87 research outputs found
Species Diversity and Phylogeographical Affinities of the Branchiopoda (Crustacea) of Churchill, Manitoba, Canada
The region of Churchill, Manitoba, contains a wide variety of habitats representative of both the boreal forest and arctic tundra and has been used as a model site for biodiversity studies for nearly seven decades within Canada. Much previous work has been done in Churchill to study the Daphnia pulex species complex in particular, but no study has completed a wide-scale survey on the crustacean species that inhabit Churchill's aquatic ecosystems using molecular markers. We have employed DNA barcoding to study the diversity of the Branchiopoda (Crustacea) in a wide variety of freshwater habitats and to determine the likely origins of the Churchill fauna following the last glaciation. The standard animal barcode marker (COI) was sequenced for 327 specimens, and a 3% divergence threshold was used to delineate potential species. We found 42 provisional and valid branchiopod species from this survey alone, including several cryptic lineages, in comparison with the 25 previously recorded from previous ecological works. Using published sequence data, we explored the phylogeographic affinities of Churchill's branchiopods, finding that the Churchill fauna apparently originated from all directions from multiple glacial refugia (including southern, Beringian, and high arctic regions). Overall, these microcrustaceans are very diverse in Churchill and contain multiple species complexes. The present study introduces among the first sequences for some understudied genera, for which further work is required to delineate species boundaries and develop a more complete understanding of branchiopod diversity over a larger spatial scale
Evolutionary factors affecting Lactate dehydrogenase A and B variation in the Daphnia pulex species complex
Background: Evidence for historical, demographic and selective factors affecting enzyme evolution can be
obtained by examining nucleotide sequence variation in candidate genes such as Lactate dehydrogenase (Ldh). Two
closely related Daphnia species can be distinguished by their electrophoretic Ldh genotype and habitat. Daphnia
pulex populations are fixed for the S allele and inhabit temporary ponds, while D. pulicaria populations are fixed for
the F allele and inhabit large stratified lakes. One locus is detected in most allozyme surveys, but genome
sequencing has revealed two genes, LdhA and LdhB.
Results: We sequenced both Ldh genes from 70 isolates of these two species from North America to determine if
the association between Ldh genotype and habitat shows evidence for selection, and to elucidate the evolutionary
history of the two genes. We found that alleles in the pond-dwelling D. pulex and in the lake-dwelling D. pulicaria
form distinct groups at both loci, and the substitution of Glutamine (S) for Glutamic acid (F) at amino acid 229
likely causes the electrophoretic mobility shift in the LDHA protein. Nucleotide diversity in both Ldh genes is much
lower in D. pulicaria than in D. pulex. Moreover, the lack of spatial structuring of the variation in both genes over a
wide geographic area is consistent with a recent demographic expansion of lake populations. Neutrality tests
indicate that both genes are under purifying selection, but the intensity is much stronger on LdhA.
Conclusions: Although lake-dwelling D. pulicaria hybridizes with the other lineages in the pulex species complex,
it remains distinct ecologically and genetically. This ecological divergence, coupled with the intensity of purifying
selection on LdhA and the strong association between its genotype and habitat, suggests that experimental
studies would be useful to determine if variation in molecular function provides evidence that LDHA variants are
adaptive
Diversity in the Reproductive Modes of European Daphnia pulicaria Deviates from the Geographical Parthenogenesis
10 páginas, 5 figuras, 3 tablas.Background: Multiple transitions to obligate parthenogenesis have occurred in the Daphnia pulex complex in North
America. These newly formed asexual lineages are differentially distributed being found predominantly at high latitudes.
This conforms to the rule of geographical parthenogenesis postulating prevalence of asexuals at high latitudes and
altitudes. While the reproductive mode of high-latitude populations is relatively well studied, little is known about the
reproduction mode in high altitudes. This study aimed to assess the reproductive mode of Daphnia pulicaria, a species of
the D. pulex complex, from high altitude lakes in Europe.
Methodology/Principal Findings: Variation at eight microsatellite loci revealed that D. pulicaria from the High Tatra
Mountains (HTM) had low genotype richness and showed excess of heterozygotes and significant deviations from Hardy-
Weinberg expectations, and was thus congruent with reproduction by obligate parthenogenesis. By contrast, populations
from the Pyrenees (Pyr) were generally in Hardy-Weinberg equilibrium and had higher genotypic richness, suggesting that
they are cyclic parthenogens. Four lakes from lowland areas (LLaP) had populations with an uncertain or mixed breeding
mode. All D. pulicaria had mtDNA ND5 haplotypes of the European D. pulicaria lineage. Pyr were distinct from LLaP and
HTM at the ND5 gene. By contrast, HTM shared two haplotypes with LLaP and one with Pyr. Principal Coordinate Analysis of
the microsatellite data revealed clear genetic differentiation into three groups. HTM isolates were intermediate to Pyr and
LLaP, congruent with a hybrid origin.
