USGS Home
Contact USGS
Search USGS

Evolutionary Ecology:

The field of evolutionary ecology is growing extremely rapidly, due in large part to major advancements in genetics and marking/monitoring technologies. Combining individual genotypes with data from multiple recaptures of tagged individuals provides a very promising approach to identify the relationship between traits of wild fish and lifetime fitness (number of grand offspring produced). This kind of analysis has been done with birds and ungulates, but has yet to be done with fishes which represent a very different slice of multidimensional life history space (indeterminate growth, strong body size-fecundity relationship, large number of offspring). Every fish in our tagging studies has been fin-clipped for a tissue sample. Approximately 3,000 brook trout have been genotyped. Before conducting pedigree reconstruction, the key step in identifying parentage, we have spent considerable effort testing pedigree reconstruction approaches because fish will have more missing observations (parents and offspring) than other types of species.

Effects of habitat fragmentation on persistence: We have estimated the effects of habitat fragmentation on population persistence using brook trout data in the West Brook. Simulations suggest that artificial (e.g. via culverts) isolation of small tributaries can result in local extinction very rapidly (< 10 generations). Because even the small tributaries serve as important sources of fish to the larger population, isolation of the small tributaries can even result in population-wide extinction, although the time frame is longer and immigration could rescue the population from the isolation effect. In the West Brook, one of the tributaries is naturally isolated from the rest of the stream network by a waterfall. Genetic data indicate that the population in the isolated tributary is reproductively isolated and demographic estimates suggest that fish in this population have evolved special life history characteristics that may allow persistence despite isolation. In the isolated tributary, all demographic rates are shifted towards smaller fish; higher survival of small fish, slow growth rates and smaller fish and shorter life-span. In the near future, we hope to test the generality of these results.

Estimating lifetime fitness in the wild: Relating performance (or traits) to lifetime fitness is one of the central goals of evolutionary ecology. For brook trout in our study area, we have identified successful reproduction (median four offspring per mother), family sizes, sibship structure (many half-sibs), and evidence for size-assortative mating. Work in the near future will relate performance (growth, movement and age at first reproduction) to production of grand offspring. This work will provide a direct estimation of fitness in the wild and will represent a major contribution to the field of evolutionary ecology and to our understanding of brook trout dynamics. These results will also be incorporated into our detailed population persistence models, increasing realism of these models and providing the ability to model response to environmental change and management activities more accurately.

Analysis of sibship and pedigree reconstruction techniques: With PhD student Jason Coombs, we have created software to test sibship analysis and pedigree reconstruction techniques. As we were developing this capability, we realized that we really needed a whole suite of software packages, from the ability to convert genotype data across 50 existing genetics data packages, to a detailed population simulation capacity, to the analysis and interpretation of sibship and pedigree reconstruction. These software packages are available at https://bcrc.bio.umass.edu/pedigreesoftware/ . With this software, we have identified which sibship and pedigree reconstruction software packages have the best power to detect known, simulated family structure similar to our field conditions. We are currently using these to estimate sibship and pedigree structure.

Effects of stocking time on growth survival and life history expression: In 2001, to test for effects of stocking/emergence time, we determined variation in growth, survival and life history expression for fish emerging naturally and for fish stocked into the brook at three stockings over a range of five weeks. Results indicated that size to smolting was directly related to timing of entry, but that survival appeared more clearly related to environmental conditions during entry. Life history expression (smolt age and extent of male parr maturation) among groups was also strongly influenced by entry timing.

Relevant Publications:

Coombs, J. A., B. H. Letcher and K.H. Nislow. Submitted. PEDAGOG: Software for simulating eco-evolutionary, population dynamics, Molecular Ecology Research

Coombs, J. A., B. H. Letcher and K.H. Nislow. Submitted. PEDAGOGGLES: Software to quantify error and assess accuracy and congruence for genetically reconstructed pedigree relationships, Molecular Ecology Research

Horton, G.E., and B.H. Letcher. 2008. Movement patterns and study area boundaries: influences on survival estimation in capture-mark-recapture studies, Oikos 117(8): 1131-1142.

Coombs, J. A., B. H. Letcher and K. H. Nislow. 2008. CREATE: a software to create input files from diploid genotypic data for 52 genetic software programs. Molecular Ecology Resources 8: 578-580.

Letcher BH, Nislow KH, Coombs JA, O’Donnell MJ, Dubreuil TL. 2007. Population Response to Habitat Fragmentation in a Stream-Dwelling Brook Trout Population. PLoS ONE 2(11): e1139. doi:10.1371/journal.pone.0001139

Pearlstein, J. H., B. H. Letcher, and M. Obedzinski. 2007. Early discrimination of Atlantic salmon smolt age: Time course of the relative effectiveness of body size and shape. Transactions of the American Fisheries Society 136: 1622-1632.

Letcher, B. H., T. Dubreuil, M. J. O'Donnell, M. Obedzinski, K. Griswold, and K. H. Nislow. 2004. Long-term consequences of variation in timing and manner of fry introduction on juvenile Atlantic salmon (Salmo salar) growth, survival, and life-history expression. Canadian Journal of Fisheries and Aquatic Sciences 61(12): 2288-2301.

Carlson, S.M., A.P. Hendry and B.H. Letcher, 2004. Natural selection acting on size, growth rate, and compensatory growth: an empirical test in a wild trout population, Evol. Ecol. Res., 6:1-19.

Hendry, A.P., B.H. Letcher and G. Gries. 2003. Estimating natural selection on stream-dwelling Atlantic salmon: implications for the restoration of extirpated populations. Cons. Biol., 17(3):795-805.

Letcher, B.H. 2003. Life history dependent morphometric variation in stream-dwelling Atlantic salmon, Oecologia, 137:533-540.