摘要:

Dendropoma meroclistahas been found on six islands and one continental site between Hawaii and Kenya; it occurs in shallow‐subtidal and low‐intertidal habitats and has either no, or very limited, planktic development. A very similar form has been found only in the Indian Ocean (Sinai and Madagascar), where it forms gregarious masses on exposed intertidal ledges. This form also produces many more, smaller eggs than the described species and has a planktotrophic larva. While adult anatomies of the two forms are indistinguishable, the Sinai‐Madagascar form has a smaller protoconch with distinctive sculpture. These apparent sibling species provide a case of speciation occurring by life‐history divergence within a very conservative morphology and present a surprising example of wider distributional range in the species with little apparent capacity for di

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00454.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Sexual and vegetative fitness components in hermaphrodite and female plants of the self‐compatible, perennial herbSaxifraga granulataare compared using material derived from a gynodioecious population in northern England.Females produced only 57% as many seeds as hermaphrodites, but their ovule offspring were 1.28 times as fit as those of hermaphrodites, and females were more vegetatively vigorous. The advantages to females in ovule offspring quality and in vegetative reproduction counteract their disadvantages in pollen and seed production and therefore probably play a role in the maintenance of the gynodioecious polymorphism. Pollination ecology, resource reallocation and inbreeding depression all appear to contribute to the observed sex differences in fitnes

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00455.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The mortality of phenotypic shell colour morphs and age classes of the snailArianta arbustorumin several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall,P<0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00456.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Rates of dental evolution are calculated for four upper first molar (M1) characters of 26 ancestral‐descendant species pairs of Cenozoic horses from North America. On average, crown height evolved significantly more rapidly (X̄= 0.104 darwins, d) than did occlusal dimensions (length and width; X̄= 0.045 d and 0.047 d, respectively). As might be expected, low‐crowned Eocene and Oligocene horses (HyracotheriumthroughMesohippus) exhibit relatively slow rates of dental evolution. During the major early Miocene adaptive shift from browsers to grazers (ParahippustoMerychippus), only crown height evolved rapidly. Advanced Miocene‐Pliocene three‐toed hipparions and one‐toed equines are generally normal, or horotelic, in their rates of dental evolution. The most rapid rates are exhibited in Miocene browsing anchitheres and the dwarf genusPseudhipparion.Horses do not show the very high rates of dental evolution reported elsewhere for Paleogene mammals. The traditional notion of horses being a prime example of rapid morphological evolution as seen from the fossil record is not corroborated by the data pre

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00457.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

There is increasing evidence that ecological variables involving stress are important in determining evolutionary rates. This paper incorporates recombination into this scenario.InDrosophila melanogaster, recombination increases at developmental temperatures above and below normal culture temperatures, giving a U‐shaped curve which is most pronounced in centromeric regions; however, at near lethal temperature extremes there is some evidence for a fall in recombination. More limited data from other organisms are generally consistent with this conclusion. Nutritional stress in the form of starvation increases recombination inD. melanogaster, and behavioural stress has been found to increase recombination in male mice.In natural populations recombination is under complex genetic control analogous to other quantitative traits. InD. melanogasterin a novel environment, there is evidence that additive genetic variability for recombination is higher than in a standard laboratory environment. During selection in populations exposed to extreme stress increased recombination may occur; this implies that in marginal (stressful) habitats, variability generated by recombination may increase.InD. melanogaster, structural heterozygosity due to inversions in one part of the genome tends to increase recombination in the remainder of the genome in a qualitatively similar manner to, and cumulative with, direct environmental effects especially temperature. Substantial recombination should be inducible under combinations of karyotypes and environments deviating from existing circumstances, especially if the suggestion that effects are often synergistic due to a dependence upon available energy levels can be confirme

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00458.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Neighourhood sizes and variance structure were determined for ten North American coniferous forest tree species, using information on seed dispersal, patterns of life history, and demography. A synthetic cohort of reproductive individuals belonging to a critical age group was constructed using normal yield tables. Data on reproductive individuals in a synthetic cohort were used to determine the neighbourhood sizes for each species. The neighbourhood sizes varied from 1244 to 50 118 individuals. Effective population sizes were calculated from data on neighbourhood sizes and replacement patterns of individuals in various species, the interdeme differentiation,Fstranged from 0.0002 to 0.007. The results suggest that large neighbourhood and effective population sizes, and hence panmixia, may be virtually common among the species examined. These conclusions are consistent with recent findings on population differentiation and estimates of gene flow in confers using allozyme markers.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00459.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Populations of the morphological species,Nilaparvata lugens(Stål), were found to breed and feed on the grass,Leersia hexandraSchwartz, at six sites in Queensland, Australia. They differ from sympatric rice‐feeding populations in characters of pulse repetition frequencies of male and female acoustic courtship signals. The two host‐derived populations hybridize freely in the laboratory, but in mate choice experiments show very significant preferences for homogametic matings. No indication of field hybridization has been found, so that the two morphologically inseparable populations represent sympatric biological species in Australia.Populations fromL. hexandraare also reported from four localities in Sri Lanka and one in Orissa, India. These resemble previously studied populations from the Philippines. They differ significantly in courtship call characters, both from sympatric rice‐associated populations and from allopatricLeersia‐associated populations from Australia.The geographical variation reported for acoustic signals is not consistent with Paterson's recognition concept of species, but may be interpreted in terms of theories of allopatric speciation involving sexual selection for mate recognition

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00460.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00454a.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY