Fefilova, E.B., N. Sukhikh, E. Abramova & I. Velegzhaninov. (2019). About the systematics of Palaearctic Eurytemora (Calanoida, Copepoda) on base of their morphological analysis. In: Conference Booklet of Abstracts. (2019). Use of Molecular-Genetic and morphologial methods to study Eurytemora species. Abstract Book, St. Petersburg, Russia. 68 pp. :45-48.

428019

10.1163/9789004465565_007 [view]

Fefilova, E.B., N. Sukhikh, E. Abramova & I. Velegzhaninov

2019

:45-48.

Publication

The first descriptions of the Eurytemora species (Temoridae, Calanoida, Copepoda) obtained in the former century do not contain information on their variability (Williams, 1906; Akatova, 1949; Borutsky, 1949). This problem is characteristic of, at least, Russian key books and identification tables for the genus representatives (Borutsky et al., 1991; Stepa-nova, 2010; Kos, 2016) and complicates the diagnostics of Eurytemora by morphological parameters. The recent descriptions of these copepods include information on the variability of their principle morphometric parameters, the structure of fine formations (mouth parts) and are often added with the analysis results of molecular-genetic variability for species and populations, ecological and behavior signs (Lee, 1999; Lee, Frost, 2002; Fefilova, 2008; Dodson et al., 2010; Alekseev, Souissi, 2011; Moon et al., 2016; Sukhikh et al., 2016 a, b). This study approach is highly required as Eurytemora easily colonize new habitats, quickly distribute and change their habitation limits. These changes complicate the research work on composition of local faunas and produce co-existence of numerous intraspecific morpho- and haplotypes, as well as interspecific hybrids (Lee, Frost, 2002). The goal of our studies is to-species determination of morphologically similar Eurytemora representatives inhabiting fresh-water coastal waterbodies of the White Sea, the Korovinskaya Bay of the Pechora Sea and the Lena River delta and the stability and changeability research of diagnostically important signs. The individuals from Siberia and the Pechora River delta have been first identified by us as Eurytemora gracilicauda (Akatova), specimens from the White Sea basin – as Eurytemora brodskyi Kos. For determination, we have used key books and morphological descriptions of E.V. Borutsky with co-authors (1991) and M.S. Kos (2016). But by the molecular-genetic study results of maxillopods from three populations, they belong to one species and show a low variability index among populations by the studied parts of mitochondrial DNA. To study the morphologic changeability of this species (Eurytemora gracilicauda), we take 13 morphometric characteristics of caudal rami and the fifth pair of thoracal legs (?5) for females, morphometric characteristics of caudal rami for males, as well as qualitative and quantitative signs characterizing these formations which are highly important in the Eurytemora systematics (Borutsky et al., 1991; Kos, 2016). Additionally, we survey the structure of distal thoracal, genital, and anal somites of females and males, armatures of segments of geniculate antennules for males. Finally, we specified the Eurytemora gracilicauda morphologic charac-teristics. Females of three populations had the majority of studied signs being stable with little variations (variation coefficient (CV) is < 10%). For any females, the back angles of the distal thoracal somite were elongated into triangle outgrowths, the genital somite was without protrudences or narrowings, the anal somite and caudal rami were covered with spinules. Females from the Lena River delta demonstrated the longest caudal rami (0.373 ± 0.009 mm) and females from the White Sea basin – the shortest caudal rami (0.251 ± 0.009 mm).The Lena delta females also had the most elongated segments and spines of P5. Both spines of distal segment of females P5 of any study sampling groups were covered with very small spinules. By the earlier data (Kos, 2016), for the Eurytemora gracilicauda diagnosis was important that only long inner spines is covered by spinules, and in the Eurytemora brodskyi diagnosis both apical annexa of female P5 are without spinules naked (Kos, 1993, 2016). The morphological signs of the studied Eurytemora males were variable in contrast with characteristics of females. A half of males (from the White Sea basin and the Pechora River delta) had caudal rami and the anal somite without spinules according to the Eurytemora gracilicauda diagnosis in the identification keys of M.S. Kos (2016). The other half of males (from the White Sea basin and the Pechora River delta) had caudal branches and the anal somite covered with seldom spinules along external edges according to the Eurytemora brodskyi diagnosis (Kos, 2016). The number of spinules on P5 of males largely varied: on the left P5 – from 2 to 3, on the right P5 – from 1 to 6 (CV = 14.2-43.5 %). Only males from the Lena River delta and one male from the Pechora River delta had a finger-like outgrowth on side of the genital somite. This sign was known as varying also for other Eurytemora species (Kos, 2016). Basipodites of only left P5 or both P5 of males from any population had a group of very small spinules on the external edge. The stable characteristics of males also were P5 shape, elongated caudal rami (shorter than female rami), no outgrowths on the end thoracal somite, and no long annexa on the 8–12th segmentes of geniculate antennule. Thus, we introduced some additions to the Eurytemora gracilicauda diagnosis: identified the changeability limits of several morphometric, qualitative and quantitative signs of the species. The variability of signs may be related with different environmental conditions. But we do not exclude the possibility of hybridization. The sampling group from the Lena River delta had Eurytemora gracilicauda together with the other species of the genus as Eurytemora arctica Wilson M.S. & Tash, E. lacustris (Poppe), E. raboti Richard. In the lake of the Pechora delta, the analyzed species was accompanied by Eurytemora lacustris. The hybrids of calanoids are known to be seldom met in natural ecosystems. They are similar to one of parents phenotypically but can have morphologic (normally morphometric) changes (Chen et al., 1997; Parent et al., 2012). The question on the lifetime of the study European populations of Eurytemora was open. This question was earlier discussed in relation to Eurytemora prope brodskyi (Sukhikh et al., 2016 a) from the White Sea basin. The species was first registered here in 1993 (Kos, 1993). Until recently, the areal of Eurytemora gracilicauda was meant to be limited by the Far East and the northern part of the Pacific coast in North America (Borutsky et al., 1991). But from the early 2000-s, this species along with Eurytemora arctica and E. foveola (Johnson M. W.) was found in plankton samples from the Lena delta (Abramova et al., 2017). Eurytemora gracilicauda occidentalis Fefilova was found on the Vaigach Island only in 2004. For the Pechora Sea, Eurytemora gracilicauda was first noted by us in 2016, 2017. These findings may evidence both a rapid areal widening of the species from east to west or just be additional information on the genus systematics and composition of native plankton communities in the regions.

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