LIFE HISTORY EVOLUTION IN THE GUPPY (POECILIA RETICULATA).

Format:

Book

Thesis/Dissertation

Author/Creator:

REZNICK, DAVID NORMAN.

Contributor:

University of Pennsylvania.

Subjects (All):

Ecology.

0329.

Local Subjects:

0329.

Physical Description:

238 pages

Contained In:

Dissertation Abstracts International 41-10B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

This study's main objective was to determine how mortality patterns mold the life histories of natural populations of guppies (Poecilia reticulata) in the Northern Range of Trinidad. These populations are exposed to differences in both the intensity and mode of predation. The three types of localities considered in this study include: (1) Crenicichla localities, where guppies co-occur with Crenicichla alta plus other species of predators and are exposed to the highest overall levels of predation plus selective predation against large, mature size classes; (2) Rivulus localities, where the only potential predator is Rivulus hartii, an omnivore that exerts moderate predation pressure and selects small, immature size classes of guppies; and (3) Aequidens localities, where guppies co-occur with the cichlid Aequidens pulchur, with R. hartii rare or absent, and are exposed to the lowest overall levels of predation.

In comparing wild-caught guppies from 16 field localities, I found that Crenicichla guppies initiate reproduction at a smaller size, produce larger packages of offspring relative to their body size, produce more and smaller offspring per litter, and reproduce more frequently than Rivulus guppies. Aequidens guppies equal Crenicichla guppies in the frequency of reproduction, have intermediate-sized packages at each reproductive event, but are similar to Rivulus guppies for the remaining variables. Studies of the second generation of laboratory-born fish from two Rivulus and two Crenicichla localities demonstrated a genetic basis for all the above differences, except for the size of the reproductive package. In addition, both male and female Crenicichla guppies matured at a younger age than Rivulus guppies. I also measured reproductive effort (RE) as the percentage of consumed calories devoted to offspring; Crenicichla guppies had significantly greater RE's than Rivulus guppies.

Evidence indicating that the predators selected for these life history patterns included: (1) Comparisons between wild-caught guppies collected within a short distance of one another, but exposed to different predator "treatments"; (2) the results of an introduction experiment; and (3) the results of a selection experiment. Three hypotheses concerning how the predators selected for these life history patterns were discussed, including interpopulation differences in: (1) Age (size) selective predation; (2) the intensity of predation; and (3) predator-mediated intra-specific competition (r- and K-selection). Predicted life history patterns based on all these hypotheses are consistent to some extent with the observed life histories.

A second objective of this study was to characterize the tradeoff between growth and reproduction. I first compared the growth of reproducing and non-reproducing siblings raised on quantified food resources. Non-reproducing females had significantly more calories in fat tissues, but exhibited no differences in somatic growth, indicating that, within a genotype, growth will not increase if reproductive investment is artificially decreased. A second comparison was made between fish which devoted different percentages of consumed energy to reproduction. Increased or decreased reproductive investment caused the opposite response in somatic investment, indicating that evolving a change in growth or reproduction results in a complementary change in the other variable. Such tradeoffs are a key element in most life history theory, but have rarely been characterized in real organisms.

Notes:

Source: Dissertation Abstracts International, Volume: 41-10, Section: B, page: 3678.

Thesis (Ph.D.)--University of Pennsylvania, 1980.

Local Notes:

School code: 0175.

Access Restriction:

Restricted for use by site license.