Temperature responses of some North AtlanticCladophora species (Chlorophyceae) in relation to their geographic distribution

The temperature responses for growth and survival have been experimentally tested for 6 species of the green algal genusCladophora (Chlorophyceae; Cladophorales) (all isolated from Roscoff, Brittany, France, one also from Connecticut, USA), selected from 4 distribution groups, in order to determine which phase in the annual temperature regime might prevent the spread of a species beyond its present latitudinal range on the N. Atlantic coasts. For five species geographic limits could be specifically defined as due to a growth limit in the growing season or to a lethal limit in the adverse season. These species were: (1)C. coelothrix (Amphiatlantic tropical to warm temperate), with a northern boundary on the European coasts formed by a summer growth limit near the 12°C August isotherm. On the American coasts sea temperatures should allow its occurrence further north. (2)C. vagabunda (Amphiatlantic tropical to temperate), with a northern boundary formed by a summer growth limit near the 15°C August isotherm on both sides of the Atlantic. (3)C. dalmatica, as forC. vagabunda. (4)C. hutchinsiae (Mediterranean-Atlantic warm temperate), with a northern boundary formed by a summer growth limit near the 12°C August isotherm, and possibly also a winter lethal limit near the 6°C February isotherm; and a southern boundary formed by a southern lethal limit near the 26°C August isotherm. It is absent from the warm temperate American coast because its lethal limits, 5° and 30°C, are regularly reached there. (5) Preliminary data forC. rupestris (Amphiatlantic temperate), suggest the southeastern boundary on the African coast to be a summer lethal limit near the 26°C August isotherm; the southwestern boundary on the American coast lies on the 20°C August isotherm. For one species,C. albida, the experimental growth and survival range was wider than expected from its geographic distribution, and reasons to account for this are suggested.Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April, 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek.     

Temperature,light, and photoperiod responses of some Northeast American and West European endemic rhodophytes in relation to their geographic distribution

The relationship between distributional boundaries and temperature responses of some Northeast American and West European endemic and amphiatlantic rhodophytes was experimentally determined under varying regimes of temperature, light, and daylength. Potentially critical temperatures, derived from open ocean surface summer and winter isotherms, were inferred from distributional data for each of these algae. On the basis of the distributional data the algae fall within the limits of three phytogeographic groups: (1) the Northeast American tropical-to-temperate group; (2) the warm-temperate Mediterranean Atlantic group; and (3) the amphiatlantic tropical-to-warm temperate group. Experimental evidence suggests that the species belonging to the northeast American tropical-to-temperate group(Grinnellia americana, Lomentaria baileyana, andAgardhiella subulata) have their northern boundaries determined by a minimum summer temperature high enough for sufficient growth and/or reproduction. The possible restriction of 2 species (G. americana andL. baileyana) to the tropical margins may be caused by summer lethal temperatures (between 30 and 35 °C) or because the gradual disintegration of the upright thalli at high temperatures (>30 °C) promotes an ephemeral existence of these algae towards their southern boundaries. Each of the species have a rapid growth and reproductive potential between 15–30 °C with a broad optimum between 20–30 °C. The lower limit of survival of each species was at least 0 °C (tested in short days only). Growth and reproduction data imply that the restrictive distribution of these algae to the Americas may be due to the fact that for adequate growth and/or reproduction water temperatures must exceed 20 °C. At temperatures 15 °C reproduction and growth are limited, and the amphiatlantic distribution through Iceland would not be permitted. On the basis of experimental evidence, the species belonging to the warm-temperate Mediterranean Atlantic group(Halurus equisetifolius), Callophyllis laciniata, andHypoglossum woodwardii), have their northern boundaries determined by winter lethal temperatures. Growth ofH. equisetifolius proceeded from 10–25 °C, that ofC. laciniata andH. woodwardii from 5–25 °C, in each case with a narrow range for optimal growth at ca. 15 °C. Tetrasporelings ofH. woodwardii showed limited survival at 0 °C for up to 4 d. For all members of the group tetrasporangia occurred from 10–20 °C. The southern boundary ofH. equisetifolius andC. laciniata is a summer lethal temperature whereas that ofH. woodwardii possibly is a winter growth and reproduction limit. Since each member of this group has a rather narrow growth and survival potential at temperatures <5 °C and >20 °C, their occurrence in northeast America is unlikely. The (irregular) distribution ofSolieria tenera (amphiatlantic tropical-to-warm temperate) cannot be entirely explained by the experimental data (possibly as a result of taxonomic uncertainties).Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April, 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek.     

