vamg6792@uxa.cso.uiuc.edu (Vincent A Mazzarella) (04/20/91)
The following is a summary of a one hour seminar given at Univ. of
Illinois in the spring of 1990. The following are my impressions
and no guarantees as to accuracy of the facts or other statements
are given.
The lobster has a urine pore just under its antennae. It exhales
water across this pore to spread the urine as a pheromone. A mating
male lobster enters its shelter, blows its pheromones, which
attracts a female. When the male and female pheromones combine, it
inhibits molting of other females in the harem. When after two
weeks the female wanders off, the male-only pheromones stimulate
other females to molt. How do other lobsters receive the pheromones
and localize their origin?
Chemoreceptors are found in four primary locations: the
lateral and medial flagella antennules ("smell" receptors), and the
walking legs and axilla beds ("taste" receptors). On the walking
legs are thick chitin structures at the end of the legs, with a
thin canal containing the receptors and an apical pore. The
antennules have fine hairs of two types: aesthetase hairs, with
receptor sensilla on them, and guard cells. The sensilla has
branched cilia with mitochondria, and are so densely packed that it
is difficult for water to penetrate between them.
The lateral flagella antennules (LFA) flick back and forth
through the water, comparing data, and this allows for
localization. Destruction of one LFA causes random searching for
food instead of orientation.
At high flow rates (i.e. when the LFA is moving briskly
through the stream), the sensilla hairs move in their sockets, thus
shaking off any odor molecules adherent to them. At low flow rate,
odor molecules stick to the sensilla and stay bound for one minute.
Thus an antennule samples the stream for odor molecules, then
flicks downward rapidly to shake off the odor molecules.
What are the receptors "tuned" for? On the lateral antennule,
most receptors respond to hydroxyproline but not to other amino
acids. Some respond to taurine and some to ammonia. On the medial
antennule, most receptors are responsive to taurine. On the walking
leg and axilla, most receptors are responsive to glutamate. These
were determined by studying isolated sensilla receptors in perfused
chambers.
What are the dynamics of the different receptor types? Some
glutamate-responding cells are fast responding (adapt quickly),
whereas others were slow responding (integrating cells). In the
legs, receptor cells tended to be slower responding and slower
recovering than in antennule cells, which recover quickly and
therefore respond to quick pulses.
How do these characteristics allow the lobster to localize the
source of odors? The time of integration of a receptor determines
its filtering capability. For turbulence sampling in which
concentrations can vary due to turbulence, a cell must determine
average concentration by integrating. Time averaging, however,
requires time, and there is a tradeoff of info vs. sampling time.
What filter time (if any) is optimal for turbulence sampling? Is
there other information, more rapidly obtainable than average
concentration amplitude, which might be measured by receptor cells?
Peak concentration slope may be a good parameter to measure.
Receptors at different positions on an aesthestase hair would see
different concentration profiles, but the problem of sampling time
would not be overcome. When the antennule is flicked, however, the
concentration slopes would be unequally affected at the different
positions, thus affording slope information for integration. Such
information could be used for spatial localization of odors in
turbulent conditions.
From a one hour seminar by Jelle Atema of Woods Hole, Spring 1990.
Olfactory Sampling in Lobster