Zooplankton sensing

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Zooplankton sensing
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Scanning electron micrograph of mouthpart region
of a freshwater copepod Friedman and Strickler
1975
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Problems for zooplankton

• Food and mates are dilute
• Predators always trying to eat you
• Lots of particles in the water that are NOT of
  interest
• Must detect and recognize things in the
  environment
• Sensing would improve detection
• detection
• handling
• selection

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Requirements for chemoreception

• Signals
• Receptors
• Detection
• Identification
• Discrimination
• For remote detection
• Physical mechanism of signal transport

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Who uses chemoreception?

• Copepods
• Jellyfish
• Cladocerans
• Euphausiids
• Decapods
• Microzooplankton
• Bacteria
• Etc, etc, etc..

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The signals

• Two general different kinds of chemosensory
  reception
• Contact signals/reception
• (taste)
• Remote, or Distance, signals/reception
• (smell)

• As opposed to one kind of mechanosensory
  reception
• - (touch)

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The signals

• Food
• A living alga is surrounded by a phycosphere
• Amino acids, sugars, pheromones, ?
• Conspecifics
• Mates
• Aggregations
• Pheromones, ?
• Predators
• Kairomones

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Physical transport of signal

• Physical processes are needed to transport the
  chemical signals to the chemoreceptors
• Molecular diffusion
• Advection by fluid motion

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Physical transportPrey detection
Shear created by feeding currents deform the
algal phycosphere, stretching the detectable
chemicals toward the copepod.
Provides early warning of incoming prey
Swimming only
Feeding current only
Moore, Fields, and Yen 1999
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Feeding current effects on phycosphere
Control (no copepod)
An herbivorous copepod
A carnivorous copepod
Moore, Fields, and Yen 1999
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Models of feeding currents
Wide shape feeding current warning and body
re-orientation large potential feeding area.
Jiang et al. 2002
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Chemical cues can mediate prey consumption in
copepods
Centropages hamatus. Mean ingestion rates of
Sephadex beads (beads copepod-1 h-1) when
phytoplankton extracts and exudates are added to
the bead suspension. Vertical lines 1 SE
asterisks additives causing significant (p lt
0.05) changes in bead concentration. SWC
seawater control CMC f/2 culture medium
control TE Thalassiosira weissflogii extract
TM T weissflogii medium SE Scrippsiella
trochoidea extract SM S. trochoidea medium
OE Olisthodiscus luteus extract van Alstyne
1996
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Mate attraction mate search mediated by
pheromones
Calanus marshallae. Conceptual drawing of
mate-attraction -- mate search behavior. 1)
female generates vertical pheromone trail 2)
male alerted by pheromone to females in the
vicinity 3) when crossing a trail, male usually
performs dance 4) male follows pheromone trail
to the female 5) female jumps away repeatedly
from pursuing male 6) mating clasp established
and spermatophore transferred from male to female.
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Mate tracking behavior
Male swimming behavior while mate-tracking. Male
begins spinning at frame 110, then tracks the
female.
Weissburg et al 1998
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• model of male tracking a female
• (http//www.uwm.edu/People/jrs/MatingDoall.htm)

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Mate attraction mate search mediated by
pheromones
What does this behavior tell us about the
habitat? Frequency of encounters between males
and females?
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Contact chemoreception
Many simple zooplankton do not use distance
reception They rely on contact e.g. Rotifers
(small freshwater zooplankton) Swim until contact
female, then can mate
Keratella sp. /encyclopediaofalabama.org
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Predator avoidance may be chemically
mediated Daphnia sink in the presence of fish
stink (kairomones)
Effect of kairomone concentration from the
predator Carassius carassius on mean day depth of
cohorts of Daphnia magna. (von Elert and
Pohnert 2000)
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Kairomones influence shadow response Percent
age of Rhithropanopeus harrisii larvae (crabs)
descending upon irradiance decreases after 3 h
conditioning in (A) odor-free sea water (clean),
(B) fish kairomones, or (C) ctenophore
kairomones. (Cohen and Forward 2003)
Control (no shadows)
Shadows
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The receptors - copepods

• Colored SEM images
• Pleuromamma, a 3 mm long calanoid copepod
• Antennae adorned with an array of "setae
• Mechano and chemo-sensory structures

Aesthetascs thin-walled chemosensory pegs on the
antennules
Tina Carvalho
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Fig. 1. Intact and ablated antennular medial and
lateral flagella of the spiny lobster. (A)
Drawing of a lobster showing the antennules
(first antennae) and antennae II (second
antennae). The higher-magnification drawing of an
antennule shows the medial and lateral flagella.
Aesthetascs are located exclusively on the distal
half of the lateral flagellum. Nonaesthetasc
chemosensilla are located along the entire length
of both the lateral and medial flagella. Letters
BG indicate the position on the antennule where
respective micrographs were taken. (B) Scanning
electron micrograph of the aesthetasc region of
an intact lateral flagellum with rows of
aesthetascs (a) and accompanying setae companion
setae (c), guard setae (g) and asymmetric setae
(as). (C) Scanning electron micrograph of the
aesthetasc tuft region after shaving aesthetascs
(a) and asymmetric setae (arrows), but not other
setae including guard setae (g). The asterisk
marks an aesthetasc whose base was not completely
removed by shaving. (D) Light micrograph of the
aesthetasc tuft region covered by cyanoacrylate
glue (arrow) after shaving all setae except
aesthetascs (a) and asymmetric setae (not visible
on this micrograph). The asterisk indicates the
original location of a guard seta prior to
shaving. (E) Light micrograph of a region of an
intact medial flagellum. Arrows indicate setae.
(F) Scanning electron micrograph of a region of
an intact medial flagellum showing two types of
non-aesthetasc sensilla hooded sensillum (hs)
and plumose seta (ps). Hooded sensilla house both
mechano- and chemosensory neurons modified from
(Cate and Derby, 2001). (G) Light micrograph of
a region of a medial flagellum covered by
cyanoacrylate glue (arrow) after shaving all
setae. Scale bars B, 100 mm C, 150 mm F, 50
mm D,E,G, 400 mm. (Steulett et al. 2002)
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Overview of chemoreception in marine
invertebrates Considerable debate about the
general presence of two different sets of
chemoreceptors (distance vs contact) in many
invertebrate groups - perhaps the function is
defined by different thresholds of the same type
of sensor Bacteria Protists - respond to
spatial gradients in odor Cnidaria - feeding
responses stimulated by dilute concentrations of
certain amino acids synchronous release of
gametes likely is stimulated by chemical cues.
(free nerve ending type of sensor) Molluscs -
prey detection suggests distance chemoreception
synchronous spawning is common escape response
to certain predators (branched free nerve ending
type of sensor)
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Overview of chemoreception in marine
invertebrates Annelids - sensitive to chemical
stimuli over entire body settlement site
selection, synchronous spawning. Echinoderms -
tube feet show response to chemical stimuli (
/ -) many pores over skin (integument)
synchronous spawning. (free nerve ending type of
sensor) Arthropods (crustaceans)- most complex
range of chemosensors and behavioral responses
among the invertebrates - yet relatively few
species have been carefully studied. We rely on
homologous structures in many Crustacea to
generalize about response to chemical stimuli.
Distance chemoreceptors (aesthetascs) are found
on antennae and smaller antennules contact
receptors (usually blunt projections or pores)
are found on mouthparts, extremities, mating
structures. Respond to many chemical stimuli -
important in prey detection and mate finding.