Gill raker variation and the feeding niche of some temperate and tropical freshwater fishes

Synopsis Variability in the mean number of gill rakers was examined in 17 tropical (Panama) and 16 temperate (Canada) freshwater fishes. Ranges for an additional 16 temperate species were obtained from the literature. Variance in gill raker number within species was significantly greater in the tropical species. The tropical species also showed significantly greater dispersion of the species means when among-species variation was compared to an overall mean for each latitude. The reduced among-species variation observed in the temperate species appears to result from a scarcity of high raker means in small, stream species of Canada. This study offers no evidence for the existence of greater feeding specialization among small, primarily stream fishes in the neotropics. The data suggest that the food resource spectrum utilized by these species may be shorter at the higher latitudes examined.     

合浦珠母贝鳃的显微与超微结构

合浦珠母贝(Pinctada fucata)是典型的滤食性瓣鳃类动物,也是我国重要的海水珍珠养殖贝类。本研究用光学显微镜、扫描电镜和透射电镜观察了合浦珠母贝鳃的显微和超微结构。结果表明,合浦珠母贝鳃结构属于异丝鳃型,左右两侧各2个鳃瓣,每个鳃瓣由内鳃瓣和外鳃瓣组成。鳃瓣由主鳃丝和普通鳃丝构成,主鳃丝在鳃瓣中主要起支架作用,每2根主鳃丝之间的9～12根普通鳃丝由"簇内连接"(intrabunchial junction)相连成簇。普通鳃丝之间通过"丝间连接"(interfilament junction)相连,丝间连接的上皮细胞与普通鳃丝的扁平细胞结构一样,为鳃的呼吸上皮。丝间连接的存在扩大了鳃的表面积,这种结构有助于进行气体交换。主鳃丝和普通鳃丝表面有前纤毛和侧纤毛,与食物运送和气体交换有关。普通鳃丝表面的纤毛为典型的"9+2"型微管结构。     

Causes and consequences of thermal tolerance limits in rocky intertidal porcelain crabs, genus petrolisthes

Vertical zonation of intertidal organisms, from the shallowsubtidal to the supralittoral zones, is a ubiquitous featureof temperate and tropical rocky shores. Organisms that livehigher on the shore experience larger daily and seasonal fluctuationsin microhabitat conditions, due to their greater exposure toterrestrial conditions during emersion. Comparative analysesof the adaptive linkage between physiological tolerance limitsand vertical distribution are the most powerful when the studyspecies are closely related and occur in discrete vertical zonesthroughout the intertidal range. Here, I summarize work on thephysiological tolerance limits of rocky intertidal zone porcelaincrab species of the genus Petrolisthes to emersion-related heatstress. In the eastern Pacific, Petrolisthes species live throughouttemperate and tropical regions, and are found in discrete verticalintertidal zones in each region. Whole organism thermal tolerancelimits of Petrolisthes species, and thermal limits of heartand nerve function reflect microhabitat conditions. Speciesliving higher in the intertidal zone are more eurythermal thanlow-intertidal congeners, tropical species have the highestthermal limits, and the differences in thermal tolerance betweenlow- and high-intertidal species is greatest for temperate crabs.Acclimation of thermal limits of high-intertidal species isrestricted as compared to low-intertidal species. Thus, becausethermal limits of high-intertidal species are near current habitattemperature maxima, global warming could most strongly impactintertidal species.     

Nouvelles formulations des regles ecologiques connues sous le nom de reegle de Bergmann et loi de Jordan: Amendments of the ecological rules known as Bergmann's and Jordan's rules

