Morphological Form Variation in a Loricate Rotifer,Keratella tropica APSTEIN from a Perennial Pond,Janaktal, Gwalior,India

Morphological form variation in a loricate rotifer, Keratella tropica APSTEIN is decribed. Form variation in this rotifer involves appearance and development of the left postero-lateral spine. The right postero-lateral spine varies, too. It increases with increasing length of lorica and left postero-lateral spine. Three morphological forms, viz. reducta, asymmetrica and heterospina are recognized.     

Linear growth in spines from Acanthaster planci (L.) involving growth lines and periodic pigment bands

We report the first observations of a linear growth pattern in aboral spine ossicles of adult Acanthaster planci (L.). This is unlike the spine development of other echinoderms. Growth in aboral spine ossicles of A. planci is essentially by addition of stereom at the base and the spine's growth history is preserved along its length. There are numerous growth lines perpendicular to the long axis of the ossicle. These are clearly evident in longitudinal spine sections and apparently caused by frequent growth episodes. There are periodic pigment bands which are parallel to the growth lines and evident on the surface of the ossicle. Basal growth of the spine ossicle and the nature of the growth lines were confirmed by tetracycline staining. Size/frequency analyses of a population of A. planci from Davies Reef (GBR) found spine ossicle growth, but not body diameter growth, over the six month period between sampling dates. The additional pigment banding in spine ossicles of 4 individuals recaptured after 6 months suggests that pigment bands are laid down seasonally. If pigment band cyclicity is validated, it offers a simple method for ageing adults of A. planci in field populations.     

Effects of an Ostracod (Cypris pubera) on the Rotifer Keratella tropica: Predation and Reduced Spine Development

This study investigates two different effects of an ostracod on a rotifer. The rotifer Keratella tropica and the ostracod Cypris pubera were cultured on the alga Cryptomonas erosa. Adult ostracods (2.2 mm body length) significantly reduced the population growth rate (r day^–1) of K. tropica from 0.42 to 0.13. Individuals of this size ingested live rotifers and produced fecal pellets with rotifer loricas. Smaller ostracods (both 0.59 and 1.61 mm body lengths) did not affect K. tropica 's population growth rate. Surprisingly, C. pubera significantly inhibited spine development in K. tropica. Rotifers cultured with juvenile, non‐predatory ostracods had similar lorica lengths but right and left posterior spines that were 10 and 30% shorter, respectively. The spine reduction induced by the ostracod kairomone is in striking contrast to the spine elongation induced in this rotifer by kairomones from copepods, cladocerans and Asplanchna. In shallow ecosystems, large ostracods that swim in the plankton may be important predators of rotifers. In addition, the presence of ostracods in plankton communities may be one of many factors affecting rotifer spine development. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Induction of different defences by two enemies in the rotifer Keratella tropica: response priority and sensitivity to enemy density

1. Keratella tropica has qualitatively distinct spine‐development responses to kairomones released by the predatory rotifer Asplanchna and the cladoceran interference competitor Daphnia. Asplanchna induces a fourfold lengthening of the right posterior spine (to c.100 μm), a shortening or loss of the left posterior spine and a lengthening of two pairs of anterior spines. Daphnia induces a moderate elongation of both right and left posterior spines. This study tests three hypotheses regarding the sensitivity of these responses to enemy density, and the response priority when both enemies are present. 2. First, since K. tropica and Brachionus calyciflorus have similarly pronounced and effective spine‐development responses to Asplanchna, with no appreciable demographic cost, they should be similarly sensitive to Asplanchna density. This was the case. Both showed an exponential response to increasing Asplanchna density, well described by an asymptotic exponential regression model, and exhibited 50% maximal spine development at statistically similar Asplanchna densities–2.5 and 1.7 μg dry weight L^?1 (1.8 and 1.2 individuals L^?1), respectively. Strong selection for these Asplanchna‐induced responses clearly has led to a coupling of exuberant and effective morphological defence with an unrivalled sensitivity to predator density. 3. Second, since K. tropica’s response to Daphnia is much less pronounced and effective than its response to Asplanchna, it should be less sensitive to Daphnia density. This hypothesis was supported. Spine development increased linearly with increasing Daphnia density and was 50% maximal at 454 μg dry weight Daphnia L^?1, a biomass density 180 times greater than that inducing a comparable response to Asplanchna. 4. Third, since K. tropica’s response to Daphnia does not reduce Asplanchna predation, K. tropica should respond to Asplanchna when both enemies are present at densities sufficient to induce spine development. This was the case. The presence of Daphnia neither reduced nor increased the length of the right posterior spine; it only limited the extent to which the left spine was reduced or lost.     

