Observational Evidences of Vocal Learning in Southern Elephant Seals: a Longitudinal Study

Vocal learning in mammals is sparsely documented, and there are few reports of vocal learning by wild mammals. In particular, no information based on longitudinal data for identified individuals exists, even for well‐studied highly social species in which vocal communication is an important aspect of social life. We present such information for the southern elephant seal (Mirounga leonina). We studied a small breeding population in the Falkland Islands over 8 yr (1995–2002). We recorded approx. 2400 agonistic vocalizations from approx. 285 different males, including many recorded over more than one breeding season (55 males were recorded for >2 yr and 29 were recorded throughout vocal development). Vocalizations are a key element of male agonistic behaviour in this species, the world's most polygynous vertebrate. For male agonistic vocalizations, we show that: (1) a limited number of discrete vocal types exists; (2) proportions of vocal types change over time; (3) observed trends of increase or decrease of vocal types are well explained by a process of vocal learning, in which younger peripheral males imitate vocal types of older more successful breeders.     

Foraging strategy in a subterranean rodent,Spalax ehrenbergi: a test case for optimal foraging theory

Summary The foraging behavior of the subterranean mole rat Spalax ehrenbergi (Rodentia, Spalacidae) was tested according to the framework of optimal foraging theory. We compared the frequencies of food species hoarded in storage chambers of mole rats with the frequencies of these species occurring in the vicinity of the mole rats' nest mounds during the winter and spring seasons. In addition, we examined the food composition of several summer nest mounds. Laboratory observations were conducted in order to test the foraging behavior of mole rats under simulated subterranean conditions. The mole rat is a generalist and collects a variety of food species. Out of 33 plant species that were hoarded by mole rats in the 21 studied nest mounds, 61% (n=20) were geophytes, 21% (n=7) perennial herbs, 15% (n=5) annual herbs and 3% (n=1) dwarf shrubs. The frequency of each collected species in the 16 winter and spring nest mounds is in general accordance with its frequency in the mole rat's territory. This implies that the mole rat randomly samples the food reserve of its territory without special preference or directed search for a particular species. The collection or avoidance of any food item is not dependent on the presence or absence of any other food item. We suggest that the foragin generalism of the mole rat is a product of the constraints of a subterranean niche — the necessity to hoard food as much as possible in a limited time period and the high energetic investment of tunneling to the food items.     

Fecundity, offspring longevity, and assortative mating: parametric tradeoffs in sexual and life history strategy

Genetic diversification of offspring represents a bet-hedging strategy that evolved as an adaptation to unpredictable environments. The benefits of sexual reproduction come with severe costs. For example, each offspring only carries half of each parent's genetic makeup through direct descent. The lower the reproductive rate, the more substantial the cost when considering the proportion of genes represented in subsequent generations. Positive assortative mating represents a conservative bet-hedging strategy that offsets some of these costs and preserves coadapted genomes in stable and predictable environments, whereas negative assortative mating serves the inverse function of genetic diversification in unstable and unpredictable environments.     

Diving for food: a switch of foraging strategy of dusky dolphins in Argentina

During winter, dusky dolphins (Lagenorhynchus obscurus) were observed in coordinated diving apparently in a feeding activity, contrasting with the surface feeding observed during summer. The aim of this work consisted in analyzing the diving activity as an alternative foraging strategy in Argentine dusky dolphins, based on sequential analysis. The study area was Golfo Nuevo, located in Northern Patagonia, Argentina. Random transects were surveyed by a research boat from 2001 to 2007. During behavioral sampling, group members were observed continuously and the predominant activity was recorded at 2-min intervals. Six predominant activities were identified. Each 2-min interval was classified according to the activity at the previous interval (preceding activity), the activity at the interval (following activity), and the season (cold or warm). Z scores were calculated and then used to construct sequence diagrams. An association between diving and milling behavior was observed. This could be another foraging tactics different to the surface foraging sequences and this could be related with the distribution or abundance of preys.     

