DNA damage in workers exposed to formaldehyde at concentrations below occupational exposure limits

Formaldehyde has been classified in group 1 as a potential source of human carcinogen by the International Agency for Research on Cancer. In this study, we evaluated the DNA damage in workers who were occupationally exposed to formaldehyde during the manufacture of melamine dinnerware.

Age, sex, smoking habits, and socioeconomic status were matched by the controls (n = 34) of workers not occupationally exposed to formaldehyde. The median value of formaldehyde time weighted average exposure in three workshops was 0.086 mg/m³. No significant difference was observed between sex and smoking habit in the assessed workers. Alkaline comet assay of peripheral blood lymphocytes was used to determine the DNA damage in the subjects. Olive moment was significantly higher in the exposed group compared with the control group.

Overall, the results suggest that respiratory exposure to low concentrations of formaldehyde causes DNA damage in peripheral blood lymphocyte. Therefore, exposure to formaldehyde should be reduced to the lowest possible level.     

基于rpoC1基因的微囊藻属分子系统学研究

测定了广东省9个水库4株铜绿微囊藻Microcystis aeruginosa、5株水华微囊藻M.flos-aquae和4株未定种微囊藻rpoC1基因部分序列,结合GenBank下载的日本5个水体11株铜绿微囊藻、5株绿色微囊藻M.viridis和5株惠氏微囊藻M.wesenbergii间源序列,进行序列分析.结果显示,34株微囊藻存在21种基因型,序列相似性达97.6%～100%.在邻接树上不同形态种和不同地理来源的藻株混杂在一起,没有形成明显的谱系结构和地理结构:同一形态种藻株可能具有不同的基因型,而相同基因型的藻株可能是不同的形态种;从同一水体中分离的微囊藻具有不同的形态种和不同的基因型,而不同水体分离的微囊藻有时又具有相同基因型,表明rpoC1基因序列无法区分形态种和地理株,支持Kondo和Otsuka提出的暂将铜绿微囊藻、水华微囊藻、惠氏微囊藻和绿色微囊藻等归为铜绿微囊藻复合种的分类处理.     

苯乙烯致DNA间接损伤效应的光电化学生物传感器快速检测

许多有机化合物自身没有致癌毒性,但进入生物体内,经过体内代谢酶的催化后转化成活性中间体,与DNA形成共价化合物.这些间接的损伤会最终导致DNA分子结构和功能的变化,对人类的健康造成威胁.因此,建立一种快速有效的方法检测间接致癌化合物对DNA的损伤,成为当前研究的热点.论文建立了一种新型的光电化学生物传感器来检测有机化合物苯乙烯对DNA的间接损伤效应,该传感器以层层自组装的方式将光电信号分子、双链DNA和血红蛋白组装在半导体电极上.在H2O2存在的条件下,传感膜中的血红蛋白可将苯乙烯转化为氧化苯乙烯,氧化苯乙烯扩散到膜内,与DNA形成加合物,引起DNA结构变化,导致光电分子光电流信号的增加.实验中,将修饰好的电极置于终浓度为2mM H2O2和2%苯乙烯(体积比)的混合液(pH7.3的磷酸缓冲液配制)中反应一段时间后,在电解质溶液中进行光电流检测.实验结果表明,光电流信号随着反应时间逐渐升高,在30min后趋于稳定,表明苯乙烯在传感膜上的氧化和DNA的损伤反应基本完成.与反应前相比,反应后光电流增加了40%,并且酶催化苯乙烯生成的氧化苯乙烯经紫外可见光谱得到验证.论文建立的光电化学生物传感器模拟了体内DNA损伤反应过程,能快速有效地检测苯乙烯对DNA的间接损伤效应,有望为有机化合物潜在基因毒性的风险评估提供一个快速筛查工具。     

Cadmium and chromium in human lung tissue in relation to smoking and lung cancer

The pulmonary Cd and Cr content was determined from 53 lung cancer patients operated for cancer and from 39 patients who died of non‐malignant diseases. The results were correlated with smoking habits, pulmonary emphysema and occupational history. Both the pulmonary Cd and Cr increased with the amount of smoking. In ex‐smokers the Cr content in lung tissue did not diminish with the time since stopping smoking, but the Cd did follow the half‐life of about 9 years. The pulmonary Cd, compared with smoking habits, behaved similarly in both the lung cancer and control patients, whereas Cr in the lung cancer patients could not be explained solely by smoking, but some of the cancer patients may have been occupationally exposed to Cr. Speciation was not studied.     

