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Abstract

Several independent methods: molecular-genetic, biogeographical, and morphological analyses — were applied to explain the origin of the continental calanoid fauna and the distribution of their recent genera. The theory of Continental Drift and the evolution of the Tethys Sea were also used for that purpose. The molecular-genetic-based phylogenetic tree that we constructed, as well as the largest number of genera and species in Diaptomidae, allow us to support the idea that this family of fresh- and brackishwater Copepoda arose earlier than the Temoridae and Centropagidae. The ancestors of the Diaptomidae likely invaded, and were distributed across, the supercontinent Pangaea before its division into two continental plates in the Mesozoic Era, i.e., not later than 180-200 Ma. Therefore, various genera of this family can be found almost everywhere on all continents, except Antarctica. The family Temoridae is known only from Europe, Asia and North America. These three continental plates stayed together long after separation of Pangaea into two parts: Laurasia and Gondwana (until circa 50 Ma). At approximately the same time (50 Ma), the genus Eurytemora should have been created, as its representatives are known from North America and Eurasia. The family Centropagidae seems to have invaded inland waters somewhere between Temoridae and Diaptomidae, as its representatives can be found on all continents except Africa. Also, as a possibly alternative option, this centropagid invasion could have happened independently in the northern and southern Pangaea blocks, by different marine ancestors, at the same time as Temoridae, as is shown herein in the molecular-genetic-based phylogenetic tree. Using the evolution model of the Tethys Sea proved to be very productive for explaining the modern ranges of continental calanoids, both within families and in individual genera, including the genus Eurytemora.

In: Crustaceana

Abstract

This study analyses the potential of stochastic phenotypic variation for investigating the population biology of Eurytemora. Stochastic variation is the third component of phenotypic variance, standing on equal footing with genotypic variation and phenotypic plasticity. This is a manifestation of developmental instability and usually increases under stress. In morphological traits, stochastic variation is most often studied using fluctuating asymmetry (FA) of bilateral traits. Here, using data on the FA of nine populations of three Eurytemora species from Europe and North America, we found no correlation between FA and temperature, salinity or tidal amplitude. Invasive American E. carolleeae in the Gulf of Finland (Baltic Sea) had lower FA than the same species in its native Chesapeake Bay, or than E. affinis in its native Gulf of Finland. This pattern may be caused by global warming, which brought Chesapeake Bay temperatures beyond E. carolleeae’s optimal conditions, but made the Gulf of Finland a more suitable environment. Stochastic variation in life history traits is technically more difficult to study, but it may provide important information on fitness. In particular, it manifests in bet-hedging, a risk-spreading strategy beneficial in unpredictable environments. As resting eggs are common in Eurytemora, bet-hedging can be considered a genus strategy. Understanding how stochastic variation contributes to total phenotypic variance may help to interpret changes under unpredictable environmental conditions. Therefore, studies of stochastic phenotypic variation may supply information about the population biology of Eurytemora and other copepods.

In: Crustaceana
Proceedings of the Eurytemora Conference, St. Petersburg, 2019
This monograph is a summary of the conference on Eurytemora, gathering renowned researchers from all over the world to discuss new advances in Phylogeny, Biogeography, Taxonomy, and Ecology of this important group of estuarine crustaceans, held the 13-17 May 2019 in St. Petersburg, Russia. The present volume includes 17 selected papers, in which you will discover new aspects of the modern theory on the history and recent geographical distribution (biogeography) of an important group of estuarine crustaceans, revealing coincidences with a modern model of continental drift. The researchers suggest a new hypothesis on time and place of origin of continental calanoid copepods. The specialists show that studying external morphology in detail helps to increase identification and differentiation between closely related sibling species within the Eurytemora group. Several ecological questions on invasive and pseudocryptic copepod species are debated. Finally, the last chapter of this monography is devoted to taxa related to the Eurytemora group, Epischura, Temora, Temoropia, and Pseudodiaptomus.

First published as a Special Issue of Crustaceana 93(3-5): 241-547.

Abstract

This study analyses the potential of stochastic phenotypic variation for investigating the population biology of Eurytemora. Stochastic variation is the third component of phenotypic variance, standing on equal footing with genotypic variation and phenotypic plasticity. This is a manifestation of developmental instability and usually increases under stress. In morphological traits, stochastic variation is most often studied using fluctuating asymmetry (FA) of bilateral traits. Here, using data on the FA of nine populations of three Eurytemora species from Europe and North America, we found no correlation between FA and temperature, salinity or tidal amplitude. Invasive American E. carolleeae in the Gulf of Finland (Baltic Sea) had lower FA than the same species in its native Chesapeake Bay, or than E. affinis in its native Gulf of Finland. This pattern may be caused by global warming, which brought Chesapeake Bay temperatures beyond E. carolleeae’s optimal conditions, but made the Gulf of Finland a more suitable environment. Stochastic variation in life history traits is technically more difficult to study, but it may provide important information on fitness. In particular, it manifests in bet-hedging, a risk-spreading strategy beneficial in unpredictable environments. As resting eggs are common in Eurytemora, bet-hedging can be considered a genus strategy. Understanding how stochastic variation contributes to total phenotypic variance may help to interpret changes under unpredictable environmental conditions. Therefore, studies of stochastic phenotypic variation may supply information about the population biology of Eurytemora and other copepods.