Optimizing protein intake as a foraging strategy to maximize mass gain in an omnivore

Energy maximization, time minimization, and linear programming models subject to various constraints have dominated foraging ecology ideas and methods for decades. However, animals must use very complex physiological processes and foraging decisions to ensure fitness that in many cases may not be adequately described by these approaches. An example of this problem occurs when brown bears, Ursus arctos, have access to both abundant salmon and fruit. Salmon are one of the most energy and nutrient dense foods available to bears. Fruits are often high in soluble carbohydrates, low to deficient in many required nutrients, and more difficult to efficiently exploit. Therefore, wild brown bears that fatten primarily on fruits without access to salmon are 50% smaller than salmon-feeding bears. Thus, we predicted based on a linear, energy-maximizing model without dietary interaction effects that wild brown bears with access to both abundant salmon and fruit would feed almost exclusively on salmon. However, wild adult females with or without accompanying offspring foraged three times longer per day on fruit than on salmon. Similarly, the relative dry matter intake of ad libitum apples and salmon by captive, adult brown bears averaged 76±5% fruit and 24±5% salmon. Captive brown bears consuming mixed diets with intermediate dietary protein levels had 60% lower maintenance energy costs, 37% to 139% higher efficiencies of mass gain, and 72% to 520% higher maximum rates of gain than when they consumed either salmon or fruit alone. These relationships were nonlinear functions of dietary protein content in which salmon and fruit provided complementary nutritional resources. Both wild and captive bears attempted to regulate total protein, energy, and carbohydrate intake within a multidimensional intake target that both maximized energy intake and mass gain.     

Resprouting as a life history strategy in woody plant communities

Resprouting is an efficient means by which woody plants regain biomass lost during disturbance, but there is a life history trade-off that occurs in all disturbance regimes between investment in the current generation through resprouting vs investment in future generations at the same or more distant sites. The relative allocation to resprouting vs seeding in woody plant communities is dictated by the nature of disturbance regimes. Resprouting is the predominant response to the least severe disturbance regimes, but is also a common response in disturbance regimes of high severity, those that destroy most or all above-ground biomass, and which occur at medium to high frequency. The response to disturbance either by resprouting or seeding is dictated by the site's productivity. We present a comprehensive model for relative allocation to resprouting vs seeding across a range of disturbance regimes. Competition between plants that mostly seed vs those that mostly resprout should accentuate differences in allocation along a gradient of disturbance frequency. However the patchy nature of disturbance in time and space, coupled with gene flow among populations undergoing different disturbance regimes, ensures that it is unlikely that either resprouting or seeding will be the sole response in most plant communities at most disturbance frequencies. Additional influences on resprouting in woody plant communities include changes in allocation during the lifespan of individual plants and phylogenetic constraints that are expressed as biogeographic patterns.     

Models of optimal foraging and resource partitioning: deep corollas for long tongues

We model the optimal foraging strategies for 2 nectarivore species,differing in the length of their proboscis, that exploit thenectar provided by 2 types of flowers, differing in the depthsof their corollas. When like flowers appear in clumps, nectarivoresmust decide whether to forage at a patch of deep or shallowflowers. If nectarivores forage optimally, at least one flowertype will be used by a single nectarivore species. Long-tonguedforagers will normally visit deep flowers and short-tonguedforagers shallow flowers, although extreme asymmetries in metaboliccosts may lead to the opposite arrangement. When deep and shallowflowers are randomly interspersed, nectarivores must decide,on encounter with a flower, whether to collect its nectar orcontinue searching. At low nectarivore densities, the optimalstrategy involves exploiting every encountered flower; however,as nectarivore densities increase and resources become scarce,long-tongued individuals should start concentrating on deepflowers and short-tongued individuals on shallow flowers. Therefore,regardless of the spatial distribution of flowers, corolla depthcan determine which nectarivore species exploit the nectar fromeach flower type in a given community. It follows that corollaelongation can evolve as a means to keep nectar thieves at bayif short-tongued visitors are less efficient pollinators thanlong-tongued visitors.     

