Reproductive success in broadcast spawning invertebrates has shown
to be limited in a number of circumstances due to low sperm availability.
Both spawning behavior and gamete traits have been shown to evolve
in response to sperm limitation, but few studies have examined what
role fluid dynamics mediated by morphology may play in fertilization
efficiency. The aerodynamic reciprocity hypothesis has been developed
for the genus Pinus, in which wind tunnel experiments revealed that
species-specific pollen had the highest probability of reaching
the ovules of its own species. This resulted from the speed and
direction of flow interacting with
This hypothesis, however, has not been tested for broadcast spawners
in the ocean, where fluid dynamics plays a large role in determining
fertilization success. One of my side projects is looking for fluid-dynamic
reciprocity in sea urchins.
Urchins are a good system to search for fluid-dynamic reciprocity
because closely related species of urchins have different spine
morphologies. Flume experiments have shown that fertilization takes
place near the urchin, and mass spawning events in nature are known
to involve several species. I have been using the gametes from Strongylocentrotus
franscicanus (red urchins) and S. purpuratus (purple
urchins) in reciprocity fertilization experiments. If fertilization
is higher for eggs in flow around conspecific species, then there
is evidence for reciprocity. |
Purple eggs in flow around a purple urchin. Purple
eggs tend to slide off the side of the urchin and settle immediately
downstream.
Red eggs (top) and purple eggs (bottom) on top of
a red urchin in a reciprocity experiment. Although equal volumes
of eggs were used, red eggs tended to stay on a pile on top of red
urchins and get advected downstream, while purple eggs slid off
the side of the urchin. |