Seaweed biogeography of the mid-Atlantic coast of the United States

The northern boundary of the warm temperate region of the mid-Atlantic coast of the United States is set at Cape Hatteras; the southern boundary lies at Cape Canaveral. There is some spillover of cool temperate species south of Cape Hatteras into North Carolina and spillover of warm temperate species south of Cape Canaveral toward Palm Beach. Elements of the warm temperate flora also extend into the northern Gulf of Mexico, but precise limits to the flora cannot be drawn there. Thirty-one species are endemic to the warm temperate flora. The inshore waters of North Carolina include approximately equal numbers of species with northern and southern centres of distribution; the species of the offshore waters have predominantly southern affinities, but also include most of the endemic species. Seasonal changes in the shallow water flora of North Carolina reflect eurythermal cool temperate and tropical elements in winter and summer respectively and a year-round warm temperate element. These groupings have been verified by experimental studies in which light and temperature were varied. The deep water flora is a summer flora dominated by perennial species. The inshore, eurythermal cool temperate and tropical species have a variety of cryptic stages by which they persist throughout the year.Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April 1984 at the Department of Marine Biology, Rijks-universiteit Groningen (The Netherlands). Convenor: C. van den Hoek.     

Temperature responses of economically important red algae and their potential for mariculture in Brazilian waters

Data are presented on temperature responses, based onin vitro growth performance, of eight species of colloid-producing red algae; these include the five most important commercial species of agarophytes in South America. The temperature optima do not conform strictly to geographic distribution, and intolerance to high temperature is not the factor that controls the spreading of temperate species ofGracilaria to warmer areas. WithinPterocladia capillacea (Gmelin) Bornet et Thuret, populations from two distinct localities had different responses to temperature optima. Data suggest that the disjunct distribution of this species in the American Atlantic is due to its poor performance at temperatures above 26 °C. The fastest maximum growth rate was observed inHypnea cornuta (Lamouroux) J. Agardh (doubling time 2.8 d), and the slowest inP. capillacea from Cabo Frio (doubling time 50.0 d). All the species studied, including the valuable Chilean and Argentinean species ofGracilaria, could tolerate the temperature regimes of the Brazilian waters.     

Search for possible latitudinal ecotypes inDumontia contorta (Rhodophyta)

Effects of daylength and temperature on the formation of erect fronds (macrothalli) from crusts (microthalli) ofDumontia contorta (S. G. Gmel.) Rupr. from three localities in Nova Scotia and one locality in Southern Iceland were investigated and compared to such effects shown by strains from three different East Atlantic localities (Isle of Man; Zeeland, S. W. Netherlands; and Roscoff, Brittany, France). Although these strains showed small differences in their temperature-daylength responses, these could not be interpreted as latitudinal adaptations, and consequently no latitudinal ecotypes could be found forDumontia contorta in the N. Atlantic Ocean. Upright fronds are formed at a broad temperature range of about 4°–18°C and at daylengths 13 h. Only in the southernmost part of its distribution area can high autumnal temperatures be expected to block the reappearance of upright fronds after passage of the critical daylength in September. In the larger part of the distribution area even summer temperatures are not high enough to block formation of uprights and here apparently only short daylengths initiate the reappearance of young upright fronds in autumn. The consequences of these aspects of the life history regulation for the geographic distribution are discussed.Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April, 1984 at the Department of Marine Biology, University of Groningen, The Netherlands. Convenor: C. van den Hoek.     

