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1.
Bi-directional sex change in a coral-dwelling goby   总被引:1,自引:0,他引:1  
Bi-directional sex change has recently been reported among obligate coral-dwelling gobies of the genus Gobiodon. However, neither the functional role of this pattern of sex change nor the frequency of sex change in either direction in natural populations is known. We investigated the social structure and pattern of sex change of Gobiodon histrio at Lizard Island on the Great Barrier Reef. The social structure of G. histrio within coral colonies usually consisted of a single juvenile or a heterosexual adult pair. The size of adult social groups was not constrained by coral colony size. In contrast to expectations for pair-forming species, G.␣histrio was primarily a protogynous hermaphrodite. All immature G. histrio were females and sex change from female to male occurred readily when two mature females were placed in a coral colony. In addition, male G. histrio were able to change back to females when two mature males were placed in a coral. Sex change from female to male, however, occurred with over twice the frequency of sex change from male to female. Where two males were placed in a coral colony, heterosexual pairs were most frequently re-established by immigration of females from outside the treatment population. This pattern might be predicted if sex change from male to female is more expensive than sex change from female to male for G. histrio. Where sex change is expensive, movement may be favoured over sex change, particularly where coral densities are high and movement among corals incurs little mortality risk. Received: 10 November 1997 / Accepted after revision: 16 May 1998  相似文献   

2.
Dimorphism and possible sex change in copepods of the family Calanidae   总被引:2,自引:0,他引:2  
Adult females of 14 of 25 species of the family Calanidae were found to be dimorphic with respect to the number of aesthetases on the first antenna. The trithek morph, in which most antennal segments bear a complement of one aesthetasc and two setae, appears to be the typical female phenotype. The quadrithek morph is less common and, as in males, odd-numbered segments 2b, 3, 5, 7 and 9 carry quadritheks, i.e., two aesthetascs as well as two setae. Segment 21 in the quadrithek female bears an aesthetasc that is absent in the trithek female. Male antennal segments are distinguished from those of trithek and quadrithek females by pronounced morphological differences in aesthetasc shape and size as well as fusion of one or more pairs of antennal segments. The quadrithek morph usually comprised only a small proportion (<10%) of a local population. Quadrithek morphs were found in tropical and subtropical genera (Cosmocalanus and Nannocalanus), broadly ranging genera (Calanoides), as well as in cool-water lineages (Calanus s.s., Calanus s.l. cristatus, C. s.l. plumchrus, C. s.l. propinquus and C. s.l. tonsus). Maximum frequencies of quadrithek morphs (10 to 12%) in Calanus pacificus californicus occurred during the upwelling season from late winter into spring. No indication of sexual or antennal dimorphism was found in CV C. pacificus californicus sexed by examination of gonad and gonaduct. The quadrithek dimorph appears to be the product of sex change by the larger-sized late-juvenile potential male. The evolutionary and ecological significance of this presumptive hypothesis is that the larger-sized potential male reaching adulthood one or more weeks before maturation of genotypic females may increase its reproductive output by sex change in the course of the final molt to mature as a functional female. Given the sex-change hypothesis, morphogenesis of secondary sexual structures would appear to be controlled by androgenic-like secretions from the genital tract, as has been shown in malacostrocans.  相似文献   

