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1.
The freshwater snails belonging to the genus Melanoides Olivier, 1804 are widespread across tropical regions of the world and endemic species have evolved in the African Lakes Malawi, Mweru and Tanganyika. The endemic Melanoides species of Lake Malawi have been investigated several times during the last century, due to their large conchological variation, but no unambiguous answer regarding the number of species has been given. The phylogenetic relationship between morphs or genetic clones of Melanoides in Lake Malawi was inferred by phylogenetic analyses of DNA sequence data from the mitochondrial genes 16S and COI. Additional sequences from GenBank were included to investigate the relationship to other morphs from different parts of the world. For the first time, a putative secondary structure was developed for a partial region of 16S in this genus to identify the variability of the secondary structure in stems and loops. The molecular analyses indicated that several genetic clones exist in Lake Malawi and that M. tuberculata is a paraphyletic taxon. It is not clear from the results whether invasions or dispersals account for the complex situation in Lake Malawi. The basal position of M. admirabilis, endemic to Lake Tanganyika, in the inferred phylogeny indicates that Africa might be the origin of the genus. The results further indicate that three major clades of Melanoides, consisting of several genetic clones, are present in Lake Malawi; one clade consisting of invasive M. tuberculata, another of native M. tuberculata and a third consisting of the M. polymorpha- complex. It appears as if the unique development of morphs within the Melanoides genus in Lake Malawi has evolved primarily by divergence of genetic clones instead of species differentiation.  相似文献   

2.
为了明确温度对红色型和绿色型豌豆蚜种群动态变化的影响,在12~32℃ 6个温度条件下研究了2种色型豌豆蚜的生长发育、繁殖和生命表。结果显示: 2种色型豌豆蚜在32℃时,不能发育至成虫。2种色型豌豆蚜的净增殖率在12~20℃时均随着温度的增高而升高,在16和20℃,红色型豌豆蚜的净增殖率显著高于绿色型(P<0.05)。在24℃时,红色型豌豆蚜的净增殖率显著低于16和20℃时同色型(P<0.05),而绿色型豌豆蚜显著高于12~20℃时同色型,红色型豌豆蚜的净增殖率显著低于绿色型(P<0.05)。到28℃时,2种色型豌豆蚜的净增殖率均显著低于12~20℃时同色型。在12~24℃条件下,2种色型豌豆蚜的内禀增长率均随着温度的上升而增加,红色型豌豆蚜的内禀增长率与绿色型相比无显著差异(P>0.05)。在28℃,红色型豌豆蚜的内禀增长率显著低于绿色型豌豆蚜(P<0.05)。表明红色型豌豆蚜在较低温度条件下适应性较强,而绿色型豌豆蚜更适合较高温度。  相似文献   

3.
以不同亚致死剂量的吡虫啉分别处理2种色型豌豆蚜,采用实验种群生命表的方法,测定了不同亚致死剂量的吡虫啉处理2种色型豌豆蚜后其F0及F1代生长发育和种群参数的变化。结果表明：经处理的2种色型成蚜后,其平均产蚜量均显著低于同色组对照（P<0.05）,平均寿命表现为LC20处理后均显著短于同色组对照（P<0.05）,而LC10和LC5处理后平均寿命与对照无显著差异,LC20处理后红、绿色型成蚜的平均产蚜量（16.82和 21.44头）和平均寿命（2.84 d,3.60 d）均达到最小值;LC20处理2种色型成蚜后,F1代若虫期与同色组对照差异不显著,而成虫寿命显著短于同色组对照（P<0.05）,若蚜存活率均高于LC10处理,LC5处理后F1代红、绿色型豌豆蚜平均繁殖力均达到最大值81.95头和72.27头;不同亚致死剂量处理后F1代2种色型成虫产蚜高峰期也存在差异,绿色型均集中在3～7 d,而红色型产蚜高峰期均晚于绿色型;除LC20处理后F1代绿色型豌豆蚜净增殖率（R0）（44.22）,平均世代周期（T）（11.29）与同色组对照差异显著外,2种色型豌豆蚜的其余参数在LC20,LC10和LC5处理下均与同色组对照差异不显著。表明吡虫啉不同亚致死剂量处理2种色型成蚜后,对其F0代寿命和繁殖力均起到抑制作用,且红色型较绿色型敏感,但对F1代影响表现为高浓度较低浓度显著。  相似文献   