The microcystins-induced DNA damage in the liver and the heart of zebrafish,Danio rerio

Microcystins (MCYST) are the freshwater cyanobacterial toxins, known to induce hepatocellular carcinoma, necrosis, intrahepatic bleeding, as well as human and livestock mortality. Within hepatocytes, MCYST selectively bind to protein phosphatases 1 and 2A, resulting in severe liver damage. The toxicology of MCYST in mice and rats has been well studied, but little is known regarding genotoxicity in aquatic animals. In this study, the zebrafish, Danio rerio was exposed to crude extract of Microcystis aeruginosa bloom. Liver and heart were examined for MCYST-induced toxicity. Light microscopy at 36?h revealed severe, widespread apoptotic necrosis of the majority of hepatocytes, and cytoskeletal deformation in myocardiocytes. Hepatocytes were dissociated with cell shrinkage and margination of nuclear chromatin. Laddering of genomic DNA from the liver and heart of the exposed fish in an increment of 180–200?bp was consistent with apoptosis. Fluorimetric analysis of DNA unwinding was carried out to determine the DNA strand breakage. After 36?h exposure, the % double-stranded DNA was significantly reduced in hepatocytes and myocardiocytes. In conclusion, the results obtained in this study indicate that, the extract of M. aeruginosa bloom is genotoxic to fish. The DNA damage observed in this study may be attributed to the activation of DNA endonucleases. This model of DNA damage may contribute for identifying novel molecular mechanisms of interest for therapeutic application.     

Inhibitory effect of antioxidants on the benz[a]anthracene-induced oxidative DNA damage in lymphocyte

Benz[a]anthracene is a ubiquitous environmental contaminant formed during the incomplete combustion of organic material. Some of the metabolites of benz[a]anthracene are known to be toxic and carcinogenic. In this investigation, benz[a]anthracene-induced oxidative damage to lymphocyte DNA was evaluated with the Comet assay (single cell gel electrophoresis). The level of oxidative DNA damage caused by benz[a]anthracene increased in a dose-dependent manner (24, 49) and oxidative DNA damage was significantly inhibited by 5 and 10 microg ml(-1) ascorbate, 5 microg ml(-1) polyphenols, as well as 5 and 10 microg ml(-1) curcumin. Moreover, traditional Korean medicinal herbs such as Acanthopanax and ginseng significantly reduced DNA damage. The results demonstrate that antioxidant supplementation to lymphocytes inhibits oxidative DNA damage in vitro, supporting an inhibitory effect against oxidative DNA damage, probably due to reduction of reactive oxygen species production induced by benz[a]anthracene.     

Effect of nickel exposure on serum amylase activity in nickel-plating workers

The objective of this study was to determine the effect of nickel (Ni) exposure on serum amylase activity in nickel-plating workers in Bangalore (India). Sixty-nine subjects using Ni during the electroplating process formed the exposed group. An equal number of age- and sex-matched subjects working in the administration section formed the control group. Urine Ni levels were determined using a flameless atomic absorption spectrophotometer. Serum amylase activity was determined using spectrophotometric method with 2-chloro-4-nitrophenyl-α-D-maltotrioside as substrate. A significant increase in urine Ni and serum amylase activity was noted in nickel platers as compared with the control group. The level of serum amylase activity was positively and significantly associated with Ni content in urine of nickel platers. Stepwise multiple regression analysis was used to assess the effects of Ni exposure, life style confounding factors and presence of gastrointestinal problems on serum amylase activity. The analysis showed that the subjects who had urine Ni levels beyond 10?µg?g^?1 of creatinine, nickel platers category, smoking and body mass index variables were significantly associated with serum amylase activity. The results of this study suggest that the increased serum amylase activity observed in nickel-exposed subjects could be used as a biomarker for investigating pancreatic function in Ni exposure.     

