The role of voucher specimens in validating faunistic and ecological research

How Many Specimens? Guidelines on Depositing Vouchers

Since the advent of passive sampling methods and large scale, replicated studies of biodiversity and ecology, the number of specimens potentially generated in research projects has increased significantly. Few institutional collections are equipped to deal with the hundreds of thousands of specimens collected or observed in all ongoing studies, and the costs of mounting, labelling and curating that much material would be prohibitive. Consultation during the planning stages of a study with curatorial staff of the collection that will eventually receive the vouchers is the most reliable way to obtain an estimate of how many vouchers are recommended for a particular study.

The number of vouchers actually retained and deposited for long-term maintenance is largely dictated by the type of study. At the very least, one specimen of each species identified in a study should be designated as a voucher. However, one specimen often is not sufficient for a reliable subsequent identification. Depositing two or more vouchers increases the probability that one of the specimens will be a member of the sex needed for species-level identification, or will be a clean, undamaged specimen with necessary morphological structures clearly visible. Multiple voucher specimens can also be useful in showing the range of variation in characters for later studies as well as indicating if more than one species was combined in the original identified series. Multiple voucher specimens are also advantageous in cases where destructive sampling is required for species confirmation, as in the case of molecular characters. At least five to ten specimens of each species are recommended to ensure subsequent identification and to determine if all specimens identified are in fact conspecific.

Systematic vouchers – In this case, the number of type specimens or vouchers is often dictated by the number of specimens available in museum collections or as a result of field work. In some cases species descriptions are based on only a single specimen. More specimens are preferable and will help to show the range of variation in characters of the species. In addition, larger numbers of specimens allow authoritatively identified specimens to be deposited in multiple collections, facilitating identification by other workers at those institutions.

Genetic vouchers – In molecular studies, the part of the specimen from which DNA for sequence data is extracted is frequently destroyed, but efforts should be made to ensure that the rest of the specimen remains intact, and preferably retains the morphological characters that allow species-level identification (e.g., genitalia, secondary sexual characters, sclerites with distinctive colour patterns). In the case of species in which individuals are small, the entire specimen must sometimes be destroyed for sequencing. If this is the case, conspecific specimens from the same collection event, identified by a specialist, may be suitable vouchers. If additional tissue samples are to be taken from voucher specimens for subsequent DNA analysis, appropriate protocols for storage of tissues for DNA extraction should be followed (e.g., storage of specimens in -70ºC freezers, 95-100% ethanol). Here again, consultation with museum curators prior to beginning the study will ensure that correct procedures are followed.

Ecological or physiological vouchers – Depending on the nature of the ecological study, thousands of specimens of a single common species may be collected; in this case, a subset of the series would obviously be sufficient to confirm the identity of the species. On the other hand, there are often differences in species characteristics or in the species assemblage of a community from habitat to habitat, or from season to season, within a larger-scale study. These differences increase the likelihood that multiple species may be collected and confused. To account for possible species or population differences, vouchers from ecological studies should include specimens of as many identified species as possible from across the range of habitats, seasons, treatments or other variables examined in the study.

Page updated on Feb 23, 2014