线粒体DNA 序列分析在中国水域真海豚物种鉴定中的初步应用

真海豚包括长喙真海豚( Delphinus capensis) 和短喙真海豚( D. delphis) 2 种, 而中国水域的真海豚到底是哪一个种或是否同时有两个种的存在, 并不清楚。本研究测定了12 头中国水域真海豚mtDNA 控制区(control region) 366 bp 和细胞色素b (cytochrome b , cyt b) 基因336 bp 的序列, 并与已发表的其它真海豚的序列合并分析,初步鉴定中国水域真海豚的分类地位。结果表明, 中国水域的真海豚与东太平洋的长喙真海豚有相同的鉴别位点, 且两者之间的核苷酸歧异度(控制区: 1.93 ±0.22 % , cyt b 基因: 0.68 ±0.19 %) 显著低于与短喙真海豚之间的差异(控制区: 2.92 ±0.41 % , cyt b 基因: 0.95 ±0.27 %) 。通过MEGA (molecular evolutionary genetic analysis) 软件中的邻接法(neighbor joining) 进行的系统发生分析中, 中国水域的真海豚与长喙真海豚聚成一支, 有明显较近的亲缘关系。因此, 中国水域的真海豚在分类上应归属于长喙真海豚。     

中国哺乳动物多样性(第2版)

鉴于哺乳动物分类系统的修订、中国哺乳动物的新发现以及保育实践的需要,有必要更新中国哺乳动物多样性编目。在收集整理2015年3月以来发表的中国哺乳动物新种和新分布记录种的基础上,我们采用新的分类系统,综合作者的最新研究,补充了以前知之甚少的藏南地区哺乳动物信息,更新了中国哺乳动物多样性编目。主要修改有:(1)将鲸偶蹄类(Cetartiodactyla)列为总目,将鲸类与偶蹄类恢复为鲸目(Cetacea)和偶蹄目(Artiodactyla);(2)劳亚食虫目增加了新种霍氏缺齿鼩(Chodsigoa hoffmanni)、林猬一新种(Mesechinus sp.)及由亚种提升为种的烟黑缺齿鼩(Chodsigoa furva);(3)翼手目增补了梵净山管鼻蝠(Murina fanjingshanensis)、渡濑氏鼠耳蝠(Myotis rufoniger)和葛氏菊头蝠(Rhinolophus subbadius),删除了毛须鼠耳蝠(Myotis hirsutus)和琉球长翼蝠(Miniopterus fuscus);(4)灵长目增补了高黎贡白眉长臂猿(Hoolock tianxing)、戴帽叶猴(Trachypithecus pileatus)、懒猴(Nycticebus coucang)和西白眉长臂猿(Hoolock hoolock);(5)食肉目增补了分布在中国藏南的懒熊(Melursus ursinus)、亚洲胡狼(Canis aureus)、孟加拉狐(Vulpes bengakensis)、灰獴(Herpestes edwardsii)和渔猫(Felis viverrinus);(6)依据Wilson和MittermeierHandbook of the Mammals of the World,Vol.2,Ungulates(2012)的偶蹄类分类系统,重新厘定了中国偶蹄目动物分类。偶蹄目增加了阿尔泰盘羊(Ovis ammon)、哈萨克盘羊(O.collium)、高黎贡羚牛(Budorcas taxicolor)和印度麂(Muntiacus muntjak)。将中国境内的梅花鹿合并为Cervus nippon、驼鹿合并为Alces alces。删去了阿拉善马鹿(Cervus alashanicus)、四川马鹿(C.macneilli)和矮岩羊(Psuodois sharferi)。将分布在西双版纳的小鼷鹿定为鼷鹿未定种(Tragulus sp.);(7)鲸目增加了恒河豚(Platanista gangetica),删除了长喙真海豚(Delphinus capensis),将短喙真海豚(D.delphis)的中文名修改为真海豚;(8)啮齿目增加了小板齿鼠(Bandicota bengalensis)、小猪尾鼠(Typhlomys nanus)、墨脱松田鼠(Neodon medogensis)、聂拉木松田鼠(N.nyalamensis)以及由亚种提升为种的大猪尾鼠(Typhlomys daloushanensis);还增加了甘肃鼢鼠(Myospalax cansus)、比氏鼯鼠(Biswamoyopterus biswasi)、白腹鼠(Niviventer niviventer)、印度小鼠(Mus booduga)。删去了休氏壮鼠(Hadromys humei)。同时厘清了我国田鼠亚科Arvicolini族的分类;(9)兔形目增加了粗毛兔(Caprolagus hispidus)和尼泊尔黑兔(Lepus nigricollis)。理清了鼠兔属(Ochotona)的分类,降级了5个鼠兔种,提升了4个鼠兔亚种为种,增加了5个新种。中国有29种鼠兔分布,北美鼠兔(O.princeps)、斑颈鼠兔(O.collaris)、荷氏鼠兔(O.hoffinanni)、阿富汗鼠兔(O.rufescens)和草原鼠兔(O.pusilla)在中国没有分布。与2015年的《中国哺乳动物多样性》比较,本编目删除了21个种,新增了41个种,其中,新增了藏南地区分布的哺乳动物16种。截至2017年8月底,中国记录到哺乳动物13目56科248属693种,比《中国哺乳动物多样性》多1目1科3属20种。人们对18种中国哺乳动物的分类地位尚存在争议。中国有146种特有哺乳动物,占中国哺乳动物总数的21%。兔形目、劳亚食虫目和偶蹄目中的特有种比率分别为37%、35%和25%。     