Detection of oxidative stress and DNA damage in freshwater snail <Emphasis Type="Italic">Lymnea leuteola</Emphasis> exposed to profenofos

Extensive production and use of organophosphate pesticide in agriculture, has risen concerned about its ecotoxicity and risk assessment of insecticides, which are more important. Therefore, the present investigation was aimed to study the induction of oxidative stress and DNA damage by organophosphate insecticide profenofos (PFF) in freshwater snail Lymnea luteola (L. luteola). The median lethal value (96 h LC₅₀) of PFF was estimated as 1.26 mg/L for L. luteola in a semi-static system and on the basis of LC₅₀ value three concentrations viz., 0.126 (1/10 of LC₅₀, Sublethal I), 0.63 (1/2 of LC₅₀, Sublethal II) and 0.84 mg/L (2/3 of LC₅₀, Sublethal III) were determined. Snails were exposed to above-mentioned concentrations of PFF along with solvent control (acetone) and negative control for 96 h. The haemolymph was collected at 24 and 96 h of after treatment. In heamolymph of PFF exposed snail, lipid peroxide, glutathione reduced glutathione S transferase and superoxide dismutase activities at the tested concentrations significantly differ from those in the control. The genotoxicity induced in hemocytes of treated snails was measured by alkaline single cell gel electrophoresis assay. The data of this experiment demonstrated significantly enhancement of oxidative stress and DNA damage in the treated snails as compared to controls. Also, we observed statistically significant correlations of ROS with DNA damage (% tail DNA) (R² = 0.9708) for 24 h and DNA damage (R2 = 0.9665) for 96 h.

Results of the current experiment can be useful in risk evaluation of PFF among aquatic organisms. The study confirmed the use of comet assay for in vivo laboratory experiments using freshwater snail for selecting the toxic potential of industrial chemicals and environmental contaminants.

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苯并[a]芘对马氏珠母贝血淋巴细胞DNA损伤的研究

通过单细胞凝胶电泳技术（彗星试验）研究了苯并[a]芘（B[a]P）对马氏珠母贝（Pinctada martensi）血淋巴细胞DNA的损伤。结果显示,在相同暴露时间内,不同质量浓度的B[a]P均能引起马氏珠母贝血淋巴细胞DNA损伤。4μg.L-1 B[a]P处理组DNA含量、彗尾长度和Olive尾矩均最大,分别为34.39%、281.73和60.31μm。随着暴露时间的延长,彗星尾长明显增加,表现出明显的时间-效应关系,而DNA含量和Olive尾矩没有呈现出规律性变化。此外,在不同的染毒时间内,对照组和各处理组之间均存在显著差异（P〈0.05）,3个指标具有很好的一致性。研究表明,彗星试验是检测B[a]P对马氏珠母贝血淋巴细胞DNA损伤的一种有效手段,马氏珠母贝血淋巴细胞DNA损伤可作为指示B[a]P污染的一种有效生物标志物用于早期预警监测。     

2,3,7,8-四氯二苯并二噁英与Aroclor 1254单独与联合作用对大鼠外周血淋巴细胞DNA的损伤效应(Damage Effects of Individual and Combined Exposure to 2,3,7,8-Tetrachlorodibenzo-p-Dioxin and Aroclor 1254 on DNA in Peripheral Blood Lymphocyte of Rats)

