Biomedical subjects

R Brian Langerhans

Publications and source records attributed to R Brian Langerhans.

5 recordsLinked to original sources

PubMed2006

Rapid temporal reversal in predator-driven natural selection.

As the environment changes, will species be able to adapt? By conducting experiments in natural environments, biologists can study how evolutionary processes such as natural selection operate through time. We predicted that the introduction of a terrestrial predator would first select for longer-legged lizards, which are faster, but as the lizards shifted onto high twigs to avoid the predator, selection would reverse toward favoring the shorter-legged individuals better able to locomote there. Our experimental studies on 12 islets confirmed these predictions within a single generation, thus demonstrating the rapidity with which evolutionary forces can change during times of environmental flux.

Animals↗

PubMed2006

Shared and unique features of diversification in Greater Antillean Anolis ecomorphs.

Examples of convergent evolution suggest that natural selection can often produce predictable evolutionary outcomes. However, unique histories among species can lead to divergent evolution regardless of their shared selective pressures-and some contend that such historical contingencies produce the dominant features of evolution. A classic example of convergent evolution is the set of Anolis lizard ecomorphs of the Greater Antilles. On each of four islands, anole species partition the structural habitat into at least four categories, exhibiting similar morphologies within each category. We assessed the relative importance of shared selection due to habitat similarity, unique island histories, and unique effects of similar habitats on different islands in the generation of morphological variation in anole ecomorphs. We found that shared features of diversification across habitats were of greatest importance, but island effects on morphology (reflecting either island effects per se or phylogenetic relationships) and unique aspects of habitat diversification on different islands were also important. There were three distinct cases of island-specific habitat diversification, and only one was confounded by phylogenetic relatedness. The other two unique aspects were not related to shared ancestry but might reflect as-yet-unmeasured environmental differences between islands in habitat characteristics. Quantifying the relative importance of shared and unique responses to similar selective regimes provides a more complete understanding of phenotypic diversification, even in this much-studied system.

Animals↗

PubMed2005

Male genital size reflects a tradeoff between attracting mates and avoiding predators in two live-bearing fish species.

Male genitalia may experience more rapid, divergent evolution than any other animal character, but why? Research during the past several decades has culminated in the view that genital diversification primarily results from postmating sexual selection (e.g., sperm competition or cryptic female choice). However, the potential roles of premating sexual selection (e.g., mate choice) and natural selection have received little attention. We examined the possible importance of these mechanisms by investigating divergence in male genitalia among populations differing in predator regime for two species of live-bearing fish (Gambusia affinis in Texas and Gambusia hubbsi in The Bahamas). When controlled for body size, males exhibited a larger gonopodium (sperm-transfer organ) in predator-free environments than in predatory environments, a trend that persisted across space (multiple populations), time (multiple years), and species. By conducting laboratory experiments with G. affinis, we found that premating sexual selection seems to favor larger male genitalia (females exhibited mating preference for males having larger gonopodia), but natural selection in the presence of predatory fishes seems to favor reduced genital size (larger gonopodium size was associated with reduced burst-swimming performance, an important antipredator behavior). Although postmating sexual selection is widely presumed to be the most important mechanism driving genital diversification, these findings suggest that alternative mechanisms, particularly for organisms that cannot retract their genitalia, may also prove important.

Analysis of Variance↗

PubMed2004

Shared and unique features of evolutionary diversification.

A fundamental question in evolutionary biology asks whether organisms experiencing similar selective pressures will evolve similar solutions or whether historical contingencies dominate the evolutionary process and yield disparate evolutionary outcomes. It is perhaps most likely that both shared selective forces as well as unique histories play key roles in the course of evolution. Consequently, when multiple species face a common environmental gradient, their patterns of divergence might exhibit both shared and unique elements. Here we describe a general framework for investigating and evaluating the relative importance of these contrasting features of diversification. We examined morphological diversification in three species of livebearing fishes across a predation gradient. All species (Gambusia affinis from the United States of America, Brachyrhaphis rhabdophora from Costa Rica, and Poecilia reticulata from Trinidad) exhibited more elongate bodies, a larger caudal peduncle, and a relatively lower position of the eye in predator populations. This shared response suggests that common selective pressures generated parallel outcomes within three different species. However, each species also exhibited unique features of divergence, which might reflect phylogenetic tendencies, chance events, or localized environmental differences. In this system, we found that shared aspects of divergence were of larger magnitude than unique elements, suggesting common natural selective forces have played a greater role than unique histories in producing the observed patterns of morphological diversification. Assessing the nature and relative importance of shared and unique responses should aid in elucidating the relative generality or peculiarity in evolutionary divergence.

Animals↗

PubMed2004

Predator-driven phenotypic diversification in Gambusia affinis.

Predation is heterogeneously distributed across space and time, and is presumed to represent a major source of evolutionary diversification. In fishes, fast-starts--sudden, high-energy swimming bursts--are often important in avoiding capture during a predator strike. Thus, in the presence of predators, we might expect evolution of morphological features that facilitate increased fast-start speed. We tested this hypothesis using populations of western mosquitofish (Gambusia affinis) that differed in level of predation by piscivorous fish. Body morphology of G. affinis males, females, and juveniles diverged in a consistent manner between predatory environments. Fish collected from predator populations exhibited a larger caudal region, smaller head, more elongate body, and a posterior, ventral position of the eye relative to fish from predator-free populations. Divergence in body shape largely matched a priori predictions based on biomechanical principles, and was evident across space (multiple populations) and time (multiple years). We measured maximum burst-swimming speed for male mosquitofish and found that individuals from predator populations produced faster bursts than fish from predator-free populations (about 20% faster). Biomechanical models of fish swimming and intrapopulation morphology-speed correlations suggested that body shape differences were largely responsible for enhanced locomotor performance in fish from predator populations. Morphological differences also persisted in offspring raised in a common laboratory environment, suggesting a heritable component to the observed morphological divergence. Taken together, these results strongly support the hypothesis that divergent selection between predator regimes has produced the observed phenotypic differences among populations of G. affinis. Based on biomechanical principles and recent findings in other species, it appears that the general ecomorphological model described in this paper will apply for many aquatic taxa, and provide insight into the role of predators in shaping the body form of prey organisms.

Analysis of Variance↗