Cyclomorphosis in Keratella tropica (Apstein) of Lake Asejire,Nigeria

Of one thousand, one hundred and four (1104), Keratella tropica collected with a 55 m mesh plankton net from the surface of Lake Asejire from February 1974 to February 1976 lorica length and width, and the lengths of the posterior spines were measured.Lake Asejire K. tropica are among the smallest in Africa. Variations in the patterns of spine length development were independent of season as individuals without left posterior spines and with relatively long left and right posterior spines occurred as commonly in the rainy as in the dry season months.Correlations between K. tropica dimensions and thirty environmental factors underscore the importance of physical environmental factors and point to biological and genetic factors as determinants of the patterns of cyclomorphosis in K. tropica.     

温度对矩形龟甲轮虫生命表统计学参数和形态特征的影响

应用单个体培养方法研究了温度(10℃、15℃、20℃和25℃)对双后棘刺、单后棘刺和无后棘刺矩形龟甲轮虫的净生殖率、内禀增长率、世代时间、平均寿命和后代混交率等生命表统计学参数以及后代体长、体宽、前中棘刺长、左右两前侧棘刺长、左右两后棘刺长、后棘刺数目等形态参数的影响.结果表明,各生命表统计学参数和后代形态参数在3种形态型轮虫间的差异因温度的不同而异,它们对温度升高的反应也因轮虫形态型的不同而异.温度显著影响轮虫的内禀增长率、世代时间、平均寿命和后代所有的形态参数(P＜0.05);形态型显著影响轮虫后代的体长、前中棘刺长和左右两后棘刺长(P＜0.05),但对轮虫的生命表统计学参数均无显著影响(P＞0.05);而温度和形态型的交互作用显著影响轮虫的世代时间和后代的形态参数(P＜0.05).3种形态型轮虫间,双后棘刺轮虫后代的体长(122.1±0.6μm)显著短于无后棘刺和单后棘刺轮虫后代的体长(分别为126.3±0.7μm和125.1±0.7 μm),前中棘刺长(32.5±0.3 μm)显著长于无后棘刺和单后棘刺轮虫后代的前中棘刺长(分别为31.l±0.3μm和30.8±0.3μm),左后棘刺长(31.2±1.0μm)和右后棘刺长(32.3±0.9 μm)均与单后棘刺轮虫后代的(分别为29.5±0.8 μm和31.5±0.6 μm)相似,但显著短于无后棘刺轮虫后代(分别为36.7±1.5 μm和37.3±1.6μm).矩形龟甲轮虫后代的棘刺长、体宽和体长之间的关系也受温度和形态型的影响.     

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub

• Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient.
• Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes.
• Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude.
• The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

     

Morphological variation of <Emphasis Type="Italic">Keratella cochlearis</Emphasis> (Gosse) in Myanmar (Burma) in relation to zooplankton community structure

Keratella cochlearis was present in 27 of 35 water bodies sampled in Myanmar, and was the most abundant rotifer in 10. Measurements of lorica length and posterior spine length from 20 localities showed that posterior spine length varied both with lorica length and with the composition of the crustacean zooplankton. Long spines were associated with dominance by Heliodiaptomus. The shortest spines were found in samples dominated by cladocerans or cyclopoid copepods. Posterior spine length was positively correlated with the number of diaptomid copepods. Forms without posterior spines were found in 17 localities. The lorica lengths of these spineless forms were generally similar to those of co-occurring spined forms (r = 0.68), but in a few samples the loricas of the spineless forms were significantly larger. These larger forms are similar to the ‘aspina’ forms recently recognised in the River Thames in England. These samples were dominated by cladocerans or cyclopoid copepods. In one locality spineless forms were found without spined forms. The crustacean zooplankton in this locality was also dominated by cladocerans. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Predator-specific inducible defenses in the rotifer Keratella tropica