中国东北六种藓类植物的细胞学观察

本文对我国东北产6种藓类的孢子母细胞减数分裂中期I的染色体数进行了报道。结果如下： 羽枝青藓Brachythecium plumosum （Hedw．)B．S．G．,n=15;钝叶绢藓Entodon obtusatus(Mitt) Jaeg．,n=11;东亚绢藓E．okamurae Mitt,n=11;丛本藓Anoctangium aestivum(Hedw．)Mitt．, n＝13;真藓Bryum argenteum Hedw．,n=10;尖叶美喙藓Eurhynchium eustegium(Besch．)Dix.,n=20+2m,其中前三种为首次报道。     

鹮嘴鹬越冬觅食地选择与食物资源调查

2010年1～3月在四川省稻城地区对有鹮嘴鹬(Ibidorhyncha struthersii)觅食的河段进行调查,发现鹮嘴鹬87只,密度为1.24只/km,集群平均个体数为(2.12±0.89)只/群。采用样方法调查其觅食地的生境特征,调查其觅食地样方41个,对照样方54个。逐步判别分析结果表明,影响鹮嘴鹬冬季觅食地选择的关键因子是:直径大于30 cm石头盖度、河心岛面积、干扰距离、水深、河滩的宽度。其觅食频率为(18.39±2.36)次/min(n=50),觅食成功率为29.39%±13.24%(n=50)。样方调查(n=50)发现9种食物资源,鹮嘴鹬觅食河段中石蛾(Trichoptera)幼虫(37.72%±12.96%)、石蝇(Plecoptera)幼虫(36.36%±6.06%)和甲壳类(17.76%±7.74%)比例较高,共占样方内食物数量91.84%。     

荒漠伯劳的递食位置与同胞竞争

亲鸟递食位置可以调控雏鸟之间的竞争,而异步孵化会使不同孵出顺序雏鸟的体况产生等级差异。雏鸟可以通过竞争巢中有利位置来获得更多的食物资源,从而提高自身生长发育速度和存活率。本研究于2013和2014年两年的4至8月对甘肃安西荒漠保护区桥子片区22巢荒漠伯劳(Lanius isabellinus)的递食行为进行研究。结果发现,荒漠伯劳亲鸟递食的位置主要集中在1个(n=13,比例超过50%)或2个(n=9,合并比例超过60%)位置上,具有一定的可预测性;处于亲鸟递食位置直线方向上的雏鸟获食次数显著高于两侧位置(n=22,P <0.001)。但异步孵化雏鸟的孵出顺序与其在巢内占据直线(df=4,F=0.211,P> 0.05)和两侧位置(df=4,F=0.068,P> 0.05)的次数都不具相关性;并且不同孵出顺序雏鸟间平均获食次数无明显差异(df=4,F=0.090,P> 0.05);拟合不同孵出顺序的雏鸟生长曲线发现,不同孵出顺序雏鸟的体重生长率也没有表现出明显差异(df=4,F=0.637,P>0.05)。研究结果表明,荒漠伯劳亲鸟趋于固定递食位置并向直线方...     

