Do molecules matter more than morphology? Promises and pitfalls in parasites

Abstract

Systematics involves resolving both the taxonomy and phylogenetic placement of organisms. We review the advantages and disadvantages of the two kinds of information commonly used for such inferences--morphological and molecular data--as applied to the systematics of metazoan parasites generally, with special attention to the malaria parasites. The problems that potentially confound the use of morphology in parasites include challenges to consistent specimen preservation, plasticity of features depending on hosts or other environmental factors, and morphological convergence. Molecular characters such as DNA sequences present an alternative data source and are particularly useful when not all the parasite's life stages are present or when parasitaemia is low. Nonetheless, molecular data can bring challenges that include troublesome DNA isolation, paralogous gene copies, difficulty in developing molecular markers, and preferential amplification in mixed species infections. Given the differential benefits and shortcomings of both molecular and morphological characters, both should be implemented in parasite taxonomy and phylogenetics.

Avian haemosporidians from Neotropical highlands: Evidence from morphological and molecular data

“…However, using only morphological data results in some difficulties; for example, it is difficult to find all parasite stages in smears, due to the low intensity of infection, and the presence of parasites which are morphologically identical but genetically different [57,69]. In this study, we believe that we have two cryptic species: H. (P.) coatneyi and H. (P.) vireonis because the same morphology exhibited different molecular lineages.…”

“…Currently, the study of avian haemosporidian diversity is being addressed by using both molecular and morphological analysis, as has been encouraged by several authors [5,57,58]. Recent information demonstrates high frequency of abortive infections [59,60], where the only presence of lineages cannot be considered a competent host-parasite relationship [6].…”

Epidemiological traits of the malaria-like parasite Polychromophilus murinus in the Daubenton¿s bat Myotis daubentonii

“…The rise of molecular techniques in parasitology also inadvertently meant a decline of light microscopy [33], not only to describe new parasite species or lineages (but see: [34]), but also to determine parasite prevalence and abundance. Although PCR and qPCR are undeniably much more efficient approaches for analysing hundreds of blood samples at a time, some pitfalls are associated with the use of molecular techniques.…”

Morphological description of Isospora alyousifi nom.n. for I. acanthodactyli Alyousif et Al-Shawa, 1997 (Apicomplexa: Eimeriidae) infecting Acanthodactylus schmidti (Sauria: Lacertidae) in Saudi Arabia

“…as Berto et al (2011) have recently argued, reliable classification is dependent on a statistically based evaluation of the morphometrics of the oocysts and, where possible, all the developmental stages of the species life cycle. it is not uncommon that a species of parasite has been described from just a single infected host (Perkins et al 2011). in terms of morphology, this small sample size may not permit an adequate examination of the variability present within a species.…”

“…in terms of morphology, this small sample size may not permit an adequate examination of the variability present within a species. thus, if the parasite is encountered again, slight morphological differences may drive investigators to describe it as a new species (Perkins et al 2011). One set of issues in species identification, therefore, is an over-reliance of oocyst morphology for identification purposes, combined with inadequate sample sizes.…”