Morphometric differences in two calanoid sibling species, Boeckella gracilipes and B. titicacae (Crustacea, Copepoda)

calanoid copepods are abundant in south american inland waters and include widespread species, such as boeckella gracilipes (daday, 1902), which occurs from the ecuador to tierra del fuego island. this species occurs under various environmental conditions, and is found in oligotrophic lakes in patagonia (39-54°s) and in shallow mountain lakes north of 39°s. the aim of the present study is to conduct a morphometric comparison of male specimens of b. titicacae collected in titicaca and b. gracilipes collected in ri？ihue lakes, with a third population of b. gracilipes collected in shallow ponds in salar de surire. titicaca and ri？ihue lakes are stable environments, whereas salar de surire is an extreme environment. these ponds present an extreme environment due to high exposure to solar radiation and high salinity levels. the results of the study revealed differences among the three populations. these results agree well with systematic descriptions in the literature on differences between the populations of titicaca and ri？ihue lakes, and population of salar de surire differs slightly from the other two populations. it is probable that the differences between the population of salar de surire and the other two populations result from the extreme environment in salar de surire. high exposure to solar radiation, high salinity and extreme variations in temperature enhance genetic variations that are consequently expressed in morphology.