为探讨2,3,7,8-四氯二苯并二噁英(TCDD)和多氯联苯(Aroclor 1254)联合染毒对大鼠外周血淋巴细胞DNA的损伤效应,将20只雄性Sprague-Dawley(SD)大鼠随机均分为4组,即对照组(橄榄油)、Aroclor 1254单独染毒组(10mg·kg-1)、TCDD单独染毒组(10μg·kg-1)和联合染毒组(TCDD 10μg·kg-1+Aroclor 1254 10 mg·kg-1).大鼠每天灌胃染毒1次,连续染毒6d.染毒过程中记录大鼠的体征和体重.末次染毒后24h取外周血,分离淋巴细胞,采用碱性单细胞凝胶电泳技术(彗星试验)检测外周血淋巴细胞DNA损伤,并采用CASP软件分析各组彗星的尾部DNA百分含量(Tail DNA%)、尾长(Tail Length)和尾矩(Tail Moment).结果表明,染毒结束时TCDD单独染毒和联合染毒组大鼠体重显著低于对照组,且联合染毒组表现更为明显.TCDD单独染毒组和联合染毒组大鼠外周血淋巴细胞DNA可见明显损伤,TailDNA%、Tail Length和Tail Moment均显著高于对照组(p<0.05),且联合染毒组大鼠细胞DNA损伤更为严重,但Arolor 1254单独染毒组大鼠未见明显DNA损伤.析因分析提示TCDD与Aroclor 1254对大鼠外周血淋巴细胞DNA损伤的联合毒性效应为协同作用.本研究结果表明TCDD与Aroclor 1254联合染毒可加重大鼠外周血淋巴细胞DNA损伤,在对PCBs与二噁英的混合暴露进行危险性评估时要注意这种联合毒性作用.     

Response of bioaerosol cells to photocatalytic inactivation with ZnO and TiO2 impregnated onto Perlite and Poraver carriers

•ZnO/Perlite inactivated 72% of bioaerosols in continuous gas phase. •TiO₂ triggered the highest level of cytotoxicity with 95% dead cells onto Poraver. •Inactivation mechanism occurred by membrane damage, morphological changes and lysis. •ZnO/Poraver showed null inactivation of bioaerosols. •Catalysts losses at the outlet of the photoreactor for all systems were negligible. Bioaerosols are airborne microorganisms that cause infectious sickness, respiratory and chronic health issues. They have become a latent threat, particularly in indoor environment. Photocatalysis is a promising process to inactivate completely bioaerosols from air. However, in systems treating a continuous air flow, catalysts can be partially lost in the gaseous effluent. To avoid such phenomenon, supporting materials can be used to fix catalysts. In the present work, four photocatalytic systems using Perlite or Poraver glass beads impregnated with ZnO or TiO₂ were tested. The inactivation mechanism of bioaerosols and the cytotoxic effect of the catalysts to bioaerosols were studied. The plug flow photocatalytic reactor treated a bioaerosol flow of 460×1 0⁶ cells/m³_air with a residence time of 5.7 s. Flow Cytometry (FC) was used to quantify and characterize bioaerosols in terms of dead, injured and live cells. The most efficient system was ZnO/Perlite with 72% inactivation of bioaerosols, maintaining such inactivation during 7.5 h due to the higher water retention capacity of Perlite (2.8 mL/g_Perlite) in comparison with Poraver (1.5 mL/g_Perlite). However, a global balance showed that TiO₂/Poraver system triggered the highest level of cytotoxicity to bioaerosols retained on the support after 96 h with 95% of dead cells. SEM and FC analyses showed that the mechanism of inactivation with ZnO was based on membrane damage, morphological cell changes and cell lysis; whereas only membrane damage and cell lysis were involved with TiO₂. Overall, results highlighted that photocatalytic technologies can completely inactivate bioaerosols in indoor environments.     

纳米MnO2与常规MnO2粉末对Hela细胞DNA损伤的对比研究

为探讨纳米MnO2与常规MnO2粉末对细胞DNA损伤作用的差别,采用不同浓度的纳米MnO2与常规MnO2粉末(0、100、200、400μg·mL-1)对Hela细胞进行染毒,应用单细胞凝胶电泳(彗星实验)检测Hela细胞的损伤效应.结果表明,与对照组相比,纳米MnO2和常规MnO2各染毒组细胞尾部DNA百分率(TailDNA%)和尾矩(TailMoment)均显著增加(p<0.01);同一浓度下,纳米MnO2组细胞尾部DNA百分率和尾矩显著高于常规MnO2组(p<0.01).以上结果表明,纳米MnO2和常规MnO2粉末均能导致Hela细胞DNA损伤,且纳米MnO2的损伤作用强于常规MnO2.     