In: Studies on Eurytemora

Abstract

Several independent methods: molecular-genetic, biogeographical, and morphological analyses — were applied to explain the origin of the continental calanoid fauna and the distribution of their recent genera. The theory of Continental Drift and the evolution of the Tethys Sea were also used for that purpose. The molecular-genetic-based phylogenetic tree that we constructed, as well as the largest number of genera and species in Diaptomidae, allow us to support the idea that this family of fresh- and brackishwater Copepoda arose earlier than the Temoridae and Centropagidae. The ancestors of the Diaptomidae likely invaded, and were distributed across, the supercontinent Pangaea before its division into two continental plates in the Mesozoic Era, i.e., not later than 180-200 Ma. Therefore, various genera of this family can be found almost everywhere on all continents, except Antarctica. The family Temoridae is known only from Europe, Asia and North America. These three continental plates stayed together long after separation of Pangaea into two parts: Laurasia and Gondwana (until circa 50 Ma). At approximately the same time (50 Ma), the genus Eurytemora should have been created, as its representatives are known from North America and Eurasia. The family Centropagidae seems to have invaded inland waters somewhere between Temoridae and Diaptomidae, as its representatives can be found on all continents except Africa. Also, as a possibly alternative option, this centropagid invasion could have happened independently in the northern and southern Pangaea blocks, by different marine ancestors, at the same time as Temoridae, as is shown herein in the molecular-genetic-based phylogenetic tree. Using the evolution model of the Tethys Sea proved to be very productive for explaining the modern ranges of continental calanoids, both within families and in individual genera, including the genus Eurytemora.

In: Studies on Eurytemora
In: Studies on Eurytemora

Abstract

We studied the morphology of Eurytemora from inland waters at the shores of the White and Pechora seas and from the Lena River delta, and revealed a ubiquitous presence of Eurytemora gracilicauda Akatova, which results we confirmed with genetic data. We found this species for the first time in the Pechora Sea basin. In the White Sea basin, this species was previously described as E. brodskyi Kos, with the name that we suggest is a junior synonym of E. gracilicauda. E. gracilicauda differs from the co-living species: E. lacustris (Poppe), E. arctica Wilson M. S. & Tash, and E. raboti Richard, by the structure and armament of the caudal rami and the fifth legs (P5) of males and females. The caudal rami of both males and females were elongated. The female caudal rami showed a surface covered by spines. The male caudal rami were bare, or with rare spines on the sides. The appendages of the female P5 were also elongated: the length of the inner spine on the distal exopod segment was 2.27 ± 0.12 times as long as the outer spine; the exopod of the male right P5 had a specific trigonal ledge with a short spinule, and the coxopods (both or at least one) had groups of spinules. The morphometric parameters of the females were quite stable, while those of the male showed high variability within and between populations (CV = 11.5-43.5%). Similarities and differences of E. gracilicauda and three allochoric Eurytemora species were analysed, and the results presented herein.

In: Crustaceana

Abstract

We studied the morphology of Eurytemora from inland waters at the shores of the White and Pechora seas and from the Lena River delta, and revealed a ubiquitous presence of Eurytemora gracilicauda Akatova, which results we confirmed with genetic data. We found this species for the first time in the Pechora Sea basin. In the White Sea basin, this species was previously described as E. brodskyi Kos, with the name that we suggest is a junior synonym of E. gracilicauda. E. gracilicauda differs from the co-living species: E. lacustris (Poppe), E. arctica Wilson M. S. & Tash, and E. raboti Richard, by the structure and armament of the caudal rami and the fifth legs (P5) of males and females. The caudal rami of both males and females were elongated. The female caudal rami showed a surface covered by spines. The male caudal rami were bare, or with rare spines on the sides. The appendages of the female P5 were also elongated: the length of the inner spine on the distal exopod segment was 2.27 ± 0.12 times as long as the outer spine; the exopod of the male right P5 had a specific trigonal ledge with a short spinule, and the coxopods (both or at least one) had groups of spinules. The morphometric parameters of the females were quite stable, while those of the male showed high variability within and between populations (CV = 11.5-43.5%). Similarities and differences of E. gracilicauda and three allochoric Eurytemora species were analysed, and the results presented herein.

In: Studies on Eurytemora

Abstract

Eurytemora represents a challenging group of species due to their taxonomy, in particular the former group of cryptic species known as E. affinis sensu lato. In this paper, we analyse DNA sequences that are all available in GenBank, along with our own data on the genus Eurytemora. For this study, a set of mitochondrial and nuclear genes (CO1, nITS and 18SrRNA) was used. In total 543 sequences were analysed (437 CO1; 54 nITS; 52 18SrRNA). However, this work is mainly meta-analytical, and only 67 sequences from unstudied earlier populations or species were obtained specifically for this work to analyse the genetic differentiation of the morphologically described species. We found that relatively young species of the E. affinis complex are different from each other in the CO1 and nITS genes, but not in the conservative 18SrRNA nuclear gene. Nucleotide differences among affinis-group species in the CO1 gene are 9.4-11.8%; in the nITS genes, 1.1-5.0%. At the same time, all other studied Eurytemora species have significant differences from each other in the CO1 and nITS genes, as well as in 18SrRNA. The level of differences among the species is 13.2-19.2% for the CO1 gene, 18.0-27.6.2% for nITS genes, and 0.4-1.8% for the 18SrRNA gene.

In: Crustaceana