3.
Marine reserves have become widely used in biodiversity conservation and are increasingly proposed as fisheries management tools. Previous modeling studies have found that reserves may increase or decrease yields, depending on local environmental conditions and on the specific life-history traits of the fishery species. Sex-changing (female-to-male) fish are targets of some of the most important commercial and recreational fisheries in the world. The potential for disproportionate removal of the larger, older sex of such species requires new theory to facilitate our understanding of how reserves will affect the yields of surrounding fisheries, relative to fishes with separate sexes. We investigated this question by modeling the effects of marine reserves on a non-sex-changing and a sex-changing population. We used demographic parameter estimates for the common coral trout as a baseline, and we conducted extensive sensitivity analyses to determine how sustainable yields of sex-changing species are likely to be affected by reserves across a broad range of life-history parameters. Our findings indicate that fisheries for sex-changing species are unlikely to receive the same yield-enhancing benefit that non-sex-changing fisheries enjoy from marine reserves, and that often reserves tend to reduce sustainable yields for a given overall population size. Specifically, the increased egg production and high fertilization success within reserves is more than offset by the reduced egg production and fertilization success in the fished areas, relative to a system in which fishing mortality is distributed more evenly over the entire system. A key reason for this appears to be that fertilization success is reduced, on average, when males are unevenly distributed among subpopulations, as is the case when reserves are present. These findings suggests that, for sex-changing populations, reserves are more suited to rebuilding overfished populations and sustaining fishery viability, rather than enhancing fishery yields. These results are robust over a range of sex-change regimes, stock-recruitment relationships, adult mortality rates, individual growth strategies, and fertilization-success functions. Our findings highlight the importance of considering the different contributions of males and females to population growth and fishery yields when evaluating the efficacy of marine reserves for enhancement of fished species.  相似文献   

4.
One of the main goals of sex allocation theory is understanding sex ratio evolution. However, theoretical studies predicting sex ratios in species with unusual sexual systems, such as protandric simultaneous (PS) hermaphroditism, are rare. In PS hermaphrodites, juveniles first develop into functional males that mature into simultaneous hermaphrodites later in life. Here, we report on the sex ratio (males/males + hermaphrodites) in the PS hermaphroditic shrimp Exhippolysmata oplophoroides. A 2-year study demonstrated that hermaphrodites dominated the population in two different bays. This skewed sex ratio may be explained by limited encounter rates among conspecifics. In agreement with this idea, the density of shrimps was extremely low (≤1 shrimp km−2) at the two study sites. Size at sex phase change and sex ratios remained relatively stable through time at the two bays. The stability of these parameters might be explained by the rather steady population structure of this species during the study period. A review of sex ratios in PS hermaphroditic shrimps (Lysmata and Exhippolysmata) revealed considerable variation; some species have male- and others hermaphrodite-skewed sex ratios. The conditions explaining inter- and intra-specific sex ratio variation in protandric simultaneous hermaphroditic species remain to be addressed.  相似文献   

5.
A study of otolith aging and growth-rate variation in the flyingfish Hirundichthys affinis (Günther) was conducted in the eastern Caribbean (10–16°N; 58–62°W) in 1987–1989. Daily otolith-increment formation was validated in laboratory-reared larvae, confirming the usefulness of otolith-increment counts for age determination of H. affinis juveniles (<150 mm fork length, FL). A mark-recapture programme to validate increment formation in wild adults was unsuccessful due to tetracycline-linked mortality and insufficient tetracycline uptake in slow-growing adult otoliths. A von Bertalanffy growth curve fitted to juvenile size-at-age data gave preliminary growth-curve parameters of t 0=2.85 d and k=0.00854 on a daily basis, with an asymptotic length, L, of 245 mm FL, for eastern Caribbean flyingfish. Juvenile growth rate in H. affinis is sensitive to spatial and temporal variation in temperature. Growth rates were higher where sea-surface temperatures were higher, and were higher for juveniles hatched in warmer months (April–July) than in colder months (November–March). Growth rates were also higher near islands than at more oceanic locations. Variation in juvenile growth rates may influence the spatial and temporal variation in spawning frequency observed in H. affinis.  相似文献   

6.
A frequent assumption in environmental risk assessment is that the underlying distribution of an analyte concentration is lognormal. However, the distribution of a random variable whose log has a t-distribution has infinite mean. Because of the proximity of the standard normal and t-distribution, this suggests that a distribution such as the gamma or truncated normal, with smaller right tail probabilities, might make a better statistical model for mean estimation than the lognormal. In order to assess the effect of departures from lognormality on lognormal-based statistics, we simulated complete lognormal, truncated normal, and gamma data for various sample sizes and coefficients of variation. In these cases, departures from lognormality were not easily detected with the Shapiro-Wilk test. Various lognormal-based estimates and tests were compared with alternate methods based on the ordinary sample mean and standard error. The examples were also considered in the presence of random left censoring with the mean and standard error of the product limit estimate replacing the ordinary sample mean and standard error. The results suggest that in the estimation of or tests about a mean, if the assumption of lognormality is at all suspect, then lognormal-based approaches may not be as good as the alternative methods.  相似文献   