二氧化锰颗粒对Hela细胞DNA损伤的尺度依赖性毒作用(英文)

为了观察二氧化锰颗粒物所致的尺度依赖性DNA损伤作用,将纳米尺度二氧化锰颗粒物(Nano-MnO2)和常规尺度二氧化锰颗粒物(Nor-MnO2)所致的DNA损伤进行了对比研究.将Hela细胞分别暴露于不同浓度(0、100、200、400μg·mL-1)的Nano-MnO2和Nor-MnO2中,染毒24h,采用彗星实验检测Hela细胞的DNA损伤水平.结果表明:与对照组相比,Nano-MnO2和Nor-MnO2均可使彗尾DNA百分比(TailDNA%)和尾矩(TailMoment)显著增加(p<0.01);而在同一浓度水平上,Nano-MnO2所致的DNA损伤则比Nor-MnO2所致的DNA损伤更为严重(p<0.01).结果提示:二氧化锰颗粒对Hela细胞DNA损伤具有尺度依赖性毒作用,纳米尺度比常规尺度二氧化锰颗粒毒作用更强烈.     

Limited effects of Antarctic ozone depletion on sea urchin development

The sea urchin, Sterechinus neumayeri, has a circumpolar distribution and is an abundant species in benthic communities of the Antarctic. Reproduction occurs during austral spring, when ozone concentrations over the past 25 years have been reduced by 50% or more, potentially exposing the planktonic embryos and larvae to elevated levels of UVB. During spring of 1996, cultures of S. neumayeri embryos incubated under ambient and partitioned sunlight (minus UVB) at static depths between 0 and 7 m were analyzed for DNA damage [cyclobutane pyrimidine dimers (CPDs)] and morphological abnormalities. At 0-m and 1-m depths, nearly 100% of embryos developed abnormally, even under UVB-shielded conditions where little or no DNA damage accumulated. At depths >3 m, reduced or no abnormality was evident and DNA damage was negligible. Although UVB contributed to 0–65% of solar-induced abnormalities, the mean contribution was 11±17% and UVB was not primarily responsible for observed defects in urchin development. Moreover, developmental responses were not linearly related to ambient UVB gradients as might be expected, but are better characterized relative to threshold levels of total UVB exposure. Accumulated exposures of 25 kJ m^–2 ambient UVB caused minimal DNA damage and allowed normal embryological development to proceed. Higher UVB exposures (especially 80 kJ m^–2) precluded normal development. An ancillary threshold limit of 17 CPDs mb^–1 has been identified as the level of DNA damage that proscribes abnormal development. While higher wavelengths of UVA and visible light are not affected by ozone concentration and do not initiate significant CPD DNA damage, they did interfere significantly with the embryological development of S. neumayeri. It is concluded that exposure to increased UVB during recent Antarctic ozone-depletion cycles probably has only a small degree of impact relative to the magnitude of other solar effects on the developmental success of Sterechinus embryos, or compared to spawning seasons before ozone depletion (i.e., years prior to 1978).Communicated by P.W. Sammarco, Chauvin     

Blood concentrations of lead,cadmium, mercury and their association with biomarkers of DNA oxidative damage in preschool children living in an e-waste recycling area

Reactive oxygen species (ROS)-induced DNA damage occurs in heavy metal exposure, but the simultaneous effect on DNA repair is unknown. We investigated the influence of co-exposure of lead (Pb), cadmium (Cd), and mercury (Hg) on 8-hydroxydeoxyguanosine (8-OHdG) and human repair enzyme 8-oxoguanine DNA glycosylase (hOGG1) mRNA levels in exposed children to evaluate the imbalance of DNA damage and repair. Children within the age range of 3–6 years from a primitive electronic waste (e-waste) recycling town were chosen as participants to represent a heavy metal-exposed population. 8-OHdG in the children’s urine was assessed for heavy metal-induced oxidative effects, and the hOGG1 mRNA level in their blood represented the DNA repair ability of the children. Among the children surveyed, 88.14% (104/118) had a blood Pb level >5 μg/dL, 22.03% (26/118) had a blood Cd level >1 μg/dL, and 62.11% (59/95) had a blood Hg level >10 μg/dL. Having an e-waste workshop near the house was a risk factor contributing to high blood Pb (r _s  = 0.273, p < 0.01), while Cd and Hg exposure could have come from other contaminant sources. Preschool children of fathers who had a college or university education had significantly lower 8-OHdG levels (median 242.76 ng/g creatinine, range 154.62–407.79 ng/g creatinine) than did children of fathers who had less education (p = 0.035). However, we did not observe a significant difference in the mRNA expression levels of hOGG1 between the different variables. Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels (β _Q2 = 0.362, 95% CI 0.111–0.542; β _Q3 = 0.347, 95% CI 0.103–0.531; β _Q4 = 0.314, 95% CI 0.087–0.557). Associations between blood Hg levels and 8-OHdG were less apparent. Compared with low levels of blood Hg (quartile 1), elevated blood Hg levels (quartile 2) were associated with higher 8-OHdG levels (β _Q2 = 0.236, 95% CI 0.039–0.406). Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels.     

