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Evolution of spinal nerve number in anuran larvae
1School of Biological Sciences, University of Kentucky Lexington.
Brain, Behavior and Evolution
|January 1, 1989
Summary
The number of spinal nerves in tadpoles varies significantly across anuran species, with reductions occurring independently multiple times in their evolutionary history. This variation is linked to tadpole size and metamorphosis time, not behavior.
Area of Science:
- Comparative anatomy
- Evolutionary biology
- Developmental biology
Background:
- The number of segmental spinal nerves in anurans exhibits phylogenetic patterns.
- Understanding spinal nerve variation provides insights into evolutionary adaptations.
Purpose of the Study:
- To investigate the phylogenetic distribution and evolutionary patterns of spinal nerve number in premetamorphic anuran tadpoles.
- To explore correlations between spinal nerve number and tadpole characteristics such as body size, tail length, and developmental stage.
Main Methods:
- Examined spinal nerve counts in 60 premetamorphic tadpoles from 43 species across 12 anuran families.
- Analyzed phylogenetic patterns and identified independent reduction events in caudal spinal nerve number.
- Correlated spinal nerve number with tadpole body size, relative tail length, developmental stage, and time to metamorphosis.
Main Results:
- A variable primitive condition of 23 to 29 pairs of spinal nerves was observed.
- Caudal spinal nerve number reduction occurred independently at least 7 times during anuran phylogeny.
- Reduced spinal nerve number correlates with tadpole body size and, in Archaeobatrachia, with a shorter time to metamorphosis.
Conclusions:
- Spinal nerve number variation in tadpoles is influenced by phylogenetic history and developmental factors.
- Independent reduction events suggest adaptive pressures related to body size and metamorphosis.
- Greater variation in tadpoles compared to adults is likely due to the expendable nature of the tail.
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