Foraging costs as a defining factor for growth and asymptotic mass

Modeling the growth of animals as parts of ecosystems often presumes the existence of an asymptotic weight which, when reached by the individual, stops its further growth. We show that the asymptotic weight is influenced by environmental conditions, and that growth is limited because of a trade-off of foraging costs and gain of feeding. We show that the so-called asymptotic mass is a comprehensive value, which also contains an environmental parameter. We develop our model for organisms of neutral buoyancy in an aquatic environment; for terrestrial and aerial animals it has limited validity only. We discuss examples and derive a critical value for resource availability in a habitat, which informs us whether foraging in that habitat is worthwhile or not.     

Iron as a target of chemoprevention for longevity in humans

Abstract

Iron is universally abundant and no life can exist without it. However, iron levels should be maintained within a narrow range. Iron deficiency causes anaemia, whereas excessive iron increases cancer risk, presumably by free radical generation. Several pathological conditions such as genetic haemochromatosis, chronic viral hepatitis B and C, conditions related to asbestos fibre exposure and ovarian endometriosis have been recognized as iron overload-associated conditions that also increase human cancer risks. Iron's carcinogenicity has been documented in animal experiments. Surprisingly, these studies have revealed that the homozygous deletion of CDKN2A/2B is a major hallmark of iron-induced carcinogenesis. Recently, the hormonal regulation of iron metabolism has been elucidated. A commonly hypothesized mechanism may be the lack of any iron disposal pathway other than for bleeding and a mechanism of iron re-uptake as catechol chelate has been discovered. Iron overload in neurons via the ferroportin block may play a role in Alzheimer's disease. Furthermore, a recent epidemiological study reported that iron reduction by phlebotomy was associated with decreased cancer risks in a general population. Given that the required amounts of iron decrease during ageing, the fine control of body iron stores would be a wise strategy for chemoprevention of several diseases.     

Iron as a target of chemoprevention for longevity in humans

Iron is universally abundant and no life can exist without it. However, iron levels should be maintained within a narrow range. Iron deficiency causes anaemia, whereas excessive iron increases cancer risk, presumably by free radical generation. Several pathological conditions such as genetic haemochromatosis, chronic viral hepatitis B and C, conditions related to asbestos fibre exposure and ovarian endometriosis have been recognized as iron overload-associated conditions that also increase human cancer risks. Iron's carcinogenicity has been documented in animal experiments. Surprisingly, these studies have revealed that the homozygous deletion of CDKN2A/2B is a major hallmark of iron-induced carcinogenesis. Recently, the hormonal regulation of iron metabolism has been elucidated. A commonly hypothesized mechanism may be the lack of any iron disposal pathway other than for bleeding and a mechanism of iron re-uptake as catechol chelate has been discovered. Iron overload in neurons via the ferroportin block may play a role in Alzheimer's disease. Furthermore, a recent epidemiological study reported that iron reduction by phlebotomy was associated with decreased cancer risks in a general population. Given that the required amounts of iron decrease during ageing, the fine control of body iron stores would be a wise strategy for chemoprevention of several diseases.     

Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

Background

Sooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management.

Methodology/Principal Findings

Tracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters.

Conclusions/Significance

The shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem.     

Foraging pauses and their meaning as an economic strategy in the honeybee Apis mellifera L.

When conditioned honeybees collect sucrose solution delivered at a range of low-profit flow rates for the hive, they increase the pause length between successive visits. If sucrose solution was delivered continuously, it accumulated at the food source in an amount proportional to the pause length and the flow rate of nectar. When the flow rate of sucrose solution was further decreased but kept constant throughout the day, a threshold level was attained in which oscillations in the length of the pauses were observed. The relationship between the amount of accumulated nectar and subsequent pause length at this threshold level can be depicted by means of a power function. The best fit allowed the calculation of the values of parameters that quantitatively describe the control system regulating foraging activity. The importance of foraging pauses as a strategy to cope with changing nectar availability is discussed. Accepted: 7 January 1998     

Heterogeneity in male horn growth and longevity in a highly sexually dimorphic ungulate