1. A Patagonian strain of Keratella tropica has very different induced morphological responses to two predators – the carnivorous rotifer Asplanchna brightwelli and the interference competitor Daphnia pulex. Asplanchna induces the most exuberant morph. Compared to the basic morph, it has a fourfold longer right posterolateral spine (up to c. 115 μm), greatly elongated anterolateral and anterosubmedian spines, and no left posterolateral spine. Transitional morphs have an incompletely developed right posterolateral spine and a reduced left posterolateral spine. Daphnia induces moderate development of both posterior spines but no elongation of any anterior spines. Induction of these morphs by Asplanchna and Daphnia is mediated by kairomones. 2. The Asplanchna‐induced morph is much better defended against large (0.9 mm) Asplanchna than either the basic or Daphnia‐induced morph. The long right posterolateral spine usually prevents capture or ingestion. The Asplanchna‐ and Daphnia‐induced morphs are similarly susceptible to interference from large (3 mm) D. pulex. 3. Life‐table experiments with cohorts of the basic and Asplanchna‐induced morphs at 5 × 10³ and 2 × 10⁴ cells of Cryptomoas erosa per millilitre indicate little or no cost of the induced defense. Lifetime fecundity (13–15 offspring per female) did not differ significantly between morphs. The mean intrinsic rate of natural increase (r_m day⁻¹) of the induced morph was very slightly but significantly lower than that of the basic morph at the lower food concentration (0.46 versus 0.48) but no different from it at the higher food concentration (0.53 versus 0.54). However, spine development may involve undetermined allocation costs and environmental costs relating to interactions with other organisms. 4. It is not clear why K. tropica has separate induced responses to Asplanchna and Daphnia. Moderate spine development probably reduces damage or ingestion by small (<1.5 mm) daphniids, as in other species of Keratella, but further development may confer no protection against larger ones. Thus, the ratio of benefit to cost with daphniids (and other cladocerans) may be highest for intermediate spine development. In contrast, much greater spine development seems necessary for effective defense against Asplanchna. The more moderate response to Daphnia also may reflect less likely spatial and temporal overlap.     

Evolutionary stasis despite selection on a heritable trait in an invasive zooplankton

Invasive species are one of the greatest threats to ecosystems, and there is evidence that evolution plays an important role in the success or failure of invasions. Yet, few studies have measured natural selection and evolutionary responses to selection in invasive species, particularly invasive animals. We quantified the strength of natural selection on the defensive morphology (distal spine) of an invasive zooplankton, Bythotrephes longimanus, in Lake Michigan across multiple months during three growing seasons. We used multiple lines of evidence, including historic and contemporary wild‐captured individuals and palaeoecology of retrieved spines, to assess phenotypic change in distal spine length since invasion. We found evidence of temporally variable selection, with selection for decreased distal spine length early in the growing season and selection for increased distal spine length later in the season. This trend in natural selection is consistent with seasonal changes in the relative strength of non‐gape‐limited and gape‐limited fish predation. Yet, despite net selection for increased distal spine length and a known genetic basis for distal spine length, we observed little evidence of an evolutionary response to selection. Multiple factors likely limit an evolutionary response to selection, including genetic correlations, trade‐offs between components of fitness, and phenotypic plasticity.     

Evolution ofNaso thynnoides and the status ofN. minor (Acanthuridae; Actinopterygii)

Naso minor was described from a single specimen (Smith, 1966). Only one other specimen has since been reported (Randall, 1986). The species apparently differed fromN. thynnoides in the ratio of fork length to head length and eye diameter, the shape of the caudal peduncle spine, and in number of dorsal spines. Collections of 24 specimens of four- and five-spined individuals (putatively assigned to both species) from the Philippines revealed that the first three differences are not valid. However, spine number, the length of the nasal groove, the pigmentation of the basal plate of the caudal peduncle spine, and the morphology of the first dorsal-fin pterygiophore confirm the distinctness of the two species.     

Maternal age and spine development in the rotifer Brachionus calyciflorus: increase of spine length with birth orders1

1. Maternal effects have long been known to influence phenotypic plasticity in rotifers. Females in Brachionus calyciflorus and several other species produce long‐spined offspring when the predatory rotifer Asplanchna is present; B. calyciflorus also develops short spines when food concentrations are low. These spines protect against predation and decrease food threshold concentrations. 2. Some strains of B. calyciflorus develop long spines even in the absence of Asplanchna and other environmental stimuli. We demonstrate in this study that spine length in such cases is dependent on the age of the mother. 3. In strains from Florida and Georgia, offspring spine length increased significantly with birth order, sometimes to lengths formerly observed only in the presence of Asplanchna. Significant variation in this trait was found among and within clones of a strain. Offspring body size also increased with maternal age. This is the first time maternal age has been shown to affect rotifer morphology. 4. These birth‐order effects may have important ecological implications and explain phenotypic plasticity and polymorphism in body size and spine length in populations when predators are absent and food concentrations are high. They may be a bet‐hedging mechanism to assure adaptation to rapid changes in predation pressure or food conditions.     

