My love for Biology started with a yellow wax bean plant, grown from a magical bean that the teacher had given out in class. It grew two nice yellow beans that my parents said were wonderful. Ending up in university studying biology in Brandon, MB was actually an accident but it happened to be a good life choice.
Afterwards I thought I would move to B.C. to do a M.Sc. at UBC under the direction of Dr. Al G. Lewis. I studied a population of oceanic copepod in the anoxic basin of Saanich Inlet for my thesis (my desire to scuba dive was kept a hobby since it was of no use here). From there I dabbled in the world of foraminifera as a technician looking at oceanic sediments for Dr. Tom F. Pedersen. Subsequently I worked on zooplankton productivity in an oceanic upwelling system off the coast of California under Dr. Sharon L. Smith. For many years later I studied the growth and behaviour of two juveniles (of the small human kind) and exposed them to as much of the natural world as possible. That was a long project…. skip to 2007 where I worked on zooplankton samples in Dr. Shelley Arnott’s lab (CAISN project) followed by technical help with Daphnia and food quality experiments in Dr. Bill Nelson’s lab.
Seasonal shifts in Daphnia pulicaria phenotype and genotype in a meromictic lake habitat
Daphnia are herbivorous creatures that feed primarily on phytoplankton but can also feed on bacteria. The community of phytoplankton and bacteria waxes and wanes through the season as light regimes, nutrients, and grazing, impact abundance. In Round Lake at QUBS the bottom 7-10 meters of this 30 m deep basin, remains low in oxygen all year long, providing a consistent environment for anaerobic bacteria. As the phytoplankton declines conceivably the bacteria becomes the reliable food source for daphnia to sustain them through the winter. Carbon and chlorophyll A data will be used to examine shifts in food abundance with respect to changes in the Daphnia pulicaria assemblage.
In Round Lake Daphnia pulicaria phenotypes are either pale, pink, or red, depending on the amount of hemoglobin (Hb) in their tissues. Pale adult individuals subjected to low oxygen lake water in the lab, have lower survival than pinks (see low oxygen tolerance tests). The presence of hemoglobin can therefore be used as an indicator of their niche habitat choice (time-delayed indicator since it takes several weeks to become rich in hemoglobin).
The genotypes will be examined for seasonal changes in abundance and fecundity. The ones carrying favourable survival traits are expected to persist through the winter. It is the wintering asexual individuals that will be able to exploit the first available phytoplankton in late winter and early spring. The life history traits of D. pulicaria in this meromictic lake should give some insight into the evolutionary trajectory of this species.
Background genetics and electrophoresis for D. pulex / D. pulicaria.
- Microsatellite work by Cristecu et al. (2012), in D. pulex and D. pulicaria Fst= .43 to .52 ; means a clear genetic divergence in the nuclear genome between these two species.
- Daphnia pulex complex may be either cyclic parthenogens (CP) (males are not always produced), or, obligate parthenogens (OP) that carry meiosis suppression (may or may not produce males).
- D. pulicaria are cyclic parthenogens, i.e. females can reproduce sexually, (males are not always produced) (Xu et al., 2013).
- Xu et al. (2013) NJ tree (neighbour-joining tree, microsatellite) 3 distinct clades; D. pulex “pure” (let’s call it clade A; this has the more anciently introgressed diagnostic alleles from D. pulicaria, most are CP but some OP SS, Ldh), D. pulex hybrids (clade B; they are all OP SF or OP SS), and D. pulicaria (clade C; they are all CP FF, Ldh)
- The hybrid index for clade A is H=0 which means the D. pulex SS (OP) individuals have almost NO D. pulicaria genes; the SF (OP),clade B, on average have an H=0.29, F1 generation hybrid simulation H=0.5 or you take SF1 X SS (CP) simulation H=0.25; two individual SF (OP) had H=0 suggesting they are individuals from a “more advanced backcross” (Xu et al., 2013).
- Obligate parthenogenesis probably originated from hybridization, backcrosses, and introgression of alleles from D. pulicaria because the meiosis suppression/OP comes from D. pulicaria diagnostic alleles (Xu et al., 2013) but, also from D. pulex OP individuals that carry an allele ”containing an identical upstream insertion of a transposable element as well as a frameshift mutation” which plays a role in meiotic cohesion (Eads et al., 2012)
- INITIAL ELECTROPHORESIS TESTS for the allozyme lactate dehydrogenase indicated that D. pulex was the predominant species in Round Lake and a hybrid occurred in lower numbers (~11%). Clay Prater (a phD candidate at Trent University) provided us with a reference cloneline of D. pulex. We can now conclusively say that we have primarily D. pulicaria in Round Lake and the species in lower numbers may in fact be D. schodlerii. The abundance of the latter species has declined in 2014/2015 so I have not been able to confirm this species taxonomically.