Measurements of populations of planktonic and micronektonicspecies from the Atlanto-mediterranean region (about 10,000specimens) have lead to improvements in Bergmann's rule relatingto the increase in size with latitude. There are three cases : Mediterranean specimens may be smaller(e.g. the mysid Eucopia hansent), equal to (e.g. the decapodcrustacean Gennadas elegans) or larger than Atlantic ones (e.g.the thecosomatous genus Cymbulia). All the species in the last group have their principal distributionin warm ocean waters. In the Atlantic, tropical species (e.g.the euphausiid Euphausia gibboides) decrease in size in thenorthern parts of their range while temperate species (e.g.the decapod crustacean Sergesles corniculum) decrease in sizetowards both the pole and the equator. The comparison with the number of vertebrae of fish, which increasesas does the size according to Jordan's rule, is interesting:though correct for cold water species (e.g. Merlucdus merluccius),this rule cannot be applied to warm water species (e.g. Merlucciussenegalensis). Thus, these rules must be corrected like this:- "a species reachesits maximal size in high, intermediate or low latitudes of itsarea if it has a boreal, temperate or tropical distribution"; - "the number of vertebrae increases with latitude for borealfish and decreases for tropical ones".     

Comparison of temperate and tropical rainforest tree species: photosynthetic responses to growth temperature

Little is known about the differences in physiology between temperate and tropical trees. Australian rainforests extend from tropical climates in the north to temperate climates in the south over a span of 33° latitude. Therefore, they provide an opportunity to investigate differences in the physiology of temperate and tropical trees within the same vegetation type. This study investigated how the response of net photosynthesis to growth temperature differed between Australian temperate and tropical rainforest trees and how this correlated with differences in their climates. The temperate species showed their maximum rate of net photosynthesis at lower growth temperatures than the tropical species. However, the temperate species showed at least 80% of maximum net photosynthesis over a 12-16°C span of growth temperature, compared with a span of 9-11°C shown by the tropical species. The tropical species showed both larger reductions in maximum net photosynthesis at low growth temperatures and larger reductions in the optimum instantaneous temperature for net photosynthesis with decreasing growth temperature than the temperate species. The ability of the temperate species to maintain maximum net photosynthesis over a greater span of growth temperatures than the tropical species is consistent with the greater seasonal and day-to-day variation in temperature of the temperate climate compared with the tropical climate.     

Acclimation of Intertidal Crabs

SVXOPSIS. Intertidal crabs are subjected to marked fluctuationsin environmental factors. Temperature and salinity influencethe distribution of organisms both on a latitudinal basis andalong a subtidal to terrestrial gradient. These factors areoperative on all stages of the life history. Resistance-adaptations. Adult fiddler crabs (genus Uca) fromthe temperate zone are more resistant to low temperature thantropical species. Also, the tolerance to low temperature ofcrabs from the temperate zone is greatly influenced by thermalacclimation, i.e. cold-acclimated crabs are more resistant thanwarm-acclimated animals. In contrast, tropical species havelimited adaptive ability. At elevated temperatures no consistentdifference in the lethal limits of crabs from tropical and temperatezones is observed. In contrast with the adults, larvae of tropicalspecies are cold-resistant. However, the larvae of all speciestested are more sensitive to reduced salinities than are theadults. Capacity-adaptatioyis. Subtidal species of crabs tend to havea lower level of respiratory performance, as measured by variousindices, than crabs from the intertidal zone. The metabolicresponse of fiddler crabs from the temperate zone is more labileat low temperature than in species from the tropical zone. Atelevated temperature the reverse response is observed. On aninterspecific basis, differences in the metabolictemperaturepatterns of acclimation of latitudinally separated populationsof U. pugilator are observed when based on the hypotheticalschemes of Bullock, Precht, and Prosser.     

BIOCHEMICAL GENETICS AND SPECIES RELATIONSHIPS WITHIN THE GENUS HALIOTIS (GASTROPODA: HALIOTIDAE)

The marine gastropod genus Haliotis includes 60–70 describedspecies distributed along the coastlines of most continentsand of islands in the Pacific, Indian and Atlantic Oceans. Theyoccur in tropical and temperate regions of both hemispheres.Protein gel electrophoresis revealed genetic relationships amongseventeen temperate species; Haliotis rubra, H. conicopora,H. laevigata, H. roei, H. scalaris, H. cyclobates, H. coccoradiata,H. midae, H. iris, H, austrails, H. virginea, H. discus hannai,H. kamtschaktkana, H. rufescens, H. corrugata, H. cracherodii,and H. fulgens. Northern temperate species clustered together, but northernand southern species shared so few allelic states that theycould not be united on a single genetic distance diagram. Nordid all the southern temperate species form a single cluster.In addition, genetic characters do not support previous sub-genericdivisions within Haliotis. The observed genetic distances betweensome species were found to be large, and in some cases larger,than those normally associated with species in the same genus.These relationships provide insight into the evolutionary historyand biogcography of the group and emphasize the need for taxonomicreview based on both morphological and genetic information. (Received 8 September 1992; accepted 1 February 1993)     

