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1.
John Boreman 《Environmental Biology of Fishes》1997,48(1-4):399-405
Sturgeons and paddlefish exhibit unusual combinations of morphology, habits, and life history characteristics, which make them highly vulnerable to impacts from human activities, particularly fisheries. Five North American sturgeons (shortnose, Gulf, pallid, Alabama, and green sturgeon) are listed as endangered or threatened by management authorities. Managers have instituted fishery closures for the three other species of North American sturgeons (Atlantic, white, and shovelnose) and paddlefish because of low stock abundance at some point in this century. Reproductive potential in four species I examined (Atlantic, white, and shortnose sturgeon, and paddlefish) is more sensitive to fishing mortality than it is for three other intensively-fished coastal species in North America: striped bass, winter flounder, and bluefish. The sturgeons and paddlefish are generally longer-lived than the three other coastal species, and also have an older age at full maturity, lower maximum fecundity values, and older ages at which 50% of the lifetime egg production is realized with no fishing mortality. 相似文献
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MAARTEN T.BASTIAENS RUDI G.J. WESTENDORP BERT J. VERMEER JAN N. BOUWES BAVINCK 《Pigment cell & melanoma research》1999,12(5):316-322
Ephelides and solar lentigines are benign pigmented spots, which are currently associated with an increased risk of skin cancer. These two pigmented spots are known to be discriminated by their clinical, histological, and electron microscopic characteristics, even though occasional misclassification can occur because of their similarity. It has also been questioned whether these spots are not one and the same. In this study, we have attempted to differentiate between these two pigmented spots with the use of a standardized protocol for clinical examinations on 272 healthy volunteers, paying particular consideration to their pigmentary and constitutional host factors. We found that solar lentigines 1) are more prevalent than ephelides, 2) increase in prevalence and number with higher age, and 3) are most prevalent on the trunk and occur more frequently in males than in females. A trend is also observed whereby ephelides 1) loose their prevalence with age, 2) become equally distributed on the face, arms, and trunk, and 3) occur more frequently in females. An intimate association of ephelides, but not solar lentigines, has been found with hair color and skin type. All of these findings are in agreement with most of those reported in the literature, supporting the view that ephelides and solar lentigines are different types of pigmented lesions. 相似文献
3.
Ricardo J. Pereira Felipe S. Barreto Ronald S. Burton 《Evolution; international journal of organic evolution》2014,68(1):204-215
Early generations of hybrids can express both genetic incompatibilities and phenotypic novelty. Insights into whether these conflicting interactions between intrinsic and extrinsic selection persist after a few generations of recombination require experimental studies. To address this question, we use interpopulation crosses and recombinant inbred lines (RILs) of the copepod Tigriopus californicus, and focus on two traits that are relevant for the diversification of this species: survivorship during development and tolerance to thermal stress. Experimental crosses between two population pairs show that most RILs between two heat‐tolerant populations show enhanced tolerance to temperatures that are lethal to the respective parentals, whereas RILs between a heat‐tolerant and a heat‐sensitive population are intermediate. Although interpopulation crosses are affected by intrinsic selection at early generational hybrids, most of the sampled F9 RILs have recovered fitness to the level of their parentals. Together, these results suggest that a few generations of recombination allows for an independent segregation of the genes underlying thermal tolerance and cytonuclear incompatibilities, permitting certain recombinant lineages to survive in niches previously unused by parental taxa (i.e., warmer thermal environments) without incurring intrinsic selection. 相似文献
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Abstract Bruchidius atrolineatus (Pic) is a common pest infesting cowpea seeds ( Vigna unguiculata Walp) in Africa. In the Sahelian zone, the adults are in reproductive diapause during the dry season. Diapause induction depends on the climatic conditions during embryonic and post-embryonic development. A strain of B. atrolineatus originating from the Niamey (13o N) was reared in different thermoperiodic and photoperiodic conditions. In the thermoperiodic regime 40:25o C, in continuous darkness, induction of diapause was dependent on the duration of the thermophase. Photoperiod could also influence diapause induction but the response depended on the temperature. When the beetles were reared in conditions of LD 12:12 h, 40:25o C, for seven generations, the proportion of diapausing adults decreased and their sensitivity to photoperiod increased. In LD 14:10 h, 40:25C C, the proportion of diapausing adults remained high regardless of the photoperiod. In these conditions, the first emerging adults were sexually active and were used for selection of a strain with a low incidence of diapause. After twelve generations, the proportion of diapausing beetles was lower than 5%. The responses of this selected strain to photo- and thermoperiods were reduced. The sensitivity of B. atrolineatus to photoperiod and thermoperiod could be controlled by genetic systems as observed in other insect species. 相似文献
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FIONA J. QUALLS RICHARD SHINE 《Biological journal of the Linnean Society. Linnean Society of London》2000,71(2):315-341
While recent experimental work on a variety of reptile species has demonstrated that incubation temperature influences hatchling phenotypes, the biological significance of such phenotypic variation remains unclear. Incubation temperature may exert significant long-term phenotypic effects. Alternatively, such influences may be temporary, or negligible relative to effects induced by genetic factors, or by the environmental conditions experienced after hatching. Even if incubation temperature exerts long-term effects on phenotype, this might occur indirectly (by influencing hatching dates) rather than by direct modifications of developmental processes. We quantified the influences of the source population, incubation temperature and rearing environment, on the phenotype of the Australian garden skink (Lampropholis guichenoti) from populations that differ in nest temperature and phenotype. Intcrpopulation differences in the phenotypes of young lizards were found to be a product of all three factors. However, the long-term effects of both population and incubation temperature operated indirectly (through variation in the date of hatching) rather than directly (through genetic or developmental factors). That is, once all temporal effects were removed, the only discernible influence on juvenile phenotypes was their rearing environment. Thus, some of the most important influences on lizard phenotypes may operate via modifications of hatching date. 相似文献
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