The relative roles of predation and sperm competition on the duration of the post-copulatory association between the sexes in the blue crab, Callinectes sapidus

In many species, post-copulatory mate guarding prevents other males from mating with the guarded female. In crabs, males stay with their mates to protect the female from predators because, in some species, mating occurs when she is soft and vulnerable after molting. I tested the relative roles of sperm competition and predation on the duration of the post-copulatory association in the blue crab, Callinectes sapidus. Unpaired females suffered greater predation mortality than paired females and males stayed with the female longer in the presence of predators than in their absence, suggesting that the post-copulatory association protects females during their vulnerable period. However, the association may also occur in blue crabs because of sperm competition since spermathecal contents of females in the field indicate that 12.4% mated twice. Females experimentally mated with two males contained both males ejaculates and each ejaculate had access to the unfertilized eggs, suggesting that the size of a male's ejaculate influences his fertilization rate in a multiply-mated female. Males stayed longest in response to a high risk of sperm competition. Longer post-copulatory associations allowed the first male's ejaculate to harden into a type of sperm plug, which limited the size of a second inseminator's ejaculate in a non-virgin female as compared with a virgin. Males passed larger ejaculates in the presence of rivals and when previous ejaculates were in the female spermathecae, another response to sperm competition. Larger ejaculates may need longer post-copulatory associations before a more effective sperm plug forms. Large males stayed with the female longer, which is consistent with their ability to pass larger ejaculates than small males and suggests that there may be costs to minimizing the duration of the post-copulatory association. In the field, associations last long enough to protect the female during her vulnerable phase and may ensure that the guarding male fertilizes the most eggs in the female, even if she remates. Thus, the post-copulatory association protects female blue crabs from additional inseminators as well as from predators. Received: 23 January 1996 / Accepted after revision: 9 November 1996     

Conservation Assessment of Southern South American Freshwater Ecoregions on the Basis of the Distribution and Genetic Diversity of Crabs from the Genus Aegla

Abstract:  We assessed the conservation priority of 18 freshwater ecoregions in southern South America on the basis of Aegla (genus of freshwater crabs) genetic diversity and distribution. Geographical distributions for 66 Aegla species were taken from the literature and plotted against ecoregions and main river basins of southern South America. Species richness and number of threatened and endemic species were calculated for each area. To assess taxonomic and phylogenetic diversity, we generated a molecular phylogeny based on DNA sequences for one nuclear (28S) and 4 mitochondrial (12S, 16S, COI, and COII) genes. All species richness and phylogenetic methods agreed, to a large extent, in their rankings of the importance of conservation areas, as indicated by the Spearman's rank correlation coefficient ( p < 0.01); nonetheless, some of the lowest correlations were observed between taxonomic and phylogenetic diversity indices. The 5 ecoregions of the Laguna dos Patos Basin (Eastern Brazil), Central Chile, South Brazilian Coast, Chilean Lakes, and Subtropical Potamic Axis (northern Argentina and southern Uruguay and Paraguay) had the highest biodiversity scores. Conservation of these regions will preserve the largest number of species and the greatest amount of genetic diversity within the South American freshwater Aegla fauna. Biodiversity across rivers and within areas was heterogeneously distributed in the ecoregions of Upper Paraná, Ribeira do Iguape, Upper Uruguay, and South Brazilian Coast (i.e., one river showed significantly more biodiversity than any other river from the same ecoregion), but homogeneously distributed in the other ecoregions. Hence, conservation plans in the former regions will potentially require less effort than plans in the latter regions.     

To court or not to court: reproductive decisions by male fiddler crabs in response to fluctuating food availability

For males, courting and foraging are often behavioral alternatives, which take time and consume energy. When males have a possibility of mating with receptive females, there may be a behavioral trade-off between courtship and feeding; the outcome of which may be affected by male physiological condition and food availability. Although many mathematical models and empirical studies suggest that the expression of male courtship signals are condition-dependent, decisions about courtship and mating strategies in relation to food availability have not attracted much attention. In this study, we tested whether daily changes in food availability affect males’ decisions about whether to court. We conducted experiments with the fiddler crab Uca lactea by providing males with additional food every other day. In food-supplemented enclosures, males did not increase courtship activity on the days when food was supplemented. However, they built more courtship structures (semidomes) and waved more on the days when they were not given additional food. Male size had a strong influence on the number of days the males courted. We also tested whether the frequency of surface mating, as an alternative reproductive tactic, decreased when food was supplemented. Contrary to our expectation, the number of males that exhibited the surface-mating tactic increased when food was supplemented whereas the number of mate-searching females did not change. Our findings in this field study suggest that reproductive decisions by male fiddler crabs are affected by fluctuating food availability and present body condition, and the alternative mating tactic of this species may be more frequently used by males under good condition.     