4.
The habitats and patterns of vertical migration of the shell banding morphs of the snail Sitala jenynsi (Pfeiffer) were studied in Dar es Salaam and Wazo regions of central coastal Tanzania Both dimorphic and trimorphic populations were arboreal throughout the year. The snails occurred randomly within mid-heights 180 to 360 cm. without apparent morph differences in micro-distribution. The pattern of circadial vertical distribution consisted of upward migrations during mornings and downward shifts during late evenings. These oscillations regressed negatively on relative humidity (RH), a unit advance in RH representing an eight-fold descent of snails on daytime height. Variations in RH accounted for much of the total variance in the mean vertical distance. During high RH, however, temperature and mating behaviour probably exerted major influences on snail micro-distribution. The effects of arboreality on snail survival and initiation of differentiating subpopulations are proposed  相似文献   

5.
The aim of the study was to evaluate semen quality in the two most popular colour morphs of the Arctic fox Alopex lagopus L., blue and white, based on ejaculate parameters, acrosin activity and analysis of sperm morphology. The research material consisted of ejaculates collected once by manual stimulation from 20 one‐year‐old male Arctic foxes (10 individuals of the blue morph and 10 of the white morph). Ejaculates were evaluated in terms of volume, sperm concentration, total number of spermatozoa and the percentage of spermatozoa with major and minor defects. The study revealed that male blue Arctic foxes produce ejaculates with much higher concentration (148.75 × 106/ml) and total number of spermatozoa (98.16 × 106) compared to white Arctic foxes (42.88 × 106/ml and 35.2 × 106 respectively). The level of acrosin activity from white foxes seemed to be higher compared to blue foxes but the difference was not statistically confirmed. Semen from Arctic foxes is characterized by high inter‐individual variability in sperm morphology. The frequency of morphological changes in sperm from Arctic foxes does not significantly depend on ejaculate volume, sperm concentration or the total number of spermatozoa in the ejaculate, but is associated with acrosin activity.  相似文献   

6.
The mechanisms for the morphological delimitation of species in Carollia remain poorly understood. This is the first study to assess variation in size and shape from strictly geometric terms. Both factors are assessed by statistical perspectives of distribution, overlap and relative distances. Despite its overlap, the size of the skull seems to be the most influential character for the discrimination of species, with shape playing a much smaller role. The smallest species seems to be the most distinct in shape, not only in terms of distance among centroids in morphometric space, but also in the overall trend and direction of variation. Contrary to previous studies, sexual dimorphism is not given by size but by distinct shapes of the skull. Characters such as the shape of the maxilla, previously described qualitatively as discrete with sharp boundaries, appear to be truly continuous with fuzzy borders among species. Because morphometric space is a gamut of continuous variation and overlap, the taxonomic error rate for size characters seems to be substantial for the medium-sized species (Carollia brevicauda Schinz, 1821), with approximately 30–40% of individuals erroneously assigned to a different species after a jackknifed discriminant function. This taxonomic error is higher for shape characters. Morphological, systematic and ecological consequences of the observed patterns of shape and size variation are commented within the context of previously proposed arguments and hypotheses.  相似文献   

7.
通过研究不同紫外(UV-B)辐射时间对2种色型豌豆蚜(Acyrthosiphon piusm)后代生物学特性的影响,以期明确其对紫外胁迫的适生性。将2种不同体色的豌豆蚜成蚜经过40 W紫外辐射1,2,4,6,8,10 h后,单头饲养在甘农3号(G3)和甘农5号(G5)紫花苜蓿(Medicago sativa)上,最终获得各处理F2代豌豆蚜的发育历期、体重差及相对日均体重增长率等生物学参数。结果表明:短时间辐射下(1,2 h),在G3上红色型豌豆蚜F2代的生长发育显著加快,但相对日均体质量增长率无显著变化,绿色型则均无显著变化,在G5上2种体色型豌豆蚜F2代均无显著变化;长时间辐射处理下(10 h),2种色型豌豆蚜的生长发育均显著延缓,在同一苜蓿品种上,绿色型豌豆蚜延缓比例均大于红色型;紫外辐射对2种色型豌豆蚜F2代的生长发育延缓比例在G5上均大于G3上。紫外辐射对2种色型豌豆蚜生长发育的影响是可遗传的,在G3上,短时间紫外辐射能够促进红色型豌豆蚜的生长发育;在G3和G5上,长时间紫外辐射均能抑制2种体色型豌豆蚜的生长发育,且绿色型比红色型敏感,表明紫外胁迫对豌豆蚜的影响与苜蓿品种存在一定的相关性。  相似文献   