Beyond the tropics: forest structure in a temperate forest mapped plot

Question: How do the diversity, size structure, and spatial pattern of woody species in a temperate (Mediterranean climate) forest compare to temperate and tropical forests? Location: Mixed evergreen coastal forest in the Santa Cruz Mountains, California, USA. Methods: We mapped, tagged, identified, and measured all woody stems (≥1 cm diameter) in a 6‐ha forest plot, following Center for Tropical Forest Science protocols. We compared patterns to those found in 14 tropical and 12 temperate forest plots. Results: The forest is dominated by Douglas‐fir (Pseudotsuga menziesii) and three species of Fagaceae (Quercus agrifolia, Q. parvula var. shrevei, and Lithocarpus densiflorus), and includes 31 woody species and 8180 individuals. Much of the diversity was in small‐diameter shrubs, treelets, and vines that have not been included in most other temperate forest plots because stems <5‐cm diameter had been excluded from study. The density of woody stems (1363 stems ha^?1) was lower than that in all but one tropical plot. The density of large trees (diameter ≥30 cm) and basal area were higher than in any tropical plot. Stem density and basal area were similar to most other temperate plots, but were less than in low‐diversity conifer forests. Rare species were strongly aggregated, with the degree of aggregation decreasing with abundance so that the most common species were significantly more regular than random. Conclusions: The patterns raise questions about differences in structure and dynamics between tropical and temperate forests; these need to be confirmed with additional temperate zone mapped plots that include small‐diameter individuals.     

A NEW SPECIES OF GRANELEDONE (CEPHALOPODA: OCTOPODIDAE) FROM THE SOUTHWEST ATLANTIC OCEAN

A new species of eledonid octopus is described from the southwesternAtlantic Ocean from depths between 90 and 1000 m off the coastsof southern Brazil, Uruguay, and Argentina. This species, Graneledoneyamana is characterized by having a papillose skin, two welldeveloped 'horns' above the eyes, small gills with 5-7 lamellaeon the outer demibranch, arms with uniserial suckers, 35-80on females and 26-70 on males. The third right arm is hectocotylized,the ligula is small, the calamus is large and well differentiated.Ink sac absent. These characters differ from all other knownGraneledone species from the southern oceans. (Received 22 July 1999; accepted 20 May 2000)     

Gill raker structure and selective predation on zooplankton by particulate feeding fish

The relationship between the gill raker structure of planktivorous fish (number, distance between gill rakers and length) and selective feeding on different species and size classes of zooplankton was studied. Gill raker structure was measured for brown trout Salmo trutta , Arctic charr Salvelinus alpinus , whitefish Coregonus lavaretus , roach Rutilus rutilus , bleak Alburnus alburnus , and three-spined stickleback Gasterosteus aculeatus . All species are facultative planktivorous fish and occur commonly in Scandinavian lakes. The effect of gill raker structure was studied by comparing prey found in fish stomachs with the availability of zooplankton from several lakes. Gill raker length and distance were significantly correlated with fish length. Although gill raker structure differed among species, all fish species selected the larger zooplankters. The minimum size of cladoceran species found in fish stomachs was much smaller than the distance between gill rakers. Despite great differences in gill raker spacing, the minimum size ingested of Daphnia galeata and Bosmina longispina was similar for all predators. The hypothesis that small zooplankton are strained and retained by the gill rakers in particulate feeding planktivorous fish, particularly in salmonids and roach, is rejected.     

