The reproductive cycle of the thorny skate (Amblyraja radiata) in the western Gulf of Maine

The thorny skate (Amblyraja radiata) is a large species of skate that is endemic to the waters of the western north Atlantic in the Gulf of Maine. Because the biomass of thorny skates has recently declined below threshold levels mandated by the Sustainable Fisheries Act, commercial harvests from this region are prohibited. We have undertaken a comprehensive study to gain insight into the life history of this skate. The present study describes and characterizes the reproductive cycle of female and male thorny skates, based on monthly samples taken off the coast of New Hampshire, from May 2001 to May 2003. Gonadosomatic index (GSI), shell gland weight, follicle size, and egg case formation, were assessed for 48 female skates. In general, these reproductive parameters remained relatively constant throughout most of the year. However, transient but significant increases in shell gland weight and GSI were obser ved during certain months. Within the cohort of specimens sampled monthly throughout the year, a subset of females always had large preovulatory follicles present in their ovaries. With the exception of June and September specimens, egg cases undergoing various stages of development were observed in the uteri of specimens captured during all other months of the year. For males (n=48), histological stages III through VI (SIII−SVI) of spermatogenesis, GSI, and hepatosomatic index (HSI) were examined. Although there appeared to be monthly fluctuations in spermatogenesis, GSI, and HSI, no significant differences were found. The production and maintenance of mature spermatocysts (SVI) within the testes was observed throughout the year. These findings collectively indicate that the thorny skate is reproductively active year round.

Age and growth estimates of the thorny skate (Amblyraja radiata) in the western Gulf of Maine

The northwest Atlantic population of thorny skates (Amblyraja radiata) inhabits an area that ranges from Greenland and Hudson Bay, Canada, to South Carolina. Despite such a wide range, very little is known about most aspects of the biology of this species. Recent stock assessment studies in the northeast United States indicate that the biomass of the thorny skate is below the threshold levels mandated by the Sustainable Fisheries Act. In order to gain insight into the life history of this skate, we estimated age and growth for thorny skates, using vertebral band counts from 224 individuals ranging in size from 29 to 105 cm total length (TL). Age bias plots and the coefficient of variation indicated that our aging method represents a nonbiased and precise approach for the age assessment of A. radiata. Marginal increments were significantly different between months (Kruskal-Wallis P<0.001); a distinct trend of increasing monthly increment growth began in August. Age-at-length data were used to determine the von Bertalanffy growth parameters for this population: L∞ = 127 cm (TL) and k= 0.11 for males; L∞ = 120 cm (TL) and k= 0.13 for females. The oldest age estimates obtained for the thorny skate were 16 years for both males and females, which corresponded to total lengths of 103 cm and 105 cm, respectively.

山西煤核中辉木植物二个新种的研究--山西枝蕨和山西始莲座蕨

辉木植物是莲座蕨目在晚古生代最重要的成员，广泛分布于当时处于热带－亚热带气候条件下的晚石炭世－二叠纪欧美植物区和华夏植物区。目前欧美植物区晚石炭世的辉木植物已经研究得非常深入和全面，但相对来说二叠纪的辉木植物的研究，尤其是关于其非茎器官的研究要薄弱得多。中国山西太原西山煤田早二叠世早期太原组7号煤层煤核中产有丰富的辉木植物各种器官化石，这就为深入了解二叠纪辉木植物的形态、解剖以及辉木植物的系统发育与演化提供了重要的化石材料。本论文利用国际上研究煤核时广泛采用的揭膜法，深入研究了山西煤核中2种分散保存的辉木植物器官：羽轴－山西枝蕨（新种）和生殖羽片－山西始莲座蕨（新种）。由于目前尚无有关二叠纪具解剖构造的辉木植物羽轴的详细研究的报道，因此，山西枝蕨（新种）是国内外目前为止第一种研究得最详细的二叠纪具解剖构造的辉木植物羽轴，它与欧美植物区枝蕨属已有的几个种（均为晚石炭世）的主要区别在于：前者为背腹扁状，后者则为两侧扁状;前者具较发育的鳞片，后者一般没有;前者的表皮下方有一条含有较大的单宁质细胞的薄壁组织带，后者没有;前者的内维管束呈“C���形，较大，位于正中央，后者的内维管束一般呈“W���形，较小，位于一侧。山西始莲座蕨（新种）是目前为止国内第一种（世界第二种）详细研究的二叠纪具解剖构造的两侧对称形的辉木植物聚合囊，同时也是目前国内发现的时代最早的华夏植物区两侧对称形的莲座蕨目聚合囊（包括印痕－压型化石和具解剖构造的矿化化石），它与欧美植物区始莲座蕨属已有的2个种（均为晚石炭世）的主要区别在于：前者的聚合囊囊托维管化，后者的囊托中无维管组织存在;前者的孢子囊侧壁细胞在近顶端呈明显的径向伸长状，后者的孢子囊侧壁细胞的形状和大小在孢子囊的上下没有很明显的变化;前者的孢子很小，数量多，纹饰简单，后者的孢子大，数量少，纹饰复杂。总的来说，本文所研究的二个新种与欧美植物区同属其它种之间的区别要大于后者彼此之间的区别，这可能是由于处于不同的植物地理区，经过长期地理隔绝和平行演化的结果。本研究成果不仅丰富了我们对二叠纪辉木植物非茎器官解剖构造的认识，而且对今后开展华夏植物区二叠纪辉木植物的分类、系统发育和演化以及整体植物的研究，都具有重要的作用和意义。