Homeotic transformations and number changes in the vertebral column of Triturus newts
2015
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We explored intraspecific variation in vertebral formulae, more
specifically the variation in the number of thoracic vertebrae and
frequencies of transitional sacral vertebrae in Triturus newts (Caudata:
Salamandridae). Within salamandrid salamanders this monophyletic group
shows the highest disparity in the number of thoracic vertebrae and
considerable intraspecific variation in the number of thoracic
vertebrae. Triturus species also differ in their ecological preferences,
from predominantly terrestrial to largely aquatic. Following Geoffroy
St. Hilaire's and Darwin's rule which states that structures with a
large number of serially homologous repetitive elements are more
variable than structures with smaller numbers, we hypothesized that the
variation in vertebral formulae increases in more elongated species with
a larger number of thoracic vertebrae. We furthermore hypothesized that
the frequency of transitional vertebrae will be correlated with the
variation in the number of thoracic vertebrae within the species. We
also investigated potential effects of species hybridization on the
vertebral formula. The proportion of individuals with a number of
thoracic vertebrae different from the modal number and the range of
variation in number of vertebrae significantly increased in species with
a larger number of thoracic vertebrae. Contrary to our expectation, the
frequencies of transitional vertebrae were not correlated with
frequencies of change in the complete vertebrae number. The frequency of
transitional sacral vertebra in hybrids did not significantly differ
from that of the parental species. Such a pattern could be a result of
selection pressure against transitional vertebrae and/or a bias towards
the development of full vertebrae numbers. Although our data indicate
relaxed selection for vertebral count changes in more elongated, aquatic
species, more data on different selective pressures in species with
different numbers of vertebrae in the two contrasting, terrestrial and
aquatic environments are needed to test for causality.
Кључне речи:
Axial skeleton; Transitional vertebrae; Geoffroy St. Hilaire's rule; Salamaders; AmphibiaИзвор:
Peerj, 2015, 3, e1397
DOI: 10.7717/peerj.1397
ISSN: 2167-8359