The fate of traditional extensive (gei wai) shrimp farming at the Mai Po Marshes Nature Reserve, Hong Kong

Extensive shrimp farming around Deep Bay, Hong Kong,began in the mid-1940‘s after the construction of intertidal ponds (gei wai) among the coastal mangroves. The ponds are increasingly being seen as an example of how wetlands can be used sustainablysince they are naturally stocked with shrimp postlarvae (e.g. Metapenaeus ensis) and young fish (e.g. Mugil cephalus) flushed into the ponds from Deep Bay. Once inside, these shrimps and fish feed on naturally occurring detritus on the pond floor. The only gei wai remaining in the Territory, are those at the WWF Hong Kong Mai Po Marshes Nature Reserve, adjacent to Deep Bay. Analysis of the shrimp production between 1990–1995 showed that there were two seasonal peaks, from April–June (Recruitment-I)and from July–October (Recruitment-II). The second peak was significantly lower than the first (p <0.001), especially from those gei wai in the southern part of the reserve which are much closer to a polluted river. The average harvest from each gei wai had also significantly declined from40.9 ±6.0 kg ha⁻¹ yr⁻¹ in 1990 to15.1 ±3.6 kg ha⁻¹ yr⁻¹ in 1995 (p <0.01). This decline can be attributed to the abundance of predatory fish in the gei wai, and increasing water pollution in Deep Bay which adversely affects the amount of shrimp larvae for stocking the gei wai, as well as the quality of water for flushing the ponds during the rearing and harvesting seasons. Despite this, those gei wai which are not-commercially viable can still support many non-commercial, more pollution tolerant fish and shrimp species. As a result, the management of the segei wai has been altered such that their objective is to provide feeding habitat for piscivorous waterbirds, which is also in line with the aims of the nature reserve. This revised version was published online in August 2006 with corrections to the Cover Date.     

深圳湾不同生境湿地大型底栖动物次级生产力的比较研究

以深圳湾红树林为例,于2010年1—12月每月1次对红树林和3种对照生境(芦苇鱼塘,基围鱼塘和光滩)的大型底栖动物进行了采样调查,并对其次级生产力、P/B值(次级生产力与生物量的比值)、优势种和生物多样性进行了计算与分析。结果表明,不同生境大型底栖动物群落次级生产力和P/B值差异明显,芦苇鱼塘、基围鱼塘、光滩和红树林生境的次级生产力分别为:6.81、147.50、74.70和105.78 g.m-.2a-1;P/B值分别为:1.10、1.53、1.41和3.58 a-1。红树林生境的次级生产力较高,仅次于基围鱼塘,P/B值显著高于其他3种生境,周转速率最快。结合大型底栖动物优势种和生物多样性的季节变化分析表明,红树林生境大型底栖动物生物多样性最丰富,生态系统抵抗力和恢复力最高,生态系统最稳定。由此说明城市化地区红树林生境对大型底栖动物周转速率和物种多样性有明显促进作用,可以增加生态系统营养的保持力和生态系统的稳定性,对于缓解城市化对湿地生态系统造成的威胁具有重要作用。     

