No behavioural compensation for fitness costs of autotomy in a lizard

Abstract Antipredator mechanisms employed by animals are obviously beneficial if they increase survival, but their use may be costly and decrease fitness. Fitness costs of antipredator mechanisms may, in turn, be defrayed by behavioural compensation. We used lizards as a model to measure behavioural fitness costs of the antipredator mechanism, autotomy, as they commonly lose their tails when attacked by predators. In addition, we examined whether male skinks, Carlia jarnoldae (Scincidae), behaviourally compensate for tail loss by comparing the behaviour of tailed and tailless males in experimental enclosures, either alone, with a conspecific male or female, or with a predator. Tailless males experience several costs of autotomy including reduced energy stores, and loss of autotomy as a defence. We identified an additional cost of tail loss: reduced mating success. However, this species did not behaviourally compensate these costs. Instead, characteristics of the ecology of C. jarnoldae may minimize the costs of autotomy. This species experiences an extended breeding season, which means that they experience reduced mating success for only 20% of this breeding season. Additionally, the presence of inguinal fat stores which supply energy in addition to stores in the tail reduce energetic costs.     

The unusual reproductive system of head and body lice (Pediculus humanus)

Insect reproduction is extremely variable, but the implications of alternative genetic systems are often overlooked in studies on the evolution of insecticide resistance. Both ecotypes of Pediculus humanus (Phthiraptera: Pediculidae), the human head and body lice, are human ectoparasites, the control of which is challenged by the recent spread of resistance alleles. The present study conclusively establishes for the first time that both head and body lice reproduce through paternal genome elimination (PGE), an unusual genetic system in which males transmit only their maternally derived chromosomes. Here, we investigate inheritance patterns of parental genomes using a genotyping approach across families of both ecotypes and show that heterozygous males exclusively or preferentially pass on one allele only, whereas females transmit both in a Mendelian fashion. We do however observe occasional transmission of paternal chromosomes through males, representing the first known case of PGE in which whole‐genome meiotic drive is incomplete. Finally, we discuss the potential implications of this finding for the evolution of resistance and invite the development of new theoretical models of how this knowledge might contribute to increasing the success of pediculicide‐based management schemes.     

Effects of elevated atmospheric CO2 on fine root length and distribution in an oak-palmetto scrub ecosystem in central Florida

Atmospheric CO₂ concentration is rising and it has been suggested that a portion of the additional carbon is being sequestered in terrestrial vegetation and much of that in below-ground structures. The objective of the present study was to quantify the effects of elevated atmospheric CO₂ on fine root length and distribution with depth with minirhizotrons in an open-top chamber experiment in an oak-palmetto scrub ecosystem at Kennedy Space Centre, Florida, USA. Observations were made five times over a period of one and a half years in three ambient chambers (350 p.p.m. CO₂), three CO₂ enriched chambers (700 p.p.m. CO₂), and three unchambered plots. Greater root length densities were produced in the elevated CO₂ chambers (14.2 mm cm^?2) compared to the ambient chambers (8.7 mm cm^?2). More roots may presumably lead to more efficient acquisition of resources. Fine root abundance varied significantly with soil depth, and there appeared to be enhanced proliferation of fine roots near the surface (0–12 cm) and at greater depth (49–61 cm) in the elevated CO₂ chambers. The vertical root distribution pattern may be a response to availability of nutrients and water. More studies are needed to determine if increased root length under CO₂ enriched conditions actually results in greater sequestering of carbon below ground.     

Garden Warbler Sylvia borin migration in sub-Saharan West Africa: phenology and body mass changes