ADAPTATIONS FOR COLD WATER SPAWNING IN LOLIGINID SQUID: LOLIGO GAHI IN FALKLAND WATERS

Inshore spawning sites of the cold water squid Loligo gahiwere found in the waters of East Falkland (Southwest Atlantic),where there is a major fishery based on this species. Egg massesoccurred in algal beds, often at the outer (seaward) edge, with ambientwater temperatures of 6.5-90C and salinity 33.75- 33.58. They wereattached to the stipes of the kelp algae Lessonia spp. and Macrocystispyrifera from 0.5 m to 2.5 m off the bottom at 8-20 m depths.The overall density of egg masses was low. The egg mass is abundle of elongated gelatinous translucent capsules with eachcapsule firmly attached to the kelp stipe at its basal end.The capsules are mainly 50-60 mm in length and contain an averageof 70 fertilized eggs. Sampled egg masses consisted of 4-161 capsulesand from 138 to 11,487 eggs. Large egg masses (. 50 capsules) wereapparently formed by several females at different times, as embryosin different capsules were at various stages of development.Eggs laid in winter are significantly larger than those laidin summer. In comparison with tropical and temperate Loligo spp.L. gahi have short egg capsules containing a small number of eggs,but the eggs (2.2-2.5 mm diameter) and hatchlings (3.1-3.4 mm mantlelength) are large. These are probable adaptations for cold waterspawning and development. (Received 30 March 2000; accepted 5 June 2000)     

Invasive Temperate Species are a Threat to Tropical Island Biodiversity

To protect the remaining biodiversity on tropical islands it is important to predict the elevational ranges of non-native species. We evaluated two hypotheses by examining land snail faunas on the eastern (windward) side of the island of Hawaii: (1) the latitude of a species' native region can be used to predict its potential elevational range and (2) non-native temperate species, which experience greater climatic fluctuations in their native range, are more likely to become established at higher elevations and to extend over larger elevational ranges than non-native tropical species. All non-native tropical species were distributed patchily among sites ≤500 m and occupied small elevational ranges, whereas species introduced from temperate regions occupied wide elevational ranges and formed a distinct fauna spanning elevations 500–2000 m. Most native land snail species and ecosystems occur >500 m in areas dominated by temperate non-native snail and slug species. Therefore, knowing the native latitudinal region of a non-native species is important for conservation of tropical island ecosystems because it can be translated into potential elevational range if those species are introduced. Because temperate species will survive in tropical locales particularly at high elevation, on many tropical islands the last refuges of the native species, preventing introduction of temperate species should be a conservation priority.     

THE GENUS TRAPANIA (NUDIBRANCHIA: GONIODORIDIDAE) IN THE INDO-WEST PACIFIC

Seven new species of the nudibranch genus Trapania Pruvot-Fol,1931 (Goniodorididae) are described from the Indo-West Pacificand an eighth species, T. japonica (Baba, 1935), originallydescribed from one preserved specimen from Japan, is redescribedfrom specimens collected in Hong Kong and tropical eastern Australia.Three of the new species are from temperate south-eastern Australiaand one from tropical eastern Australia. Two species are knownonly from Hong Kong and a third is recorded from the SudaneseRed Sea as well as Hong Kong. Only ten other species of Trapania have been described, sixof those from Europe, and one each from Brazil, California,Japan and New Zealand. The anatomy and external colour patternof these species is compared with that of the seven new species. (Received 12 December 1986;     

Life history strategies of cladocerans: comparisons of tropical and temperate taxa

