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1.
The debate about the biological species concept - a review 总被引:1,自引:0,他引:1
C. L. HÄUSER 《Journal of Zoological Systematics and Evolutionary Research》1987,25(4):241-257
The importance of the species concept in biology has led to a continuing debate about the definition of species. This paper summarizes the recent literature in relation to the ‘biological species concept’ (MAYR 1942). Among the general attributes demanded, possible limitations of the universality and applicability of a species definition are discussed. Three different areas of criticism of the biological species concept are considered: 1. The impracticability of the criterion of reproductive isolation. The demand for more practical criteria is rejected, because reproductive isolation is seen as the factor that produces and maintains species as discrete entities in nature. 2. The inapplicability to non-bisexual organisms. A brief survey of modes of uniparental reproduction and their relative importance suggests that obligatory apomicts are of little evolutionary significance. 3. The inapplicability to multidimensional situations. Despite practical difficulties, the biological species concept is held to apply to organisms separated in space. The impossibility to delimit species in time by reproductive isolation is recognized. Out of two ways to divide continuous evolutionary lineages in time, the phylogenetic approach, which considers only speciation events (cladogenesis), is preferred as it is more objective. A list of recently published alternative definitions of species, none of which is found acceptable, is given. It is concluded that the biological species concept needs not be changed or dismissed on the basis of the discussed criticisms. 相似文献
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Ann Bucklin 《Journal of experimental marine biology and ecology》1987,110(3):225-243
Individual size, rate of growth, and mode and frequency of asexual reproduction are life-history traits of primary importance for sea anemones. These traits determine sexual reproductive output, affect an individual's probability of survival, and are crucial in adapting an individual to its environmental surroundings. The sea anemone Metridium senile (L.) is highly variable in ecological distribution and life history, including rate of growth, individual size, and rate of asexual reproduction. Gonad size (measured as cross-sectional area of gonadal tissue) increases with body weight, so individuals should grow as large and as rapidly as possible to maximize individual sexual reproductive output. Cessation of growth and small body size in intertidal populations suggest that growth is constrained by genetic or environmental conditions. The growth of intertidal individuals transplanted to harbor-float panels demonstrated that growth limits are imposed by environmental factors, most probably limited food and feeding time and damage from wave exposure (which stimulates fragmentation). Individuals in harbor-float populations, which are continuously immersed, grow much larger, and large individuals comprise a greater proportion of the population than in the intertidal zone. The highest rate of fragmentation observed was on harbor-float panels. Patterns of growth and asexual reproduction provide adaptive advantages for M. senile. For harborfloat individuals, large individual size increases gamete production and may increase feeding efficiency. For intertidal individuals, asexual reproduction allows growth despite individual size constraints and rapid population growth, with specific advantages resulting from clone formation. 相似文献
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DNA methylation can be environmentally modulated and plays a role in phenotypic plasticity. To understand the role of environmentally induced epigenetic variation and its dynamics in natural populations and ecosystems, it is relevant to place studies in a real-world context. Our experimental model is the wild potato Solanum kurtzianum, a close relative of the cultivated potato S. tuberosum. It was evaluated in its natural habitat, an arid Andean region in Argentina characterised by spatial and temporal environmental fluctuations. The dynamics of phenotypic and epigenetic variability (with Methyl Sensitive Amplified Polymorphism markers, MSAP) were assayed in three genotypes across three growing seasons. These genotypes were cultivated permanently and also reciprocally transplanted between experimental gardens (EG) differing in ca. 1000 m of altitude. In two seasons, the genotypes presented differential methylation patterns associated to the EG. In the reciprocal transplants, a rapid epigenomic remodelling occurred according to the growing season. Phenotypic plasticity, both spatial (between EGs within season) and temporal (between seasons), was detected. The epigenetic and phenotypic variability was positively correlated. The lack of an evident mitotic epigenetic memory would be a common response to short-term environmental fluctuations. Thus, the environmentally induced phenotypic and epigenetic variation could contribute to populations persistence through time. These results have implications for understanding the great ecological diversity of wild potatoes. 相似文献
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《Journal of bryology》2013,35(1):12-19
AbstractScotland’s mountains are home to a rare and unique liverwort community, ‘the oceanic-montane liverwort-rich heath’, but its component species are absent from regions where they could potentially thrive. Many biological characteristics of these species are unknown, making it impossible to explain the reasons for their rarity; however, they have not been observed to produce sporophytes within Britain. We use ex situ cultivation of whole liverworts and fragments, and in situ cultivation of fragments, to assess the growth rate and the potential for vegetative reproduction of several species. Most of the species grew from both fragments and as whole plants, indicating that the rarity of the liverwort heath is not due to poor powers of regeneration. We propose that growth rate and the potential to regenerate from fragments are important factors structuring the liverwort heath community, at least locally. Furthermore, this study demonstrates that there is potential for ex situ conservation of rare liverwort species, in situ enhancement of existing populations, and creation of new ones. 相似文献
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The relationship between probability of survival and the number of deleterious mutations in the genome is investigated using
three different models of highly redundant systems that interact with a threatening environment. Model one is a system that
counters a potentially lethal infection; it has multiple identical components that act in sequence and in parallel. Model
two has many different overlapping components that provide three-fold coverage of a large number of vital functions. The third
model is based on statistical decision theory: an ideal detector, following an optimum decision strategy, makes crucial decisions
in an uncertain world. The probability of a fatal error is reduced by a redundant sampling system, but the chance of error
rises as the system is impaired by deleterious mutations. In all three cases the survival profile shows a synergistic pattern
in that the probability of survival falls slowly and then more rapidly. This is different than the multiplicative or independent
survival profile that is often used in mathematical models. It is suggested that a synergistic profile is a property of redundant
systems.
Model one is then used to study the conservation of redundancy during sexual and asexual reproduction. A unicellular haploid
organism reproducing asexually retains redundancy when the mutation rate is very low (0001 per cell division), but tends to
lose high levels of redundancy if the mutation rate is increased (001 to 01 per cell division). If a similar unicellular haploid
organism has a sexual phase then redundancy is retained for mutation rates between 0001 and 01 per cell division. The sexual
organism outgrows the asexual organism when the above mutation rates apply. If they compete for finite resources the asexual
organism will be extinguished. Variants of the sexual organism with increased redundancy will outgrow those with lower levels
of redundancy and the sexual process facilitates the evolution of more complex forms. There is a limit to the extent that
complexity can be increased by increasing the size of the genome and in asexual organisms this leads to progressive accumulation
of mutations with loss of redundancy and eventual extinction. If complexity is increased by using genes in new combinations,
the asexual form can reach a stable equilibrium, although it is associated with some loss of redundancy. The sexual form,
by comparison, can survive, with retention of redundancy, even if the mutation rate is above one per generation.
The conservation and evolution of redundancy, which is essential for complexity, depends on the sexual process of reproduction. 相似文献
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