烟蚜茧蜂寄生对烟蚜生长发育和繁殖的影响

【目的】为探究烟蚜茧蜂Aphidius gifuensis对烟蚜Myzus persicae寄生后烟蚜生长发育和繁殖影响及其在烟蚜防控中的作用。【方法】采用室内叶片培养皿法,测定了不同龄期烟蚜(1-4龄若蚜及成蚜)被烟蚜茧蜂寄生后烟蚜当代(F₀)及后代(F₁)的发育历期、寿命、产仔量。【结果】烟蚜1龄若蚜被烟蚜茧蜂寄生后,1龄若蚜历期受到显著影响,较未被寄生对照缩短了0.65 d (33.00%),而2-4龄若蚜期和成蚜历期未受显著影响;2龄若蚜被寄生后,4龄若蚜和成蚜历期均受到显著影响,较未被寄生的对照分别缩短了1.50 d (100.00%)和0.83 d (100.00%),而2和3龄若蚜期未受显著影响;3龄若蚜被寄生后,4龄若蚜和成蚜期均受到显著影响,较未被寄生对照分别缩短了1.50 d (100.00%)和0.83 d (100.00%),而3龄若蚜期未受显著影响。2龄若蚜被寄生后烟蚜的寿命和产仔量均受到显著影响,寿命较未被寄生对照缩短了8.39 d(54.00%),每雌产仔量较未被寄生对照减少了48.67头(100.00%)。此外,2-3龄若蚜被寄生后其后代(F₁)1龄若蚜历期受影响最大,较未被寄生烟蚜后代1龄若蚜期缩短了0.80 d(40.00%),其F₁代平均寿命较未被寄生烟蚜后代平均寿命延长了5.72 d(41.20%),但其产仔量与对照差异不显著。【结论】不同龄期烟蚜被烟蚜茧蜂寄生后,其发育历期和寿命比未被寄生的缩短,产仔量比被未寄生的少,但其F₁代平均寿命比未被寄生后代烟蚜的长且其产仔量未受显著影响。当代2龄若蚜期是控制烟蚜增长的关键时期。这些结果对确定烟蚜茧蜂防治烟蚜适期及认识其机理具有重要参考意义。     

Variation in Age and Size in Fennoscandian Three-Spined Sticklebacks (Gasterosteus aculeatus)

Average age and maximum life span of breeding adult three-spined sticklebacks (Gasterosteus aculeatus) were determined in eight Fennoscandian localities with the aid of skeletochronology. The average age varied from 1.8 to 3.6 years, and maximum life span from three to six years depending on the locality. On average, fish from marine populations were significantly older than those from freshwater populations, but variation within habitat types was large. We also found significant differences in mean body size among different habitat types and populations, but only the population differences remained significant after accounting for variation due to age effects. These results show that generation length and longevity in three-spined sticklebacks can vary significantly from one locality to another, and that population differences in mean body size cannot be explained as a simple consequence of differences in population age structure. We also describe a nanistic population from northern Finland exhibiting long life span and small body size.     

Life history variation in Pisidium (Bivalvia: Pisidiidae)

Intraspecific variation in the maximum shell length of Pisidium is small in comparison with variation in the life span of the clams, from 4 mo to 4 yr. The use of shell length as a measure of size is complicated by large intraspecific variation in the weight-length relationship, a possible reflection of resource availability on the weight of the soft parts. Maximum embryo length is relatively constant (1 mm) in the majority of species but litter size is variable (1 to 40), generally increasing with parent size. The time of egg-laying is determined by the size of the clam, season, and previous episode of reproduction, while the timing of the release of embryos, depending also on embryonic growth rate, is additionally affected by temperature and oxygen conditions. In brief, the maximum adult and embryo lengths are relatively conservative traits while growth rates vary by an order of magnitude.
Reproductive effort, when measured by the ratio of litter weight to parent weight, may increase or decrease with parent length and age. Both semelparous and iteroparous populations are known in several species. We suggest that if maximum adult length can be reached by the first reproductive season (in a favourable environment) the population is semelparous, otherwise (in an unfavourable environment) the population is iteroparous. Gravid clams in semelparous populations continue to grow, and thus assimilation cannot be meaningfully partitioned into reproduction, somatic growth and maintenance.
Along a depth gradient from 8 to 65 m, maximum and mature shell lengths, embryo length and litter size varies significantly in Pisidium conventus subpopulations not distinguishable electrophoretically. Large clams in deep water produce large embryos but small litters, which is contrary to the general trend of increasing litter size with parent length. Low food availability that decreases juvenile growth rate may restrict litter size in this case.     

Does basal metabolic rate contain a useful signal? Mammalian BMR allometry and correlations with a selection of physiological, ecological, and life-history variables

Basal metabolic rate (BMR, mL O2 h(-1)) is a useful measurement only if standard conditions are realised. We present an analysis of the relationship between mammalian body mass (M, g) and BMR that accounts for variation associated with body temperature, digestive state, and phylogeny. In contrast to the established paradigm that BMR proportional to M3/4, data from 619 species, representing 19 mammalian orders and encompassing five orders of magnitude variation in M, show that BMR proportional to M2/3. If variation associated with body temperature and digestive state are removed, the BMRs of eutherians, marsupials, and birds do not differ, and no significant allometric exponent heterogeneity remains between orders. The usefulness of BMR as a general measurement is supported by the observation that after the removal of body mass effects, the residuals of BMR are significantly correlated with the residuals for a variety of physiological and ecological variables, including maximum metabolic rate, field metabolic rate, resting heart rate, life span, litter size, and population density.     