几种杀虫药剂敏感蚊类酯酶多态性的研究

通过蚊虫酯酶蛋白的淀粉凝胶电泳分析和基因组DNA的限制性酶切片段长度多态性(RFLPs)比较, 对尖音库蚊Culex pipiens、三带喙库蚊Culex tritaeniorhynchus和中华按蚊Anopheles sinensis有机磷杀虫药剂敏感种群的酯酶蛋白和结构基因的多态性进行分析。发现在蛋白质水平上,三带喙库蚊敏感种群(n=54)在酯酶α和β位点分别存在2个和3个等位基因,在DNA水平上有2.9%的个体具有与酯酶β1¹基因1.3 kb Cdna片段同源的1.3 kb单拷贝带存在。发现中华按蚊敏感种群 (n= 50)中具有低活性的非特异性酯酶存在,在蛋白质水平上,酯酶α和β位点各有一个等位基因;在DNA水平上,通过对单个蚊虫基因组DNA的研究未发现有与酯酶β1¹基因同源的酯酶编码基因的存在。对尖音库蚊北京敏感种群(n= 64)的研究发现,在酯酶α和β位点都存在5个等位基因,在DNA水平上,使用一个限制性内切酶(EcoRI),15只蚊虫的样本在酯酶β位点发现了5个等位基因,说明在尖音库蚊北京敏感种群的酯酶β基因周围存在着较大的中性多态性,在有机磷杀虫剂的选择下,这些中性多态性可能会成为基因扩增的潜在因素。     

RP-HPLC法测定北柴胡地上部分山柰酚的含量

目的:建立RP-HPLC法测定北柴胡地上部分山柰酚含量的色谱方法。方法:采用RP-HPLC,C18柱(150 mm×4.6 mm,5μm),流动相甲醇-(0.5%磷酸)水(体积比为48∶52),检测波长360 nm,柱温34℃。结果:山柰酚质量浓度在0~0.048 g/L内与峰面积呈良好的线性关系,r=0.999 5(n=6);平均回收率为100.7%,RSD=1.8%(n=6)。结论:测定方法准确,可靠,为北柴胡地上部分的质量评价提供了可靠的依据。     

四川省石渠县藏原羚秋季取食行为特征

20 0 3年 8～ 10月 ,用固定观察和扫描取样法对四川石渠县藏原羚 (Procaprapicticaudata)的取食行为进行了研究。设置 4 0个 2 0m× 2 0m的样地 ,测量藏原羚的 13个取食生境因子。利用单个样本的Kolmogorov Smirnovtest检验 ,呈正态分布的用参数检验 ,否则用非参数检验。结果显示 :(1)藏原羚主要以集群的形式取食 ,集群大小为 6 8头 (n =4 9) ,最大群为 34头 ;雄性群具有小集群的倾向 (即除存在独雄外 ,2～ 3头一群的群体数占 33 33% ,n =9) ,母子群也以小集群为主 ,两母子为一群的集群占 5 3% (n =15 ) ,但是没有发现<4头的雌性群。 (2 )藏原羚的取食时间以晨昏为主 ,取食高峰在早晨 (8:0 0～ 9:0 0 )和傍晚 (17:0 0～ 18:0 0 ) ,两者各占该时间段全部活动的 5 4 %以上。 (3)藏原羚更喜欢选择蒿草属、火绒草属和棘豆属中数种营养高的植物为食 ,比例高达 80 %以上。 (4) 13个生境因子的聚类和主成分分析表明 :前 4个主成分累积贡献率达到 71% ,能够反映藏原羚主要的取食生境特征 ;影响藏原羚取食生境选择的主要因子分为植物营养度 (特定的植被类型和中等的植被高度 )、干扰度 (隐蔽条件好、人为和动物干扰小 )、水源 (离水源较近和避风性良好 )3个方面。     

