AOBPreview originally published online on April 18, 2006
Annals of Botany 2006 97(6):1063-1071; doi:10.1093/aob/mcl053
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Inter- and Intraspecific Variation in the Germination Response to Light Quality and Scarification in Grasses Growing in Two-phase Mosaics of the Chihuahuan Desert
Departamento de Biología Evolutiva, Instituto de Ecología A.C., Antigua Carretera a Coatepec km 2.5, Xalapa 91070, Veracruz, México
* For correspondence. E-mail montana{at}ecologia.edu.mx
Received: 13 July 2005 Returned for revision: 2 December 2005 Accepted: 30 January 2006 Published electronically: 18 April 2006
• Background and Aims In many locations, plants are faced with adjacent, contrasting environments, and the between-species differential evolution of life history traits can be interpreted as an evolutionary response to this environmental heterogeneity. However, there has been little research on the intraspecific variability in these attributes as a possible evolutionary response of plants.
• Methods In the two-phase mosaic of the Chihuahuan Desert (adjacent patches with contrasting resource availability), analyses were carried out of the germination response to the scarification and light quality to which grass seeds growing on these patches are exposed (open and closed habitats).
• Key Results Species that grow in open habitats exhibited a higher germination success than those from closed habitats after scarification. At both the inter- and intraspecific level, there were differences in the germination percentage and in the germination speed in response to light quality. Intraspecific variation in the species from the closed habitat (Pleuraphis mutica and Trichloris crinita) and in Chloris virgata (which grows in both habitats) was due to genetic variation (the family factor was significant), but there was no genetic variation in phenotypic plasticity (non-significant interaction between family and light quality). In contrast, for the species that grows only in the open habitat (Dasyochloa pulchella), the family did not have a significant effect, but there was genetic variation in the phenotypic plasticity (significant interaction between family and light quality).
• Conclusions In C. virgata, P. mutica and T. crinita, natural selection could be favouring those genotypes that responded better in each light environment, but it is not possible that the natural selection resulted in different optimal phenotypes in each habitat. On the contrary, in D. pulchella, selection could have reduced the genetic variation, but there is the possibility of the evolution of reaction norms, resulting in the selection of alternative phenotypes for each habitat.
Key words: Arid zones, Chloris virgata, Dasyochloa pulchella, environmental heterogeneity, germination, inter- and intraspecific variation, light quality, phenotypic plasticity, Pleuraphis mutica, reaction norm, scarification, Trichloris crinita
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