Extreme cyclomorphosis in Daphnia lumholtzi

1. Daphnia lumholtzi, not previously reported in North America, was found in a small reservoir in East Texas in January, 1991, This species possesses extremely long spines and large fornices; an allometric study was performed to detect any temporal differences in specific growth rates of the spines relative to the body. 2. In nature, mature females attained 1.8mm body length, excluding spines, but when the head and tail spines are included, the total length reached a maximum of 5.6mm. 3. Differences in the growth patterns of the head spine and the tail spine relative to the body existed for D. lumholtzi from January to March 1991. Both the head and the tail spines grew at a faster rate than the body during all 3 months although the rates varied between them. The results contradict the invertebrate predation hypothesis (Dodson, 1974) in that D. lumholtzi's head and tail spines continue to grow during adulthood instead of stopping after the juvenile instars. 4. The head spines grew at a constant allometric rate over time while the tail spine grew faster as the temperature increased. Both varied significantly in length over the 3 months, with animals having the shortest spines in February and the longest in March.     

Two morphological types in the reproductive stock of three-spined stickleback,Gasterosteus aculeatus,in Lake Harutori,Hokkaido Island

Synopsis Two morphological types of the trachurus form (completely plated morph) of three-spined stickleback, Gasterosteus aculeatus, are found in Lake Harutori, Kushiro, east district of Hokkaido Island. For convenience, the two forms are referred to as ‘large type’ and ‘small type’ on the basis of body length (discrimination at 70 mm in length). The two types were examined for morphometric, meristic and reproductive characteristics. They differ in body length, the number of lateral plates, means of the 2nd dorsal spine length/body length and of the pelvic spine length/body length, the relationship between body length and head length, between body length and gonad weight, between body weight and gonad weight, and between body length and ovarian egg number; significant differences were present for each sex. These two types were compared with the anadromous stickleback migrating into the freshwater area near Lake Harutori to breed. The anadromous fish was morphologically much more similar to the large type than the small type. It is suggested that the large type is also an anadromous form and the small type is the permanent freshwater resident.     

Predator‐induced spine length and exocuticle thickness in Leucorrhinia dubia (Insecta: Odonata): a simple physiological trade‐off?

1. Morphological defence structures evolve against predators but are costly to the individual, and are induced only when required. A well‐studied example is the development of longer abdominal spines in dragonfly larvae in the presence of fish. Numerous attempts to discover trade‐offs between spine size and behaviour, development time or body size have, however, produced little evidence. 2. We considered a physiological trade‐off. Spines consist of cuticle and using material to build longer structures may result in less material remaining elsewhere. We therefore measured exocuticle thickness at nine locations on Leucorrhinia dubia larvae from habitats with and without fish. 3. Our results show a significant effect of the interaction between fish presence and spine length on head and fore leg exocuticle thickness. Relative thickness increased with relative length of lateral spine 9 in the absence of fish, whereas no such relationship existed with fish. Hence, synthesis and secretion of cuticle material occur as a trade‐off when larvae react to fish presence. 4. We assume the mechanism to be a selective synthesis of material with different responses in different parts of the larval body. These findings offer a new angle to the fish/spine trade off debate.     

剪形臂尾轮虫形态的时空变化及其与生态因子间的关系

对芜湖市镜湖和汀棠湖中剪形臂尾轮虫(Brachionus forficula)的发生及其形态特征进行了一年的观察,并分析了其与环境因子间的关系。结果表明,镜湖中,剪形臂尾轮虫出现于7月至10月,且仅存在短后棘刺型个体;2样点内,除了前外棘刺长以外,轮虫的其他各形态参数均随季节显著变化,形态参数的样点间差异也因季节的不同而异;轮虫的各形态参数均随pH的升高而延长,随过滤水体中叶绿素a含量和水体中总叶绿素a含量的升高而缩短;体长和体宽均随晶囊轮虫密度的升高而增大。汀棠湖中,短后棘刺型个体出现于6月至10月,而长后棘刺型个体仅出现于6月至8月;2种形态型个体同时存在时,长后棘刺型个体在种群中所占比例始终高于短后棘刺型个体,并与水温、水体中总叶绿素a含量以及枝角类、桡足类和晶囊轮虫的密度均呈显著的正相关;2样点轮虫短后棘刺型个体各形态参数均随季节显著变化;长后棘刺型个体在1号样点内仅前外棘刺和后棘刺长有显著变化,而2号样点内仅体长、体宽和后棘刺长有显著变化;2样点内长后棘刺型个体的体长、体宽以及前外棘刺和后棘刺均显著长于短后棘刺型个体;同一形态型个体形态参数的样点间差异因季节的不同而异;短后棘刺型个体的前外棘刺和后棘刺长均与水体中总叶绿素a含量呈显著的正相关,后者与过滤水体中叶绿素a含量和枝角类密度也呈显著的正相关;长后棘刺型个体的后棘刺长与桡足类密度呈显著正相关,前内棘刺长与水温、溶氧量和晶囊轮虫密度呈显著负相关。两湖泊内剪形臂尾轮虫的后棘刺长和体长之间均呈显著的正相关,提示其后棘刺的延长并不是对体长的异速增长。     