Temperature tolerance and biogeography of seaweeds: The marine algal flora of Helgoland (North Sea) as an example

Temperature tolerance (1 week exposure time) was determined at intervals during two successive years in 54 dominant marine benthic algae growing near Helgoland (North Sea). Seawater temperatures near Helgoland seasonally range between 3°C (in some years 0°) and 18°C. All algae survived 0°C, and none 33°C. Among the brown algae,Chorda tomentosa was the most sensitive species surviving only 18°C, followed by theLaminaria spp. surviving 20°, however not 23°C.Fucus spp. andCladostephus spongiosus were the most heat-tolerant brown algae, surviving 28°C. Among the red algae, species of the Delesseriaceae(Phycodrys rubens, Membranoptera alata) ranged on the lower end with a maximum survival temperature of 20°C, whereas the representatives of the Phyllophoraceae(Ahnfelitia plicata, Phyllophora truncata, P. pseudoceranoides) exhibited the maximum heat tolerance of the Helgoland marine algal flora with survival at 30°C. The latter value was also achieved byCodium fragile, Bryopsis hypnoides andEnteromorpha prolifera among the green algae, whereas theAcrosiphonia spp. survived only 20°C, andMonostroma undulatum only 10°C, not 15°C. Seasonal shifts of heat tolerance of up to 5°C were detected, especially inLaminaria spp. andDesmarestia aculeata. The majority of the dominant marine algal species of the Helgoland flora occurs in the Arctic, and it is hypothesized that also there the upper lethal limits of these species may hardly have changed even today. The data presented should provide a base for further analysis of the causes of geographical distribution of the North Atlantic algal species, but have still to be supplemented with similar investigations on other coasts, and supplemented with determinations of temperature requirements throughout the life cycle.Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek     

World-wide latitudinal and longitudinal seaweed distribution patterns and their possible causes,as illustrated by the distribution of Rhodophytan genera

The degree of similarity between red algal generic floras in each pair of 22 climatically defined biogeographic regions was established on a world-wide scale by Jaccard's similarity index and by an hierarchical clustering with an agglomerative centroid method. Two clusterings were carried out, the first one on the basis of all 637 genera, and the second one on the basis of genera not occurring in the tropics and non-endemic to any one of the 22 regioms (145 genera). This latter clustering served to detect better the relationships among non-tropical floras. The results indicate the following division of the earth's rhodophytan seaweed floras: (1) A rich tropical-warm temperate "Tethyan" group including the rich tropical Indo W Pacific and W Atlantic floras, and the rich warm temperate NW Pacific and NE Atlantic floras; (2) the depauperate extensions of the above group (the tropical E Pacific and E Atlantic floras, and the warm temperate NW and SW Atlantic floras); (3) a cold temperate and a warm temperate N Pacific group; (4) an Arctic-cold temperate N Atlantic group and a NE Atlantic warm temperate flora; (5) an Antarctic-cold temperate southern hemisphere group including the cold temperate SE Pacific, SW Atlantic, SE Atlantic floras, and the Antarctic flora; (6) the two highly individual, but slightly related warm temperate SE Atlantic flora (S. Africa) and SW Pacific flora (Southern Australia and Northern New Zealand); (7) the depauperate warm temperate SE Pacific flora. Although the northern and southern hemisphere temperate and polar floras are quite unrelated (on the basis of genera lacking in the tropics), they share nonetheless a number of cool water genera which apparently have succeeded in passing the adverse tropical belt. The rich tropical-warm temperate group is thought to consist of vicariant portions of a formerly continuous Tethyan flora. The N Pacific and N Atlantic temperate floras are thought to have developed independently since the Oligocene (~ 40.10⁶ y) deterioration of the climate and to have partially mixed their cool water genera only after the Pliocene inundation (2.10⁶ y) of the Bering Land Bridge. The warm-temperate floras of S Africa and southern Australia probably owe their richness and individuality to a very long isolation (already at the start of the Cenozoicum) and a continued residence in warm temperate conditions with small seasonal fluctuations.Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April 1984, at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek.     

