Marine snails lay eggs and give birth

Summary: Marine snails lay eggs and give birth

Animals exhibit either egg-laying or live birth as their primary reproductive method. A collaborative study involving the Institute of Science and Technology Austria (ISTA), the University of Sheffield, and the University of Gothenburg delves into the genetic transformations associated with the recent evolutionary shift from egg-laying to live-bearing in a marine snail. The findings, published in Science, provide valuable insights into the mechanisms underlying reproductive transitions in organisms.

Genetic Basis of Live-Bearing Evolution in Marine Snails

An international research team, led by ISTA postdoc Sean Stankowski, utilized a common marine snail to unveil the genetic modifications responsible for the transition to live-bearing. The significance of this study lies in the fact that live-bearing behaviour emerged in these snails within the last 100,000 years, offering a unique opportunity to examine rapid evolutionary shifts. The central discovery of the research indicates that approximately 50 genetic changes, distributed across the snail genome, are responsible for the transition to live-bearing in these organisms.

The Enigmatic Littorina Saxatilis – A Misunderstood Marine Snail

The marine snail, Littorina saxatilis, has earned the dubious distinction of being the most misidentified creature globally, as reported by The Guardian in 2015. Despite its widespread presence along the North Atlantic shores, scientists have mistakenly classified it as a new species or subspecies over a hundred times throughout history. This confusion arises from the snail’s diverse shell variations and ability to adapt to various habitats.

Adding to the intrigue, L. saxatilis boasts a unique reproductive strategy. This species has evolved a live-bearing mechanism, unlike its fellow marine snails that lay eggs. Despite its significance, the scientific focus has primarily centred around studying the variations in the snail’s shell, rather than delving into what sets it apart reproductively from its egg-laying counterparts. In essence, Littorina saxatilis stands out for its shell diversity and unconventional breeding strategy, making it an intriguing subject for further exploration and understanding.

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Evolution of Live-Bearing in Littorina Snails

Stankowski utilized whole-genome sequences to construct the phylogenetic tree of Littorina saxatilis and its egg-laying relatives. While live-bearing is the distinguishing trait of L. saxatilis, the evolutionary analysis revealed that it did not form a distinct evolutionary group.

The discrepancy between reproductive strategy and ancestry became crucial in unravelling the genetic basis of live-bearing. Stankowski and collaborators identified 50 genomic regions associated with whether snails lay eggs or give birth to live young. This finding suggests that the evolution of live-bearing in L. saxatilis occurred gradually, driven by the accumulation of mutations over the past 100,000 years.

Evolution of Live-Bearing in Snails

The study indicates that the transition to live-bearing enabled snails to inhabit novel environments where egg-laying counterparts struggle to thrive. Despite this, the specific advantages of live-bearing in these snails remain unclear. Live-bearer offspring enjoy protection from external factors until they attain self-sufficiency. The research seeks to unravel the incremental impact of individual genetic changes on the snails’ morphology and functionality throughout the evolutionary journey towards live-bearing.

Journal Link: https://www.science.org/doi/10.1126/science.adi2982