Local Adaptability Test Research Articles

Differentiation in populations of Hordeum spontaneum along a gradient of environmental productivity and predictability: life history and local adaptation

Reciprocal introduction of seeds and seedlings of wild barley, Hordeum spontaneum , originating in four different environments of Israel was used to: (1) test for local adaptation, (2) make inferences about environmental effects on life-history and reproductive traits, and (3) identify trait combinations with recognizable ‘strategies’. The four populations examined represented the following environments: (1) desert − low productivity and predictability, drought stress; (2) semi-steppe batha − moderate productivity and predictability; (3) grassland − high productivity and predictability; and (4) mountain − high productivity and predictability but with severe frost stress. Significant genotype-by-environment interactions were observed for yield and reproductive biomass, seedling biomass and percentage germinated and survived seeds, suggesting local ecotype adaptation. Increasing productivity and predictability of environment in respect to rainfall, without concomitant frost stress, was found to select for high reproductive biomass and large seeds, a high fraction of germinating seeds and high vigour of seedlings. The optimal strategy changes with increasing productivity and predictability and involves a trade-off between seed size and number, with reduced yield but increased seed mass, consistent with competition selection (or K-selection sensu MacArthur & Wilson (1967)) type. No specific life-history adaptations to predictable frost stress were detected for the mountain ecotype, but there was higher survival of seedlings in their indigenous (mountain) environment compared with other ecotypes. The latter appears to be a physiological adaptation to frost, which is consistent with selection for stress tolerance (or S-selection sensu Grime (1977)) type. The other stress factor, drought, which is very unpredictable in deserts, was associated with high seed dormancy, small seed size and low vigour of seedlings, but relatively high yield, which is consistent with a stress-escape bet-hedging strategy. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 479–490.

EVIDENCE FOR NONADAPTIVE EVOLUTION IN PARASITOID VIRULENCE FOLLOWING A BIOLOGICAL CONTROL INTRODUCTION

Biological control systems can evolve; founder effects, drift, inbreeding, and adaptation to new environments can occur during the introduction and establishment of exotic pests and their natural enemies. It has been hypothesized that successful biological control agents are those that become locally adapted to their new environment or populations of hosts. However, there are no explicit comparisons of native and introduced populations of biological control agents testing for local adaptation. The pea aphid, Acyrthosiphon pisum, is an introduced pest of legumes. Aphidius ervi, a parasitoid wasp, was introduced from France to control pea aphids. Using reciprocal transplant experiments, I compared introduced populations of pea aphids and A. ervi from New York State with native populations from France. I documented patterns of aphid resistance to parasitism and A. ervi ability to overcome aphid resistance (virulence) in the two localities and explored whether the introduced parasitoids are locally adapted to the introduced pea aphids. I found that parasitoids from native French populations have high rates of parasitism on pea aphids specialized on clover and on pea aphids specialized on alfalfa, regardless of whether the aphids are collected from France or New York. Introduced parasitoids from New York have high rates of parasitism on pea aphids from clover, but low rates of parasitism on pea aphids from either New York or French alfalfa fields. Thus, there is no evidence that the introduced wasps have become adapted to their local populations of pea aphid hosts. On the contrary, the ability of the introduced parasitoids to develop successfully in pea aphids from alfalfa may have been compromised by the biological control introduction. This apparently nonadaptive evolution was cryptic until examined experimentally. A better understanding of the effects of biological control introductions on natural enemies will come through additional comparisons of native and introduced populations of biocontrol agents. Such comparisons may provide valuable insights into the role of microevolutionary change in biological control and suggest useful avenues to enhance the success of biological control introductions.

Local adaptation and transplant dominance in genets of the marine clonal plant Zostera marina

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 242:111-118 (2002) - doi:10.3354/meps242111 Local adaptation and transplant dominance in genets of the marine clonal plant Zostera marina August Hämmerli*, Thorsten B. H. Reusch Max Planck Institute for Limnology, August-Thienemann-Str. 2, 24306 Plön, Germany *E-mail: haemmerli@mpil-ploen.mpg.de ABSTRACT: Worldwide decline of seagrass beds has increased the need for information on potential source populations for recolonization and conservation purposes. The aim of the present study was to test for local adaptation in Zostera marina, the dominant seagrass species of the northern hemisphere. To this end, we performed a reciprocal transplant experiment at the level of the genetic individual (= clone or genet) in 2 Baltic Sea populations for which the clonal structure had been mapped in detail. The treatment effects were tested on aboveground and belowground dry weight of physiologically independent rhizome fragments of replicated genets at the end of the season. We found that genets from both populations produced more biomass in their home population (local adaptation). Genets from 1 population produced more biomass overall (overall dominance) and the range of cross-site performance indicated a high degree of variability among genets within the 2 populations. Our results provide a first test for local adaptation in established seagrass genets and demonstrate home site advantage of clones that are part of a highly connected system of Z. marina populations along the Baltic Coast. KEY WORDS: Clonal plants · Local adaptation · Microsatellite · Population differentiation · Transplant experiment · Zostera marina Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 242. Online publication date: October 25, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Introduction: Experimental Approaches to Testing Adaptation

How natural selection acts on traits to produce adaptation to different environments is a central question in evolutionary biology. Recently there has been a revival of interest in this question, in part because of the development of new tools in several fields (Rose and Lauder 1996). Modern methods for phylogenetic analysis now provide a framework for testing the hypothesis that a trait is an adaptation using comparative data (Larson and Losos 1996). It is also possible to test the current adaptive value of specific traits. Within-species phenotypic selection analysis (Lande and Arnold 1983) allows the measurement of direct and indirect selection on correlated characters in natural populations, and it can be combined with quantitative genetic data to predict short-term responses to selection. However, testing hypotheses concerning the ecological causes of natural selection usually requires experimental manipulation (Wade and Kalisz 1990). The objective of this volume is to explore how modern techniques for genetic and physiological manipulation can be used to elucidate the causes and mechanisms of adaptation. Experimental studies of adaptation are not new. The classical approach to testing for intraspecific local adaptation is the reciprocal transplant experiment. If the relative fitness of genotypes from each population is highest in their “home” environment, there is strong evidence for local adaptation. However, classical reciprocal transplant experiments cannot tell us the ecological causes of adaptation or what specific traits are under selection. More recently, evolutionary ecologists have used multivariate selection analysis (Lande and Arnold 1983; Rausher 1992) to examine direct and indirect selection on specific characters. This technique can be combined with experimental manipulation of environmental factors to elucidate the ecological causes of natural selection (Wade and Kalisz 1990). If the strength or direction of selection on a set of