{"id":3795,"date":"2026-09-15T14:08:37","date_gmt":"2026-09-15T14:08:37","guid":{"rendered":"https:\/\/metamorphosis-project.org\/?p=3795"},"modified":"2026-09-15T15:15:53","modified_gmt":"2026-09-15T15:15:53","slug":"two-life-cycles-one-species-the-alpine-newt-in-all-its-forms","status":"publish","type":"post","link":"https:\/\/metamorphosis-project.org\/fr\/editions-2\/two-life-cycles-one-species-the-alpine-newt-in-all-its-forms\/","title":{"rendered":"Two life cycles, one species: the Alpine newt in all its forms"},"content":{"rendered":"

Why the Alpine newt?<\/h4>\n\n\n\n
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The different life stages in triphasic and paedomorphic individuals of the Alpine newt.
\u00a9 Morgane Fournier<\/figcaption><\/figure>\n\n\n\n

During its life, the Alpine newt, like many amphibians, goes through several stages (cf. triphasic<\/strong><\/span>): it begins life as an egg, then becomes a larva, a juvenile, and finally an adult. These different stages are associated with significant morphological changes, particularly during metamorphosis. Driven by hormones, this stage leads to a complete restructuring of the organism: certain organs and tissues transform to enable the newt to transition from an aquatic lifestyle to a primarily terrestrial one.<\/p>\n\n\n\n

However, not all populations of the Alpine newt follow this pattern. In some populations, found mainly in Italy and the Balkans, metamorphosis can halt before it is fully complete. These individuals then become adults and can reproduce while retaining certain characteristics of their larval form and remaining in the water. <\/p>\n\n\n\n

This strategy, called paedomorphosis<\/span><\/strong>, is optional and reversible: if environmental conditions become less favorable, these individuals can still resume their metamorphosis and transition to a terrestrial lifestyle. Facultative paedomorphosis<\/span><\/strong> can thus be considered a form of life cycle flexibility, allowing newts to take advantage of favorable conditions in the aquatic environment while avoiding the energy cost of a complete metamorphosis when it is not necessary. It is an example of variation in the life cycle within a single species, in other words, intraspecific variation<\/strong>.<\/p>\n\n\n\n

We wanted to understand how this difference in life cycle might influence the morphology of adults, particularly that of the body and the masticatory system (the bones of the head), which also undergoes significant changes during metamorphosis.<\/p>\n\n\n\n

To this end, we studied specimens preserved in European museum collections. <\/p>\n\n\n\n

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Spatial distribution of the Alpine newt in Europe (grey) and samples used for the study.
Fournier et al. 2026. ICB<\/figcaption><\/figure>\n\n\n\n

Body morphology was studied using measurements<\/a> taken from various parts of the body. For the head bones, which is much more difficult to study directly, the specimens were X-ray scanned<\/a> to obtain three-dimensional models of the bones. We then used a method called geometric morphometry<\/a>, which allows for precise comparisons of bone shapes.<\/p>\n\n\n\n

<\/p>\n\n\n\n

What did we find?<\/h4>\n\n\n\n
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Illustrated summary of the differences between paedomorphs and triphasic organisms.
\u00a9 Morgane Fournier<\/figcaption><\/figure>\n\n\n\n

Our results show that paedomorphic individuals<\/strong><\/span> are smaller<\/strong> and exhibit morphological characteristics adapted to aquatic life<\/strong>. For example, their metacarpals (certain bones in the forelimbs) are relatively shorter, which may be related to a different use of their limbs when moving through water. The bones of the head also exhibit a morphology particularly well-suited to suction<\/strong>, a highly efficient feeding method in an aquatic environment.<\/p>\n\n\n\n