In a significant breakthrough for marine biology, researchers have finally unveiled the mysteries behind the peculiar size discrepancy observed in thorny skates, a species of ray-finned fish inhabiting the North Atlantic. For decades, scientists have puzzled over why this species presents in two distinct sizes across the Atlantic shores of North America, a phenomenon that has left many in the scientific community baffled. The urgent need to understand the size variation arose after their populations not only began to decline sharply but also failed to recover despite conservation efforts.
The journey to uncovering the truth about thorny skate sizes began in the early 2000s, when a college student named Jeff Kneebone embarked on a research project aiming to crack the code behind this marine enigma. At that time, the fish had become known for their striking size difference—one variety growing significantly larger than the other irrespective of their sex. Kneebone, now a senior scientist at the Anderson Cabot Center for Ocean Life at the New England Aquarium, recalls the initial intrigue that would develop into a two-decade quest for answers.
The plight of the thorny skate took a drastic turn in the 1970s when researchers began to notice alarming population declines. Once prevalent along the eastern coast of the United States, these skates plummeted due to overfishing. To combat the dire situation, a stern fishing moratorium was issued in 2003, targeting both the thorny skate and the barndoor skate, another species facing a similar fate. Remarkably, the barndoor skate swiftly rebounded, allowing for some harvesting once again. In stark contrast, the thorny skate’s numbers continued to dwindle, raising further concerns among scientists and conservationists alike.
Data from the National Oceanic and Atmospheric Administration revealed a staggering decline of 80% to 95% in thorny skate populations, particularly near the Gulf of Maine and Canadian waters off the Scotian Shelf. This marked a critical moment for researchers, as they were armed with an imperative goal: understand the underlying reasons for the population depletion and whether the size variations were contributing factors.
Geographical distribution analysis showed that thorny skates thrive across a vast range, extending from South Carolina to the Arctic Circle and into European seas. However, a notable finding was that in regions outside of North America, only one size variety existed, suggesting that environmental or genetic factors specific to the Atlantic coastline might be at play. Scientists, including study co-author Gavin Naylor from the Florida Program for Shark Research, began to hypothesize about the genetic makeup of both size types in hope of finding clarity regarding their differences.
Previous research endeavors had attempted to identify genetic differences between large and small thorny skates, unfortunately yielding inconclusive results. Many researchers concentrated on short DNA sequences from a limited number of samples, which proved inadequate for drawing any meaningful conclusions. Naylor, however, believed a more comprehensive approach was necessary. He proposed a gene capture method designed to acquire extensive genetic data across thousands of sequences in the thorny skate genome, laying the groundwork for a more thorough investigation.
In an unexpected twist, the onset of the COVID-19 pandemic posed a significant challenge to Naylor’s efforts, putting on hold extensive lab work necessary for the project. The restrictions associated with the pandemic prompted one of Naylor’s postdoctoral researchers, Shannon Corrigan, to devise a new strategy—rather than sequencing DNA from hundreds of skates, they would focus on generating a complete genome sequence from just a handful of individuals to maintain progress despite the limitations.
Naylor’s risky pivot paid off. By sequencing the entire genome of four or five thorny skates, researchers significantly reduced in-person labor requirements while managing to gather indispensable data. When Pierre Lesturgie, the study’s first author, delved into the enormity of data gathered from this sequencing, he unearthed an unusual anomaly on chromosome two, which initially presented as an enigmatic region. If it documented mere random sequencing error, it would have been discarded. However, Naylor’s insight regarding a potential gene inversion motivated a closer inspection; this chance encounter became pivotal.
As careful analysis continued, it became apparent that this inverted stretch of DNA was exclusive to the larger varieties of thorny skates. This revelation hinted at a genetic divergence underlying the species’ size differences. Given the historical challenges researchers faced in differentiating between the two morphs, the discovery of this gene inversion marks an extraordinary step forward for understanding thorny skate biology.
Kneebone highlights that further research is essential to develop a robust conservation plan, emphasizing the importance of subsequent observational studies. Understanding the life histories of both sizes of thorny skates has proven challenging due to their inconspicuous characteristics, especially in smaller females. Now equipped with the means to identify size variations genetically, researchers will be better positioned to assess the population dynamics and reproductive success of these skates moving forward, bridging gaps that have long hindered conservation efforts.
As scientists delve deeper into the complexities surrounding this enigmatic species, they will also focus on addressing broader concerns regarding ongoing population declines. Preliminary evidence suggests difficulties in interbreeding between size types may be a contributing factor in areas characterized by dwindling populations. Compounding this issue is the looming threat of climate change, with rising sea temperatures in regions like the Gulf of Maine exacerbating the challenges that thorny skates face in their habitats.
Moving into the future, Kneebone and his colleagues are determined to unravel all the threads intertwined in the thorny skate’s struggle for survival, utilizing advancements in genomic research to inform their conservation strategies. Scientists hope to discern why this species is disproportionately impacted compared to other more resilient skate populations inhabiting the same environments. Through ongoing research and collaboration, the scientific pursuit continues, fueled by a desire not just to understand the past but to ensure the future of this fascinating marine creature.
In conclusion, the recent progress made in understanding the genetic underpinnings driving the size differences in thorny skates is not simply an isolated finding. It represents a passionate pursuit of knowledge within the scientific community, driven by the urgency to protect biodiversity. The implications of this research extend beyond the thorny skate to broader conservation practices, highlighting the interconnectedness of genetics, environmental health, and species survival in the face of unprecedented change.
Subject of Research: Thorny skates’ size variation and population decline
Article Title: Short-term evolutionary implications of an introgressed size-determining supergene in a vulnerable population
News Publication Date: 27-Jan-2025
Web References: Nature Communications
References: DOI: 10.1038/s41467-025-56126-z
Image Credits: Illustration by Jorge Machuski
Keywords: Marine biology, Thorny skates, Conservation genetics, Genomic sequencing, Climate change, Population decline.
