The use of morphometric characters to discriminate specimens of laboratory-reared and wild populations of Gyrodactylus salaris and G. thymalli (Monogenea)

Abstract

Abstract. Gyrodactylus thymalli Žitňan, 1960 and G. salaris Malmberg, 1957 have an indistinguishable ribosomal internal transcribed spacer (ITS) DNA sequence, but exhibit surprisingly high levels of intra-and interspecific sequence variation of the mitochondrial cytochrome oxidase I (CO1) gene. To test whether different populations of these reportedly very similar species could be discriminated using morphometric methods, we examined the morphometry of four different populations representing different mitochondrial clades. Twenty five point-to-point measurements, including five new characters of the attachment hooks, were recorded from three Norwegian laboratory populations (G. salaris from the Rivers Lierelva and Rauma, and G. thymalli from the River Rena), and from one wild population of G. thymalli from the River Test, UK. The Norwegian populations were kept under identical environmental conditions to control for the influence of temperature on the haptoral attachment hooks. Data were subsequently subjected to univariate and linear stepwise discriminant analyses. The model generated by the linear stepwise discriminant analysis used 18 of the 25 original variables, the first two roots accounting for 96.6% of the total variation between specimens. The hamulus shaft length accounts for 66.7% of the overall correct classification efficiency. Based on morphometry, all specimens were assigned to the correct species. Apart from three specimens of G. salaris from the River Lierelva population which were misclassified as belonging to the G. salaris Rauma population, all specimens were assigned to the correct population. Thus, populations of Gyrodactylus identified by mtDNA can also be discriminated using morphometric landmark distances.

The first report of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes, Monogenea) on Italian cultured stocks of rainbow trout (Oncorhynchus mykiss Walbaum)

“…For identification, a total of 25 point-to-point morphometrics (11 on the hamulus, 6 on the ventral bar and 8 on the marginal hooks) were made on each specimen (see Shinn et al, 2004) using the purpose written software PointR ver 1.0 (ß Shinn and Bron, 2003, University of Stirling, UK) within KS300.…”

Description of three new species of Gyrodactylus von Nordmann, 1832 (Monogenea) parasitising Oreochromis niloticus niloticus (L.) and O. mossambicus (Peters) (Cichlidae)

“…3.0 image analysis software (Carl Zeiss Vision GmbH, München, Germany, 1997). A total of 25 point-to-point measurements detailed by Shinn et al (2004) were made on each specimen (see Table I). Type specimens were deposited in the Institute of Parasitology, Biology Centre of the Academy of Sciences of the Czech Republic, České Budějovice, Czech Republic and in the Parasitic Worms Division, The Natural History Museum, London, UK.…”

Gyrodactylids (Gyrodactylidae, Monogenea) infecting Oreochromis niloticus niloticus (L.) and O. mossambicus (Peters) (Cichlidae): A pan-global survey

“…Measurements were made on the attachment hooks using the Point-R software (version 1.0 © University of Stirling, 2003) employing the Zeiss KS300 iC/Windows release version 3.0 (1997) (Carl Zeiss Vision GmbH, München, Germany) application platform. From each specimen, a total of 25 point-to-point measurements were made following the protocol detailed in Shinn et al (2004). Digital images of the attachment hooks of each type species and from representative specimens within clusters of interest highlighted by the subsequent morphological, statistical and molecular studies were captured using the same equipment previously described.…”