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Crease TJ, Floyd R, Cristuescu ME, Innes D (2011) Evolutionary factors affecting Lactate dehydrogenase A and B variation in the Daphnia pulex species complex. BMC Evolutionary Biology 11: 212.
Crease TJ, Stanton DJ, Hebert PDN (1989) Polyphyletic origins of asexuality in Daphnia pulex. 11. Mitochondrial-DNA variation. Evolution 43: 1016-1026.
Cristescu, ME, Constantin A, Bock DG, Cáceres CE, Crease TJ (2012) Speciation with gene flow and the genetics of habitat. Molecular Ecology. 21, 1411-1422.
Eads BD, Tsuchiya D, Andrews J, Lynch M, Zolan ME (2012) The spread of a transposon insertion in Rec8 is associated with obligate asexuality in Daphnia. Proceedings of the National Academy of Sciences, USA, 109, 858–863.
Hebert PDN, Beaton MJ (1993) Methodologies for Allozyme Analysis using cellulose acetate electrophoresis. A Practical handbook, Helena laboratories 1-34.
Heier CR, Dudycha JL (2009) Ecological speciation in a cyclic parthenogen: sexual capability of experimental hybrids between Daphnia pulex and Daphnia pulicaria. Limnology and Oceanography, 54, 492–502.
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Lynch M, Seyfert A, Eads B, Williams E (2008) Localization of the genetic determinants of meiosis suppression in Daphnia pulex. Genetics, 180, 317–327.
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Xu S, Innes DJ, Lynch M, Cristescu ME (2013) The role of hybridization in the origin and spread of asexuality in Daphnia. Molecular Ecology (2013) 22, 4549–4561.
Low oxygen tolerance in D. pulicaria.
Low oxygen tolerance tests, run October, 2011. Adults were collected from Round Lake, individuals were sorted according to phenotype (pales or pinks) and then subjected to low oxygen (by bubbling nitrogen) lake water, for 2-4 days. Daphnia were kept at 5-8° C (fridge, in darkness) since this was representative of temperatures at depth in Round Lake.
- “Pinks” (contain hemoglobin) survive better than the “pales” under low oxygen stress. Acclimation by up-regulating hemoglobin and producing carbohydrate-degrading enzymes are “a process to improve oxygen transport and carbohydrate provision for the maintenance of ATP production” in D. pulex (Zeis et al., 2009).
- Some “pales” can survive 2-4 days under low oxygen stress (≤1 mg O2/L)
- The only signs of immediate up-regulation of hemoglobin was in the redness of the gastro-intestinal tract in some individuals (Hb production occurs in epithelial and fat cells in the epipodites or in fat cells of the gut region; Paul et al., 2004).
- Ariel Gittens (MSc thesis, 2014) had “pales” in her mesocosm experiments in Round Lake turn “red” after 4 weeks. She did not disturb the mesocosms before the end of the 4 week period so we do not know exactly how long it takes Round Lake daphnia to become rich in hemoglobin. (Earlier experiments where gradual lowering of oxygen conditions in the Nelson Lab, over 2 weeks in combo media, did not result in hemoglobin production).
- It took 3 weeks to several months to get sufficient hemoglobin up-regulation in D. pulex for physiology experiments by Zeis et al. (2009).
- Individual “pales” caught in low oxygen zones by the Schindler trap are assumed to be representative of their true depth at the time of capture. The “pales” are likely able to move in and out of these low oxygen zones while they acclimate.
Paul RJ, Zeis B, Lamkemeyer T, Seidl M and Pirow R. 2004. Control of oxygen transport in the microcrustacean Daphnia: regulation of haemoglobin expression as central mechanism of adaptation to different oxygen and temperature conditions. Acta Physiol Scand, 182, 259-275.
Zeis B, , Lamkemeyer T, Paul RJ, Nunes F, Schwerin S, Koch M, Schütz W, Madlung J, Fladerer C & Pirow R. 2009. Acclimatory responses of the Daphnia pulex proteome to environmental changes. I. Chronic exposure to hypoxia affects the oxygen transport system and carbohydrate metabolism BMC Physiology 2009, 9:7 doi:10.1186/1472-6793-9-7 http://www.biomedcentral.com/1472-6793/9/7