Category: stickleback (Page 2 of 2)

Stickleblog: Plastic stickleback

April 3, 2009 / pcwainwr

When I was an undergraduate at UNC, I worked in the Pfennig lab on spadefoot toads, which exhibit a striking form of polyphenism. Polyphenism occurs when one genotype can produce multiple phenotypes in response to environmental conditions. As it turns out, stickleback have polyphenic traits too!

Matthew Wund in Susan Foster’s lab at Clark University published a paper in American Naturalist this past year that deals with an especially interesting form of plasticity called the “flexible stem” hypothesis. The idea is that polyphenism in an ancestral species may influence the pattern of diversification in its descendant lineages.

Stickleback are a great system for testing this idea, because freshwater sticklebacks have repeatedly diverged into “benthic” and “limnetic” forms when the ancestral marine form colonized freshwater habitats at the end of the last glaciation period.

Matthew and the Foster lab collected stickleback from a marine population, a freshwater limnetic population, and a freshwater benthic population, and bred them in the lab. They then took the young sticklebacks and fed them either limnetic food(small swimming crustaceans) or benthic food(bottom-dwelling insect larva).

Interestingly, the head morphology of marine fish changed; fish fed a benthic diet developed a head that looked like a benthic freshwater fish, and marine fish fed a limnetic diet developed a limnetic-like head.

The ancestral marine fish exhibit a polyphenism that resembles the descendent freshwater populations, which suggests that this ancestral polyphenism may be important in governing how a lineage diversifies.

Wund, M., Baker, J., Clancy, B., Golub, J., & Foster, S. (2008). A Test of the “Flexible Stem” Model of Evolution: Ancestral Plasticity, Genetic Accommodation, and Morphological Divergence in the Threespine Stickleback Radiation The American Naturalist, 172 (4), 449-462 DOI: 10.1086/590966

Stickleblog: The stickleback family tree

March 27, 2009 / pcwainwr

Until recently, sticklebacks were thought to be pretty closely related to seahorses and pipefish. At first glance, it seems reasonable: both groups of fish have bony armor plates, male parental care, and species with elongated bodies and snouts. Many of the species also share a mode of swimming called “labriform” that I’ll be talking about more in a later entry.

So, the pipefishes and sticklebacks share parental care, bony armor, elongation, swimming mode – seems like a slam dunk, right? Wrong.

Things are rarely that simple when you’re dealing with the incredible diversity of teleost fishes, particularly within the Percomorpha, often referred to as the “bush at the top of the tree of life”. Fish are just too diverse for simple morphology-based relationships – you need genetic data to really see what’s going on, and you need a lot of it, because there are so many groups.

In a paper published early last year, Kawahara et al used 75 sequenced mitogenomes to generate a phylogeny of the Gasterosteiformes and related species, and…bam, there goes the neighborhood!

Gasterosteiformes(bolded in the figure above) was split into three pieces: seahorses, pipefishes and their relatives ended as sister to the gurnards, the weird indostomids were sister to the weird synbranchiformes, and finally, the closest relatives of the Gasterosteidei(sticklebacks) were eelpouts and pholids.

A pholid (from Wikimedia Commons)

Obviously, there’s still a lot of work to be done with these fishes – nuclear genes need to be sequenced to back up the mitochondrial genome data, and given the number of species in the presumed stickleback sister group, it’s conceivable that there could be a paraphyly issue as well.

Either way, it looks like the sticklebacks are in for a wild ride!

KAWAHARA, R., MIYA, M., MABUCHI, K., LAVOUE, S., INOUE, J., SATOH, T., KAWAGUCHI, A., & NISHIDA, M. (2008). Interrelationships of the 11 gasterosteiform families (sticklebacks, pipefishes, and their relatives): A new perspective based on whole mitogenome sequences from 75 higher teleosts Molecular Phylogenetics and Evolution, 46 (1), 224-236 DOI: 10.1016/j.ympev.2007.07.009

Stickleblog: Get ready for sticklebacks!

March 20, 2009 / pcwainwr

This is the first installment of a weekly feature on the Wainwright Lab blog.

First, a little introduction: My name is Matthew McGee, and I’m a graduate student in the Population Biology program at UC Davis with Peter Wainwright.

(For those wondering, Peter is the derived fish on the left.)

The species I’m primarily interested in is the threespine stickleback, Gasterosteus aculeatus (which I generally refer to as just “stickleback”, because they’re much more commonly used in research than the other stickleback species).

My research deals with stickleback functional trophic morphology and evolution; or put another way, how the food sticklebacks eat shapes their appearance and how they change over time.

Threespine stickleback, Gasterosteus aculeatus

(Image courtesy of Wikimedia Commons)

So why sticklebacks in particular?

Clearly, because sticklebacks are awesome.

They’re awesome because they have a few key qualities that make them an excellent model system for evolutionary biology. Sticklebacks are marine fish that can tolerate freshwater, and populations of stickleback will often colonize lakes and streams from the ocean, then diverge from the marine population in interesting ways.

From a functional perspective, they’ve got a great assortment of interesting traits: lateral “armor” plates, serrated pelvic spines instead of fins, different mouth shapes, and they produce their own form of glue!

Stickleback are also a great genetic system, because they have a fully sequenced genome, and it’s easy to cross different types of stickleback with each other, which can help us locate the genes involved in particular traits.

As if that wasn’t enough, stickleback are also a model system for behavior, toxicology, and development.

In short, sticklebacks = awesome.

Every week, I’ll be blogging on a different aspect of stickleback biology, which will usually involve a discussion of a stickleback-themed peer-reviewed research publication.

Join me next week, when I talk about phylogenetics and the stickleback family tree!