8.
This study was intended to determine the number and regional distribution of photoreceptor cells and different colored oil droplets in the retina of the Mallard Duck (Anas platyrhynchos var. domesticus). To estimate the number and density of photoreceptor cells, adult ducks were killed and both eyes were enucleated under deep anesthesia to prepare Nissl‐stained retinal whole‐mount samples. Different colored oil droplets were counted from color microphotographs of the freshly prepared retina. The mean number of retinal photoreceptors was approximately 6 308 828 ± 521 927, with a peak density of 33 573/mm2 in the central retina. The density was similar in the nasal, temporal, ventral and dorsal areas of the retina. Five types of oil droplets were identified on the basis of color: red, orange, greenish‐yellow, yellow and clear. The mean density of oil droplets was highest in the central retina (17 639/mm2) and gradually declined towards the nasal, temporal, ventral and dorsal areas. The size of oil droplets gradually increased with retinal eccentricity and varied even within an area. The greenish‐yellow oil droplets were most abundant across the retina. Taken together, these results demonstrate the differential retinal distribution of photoreceptor cells and oil droplets in duck retina. We conclude that the area of high photoreceptor cell density, which is matched by high neuron densities of the ganglion cell layer, corresponds to the site of acute vision in duck retina.  相似文献   

9.
Group living provides various advantages to individuals in regards to protection avoidance, intergroup competition, productive success and social information. Stable one‐male units (OMUs) consist of relationships between the adult females and the resident male as well as the relationships among adult females. Based on continuous observation of a reproductive group of golden snub‐nosed monkeys (Rhinopithecus roxellana) in the Qinling Mountains, we analyzed the relationships among adult individual dyads within 4 OMUs. The results indicated that in golden snub‐nosed monkey societies, females not only had no strong tendency to build a relationship with the resident male in the OMU but also had no strong tendency to build relationships with other females in the OMU. In comparison with hamadryas (Papio hamadryas) and gelada baboons (Theropithecus gelada), the relationships within golden snub‐nosed monkeys OMUs showed neither the star‐shaped pattern observed in hamadryas baboons nor the net‐shaped pattern observed in gelada baboons. We concluded that the relationships within golden snub‐nosed monkey OMUs indicated a third pattern in nonhuman primate societies. Future research is required to determine the potential mechanisms for such a pattern.  相似文献   

10.
The yellow clam Mesodesma mactroides (Mesodesmatidae) is a sandy beach bivalve that is distributed from Rio de Janeiro, Brazil, to the south of Buenos Aires province, Argentina. The yellow clam population has been declining in recent decades. To increase our understanding of this species, we evaluated the immunological status of yellow clams collected during different seasons from various areas in the state of Rio Grande do Sul, Brazil. We characterized the hemocytes, determined the differential hemocyte counts (DHCs), calculated the apoptotic index, and evaluated the incidence of parasites in yellow clams through histological analysis. We identified two types of hemocyte (hyaline and granular) that showed significant variation in DHCs among sampling areas during the summer and winter. The apoptotic index only exhibited significant variation during the summer. Histopathological analysis results did not significantly differ among sampling areas. This work demonstrated that environmental variation (e.g., temperature and salinity) associated with anthropogenic actions may be affecting the immune system of yellow clams. However, more studies are needed to determine the full influence of these factors on the yellow clam’s immune system and thus contribute to future management and aquaculture of the species.