In sexually dimorphic ungulates, sexual selection favoring rapid horn growth in males may be counterbalanced by a decrease in longevity if horns are costly to produce and maintain. Alternatively, if early horn growth varied with individual quality, it may be positively correlated with longevity. We studied Alpine ibex Capra ibex in the Gran Paradiso National Park, Italy, to test these alternatives by comparing early horn growth and longevity of 383 males that died from natural causes. After accounting for age at death, total horn length after age 5 was positively correlated with horn growth from two to four years. Individuals with the fastest horn growth as young adults also had the longest horns later in life. Annual horn growth increments between two and six years of age were independent of longevity for ibex whose age at death ranged from 8 to 16 years. Our results suggest that growing long horns does not constrain longevity. Of the variability in horn length, 22% could be explained by individual heterogeneity, suggesting persistent differences in phenotypic quality among males. Research on unhunted populations of sexually dimorphic ungulates documents how natural mortality varies according to horn or antler size, and can help reduce the impact of sport hunting on natural processes.     

Infanticide as an alternative male reproductive strategy in langurs: A mathematical model

This paper makes explicit some of the assumptions underlying the view that infanticide is one of two (or more) alternative reproductive strategies utilized by adult male langur monkeys (genus Presbytis). A mathematical model has been developed from these assumptions, and formulae derived which give the equilibrium proportion of infanticidal males expected in langur populations under any given set of reproductive and demographic conditions. Together with estimates of adult male reproductive success obtained from a previous analysis of langur infanticide, these formulae were then used to calculate the precise proportion of infanticidal males expected in natural populations of langurs characterized by specific average male tenures. Further, the number of generations required for such populations to reach their predicted equilibrium was estimated using a simple computer model of langur population dynamics. The present work has thus produced several quantitative predictions which are directly falsifiable with observational data obtainable from wild populations of langur monkeys. With only slight modification, the present model may also be applied to the numerous other primate and non-primate species whose mating systems include many of the same general features as that of langurs.     

Scrapie transmission in Britain: a recipe for a mathematical model

Responses to an anonymous postal survey concerning scrapie are analysed. Risk factors associated with farms that have had scrapie are identified as size, geographical region, lambing practices and holding of certain breeds. Further analysis of farms that have scrapie only in bought-in animals reveals that such farms tend to breed a smaller proportion of their replacement animals than farms without scrapie. Farms that have had scrapie in home-bred animals have attributes associated with breeding many animals: large numbers of rams bought, few ewes bought, and many animals that are home-bred. The demography of British sheep farms as described by size, breeds, purchasing behaviour, age structure and proportion of animals that are home-bred is summarized. British farms with scrapie reveal certain special features: they have more sheep that are found dead, more elderly ewes and more cases of scab.     

Evidence for a life span-prolonging effect of a linear plasmid in a longevity mutant of Podospora anserina

The linear mitochondrial plasmid pAL2-1 of the long-lived mutant AL2 of Podospora anserina was demonstrated to be able to integrate into the high molecular weight mitochondrial DNA (mtDNA). Hybridization analysis and densitometric evaluation of the mitochondrial genome isolated from cultures of different ages revealed that the mtDNA is highly stable during the whole life span of the mutant. In addition, and in sharp contrast to the situation in certain senescence-prone Neurospora strains, the mutated P. anserina mtDNA molecules containing integrated plasmid copies are not suppressive to wild-type genomes. As demonstrated by hybridization and polymerase chain reaction (PCR) analysis, the proportion of mtDNA molecules affected by the integration of pAL2-1 fluctuates between 10% and 50%. Comparative sequence analysis of free and integrated plasmid copies revealed four differences within the terminal inverted repeats (TIRs). These point mutations are not caused by the integration event since they occur subsequent to integration and at various ages. Interestingly, both repeats contain identical sequences indicating that the mechanism involved in the maintenance of perfect TIRs is active on both free and integrated plasmid copies. Finally, in reciprocal crosses between AL2 and the wild-type strain A, some abnormal progeny were obtained. One group of strains did not contain detectable amounts of plasmid pAL2-1, although the mtDNA was clearly of the type found in the long-lived mutant AL2. These strains exhibited a short-lived phenotype. In contrast, one strain was selected that was found to contain wild-type A-specific mitochondrial genomes and traces of pAL2-1. This strain was characterized by an increased life span. Altogether these data suggest that the linear plasmid pAL2-1 is involved in the expression of longevity in mutant AL2.