In a remote corner of Russia’s Kamchatka Peninsula, an ancient glacial lake known as Tymgygytgyn is home to a truly extraordinary and unsettling phenomenon: a unique population of char fish that have evolved to become cannibals. This remarkable discovery, stemming from a joint expedition by employees of the ‘Volcanoes of Kamchatka’ natural park network alongside scientists from Vitus Bering Kamchatka State University and the A.N. Severtsov Institute of Ecology and Evolution (IPEE RAS), casts new light on the raw, relentless forces of natural selection in one of the planet’s most pristine environments.
Tymgygytgyn Lake, measuring approximately 0.35 square kilometers with depths reaching 11 meters, is the most frequently visited among a cascade of water bodies nestled on the northern slopes of the Ichinsky volcano in the Bystrinsky District. Its formation, dating back to glacial periods, has left it uniquely sculpted, with a moraine — a ridge of rocks and earth left by a retreating glacier — damming its southern edge, while a steeply descending stream flows from its northern reaches. Over millennia, this ancient basin has gradually undergone significant changes, with its shores increasingly overgrown by floating vegetation and its bed accumulating layers of silt.
The lake’s dramatic history is intrinsically linked to the region’s volcanic past. Approximately 7,500 years ago, a powerful eruption from the Northern Cherpuk volcano unleashed a lava flow that effectively dammed the valley. Before this seismic event, Tymgygytgyn was merely the headwaters of the Ketachan River. When the glaciers eventually receded, an anadromous form of Dolly Varden char, locally known as ‘malma,’ found its way into this newly formed lake. Crucially, the subsequent isolation of this population created a natural laboratory for evolution, forcing the fish to adapt to radically new and challenging conditions.
Cut off from their ancestral migratory paths, the char embarked on an accelerated evolutionary journey. Their spawning cycle, for instance, dramatically shifted from September to January, and the fish developed a distinctive black breeding coloration. However, arguably the most striking adaptation observed in this isolated population is the periodic emergence of gigantic, cannibalistic individuals, a behavior driven by the lake’s fluctuating resources.
Faced with an unpredictable and often scarce food supply, a subset of the adult char, weighing up to 300 grams, resorts to consuming their own young. This high-calorie diet provides a crucial advantage, accelerating their growth significantly, with some individuals reaching an impressive 900 grams. Intriguingly, even these giants cease feeding before spawning, joining their smaller counterparts in the reproductive cycle, highlighting a complex interplay of survival and reproduction within the species.
The population dynamics within Tymgygytgyn Lake are characterized by extreme volatility. Food availability, suitable spawning grounds, and nursery areas for juveniles are severely limited. During lean periods, entire generations can perish, leading to precipitous drops in population density. Conversely, when conditions improve, the initial generations experience explosive growth. Yet, as the population density increases and food resources dwindle, the maturing fish become smaller, prompting a desperate shift among some to cannibalism, with the proportion of ‘cannibal char’ peaking during these harsh times.
Scientists hypothesize that these drastic population fluctuations, where only a fraction survives, have recurred hundreds of times throughout the lake’s history. Each such ‘bottleneck’ has acted as a powerful evolutionary pressure, altering the gene pool and solidifying random mutations within the fish. Consequently, the Tymgygytgyn char have evolved at an astonishing pace, far outstripping their anadromous relatives. They possess a unique genetic makeup and physical characteristics that underscore the profound impact of isolation and extreme environmental pressures on species development.
This remarkable ecosystem in Tymgygytgyn Lake stands as a living testament to evolutionary resilience, a natural laboratory where fish have adapted to severe conditions and forged extraordinary survival strategies. The findings from this remote Kamchatkan site offer invaluable insights into evolutionary biology, highlighting the importance of preserving such unique and globally significant natural phenomena for future scientific study and understanding of life’s incredible diversity. It underscores Kamchatka’s role as a vital repository of unique biodiversity, contributing to our collective global knowledge of adaptation and survival.