Importance Of Asexual Reproduction Research Articles

Fine-scale spatial structuring of genotypes and phenotypes in natural populations of Asclepias syriaca

The majority of plants have the ability to reproduce asexually. Despite the importance of asexual reproduction, we still have a limited understanding of how clonality impacts phenotypic and genetic variation within natural populations. Here, we collected phenotypic and genetic data on spatially mapped ramets of common milkweed (Asclepias syriaca) from 10 belt transects from three populations to determine the average size and extent of milkweed clones, whether genotypes and phenotypes were spatially clustered, and whether ramets from the same clone were more similar to each other phenotypically than ramets from different clones. Only 14 % of the 141 ramets that were genotyped belonged to the same clone as another genotyped ramet. Although ramets from the same clone were, on average, closer together than ramets from different clones, we found that the minimum distance between ramets from the same clone was significantly larger than the minimum distance observed between non-clone ramets. Ramets within half a meter of each other had less than a 7% probability of being the same genotype. The high degree of unique genotypes within a single belt transect indicates that sexual reproduction is much more common in milkweed populations than previously thought. Ramets from the same clone were not more similar to each other in height, reproductive allocation, herbivory severity, or leaf traits than ramets from different clones. Our data support the conclusion that even small patches of milkweed that are phenotypically similar are unlikely to be a single clone.

The role of colonization in determining spatial patterns of Proscoloplos bondi sp. nov. (Orbiniidae: Annelida) in coralline algal turf

We describe Proscoloplos bondi sp. nov., a new species of orbinid polychaete found in coralline algal turf on rocky intertidal shores near Sydney, Australia. We used field sampling to describe P. bondi's patterns of spatial and temporal variation on a number of shores. P. bondi was significantly more abundant in low- than in mid-shore areas (ANOVA, P<0.05), but local populations were extremely variable in space and time. Despite extensive sampling, we did not find evidence of sexual reproduction in P. bondi, but commonly observed worms with regenerating heads and tails, which indicated the importance of asexual reproduction. We, therefore, tested the hypothesis that adult colonization contributes to its patterns of abundance. First, patches of artificial turf were placed near to and away from natural coralline turf and sampled after 2, 4 and 12 months. Generally, populations established themselves more quickly in patches of new habitat directly adjacent to coralline turf than in patches that were isolated. Second, patches of turf were deployed for 2-week periods in low- and mid-shore areas (repeated four times). Proscoloplos bondi were found significantly more often in patches in low-shore areas than in mid-shore areas and at some sites more than others (ANOVA, P<0.05), demonstrating the importance of adult colonization in determining patterns of abundance. Overall, the limited dispersal from spatially and temporally ephemeral populations of P. bondi combined with the patchiness of coralline turfs suggest that metapopulation dynamics may be important in the persistence of P. bondi on rocky shores.

Evolutionary Modification of Ecology in a Common Lichen Species

The very common foliose lichen Pseudoparmelia caperata (Ascomyco- tina, Parmeliaceae) has an exceptionally broad amplitude of ecological tolerance, growing on trees and noncalcareous rocks on all continents. In most of eastern North American, however, it is primarily epiphytic, its place on rock being taken by the closely related, exclusively American P. baltimorensis. Juveniles of both species are morphologically indistinguishable but the frequent presence of gyrophoric acid in P. baltimorensis in much of its range gives a chemical marker for identifying most immature thalli. Juveniles are distributed approximately like adults, indicating that the factors responsible for excluding most P. caperata from rock and most P. balti- morensis from tree trunks must act very early, perhaps at the stage of first growth of the asexual propagules that account for most individuals in populations. Pseudopar- melia caperata in eastern North America may have sustained genetic impoverishment through the loss of gamodemes adapted to the microhabitat of rock as a result of intense competition with P. baltimorensis in the past. Each species still occasionally grows in the other's preferred microhabitat and both may grow in approximately equal numbers on tree bases, which seem to be ecologically intermediate, having the chemistry and texture of bark and the reduced light and increased moisture of the forest floor. In spite of the importance of asexual reproduction in propagating the best genotypes, apothecia with spores are still regularly produced in both species. Widely distributed or disjunct species in which long-isolated popula- tions have seemingly not diverged are evolutionary enigmas. This phe- nomenon has been interpreted as evidence that gene flow is not the major evolutionary force that integrates the biological species (Ehrlich and Raven 1969). Many species of cryptogams, including lichen-forming fungi, consist of such old discontinuities without obvious divergence, a situation traditionally dismissed as reflecting genetic stagnation in these organisms. The present paper analyzes a widely distributed lichen species that would superficially seem to fit the model of ancient discontinuity without differentiation. Closer examination, however, shows that the representation of this species in one part of its range has actually sub- stantially diverged-not in morphology, which would be easier to per- ceive, but rather in amplitude of ecological tolerance, which is more elusive. We believe that this modification resulted from past competition with a similar and closely related species that is still extant today. Pseudoparmelia caperata (L.) Hale is one of the best-known of all foliose lichens. It is native to all continents and in many parts of the world is among the commonest of all lichen species, growing on trees and non- calcareous rocks. It varies little morphologically, is usually sterile, and produces soredia in characteristic erumpent soralia (fig. 1). In the late 1960s we became interested in a morphologically different species then