7.
In this paper we describe and test a sub-model that integrates the cycling of carbon (C), nitrogen (N) and phosphorus (P) in the Soil Water Assessment Tool (SWAT) watershed model. The core of the sub-model is a multi-layer, one-pool soil organic carbon (SC) algorithm, in which the decomposition rate of SC and input rate to SC (through decomposition and humification of residues) depend on the current size of SC. The organic N and P fluxes are coupled to that of C and depend on the available mineral N and P, and the C:N and N:P ratios of the decomposing pools. Tillage explicitly affects the soil organic matter turnover rate through tool-specific coefficients. Unlike most models, the turnover of soil organic matter does not follow first order kinetics. Each soil layer has a specific maximum capacity to accumulate C or C saturation (Sx) that depends on texture and controls the turnover rate. It is shown in an analytical solution that Sx is a parameter with major influence in the model C dynamics. Testing with a 65-yr data set from the dryland wheat growing region in Oregon shows that the model adequately simulates the SC dynamics in the topsoil (top 0.3 m) for three different treatments. Three key model parameters, the optimal decomposition and humification rates and a factor controlling the effect of soil moisture and temperature on the decomposition rate, showed low uncertainty as determined by generalized likelihood uncertainty estimation. Nonetheless, the parameter set that provided accurate simulations in the topsoil tended to overestimate SC in the subsoil, suggesting that a mechanism that expresses at depth might not be represented in the current sub-model structure. The explicit integration of C, N, and P fluxes allows for a more cohesive simulation of nutrient cycling in the SWAT model. The sub-model has to be tested in forestland and rangeland in addition to agricultural land, and in diverse soils with extreme properties such high or low pH, an organic horizon, or volcanic soils.  相似文献   

8.
The aim of this study was to estimate the growth rate of saithe, Pollachius virens L., in wild populations collected from around the Beryl Alpha oil platform in October 1988 and from Loch Ewe on the west coast of Scotland in August 1989, by comparing the concentrations of various growth-rate indicators in the white muscle with those of laboratory-maintained individuals of known growth rates. There were significant correlations between the individual growth rates of laboratory-maintained saithe and concentrations of white muscle RNA expressed as g RNA mg-1 protein, mg RNA mg-1 DNA and as mg RNA g-1 muscle. Growth rate was also correlated with the activities of the enzymes citrate synthase, cytochrome oxidase and lactate dehydrogenase. RNA concentrations decreased with increasing body size, and weight-corrected estimates of RNA concentrations for a standard-sized individual were determined from the scaling relationships. RNA concentrations expressed in three different ways gave similar estimates of the growth rate for two samples of wild saithe, one from around an oil platform and the other from the west coast of Scotland. RNA concentrations were correlated with aerobic enzyme levels in oil-platform fish, although the growth rate estimates of the same wild fish were lower when expressed as a function of aerobic enzyme levels than when expressed as a function of lactate dehydrogenase concentration. It is concluded that the capacity for protein synthesis of white muscle expressed as RNA concentrations in relation to wet or dry weight may be used as an estimate of instantaneous growth rate and that additional confidence in such estimates may be gained from measurement of the levels of aerobic enzymes.  相似文献   

9.
P. Munday  B. Molony 《Marine Biology》2002,141(6):1011-1017
To investigate the relative cost of protogynous versus protandrous sex change we induced sex change in each direction in Gobiodon histrio (Gobiidae) and then compared growth, body condition and biochemical condition between sex-changed and non-sex-changed fish in treatment and control groups. Sex change in each direction was induced by establishing pairs of adult males and pairs of adult females on isolated coral colonies. Heterosexual pairs were used as controls. For both males and females, growth and body condition did not vary between fish that changed sex and those that did not. The relatively low cost of sex change, compared to the likely costs of searching for a mate of the correct sex, appears to explain the evolution of bi-directional sex change in coral-dwelling gobies. Lipid concentrations in the liver of males and females that changed sex were reduced by similar amounts (34% and 41%, respectively) compared to male and female controls that did not change sex. Therefore, changes in biochemical condition were approximately equal for fish that sex change in each direction and cannot explain the unequal frequency of sex change in each direction in natural populations of G. histrio.  相似文献   