Phenology of temperate trees in tropical climates

Several North American broad-leaved tree species range from the northern United States at 47°N to moist tropical montane forests in Mexico and Central America at 15–20°N. Along this gradient the average minimum temperatures of the coldest month (T _Jan), which characterize annual variation in temperature, increase from –10 to 12°C and tree phenology changes from deciduous to leaf-exchanging or evergreen in the southern range with a year-long growing season. Between 30 and 45°N, the time of bud break is highly correlated with T _Jan and bud break can be reliably predicted for the week in which mean minimum temperature rises to 7°C. Temperature-dependent deciduous phenology—and hence the validity of temperature-driven phenology models—terminates in southern North America near 30°N, where T _Jan>7°C enables growth of tropical trees and cultivation of frost-sensitive citrus fruits. In tropical climates most temperate broad-leaved species exchange old for new leaves within a few weeks in January-February, i.e., their phenology becomes similar to that of tropical leaf-exchanging species. Leaf buds of the southern ecotypes of these temperate species are therefore not winter-dormant and have no chilling requirement. As in many tropical trees, bud break of Celtis, Quercus and Fagus growing in warm climates is induced in early spring by increasing daylength. In tropical climates vegetative phenology is determined mainly by leaf longevity, seasonal variation in water stress and day length. As water stress during the dry season varies widely with soil water storage, climate-driven models cannot predict tree phenology in the tropics and tropical tree phenology does not constitute a useful indicator of global warming.     

Relative importance of temperature and other factors in determining geographic boundaries of seaweeds: Experimental and phenological evidence

Experimentally determined ranges of thermal tolerance and requirements for completion of the life history of some 60 seaweed species from the North Atlantic Ocean were compared with annual temperature regimes at their geographic boundaries. In all but a few species, thermal responses accounted for the location of boundaries. Distribution was restricted by: (a) lethal effects of high or low temperatures preventing survival of the hardiest life history stage (often microthalli), (b) temperature requirements for completion of the life history operating on any one process (i.e. [sexual] reproduction, formation of macrothalli or blades), (c) temperature requirements for the increase of population size (through growth or the formation of asexual propagules). Optimum growth/reproduction temperatures or lethal limits of the non-hardiest stage (often macrothalli) were irrelevant in explaining distribution. In some species, ecotypic differentiation in thermal responses over the distribution range influenced the location of geographic boundaries, but in many other species no such ecotypic differences were evident. Specific daylength requirements affected the location of boundaries only when interacting with temperature. The following types of thermal responses could be recognised, resulting in characteristic distribution patterns: (A) Species endemic to the (warm) temperate eastern Atlantic had narrow survival ranges (between ca 5 and ca 25°C) preventing occurrence in NE America. In species with isomorphic life histories without very specific temperature requirements for reproduction, northern and southern boundaries in Eur/Africa are set by lethal limits. Species with heteromorphic life histories often required high and/or low temperatures to induce reproduction in one or both life history phases which further restricted distribution. (B) Species endemic to the tropical western Atlantic also had narrow survival ranges (between ca 10 and ca 35°C). Northern boundaries are set by low, lethal winter temperatures. Thermal properties would potentially allow occurrence in the (sub) tropical eastern Atlantic, but the ocean must have formed a barrier to dispersal. No experimental evidence is so far available for tropical species with an amphi-Atlantic distribution. (C) Tropical to temperate species endemic to the western Atlantic had broad survival ranges (<0 to ca 35°C). Northern boundaries are set by low summer temperatures preventing (growth and) reproduction. Thermal properties would permit occurrence in the (sub)tropical eastern Atlantic, but along potential “stepping stones” for dispersal in the northern Atlantic (Greenland, Iceland, NW Europe) summer temperatures would be too low for growth. (D) In most amphi-Atlantic (tropical-) temperate species, northern boundaries are set by low summer temperatures preventing reproduction or the increase of population size. On European shores, species generally extended into regions with slightly lower summer temperatures than in America, probably because milder winters allow survival of a larger part of the population. (E) Amphi-Atlantic (Arctic-) temperate species survived at subzero temperatures. In species with isomorphic life histories not specifically requiring low temperatures for reproduction, southern boundaries are set by lethally high summer temperatures on both sides of the Atlantic. None of the species survived temperatures over 30°C which prevents tropical occurrence. Species with these thermal responses are characterized by distribution patterns in which southern boundaries in Eur/Africa lie further south than those in eastern N America because of cooler summers. In most species with heteromorphic life histories (or crustose and erect growth forms), low temperatures were required for formation of the macrothalli (either directly or through the induction of sexual reproduction). These species have composite southern boundaries in the north Atlantic Ocean. On American coasts, boundaries are set by lethally high summer temperatures, on European coasts by winter temperatures too high for the induction of macrothalli. Species with this type of thermal responses are characterized by distribution patterns in which the boundaries in Eur/Africa lie further north than those in eastern N America because of warmer winters. Paper presented at the XIV International Botanical Congress (Berlin, 24 July–1 August, 1987), Symposium 6-15, “Biogeography of marine benthic algae”.     

