Impact of copepod predation on the fecundity of Keratella cochlearis Rotifera

1
Impact of copepod predation on the fecundity of
Keratella cochlearis (Rotifera)

• Eloìsa Ramos-Rodriguez and José M. Conde-Porcuna
• Arch. Hydrobiol. 161 . 4 . 541-552 Stuttgart,
  December 2004

Paper presented by Harvey Harbach
2
Content of this study

• Research reasons
• ? Copepod predation on rotifers affects the
  dynamics and structure of zooplankton communities
• Material and Methods
• ? Direct observations to describe the predatory
  effect of two freshwater copepod species on
  egg-bearing females of the rotifer Keratella
  cochlearis.
• Results
• ? Probability of suppression of Keratella eggs
  after capture
• Conclusion
• ? Rotifer reproduction may be regulated not only
  by food availability but also by copepod
  predation.

3
Research reasons

• Rotifers may occasionally contribute a
  significant proportion of the zooplankton biomass
  and community grazing rate.
• Studies demonstrated the intense and selective
  nature of the predation of cyclopoid copepods on
  natural assemblages of rotifers (Williamson 1984,
  Lair 1990, Plass-Mann et al. 1997, Dieguez and
  Gilbert 2002).
• Less information available on consumption of
  rotifers by calanoid copepods although remains of
  rotifers in the gut of calanoids
• Valuable information of interactions and
  mechanisms of predators influence on the
  population dynamics and structure of prey
  communities and potentially fecundity
• Planktonic food webs

4
Materials and Methods

• Keratella cochlearis individuals (body length 105
  /- mm cultured in 500ml glass vessels with
  commercial mineral water (274mS/cm) at 20 /-
  0,5C and routinely fed with Cryptomonas sp.
  cells.

Male
Female
Plingfactory.de
Plingfactory.de
5
Materials and Methods

• Lovenula alluaudi (calanoid copepod) as adult
  females and males (total length exl. The furcal
  rami 1,2-1,7mm). Cultured in 500ml glass vessels
  with commercial mineral water at 20 /- 0,5C and
  fed every 1-2days with mixture of Cryptomonas and
  K. cochlearis.

Male
Female
hydro-kosmos.de
hydro-kosmos.de
tolweb.org
6
Materials and Methods

• Acanthocyclops vernalis (cyclopoid) as adult
  females and males (total length 1-1,2mm).
  Cultured in 500ml glass vessels with commercial
  mineral water at 20 /- 0,5C and fed every
  1-2days with mixture of Cryptomonas and K.
  cochlearis.

Female
Male
elacuarista.com
stetson.edu
7
Materials and Methods

• Copepod feeding observations
• 20 egg-bearing Keratella females were placed into
  a 2ml well of 24 well, sterile, polystryene
  tissue culture plates containing commercial
  mineral water with 300cells/ml Cryptomonas, and a
  single adult predatory copepod was added.
  (Feeding behaviour observed for 15min with
  microscope)
• 22 observations with Lovenula (half/half
  genders)
• 10 observations with Acanthocyclops
  (no males available)
• All captures, ingestions and rejections were
  recorded
• 1) ingestion of the whole prey, i.e. the female
  with its eggs
• 2) ingestion of egg but not the female
• 3) rejection of the whole prey, with no
  separation of egg from ist mother
• 4) rejection of the female with separation of the
  egg sank to bottom of experiment well.

8
Materials and Methods

• Effect of copepod predation on fecundity of K.
  cochlearis
• 20 pathenogenetic rotifer females (10 egg-bearing
  adults with advanced embryonic development plus
  10 non egg-bearing) were placed in a 2ml well
  containing commercial mineral water with 300
  cells/ml Cryptomonas a single adult predator
  was added.
• Plates with prey and predators were incubated in
  a culture chamber at 20C for 30 min in darkness
  to avoid formation of patchiness of Cryptomonas
  during experminent.
• 46 incubations with calanoid Lovenula (20
  males and 26 non-ovigerous females)
• 20 incubations with cyclopoid
  Acanthocyclops (20 non-ovigerous females)
• After incubation period the remaining egg-bearing
  and non-egg-bearing Keratella females and
  separated eggs were counted.

9
Results

• Copepod feeding behaviour
• Both copepod species ingested Keratella eggs and
  egg-bearing females.

10
Results

• Effect of copepod predation on fecundity of K.
  cochlearis
• ? Lovenula significantly reduced the number of
  egg-bearing Keratella females, but not the number
  of non-egg bearing Keratella females.
• ? Acanthocyclops reduced the number of both types
  of females egg/female ratio remained unchanged.

Fecundity was estimated as the total number of
eggs divided by the total number of rotifer
females (egg-ratio).
11
Conclusion

• Lovenula alluaudi ingested both the eggs of
  Keratella and the Keratella females with attached
  eggs. No size problems as in other calanoid
  (Williamson and Butler 1986)
• ? Lovenula reduces the relative fecundity and
  birth rate of Keratella and could reduce the
  absolute fecundity.
• Acanthocyclops vernalis preys on non-egg-bearing
  and egg-bearing rotifers no selectively prey.
• ? Acanthocyclops could reduce the absolute
  fecundity densities lower in future because of
  feeding.
• Both can produce separation of Keratella eggs
  after rejection of the egg-bearing prey.
  Considerable reduction of the number of viable
  eggs in natural populations (sink to deeper and
  cooler waters)

Rotifer reproduction may be regulated not only
by food availablity but also by copepod
predation!