Received May 10, 2015; accepted October 28, 2015.  相似文献   


11.
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12.
The yellow clam Mesodesma mactroides is a valuable shellfish occurring from the southeastern coast of Brazil to the northern coast of Argentina. Populations of yellow clams are disappearing from their entire range, and the cause is still unknown. The objective of this paper was to search for World Organisation for Animal Health (OIE)–listed pathogens and their relatives in the genera Marteilia, Bonamia, and Perkinsus as well as Mikrocytos mackini and the virus OsHV-1 μ var the yellow clam population in southern Brazil using molecular techniques and classic histology protocols. A total of 180 clams were manually collected in the intertidal region at six sampling points covering the entire coast of Rio Grande do Sul State (length, 622 km) in 2013. Tissue samples were tested by OIE-recommended single-step conventional polymerase chain reaction assays. The screening showed no evidence of the specific sequences of the protistan parasites and viral pathogens at any site within the six zones under study. We recommend continuous monitoring of the mollusks in the region.

Received July 3, 2015; accepted February 3, 2016  相似文献   


13.
Amphibians produce defensive chemicals which provide protection against both predators and infections. Within species, populations can differ considerably in the composition and amount of these chemical defenses. Studying intraspecific variation in toxins and linking it to environmental variables may help us to identify the selective drivers of toxin evolution, such as predation pressure and infection risk. Recently, there has been a renewed interest in the unique toxins produced by salamanders from the genus Salamandra: the samandarines. Despite this attention, intraspecific variation has largely been ignored within Salamandra-species. The aim of this study was to investigate whether geographic variation in profiles of samandarines exists, by sampling 4 populations of Salamandra atra over its range in the Dinaric Alps. In addition, we preliminary explored whether potential variation could be explained by predation (counting the number of snake species) and infection risk (cultivation and genomic analyses of collected soil samples). Salamanders from the 4 populations differed in toxin composition and in the size of their poison glands, although not in overall toxin quantity. Nor predation nor infection risk could explain this variation, as populations barely differed in these variables. Sampling over a much broader geographic range, using better estimators for predation and infection risk, will contribute to an improved understanding of how environment may shape variation in chemical defenses. Nevertheless, as the 4 populations of S. atra did differ in their toxin profiles, we propose that this species provides an interesting opportunity for further ecological and evolutionary studies on amphibian toxins.  相似文献   

14.
From data collected over the course of a year in a commercial broiler hatchery it was possible to infer the positions in the boxes that had been occupied during transit from farm to hatchery by 25,179 eggs subsequently downgraded upon candling. Two thousand seven hundred eggs were sampled from each of 168 consignments; the total number of eggs sampled was nearly half a million. They came from flocks of two strains and were candled by four candlers. Analysis of variance showed the downgrading rate to depend on (a) identity of the candler, (b) strain, (c) sample, which was confounded with flock and season, and (d) position of the egg in the box. Positional variation occurred in all three dimensions. Vertically (between trays) the downgrading showed a linear increase from top to bottom. Horizontally (within trays) the variation was such that eggs near the corners were at greatest risk, followed by those in the middle of the sides. Those in the centre of the tray were at least risk. The horizontal variation is believed to be due to damage caused by unidentified external objects (at the corners) and by the string with which the boxes were tied (at the middle of the sides). Within‐box variation accounted for the downgrading of 1 egg in 200. There is a need for further work on the design of egg trays and boxes.  相似文献   

15.
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16.
Recent evidence suggests that many Australian agamids show temperature‐dependent sex determination (TSD) with variation in sex determining mechanisms among closely related taxa. However, as shown in other vertebrates, sex ratios can also be influenced by genetic or phenotypic differences among females in their propensity to produce sons or daughters, and these influences might confound any thermal effects of incubation per se. To address these issues, we investigated the determinants of sex ratios in the mallee dragon Ctenophorus fordi, together with a detailed analysis of karyotypes. There was no detectable variation in sex ratios arising from variation among females, clutches or incubation temperatures, which might indicate genetic sex determination for this species. However, there was no evidence of cytologically distinct sex chromosomes using standard banding techniques. The sex ratio pattern in C. fordi strongly contrasts with the results for the congener Ctenophorus pictus, where sex ratios show variation among females. Thus, Australian agamids offer promising opportunities to address fundamental issues in sex ratio biology.  相似文献   

