1,923 research outputs found
Inter- and Intra-specific variation in egg size among reef fishes across the Isthmus of Panama
Effects of planktonic food supplies and temperature on pelagic fish larvae are thought to be the primary environmental determinants of adaptive variation in egg size. Differences between the Atlantic and Pacific coasts of Panama in primary production (higher in the Pacific due to upwelling) and temperature (less seasonal in the non-upwelling Caribbean) allow testing such ideas. We compared the volumes, dry weights and energy content of eggs of 24 species of reef fishes from the two sides of the isthmus during the cool and warm seasons. Both egg volume and egg dry weight were good predictors of egg energy content among species, although not within species. Caribbean species produced larger eggs than their close relatives in the Pacific. In the Pacific, eggs were significantly larger during the cool upwelling season than during the warm, non-upwelling period, with a similar but weaker seasonal pattern evident in the Caribbean. The production of larger eggs in the low-productivity Caribbean is consistent with the hypothesis that species produce larger eggs and offspring when larval food supplies are lower. Parallel patterns of seasonal variation in eggs size and the greater strength of that relationship in the Pacific indicate that temperature drives seasonal variation in egg size within species. The decline in egg size with increasing temperature, a general pattern among ectotherms, may be a physiological side-effect, due to differing effects of temperature on various metabolic processes during oogenesis or on hormones that influence growth and reproduction. Alternatively, the seasonal pattern may be adaptive in these fishes, by affecting larval performance or maintaining a particular timeline of major events during embryonic development
Tropical Transpacific Shore Fishes
Tropical transpacific fishes occur on both sides of the world's largest
deep-water barrier to the migration of marine shore organisms, the 4,000- to
7,000-km-wide Eastern Pacific Barrier (EPB). They include 64 epipelagic oceanic
species and 126 species of shore fishes known from both the tropical eastern
Pacific (TEP) and the central and West Pacific. The broad distributions of 19
of 39 circumglobal transpacific species of shore fishes offer no clues to the origin
of their TEP populations; TEP populations of another 19 with disjunct Pacific
distributions may represent isthmian relicts that originated from New World
populations separated by the closure of the Central American isthmus. Eighty
species of transpacific shore fishes likely migrated eastward to the TEP, and 22
species of shore fishes (12 of them isthmian relicts) and one oceanic species
likely migrated westward from the TEP. Transpacific species constitute ~12%
of the TEP's tropical shore fishes and 15-20% of shore fishes at islands on the
western edge of the EPB. Eastward migrants constitute ~7% of the TEP's
shore-fish fauna, and a similar proportion of TEP endemics may be derived
from recent eastward immigration. Representation of transpacific species in
different elements of the TEP fauna relates strongly to adult pelagic dispersal
ability-they constitute almost all the epipelagic oceanic species, ~25% of
the inshore pelagic species, but only 10% of the demersal shore fishes. Taxa
that have multiple pelagic life-history stages are best represented among the
transpacific species. Among demersal teleosts that have pelagic larvae, pelagic
spawners are better represented than demersal spawners among transpacific
species, perhaps because offshore larval development and longer pelagic larval
durations provide the former with greater dispersal capabilities. There are
strong phylogenetic effects on representation in the transpacific fauna: (1) elasmobranchs
are proportionally better represented than teleosts, even teleosts
with more pelagic life-history stages; (2) a pelagic juvenile stage with great dispersal
potential allows tetraodontiforms that produce demersal or pelagic eggs
to be well represented; and (3) various speciose central Pacific families with
"adequate" larval dispersal characteristics lack transpacific species. El Niiios
potentially enhance eastward migration by increasing eastward flow and halving
transit times across the EPB. However, that effect may be offset by low productivity
and high temperatures in those eastbound flows. There is little clear
evidence of strongly increased migration across the EPB during El Niiios, including
recent extreme events (1982-1983 and 1997-1998). During such events
shore fishes in the TEP experience range expansions and become locally abundant at marginal areas such as the Galapagos, changes that can be confused with
increased migration across the EPB. Although there is a strong bias toward
eastward migration among the transpacific shore fishes, there likely is much
more westward migration than previously realized: 20-25% of transpacific species
may have migrated in that direction. Stronger eastbound than westbound
currents can account for this bias. Westward migrants have better developed
pelagic dispersal characteristics than many eastward migrants, suggesting that
westward migration is more difficult. Many westward migrants associate with
flotsam and flotsam-mediated migration is more likely to be westward. All
westward migrants occur at Hawai'i, but only about one-fifth of them at the
Marquesas. This bias may be due to: Hawai'i being a larger target and in the
path of most of the flotsam dispersal from the TEP; an eastward current that
impinges on the Marquesas, reducing westward arrivals; and most propagules
dispersing toward the tropical Marquesas originating in the temperate eastern
Pacific. However, the Hawaiian Islands also are much better sampled than the
Marquesas. Although the TEP reef-fish fauna may be depauperate relative to
that of the Indo-Malayan "center of diversity," it is as rich as the faunas of islands
on the western side of the EPB. Hence a preponderance of eastward migration
does not represent a response to a richness gradient across that barrier.
