Morphological and molecular analysis of centropagids from the high Andean plateau (Copepoda: Calanoidea)

Abstract

In small metazoan invertebrates classical taxonomic analyses can be ambiguous due to the limited number of morphological characters available. This difficulty can yield incorrect estimates of species richness or taxa distribution. The Boeckella genus has been described as the dominant taxon of zooplankton assemblages in the Andean biogeographical region. In this genus, taxonomic classification and delimitation of boundaries between species has long been problematic and controversial. Among South American centropagids Boeckella gracilipes has been regarded as one of the most broadly distributed species, its presence having been reported from Ecuador to Tierra del Fuego. However, in the high Andean plateau some centropagid populations identified as Boeckella gracilipes have also been considered as B. gracilipes titicacae or even identified as a different species, namely Boeckella titicacae. In an attempt to resolve the taxonomic status of the Centropagidae family from the high Andean plateau, we combined traditional and multivariate morphological analyses (integral approach) with the molecular phylogenetic approach. The results obtained allow us to conclude that centropagids collected from the high Andean plateau actually represent a different species, B. titicacae, not B. gracilipes. The phylogenetic reconstruction of the South American Centropagidae family indicated that B. gracilipes represents a sister taxon to B. titicacae. The present study stresses the usefulness of integrating alfa-taxonomy with morphometric and molecular approaches in order to resolve species boundaries, to determine geographical distributions and to investigate evolutionary processes.

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

“…In contrast, the Salar de Surire is a habitat with extreme environmental conditions. Specifically, this habitat shows marked temperature variations and is exposed to high levels of natural ultraviolet radiation (SCheihing et al, 2010). The morphological variation described in the current study agrees with the descriptions in VillaloBoS & Zúñiga (1991).…”

“…Suppose that one species, B. gracilipes (Menu-Marque et al, 2000;SCheihing et al, 2010), inhabits a wide geographical gradient and variety of habitats that includes lakes, ponds and pools between Ecuador and Tierra del Fuego island (Menu-Marque et al, 2000), including subsaline lakes of the South American Altiplano (Bayly, 1993(Bayly, , 1995De loS ríoS & ContreraS, 2005). It is possible to find differences in the fifth thoracopod pair within the same species.…”

“…For example, B. poopensis can tolerate salinities between 5-90 g/l (De loS ríoS & ContreraS, 2005), and B. gracilipes and B. gracilis inhabit shallow ponds and large lakes (Menu-Marque et al, 2000). If we consider the environmental variation of these habitats and the exposure to extreme conditions that may include temperature variation, high salinity or natural ultraviolet radiation exposure, it is probable that substantial interpopulational variation occurs for each species as a consequence of the distinct geographical characteristics of different populations (SCheihing et al, 2010). The species cited above include B. gracilipes, which is found from Ecuador to Tierra del Fuego Island (Bayly, 1992a;Menu-Marque et al, 2000).…”

“…Many of these habitats are oligotrophic, with low conductivity (3.1 mS/cm) and with high exposure to natural ultraviolet radiation (De loS ríoS-eSCalante, 2010). Boeckella titicacae Harding, 1955 was described as a species that inhabits Titicaca Lake and surrounding bodies of water (Bayly, 1992a;SCheihing et al, 2010). Bayly (1992a,b) suggested that this species differs from others in the dimensions of the fifth thoracopod.…”

“…In contrast, Menu-Marque et al (2000) stated that B. titicacae is a synonym of B. gracilipes. SCheihing et al (2010) rejected this argument and proposed that the populations of Titicaca Lake represent a distinct to the species B. titicacae. This proposal is based on molecular evidence and on features of body morphology described by VillaloBoS & Zúñiga (1991).…”