Data from: Dealing with allometry in linear and geometric morphometrics: a taxonomic case study in the Leporinus cylindriformis group (Characiformes: Anostomidae) with description of a new species from Suriname

To achieve maximum efficacy, taxonomic studies that seek to distinguish
amongst species must first account for allometric shape variation within
species. Two recently developed software packages (SMATR and MorphoJ)
offer regression-based allometric approaches that are notable for their
statistical power and ease of use and that may prove highly useful to
taxonomists working with linear or geometric morphometric data. We
investigate species delimitation of the slender-bodied fishes in the
Leporinus cylindriformis group using these programs and demonstrate the
utility of the allometric corrections that they provide. Without
allometric correction, many pairs of species are difficult to distinguish
on the basis of morphometrics, but once regressions are used to account
for marked allometric variation within species, most of the recognized
species in this group can be readily distinguished with linear or
geometric morphometrics, particularly using variation in the depth of the
body. Both approaches returned congruent patterns of separation amongst
putative species, but the geometric approach in MorphoJ distinguished
amongst four more pairs of species than did the linear approach in SMATR
and appears to provide slightly more statistical power. Based on
distinctive morphometrics, meristics, and coloration, a highly elongate
species of Leporinus from the Suriname, Corantijn, and Coppename rivers of
Suriname is described herein as a new species, Leporinus apollo sp. nov.
The unique L. cylindriformis holotype from Porto de Moz, Brazil differs in
morphology, meristics, and pigmentation from specimens commonly referred
to that species from the main basin of the Amazon; the latter specimens
may represent an additional undescribed species. The L. cylindriformis
holotype itself may represent a rare species or a specimen collected at
the edge of its native range. Measurements of the holotype and paratype of
Leporinus niceforoi, which were collected in the Amazonian slope of
Colombia, differ substantially from similarly pigmented and putatively
conspecific specimens from Amazonian portions of Ecuador and Peru.
Recently collected specimens from Colombia are needed to determine whether
the observed morphometric variation encompassed by the current concept of
L. niceforoi indicates a morphocline within a single species, suggests the
presence of multiple cryptic species, or results from shrinkage of the
types. In all these cases, linear or geometric morphometric data can
reliably differentiate amongst species, but only after one accounts for
allometric shape variation. The new SMATR and MorphoJ software packages
both offer easy and effective approaches to such allometrically informed
taxonomy, and may prove useful to any systematist working on taxa that
change shape as they grow.