There is little evidence that a paucity of ecological groups in the native TEP
fauna is primarily responsible for the structure of the eastward-migrant fauna.
Rather, eastward migrants may simply represent a cross section of those in the
donor fauna, tempered by phylogenetic variation in dispersal ability. Because
few central Pacific fishes can live only on live corals and coral reefs, the rarity of
such reefs in the TEP is unlikely to strongly limit eastward migration. Differences
between oceanic and adjacent continental reef-fish faunas in the West
Pacific indicate that each is strongly tied to its respective habitat. Hence, the
rarity in the TEP of the (overwhelmingly) most abundant habitat present in the
central Pacific-tropical oceanic reefs-may strongly limit migration in both
directions across the EPB: there is little suitable habitat for eastward migrants in
the TEP and few suitable species and tiny source populations for westward migrants.
The global effects that oceanic/continental habitat differences have on
reef-fish biogeography need further assessment. Genetic data on ~18% of the
transpacific species indicate: that conspecific populations of oceanic species
(especially) and shore fishes are genetically well connected across the EPB; that
circumtropical taxa in the TEP include isolated isthmian relicts and recent
eastward migrants; that all five TEP species of one circumtropical genus (Thalassoma)
were derived by several eastward invasions after the closure of the
Isthmus of Panama; that some isolated Hawaiian central Pacific populations
were established by postisthmian invasion from the TEP; and that Indo-central
Pacific species unsuspectedly can co-occur with their endemic sibling sisters
in the TEP. Genetic data support distributional data that indicate a strong
preponderance of eastward migration across the EPB but also more westward
migration than previously thought. Future genetic studies should resolve
a question that distributional data cannot: how many widespread presumed
eastward-migrant transpacific species actually originated by westward migration
from the TEP
Corrigendum: Inter- and Intra-specific variation in egg size among reef fishes across the Isthmus of Panama
Simplification of Caribbean Reef-Fish Assemblages over Decades of Coral Reef Degradation
Caribbean coral reefs are becoming structurally simpler, largely due to human impacts. The consequences of this trend for reef-associated communities are currently unclear, but expected to be profound. Here, we assess whether changes in fish assemblages have been non-random over several decades of declining reef structure. More specifically, we predicted that species that depend exclusively on coral reef habitat (i.e., habitat specialists) should be at a disadvantage compared to those that use a broader array of habitats (i.e., habitat generalists). Analysing 3727 abundance trends of 161 Caribbean reef-fishes, surveyed between 1980 and 2006, we found that the trends of habitat-generalists and habitat-specialists differed markedly. The abundance of specialists started to decline in the mid-1980s, reaching a low of ~60% of the 1980 baseline by the mid-1990s. Both the average and the variation in abundance of specialists have increased since the early 2000s, although the average is still well below the baseline level of 1980. This modest recovery occurred despite no clear evidence of a regional recovery in coral reef habitat quality in the Caribbean during the 2000s. In contrast, the abundance of generalist fishes remained relatively stable over the same three decades. Few specialist species are fished, thus their population declines are most likely linked to habitat degradation. These results mirror the observed trends of replacement of specialists by generalists, observed in terrestrial taxa across the globe. A significant challenge that arises from our findings is now to investigate if, and how, such community-level changes in fish populations affect ecosystem function
Tetraamine Me6TREN induced monomerization of alkali metal borohydrides and aluminohydrides
Monomeric 1:1 complexes of MEH4 (M, E = Li, B, 1; Na, B, 2; Li, Al, 3; Na, Al, 4) and the tripodal tetradentate ligand (Me2NCH2CH2)3N (Me6TREN) have been prepared in good yields by refluxing in THF and allowing the solutions to cool slowly. X-ray diffraction studies show that the BH4 group binds to either Li or Na via three hydride bridges while the AlH4 group connects to Li via a single hydride bridge. Surprisingly, Me6TREN·LiAlH4 represents the first monomeric contacted ion pair LiAlH4 derivative to be structurally characterized. In every case the tetraamine coordinates via all four of its Lewis basic nitrogen atoms. A similar protocol using the alkyl-rich borohydride MBEt3H also gives monomeric species (M = Li, 5; Na, 6). All complexes have been characterized in solution by multinuclear (1H, 7Li, 11B, 13C and 27Al, where appropriate) NMR spectroscopy which reveals excellent textbook examples of 1J coupling between B/Al and H in the cases of complexes 1-4 and between B and C in the cases of complexes 5 and 6
Lithium dihydropyridine dehydrogenation catalysis : a group 1 approach to cyclisation of diamine-boranes