Temperature responses of tropical to warm temperateCladophora species in relation to their distribution in the North Atlantic Ocean

The relationship between distribution boundaries and temperature responses of some North AtlanticCladophora species (Chlorophyta) was experimentally examined under various regimes of temperature, light and daylength. Experimentally determined critical temperature intervals, in which survival, growth or reproduction was limited, were compared with annual temperature regimes (monthly means and extremes) at sites inside and outside distribution boundaries. The species tested belonged to two phytogeographic groups: (1) the tropical West Atlantic group (C. submarina: isolate from Curaçao) and (2) the amphiatlantic tropical to warm temperate group (C. prolifera: isolate from Corsica;C. coelothrix: isolates from Brittany and Curaçao; andC. laetevirens: isolates from deep and shallow water in Corsica and from Brittany). In accordance with distribution from tropical to warm temperate regions, each of the species grew well between 20–30°C and reproduction and growth were limited at and below 15°C. The upper survival limit in long days was <35°C in all species but high or maximum growth rates occurred at 30°C.C. prolifera, restricted to the tropical margins, had the most limited survival at 35°C. Experimental evidence suggests thatC. submarina is restricted to the Caribbean and excluded from the more northerly American mainland and Gulf of Mexico coasts by sporadic low winter temperatures in the nearshore waters, when cold northerly weather penetrates far south every few years. Experimental evidence suggests thatC. prolifera, C. coelothrix andC. laetevirens are restricted to their northern European boundaries by summer temperatures too low for sufficient growth and/or reproduction. Their progressively more northerly located boundaries were accounted for by differences in growth rates over the critical 10–15°C interval.C. prolifera andC. coelothrix are excluded or restricted in distribution on North Sea coasts by lethal winter temperatures, again differences in cold tolerance accounting for differences in their distribution patterns. On the American coast, species were probably restricted by lethal winter temperatures in the nearshore and, in some cases, by the absence of suitable hard substrates in the more equable offshore waters. Isolates from two points along the European coast (Brittany, Corsica) ofC. laetevirens showed no marked differences in their temperature tolerance but the Caribbean and European isolates ofC. coelothrix differed markedly in their tolerance to low temperatures, the lethal limit of the Caribbean isolate lying more than 5°C higher (at ca 5°C).     

