Grantee Research Project Results
2004 Progress Report: How Likely is it That Fish Populations Will Successfully Adapt to Global Warming?
EPA Grant Number: R829420E02Title: How Likely is it That Fish Populations Will Successfully Adapt to Global Warming?
Investigators: Klerks, Paul L. , Leberg, Paul L.
Institution: University of Louisiana at Lafayette
EPA Project Officer: Chung, Serena
Project Period: June 10, 2002 through June 9, 2004 (Extended to June 9, 2006)
Project Period Covered by this Report: June 10, 2004 through June 9, 2005
Project Amount: $121,598
RFA: EPSCoR (Experimental Program to Stimulate Competitive Research) (2001) RFA Text | Recipients Lists
Research Category: EPSCoR (The Experimental Program to Stimulate Competitive Research)
Objective:
The objective of this research project is to investigate how likely it is that populations of fish will successfully adapt to temperature changes associated with global warming. This is being addressed for both normal populations and populations that have undergone a drastic reduction in population size. A major factor determining the long-term ecological effects of global warming is if organisms will be able to adapt to global warming. Successful adaptation would mean that global warming does not displace species from their current habitats. Distribution shifts and extinctions would occur if the organisms would fail to adapt to deleterious effects of global warming. At present, there is insufficient information to predict almost any species’ evolutionary response to climate change. The question is of special importance to the southeastern United States, as organisms in warm waters may already be living close to their temperature tolerance limit and because of the importance of fishery resources to the region’s economy.
Progress Summary:
We earlier completed the development of the microsatellites to be used for quantifying genetic variation, identifying seven primers that worked consistently for the least killifish and had considerable variation (3-7 alleles). The quantification of the genetic diversity in the least killifish bottlenecked and normal lines, using these microsatellite markers, was completed during the current reporting period. Gene diversity was significantly lower in the bottlenecked line than it was in the normal line for two of the three pairs of lines. Gene diversity averaged 0.750 in the normal lines, whereas it averaged 0.695 for the bottlenecked lines from the three source populations.
For the least killifish, we have quantified temperature tolerance in the starting populations (generation 0) and for a large proportion of the generation 1 fish. In generation 0, there were no statistically significant differences for median temperature-to-death between selection and control lines. For results obtained to date in generation 1, heat tolerance for fish from one of the six lines is significantly higher in the selection line than the control line. In general, our results verify that in generation 0 (prior to the actual start of the selection), the control and selection lines did not differ in resistance. These results also show that there were no consistent differences (prior to the start of the selection) between the control and bottlenecked populations. In generation 1, there are some indications that the temperature tolerance is already starting to increase in the selection lines. Although statistically significant for one of the pairs of lines, differences between control and selection lines are still relatively small. This also makes it difficult to discern differences between the normal and bottlenecked lines.
For quantifying the heritability of temperature tolerance, we have taken newborn fish from two sets of Heterandri formosa base populations (each set consisting of a bottlenecked and a regular population from the same site), placed these together in pairs of virgin females and males, and maintained these pairs until at least 10 offspring were obtained from each pair. Offspring (once they reach adult size) and their parents are then subjected to a heat exposure to determine their thermal tolerance. This has been completed for 38 families, and we are continuing to obtain more pairs of fish and their offspring to increase sample sizes and statistical power in quantifying heritabilities of heat tolerance. Heritabilities are determined using resemblance among relatives, especially parent-offspring regressions. At this point, we have enough data for preliminary estimates of the heritability for a normal line and a bottlenecked line, with these estimates being respectively 0.041 and 0.685. This would indicate that heritabilities might actually be higher in bottlenecked populations. This is in contrast to expectations, though the same phenomenon has been reported for fruit fly populations.
We have compared heat tolerance among populations of least killifish and among western mosquitofish (populations subjected to different thermal regimes) for five pairs of populations. For three of the comparisons, thermal regime did not have a statistically significant effect on heat tolerance. For the fourth pair of populations, thermal tolerance was actually slightly higher in fish from the site with lower ambient temperatures. For the fifth pair of populations, thermal tolerance was higher in fish collected from the warmer site than it was in fish collected from the normal-temperature site. These two fish populations were maintained in the laboratory and tested again in the first and second generation reared under laboratory conditions. The differences in heat tolerance observed in the field-collected fish were no longer observed in the offspring born in the laboratory, indicating that the initial differences in heat tolerance did not have a genetic basis (i.e., were caused by physiological acclimation rather than genetic adaptation). These results indicate that populations may not be able to adapt to global warming. This component of our research, however, is only one of the three approaches being used to assess the potential for the evolution of temperature tolerance, rendering premature any discussion of the implications of these results to the U.S. Environmental Protection Agency’s mission.
Future Activities:
Selection Experiment
We have now quantified resistance in generation 0 and most of the generation 1 least killifish. The selection process and heat-tolerance quantification will be continued for subsequent generations. Because of the large amount of labor and time involved in the selection process, and because we are making good progress with the least killifish, the same approach with the western mosquitofish is being given lower priority.
Quantification of Overall Genetic Variation Using Microsatellites
We will shift our analyses of genetic variation from the initial normal and bottlenecked populations to the selection and control lines once resistance has evolved.
Quantification of Heritability for Heat Tolerance
We will continue quantifying the heritability of resistance in the original (normal and bottlenecked) populations.
Comparison of Temperature Tolerance Among Populations From Environments With Different Temperature Regimes
We plan to compare temperature tolerance among three sets of populations of the western mosquitofish. On the basis of results to date on the other species, however, this comparison has been assigned a lower priority than the other research.
Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
global climate, ecological effects, vulnerability, aquatic, ecology, temperature, adaptation, genetic variation, RFA, Scientific Discipline, Air, Geographic Area, Hydrology, climate change, State, Environmental Monitoring, Atmospheric Sciences, Ecological Risk Assessment, wetlands, fish habitat, watershed, global change, Louisiana (LA), coastal ecosystems, aquatic ecology, global warming, land and water resources, climate variability, Global Climate ChangeRelevant Websites:
http://biology.louisiana.edu/klerks.html Exit
http://biology.louisiana.edu/leberg.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.