烟草品种、育苗方式和烟蚜来源对烟蚜茧蜂寄生能力的影响

【目的】本研究旨在筛选出适合烟蚜茧蜂Aphidius gifuensis寄生烟蚜Myzus persicae的烟草品种、育苗方式和烟蚜来源,为烟蚜茧蜂人工繁殖和复壮提供科学参考。【方法】采用盆栽法,调查了不同烟草品种(云烟87、K326、翠碧1号和红花大金元)繁殖烟蚜若蚜、不同来源烟蚜(来自烟区、来自非烟区和室内繁殖种群)若蚜和烟草不同育苗方式(土壤育苗和湿润育苗)繁殖烟蚜若蚜时,烟蚜茧蜂成蜂对烟蚜若蚜的寄生率以及成蜂羽化率、寿命、体型大小和雌蜂比。【结果】结果表明,不同烟草品种繁殖烟蚜若蚜对烟蚜茧蜂成蜂寄生率存在显著影响。其中,在红花大金元和翠碧1号繁殖烟蚜上的烟蚜茧蜂成蜂寄生率分别比在K326繁殖烟蚜上的烟蚜茧蜂成蜂寄生率高19.00%和14.00%,但对烟蚜茧蜂的其他指标没有显著影响;不同烟蚜来源对烟蚜茧蜂寄生率也存在显著影响,其中,烟蚜茧蜂成蜂对非烟区烟蚜若蚜和烟区烟蚜若蚜的寄生率比对室内繁殖种群烟蚜若蚜的寄生率分别高20.25%和16.75%,但对烟蚜茧蜂成蜂的羽化率、寿命、体型大小和雌蜂比没有显著影响;烟草不同育苗方式对烟蚜茧蜂成蜂的寄生率无显著影响。【结论】烟蚜茧蜂对烟蚜...     

Patterns of individual growth of gray garden slug <Emphasis Type="Italic">Deroceras reticulatum</Emphasis>

Individual growth of gray garden slug Deroceras reticulatum was studied under laboratory conditions in the period from collection to death. The studied population demonstrated different patterns of growth. Three groups of slugs were recognized: (1) slugs that reached the maximum weight after 4 months of raring, after which their weight rapidly decreased (the life span in culture was 6–7 months); (2) slugs that have not reached the maximum weight until death (the life span was 6–7 months); (3) slugs that reached the maximum weight after 7–8 months, after which their weight oscillated with a trend to decrease (the life span was about 10 months). The obtained data were approximated by the equation of finite growth.     

The population dynamics of some freshwater carideans (Crustacea: Decapoda) in Hong Kong,with special reference to Neocaridina serrata (Atyidae)

During a 15-month investigation of the population dynamics of three caridean shrimp species in the Lam Tsuen River, New Territories, Hong Kong, the numbers of the commonest species, Neocaridina serrata (Stimpson)(Atyidae), were reduced as water temperatures fell. By contrast, Caridina lanceifrons Yu became more numerous during the winter. The relatively scarce Macrobrachium hainanense (Parisi)(Palaemonidae) tended to be more abundant during the summer, and the abundance of this species was directly correlated with that of N. serrata. The population size of these two species was positively correlated with water temperatures prevailing one and two months prior to the collection of samples, but there was no significant relationship between C. lanceifrons abundance and water temperature.All species exhibited similar growth patterns with an inflection at the attainment of sexual maturity, occurring after the (presumed) 14th moult for N. serrata and in the (presumed) 13th and 18th stadium for C. lanceifrons and M. hainanensis respectively. Ovigerous shrimps of all species were only recorded when water temperatures exceeded 20 °C and the % incidence of ovigerous N. serrata was positively correlated with prevailing temperatures. It is suggested that restriction of freshwater caridean breeding periods by low temperatures may be common in the subtropics while perennial breeding is more likely to be typical of tropical regions.The mean carapace length of N. serrata populations was negatively correlated with prevailing temperatures, but more strongly correlated with temperatures recorded one and two months prior to sampling when gametogenesis may have taken place. Smallest mean sizes were recorded in late summer upon the cessation of juvenile recruitment. N. serrata has a maximum longevity of approximately 12 months and reproduction occurs in the 7th month of life or later. The hatchlings are well developed and clutch size is not related to the size of the brooding female. An annual life cycle, as seen in N. serrata, may be typical of many small freshwater carideans.Department of Zoology, The University of Hong Kong     