TEMPERATURE RESPONSES AND EVOLUTION OF THERMAL TRAITS IN CLADOPHOROPSIS MEMBRANACEA (SIPHONOCLADALES,CHLOROPHYTA)1

Temperature tolerances and relative growth rates were determined for different isolates of the tropical to warm temperate seaweed species Cladophoropsis membranacea (C. Agardh) Boergesen (Siphonodadales, Chlorophyta) and some related taxa. Most isolates of C membranacea survived undamaged at 18° C for at least 8 weeks. Lower temperatures (5°–15°C) were tolerated for shorter periods of time but caused damage to cells. All isolates survived temperatures up to 34° C, whereas isolates from the eastern Mediterranean and Red Sea survived higher temperatures up to 36°C. Growth occurred between 18° and 32° C, but an isolate from the Red Sea had an extended growth range, reaching its maximum at 35°C. Struvea anastomosans (Harvey) Piccone & Grunow, Cladophoropsis sundanensis Reinbold, and an isolate of C. membranacea from Hawaii were slightly less cold- tolerant, with damage occurring at 18°C. Upper survival temperatures were between 32° and 36° C in these taxa. Temperature response data were mapped onto a phylogenetic tree. Tolerance for low temperatures appears to be a derived character state that supports the hypothesis that C. membranacea originated from a strictly tropical ancestor. Isolates from the Canary Islands, which is near the northern limit of distribution, are ill adapted to local temperature regimes. Isolates from the eastern Mediterranean and Red Sea show some adaptation to local temperature stress. They are isolated from those in the eastern Atlantic by a thermal barrier at the entrance of the Mediterranean.     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

Behavioral thermoregulatory abilities of tropical coral reef fishes: a comparison with temperate freshwater and marine fishes

Synopsis Eight species in six different families of tropical marine reef fishes from the Indo-West Pacific region (Naso lituratus, Zebrasoma.flavescens, Balistes fuscus, B. vidua, Forcipiger longirostris, Echidna zebra, Cromileptes altivelis, Canthigaster jactator) were tested for ability to thermoregulate behaviorally in electronic shuttleboxes. All of these species preferred mean temperatures between 20 and 30°C, but differed considerably in thermoregulatory precision. All species avoided lethal high or low temperatures (i.e., they did not die during the tests), and some species thermoregulated as precisely as temperate species. Some temperate species prefer higher temperatures (above 30°C) than do these tropical reef species.     

A comparison of the responses of tropical and temperate flies (Diptera: Sarcophagidae) to cold and heat stress

Summary Two flesh fly species from the tropical lowlands (Peckia abnormis and Sarcodexia sternodontis) were more susceptible to both cold-shock and heatshock injury than temperate flies (Sarcophaga crassipalpis and S. bullata) and a fly from a tropical high altitude (Blaesoxipha plinthopyga). A brief (2-h) exposure to 0°C elicits a protective response against subsequent cold injury at–10°C in the temperate flies and in B. plinthopyga but no such response was found in the flies from the tropical lowlands. However, both tropical and temperate flies could be protected against heat injury (45°C) by first exposing them to a mild heat shock (2 h at 40°C). The supercooling point is not a good indicator of cold tolerance: supercooling points of pupae were similar in all species, ranging from–18.9 to–23.0°C, and no differences were found between the tropical and temperate species. Among the temperate species, glycerol, the major cryoprotectant, can be elevated by short-term exposure to 0°C, but glycerol could not be detected in the tropical flies. Low-temperature (0°C) exposure also increased hemolymph osmolality of the temperate species, but no such increase was observed in the tropical lowland species. Adaptations to temperature stress thus differ in tropical and temperate flesh flies: while flies from both geographic areas share a mechanism for rapidly increasing heat tolerance, only the temperate flies appear capable of responding rapidly to cold stress. The presence of a heat shock response in species that lack the ability to rapidly respond to cold stress indicates that the biochemical and physiological bases for these two responses are likely to differ.     

