicuous markings are not permanent fixtures in an evolutionary timeline but are subject to frequent loss. When environmental conditions change—particularly when species transition into deeper, darker habitats—the selective pressures favoring eyespots diminish. Since the visual signals become ineffective without adequate light, and indeed may even increase predation risk by making the organism more noticeable to predators with enhanced sensory modalities other than vision, the markings tend to fade or disappear altogether. This dynamic pattern underscores the reversible nature of some evolutionary traits, dictated by fluctuating ecological demands.

In addition to ecological factors, body size appears to influence the propensity for developing eyespots. Smaller species, which often lack the means for powerful physical defense, lean more heavily on visual deterrence, while larger species with formidable mechanical or electrical defenses have reduced need for such signals. This interplay of size, defense mechanism, habitat, and environmental light availability shapes a complex adaptive landscape in which multiple selective factors operate concurrently.

This research offers profound implications for understanding the evolutionary biology of visual signaling beyond skates and rays. The nuanced insights into how diverse defensive systems integrate and trade off against each other provide a fresh perspective on the evolution of warning coloration in marine and terrestrial animals alike. By advancing the paradigm that eyespots are not standalone features but components of multifaceted defense strategies influenced by environmental and physiological contexts, this study paves the way for further investigation into the evolutionary ecology of visual communication.

The use of comprehensive phylogenetic analysis combined with broad ecological data enhances the robustness of the findings, showcasing the power of multidisciplinary approaches to evolutionary questions. Moreover, the findings invite renewed attention to the evolutionary arms race between predator and prey, revealing that adaptation is a balance of multiple strategies rather than a singular optimization. Ultimately, this study exemplifies how integrating detailed natural history, morphology, and environmental variables can disentangle complex evolutionary processes.

Subject of Research: Animals
Article Title: The evolution of eyespots in skates and rays
News Publication Date: 24-Apr-2026
Web References: https://doi.org/10.1038/s41559-026-03059-5
Image Credits: Anette Gärdeklint Sylla/Stockholm University
Keywords: eyespots, skates, rays, evolutionary biology, visual signals, anti-predator defense, camouflage, marine biology, phenotype evolution, predator-prey interaction, animal coloration, stepwise evolution

Utilizing cutting-edge genomic techniques, the researchers applied ddRAD sequencing in tandem with mitochondrial DNA analyses to unravel the population structure of this commercially and ecologically significant crustacean. By sampling four geographically distinct regions — Florida in the USA, Northeastern Brazil, Eastern Brazil, and Southeastern Brazil — they achieved comprehensive coverage of the species’ entire distribution. The study aimed to test whether oceanographic features, particularly the famed Amazon–Orinoco Plume, act as semi-permeable barriers influencing genetic differentiation despite the species’ high dispersal potential.

Strikingly, the analysis exposed two genetically distinct clusters that correspond to northern and southern population groups. The northern group, encompassing Florida and Northeastern Brazil samples, exhibited notably higher levels of genetic diversity compared to their southern counterparts collected from Eastern and Southeastern Brazil. This bifurcation occurs despite an absence of strict physical barriers, suggesting that factors beyond mere geography sculpt the population structure.

One critical insight derived from demographic modeling revealed that these divergence events likely initiated approximately two million years ago, coinciding with climatic fluctuations during the Pleistocene epoch. The temporal scale points to allopatric divergence fuelled by historical isolation, followed by secondary contact where gene flow resumed but remained asymmetric and limited. Instead of complete reproductive isolation, the populations exhibit a classic divergence-with-gene-flow scenario, wherein enough genetic separation is maintained to promote distinct evolutionary trajectories while allowing intermittent interbreeding.

Ecologically, the Amazon–Orinoco Plume emerges as a fundamental oceanographic feature influencing these dynamics. The plume, a massive freshwater outflow rich in sediments and nutrients extending from northern South America, creates unique salinity gradients and turbidity barriers that affect larval dispersal and survival. Such semi-permeable barriers impede but do not entirely block larval exchange, facilitating a balance between connectivity and isolation. This oceanographic complexity underlines how ecological differentiation paired with environmental discontinuities can drive speciation even in high-mobility marine species.

Complementing the genomic insights, mitochondrial DNA analyses and species delimitation algorithms robustly supported the taxonomic distinctness of the northern and southern populations. The authors propose that these clusters might represent cryptic species, a revelation with profound implications for biodiversity assessments, fisheries management, and conservation policies. Recognizing genetically discrete units enhances management precision, ensuring sustainable exploitation and protection aligned with evolutionary and ecological realities.

