Ca2+-induced conformational transitions of phosphorylated peptides

CD spectroscopic studies on protected peptides containing lysine and serine, or phosphoserine, and on serine-containing fragments of the neurofilament protein midsized subunit, both in the unphosphorylated and phosphorylated form, are reported. The introduction of the phosphoryl group was not found to have a significant spectral effect in aqueous solution. In trifluoroethanol (TFE), spectral shifts toward unordered (type U) spectra or the appearance of distorted spectra likely reflect the adoption of aperiodic polypeptide conformations due to salt bridge(s) between negatively charged phosphoserine and positive lysine side-chain groups. A turn-stabilizing effect of phosphorylation was also observed. CD-monitored titration experiments in TFE revealed a high conformational sensitivity of phosphopeptides toward Ca²⁺ ions. The appearance of the unordered spectra or spectral shifts were the sign of a bulk disordering effect of Ca²⁺ ions. Spectra with specific spectroscopic features reflect the formation of Ca²⁺complexes and the adoption of ordered unique backbone conformations. When ordered structures were obtained on addition of Ca²⁺ ions, the observed CD curves showed a resemblance to the spectrum of β-pleated sheets. This may originate from chain extension and the formation of β-pleated sheet segments fixed by Ca²⁺ bridges between PO₃H groups of adjacent peptide chains. The data clearly show that the effect of the Ca²⁺ ions is highly specific: the sequence, chain length, presence and distribution of charged side-chain groups, degree and site of phosphorylation, and environmental factors appear to be determining in the process of chain extension or β-sheet formation. © 1993 John Wiley & Sons, Inc.     

Whales in warming water: Assessing breeding habitat diversity and adaptability in Oceania's changing climate

In the context of a changing climate, understanding the environmental drivers of marine megafauna distribution is important for conservation success. The extent of humpback whale breeding habitats and the impact of temperature variation on their availability are both unknown. We used 19 years of dedicated survey data from seven countries and territories of Oceania (1,376 survey days), to investigate humpback whale breeding habitat diversity and adaptability to climate change. At a fine scale (1 km resolution), seabed topography was identified as an important influence on humpback whale distribution. The shallowest waters close to shore or in lagoons were favored, although humpback whales also showed flexible habitat use patterns with respect to shallow offshore features such as seamounts. At a coarse scale (1° resolution), humpback whale breeding habitats in Oceania spanned a thermal range of 22.3–27.8°C in August, with interannual variation up to 2.0°C. Within this range, both fine and coarse scale analyses of humpback whale distribution suggested local responses to temperature. Notably, the most detailed dataset was available from New Caledonia (774 survey days, 1996–2017), where encounter rates showed a negative relationship to sea surface temperature, but were not related to the El Niño Southern Oscillation or the Antarctic Oscillation from previous summer, a proxy for feeding conditions that may impact breeding patterns. Many breeding sites that are currently occupied are predicted to become unsuitably warm for this species (>28°C) by the end of the 21st century. Based on modeled ecological relationships, there are suitable habitats for relocation in archipelagos and seamounts of southern Oceania. Although distribution shifts might be restrained by philopatry, the apparent plasticity of humpback whale habitat use patterns and the extent of suitable habitats support an adaptive capacity to ocean warming in Oceania breeding grounds.     

Cross‐genus adoptions in delphinids: One example with taxonomic discussion

Although relatively rare, adoptions have been reported in a number of mammals, involving almost exclusively individuals of the same species, and hardly ever between species or across genera. Adoption remains poorly documented and its proximate causes are controversial. Here, we describe a unique case of a cross‐genus adoption within a small community of common bottlenose dolphins (Tursiops truncatus) at Rangiroa Atoll in French Polynesia. It involves a foster female adopting a presumed melon‐headed whale (Peponocephala electra) calf while already mothering its presumed biological offspring. While the inclusive fitness hypothesis can be rejected for this adult female mother, acquisition of parental skills is also unlikely to have driven adoption in parallel to natural motherhood. We argue that the primiparous foster mother’s inexperience and personality may have contributed to factors driving such non‐adaptive behavior. We also propose that the adoptee’s persistence in initiating and maintaining an association with the adult female bottlenose dolphin could have played a major role in the adoption’s ultimate success, as well as the persistence of this cross‐genus adoption after the disappearance of the biological offspring. A brief discussion of adoption and hybridization within the Delphinidae taxon is included to identify how this cross‐genus adoption fits into context of marine mammal parental care.     