The phytogeography ofCladophora (Chlorophyceae) in the northern Atlantic Ocean,in comparison to that of other benthic algal species

About 43Cladophora species inhabit the coasts of the northern Atlantic Ocean. These can be subdivided into seven distribution groups: (a) the tropical western Atlantic group (16 species); (b) the warm temperate Mediterranean-Atlantic group (9 species); (c) the warm temperate North American group (1 species); (d) the Arctic group (1 species); (e) the amphiatlantic tropical to warm temperature group (7 species); (f) the amphiatlantic tropical to temperate group (4 species), and (g) the amphiatlantic temperate group (5 species). These groups agree with general phytogeographic patterns. Thus, the high numbers of species restricted to the tropical western Atlantic region and the warm temperate Mediteranean-Atlantic region are in agreement with the richness and high degree of endemism of these regions. The fact that all species occurring in northeast America also occur in Europe agrees with the high floristic similarity of the boreal areas in America and Europe. The sediment coasts of the Carolinas are an efficient barrier to the south-north dispersal of benthic algae. The temperature bound phytogeographic limits are set in most cases by the species ability to survive adverse temperatures; for “northern” species to survive a high summer temperature in the south, and for “southern” species to survive a low winter temperature in the north. The limits in the Arctic region are all set by the species ability for sufficient growth and reproduction in summer. Conversely, only few northern species have a southern limit which is set by a winter temperature that is not too high for sufficient growth and reproduction. Most species of this group are winter-annuals at their southern limit, and summer-annuals at their northern limit. A comparatively small number of species with a tropical-to-warm temperate distribution have a northern limit at temperate latitudes which is set by a sufficiently high summer temperature for growth and reproduction. A high proportion of this group are lagoonal or quiet water species, which profit by higher summer temperatures in sheltered waters.C. vagabunda is an example.C. rupestris andC. sericea have an amphiboreal distribution and also occur in the southern temperate belt. They probably used a Pleistocene temperature drop to disperse, through the Atlantic along the African coast, from one hemisphere to the other. In the Pacific temperatures were not sufficiently low for this dispersal; and hence these two species reached the Pacific probably by way of the Bering Strait.     

Bioactive compounds in seaweed: functional food applications and legislation

Seaweed is more than the wrap that keeps rice together in sushi. Seaweed biomass is already used for a wide range of other products in food, including stabilising agents. Biorefineries with seaweed as feedstock are attracting worldwide interest and include low-volume, high value-added products and vice versa. Scientific research on bioactive compounds in seaweed usually takes place on just a few species and compounds. This paper reviews worldwide research on bioactive compounds, mainly of nine genera or species of seaweed, which are also available in European temperate Atlantic waters, i.e. Laminaria sp., Fucus sp., Ascophyllum nodosum, Chondrus crispus, Porphyra sp., Ulva sp., Sargassum sp., Gracilaria sp. and Palmaria palmata. In addition, Undaria pinnatifida is included in this review as this is globally one of the most commonly produced, investigated and available species. Fewer examples of other species abundant worldwide have also been included. This review will supply fundamental information for biorefineries in Atlantic Europe using seaweed as feedstock. Preliminary selection of one or several candidate seaweed species will be possible based on the summary tables and previous research described in this review. This applies either to the choice of high value-added bioactive products to be exploited in an available species or to the choice of seaweed species when a bioactive compound is desired. Data are presented in tables with species, effect and test organism (if present) with examples of uses to enhance comparisons. In addition, scientific experiments performed on seaweed used as animal feed are presented, and EU, US and Japanese legislation on functional foods is reviewed.     

The effects of acclimation and rearing conditions on the response of tropical and temperate populations ofDrosophila melanogaster andD. simulans to a temperature gradient (Diptera: Drosophilidae)

The effects of rearing and acclimation on the response of adultDrosophila to temperature were investigated in a gradient.D. melanogaster flies preferred a higher mean temperature and were distributed over a wider range of temperatures thanD. simulans flies. Acclimating adults at different temperatures for a week did not influence the response of either species. Adults reared at 28°C as immatures had a lower mean preference than those reared at cooler temperatures, suggesting that flies compensated for the effects of rearing conditions. Adults from tropical and temperate populations ofD. melanogaster andD. simulans did not differ in the mean temperature they preferred in a gradient, suggesting little genetic divergence for this trait within species. The species differences and environmental responses may be related to changes in optimal physiological conditions for the flies.     