沟眶象转录组微卫星特征分析

本研究基于高通量测序获得的沟眶象Eucryptorrhynchus chinensis(Olivier)转录组数据,采用MISA(Micro Satellite)软件对其简单序列重复(simple sequence repeat,SSR)位点进行了高通量发掘。对筛选得到的1 kb以上的Unigene(17590条,占Unigene总数的26.98%)进行了SSR分析,结果发现含SSR的序列有1665条,共发现1823个SSR,平均32.52 kb出现一个SSR。沟眶象微卫星主要以三碱基重复类型为主(637,34.94%),其次为单碱基重复(576,31.60%)。共发现104种碱基重复基元,所占比例最高的为(A/T)n(30.39%),其次为(AT/AT)n(6.91%)。沟眶象SSR的平均长度为15.74 bp,长度大于20 bp的SSR仅占总数的12.70%。研究还发现沟眶象微卫星出现的频率和其长度呈极显著负相关(P0.01),相关系数为-0.572。研究结果为开发高多态性微卫星引物来进行沟眶象功能基因组学、种群遗传结构、种群遗传多样性等研究奠定了基础。     

河南董寨赤腹鹰孵卵节律与巢防卫行为

2016和2017年的5月至8月,在河南省董寨国家级自然保护区利用红外相机监控和野外直接观察赤腹鹰(Accipiter soloensis),对其孵卵节律和巢防卫行为进行了研究。为了更好地获得巢防卫数据,我们以人作为入侵者攀爬巢树,观察人停留在巢树上10 min内不同赤腹鹰个体的巢防卫行为。共发现赤腹鹰繁殖巢52个,累计拍摄红外照片661 306张,将15个繁殖巢内的30只个体的巢防卫行为分成了4个等级。研究表明:1)雄鸟的巢防卫等级与雄鸟的日孵卵次数(r=0.751,n=15,P0.01)、雄鸟日孵卵时间(r=0.803,n=15,P0.01)、每日雌雄孵卵总时间(r=0.527,n=15,P0.05)均呈显著正相关,雌鸟的巢防卫等级与雄鸟的日孵卵次数(r=0.717,n=15,P0.01)、雄鸟的日孵卵时间(r=0.619,n=15,P0.05)呈显著正相关(Sperman rank correlation);2)雌鸟巢防卫强度与雄鸟巢防卫强度呈显著正相关(r=0.743,n=15,P0.01);3)亲鸟的平均离巢时间与雄鸟的日孵卵次数(r=﹣0.680,df=11,P0.05)、雄鸟的日孵卵时间(r=﹣0.640,df=11,P0.05)、雌鸟的孵卵次数(r=﹣0.558,df=11,P0.05)、每日雌雄孵卵总时间(r=﹣0.772,df=11,P0.01)均呈负相关。可见,赤腹鹰的巢防卫强度和孵卵投入密切相关,并且配偶间的巢防卫行为存在相似性,可能与配偶选择和学习行为有关。     

Intestinal length of three California pinniped species

Forty-eight intestinal tracts, extracted from both sexes of California sea lions, Harbour seals and Northern elephant seals, were measured. The majority of intestinal tracts were removed from stranded animals that died from various causes. The sea lions and elephant seals, approximately equal in size, were larger than the Harbour seals. All species possess a small intestine which is significantly longer than even the entire gastrointestinal tract of herbivores of comparable size. Elephant seal small intestines, averaging approximately 25 times the seal's body length, were considerably longer than the small intestines of either sea lions (averaged more than 18 times the body length) or Harbour seals (averaged nearly 16 times the body length). However, the large intestines of elephant seals were shorter than either of the other two species. Among the sea lions and Harbour seals the large intestines were approximately equal in length. Sea lions and Harbour seals also showed a close correlation between standard length and total intestinal length. Among elephant seals these two parameters showed greater variability. The functional significance of the extremely long small intestine remains unclear. Certainly, the large body mass and high energy requirements of these animals has contributed to the development of a long intestinal tract. It also appears likely that diet and the high motility rate of digesta influenced the intestinal development. Comparatively, the significantly shorter large intestine of elephant seals probably relates to this species' remarkable capabilities in water conservation and metabolic water retention.     

Leptospirosis in northern elephant seals (Mirounga angustirostris) stranded along the California coast

Leptospirosis was identified in six northern elephant seals (Mirounga angustirostris) that were stranded in 1995 along the coast of California (USA). Histologic lesions in all seals included tubulointerstitial nephritis with tubular degeneration and necrosis. Infection was confirmed through identification of spirochetes using an immunohistochemical stain for Leptospira sp. antigens. One affected seal had an elevated titer to Leptospira interrogans serovar pomona. Four of the six seals developed leptospirosis during rehabilitation, and two seals had evidence of exposure in the wild. Potential sources of infection during rehabilitation include other elephant seals, California sea lions (Zalophus californianus), Pacific harbor seals (Phoca vitulina richardsii), or free-ranging wildlife. These results indicate that northern elephant seals are susceptible to leptospirosis and can develop disease both in the natural environment and in a rehabilitation setting.     

