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Concept of species

Perhaps the greatest challenge for the classification of Triatominae is the lack of a unifying concept of species. To discuss some of the conflicts which arise from applying modern concepts to traditional classification, and to highlight some recurrent practices regarding the systematics of the subfamily, we needed a theoretical framework; we opted for developing our discussion in parallel with the traditional and modern concepts of species. The most important of them are shortly described below.

Historical concept

Morphological or Typological Concept of Species (“morphological species,” “morphospecies,” see column TYPO of Table 6.5). This is the historical concept of species, the one accepted by many generations of naturalists, zoologists, and even today, by many biologists.

Most if not all the presently known species of Triatominae are morphospecies.7 They have been described on a few,7 very few individuals,77 or even a single individual only.78,79 This might be one of the most recurrent problem in morphospecies description: the lack of consideration for natural variation. When more sampling is available, it may become difficult to draw a clear demarcation line between simple geographical variation and species difference.22 Although the idea is that morphological differences are the reflection of biological divergence, it may happen that morphology appears disconnected from other biological properties. T. platensis and T. infestans are two morphospecies, but they could appear as the same biological entities: not only do they interbreed, but they are genetically very similar.64,80,81

The most important objection to the TYPO concept is the existence of sibling species. Sibling (also “cryptic,” or “isomorphic”) species are morphologically identical or nearly identical entities recognized as different species according to other concept(s) of species. This objection to the TYPO concept is weakened by the modern possibilities of morphological comparisons, such as electron microscopy of the egg-shell,82 biometric methods exploring the antennal phenotype (APH), , or geometric morphometrics. , Sibling species do not seem to be frequent in Triatominae. Known cases are T. sordida , and T. dimidiata, , 9 which have been split into sibling species on the basis of cytogenetic and molecular characterization techniques. However, even admitting that sibling species are infrequent in Triatominae, many morphospecies are very similar. Triatominae do not show discrete characters allowing clear-cut species differentiation, and some morphospecies are difficult to recognize without dissection of the genitalia. For morphologically very close species, the typological concept can produce confusion. For instance, R. prolixus and R. robustus are so similar that their geographical distribution is not ascertained. In their revision of the Triatominae from Guyana, the type locality of R. robustus,9091 reported R. prolixus, not robustus. To help distinguish these two entities and some other closely related species of the so-called prolixus group, geometric92-94 and molecular tools95 have been suggested.

 
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