We review recent works on different life history variables of cladoceran taxa in tropical and temperate freshwater bodies, comparing the strategies that cladocerans have evolved to adapt to contrasting environmental conditions in the two geographical regions. These life-history parameters relate to age and size at maturity, survival, fecundity, life-expectancy at birth, lifespan, gross, and net reproductive rates, generation time, the rate of population increase, peak population density and day of peak abundance. We also discuss the role of photoperiod and temperature on some of these life history parameters. We found a general paucity of experimental work and field data in tropics on cladocerans. There is very limited information on the few Daphnia species found in the tropics. The misconception of low species diversity of cladocerans in the tropics arose due to several reasons including lack of extensive and intensive field collections. Higher water temperatures apparently promote permanent infestation of tropical waters with toxic cyanobacteria, which reduce the zooplankton diversity. In addition to higher temperatures in the tropics, the year-round high predation pressure of planktivorous fish probably causes the tropical species, particularly in pelagic habitats, to reach maturity earlier (< 3 days) than in temperate regions. Species of Daphnia in temperate regions are particularly adapted to living at food concentrations that are much lower and seasonably more variable than those for tropical genera such as Diaphanosoma. This is further corroborated by the more than an order of magnitude higher threshold food concentration (TFC) for tropical Cladocera than for their temperate counterparts. Fecundity patterns differ between tropical and temperate cladoceran taxa: cultured under optimal temperature regimes, tropical taxa have fewer eggs than temperate species of a comparable body size. Predation pressure may act differently depending on the size of the cladoceran neonates and thus on their population size structure. Global warming and climate changes seem to affect the behaviour (migration), distribution, and abundance of cladocerans. Apparently, in direct response to these changes, the possibility of encountering the tropical cladocerans in the northern, temperate hemisphere (bioinvasions) is on the rise.     

A REVISION OF THE DEEP-WATER OCTOPUS GENUS SCAEURGUS (CEPHALOPODA: OCTOPODIDAE) WITH DESCRIPTION OF THREE NEW SPECIES FROM THE SOUTHWEST PACIFIC OCEAN

Deep-water trawl surveys on seamounts around New Caledonia yielded62 specimens of the little-known genus, Scaeurgus. Members ofthis genus of octopuses typically occur at depths of 200–500m in temperate and tropical latitudes worldwide. Prior to thisstudy, Scaeurgus was considered to contain one to two species.The new material from New Caledonia contained a surprising diversityof Scaeurgus species from a small area: three distinct new speciesare described and limited material of a further two taxa isreported. A pygmy member of this genus is reported for the firsttime. Distributions of these new taxa are consistent with reportsof high endemism on the seamount systems in this region. Fifty-eightof the 62 specimens were collected from seamounts, with fourof the five taxa unique to a single seamount. (Received 12 January 2004; accepted 28 January 2005)     

Larger seeds in tropical floras: consistent patterns independent of growth form and dispersal mode

Many species of tropical moist forests have large seeds compared to those found in temperate floras. This could be attributed to a prevalence of woody growth forms, or adaptation to dispersal by vertebrates, or the dense shade of a closed canopy, rather than to an intrinsic tropical v. temperate difference. We compared tropical v. temperate seed mass data at two geographic scales; firstly within Australia between tropical, subtropical and temperate open woodlands, then between six tropical and temperate datasets from five continents. Within Australia we found that seed mass increased with decreasing latitude in ten out of eleven growth form-dispersal mode combinations: only wind-dispersed graminoids showed no significant effect. While the pattern of generally larger seeds in the tropical flora was associated with tropical families tending to have larger seeds than temperate families, we also found that tropical species had larger seeds than temperate cofamilials. As a preliminary test of the generality of these findings we included a further four tropical and temperate data sets in a second analysis. Average tropical seed masses were larger than temperate seed masses in all testable growth form-dispersal mode combinations, and statistically larger in five out of seven cases: unassisted, vertebrate- and wind-dispersed woody species, and unassisted and vertebrate-dispersed forbs. No difference was found for wind-dispersed forbs or for graminoids lacking dispersal structures. That an effect was found in these combinations rules out explanations based solely on characteristics of tropical v. temperate dispersers, although this may be a contributing factor. Instead we suggest that some aspect of tropical systems, for example higher metabolic costs of seedling production, has selected for a general increase in seed mass among tropical taxa.     