Intriguingly, the study also identifies signs of recent demographic shifts, including expansions and contractions linked to climate cycles. Both populations experienced expansion post-Last Glacial Maximum, roughly 20,000 years ago, reflecting habitat suitability improvements as ice sheets receded and oceanic conditions stabilized. More concerning is evidence of recent population declines, especially in the southern group, which may reflect anthropogenic pressures such as overfishing, habitat degradation, and climate change. These trends warrant urgent attention to safeguard the species’ long-term viability.

The implications of this research transcend the pink shrimp and extend to broader marine biodiversity paradigms. It challenges the traditional notion that marine species with high dispersal abilities are genetically homogenous across broad ranges. Instead, it affirms that subtle environmental factors and historical demographic processes can foster significant genomic divergence that may underpin speciation events. Studies like this reshape our comprehension of marine evolutionary biology, signaling the need for nuanced frameworks accommodating gene flow and environmental heterogeneity.

From a methodological perspective, the integration of high-resolution genomic data with sophisticated demographic modeling exemplifies the future of marine population genetics. Techniques such as ddRAD sequencing enable fine-scale detection of genetic structure that conventional markers often miss. This precision is vital for uncovering ‘cryptic’ diversity that might be invisible to classic taxonomy based solely on morphology. The study thus sets a gold standard for investigating population connectivity in other elusive or economically vital marine taxa.

The dichotomy discovered between northern and southern Farfantepenaeus brasiliensis populations also raises questions about the evolutionary pressures shaping these groups. Differences in genetic diversity hint at varied evolutionary histories, possibly linked to distinct ecological niches or historical population sizes. The northern cluster maintains greater heterozygosity, indicating larger effective population sizes and potentially higher resilience. Conversely, the southern cluster’s reduced diversity and evidence of recent decline signal vulnerability, emphasizing the need for geographically tailored management strategies.

Moreover, the influential role of the Amazon–Orinoco Plume as a partial barrier reinforces the importance of integrating physical oceanography with evolutionary biology. Understanding oceanographic features such as currents, salinity gradients, and freshwater outflows provides crucial context for interpreting gene flow patterns. These insights transcend the pink shrimp case, highlighting how dynamic environmental forces sculpt marine biodiversity mosaics across the globe.

As fisheries worldwide grapple with sustainability challenges, this research signals a pivotal direction. Conservation efforts must acknowledge hidden genetic subdivisions to avoid the pitfalls of managing species as monolithic units. Genetic data can guide the designation of management units, inform breeding stock selections, and support ecosystem-based approaches that preserve evolutionary potential. In the face of accelerating climate change and habitat alteration, adaptive management informed by contemporary evolutionary science becomes indispensable.

In summary, the study by Teles and colleagues offers a compelling narrative of marine divergence driven by a nuanced interplay between gene flow, historic isolation, and ecological barriers. It underscores that speciation in the ocean is neither a purely physical nor a simplistic process but a layered dynamic shaped by genetic, environmental, and demographic factors. This work enriches our understanding of marine evolution and provides a practical framework for enhancing biodiversity management in a changing world.

Looking ahead, further research could explore how ecological differences between these populations influence phenotype, behavior, and reproductive isolation mechanisms. Additionally, assessing how contemporary oceanographic changes may alter gene flow patterns would deepen our grasp of species resilience. Ultimately, this study opens avenues to redefine marine biodiversity conservation in multidimensional genetic and ecological landscapes.

The revelations from this investigation redefine our comprehension of marine species complexity, offering a window into the evolutionary tapestry woven beneath the waves. Pink shrimp, long a staple in commercial fisheries, now present a fascinating case of cryptic divergence and ongoing genomic interplay. Integrating such knowledge promises to revolutionize marine biodiversity stewardship, aligning industry, science, and conservation in a shared quest to sustain the ocean’s living treasures.

Subject of Research: Genomic structure and demographic history of the pink shrimp Farfantepenaeus brasiliensis across the Western Atlantic.

Article Title: Genomic evidence of divergence-with-gene-flow in the pink shrimp Farfantepenaeus brasiliensis.

Article References:
Teles, J.N., Peres, P.A., Bracken-Grissom, H. et al. Genomic evidence of divergence-with-gene-flow in the pink shrimp Farfantepenaeus brasiliensis. Heredity 134, 705–717 (2025). https://doi.org/10.1038/s41437-025-00811-8

Image Credits: AI Generated

DOI: 27 November 2025

Keywords: marine divergence, population genomics, pink shrimp, Farfantepenaeus brasiliensis, gene flow, cryptic species, marine biodiversity, oceanographic barriers, Amazon–Orinoco Plume, demographic history, high dispersal species, population structure, evolutionary biology, conservation genetics