Bubbly

A common question in marine biology is how do life histories evolve?  Less common is how do life histories contribute to new evolutionary innovations?

Intermediate species with a bubble raft and egg masses (pink below the bubbles). photograph by Denis Riek

It has long been a wonder how snails walk on (or more accurately, under) the surface of water. These snails float in the neuston (at the air-water interface) on rafts made of bubbles resembling the bubble wrap you'll soon be pulling out of holiday packages. How the snails transitioned from a bottom dwelling lifestyle to one closer to the sun has remained a mystery. The key is determining how the bubble rafts evolved. Churchill and her colleagues unraveled the solution by using DNA evidence to piece together a family/evolutionary tree (phylogenetics). Like a court room, the DNA revealed the source of the commotion.  The bubble-rafting snails' closest relatives were bottom-dwelling snails which made egg masses encapsulated in mucus. Bubble-rafters have modified this mucus to be quick hardening in order to trap air for floats.  Intermediate species (see picture) have maintained both the bubble floats and egg masses; however some of the most derived snails have transitioned to brooding instead producing egg masses.

Reference: Females floated first in bubble-rafting snails. CKC Churchill, DO Fioghil, EE Strong and A Gittenberger. Current Biology. 2011.

also see coverage by National Geographic News

Currents vs larval biology: The biology matters

Dr Shima at Victoria's Marine Lab reports that fish larvae can actively control their distribution in the ocean - not just vertically - and that where they grow up has a large effect on their chances of survival. I can't wait to see the publication(s), since these ideas are both counter to much prevailing dogma regarding marine larvae.

Larvae are small and generally believed to be weak swimmers with little to no capacity to counter the strong ocean currents. Fish larvae are more proficient swimmers than their invertebrate counterparts, but are still quite weak especially during early stages. Yet, Dr. Shima reports that fish larvae are preferentially found along the coast, rather than swept out to sea as current flow would predict. It is not clear how the larvae are accomplishing this feat, but it highlights the importance of considering biology in estimates of larval dispersal and population connectivity.

Although it really shouldn't be, the importance of WHERE larvae grow up may be even more revolutionary for considering population connectivity - which is in essence a network of lines connecting larval birth places with the location where they spend adulthood. There is no consideration of the planktonic trajectory in between - just beginning and end.  However, more and more experimental evidence and now field observations support the idea that larval quality which is a function of its experience in the water column has a profound effect on which larvae are successful once they settle. Dr Shima suggests that Wellington Harbor may act as a type of nursery habitat, increasing the success of triplefin larvae. For some (many?) species, it may not be enough that they simply get there, but that the larvae also experienced favorable environmental conditions for rapid growth and development to facilitate survival to adulthood.

It is likely these biological factors that can account for differences between observed or actual population connectivity and the output of oceanographic models.


Reference: More than chance determines future for baby fish, Voxy.co.nz

Ah....

...an interview!!  Yeah!

Shorted

I didn't realize it would feel so good to get short-listed somewhere... I'm not telling where, but it would be a good fit for me and a good area for my husband to get a job. Here's hoping for more short lists and to move to the short-short list of candidates.  Is it too soon to feel optimistically hopeful about this year?

Sight for the blind?

Larvae across many phyla have distinct eye spots or eyes. Even 'primative' sponge larvae have a pigmented ring of cells that can sense light. This may not be surprising since light is pervasive in most environments and serves as an important cue for feeding and predator avoidance, amongst other things. (For additional gorgeous pictures and information about marine larvae check out the Friday Harbor Invertebrate Embryology Course Blog.

Yet, sea urchin larvae (below) seem to lack any discernible light sensing organs. There are pigment cells (red) scattered across the body and concentrated often at the tips of the arms.

 

However, a light sensing function has not (yet?) been assigned to these cells or regions. So why might sea urchin larvae have lost their ability to sense light?  Or do they have a way to sense light, possibly a novel way, that is yet to be discovered? 

Adult sea urchins do it in a strange, unique way (Ullrich-Luter et al 2011). Why not larvae too?  The entire adult sea urchin serves as a type of eye. Visual opsins are found in the tube feet all around the urchin, but there is no associated pigment. The test (shell) of the sea urchin serves as a 'shading pigment' to provide directional information about the ambient light. 

So what do sea urchin larvae do to sense light? There are projects going on around the world that are starting to shed light on this question.  We've got a handful of genes that specifying putative (novel?) light-sensing cells. It will be a collaborative, international effort... and I hope a fruitful one.

Ullrich-Luter ME, Dupont S, Arboleda E, Hausen H, and Arnone MI. 2011. Unique system of photoreceptors in sea urchin tube feet. Proceedings of the National Academy of Sciences USA. 108(20):8367-72.

Jobs, jobs, and more jobs

My own dispersal depends on applying to jobs and hopefully getting one. At least this year there are lots of jobs to which to apply. There are even some 'dream jobs' on the list, including my Alma mater, UC Santa Barbara.

For anyone out there looking for ecology or evolution academic positions, check out the Ecology and Evolution Jobs Forum.  I probably shouldn't be sharing this because it will only increase the competition, but we all could use a little help in this job market.  Its not totally inclusive, but pretty darn good.

Good luck to everyone in their searches! Maybe I'll pass you in the airport on the way to an interview.