The Garden Warbler is a classic subject for the study of Palaearctic–African bird migration strategies. Most studies have considered the situation close to the breeding areas, while the African and especially the sub‐Saharan part of the species’ migration have received comparatively little attention. Here we use autumn and spring ringing data from Nigeria and The Gambia to study the movements and energetics of the species in West Africa during the non‐breeding season. The first Garden Warblers arrive south of the desert around the beginning of September, roughly at the same time as the median date for their passage through the Baltic Sea region and c. 3 weeks before their median passage date through southern Italy. In the Nigerian Sahel savannahs, where, owing to the rainy season and its associated increase in food availability, many more Garden Warblers stop over in autumn than in the dry spring, the median date of passage is 1 October. The body mass on arrival south of the desert is normally only a few grams more than the lean body mass (LBM; 15 g) – with a mean of 16.6 g (sd = ±1.8 g) in The Gambia and 17.4 g (sd = ±1.8 g) in the Nigerian Sahel. After resting and refuelling in the Sahel, Sudan and Guinea‐type savannahs the Garden Warblers depart during November–December for wintering areas further south. Before leaving, they again increase their body mass, with an average fuel load of c. 20%, and often more than 50% relative to LBM. Some of the birds passing through Nigeria probably spend midwinter around the Congo Basin. During spring they return northwards to the Guinea savannah zone in April and fuel‐up there for the trans‐Sahara passage. At this time they normally increase their body reserves to around 50% of the LBM, but c. 10% of the birds gain 100%, thus doubling their mass. The passage there peaks around 20 April and continues well into May. That the main take‐off northwards is directly from the Guinea savannahs is indicated by the very low numbers trapped in the Sahel during spring.     

Promotion of flowering in the Pinaceae by gibberellins

Significant male and female flowering (cone bud production) by girdled branches of 6-year-old Douglas fir (Pseudotsuga menziesii (Mirb. Franco) seedlings was promoted by applications (mid-April to June) of 1.6 or 3.2 mg per branch (in total) of certain non-polar gibberellins (GA's). Girdling alone was ineffective. When tested alone, a mixture of GA_4/7 was most effective. GA₉ less so, while GA₅ and the more polar GA₃ were essentially ineffective. For female cone buds GA_4/7+ GA₉ were synergistically effective, but for male cone buds GA_4/7 alone was best. The auxin naphthaleneacetic acid (NAA) was not tested alone, but at low dosage (0.175 mg/branch in total) NAA enhanced the flowering efficacy of GA's for both sexes; at a high dosage (0.875 mg/branch in total) male cone bud production was further enhanced, but only at the expense of females. For female flowering the best treatment (90% frequency of flowering 6.8 cone buds/branch), was GA_4/7+ GA₉+ low NAA; for male flowering, it was GA_4/7+ high NAA (30% frequency and 4.2 cone buds/branch. Frequency of flowering for controls was 18% and 0%, average number of cone buds/branch was 0.9 and 0, for females and males, respectively. The successful treatments did not affect promordia initiation, rather they caused the differentiation of previously initiated, but undetermined, lateral primordia into cone and latent buds at the expense of vegetative bud differentiation. The lack of success reported by earlier workers in promoting flowering in Pinaceae species by GA's appears to be the unfortunate result of selecting GA₃ for initial testing. The practical implications of this early and enhanced flowering by non-polar GA's seedlings of a commercially important conifer are discussed in relation to accelerating the processes of tree improvement.     

Formation of Catechol Compounds from Phenylalanine and Tyrosine with Isolated Nerve Endings

THERE is much evidence that catecholamines may act as synaptic transmitters in the mammalian brain¹. Enzymatic activities necessary for the synthesis of catecholamines have been located in central neurones¹ and it is generally believed that tyrosine hydroxylase² is the rate limiting enzyme in brain as well as peripheral tissues containing catecholamines³. While it is clear that tyrosine can serve as a precursor of catecholamine synthesis in the brain^{1, 3, 4}, the significance of phenylalanine is problematic. It was believed that the mammalian brain is devoid of enzymatic activity necessary to convert phenylalanine to tyrosine^{6, 7}, while liver is known to be rich in the enzyme phenylalanine hydroxylase⁸. The earlier attempts to demonstrate hydroxylation of phenylalanine in brain tissue may have been unsuccessful due to methodological problems⁹. Recent evidence suggests that tyrosine hydroxylase prepared from peripheral sympathetically innervated tissues or from brain can hydroxylate either phenylalanine or tyrosine⁹. Initially, the rate of hydroxylation of phenylalanine by tyrosine hydroxylase was thought to be as little as 5% that of tyrosine⁹. It has been found recently, however, that structural variations in the pteridine cofactor present in the incubation mixture lead to striking changes in the ability of partially purified tyrosine hydroxylase from bovine adrenal medulla to hydroxylate phenylalanine¹⁰. Thus, tetrahydrobiopterin allowed the hydroxylation of phenylalanine to proceed at least as rapidly as that of tyrosine or faster¹⁰. As the structure of the endogenous pteridine cofactor of tyrosine hydroxylase is not known, it is possible that synthesis of catecholamines from phenylalanine as well as tyrosine could occur in intact neuronal tissues. Evidence has been presented that after the injection of large quantities of ¹⁴C-phenylalanine into the lateral ventricle of the rat brain, small amounts of labelled tyrosine and traces of newly synthesized catecholamines were detected in brain tissues, giving qualitative evidence that catecholamines may be synthesized in brain from phenylalanine in vivo¹¹.     