10.
The nitrification process in many river water quality models has been approximated by a simple first order dependency on the water column ammonia concentration, while the benthic contribution has routinely been neglected. In this study a mathematical framework was developed for sediment bed nitrification based on mass transfer theory and Monod bacterial growth kinetics. The model describes ammonia transport across the boundary layer and consumption within the biofilm to quantify the overall nitrification flux. Model results suggest that nitrification is usually controlled by the boundary layer thickness, and we estimated a nitrification velocity range between 0.14 and 0.97 m d−1, assuming typical boundary thicknesses of 0.1–1.0 mm. These ranges compared favorably with reported literature values, including our own measurements. The model was applied to several river systems of different depths where nitrification rates and river depths were available. Assuming that nitrification is exclusively a benthic process, the average velocity of all the rivers evaluated was 0.85 m d−1 (r2 = 0.72).  相似文献   

11.
A spatially explicit individual-based simulation model has been developed to represent aphid population dynamics in agricultural landscapes. The application of the model to Rhopalosiphum padi (L.) population dynamics is detailed, including an outline of the construction of the model, its parameterisation and validation. Over time, the aphids interact with the landscape and with one another. The landscape is modified by varying a simple pesticide regime, and the multi-scale spatial and temporal implications for a population of aphids is analysed. The results show that a spatial modelling approach that considers the effects on the individual of landscape properties and factors such as wind speed and wind direction provides novel insight into aphid population dynamics both spatially and temporally. This forms the basis for the development of further simulation models that can be used to analyse how changes in landscape structure impact upon important species distributions and population dynamics.  相似文献   

12.
Sex determination and sex differentiation in three local Istrian (Yugoslavia) populations of the polychaeteTyposyllis prolifera were studied both in the field and the laboratory. Significant differences in sex habits were revealed among the populations, the biological significance of which is unknown. (1) Sex ratios (% ) in natural populations from the Adriatic Sea amounted to 50% (Rovinj), 62% (Pore) and 77% (Pula). In the Pula-(but not in the Rovinj-)population, a correlation was found between population density on individualHalopteris scoparia thalli (the favorite habitat ofT. prolifera) and the respective sex ratio: The mean male protion was only a little more than 50% in densely populated thalli, and increased to more than 80% in sparsely populated thalli. Laboratory studies provided the information necessary to explain these field findings. (2) Laboratoryraised progenies showed an overall 1:1 primary (first sexual phase) sex ratio, independent of the local origin of the material and of whether worms were raised singly or under conditions of social contact. Nevertheless, the studied populations may differ with respect to the genetic mechanisms of sex determination: In the Pore- and Pulapopulation individual progenies often departed significantly from the 1:1 sex ratio, whereas individual progenies in the Rovinj- population never did so. (3) The populations proved to be partially protogynous. Sex differentiation in that half of the individuals which differentiated into males (primary males) was absolutely stable during sequential sexual phases. Worms which differentiated into females, however, often changed sex at an earlier or later stage of their life cycle (secondary males). Sex change was irreversible. As to the degree of lability of female differentiation under conditions of isolation, the findings suggest a genetic divergence among both populations and individuals of the same population. Female differentiation in the Rovinj-population was virtually stable, but Pula-females underwent rapid and complete masculinization. Pore-females were between these extremes. (4) In addition to genetic factors, exogenous conditions affected the incidence and time of sex change (Pula-population): Under conditions of social contact, sex change was delayed or suppressed as compared with isolated individuals. The degree of delay or inhibition was independent of the sex of the social partners, yet increased (to the point of saturation) with population density.  相似文献   

