Detecting conspecific brood parasitism using egg morphology in black brant Branta bernicla nigricans

Numerous methods have been proposed to indirectly detect conspecific brood parasitism (CBP) in birds. Egg morphology has been suggested as a predictor of parasitism, assuming that variation in egg size is greater among females than within females. Here we use microsatellite data to assess the use of egg morphology to detect CBP in a sample of black brant Branta bernicla nigricans nests. We attempted to repeat a previously demonstrated technique using cluster analysis and maximum Euclidean distance (MED) to detect parasitized nests within black brant. Additionally we attempted a new technique based on a discriminant function analysis of egg morphology in an attempt to detect brood parasitic eggs. When detecting parasitized nests using egg morphology, the cluster analysis revealed that the MED between the two most dissimilar eggs in each nest was significantly greater for parasitized nests than for non‐parasitized nests (1.62±0.06 and 1.43±0.08, respectively). The extent of overlap in sizes of eggs between parasitized and non‐parasitized nests, however, was such that we were unable to effectively identify parasitized nests. In most cases for each parasitized nest correctly identified, 3 non‐parasitized nests were incorrectly identified as parasitic. When we attempted to detect parasitic eggs we found that parasitic eggs were more different from the expected egg volume than host eggs: mean absolute residual volume of parasitic eggs=2.59±5.79 cm³ while that for host eggs=1.82±2.14 cm³. Overall, we found that the discriminant function analysis was moderately effective in determining whether eggs belonged to the host female using a resubstitution technique (error rate=9.71%) or a jackknife technique (error rate=6.12%). Additionally, we found a higher but moderate error rate when using an independent data set to validate the function (error rate=14.07%). In both cases, however, parasitic eggs accounted for most of the error and were not correctly classified 75%, 70% and 100% of the time respectively. We suggest when developing a predictive function for detecting conspecific brood parasitism based on egg morphology that an appropriate technique be used to validate the function, particularly those techniques that utilize unambiguous identifiers such as molecular and protein fingerprinting techniques.     

Aneuploidy: a matter of bad connections

Proper chromosome segregation is required to maintain the appropriate number of chromosomes from one cell generation to the next and to prevent aneuploidy, the condition in which a cell has gained or lost one or several chromosomes during cell division. Aneuploidy is a hallmark associated with birth defects and cancer, and is observed at relatively high frequencies in human somatic cells. Recent studies in mammalian tissue culture cells suggest that the persistence of kinetochore-microtubule misattachments through mitosis is a major cause of chromosome mis-segregation and aneuploidy. Furthermore, studies in mice and humans suggest that small changes in the expression, rather than complete inactivation, of genes encoding specific proteins might be associated with aneuploidy in living organisms. In this article (which is part of the Chromosome Segregation and Aneuploidy series), we survey the outcome of these studies, focusing on the importance of kinetochore misattachments in producing aneuploid cells.     

Geographical variation in egg mass and egg content in a passerine bird

Reproductive, phenotypic and life-history traits in many animal and plant taxa show geographic variation, indicating spatial variation in selection regimes. Maternal deposition to avian eggs, such as hormones, antibodies and antioxidants, critically affect development of the offspring, with long-lasting effects on the phenotype and fitness. Little is however known about large-scale geographical patterns of variation in maternal deposition to eggs. We studied geographical variation in egg components of a passerine bird, the pied flycatcher (Ficedula hypoleuca), by collecting samples from 16 populations and measuring egg and yolk mass, albumen lysozyme activity, yolk immunoglobulins, yolk androgens and yolk total carotenoids. We found significant variation among populations in most egg components, but ca. 90% of the variation was among individuals within populations. Population however explained 40% of the variation in carotenoid levels. In contrast to our hypothesis, we found geographical trends only in carotenoids, but not in any of the other egg components. Our results thus suggest high within-population variation and leave little scope for local adaptation and genetic differentiation in deposition of different egg components. The role of these maternally-derived resources in evolutionary change should be further investigated.     

Early egg contractions and patterned parasynchronous cleavage in a living insect egg

Summary Fifteen movements of egg ooplasm occur prior to the formation of the embryo of the beetle,Callosobruchus maculatus. These movements are associated with nuclear division taking place before formation of the embryo. Yolk globules exhibit a coordinated pattern of saltation and quiescence with these movements. The significance of this yolk activity for the movement of nuclei within the yolk mass is discussed. During the syncytial blastoderm stage the surface of the egg is infolded around the surface nuclei. Nuclear division during this period appears to produce localized stretching of the surface which in turn results in a yolk contraction. Division is parasynchronous and patterned with a wave of anaphase configurations spreading across the egg. The significance of such mitotic gradients to patterning of insect segments is discussed.     

The point of a Guillemot's egg

The adaptive significance of avian egg shape in birds is poorly understood. The pyriform (pear‐like) shape of the Common Guillemot's Uria aalge egg has long been considered to be an adaptation to prevent eggs rolling off the bare cliff ledges on which this species breeds. Rolling was thought to be prevented either by the egg spinning like a top, which is not the case, or by rolling in an arc, which it does but with little influence on whether the egg will fall from a ledge. We therefore sought alternative explanations for the pyriform shape of the Common Guillemot's egg. This species breeds in extremely dense colonies, which makes their eggs vulnerable to mechanical damage from conspecifics, and to contamination by debris such as faeces and soil. We present evidence consistent with both these possible explanations. First, the pyriform shape of Common Guillemot eggs means that a higher proportion of the eggshell lies in contact with the substrate and this may minimize the effect of impacts. Resistance to impacts may be further enhanced because their eggshells are especially thick where they are in contact with the substrate. Secondly, Common Guillemot eggs are often heavily contaminated with faecal material and other debris during incubation. Most contamination is on the pointed end of the egg where it is in contact with the substrate; the pyriform shape thus keeps the blunt end of the egg, which has the highest porosity, relatively free of contamination, which in turn may facilitate both gas exchange during incubation and the hatching process, because the chick emerges from the blunt end of the egg.