The population dynamics, reproductive strategy and life history tactics of Musculium lacusfre (Bivalvia: Pisidiidae) in Hong Kong

Hitherto uninvestigated in Hong Kong are the population dynamics, reproductive strategies and life history tactics of the Pisidiidae of which three species are known to occur locally. This study is of Musculium lacustre inhabiting a drainage ditch of the Lam Tsuen River in the New Territories of Hong Kong and extended over 15 months during 1983–84.
In Hong Kong, M. lacustre is a protandric, simultaneous hermaphrodite that matures at a length of 2 mm; the majority of each generation is, however, not mature until a length of between 4–6 mm is attained. Fertilized eggs are brooded in the inner demibranchs until they reach a length of 1.5 mm when they are released as post-foetal larvae. Musculium lacustre is univoltine. Reproduction occurs twice a year but, since M. lacustve is semelparous, the population contains, at any one time, two overstepping generations. Thus, a spring generation is recruited and grows rapidly to generate a second, smaller, autumn generation. This in turn grows rapidly and matures to produce the spring generation of the succeeding year. Adult mortality occurs in late summer and winter. A few of the late-born spring generation may overwinter to contribute to the spring generation of the succeeding year. This is not so with the autumn generation.
Such sexual and life history tactics can be related to the climate and hydrology of Hong Kong and its freshwater habitats. Reproduction takes place in spring and autumn when temperatures are moderate. Mortality is high in summer and winter when the habitat is either, respectively, hot and flushed out by summer rains or cold and dry. As M. larustre is able to overwinter but not aestivate at these latitudes (22° N), it is postulated that this holarctic species is approaching the southern limit of its asiatic range. Musculium larustre is compared with the other bivalves inhabiting fresh and brackish-water habitats in southern China.     

Life-history characteristics and sexual strategy of Mytilopsis sallei (Bivalvia: Dreissenacea), introduced into Hong Kong

First recorded from Hong Kong in 1980, Mytilopsis sallei now dominates the intertidal pier community within the Government Dockyard, Victoria Harbour. Analysis of monthly samples of M. sallei has demonstrated aspects of the reproductive strategy and life-history characteristics correlated with seasonal changes in local water quality.
Mytilopsis sallei is dioecious, has a high fecundity, matures early (at 8–10 mm shell length), grows fast and the majority of the population is probably semelparous. These are characteristic traits of opportunistic r -strategists. Comparable characteristics are typical of other introduced bivalves. Maximum life span of M. sallei in the Dockyard is probably less than 20 months with, however, most of the population dying before that. Heavy recruitment, particularly during spring-summer, suffocates older individuals. The shells of dead animals similarly last for little more than one year, dissolution and crushing effecting this. A mat of byssal threads serves to bind the mass and anchor it to the substratum.
Mytilopsis sallei exhibits two periods of reproductive activity and settlement per year. These are possibly two elements of a single recruitment divided into minor (autumn-winter) and major (spring-summer) components by either high summer temperatures or low salinities. Summer and winter recruits of M. sallei , respectively, mature to produce the summer and winter juveniles of the following year. Over-stepping generations plus survival of a few individuals into their second year thus ensure continued success of M. sallei , and account for its spread and dominance in its introduced range. Such a bimodal pattern appears typical of many Hong Kong intertidal, estuarine and freshwater bivalves.     