Conclusion/Significance: Inferred transitions to obligate parthenogenesis have occurred only in HTM, most likely as a result
of hybridizations. In contrast to North American populations, these transitions do not appear to involve meiosis suppressor
genes and have not been accompanied by polyploidy. The absence of obligate parthenogenesis in Pyr, an environment
highly similar to the HTM, may be due to the lack of opportunities for hybridization.Peer reviewe
Nucleic Acid Content in Crustacean Zooplankton: Bridging Metabolic and Stoichiometric Predictions
Metabolic and stoichiometric theories of ecology have provided broad complementary principles to understand ecosystem processes across different levels of biological organization. We tested several of their cornerstone hypotheses by measuring the nucleic acid (NA) and phosphorus (P) content of crustacean zooplankton species in 22 high mountain lakes (Sierra Nevada and the Pyrenees mountains, Spain). The P-allocation hypothesis (PAH) proposes that the genome size is smaller in cladocerans than in copepods as a result of selection for fast growth towards P-allocation from DNA to RNA under P limitation. Consistent with the PAH, the RNA:DNA ratio was >8-fold higher in cladocerans than in copepods, although ‘fast-growth’ cladocerans did not always exhibit higher RNA and lower DNA contents in comparison to ‘slow-growth’ copepods. We also showed strong associations among growth rate, RNA, and total P content supporting the growth rate hypothesis, which predicts that fast-growing organisms have high P content because of the preferential allocation to P-rich ribosomal RNA. In addition, we found that ontogenetic variability in NA content of the copepod Mixodiaptomus laciniatus (intra- and interstage variability) was comparable to the interspecific variability across other zooplankton species. Further, according to the metabolic theory of ecology, temperature should enhance growth rate and hence RNA demands. RNA content in zooplankton was correlated with temperature, but the relationships were nutrient-dependent, with a positive correlation in nutrient-rich ecosystems and a negative one in those with scarce nutrients. Overall our results illustrate the mechanistic connections among organismal NA content, growth rate, nutrients and temperature, contributing to the conceptual unification of metabolic and stoichiometric theories.This research was supported by the Spanish Ministries of Science and Innovation (CGL2011-23681/BOS), and Environment, Rural and Marine Affairs (OAPN2009/067); ‘Consejería de Innovación, Ciencia y Empresa – Junta de Andalucía’ (Excelencia CVI-02598; P09-RNM-5376); The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and Stockholm University’s strategic marine environmental research program ‘Baltic Ecosystem Adaptive Management’, and a Spanish government ‘Formación de Profesorado Universitario’ fellowship to F.J. Bullejos
Evolutionary Origin and Phylogeography of the Diploid Obligate Parthenogen Artemia parthenogenetica (Branchiopoda: Anostraca)
Background: Understanding the evolutionary origin and the phylogeographic patterns of asexual taxa can shed light on the origin and maintenance of sexual reproduction. We assessed the geographic origin, genetic diversity, and phylogeographic history of obligate parthenogen diploid Artemia parthenogenetica populations, a widespread halophilic crustaceanPeer reviewe
Relationships among nutrient enrichment, detritus quality and quantity, and large-bodied shredding insect community structure
This is a post-peer-review, pre-copyedit version of an article published in Hydrobiologia. The final authenticated version is available online at: https://doi.org/10.1007/s10750-015-2208-2Anthropogenic nutrient enrichment of
forested headwater streams can enhance detrital quality, decrease standing stocks, and alter the community structure of detrivorous insects, reducing nutrient retention and decreasing ecosystem functioning. Our objective was to determine if stoichiometric
principles could be used to predict genus-specific shifts in shredding insect abundance and biomass across a dissolved nutrient and detritus food quality/quantity gradient. Detritus, insect, and water samples were collected from 12 Ozark Highland headwater
streams. Significant correlations were found between stream nutrients and detrital quality but not quantity. Abundance and biomass responses of four out of five tested genera were accurately predicted by consumerresource stoichiometric theory. Low carbon:phosphorus (C:P) shredders responded positively to increased total phosphorus and/or food quality, and high C:P shredders exhibited neutral or negative responses to these variables. Genus-specific declines were
correlated with decreased overall biomass in shredder assemblages, potentially causing disruptions in nutrient flows to higher level consumers with nutrient enrichment. This work provides further evidence that elevated nutrients may negatively impact shredding
insect communities by altering the stoichiometry of detritus–detritivore interactions. A better understanding of stoichiometric mechanisms altering macroinvertebrate populations is needed to help inform water quality criteria for the management of headwater streams
Alternative antipredator defenses and genetic-polymorphism in a pelagic predator-prey system
DIEL vertical migration (DVM) of zooplankton is generally considered to be a predator-avoidance strategy: zooplankton migrate to greater depths during the day to reduce their chance of being detected by visual predators (fish)(1). Both phenotypic plasticity and interpopulational genetic variability in DVM patterns exist in zooplankton(2,3). We used large indoor mesocosms ('plankton towers'(4)) to study intrapopulational genetic variation for day depth in a Daphnia hyalina x galeata hybrid population. Clones differing in body size also differed in vertical distribution, with the largest clone residing at the greatest depth during the day. A selection experiment in the presence of fish indicates that alternative antipredator strategies, which involve a complex association between habitat-selection traits and life-history strategies, might be an important factor underlying intrapopulational genetic polymorphism in zooplankton, through a balancing of fitness effects in the presence of visual predators.status: publishe
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