Haematological and rheological characteristics of blood in seven marine mammal species: physiological implications for diving behaviour

The haeniatological and rheological characteristics of blood from seven marine mammal species have been examined to determine the relationship between increased haematocrit. which is correlated with the ability to increase aerobic dive limits. and blood viscosity. The species examined reflect adaptations to a variety of marine niches ranging from coastal to pelagic to iceedge environments. and exhibit a wide range of diving behaviours. Average haematocrits ranged from43–45% in bottlenose dolphins. killer whales and California sea lions to more than 60% in the deeper diving species (beluga whales and northern elephant seals). Whole blood viscosity () increased exponentially with haematocrit (= 0.96*e^0-0335*Hct). representin a two-fold increase from 4.1 cP for killer whale blood to 8.9 cP for northern elephant seal. There was no apparent compensatory mechanism to reduce viscosity at any shear rate. The optimal haematocrit for oxygen transport was calculated to be40–50% for all species tested. The species with lower haematocrits were within optimal values for oxygen transport. while the two species with the highest haematocrits (beluga whales and northern elephant seals) were above predicted optimal oxygen transport values. On the basis of comparisons of the diving behaviour of these seven species, we suggest that marine mammal species with the greatest adaptation for increased oxygen stores via increased haematocrit have the capacity for deep, long-duration dives, but a limited oxygen transport capacity. We predict that this compromise precludes fast sustainable swimming behaviour in these species.     

Total mercury in stranded marine mammals from the Oregon and southern Washington coasts

Muscle samples from 105 marine mammals stranded along the Oregon and Washington coasts (2002–2009) were tested for levels of total mercury (THg) by Cold Vapor Atomic Fluorescence Spectrometry. The THg present is in the form of the highly toxic methylmercury. After normalizing tissue to 75% water weight, Steller sea lions and northern elephant seals exhibited the highest mean concentrations of THg followed by harbor seals, harbor porpoises, and California sea lions, 0.34 ± 0.278, 0.34 ± 0.485, 0.21 ± 0.216, 0.17 ± 0.169, and 0.15 ± 0.126 mg/kg normalized wet weight (ww), respectively. The mean normalized values demonstrate limited muscle methylmercury accumulation in these species in the Pacific Northwest. However, actual ww concentrations in some of the stranded carcasses may pose a risk to scavengers. Normalizing muscle mercury concentrations eliminated the variability from desiccation, and allowed for a clearer indication of the amount of mercury the animal accumulated before stranding.     

The role of Steller sea lions in a large population decline of harbor seals

We provide the first direct evidence that Steller sea lions will prey on harbor seals. Direct observations of predation on marine mammals at sea are rare, but when observed rates of predation are extrapolated, predation mortality may be found to be significant. From 1992 to 2002, harbor seals in Glacier Bay declined steeply, from 6,200 to 2,500 (∼65%). After documenting that Steller sea lions were preying on seals in Glacier Bay, we investigated increased predation by sea lions as a potential explanation for the large decline. In five independent data sets spanning 21–25 yr and including 14,308 d of observations, 13 predation events were recorded. We conducted a fine-scale analysis for an intensively studied haul-out (Spider Island) and a broader analysis of all of Glacier Bay. At Spider Island, estimated predation by sea lions increased and could account for the entirety of annual pup production in 5 of 8 yr since 1995. The predation rate, however, was not proportional to the number of predators. Predation by Steller sea lions is a new source of mortality that contributed to the seal declines; however, life history modeling indicates that it is unlikely that sea lion predation is the sole factor responsible for the large declines.     

