Continuous characters analyzed as such

GOLOBOFF, PABLO; MATTONI, CAMILO; QUINTEROS, SEBASTIAN

CLADISTICS (PRINT)

Blackwell Publishing

Lugar: Londres; Año: 2006 vol. 22 p. 589 - 601

0748-3007

Abstract.-  Quantitative and continuous characters have rarely been included in cladistic analyses of morphological data; when included, they have always been discretized, using a variety of ad hoc methods.  Since continuous characters are typically additive, they can be optimized with well known algorithms, so that with a proper implementation they could be easily analyzed without discretization.  The program TNT has recently incorporated continuous characters.  One of the problems that has been pointed out with existing methods for discretization is that they can attribute different states to terminals that do not differ significantly –or viceversa.  With the implementation in TNT, this problem is diminished (or avoided entirely) by simply assigning to each terminal a range that goes from the mean minus one (or two) standard deviation to the mean plus one (or two) standard deviation; given normal distributions, terminals that do not overlap thus differ significantly (more significantly if using more than one standard deviation).  Three real data sets (for scorpions, spiders, and lizards) comprising both discrete and quantitative characters are analyzed to study the performance of continuous characters.  One of the matrices has a reduced number of continuous characters, and thus continuous characters analyzed by themselves produce only poorly resolved trees; the support for many of the groups supported by the discrete characters alone, however, is increased when the continuous characters are added to the analysis.   The other two matrices have larger numbers of continuous characters, so that the results of separate analyses for the discrete and the continuous characters can be more meaningfully compared.  In both cases, the continuous characters (analyzed alone) result in trees that are relatively similar to the trees produced by the discrete characters alone.  These results suggest that continuous characters carry indeed phylogenetic information, and that (if they have been observed) there is no real reason to exclude them from the analysis.