Evolutionary Diversification

Lessons from a Threespine Stickleback Radiation in the Cook Inlet Region of Alaska

"May you live in interesting times", says a common phrase. This phrase seems to fit biologists living in the twenty-first century particularly well. Never have we had so many resources to study life's diversity, our forerunners would hardly have believed that such progress could be made so quickly. Most biologists are now well trained in statistics and experimental design and count with incredibly powerful computers and software for carrying out sophisticated analyses. Hand held gps (geographic positioning systems), microchemical analysis systems, GIS (geographic information system)/satellite technology, etc., are all available for routine use. Advances in molecular biology have even come farther, such that generating DNA sequences is easy and inexpensive. Under adequate supervision, the average undergraduate is quite capable of generating sequences for common genes in a matter of two weeks, if not sooner! Yet we also live in a time of unprecedented loss of species and destruction of ecosystems. Estimates of the number of species that go extinct annually range in the tens of thousands (Wilson, 1986). Rates of habitat loss are in many cases unbearably high, especially in tropical habitats rich in biodiversity such as rainforests. In addition, countless species exist now in fragmented and highly degraded habitats. For many, the end will be as slow and excruciating as it is inevitable. The political instability and poverty of many tropical nations, harboring much of the planet's biodiversity, and the unfair distribution of the benefits from the exploitation of natural resources, makes the situation worse. Yes, for those interested in understanding life's diversity, "times" certainly are "interesting".

Left: Cut trees in a forest off of the Rio Negro near Manuas, Brazil. Picture taken in June of 2003. Right: Children looking at dead fish from a fish kill in Valdivia, Guayas province, Ecuador. Photograph taken by Jose Alvarado from article appearing in El Universo in February 2004.

Given the urgency of the environmental crisis, scientists and policy makers are scrambling to find the most efficient ways of conserving our biodiversity. Thus one would assume that information on how this biodiversity was generated in the first place would be incorporated into management decisions. Unfortunately, surprisingly little is known on the process of diversification in natural populations. How is it that organisms diversify? Are there rules for the assembly of guilds composed of species closely related phylogenetically? Are there factors that constrain or facilitate evolution in particular directions? If we understood these factors, could we make predictions on potential short to mid-term responses to environmental change? What is the nature of the differences that exist among populations and species? How are species created/how does assortative mating evolve in natural populations? On a broader scale, how do "novel" traits and functions evolve? These questions remain largely unanswered for natural populations.

The goal of my research is to try to provide insight into some of these questions by using a species that is rapidly becoming a model system for the study of evolution in natural populations, the threespine stickleback Gasterosteus aculeatus. Threespine stickleback are ubiquitous in temperate waters of the northern hemisphere. They are small fish, easily reared in the lab, with elaborate breeding behaviors. They are primitively anadromous (live in the ocean but enter freshwater to reproduce), and have repeatedly invaded newly formed postglacial lakes and rivers throughout their range and evolved rapidly (within 20,000 years) in response to the novel conditions. Consequently, stickleback exhibit extraordinarily high levels of morphological variability. There is also a large literature on their ecology and evolution, thus we have a solid base of knowledge on their biology.

Left: View of Loberg Lake, Alaska. Picture taken in June of 2003. Right: Me standing near the outlet stream at Tommelson Lake, Alaska.

My work focuses on microevolutionary events that have or are taking place in the Cook Inlet region of Alaska. The two primary components of my research are:

• I am studying rapid (contemporary) evolution in a recently established population (Loberg Lake) which is in the process of adapting to conditions in a lake and quickly approaching the phenotype typical of lake populations in the region. This part of my research will tell us how quickly stickleback adapt to lake conditions, what trajectory they take as they adapt, how phenotypic covariation among traits changes as stickleback evolve, and whether levels of ancestral phenotypic variation can be used to predict what traits are most likely to respond first.
• I am studying the population structure of the threespine stickleback adaptive radiation in the Cook Inlet region of Alaska. This part of my research will help us understand the degree of gene flow among freshwater populations, the extent to which different ecomorphs have evolved independently within the region, and the scales at which gene flow and natural selection become more important in influencing phenotypes.

Left: Anadromous stickleback from Rabbit Slough, which is within 2.5 km. of Loberg Lake. Right: Low morph stickleback collected in Loberg Lake, Alaska in 2002. Both specimens are stained with alazirin red, which stains bone.

You can get more info and an overview of some preliminary results of my research at the following links (coming soon):

• The Loberg Lake story.
• Defining the ancestral phenotype- Morphological variation and sexual dimorphism of an anadromous population from Rabbit Slough.
• The pattern of morphological adaptation in Loberg Lake- A time series.
• Population structure and genetic variation in Loberg Lake.
• A contrast to Loberg Lake- Stable armor polymorphism and population structure in Tommelson Lake.
• Phylogeography and morphological diversification of threespine stickleback in the Cook Inlet Region of Alaska.

You can also get some background info on the tools/methods I am using:

• Microsatellites as genetic markers. Read
• The value of geometric morphometrics for assessing shape variation.
• An introduction to some multivariate tools for "quantitatively-challenged" biologists.

Literature Cited:

Bell, M.A., and Foster, S.A. 1994. The evolutionary biology of the threespine stickleback. Oxford University Press.

Wilson, E.O. 1986. The current state of biological diversity. Pages 3-18 in Wilson, E.O. (ed.) Biodiversity. National Academy Press. Washington, D.C.

Acknowledgements:

My research is supported by a W. Burghardt Turner Fellowship, by the Alliance for Graduate Education and the Professoriate (AGEP), and by an NSF Doctoral Dissertation Improvement Grant (DEB-0509070).

Date last updated: 16 May 2006