The challenge of estimating the age of subterranean lineages: examples from Brazil
Eleonora Trajano - (36/1,2007)
The applicability and effectiveness of different kinds of evidence
used to estimate the age of lineages – morphological, molecular,
phylogenetic, biogeographical, geological – are discussed.
Examples from the Brazilian subterranean fauna are presented,
using mainly fishes, one of the best studied groups, as a model.
Only three taxa including troglobites are object of molecular
studies, all in progress. Therefore, molecular clocks cannot be
applied yet, and indirect evidence is used. Few phylogenies are
available, e.g. for the catfish families Heptapteridae and Trichomycteridae.
Theoretically, basal troglobitic clades are older than
apical ones, but the possible existence of extinct epigean taxa
belonging to such clades hampers the comparison. As well, the
limitations of the use degrees of troglomorphism to estimate
phylogenetic ages are analyzed with focus on the complexity
of the mechanisms underlying morphological differentiation.
Paleoclimatic reconstructions based on dating of speleothems
from caves in northeastern and southeastern Brazil are available,
but limited up to the last 200,000 years, thus useful for
relatively recent lineages. Topographic isolation, probable for
some fish groups from Central Brazil, is also within the time
range of 105 years. Older dated events (in the order of 106 years
or more) that may represent vicariant events affecting aquatic
lineages with subterranean derivatives are related to the establishment
of the modern South American main river basins. In
view of the paucity of data useful for estimating the age of Brazilian
troglobitic lineages, combined evidence, including morphology,
systematics and biogeography, seems to be the best
approach at the moment.