13.
Sex change in marine teleost fishes is commonly regulated by social factors. In species that exhibit protogynous sex change, such as the bluebanded goby Lythrypnus dalli, the most dominant female typically initiates sex change when a male is removed from the social group. Females can use visual, chemical or tactile cues to assess the presence or absence of a male. The primary goal of our study was to determine whether the olfactory and visual presence of a male versus its behavioural interactions with females were important for mediating sex change. We exposed females to three different treatments: absence of a male, presence of a male that could physically interact with her and presence of a male behind a barrier that allowed visual and olfactory interactions but prohibited physical interactions. Sex change occurred in the absence of a male but not in the presence of a male that could physically interact with the female. The presence of a male behind the barrier did not prevent sex change but affected the timing of sex change. Season appeared to affect the latency to initiate male typical courtship, with a delay at the end of the reproductive season only when the male was present behind the barrier. We discuss the seasonal results in terms of L. dalli life history and the potential benefits and costs of changing sex late in the season in the presence or absence of aggressive reinforcement by the male. Our results identify direct behavioural interactions as an important proximate mechanism in the social regulation of sex change in L. dalli.  相似文献   

14.
Prior residency advantages have been explained by an asymmetry between the ‘owner’ and the ‘intruder’ in fighting ability (resource-holding potential) or motivation (value asymmetry (VA)). Here, we tested for the extent of prior residence effects in individually tagged Atlantic salmon juveniles being released in two bouts (4 days apart) during spring along a natural stream, and recaptured 3 months later. A prior residency advantage was detected both in terms of body growth, energy density and male gonad size. As we controlled for effects of initial body size, which correlates with dominance, these findings are in accordance with the VA hypothesis. The growth advantage of first arrivals also increased with local shelter abundance in the stream, which can be expected if a higher resource value of the habitat results in a higher defence motivation. We also found a prior residence effect on spatial distribution, with the second arrivals within each release site being recaptured further downstream. No effect on apparent survival rates was found. The observed reduced growth and energy density may have fitness consequences for the second arrivals, both in terms of lower winter survival rates and later age at maturity. For mature male parr, both decreased body and gonad growth may give an additional disadvantage through reduced fertilization rates during breeding. These costs may help to explain the tendency for stationary behaviour of stream salmonids, as the potential benefits of moving into less crowded areas would be reduced by the risk of becoming an intruder. Prior residence effects may therefore have influenced the evolution of movement behaviour in these organisms.  相似文献   

15.
The scientific community, forest managers, environmental organizations, carbon-offset trading systems and policy-makers require tools to account for forest carbon stocks and carbon stock changes. In this paper we describe updates to the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) implemented over the past years. This model of carbon-dynamics implements a Tier 3 approach of the Intergovernmental Panel on Climate Change (IPCC) Good Practice Guidance for reporting on carbon stocks and carbon stock changes resulting from Land Use, Land-use Change and Forestry (LULUCF). The CBM-CFS3 is a generic modelling framework that can be applied at the stand, landscape and national levels. The model provides a spatially referenced, hierarchical system for integrating datasets originating from different forest inventory and monitoring programs and includes a structure that allows for tracking of land areas by different land-use and land-use change classes. Ecosystem pools in CBM-CFS3 can be easily mapped to IPCC-defined pools and validated against field measurements. The model uses sophisticated algorithms for converting volume to biomass and explicitly simulates individual annual disturbance events (natural and anthropogenic). Several important scientific updates have been made to improve the representation of ecosystem structure and processes from previous versions of CBM-CFS. These include: (1) an expanded representation of dead organic matter and soil carbon, particularly standing dead trees, and a new algorithm for initializing these pools prior to simulation, (2) a change in the input data requirement for simulating growth from biomass to readily available merchantable volume curves, and new algorithms for converting volume to biomass, (3) improved prediction of belowground biomass, and (4) improved parameters for soil organic matter decay, fire, insect disturbances, and forest management. In addition, an operational-scale version of CBM-CFS3 is freely available and includes tools to import data in standard formats, including the output of several timber supply models that are commonly used in Canada. Although developed for Canadian forests, the flexible nature of the model has enabled it to be adapted for use in several other countries.  相似文献   