Life history variation within a parthenogenetic population of Daphnia parvula (Crustacea: Cladocera)

Summary Evidence for genetically determined life history variability within a population or a species is rare. In this three year experimental examination of a parthenogenetically reproducing population of the planktonic crustacean Daphnia parvula, we found evidence for a succession of clones or groups of clones that exhibited distinctive body size and reproductive differences that were maintained after numerous generations under standardized conditions in the laboratory. The D. parvula population reached maximum density in the fall and maintained relatively high densities through the winter and spring. Isolates from this fall-winter-spring period all had a larger body size at death and higher fecundity when compared with summer isolates under natural food and temperature conditions. These differences could not be accounted for by differences in temperature and food abundance among the seasons. An additional difference in these experiments was a shift in reproductive effort by the summer isolate which produced a higher proportion of its offspring in the first two broods. The shift in life history characteristics and a summer decline of the Daphnia parvula population was correlated with both an increase in inedible and perhaps toxic blue-green algae and an increase in a dipteran predator Chaoborus. Comparison of the survivorship curves for all of the seasonal life history experiments indicated that D. parvula survivorship was not lower during the summer discounting a toxic effect from blue-green algae. Positive population growth on natural food in the laboratory at this time indicated food was not limiting and that predation was the probable cause of the population decline.Laboratory life history experiments under standardized food and temperature conditions were run with D. parvula isolates from the spring and summer plankton. Genetically based differences as determined in these experiments were smaller body size, lower fecundity, smaller brood size, and shorter life span for the summer animals relative to spring animals. Thirty seven percent of the summer animals also reproduced at an earlier age under standardized conditions. The shift in reproductive effort to earlier broods by summer animals rnder natural conditions appeared to be a phenotypic response as the summer isolate did not produce a higher proportion of its offspring in early broods under standardized conditions.When estimates of predatory mortality were added to the life tables of the standardized experiments, the earlier reproduction of some of the summer animals allowed a population increase under a regime of intense predation. Life tables for the spring animals predicted a population decline under these circumstances. Predictable seasonal changes in biotic factors such as predation suggest a mechanism whereby diverse life history patterns with corresponding differences in r may be maintained within a population.     

Effect of stress on the life span of the yeast Saccharomyces cerevisiae

A correlation is known to exist in yeast and other organisms between the cellular resistance to stress and the life span. The aim of this study was to examine whether stress treatment does affect the generative life span of yeast cells. Both heat shock (38 degrees C, 30 min) and osmotic stress (0.3 M NaCl, 1 h) applied cyclically were found to increase the mean and maximum life span of Saccharomyces cerevisiae. Both effects were more pronounced in superoxide dismutase-deficient yeast strains (up to 50% prolongation of mean life span and up to 30% prolongation of maximum life span) than in their wild-type counterparts. These data point to the importance of the antioxidant barrier in the stress-induced prolongation of yeast life span.     

Big mice die young: early life body weight predicts longevity in genetically heterogeneous mice

Small body size has been associated with long life span in four stocks of mutant dwarf mice, and in two varieties of dietary restriction in rodents. In this study, small body size at ages 2-24 months was shown to be a significant predictor of life span in a genetically heterogeneous mouse population derived from four common inbred mouse strains. The association was strongest for weights measured early in adult life, and somewhat weaker, though still statistically significant, at later ages. The effect was seen both in males and females, and was replicated in an independent population of the same genetic background. Body size at ages 2-4 months was correlated with levels of serum leptin in both males and females, and with levels of IGF-I and thyroid hormone in females only. A genome scan showed the presence of polymorphic alleles on chromosomes 2, 6, 7 and 15 with significant effects on body weight at 2-4 months, at 10-12 months, or at both age ranges, showing that weight gain trajectory in this stock is under complex genetic control. Because it provides the earliest known predictor of life span, body weight may be usefully included in screens for induced mutations that alter aging. The evidence that weight in 2-month-old mice is a significant predictor of life span suggests that at least some of the lethal diseases of old age can be timed by factors that influence growth rate in juvenile rodents.     

