摘要:

Nucula turgidais a protobranch bivalve of the shallow sublittoral which produces, for a bivalve, unusually large eggs with a high lipid content to sustain the lecithotrophic development of the larvae. Males and females have similar reproductive investments, and the most noticeable feature of their output is the proportional increase in reproductive output as the animals age. Reproduction, as a proportion of the assimilation (Rep/C), was around 0.17 at population level but ranged from 0.055 in the 3 + year class to 0.54 in the 7 + year class. Similarly,C(=1 − [(A − G/R]) whereAis assimilation,Ggonad production andRis respiration, which appeared to be almost perfectly balanced at population level (C= −0.05) in fact varied from very conservative (C= −1.63) at 3 + to very “reckless” at 7+ (C=0.57). Using age-specific data, more accurate estimates can be made of future recruitment, and by back-calculation the survival rate from spawning to appearance in the benthos can be calculated.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672280

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The relationship between environmental factors, sex ratio, mode of reproduction, and female reproductive effort was examined in the cyclically parthenogeneticDaphnia magna.Female reproductive effort was found to decline before a significant production of males and sexual eggs takes place. Unlike factors such as crowding, poor nourishment, low (sometimes high) temperature and short or long day length, lowered reproductive effort is not a cue but rather an indicator of the selective advantage that would accrue from a changed sex ratio and mode of reproduction. The mechanism of the complex system of environmental sex determination inDaphniais reviewed, and the adaptivity of ESD is discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672281

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Bryozoans are common encrusting organisms in many shallow-water marine environments. Although reproducing sexually, their success as space occupiers resides largely in their capacity for colonial growth by zooidal budding (regarded by some as a form of asexual reproduction). This paper examines the reproductive strategies of several bryozoan species commonly associated with the fronds of coastal macroalgae. These range from ephemeral species that grow rapidly, reproduce and die (Electra pilosa, Celleporella hyalina, Membranipora membranacea) to more or less annual species with well-developed reproductive and growth cycles (Flustrellidra hispida, Alcyonidiumspp.). Whilst many of these bryozoans brood relatively few short-lived lecithotrophic larvae, others produce large numbers of longer-lived planktotrophic larvae. The seasonal and daily patterns of larval release are described for selected species. Resource allocation to sexual and colonial functions is considered in the context of environment-genotype interactions. Reproductive strategy is especially important in determining dispersal and colonising ability, and these in turn are major determinants of ecological pattern in epialgal bryozoan communities.

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672282

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672283

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672284

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672285

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1992.9672249

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor