Chemical information transfer in freshwater plankton and Sexual dimorphism in Bosmina: the role of m

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Chemical information transfer in freshwater
plankton and Sexual dimorphism in Bosmina
the role of morphology, drag, and swimming
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Introduction

• Chemical information transfer in freshwater
  plankton
• - consumer-induced defences in phytoplankton
• - consumer-induced defences in zooplankton
• - benefits and costs of induced defences
• - the transportation of infochemicals
• Scientific classification Bosmina
• Sexual dimorphism in Bosmina

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Chemical information transfer in freshwater
plankton

• exchange of chemical information in freshwater
  ecosystems is shaping structure and functioning
  of these systems
• consumer-induced defences include modification
  of the characteristics relating to life history,
  behaviour, morphology and biochemistry
• inducible defences affect trophic interactions by
  altering predator feeding rates through changes
  in attack rate and/or handling time

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Consumer-induced defences in phytoplankton

• grazing daphnia induced the formation of colonies
  in the green alga Scenedesmus subspicatus
• exposure to water in which daphnids had been
  cultured, the algae formed four- to eight-celled
  colonies with longer spines
• induced changes in the algae conferred grazing
  resistance against small zooplankters ? adaptive
  antiherbivore strategy

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Consumer-induced defences in zooplankton I

• response to infochemicals was first observed in
  Rotifers (Brachionus calyciflorus in 1966)
• inducible morphol. changes also in chiliates
  (Euplotes exposed to predator infochemicals genus
  Lembadion)
• Cladoceran Daphnia also developed behavioural
  defence mechnisms

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Consumer-induced defences in zooplankton II

• one Daphnids behavioural response mechnism is
  diel vertical migration (DVM)
• - migrate down during day to avoid fish
• - ascend to the warmer surface during night,
  where algal food is more abundant
• - DVM seem to be triggered by a chemical
  signal
• - not sure if migration is triggered by fish
  infochemicals or by infochemicals from bacteria
  associated with the fish
• analogous mechanism is DHM
• - horizontal migration to aquatic plants which
  act as shelter

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Consumer-induced defences in zooplankton III

• Daphnia can change morphologically following the
  exposure to predator infochemicals
• - neckteeth, helmets and crests formed when D.
  where exposed to different predator
• synchronisation of sexual reproduction can also
  be influenced by predator infochemicals (in times
  of high predation risk)
• D. also react on chemical signals released by
  injured conspecifics

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Consumer-induced defences in zooplankton IV

• some copepods in oligotrophic lakes defend
  themselves by becoming less visible
• carotinoid-pigmentation, which protect them
  against UV radiation, decreased when predators
  where present
• ? higher mortality due to UV radiation

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benefits and costs of induced defences

• Despite the fact that some machinery is required
  to initiate defence, the costs of inducible
  defence can be low, because it is only initiated
  in the presence of predators.
• Otherwise constitutive defences would have been
  favoured by natural selection!

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Scientific classification

• Bosmina

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• Bosmina
• males vary in size from 0.4-0.5mm and females
  vary in size from 0.4-0.6mm
• more females than males
• major characteristics to males are notched
  antennules and modified first legs
• females have antennules that are large and fixed
  to the head
• Bosmina are found worldwide in lakes and ponds,
  there are also marine species.
• Bosmina are filter feeders consuming 1-3
  micrometers big algae and protozoans
• Bosmina reproduce by parthenogenesis
• they overwinter as resting eggs and when
  conditions become favorable rapid reproduction
  commences
• reproduction response can be initiated by local
  temperature and food abundance
• females carry 9-12 eggs

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Sexual dimorphism in Bosmina I

• some bosmina water flea species develop
  antipredatory defences (long antennules, high
  carapace)
• in Bosmina (Eubosmina) coregoni gibbera (and B.
  longispina) traits are larger/more variable in
  females
• Thesis sexual dimorphism derives from
  differential costs of hydrodynamic drag and
  selection for mobility in males

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• the three reproductive categories of B. corigoni
  gibbera

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Sexual dimorphism in Bosmina II

• in general the external morphology of cladocerens
  is influenced by genetic and environmental
  factors
• Kairomones (infochemicals) derived from predators
  may induce the development of
• long spines/antennules, extreme carapace
  shapes/crests
• ? when predation pressure declines morphs are
  replaced by short-featured morphs

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Sexual dimorphism in Bosmina III

• male cladocerans are usually smaller than both
  sexual and asexual females and do not develop as
  extreme body shapes and morphological structures
• male zooplankton often swim faster than females
• aim of the study was to test if males of B. c. g.
  experienced lower drag than asexuel and sexual
  females

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Sexual dimorphism in Bosmina IV

• they used plastic models of the two species
  (sinking in glycerin) to drag measurement
• from these drag calculations they predicted
  travel distance per swimming stroke and compared
  that with actual travel distance using video
  observation

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Sexual dimorphism in Bosmina V

• for a given body length or volume, male models
  had lower drag
• males can swim 14-28 faster with the same energy
  consumption
• video recordings showed that males of B. c.
  gibbere advanced 55-73 farther than females

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conclusion

• hydrodynamic drag may have significant
  implications for swimming and evolution of
  sexual dimorphism in water fleas
• males lack the defensive structures (e. g. high
  carapaces) because competition over mates favors
  low drag
• males may optimize drag on the basis of body
  length because swimming speed increases with
  length
• ? bosminid morphology may be a gender-spezific
• compromise between selection for low
  hydrodynamic drag and defense against
  invertebrate predators