Effect of fomesafen on glutathione S-transferase and cellulase activity and DNA damage in the earthworm (Eisenia fetida)

Biochemical responses and DNA damage of earthworm (Eisenia fetida) exposed to various concentrations of fomesafen (0, 10, 100, and 500 μg kg^?1) for 3, 7, 14, 21, and 28 days were investigated in vivo. Glutathione S-transferase (GST) activity was significantly stimulated upon treatment with 500 μg kg^?1 fomesafen for 21 days, while the cellulase activity was markedly inhibited after 14 days of treatment. On day 28, the activities of GST and cellulase had recovered to the level similar to that of controls. Low or mild DNA damage in earthworm was induced within 14 days of exposure, and the damage was reduced or disappeared with the extension of exposure.     

糯小麦回交改良群体中Wx基因的遗传和品质效应

在基因型鉴定的基础上,利用糯小麦杂交后代BC5F2代回交改良群体研究了各基因缺失对降低直链淀粉含量的效果和各基因合成直链淀粉的能力,以及直链淀粉含量与农艺性状、品质性状、淀粉糊化特性等的相关性。研究发现,在Wx基因的所有8种基因型之间,直链淀粉含量差异显著;研究单缺失基因型发现,对直链淀粉含量减少效应最大的是Wx-B1b,减少效应最小的是Wx-A1b,而Wx-B1b和Wx-D1b没有显著差异;研究双缺失基因型发现,Wx基因合成直链淀粉的能力以Wx-B1a最高,Wx-A1a最低,而Wx-B1a和Wx-D1a差异很小.直链淀粉含量与株高、穗长、小穗数、穗粒数、千粒重等农艺性状相关不显著,表明淀粉品质育种可以与高产育种实现有机结合.直链淀粉含量与SDS-沉降值呈显著负相关(r=-0.726),说明直链淀粉含量降低在一定程度上有利于提高小麦营养与加工品质.全糯类型的淀粉糊化特性与其他类型显著不同,具有最高的峰值粘度和稀懈值,最低的低谷粘度、最终粘度、反弹值、峰值时间、糊化温度、起始糊化温度,表明糯小麦淀粉在食品和工业上具有特殊用途;稀懈值与直链淀粉含量呈极显著负相关(r=-0.969),其它粘度参数与直链淀粉含量呈显著正相关(最终粘度r=0.797,低谷粘度r=0.910、反弹值r=0.954、峰值时间r=0.970、糊化温度r=0.962、起始糊化温度r=0.932).表5参37     

Distribution of male and female mtDNA lineages in populations of blue mussels,Mytilus trossulus and M. galloprovincialis,along the Pacific coast of North America

Geographic variation in mitochondrial large subunit (16S) ribosomal RNA haplotypes was examined for blue mussels, Mytilus trossulus Gould, 1850 and M. galloprovincialis Lamarck, 1819, sampled from ten sites along the Pacific coast of the USA in January of 1993. Using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assays we determined haplotype frequencies for both the male and female mussel mitochondrial DNA (mtDNA) lineages. Populations from Morro Bay south to San Diego, California, contained only M. galloprovincialis male and female haplotypes, while those from Arcata Bay, California, north to Port Orford, Oregon, were fixed for M. trossulus haplotypes. Populations from Monterey Bay to Bodega Bay, California, contained a mixture of M. trossulus and M. galloprovincialis haplotypes. Overall only 2 of 97 heteroplasmic individuals had a mixed M. trossulus/M. galloprovincialis mitochondrial genotype indicating that hybridization is uncommon in the populations sampled. Further, there was no evidence of extensive introgression between these mussel taxa at the level of mtDNA. This is in contrast to previously published results which suggested the significant introgression of M. trossulus haplotypes into southern populations containing primarily M. galloprovincialis nuclear genotypes. We feel the discrepancy lies in the ability of our assays to detect haplotypes corresponding to both the male and female mtDNA lineages. Potential explanations for the lack of mtDNA introgression include, low levels of backcrossing between hybrids and parental taxa, epistatic interaction between nuclear and mitochondrial genes and the breakdown of a sex-specific inheritance pattern for mtDNA in hybrids.     

