Jerald B. Johnson

Female green swordtails, Xiphophorus helleri, show a mating preference for males with brightly colored, elongated swords. This preference is thought to be due to a preexisting receiver bias favoring longer sworded males. In this study, we examined variation in the expression of this sword bias in females. Specifically, we tested the hypothesis that an increase in perceived predation risk will decrease female response to males with longer swords. We used a video playback experiment to evaluate female choice between two recordings of a displaying male that differed only in sword length. We scored responses of females to these recordings immediately before and after they had been exposed to a video recording of a predation event between a cichlid and a male possessing a long sword. We found that prior to exposure to this predation event, females preferred the male with the longer sword. However, after exposure to the predator, females altered their mating response, preferring the male with the sword removed. Exposure to the predator also caused an increase in the frequency with which females moved from potential mating positions to a neutral zone. The results presented here suggest that the female preference for males with longer swords can be modulated based on the perceived risk of predation.

▪ Abstract Politicians, scientists, government agencies, and the public are all engaged in recovery planning for Pacific salmon. In order for science to fulfill its potential in the arena of salmon recovery planning, several shortcomings of the science and its application to decision-making must be rectified. The definition of conservation units using genetic and phylogenetic inference needs to be sharpened. Ecological analyses must get beyond casting blame for past declines in salmon numbers and examine mixed strategies of management that consider interactions between hatcheries, harvest, hydropower, and habitat factors as well as background natural stresses and invasive species. Glib acceptance of expert opinion and extrapolated or inferred data should be tempered. To deal with uncertainty, recovery teams should engage in scenario analyses in which a wide variety of assumptions are played out. Finally, there is a pressing need for analyses aimed at determining what circumstances and communication strategies give science an effective voice in decision-making.

The Bonneville Basin and upper Snake River drainage of western North America underwent extensive hydrological changes during the late Pleistocene, potentially influencing the geographic distribution and evolutionary trajectories of aquatic species that occupied this region. To test this hypothesis, I reconstructed the phylogeographic history of the desert fish Utah chub (Gila atraria) by examining 16 populations that span the natural distribution of this species across the Bonneville Basin and upper Snake River. I compared mitochondrial control region sequences (934 bp) among 77 individuals revealing 24 unique haplotypes. Geographic and phylogenetic relationships among haplotypes were explored using parsimony, maximum likelihood, nested clade analysis, and analysis of molecular variance. I found that G. atraria is composed of two distinct clades that represent an early Pleistocene split between the upper Snake River and Bonneville Basin. Within each of these clades, geographic structuring was highly concordant with the hydrological history of late Pleistocene Lake Bonneville and the upper Snake River, suggesting that glacial-induced shifts in climate and unpredictable geological events have played a major role in shaping genetic subdivision among populations. To examine the effects of vicariant events on phenotypic divergence among Utah chub populations, I mapped chub life histories to the control region haplotype network. I found a nonrandom association between haplotypes and life-history phenotypes. These results suggest that historical events responsible for population fragmentation may have also contributed to phenotypic shifts in life histories, both indirectly by limiting gene flow among populations and directly by altering the selective environments where populations persisted.

Studies of natural selection in the wild almost always begin by examining patterns of association between phenotypic adaptations and environmental factors thought to shape evolutionary change. Unfortunately, many studies pay little attention to the effects of model selection on the evolutionary inferences drawn from such correlative data. In this study, I employed a candidate model analysis to examine four potential causes of life‐history evolution in the livebearing fish Brachyrhaphis rhabdophora . Combining factor analysis with path analysis, I constructed a nested set of 17 models that represent the hypothetical effects of four putative selective agents (mortality, density, resource availability, and habitat stability) on life‐history evolution in this species. These models represent both direct and indirect effects of selection on the life history. Using the Akaike Information Criterion to distinguish among models, I found that simple models that contained only single selective agents most parsimoniously explained life‐history divergence among 27 B. rhabdophora populations. Surprisingly, the four putative selective agents could not be distinguished, suggesting that the selective environment could be composed of a single selective agent confounded with other environmental factors, or could be composed of a suite of environmental factors that act in concert to shape the life history. In addition, comparisons among more complex models indicated that direct effects of selective agents appear to have primacy over combinations of indirect selective interactions in explaining intraspecific variation in B. rhabdophora life histories.

I document a genetic basis for parallel evolution of life-history phenotypes in the livebearing fish Brachyrhaphis rhabdophora from northwestern Costa Rica. In previous work, I showed that populations of B. rhabdophora that co-occur with predators attain maturity at smaller sizes than populations that live in predator-free environments. I also demonstrated that this pattern of phenotypic divergence in life histories was independently repeated in at least five isolated drainages. However, life-history phenotypes measured from wild-caught fish could be attributed to environmental effects rather than to genetic differences among populations. In the present study, I reared male fish from four populations (two that co-occur with predators and two from predator-free environments) under four sets of environmental conditions. The pattern of phenotypic divergence in maturation size documented in the field between populations collected from different predation environments persisted after two generations in the laboratory. I also found a genetic basis for differences between populations in the age at which males attain maturity and in growth rates. By rearing fish in four different common environments, I tested for phenotypic plasticity in male life-history traits in response to nonlethal exposure to predators. There was a significant delay in the onset of sexual maturity in fish exposed to predators relative to those in the control, but no differences among treatments in size at maturity or growth rates. These results, coupled with previous work on B. rhabdophora, demonstrate a repeated pattern of parallel evolutionary divergence among genetically isolated populations that is strongly associated with predation.

I document a genetic basis for parallel evolution of life-history phenotypes in the livebearing fish Brachyrhaphis rhabdophora from northwestern Costa Rica. In previous work, I showed that populations of B. rhabdophora that co-occur with predators attain maturity at smaller sizes than populations that live in predator-free environments. I also demonstrated that this pattern of phenotypic divergence in life histories was independently repeated in at least five isolated drainages. However, life-history phenotypes measured from wild-caught fish could be attributed to environmental effects rather than to genetic differences among populations. In the present study, I reared male fish from four populations (two that co-occur with predators and two from predator-free environments) under four sets of environmental conditions. The pattern of phenotypic divergence in maturation size documented in the field between populations collected from different predation environments persisted after two generations in the laboratory. I also found a genetic basis for differences between populations in the age at which males attain maturity and in growth rates. By rearing fish in four different common environments, I tested for phenotypic plasticity in male life-history traits in response to nonlethal exposure to predators. There was a significant delay in the onset of sexual maturity in fish exposed to predators relative to those in the control, but no differences among treatments in size at maturity or growth rates. These results, coupled with previous work on B. rhabdophora, demonstrate a repeated pattern of parallel evolutionary divergence among genetically isolated populations that is strongly associated with predation. Corresponding Editor: J. Losos