Life history implications of allocation to growth versus reproduction in dynamic energy budgets

We compare the implications of determinate vs. indeterminate growth of a parthenogenetic iteroparous ectotherm at constant food density in the context of the dynamic energy budget theory, which specifies the tight links between life history traits, such as feeding, aging, growth and reproduction. We do a comparative analysis using, as measure of fitness, the life span reproduction, the population growth rate, and the conversion efficiency of food to biomass. When extrinsic mortality is constant, indeterminate growth cannot maximize fitness if measured by the population growth rate or the conversion efficiency, except when mortality is low, in which case both types of animals are similar. If the fitness measure is life span reproduction, indeterminate growth maximizes fitness even with constant mortality, provided it is not very high. When mortality decreases with size, indeterminate growth maximizes fitness for almost all measures of fitness. Finally, we suggest an evolutionary link between allocation strategies and expected life span. In populations of long living species, each type of animal can establish in the population of the other. In populations of short living species, determinate growers can invade, and displace, a population of indeterminate ones. However, when the mortality risk of organisms with small size is much higher than those of large size, indeterminate growers can be superior.     

The multivoltine life history of Cheumatopsyche brevilineata (Iwata, 1927) (Trichoptera: Hydropsychidae), with a new method to estimate the population size of generations

Cheumatopsyche brevilineata (Iwata, 1927 Iwata, M. (1927), ‘Trichopterous Larvae from Japan’, Zoological Magazine, 39, 209–272. (In Japanese) [Google Scholar]) is a filter-feeding caddisfly without distinct separable generations. We conducted a life history survey of C. brevilineata under a natural thermal regime. This caddis species had a multivoltine life history and their generations partially overlapped each other. From the seasonal change of larval and pupal density, we recognized one overwintering generation and three non-winter generations. We propose a new method to estimate the population size of fourth instar larvae from each generation by using the ‘development zero’ and ‘effective degree-days’ methods. The second non-winter generation, developing under the hottest water temperature regime, had the largest population size and highest observed density. The overwintering generation, which developed under the coolest thermal regime, showed the smallest population size but its observed density was not the smallest.     

Ontogenetic model of ageing and disease formation and mechanisms of natural selection

It is known that increased mortality due to environmental hazards results, in the course of natural selection, in the shortening of maximum life span and acceleration of sexual maturation in a population subjected to an intensified pressure from external environment. As a consequence, the prereproductive period/maximum life span ratio appears to be approximately the same in each species. Mechanisms responsible for this are not clear yet. Since maximum life span is limited by both ageing and formation of certain diseases (in humans, the so-called main noninfectious diseases), the paper discusses four possible models of development of ageing and age-linked disease--ecological, genetic, degenerative (metabolic) and ontogenetic. It was found that it is the ontogenetic model only that can adequately account for the development of moderate shifts in the duration of both sexual maturation and maximum life span. It also provides the rationale for the pleotropic activity of genes during the development of the organism, its ageing and formation of age-connected diseases.     

Local habitat-induced variations in the population dynamics of Patella vulgata L.

The recruitment, growth and maximum size, life span, standing crop and biomass of Patella vulgata L. reveal considerable local differences in a range of habitats on the same shore. While some differences are related to physical conditions (e.g., standing water, tidal level), others arise from local biological interactions and may reverse expectations based on tidal level alone. Wet and bare surfaces apart, juvenile input is regularly highest among mid- and upper-shore mussels, while growth and maximum size are least among barnacles at any tidal level. The extreme permutations of population characteristics range from high-level, dry barnacle areas where limpet recruitment averages 15 % of standing crop, growth rate and maximum size are low and survival for 15–17 years is possible to low-level, bare rock where input averages 66 %, growth and maximum size are high and life span unlikely to exceed 4–5 years. Population densities vary annually but the relative densities of the different habitats have remained fairly steady as long as the biological conditions have remained similar; the latter largely control the recruitment and survival characteristics upon the balance of which the population density appears to depend. Although liable to distortions due to years of abnormal recruitment, the size-frequency structure of their populations is highly diagnostic of many habitats.     

Encephalization and the evolution of longevity in mammals

Allometric principles account for most of the observed variation in maximum life span among mammals. When body-size effects are controlled for, most of the residual variance in mammalian life span can be explained by variations in brain size, metabolic rate and body temperature. It is shown that species with large brains for a given body size and metabolic rate, such as anthropoid primates, also have long maximum life spans. Conversely, mammals with relatively high metabolic rates and low levels of encephalization, as in most insectivores and rodents, tend to have short life spans. The hypothesis is put forward that encephalization and metabolic rate, which may govern other life history traits, such as growth and reproduction, are the primary determinants directing the evolution of mammalian longevity.