17.
In Tunisia both Psammomys obesus and P. vexillaris are found. These taxa have been the subject of taxonomic controversy for some time, due to variability in the classical morphological characters used for taxonomic recognition. In this study we investigated skull size and shape variation in the genus Psammomys by using geometric morphometrics to evaluate the extent of intra- and interspecific shape variation and explicitly tested for the impact of allometric shape variation on species discrimination. Eleven populations of the two species from 10 localities in Tunisia were studied. Statistical analyses of size and shape showed large size variation within P. obesus, but no shape differences were revealed among populations of this species. Interspecific analysis revealed that P. vexillaris had the smallest skull. Principal component analysis and Procrustes distances showed good discrimination between the two species after removal of the allometric component of shape variation. The results obtained show that allometric-related shape variation could mask discrimination between the two Psammomys species. This finding might explain the uncertainty in classification of these species in the past. The interspecific allometric-free phenotypic differences observed may be associated with adaptive processes linked to the different environmental and trophic preferences of the two species.  相似文献   

18.

Fifteen West African Dwarf grower bucks of about 6–8 months of age and average weights of 8.39 kg were used in a 70-day study to assess the intake and blood profile of West African Dwarf (WAD) goats fed diets containing graded levels of treated sweet orange peel meal (TSOPM), in a completely randomized design. Sweet orange peels were collected from sweet orange retailers within Makurdi, Benue State, Nigeria. The peels were packed into synthetic bags, compressed, and allowed to ferment for 12 h before sun-drying. The sun-dried peels were crushed into a meal and used to compound four treatments diets which consisted of 0, 60, and 80% TSOPM, designated diets A, B, and C respectively. Results showed that there were no significant differences (P?>?0.05) among the treatments in all the performance parameters except in the total forage intake values in which treatment A (19.74 kg) was significantly lower (P?<?0.05) than treatment B (21.77 kg) and treatment C (21.96 kg). But between treatment B and treatment C, there was no difference. Effect of treatments was also not apparent on the haematological indices measured, but the serum biochemical parameters showed significant difference (P?<?0.05) among the treatments for total protein values. The total protein value for treatment C (8.02 g/dl) was significantly higher (P?<?0.05) than treatments A (7.10 g/dl) and B (6.62 g/dl). The study showed that treated sweet orange peel meal can be used up to 80% level to replace maize offal in the diets of goats without adverse effects on the performance blood indices.

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19.
Riemerella columbina (RC) and Riemerella anatipestifer (RA) belong to the genus Riemerella within the family Flavobacteriaceae. While RA is a well-described pathogen of waterfowl and other avian species, only little is known about RC. Previous work reporting the isolation of RC from internal organs of clinically diseased pigeons suggested a potential pathogenic role in this avian species. In this study we examined pharyngeal swabs collected from pigeons and found RC to be widely distributed also among healthy birds. Further characterization of 81 RC-isolates revealed several atypical strains, which differed from all previously described RC-isolates by the lack of aesculin-hydrolysis activity (17 isolates) or by expression of yellow or orange pigmentation (6 isolates). Sequence analysis of the 16S rRNA and outer membrane protein A (ompA) gene supported the affiliation of these strains to the species RC. Aesculin-hydrolysis negative isolates were found to be biochemically indistinguishable from RA. We demonstrated that bacterial fingerprinting using matrix assisted laser desorption/ionisation–time of flight mass spectrometry (MALDI–TOF MS) analysis is useful for the identification and differentiation of RC and RA.  相似文献   

20.
Molecular biology has contributed to our knowledge and understanding of the structure of Mycobacteriumavium subspecies paratuberculosis and has been particularly useful in determining those components that elicit immune responses in the host or discriminate M. avium paratuberculosis from other closely related environmental mycobacteria. As such, it has made a significant impact in the field of diagnosis, and has been instrumental in the development of specific and sensitive diagnostic tests. The next decade will see exciting new developments in paratuberculosis research as a consequence of substantial advances made in the construction of gene transfer systems in mycobacteria. These will provide opportunities for applying new strategies to determine the genetic basis for pathogenesis and the mechanisms of drug resistance and will offer new prospects for the rational design of efficient vaccines.  相似文献   

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