A reappraisal of the genus Phyllodiaptomus Kiefer, 1936, with the description of P. wellekensae n.sp. from India,and a redescription of P. tunguidus Shen & Tai, 1964 from China (Copepoda,Calanoida)

Phyllodiaptomus wellekensae n. sp. is described from south India. In the female, the genital somite is dilated at the left proximal margin and armed with an extraordinarily large, somewhat curved, laterally-directed spine; the right genital spine is much smaller than the left one. The terminal claw of leg 5 has a secretory pore at its tip and a characteristic conveyor canal on its anterior surface. In the right male P5, the coxal plate is short and unique in shape. The basis is 1.3 times as long as wide, with a long, sinuous, hyaline lamella on its medial margin. The first exopodite segment is short and optuse at its outer distal corner. The second segment is rectangular and has a short, hyaline, spinous projection between the lateral spine and the terminal claw. The left P5 has a large, serrate, hyaline fan between its apical thumb and medial apical seta. P. tunguidus is redescribed based on material newly collected from three localities in China.     

A new species of anglerfish (Lophiidae: <Emphasis Type="Italic">Lophiodes</Emphasis>) from the western Pacific

Lophiodes endoi sp. nov. is described from the western Pacific Ocean. Within the genus Lophiodes, the new species belongs in the L. mutilus group mainly defined by the absence of the fourth dorsal fin spine and differs from other species in the L. mutilus group in having a rounded esca with a paler tip, a third dorsal spine bearing a pair of black tendrils at two-thirds its length, 20–21 pectoral fin rays, a relatively short head, a relatively short illicium, a relatively short third dorsal spine, and a relatively long fifth dorsal spine, reaching the third soft dorsal fin ray when folded back. Comments on a similar species, L. bruchius, newly collected from the Kyushu–Palau Ridge, and notes on the distribution of congeneric species in the northwestern Pacific are provided.     

Periodic shedding and replacement of venomous caudal spines,with special reference to South American freshwater stingrays,Potamotrygon spp.

Synopsis The number of venomous caudal spines and their length and position relative to one another were determined in seven species of South American freshwater rays (Potamotrygonidae) and eight marine or euryhaline species of four families from the Caribbean Coast of South and Central America. Most species have two visible spines at certain stages in the shedding-replacement cycle and only one visible spine at other stages (following shedding). If we include the embryological beginnings of the spines before they erupt and become visible, the spine counts of most rays are actually 2 rather than 1 or 2. Since most species apparently follow this pattern, spine counts are of little use in distinguishing between species except in the relatively few that may have only one, or no spines. Eight captive Potamotrygon specimens maintained in simulated tropical temperature conditions over 12 months showed periodic shedding and replacement of spines. The molts were biannual for a given ray but annual for a given spine. They alternated between two spine loci and their cycles were approximately six months out of phase with each other. Recent studies on Dasyatis sabina by others report only one molt per year, with replacement spines forming always posterior to the primary spine rather than alternating between posterior and anterior. Supernumerary spines (counts of more than two, up to five) are also discussed, as are counts of one and zero.     

Cyclomorphosis in Daphnia: an adaptation to avoid invertebrate predation

Seasonal morphological changes in three Daphnia species were followed over a two-year period in two lakes that differ in invertebrate and fish pressure. Whereas the morphology of D. hyalina, the biggest of the three species, varied little from season to season, D. cucullata, the smallest, exhibited the most pronounced seasonal changes in head height/carapace length ratio. The pattern of seasonal changes of body proportions was similar in all size classes and isometric growth of the head was reported for D. cucullata. Unlike the head, tail spine length/carapace length ratio almost did not vary seasonally. Strong negative allometry of tail spine growth was observed. These results are consistent with the hypothesis that helmets and tail spines provide protection against invertebrates in the two smallest, thus most endangered species.