长江下游中华绒螯蟹成蟹资源现状(2007~2011年)

根据2007~2011年在长江安徽段和江苏段的中华绒螯蟹成蟹汛期调查结果,研究了长江下游中华绒螯蟹的资源变动特征。中华绒螯蟹平均体重在空间分布上基本呈现由上游至下游逐步下降的趋势,在时间上各江段变动规律各有不同,最大平均体重出现于2010年的安庆江段,为0.25kg;最小平均体重出现于2008年的靖江江段,为0.05kg。安徽段总捕捞量为9.07~30.44t,汛末瞬时资源量为3.01~6.07t,总资源量为12.09~36.50t;江苏段总捕捞量为6.76~48.28t,汛末瞬时资源量为2.85~10.19t,总资源量为9.88~55.92t。近5a长江下游中华绒螯蟹汛期捕捞强度为0.75~0.86,捕捞压力处于高位,加之长江下游中华绒螯蟹幼蟹、蟹苗捕捞作业逐步恢复,中华绒螯蟹资源仍面临着严峻的问题。为促进中华绒螯蟹资源的可持续利用,建议全江禁捕,建立中华绒螯蟹保护区,加大增殖放流力度、加强科学研究及渔政管理。     

Ecology of reproduction of the red king crab

Conditions for reproduction of the red king crab Paralithodes camtschatica (Tilesius) on scallop plantations in Primorye have been studied. It has been found that the settling of larvae and the growth of juveniles to the size sufficient for their survival take place only in the cleanest water areas of Peter the Great Bay. Solar activity (expressed as the Wolfer number) is one of the most important abiotic factors affecting P. camtschatica reproduction. The population dynamics of juvenile crabs are characterized by fluctuations with two-year and five-year cycles.     

An integrated investigation of biomarkers’ response in crabs (Liocarcinus depurator) and benthic indices at a metalliferous waste discharge area in North Evoikos gulf,Greece

This study applied biomarkers and benthic indices at an area in North Evoikos Gulf, Greece, affected by metalliferous slag disposal. Biomarkers of antioxidant defense (catalase, glutathione S-transferase), and neurotoxicity (acetylcholinesterase) were measured in crabs Liocarcinus depurator. Iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), and zinc (Zn) concentrations in sediments and crabs were also measured. High levels of all metals were found in sediments at the disposal area. Metal levels in the crabs were also higher in the disposal area although spatial differences were not as marked as in the sediments. Accordingly, biomarker responses of crabs in the disposal area were also noted suggesting impact on the antioxidant defense of the organisms against oxidative stress. Benthic indices showed disturbance in the disposal area. The combined approach of measuring biomarkers and contaminant levels in the crabs and sediment was complementary to the benthic indices approach providing indications of metal exposure related effects. Our results support the idea that a twofold monitoring approach of assessing both the benthic community structure shifts and the biomarkers and metal accumulation levels may integrate and capture both the structural and the toxicological effects of dumping onto the benthic communities.     

Toxicity of Brachuryan crabs in India

Crabs are the most abundant macrofauna in the coastal environment, and may belong to many different species and even families. Some of these crabs contain specialized protein substances that act as toxins. Toxins, especially proteins that are produced by living cells or organisms, are poisonous substances. Toxins can be divided according to their pharmacological effects (neurotoxins, myotoxins, hepatotoxins, nephrotoxins, hematological toxins, and locally acting toxins) and their sources, such as snakes, scorpions, mussels, spiders, marine creatures, or sea anemones. Crab toxins are heat resistant and are found in the crabs’ viscera. Hence, they cannot be destroyed by cooking, and there is also no known treatment available for these toxins. The only alternative is to educate fishermen, holiday makers, and seafood consumers to recognize these poisonous species and avoid them. Several toxins identified from crabs are neurotoxins, related to tetradotoxin (TTX), which is found in pufferfish. Other toxins include saxitoxin (STX), neurosaxitoxin (NeoSTX), and some unidentified toxins. Some poisonous crabs possess a mixture of these toxins. This article describes the toxins and Brachuryan crabs producing toxicity.     

五种不同养殖生物中氯化二苯并二噁英和呋喃的污染水平及特征

对五种养殖生物进行二噁英类化合物污染水平和指纹特征的研究结果显示,鱼、虾、蟹、扇贝和牡蛎的平均浓度分别是0.35pg·g-1,0.57pg·g-1,0.62pg·g-1,0.11pg·g-1和1.38pg·g-1.OCDD是五种养殖生物的最主要污染物,其次是2,3,7,8-TCDF, 1,2,3,4,6,7,8-HpCDD和OCDF. 1,2,3,7,8-PeCDD和2,3,4,7,8-PeCDF是五种养殖生物中二噁英毒性最主要的贡献者.初步认为,生活习性的差异是造成五种不同养殖生物二噁英污染水平差异的重要原因.     

广西北海中国鲎资源现状以及保育工作进展

中国鲎种群数量近年来急剧下降,资源面临枯竭.位于北部湾的广西北海作为中国鲎理想栖息地,是我国中国鲎的主要产地,因此在北海开展中国鲎的保育工作尤为重要.本文调查分析了广西北海地区中国鲎幼体集聚地西背岭潮间带(21°24′30″N-21°25′24″N及109°11′12″E-109°13′14″E)中国鲎幼体分布现状以及...     

蟹类活动对河口潮滩沉积物重金属分布的影响

利用现场样方调查以及室内蟹箱模拟试验,研究了蟹类的掘穴、取食等活动对河口潮滩沉积物中Cu、Pb、Fe、Mn、Zn、Cr等重金属分布的影响.结果表明,蟹类活动可以显著地增加潮滩沉积物用以交换的表面积,改变周围沉积物的有机质含量和粒度特征,使沉积物中的重金属含量显著增加,为在沉积物-水界面发生的重金属交换过程提供了更多的物质来源.蟹类活动对沉积物中重金属垂向分布的影响与沉积物类型密切相关.图6表1参10