Staying close to home? Genetic differentiation of rough-toothed dolphins near oceanic islands in the central Pacific Ocean

Rough-toothed dolphins have a worldwide tropical and subtropical distribution, yet little is known about the population structure and social organization of this typically open-ocean species. Although it has been assumed that pelagic dolphins range widely due to the lack of apparent barriers and unpredictable prey distribution, recent evidence suggests rough-toothed dolphins exhibit fidelity to some oceanic islands. Using the most comprehensively extensive dataset for this species to date, we assess the isolation and interchange of rough-toothed dolphins at the regional and oceanic scale within the central Pacific Ocean. Using mtDNA and microsatellite genotyping (nDNA), we analyzed samples of insular communities from the main Hawaiian (Kaua‘i n = 93, O‘ahu n = 9, Hawai‘i n = 57), French Polynesian (n = 70) and Samoan (n = 16) archipelagos, and pelagic samples off the Northwestern Hawaiian Islands (n = 18). An overall AMOVA indicated strong genetic differentiation among islands (mtDNA F_ST = 0.265; p < 0.001; nDNA F_ST = 0.038; p < 0.001), as well as among archipelagos (mtDNA F_ST = 0.299; p < 0.001; nDNA F_ST = 0.055; p < 0.001). Shared haplotypes (n = 4) between the archipelagos may be a product of a relatively recent divergence and/or periodic exchange from poorly understood pelagic populations. Analyses using STRUCTURE and GENELAND identified four separate management units among archipelagos and within the Hawaiian Islands. These results confirm the presence of multiple insular populations within the Pacific and island-specific genetic isolation among populations attached to islands in each archipelago. Insular populations seem most prevalent where oceanographic conditions indicate high local productivity or a discontinuity with surrounding oligotrophic areas. Our findings have important implications for a little studied species that faces increasing anthropogenic threats around oceanic islands.     

A 'polarisation sun-dial' dictates the optimal time of day for dispersal by flying aquatic insects

1. Daily changes in the flight activity of aquatic insects have been investigated in only a few water beetles and bugs. The diel flight periodicity of aquatic insects and the environmental factors governing it are poorly understood. 2. We found that primary aquatic insects belonging to 99 taxa (78 Coleoptera, 21 Heteroptera) fly predominantly in mid‐morning, and/or around noon and/or at nightfall. There appears to be at least four different types of diurnal flight activity rhythm in aquatic insects, characterised by peak(s): (i) in mid‐morning; (ii) in the evening; (iii) both in mid‐morning and the evening; (iv) around noon and again in the evening. These activity maxima are quite general and cannot be explained exclusively by daily fluctuations of air temperature, humidity, wind speed and risks of predation, which are all somewhat stochastic. 3. We found experimental evidence that the proportion (%) P(θ) of reflecting surfaces detectable polarotactically as ‘water’ is always maximal at the lowest (dawn and dusk) and highest (noon) angles of solar elevation (θ) for dark reflectors while P(θ) is maximal at dawn and dusk (low solar elevations) for bright reflectors under clear or partly cloudy skies. 4. From the temporal coincidence between peaks in the diel flight activity of primary aquatic insects and the polarotactic detectability P(θ) of water surfaces we conclude that the optimal times of day for aquatic insects to disperse are the periods of low and high solar elevations θ. The θ‐dependent reflection–polarisation patterns, combined with an appropriate air temperature, clearly explain why polarotactic aquatic insects disperse to new habitats in mid‐morning, and/or around noon and/or at dusk. We call this phenomenon the ‘polarisation sun‐dial’ of dispersing aquatic insects.     

Occurrence and infective potential of the endophyte ofHippophaë rhamnoides L. ssp.rhamnoides in coastal sand-dune areas

Summary The infective potential (IP) of nodule homogenates from field-grownHippophaë rhamnoides L. ssp.rhamnoides was determined by counting the number of nodules formed on test plants after inoculation with various dilutions of the homogenates. The IP was almost constant,i.e. 10⁵ to 10⁶ per gram of fresh nodule material. Methods to store nodule material without loss of IP were tested. The IP of air-dried nodule powders stored at 6°C hardly decreased during a period of more than a year.Data are presented on the IP of soil samples from sites representing various stages of dune formation. BeforeH. rhamnoides appeared, the IP was low: 1 to 36 nodules were formed on test plants per kg of soil. This low IP was due to low numbers of infective endophyte particles in these soils. During the succession of theH. rhamnoides scrub, the IP of the soil increased, due to the increase in the number of endophyte particles in the soil. Gradually, however, nodulation was limited by other environmental factors. The nature of these factors is discussed.