Editing Daphnia (section)

==Ecology and behaviour==
''Daphnia'' species are normally [[r/K selection theory|''r''-selected]], meaning that they invest in early reproduction, so have short lifespans. An individual ''Daphnia''  lifespan depends on factors such as [[temperature]] and the abundance of [[predator]]s, but can be 13–14 months in some cold, [[oligotrophic]], fish-free lakes.<ref name="Pietrzak">{{cite journal |author1=Barbara Pietrzak |author2=Anna Bednarska |author3=Magdalena Markowska |author4=Maciej Rojek |author5=Ewa Szymanska |author6=Miroslaw Slusarczyk |year=2013 |title=Behavioural and physiological mechanisms behind extreme longevity in ''Daphnia'' |journal=[[Hydrobiologia]] |volume=715 |issue=1 |pages=125–134 |doi=10.1007/s10750-012-1420-6|doi-access=free }}</ref> In typical conditions, however, the lifecycle is much shorter, not usually exceeding 5–6 months.<ref name="Pietrzak"/>

''Daphnia'' spp. are typically [[filter feeder]]s, ingesting mainly unicellular [[algae]] and various sorts of organic detritus including [[protist]]s and [[bacteria]]<ref name=Ebert /><ref name="Gliwicz">{{cite book |author=Z. Maciej Gliwicz |year=2008 |chapter=Zooplankton |pages=461–516 |editor1=Patrick O'Sullivan |editor2=C. S. Reynolds |title=The Lakes Handbook: Limnology and Limnetic Ecology |publisher=[[John Wiley & Sons]] |isbn=978-0-470-99926-4 |chapter-url=https://books.google.com/books?id=IEea4VHsgXwC&pg=PA466}}</ref> Beating of the legs produces a constant current through the carapace, which brings such material into the digestive tract. The trapped food particles are formed into a food ''bolus'' which then moves down the digestive tract until voided through the anus located on the ventral surface of the terminal appendage.<ref name="Gliwicz"/> The second and third pairs of legs are used in the organisms' filter-feeding, ensuring large, unabsorbable particles are kept out, while the other sets of legs create the stream of water rushing into the organism.<ref name="Gliwicz"/>

[[File:CladoceraTrunkLimbs.png|thumb|upright=0.7|left| The five trunk limbs, used in filter feeding]]

Swimming is powered mainly by the second set of antennae, which are larger in size than the first set.<ref name="Dodson">{{cite book |author1=Stanley L. Dodson |author2=Carla E. Cáceres |author3=D. Christopher Rogers |year=2009 |chapter=Cladocera and other Branchiopoda |pages=773–828 |editor1=James H. Thorp |editor2=Alan P. Covich |title=Ecology and Classification of North American Freshwater Invertebrates |edition=3rd |publisher=[[Academic Press]] |isbn=978-0-08-088981-8 |chapter-url=https://books.google.com/books?id=gKHmGKqMrgQC&pg=PA776}}</ref> The action of this second set of antennae is responsible for the jumping motion.<ref name="Dodson"/>

''Daphnia'' spp. are known to show behavioral changes or modifications to their morphology in the presence of predator kairomones (chemical signals), including larger size at hatching, increased bulkiness, and the development of "neck-teeth". For example, juveniles of ''D. pulex'' and ''D. magna'' have a larger size after hatching, along with developing neck-teeth at the back of the head, when in the presence of ''[[Chaoborus]]'' kairomones. These morphological defenses have shown to reduce mortality due to ''Chaoborus'' predation, which is a gape-limited predator. Chitin-related genes (deacetylases) are thought to play an important part in the expression/development of these morphological defenses in ''Daphnia''. Chitin-modifying enzymes (chitin deacetylases) have been shown to catalyse the N-deacetylation of chitin to influence the protein-binding affinity of these chitin filaments.<ref>{{Cite journal|last=Christjani|first=Mark|date=2016|title=Phenotypic plasticity in three Daphnia genotypes in response to predator kairomone: evidence for an involvement of chitin deacetylases.|url=https://www.researchgate.net/publication/298897997|journal=The Journal of Experimental Biology|volume=219|issue=Pt 11|pages=1697–704|doi=10.1242/jeb.133504|pmid=26994174|s2cid=36557263|doi-access=free}}</ref> In case of ''D. magna'' it was shown that the response to different kairomones also differ: While the presence of fish kairomones up-regulated one specific gene in the folding of proteins, whereas ''Chaoborus'' kairomone down-regulated the same gene. Based on this the response is a reduction of size at first reproduction in response to kairomones from fish whereas it shows increased size when confronted with larvae of ''Chaoborus''.<ref name="Schwarzenberger et al. 2009">{{Cite journal|last=Schwarzenberger|first=Anke|last2=Courts|first2=Cornelius|last3=von Elert|first3=Eric|date=2009|title=Target gene approaches: Gene expression in Daphnia magna exposed to predator-borne kairomones or to microcystin-producing and microcystin-free Microcystis aeruginosa.|url=https://bmcgenomics.biomedcentral.com/articles/10.1186/1471-2164-10-527|journal=BMC Genomics|volume=10|issue=527|pages= |doi=10.1186/1471-2164-10-527|pmid= |s2cid= |doi-access=free|pmc=2784803}}{{Creative Commons text attribution notice|cc=by2|from this source=yes}}</ref> With the same publication it was shown that genes for [[glyceraldehyde 3-phosphate dehydrogenase]] and [[ubiquitin]] conjugating enzyme were up-regulated in the presence of [[microcystins]] in the food of ''D. magna'' and with this the enzymes of [[glycolysis]] and [[protein catabolism]] are significantly upgregulated when daphnids ingest these toxins.<ref name="Schwarzenberger et al. 2009" />

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