16.
17.
《Ecological modelling》2007,201(2):97-117
The potential for marine plankton ecosystems to influence climate by the production of dimethylsulphide (DMS) has been an important topic of recent research into climate change. Several General Circulation Models, used to predict climate change, have or are being modified to include interactions of ecosystems with climate. Climate change necessitates that parameters within ecosystem models must change during long-term simulations, especially mortality parameters that increase as organisms are pushed toward the boundaries of their thermal tolerance. Changing mortality parameters can have profound influences on ecosystem model dynamics. There is therefore a pressing need to understand the influence of varying mortality parameters on the long-term behaviour of ecosystem models. This work examines the sensitivity of a model of DMS production by marine ecosystems to variations in three linear mortality coefficients. Significant differences in behaviour are observed, and we note the importance of these results in formulating ecosystem models for application in simulations of climate change.  相似文献   

18.
Offspring sex ratios in mammals vary in potentially adaptive yet unpredictable ways. An integrative approach that simultaneously examines proximate and ultimate explanations of mammalian sex ratios would greatly advance the field. We examined the importance of maternal glucose and stress hormones for offspring sex (male or female) as mechanisms associated with the Trivers–Willard and the local resource competition hypotheses of sex allocation. We tested this framework in a marsupial mammal, the tammar wallaby (Macropus eugenii). Mothers that were better able to maintain body condition over the driest part of the year, a presumptive proxy for local resource availability, were more likely to produce daughters (the philopatric sex), consistent with local resource competition. Maternal glucose was correlated with offspring sex, but in the opposite direction than we predicted—higher maternal glucose was associated with female pouch young. These patterns, however, were not consistent across the 2 years of our study. Maternal stress hormone metabolites measured from fecal samples did not predict glucose or offspring sex. A causative glucose mechanism may underlie an adaptive strategy for mothers with high local resources (high glucose) to produce philopatric daughters that will benefit from inheriting resource access. Examining species-specific relationships between glucose and offspring sex across mammals could provide crucial insight into the disparate ecological and selective pressures faced by mammals with respect to offspring sex ratio.  相似文献   

19.
This paper proposes an analytical toolkit to measure the sustainability of industrialization across countries. Drawing from a methodology developed to analyze economic development as a process of modernization, it ranks countries on the basis of the emissions they produce and their stage of development. The proposed index penalizes environmental pressures taking into account the modernization level of a country. The paper also proposes an assessment of the environmental performance of countries at the same level of modernization. It introduces the notion of policy space as the difference between the best and worst environmental performer at a given level of modernization. An important finding of the paper is that the magnitude of the policy space is not homogenous across different levels of income and environmental targets.  相似文献   

20.
C.A. Ng  K.A. Gray 《Ecological modelling》2009,220(9-10):1266-1273
We have developed a dynamic model to track the evolution of contaminant concentration in an aquatic organism as a function of season and ontogeny throughout its life cycle. We have focused our analysis on the round goby (Apollonia melanostoma), a globally distributed invasive forage fish. By integrating bioenergetics with a bioaccumulation model, we illustrate how life history characteristics interact to influence contaminant accumulation. We use uncertainty and sensitivity analyses to assess how the model output is affected by uncertainty and variability in model parameters. We then demonstrate the influence of important physiological characteristics on contaminant accumulation with two scenarios. First, we probe the influence of sexual dimorphism by comparing gender-specific accumulation of a standard polychlorinated biphenyl congener, PCB153, in male and female round gobies. We hypothesize that lipid loss in female gobies during spawning season leads to a decrease in the PCB body burden compared to male gobies. Second, we compare PCB accumulation in the round goby and in the mottled sculpin (Cottus bairdi), the native forage fish that the round goby displaced in southern Lake Michigan, to determine whether the invasive species has an intrinsically different bioaccumulation potential than the native one. Our non-intuitive findings from these simulations illustrate how the interaction of growth rate with other life history characteristics lead to unexpected bioaccumulation patterns. The model we present is a flexible tool that integrates complex and dynamic interactions among environmental parameters, thus providing a means to better assess the potential for chemical accumulation in human and wildlife populations, and aiding the development of ecological forecasts.  相似文献   

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