Mate choice among sympatric fur seals: female preference for conphenotypic males

When closely related species breed in sympatry, and where hybrids have lower fitness, reinforcement theory predicts that selection should favour mechanisms that reduce the probability of interspecific matings. If this situation arises among species that exhibit resource defence polygyny where males and females of different species reside in the same territories, there may be some conflict between mate choice based on territory-holding ability (sexual selection) and mate choice for correct species. We investigated this in a population of fur seals where three species are sympatric and where some females breed in the territories of heterospecific males, and where interspecific matings and hybrid pups are observed. The territorial status of males and the birthing sites of females were determined during daily observations, as were the movements of males and females, the location of matings and mating partners. DNA extracted from skin samples was used to determine paternities using DNA fingerprinting and the mtDNA genotype of individuals. Individuals were also classed on the basis of species-typical phenotype. We found that extra-territory inseminations (ETIs) were significantly more prevalent (67%) when territorial males and resident females were of different phenotype than when of similar phenotype (27%), but mtDNA genotype had no effect on the rate of ETIs. ETIs were probably by males with the same phenotype, as pups born to these females in the following season had the same phenotype as their mothers, suggesting they were not hybrids. These results suggest that within the resource defence polygynous mating system of these sympatric fur seals, female mate choice is more influenced by male phenotype than genotype. Contrary to our predictions, our study indicates that potential conflict between mate choice based on sexual selection and species recognition is unlikely, because females have some capacity to discriminate between males both within and between species on phenotypic traits additional to those under sexual selection. Although at least 25% of the pups born in this study were hybrid, this study can only support reinforcement theory if hybrids have reduced fitness. The fitness of hybrids among the species studied is currently unknown. Received: 19 January 1998 / Accepted after revision: 12 September 1998     

Genetic structure of hybrid mussel populations in the west of Ireland: two hypotheses revisited

In Ireland, mussels on exposed rocky shores constitute an interbreeding mixture of two forms of mussels, the blue mussel, Mytilus edulis, and the Mediterranean mussel, M. galloprovincialis. Results from an Irish study in the 1980s, using partially diagnostic allozyme markers, indicated that mussels higher up the shore were more galloprovincialis-like than those lower down. In this study we set out to test two hypotheses: (a) recruits arriving on the shore are composed of genetically distinct cohorts that settle preferentially at different levels on the shore, and maintain genetic distinctiveness into adulthood; (b) recruits are genetically homogeneous, but once settled they diverge genetically over time, due to within-habitat site specific-selection. The diagnostic Me 15/16 DNA marker was used to analyse the genetic composition of newly-settled spat recruiting to artificial substrates, which were placed at two-week intervals from May–October 2002, on the mid- and low shore areas of two exposed sites in Galway Bay. Adult mussels were also collected on each sampling date. Results did not support the preferential settlement hypothesis, i.e., the genetic composition of primary settlers (≤ 500 μm) was similar between tidal heights and shores. Neither was there evidence of post settlement selective mortality, as adults were genetically similar to settling spat. In spat and adults the frequency of the M. galloprovincialis allele was high (0.56–0.80), due to high frequencies of M. galloprovincialis (> 37%) and hybrid (> 33%) genotypes, and correspondingly low frequencies of the M. edulis genotype (< 11%). Adult mussels from a nearby sheltered estuarine site, while significantly different to exposed shore mussels, still had low frequencies of the M. edulis genotype (< 17%), indicating no apparent advantage for the genotype in this environment. There are indications that the genetic composition of mussels may be changing on the Atlantic coasts of Ireland.