In reactions restricted previously to a ruthenium catalyst, a 1-lithium-2-alkyl-1,2-dihydropyridine complex is shown to be a competitive alternative dehydrogenation catalyst for the transformation of diamine boranes to cyclic 1,3,2-diazaborolidines, which can in turn be smoothly arylated in good yields. This study establishes the conditions and solvent dependence of the catalysis via NMR monitoring, with mechanistic insight provided by NMR (including DOSY) experiments and X-ray crystallographic studies of several model lithio intermediates
Two new species of Varicus from Caribbean deep reefs, with comments on the related genus Pinnichthys (Teleostei, Gobiidae, Gobiosomatini, Nes subgroup)
Tropical deep reefs (~40–300 m) are diverse ecosystems that serve as habitats for diverse communities of reef-associated fishes. Deep-reef fish communities are taxonomically and ecologically distinct from those on shallow reefs, but like those on shallow reefs, they are home to a species-rich assemblage of small, cryptobenthic reef fishes, including many species from the family Gobiidae (gobies). Here we describe two new species of deep-reef gobies, Varicus prometheus sp. nov. and V. roatanensis sp. nov., that were collected using the submersible Idabel from rariphotic reefs off the island of Roatan (Honduras) in the Caribbean. The new species are the 11th and 12th species of the genus Varicus, and their placement in the genus is supported by morphological data and molecular phylogenetic analyses. Additionally, we also collected new specimens of the closely-related genus and species Pinnichthys aimoriensis during submersible collections off the islands of Bonaire and St. Eustatius (Netherland Antilles) and included them in this study to expand the current description of that species and document its range extension from Brazil into the Caribbean. Collectively, the two new species of Varicus and new records of P. aimoriensis add to our growing knowledge of cryptobenthic fish diversity on deep reefs of the Caribbean
Exposing elusive cationic magnesium-chloro aggregates in aluminate complexes through donor control
The cationic magnesium moiety of magnesium organohalo aluminate complexes, relevant to rechargeable Mg battery electrolytes, typically takes the thermodynamically favourable dinuclear [Mg2Cl3]+ form in the solid-state. We now report that judicious choice of Lewis donor allows the deliberate synthesis and isolation of the hitherto only postulated mononuclear [MgCl]+ and trinuclear [Mg3Cl5]+ modifications, forming a comparable series with a common aluminate anion [(Dipp)(Me3Si)NAlCl3]. By pre-forming the Al-N bond prior to introduction of the Mg source, a consistently reproducible protocol is reported. Usage of the green solvent 2-methyltetrahydrofuran in place of THF in the context of Mg/Al battery electrolyte type complexes is also promoted
Ecological traits influencing range expansion across large oceanic dispersal barriers: insights from tropical Atlantic reef fishes
How do biogeographically different provinces arise in response to oceanic barriers to dispersal? Here, we analyse how traits related to the pelagic dispersal and adult biology of 985 tropical reef fish species correlate with their establishing populations on both sides of two Atlantic marine barriers: the Mid-Atlantic Barrier (MAB) and the Amazon-Orinoco Plume (AOP). Generalized linear mixed-effects models indicate that predictors for successful barrier crossing are the ability to raft with flotsam for the deep-water MAB, non-reef habitat usage for the freshwater and sediment-rich AOP, and large adult-size and large latitudinal-range for both barriers. Variation in larval-development mode, often thought to be broadly related to larval-dispersal potential, is not a significant predictor in either case. Many more species of greater taxonomic diversity cross the AOP than the MAB. Rafters readily cross both barriers but represent a much smaller proportion of AOP crossers than MAB crossers. Successful establishment after crossing both barriers may be facilitated by broad environmental tolerance associated with large body size and wide latitudinal-range. These results highlight the need to look beyond larval-dispersal potential and assess adult-biology traits when assessing determinants of successful movements across marine barriers.International Macquarie University; Australian Research Council; Smithsonian Tropical Research Institute; National Geographic Society [7937-05]; CNPq; NSF [DEB-0072909]; University of Californi
Accessible heavier s-block dihydropyridines : structural elucidation and reactivity of isolable molecular hydride sources
The straightforward metathesis of 1-lithio-2-tbutyl-1,2-dihydropyridine using metal tert-butoxide (Na/K) has resulted in the first preparation and isolation of a series of heavier alkali metal dihydropyridines. By employing donors, TMEDA, PMDETA and THF, five new metallodihydropyridine compounds were isolated and fully characterised. Three distinct structural motifs have been observed; a dimer, a dimer of dimers and a novel polymeric dihydropyridylpotassium compound, and the influence of cation π-interactions therein has been discussed. Thermal volatility analysis has shown that these complexes have the potential to be used as simple isolable sodium or potassium hydride surrogates, which is confirmed in test reactions with benzophenone
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