MEPS 249:297-303 (2003)  -  doi:10.3354/meps249297

Power of a multidisciplinary approach: use of morphological, molecular and digital methods in the study of harpacticoid cryptic species

Ernestina Castro-Longoria1,*, Josué Alvarez-Borrego1, Axayácatl Rocha-Olivares2, Samuel Gomez3, Vitaly Kober4

1Departamento de Óptica, Centro de Investigación Científica y de Educación Superior de Ensenada,
2Departamento de Ecología, and
4Departamento de Ciencias de la Computación, AP 2732, Ensenada Baja California 22860, Mexico
3Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, AP 811, Mazatlán, Sinaloa 82040, Mexico

ABSTRACT: A multidisciplinary approach amenable to automation and involving digital techniques in conjunction with detailed taxonomical observations and molecular genetic analyses was used to assess the phenotypic and genetic variability of 3 harpacticoid copepods previously identified as Cletocamptus deitersi. C. deitersi may be the most problematic species among congeners due to its intraspecific morphological variability. Specimens of C. deitersi collected from inland and coastal habitats in Alabama, California and Louisiana were analyzed to determine the degree of separation between specimens. Levels of extreme genetic differentiation at both mitochondrial and nuclear loci and incipient but congruent morphological differences among specimens of the 3 populations strongly suggest that each genetic lineage belongs to a different species. Discrimination among species was also detected using a digital correlation method invariant to position and rotation. This analysis involved an algorithm using the square module of the fast Fourier transform. Digital images of specimens from the 3 populations were processed to obtain their diffraction patterns. To discriminate among species, all diffraction patterns were correlated with a special filter containing different random fixed views of each species. Results indicate that new identification methods of microscopic organisms could be developed to reduce the amount of time of direct observation. In order to build these methods on a solid taxonomic validation, it is necessary to implement a multidisciplinary approach in which expertise in taxonomy, molecular biology and digital processing work in conjunction to maximize their reliability and precision.

KEY WORDS: Cletocamptus deitersi · Cryptic species · Digital correlation · mtDNA · ITS · Morphological variation

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