In situ growth rates of marine phytoplankton: approaches to measurement, community and species growth rates

Taxonomic structure and biomass weighting are important determinantsof measurable marine phytoplankton community growth potential.Maximal diel-averaged growth rates of communities appear tofall between 3 and 3.6 doublings day^–1. Mean net growthrates are considerably lower. Ranges of community growth ratesmeasured in tropical, sub-tropical and (summer) temperate ecosystemsare similar. There appears to be a broad dichotomy between thegrowth potential of diatom species as compared to non-diatoms.Doubling rates of small diatoms frequently exceed communitybiomass doubling rates by wide margins. Diel-averaged growthrates of large diatoms, microflagellates and non-motile ultraplanktonpopulations are lower and similar in magnitude to communitygrowth estimates. Maximum growth rates of species measured insitu are in good agreement with maximum growth rates measuredin laboratory cultures. High specific productivity of sub-dominantor rare diatom species or assemblages will be diluted in thelower specific growth rates of microflagellate and non-motileultraplankton assemblages. Specific rates of grazing upon speciesand functional groups remain to be quantified, but stabilityof community size and taxonomic structure implies close linkagebetween growth and mortality rates at the species level overtime intervals of several generations.     

Genome size variation in the Fagaceae and its implications for trees

Polyploidization is a major source of diversification among plants, particularly during cladogenesis, but most evidence involves herbaceous temperate species. The prevalence of polyploidy among woody taxa is largely unknown, especially among tropical groups. In this study, we examined genome size variation globally and at several taxonomic levels within the Fagaceae. This family has diversified in the northern temperate zone (Quercus) and at least twice in the Asian tropics (Lithocarpus and Castanopsis), allowing us to examine genomic size evolution across a broad latitudinal range. We compared nuclear DNA contents from 78 species in six genera, including new measurements for 171 individuals from 47 Chinese species using standard flow cytometry methods. No evidence suggests that polyploidization or whole genome duplication has occurred in the family. Genome size varied among genera, but limited variation was present in each genus and species. In general, tropical species had larger genomes than temperate species, but the ancestral state cannot be determined given current evidence. Partial duplication does seem to occur among species as within genus variation was larger than within species variation. A review of the literature suggests that genome size and even chromosome structure is highly conserved among woody plants and trees. We propose that ploidy level and genome size are conserved among trees because they participate in diverse syngameons. This behavior would provide similar benefits to polyploidization but avoid exclusion from the syngameon. This conservatism in genome size and structure should enhance ongoing whole genome studies.     

Organic matter sources and size structuring in stream invertebrate food webs across a tropical to temperate gradient

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不同NaHCO3碱度对瓦氏雅罗鱼鳃组织结构的影响

研究采用组织学方法观察和比较了达里诺尔湖瓦氏雅罗鱼(Leuciscus waleckii, 碱水种)和松花江瓦氏雅罗鱼(淡水种)在相同碳酸盐碱度胁迫下(C_A0、C_A30和C_A50)鳃组织结构的差异, 探究瓦氏雅罗鱼碱水种耐高碱特性与鳃组织结构微观调整的适应性关系。结果显示, 随着碱度增加, 碱水种鳃丝变宽、鳃小片变长、鳃小片间距变大(P<0.05); 淡水种鳃丝变宽、鳃小片间距变大(P<0.05), 鳃小片长度在C_A30时显著变长(P<0.05), 而在C_A50时与对照组无明显差异(P>0.05)。碱水种在C_A30和C_A50的氯细胞数量与对照组相比明显增加, C_A50的氯细胞排列更加紧密并且有叠加现象, 扁平上皮细胞变大, 细胞表面增厚; 淡水种在C_A30时的氯细胞数量明显多于C_A50, 但在碱度胁迫下, 鳃小片出现破损, 扁平上皮细胞、柱细胞和血细胞融合、脱落现象严重。另外, 在碱水种和淡水种鳃耙上皮细胞中发现了大量黏液细胞分泌, 随着碱度增加, 黏液细胞由大而稀疏变为小而密集, 其中碱水种的黏液细胞数量较淡水种多, 而且排列更为整齐、密集。鳃组织学研究结果表明, 瓦氏雅罗鱼碱水种通过保持鳃组织结构和生理功能的完整性达到对高碱环境的长期适应, 而淡水种则因鳃细胞融合、脱落造成生理功能丧失, 不能长期适应高碱环境。研究结果可为淡水鱼类在盐碱水的移植驯化提供依据和指导。