Haemoglobin Polymorphism in the Rhesus Macaque

INTRASPECIFIC polymorphism of the principal haemoglobin component is common among macaque monkeys^1–3 and other non-human primates^4–9, but although electrophoretically demonstrable it has not been found in populations of rhesus monkeys (M. mulatto)^10,11. Using the technique of isoelectric focusing in acrylamide gel, I have found variant haemoglobins in many samples of rhesus red blood cell haemolysates. The detection of these variants is apparently a result of the greatly increased resolution of the isoelectric focusing method as compared with the older electrophoretic methods.     

Behavioral and Physiological Characteristics of the Antarctic Krill, Euphausia superba

The antarctic krill, Euphausia superba, is considered a successin the intensely seasonal environment of the Southern Oceanbecause of its abundance and central role as an important fooditem for many of the larger carnivores in the ecosystem. Thebehavioral and physiological characteristics that foster thissuccess are: (1) the ability to find concentrations of foodin several types of habitat and efficiently exploit whateverfood is available; (2) the close correspondence of the lifecycle with seasonal cycles of food availability; and (3) a combinationof physiological mechanisms that enable krill to survive thelong winter period of low food availability. We evaluated therelative importance of the following four major winter-overmechanisms that have been proposed for adult krill west of theAntarctic Peninsula. The three-fold reduction in metabolic rateis the most important winter-over mechanism for these adults,although lipid utilization and shrinkage also help satisfy energyrequirements in the winter. Alternate food sources did not appearto contribute significantly as a winter energy source. However,the extent, predictability and complexity of the ice cover ina region during winter may have a great influence on the relativeimportance of these winter-over mechanisms for different populations.Ice cover in the waters west of the Antarctic Peninsula is unpredictableand smooth surfaced when it occurs, providing the krill withlittle refuge from predation. In multi-year pack ice of theWeddell Sea, however, ice cover is predictable and extensive,and there is a complex undersurface that provides hiding places.In this multi-year ice, adult krill have been observed underthe ice feeding, whereas west of the Antarctic Peninsula mostadult krill are in the water column in the winter and are notfeeding. The balance between acquiring energy and avoiding predationmay be different in these two regions in the winter becauseof differences in predictability and complexity of the ice cover.     

Simulated mechanisms of soil N feedback on the forest CO2 response

An improved understanding of the response of forest ecosystems to elevated levels of CO₂ in the atmosphere is crucial because atmospheric CO₂ concentration continues to increase at an accelerating rate and forests are an important sink in the global carbon cycle. Several CO₂‐enrichment experiments have now been running for more than 10 years, with highly variable short‐term results after the first decade. Responses to rising [CO₂] over the next few decades will depend on several plant and ecosystem feedbacks that are inadequately understood. In this study, we conduct a sensitivity analysis, within the context of the simulated CO₂ response, using a new version of the G'DAY ecosystem model, with an improved decomposition submodel, applied to a nitrogen‐limited Norway spruce forest site in the north of Sweden. The new decomposition model incorporates important modifications to soil processes, including some that constitute negative feedbacks on an ecosystem's growth response to elevated [CO₂]. The sensitivity analysis reveals key parameters and processes that are important for the simulated CO₂ response on the short term and others that are more important on the long term. A process that has a strong impact on the short‐term response is a change in decomposer composition, potentially in response to altered litter quality. Parameters that become increasingly important in the long term are carbon allocation to root exudates that are directly or indirectly associated with atmospheric N₂ fixation, and the rate of humification of soil organic matter. We identify factors intrinsic to species and site (microbes and resources) and ecosystem nutrient supply that determine the duration of the enhanced simulated growth response to elevated [CO₂].