Identifying Environmental Conditions to Promote Species Coexistence: An Example with the Native Barrens Topminnow and Invasive Western Mosquitofish

Coexistence of a native and invasive species may be possible at certain conditions along an environmental gradient where the individual responses of each species are maximally apart. Water temperature may differentially affect the growth of a native cool-water species like the Barrens topminnow, Fundulus julisia, and an originally warm-water adapted western mosquitofish, Gambusia affinis, who is a recent invader in Barrens Plateau region of middle Tennessee. We measured the specific growth rate (SGR) of the two species separately in laboratory aquaria at 10, 15, 20 and 25 °C, representing a range of temperatures that occur in topminnow habitats throughout the year. Both species grew faster with increasing temperature and SGRs were highest at 25 °C. The interspecific difference in SGR was maximized at 15 °C. At this temperature, mean growth rate of topminnows was 0.78% per day, more than twice that of mosquitofish (0.38% per day). These results suggest that cool springhead habitats with a near-constant thermal environment of 15 °C throughout the year may provide a growth advantage to the Barrens topminnow over the mosquitofish. Other environmental, density-dependent, or behavioral factors not examined here may act along with temperature to mediate the coexistence of the topminnow and mosquitofish.     

DNA base composition heterogeneity in some agarophytes (Gracilariales,Rhodophyta) from Mexico and the Philippines

Estimates of nuclear DNA base composition by determination of thermal denaturation temperatures (T_m) indicate guanine + cytosine (G + C) levels of 35.4–46.8% for ten species of the Gracilariaceae, representing the generaGracilaria andHydropuntia. T_m values were found to be reproducible with variation among most samples and replicates of less than 1 °C and 2 mol%. Interspecific variation in G + C values was less than 11.4% amongGracilaria species. Calculation of intragenomic base pair composition distribution based on mid-resolution thermal denaturation (A 1 °C/min with 4s interval H and dT logging) indicated an inverse relationship between maximum similarity values and taxonomic rank. Intraspecific (population level) maximum similarity (homology) values were estimated to range from 79–90% inGracilaria tikvahiae (4 isolates). Interspecific values of 46–69% were found in 13 species ofGracilaria. Nucleotide distribution similarity values for the Gracilariaceae are compared with previous information for genome organization and complexity, genome size and karyotype patterns.Author for correspondence     

Intraspecific diversity in the fungal speciesChaunopycnis alba: Implications for microbial screening programs

Intraspecific variation among 84 isolates of the anamorphic fungusChaunopycnis alba from 26 different geographical locations was analyzed by investigating optimal growth temperatures, differences in the production of secondary metabolites and presence or absence of the cyclosporin synthetase gene. The genetic diversity was assessed using random amplified polymorphic DNA (RAPD). Analysis of these data showed high genetic, metabolic and physiological diversity within this species. Isolates from the Antarctic represented the most homogeneous group withinC. alba and together with isolates from the Arctic these polar strains differed from alpine, temperate and tropical strains by low optimal growth temperatures and by low production of secondary metabolites. Isolates from tropical climes were characterized by high optimal growth temperatures and by the production of comparatively diverse metabolite spectra. Most of the isolates that were similar in the combination of their physiological and metabolic characters were also genetically related. Isolates from different geographical origins did not show many similarities, with the exception of the cyclosporin A-producing isolates, and large diversity could be observed even within a single habitat. This leads us to the suggestion that for pharmaceutical screening programs samples should be collected from a diversity of different geographical and climatic locations. For the selection of strains for screening the RAPD assay seems to be the most powerful tool. It reflected the highest intraspecific diversity and the results corresponded well with the other characteristics.