DARK ADAPTATION AND VISUAL SENSITIVITY IN SHALLOW AND DEEP-DIVING PINNIPEDS1

Pinnipeds forage almost exclusively underwater. Consequently, observing them is difficult and relatively little is known of how they use their senses to locate prey, avoid predators, and navigate while diving. Vision has been presumed to be of primary importance, although previous measurements of visual functioning in pinnipeds have been restricted to just a few shallow-diving species. As diving pinnipeds experience rapid changes in light levels during descent/ascent and low light levels at depth, it has not been clear whether they possess visual capabilities adequate for use while diving, particularly in the case of deep-diving species. To examine this issue, behavioral psychophysics have been used to assess and compare the dark adaptation rates and relative light sensitivities of a deep-diving pinniped (northern elephant seal, Mirounga angustirostris), two shallow-diving species (California sea lion, Zalophus californianus, and harbor seal, Phoca vitulina), and a human subject. In comparison to the human subject, both the California sea lion and the harbor seal dark-adapted relatively quickly and were more light sensitive. These findings suggest that both of these species are well suited for vision in the moderately dim shallow-water environments in which they dive to forage. In contrast, the elephant seal reached complete dark adaptation in less than half the time taken by the other pinnipeds, and it was significantly more light sensitive. Unlike the shallower-diving species, the visual abilities of the elephant seal are commensurate with the extreme conditions experienced while deep diving. Thus, we conclude that elephant seals are sufficiently adapted to rely on vision underwater, even while diving to depths in excess of 1000 meters where bioluminescence may be the sole source of ambient light.     

Harbor seal population decline in the Aleutian Archipelago

Populations of Steller sea lions, northern fur seals, and northern sea otters declined substantially during recent decades in the Bering Sea and Aleutian Islands region, yet the population status of harbor seals has not been assessed adequately. We determined that counts obtained during skiff‐based surveys conducted in 1977–1982 represent the earliest estimate of harbor seal abundance throughout the Aleutian Islands. By comparing counts from 106 islands surveyed in 1977–1982 (8,601 seals) with counts from the same islands during a 1999 aerial survey (2,859 seals), we observed a 67% decline over the ～20‐yr period. Regionally, the largest decline of 86% was in the western Aleutians (n= 7 islands), followed by 66% in the central Aleutians (n= 64 islands), and 45% in the eastern Aleutians (n= 35 islands). Harbor seal counts decreased at the majority of islands in each region, the number of islands with >100 seals decreased ～70%, and the number of islands with no seals counted increased ～80%, indicating that harbor seal abundance throughout the Aleutian Islands was substantially lower in the late 1990s than in the 1970s and 1980s.     

Characterization of Otostrongylus circumlitus from Pacific harbor and northern elephant seals

Otostrongylus circumlitus (Railliet, 1899) from Pacific harbor seals (Phoca vitulina richardsi) and northern elephant seals (Mirounga angustirostris) were examined using morphological and molecular methods to determine whether northern elephant seals along the central California coast are infected by the same species of Otostrongylus as are Pacific harbor seals in the same area. Fixed nematodes were examined and measured using light microscopy. The polymerase chain reaction (PCR) was used to amplify and sequence the second internal transcribed spacer (ITS-2) and D3 expansion (26S) regions of ribosomal DNA of O. circumlitus from Pacific harbor and northern elephant seals. The ITS-2 region was also amplified from Parafilaroides sp. from the Pacific harbor seal, northern elephant seal, and California sea lion (Zalophus californianus) and used for restriction fragment length polymorphism (RFLP) analysis. Morphologically, it was not possible to distinguish O. circumlitus from Pacific harbor and northern elephant seals, and over a consensus length of 443 base pairs (bp) for ITS-2 and 321 bp for D3 the sequences of O. circumlitus from both hosts were identical. With the PCR-RFLP assay, it was possible to distinguish O. circumlitus from Parafilaroides sp. The results suggest that O. circumlitus is the same species in Pacific harbor and northern elephant seals, and molecular methods make it possible to distinguish this nematode from related nematodes.     

Parasites and associated pathology observed in pinnipeds stranded along the Oregon coast

Forty-two seals and sea lions found dead along the Oregon Coast were examined for parasites and associated pathology. Nematode infections of the lung and/or gastrointestinal tract were the primary cause of death in 5 of 42 animals examined. New distribution records were established for Pricetrema zalophi and Zalophotrema hepaticum. New host records include Z. hepaticum and Diphyllobothrium cordatum in the Steller's sea lion (Eumetopias jubatus); Nanophyetus salmincola in the California sea lion (Zalophus californianus); P. zalophi in the harbor seal (Phoca vitulina); and P. zalophi, Trigonocotyle sp. and Otostrongylus circumlitus in the northern elephant seal (Mirounga angustirostris).