Forest Trees (1991) / Chapter Skim
Currently Skimming:
3 Structure of Genetic Variation
3 Structure of Genetic Variation
Pages 51-72
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 51... ...
Most tropical forest trees have hermaphroditic flowers; that is, the flowers contain male and female reproductive organs (Ashton, 1969; Bawa, 1974, 1979~. In contrast, a vast majority of temperate tree species are monoecious; that is, they are characterized by the presence of unisexual flowers, but male and female flowers occur on the same plant.
|
From page 52... ...
Many tropical species are genetically self-incompatible; that is, little or no seed is set following self-pollination (Bawa, 1974; Bawa et al., 1985~. Surprisingly little is known about self-incompatibility in temperate species with hermaphroditic flowers; in the monoecious species, two mechanisms prevail that prevent or reduce selling.
|
From page 53... ...
Gene Flow Gene flow implies an exchange of gametes or genes among dispersed trees, and it is inversely related to population differentiation. It occurs through the movement of pollen and seed, which can be dispersed by a wide variety of nonliving and living mechanisms.
|
From page 54... ...
Many species, however, are pollinated by medium-sized to large bees (Bawa et al., 1985~. Other pollen vectors are moths, beetles, and the generalist insects, which are the wide variety of small bees, beetles, butterflies, wasps, and flies that visit flowers.
|
From page 55... ...
The "average" gene is thought to have up to a thousand base pairs; thus, the DNA structure provides for a phenomenal amount of variation in the genetic code. The difference between two alleles is often as simple as a substitution of a single base pair, but this may correspond to a significant difference in the phenotype resulting from those alleles.
|
From page 56... ...
< Seeds am also diapered by a number of mechanisms. The seeds of temperate conifers and many h.a~d~ood species, such as Pappas, poplars, and willows/ are dispersed by grind.
|
From page 57... ...
Nonrandom assemblages of genotypes impose a structure on the TABLE 3-1 Relation of Levels of Gene Flow (Nm) to Pollination Mechanism in Selected Forest Tree Species Number of Populations Pollination Species Sampled Nma Mechanism' Abies balsamea 4 4.546 W A
|
From page 58... ...
If TABLE 3-1 s(O~f~ Number of Populates ~P6llina~S~= Species ampler \ ~{chanis~' S
|
From page 59... ...
The scientific methods used to distinguish levels of variation are the working tools for shaping decisions on which resources should be devoted to managing distinct tree characteristics. Two approaches have been used to study genetic diversity in tree populations: provenance testing and allozyme screening.
|
From page 60... ...
,fore~xa~mp~le' grave been son to containless genetic variation than the ~en~tr~lpsp! p~ul~5on~s This Neil n~ot-~ell documented ~^~^p^~s~periphe~y.Pe~.~p~heral.-po~pulati!
|
From page 61... ...
Forest tree species differ greatly with respect to genetic divergence among populations. There are two major problems in comparing levels of genetic differentiation within a species.
|
From page 62... ...
floss: two mods Am 4,' :~s Was ~ +~ yews w ~ ~ :~. ~ ~ ~ sale ~ 7,~ k 91~ ~ )
|
From page 63... ...
63 _` us 0 0 0 {t ._ ~a, 0 0 0 ~ :, .
|
From page 66... ...
~ If ~ Knowledge about the d~i~sidbuti~on and reductive bi~ol~gv of tropical Mast trees is Mined throug~b botanical surveys and plant inv~n~es in the tonics. there a research assistant climbs a tree of the ~2 sp.
|
From page 67... ...
A very preliminary analysis of a few tropical forest tree species reveals that levels of population genetic divergence are similar to those observed for temperate tree species. This is contrary to expectations based on the limited gene dispersal that might be typical of many tropical species whose populations are more isolated (Bawa, 1976~.
|
From page 68... ...
, it would be difficult to justify maintaining multiple populations of trees to preserve their potentially useful genetic diversity based solely on allozyme variations. Unfortunately, allozyme studies in forest trees generally have not been accompanied by parallel work on variation in morphological traits that are known to contribute to the fitness of plants.
|
From page 69... ...
For species witch mom ~std~cted pollen or weds migration, mosaics Kitchen Faust sands are expressed as Awe inte~opulabonal vadabons of Ionizer dungeon. Selection awes operating on diffedng gene f~q~ue~ncies can abut the d~bibuLon oigenedcvadabon among and Within those popu~bons.
|
From page 70... ...
, and the probability distributions of unique alleles (Gregorius and Namkoong, 1983; Namkoong and Gregorius, 19851. Differences also exist in the patterns of population subdivision indicated by isozyme versus morphological traits, in the traits associated with broad climatic adaptability (e.g., bud break or bud set times)
|
From page 71... ...
RECOMMENDATIONS To support conservation efforts, study of the patterns of genetic variation in tree populations should be accelerated and expanded in scope, especially in the tropics and subtropics. Although genetic variation has been surveyed in a wide range of species, the existing data base is largely derived from the study of conifers in the north temperate zone.
|
From page 72... ...
Genetic management techniques for resource areas that are managed for agroforestry and for industrial forestry should be studied to develop inexpensive means for monitoring the distribution of genetic variation and ensuring the maintenance of genetic diversity. Research on population sizes, structures, dynamics, and reproductive systems should also be expanded, particularly in the following three areas: · Research should be increased on reproductive systems, the genetic architecture of populations, and the minimum viable population size of trees.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.