Evolution of avian eggshell structure

Data are presented suggesting that birds have evolved eggs with shells containing different structures (numbers of mammillae per unit of inner eggshell surface area, i.e., mammillary densities) to cope up with different calcium requirements imposed by different growth rates and modes of development. Precocial bird species grow slowly, but have high mammillary density, while altricial bird species grow rapidly, but have low mammillary density. These results suggest an adaptation associated with growth rate and mode of development and show, moreover, that the mammillary layer is indicative of the breeding biology of the bird. J. Morphol. 2012. © 2011 Wiley Periodicals, Inc.     

Condition‐dependent mutation rates and sexual selection

‘Good genes’ models of sexual selection show that females can gain indirect benefits for their offspring if male ornaments are condition‐dependent signals of genetic quality. Recurrent deleterious mutation is viewed as a major contributor to variance in genetic quality, and previous theoretical treatments of ‘good genes’ processes have assumed that the influx of new mutations is constant. I propose that this assumption is too simplistic, and that mutation rates vary in ways that are important for sexual selection. Recent data have shown that individuals in poor condition can have higher mutation rates, and I argue that if both male sexual ornaments and mutation rates are condition‐dependent, then females can use male ornamentation to evaluate their mate’s mutation rate. As most mutations are deleterious, females benefit from choosing well‐ornamented mates, as they are less likely to contribute germline‐derived mutations to offspring. I discuss some of the evolutionary ramifications of condition‐dependent mutation rates and sexual selection.     

Experimental support for the role of nest predation in the evolution of brood parasitism

In 1965, Hamilton and Orians (HO) hypothesized that the starting point for the evolution of obligate interspecific brood parasitism in birds was the facultative laying of physiologically committed eggs in neighbouring active nests of con‐ and heterospecifics, following predation of a bird’s own nest during the laying stage. We tested this prediction of the HO hypothesis by using captive pairs of zebra finches (Taeniopygia guttata), a species with evidence for intraspecific parasitism both in the wild and in captivity. As predicted, in response to experimental nest removal, subjects laid eggs parasitically in simulated active conspecific nests above chance levels. Across subsequent trials, we detected both repeatability and directional change in laying patterns, with some subjects switching from parasitism to depositing eggs in the empty nest. Taken together, these results support the assumptions and predictions of the HO hypothesis, and indicate that the zebra finch is a potential model species for future behavioural and genetic studies in captive brood parasite research.     

Developmental costs of rapid growth in a damselfly

Abstract.  1. Developmental costs of rapid growth in terms of increased fluctuating asymmetry are expected to contribute to the widespread occurrence of growth rates below the physiological maximum, but have rarely been demonstrated. Here, these costs are studied for the first time in an invertebrate, the damselfly Lestes viridis , using a rearing experiment where early- and late-hatched larvae of both sexes were reared at decreasing or permanent water levels.
2. Late-hatched animals were more asymmetrical than early-hatched animals except for males in the drying treatment. Also, females were more asymmetrical than males except in early-hatched animals in the drying treatment.
3. The data presented suggest that in females but not in males treatment groups with higher growth rates have more asymmetrical wings. However, at the individual level no relationship between growth rate and asymmetry was present.
4. Possible reasons why the suggested trade-off between growth and developmental instability was not present at the individual level, and at the group level only in females, are discussed.     

Orientation and ingestion rates of larval Anopheles albimanus in response to floating particles

Response of fourth-instar larvae of Anopheles albimanus Wiedemann (Diptera: Culicidae) to food and inert particles floating at the water surface was studied. In a choice test, larvae aggregated at powdered organic materials (blood meal, liver powder alfalfa flour and wheat flour) but not at inert materials (kaolin, chalk or charcoal). Larvae responded positively to proteins as well as some carbohydrates, but not to cellulose. Retention of larvae at food sources found by random locomotion was found to be responsible for larval aggregation. Larvae ingested food particles 6–9 times faster than insert particles. The significance of Anopheline feeding behavior in the development of formulations of stomach toxins (bacterial agents) used in larval control is discussed.

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Zusammenfassung Die vorliegende Studie befasst sich mit Verhaltensreaktionen von Anopheles albimanus Viertlarven auf an der Wasseroberfläche schwimmende Partikel. Verteilung und Orientierung der Larven wurde in einer Wahlapparatur quantifiziert. Nach Auftrag von Alfalfamehl, Weizenmehl, Stärke, Blutmehl, Leberpulver und Fischmehl wurde Aggregation der Larven in den beköderten Fächern der Apparatur beobachtet. Sowohl Proteine (Casein) als auch einige Kohlehydrate (Amylose, Amylopectin) lösten Aggregationen der Larven aus. Im Unterschied dazu führte Auftrag von Kreide, Kaolin, Polyaethylenpulver, Talcum oder Cellulose nicht zu Aggregationen. Zur Beschreibung der Entstehung larvaler Aggregationen bei Futterstoffen wurden die Schwimmbewegungen der Larven in Anwesenheit von Weizenmehl als Ködersubstanz quantifiziert. Da keine Attraktion der Larven im Sinne einer gerichteten Schwimmbewegung beobachtet werden konnte, wird geschlussfolgert, dass sofortige Beendung der Suchaktivität der Larven bei zufällig gefundenen Futterquellen für die beobachteten Aggregationen bei organischen Substanzen verantwortlich ist.Die Fressraten der Larven bei Angebot verschiedener Substanzen im Überschuss wurde bestimmt. Larven fülten drei von insgesamt sechs Darmabschnitten innerhalb von 15–30 min bei Angebot von Futtersubstanzen, während die Füllung von nur zwei Darmabschnitten mit inerten Materialien erst nach 90–120 min zu beobachten war. Die Resultate werden in Bezug auf wasseroberflächengebundene Formulierungen von Frassgiften diskutiert. Inerte Trägersubstanzen werden wahrscheinlich wesentlich langsamer aufgenommen als Futtersubstanzen. Da An. albimanus Larven nicht von Futterquellen angezogen werden, ist eine rasche und wirksame Giftaufnahme besonders dann zu erwarten, wenn die gesamte Oberfläche der Brutgewässer mit toxinhaltigen Trägerpartikeln bedeckt werden kann.

     

Age-Dependent Changes in Brain GABA Turnover Rates in Two Inbred Strains of Mice

gamma-Aminobutyric acid (GABA) steady-state levels and turnover rates have been determined in 15 brain areas of 21-day- and 3-month-old DBA/2J (DBA) and C57B1/6J (C57) mice. These two inbred strains differ by their susceptibility to audiogenic seizures; moreover, the involvement of GABAergic neurotransmission has been suggested in the control of this behavior. Turnover rates are generally higher at 21 days than at 3 months of age. There are few significant differences in the GABA steady-state levels between 21-day-old seizure-prone DBA mice when compared with seizure-resistant C57 mice. In the DBA mice, the steady-state level is higher in the olfactory bulbs and lower in the posterior colliculus and the olfactory tubercles than in the C57 mice. Although there are some significant differences in GABA turnover rates and steady-state levels, intra or inter strains, it is difficult to correlate directly these differences with seizure susceptibility.