Anderson's salamander

The adult Anderson's salamander, exclusive to Lake Zacapú, Mexico, is a neotenic mole salamander. Its delicate feathery gills and the fin tracing its tail are hallmark features observed in aquatic larval salamanders and newts.

Scientists from Swansea University have uncovered evolutionary insights into the fascinating phenomenon of neoteny among mole salamanders. Neoteny, characterized by organisms reaching sexual maturity while retaining juvenile traits, has been a subject of intrigue in biology for its unusual developmental strategy.

The study, recently published in Ecology and Evolution, explores how certain species of mole salamanders in North America defy the typical amphibian life cycle, staying forever young. Dr Kevin Arbuckle explained: "Neoteny is like staying a baby forever, even as a normally reproducing adult".

Dr Arbuckle and MRes student Thom Lyons delved into the diverse locations of mole salamanders, from the high mountains to near sea level and latitudes spanning Alaska and Canada to Mexico. They uncovered a critical discovery – neoteny thrives in a "neoteny Goldilocks zone" between 20-30 degrees North latitude, where conditions are just right for salamanders to remain perpetually youthful.

"Imagine this as a special area where salamanders never grow up, similar to the story of Peter Pan," said Dr Arbuckle. This zone provides stable, year-round conditions, essential for aquatic life cycles, allowing these unique salamanders to forego the typical transformation into adult forms. What’s more, the isolation provided by the mountain terrain allows populations to diverge from others, and overall diversify into specialised, neotenic species.

One of the study's key findings is the pivotal role of this narrow latitudinal band in the southern range of mole salamanders. Here, species exhibit obligate neoteny, never undergoing metamorphosis, unlike their counterparts in other regions which - if at all - are only neotenic in some populations or some individuals.

"The neoteny Goldilocks zone offers stable habitats and reduced seasonal cues, making it ideal for evolving neoteny. These salamanders have adapted to a life without the need for metamorphosis, which requires significant energy", explained Lyons.

Interestingly, the study challenges previous assumptions about neoteny's relationship with temperature. Unlike expectations, neoteny is not linked to cooler climates but thrives in areas with stable aquatic environments and consistent precipitation.

Lyons and Dr Arbuckle hope their findings shed light on the evolutionary pressures shaping amphibian diversity and adaptation.

Dr Arbuckle added: "Understanding neoteny helps us appreciate the intricate ways organisms adapt to their environments".

Their research underscores the importance of conservation efforts for neotenic species, many of which face threats due to climate change and habitat loss. "These unique salamanders are highly vulnerable and need targeted conservation actions," emphasized Lyons.

Moving forward, the team aims to explore how environmental changes, such as climate shifts caused by human activities, may impact the distribution and survival of these neotenic populations.

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