Can environmental conditions experienced in early life influence future generations?

The consequences of early developmental conditions for performance in later life are now subjected to convergent interest from many different biological sub-disciplines. However, striking data, largely from the biomedical literature, show that environmental effects experienced even before conception can be transmissible to subsequent generations. Here, we review the growing evidence from natural systems for these cross-generational effects of early life conditions, showing that they can be generated by diverse environmental stressors, affect offspring in many ways and can be transmitted directly or indirectly by both parental lines for several generations. In doing so, we emphasize why early life might be so sensitive to the transmission of environmentally induced effects across generations. We also summarize recent theoretical advancements within the field of developmental plasticity, and discuss how parents might assemble different ‘internal’ and ‘external’ cues, even from the earliest stages of life, to instruct their investment decisions in offspring. In doing so, we provide a preliminary framework within the context of adaptive plasticity for understanding inter-generational phenomena that arise from early life conditions

Experimental demonstration that offspring fathered by old males have shorter telomeres and reduced lifespans

Offspring of older parents frequently show reduced longevity, but the mechanisms driving this so-called 'Lansing effect' are unknown. While inheritance of short telomeres from older parents could underlie this effect, studies to date in different species have found mixed results, reporting positive, negative or no association between parental age and offspring telomere length (TL). However, most of the existing evidence is from non-experimental studies in which it is difficult to exclude alternative explanations such as differential survival of parents with different telomere lengths. Here we provide evidence in the zebra finch that offspring from older parents have reduced lifespans. As a first step in disentangling possible causes, we used an experimental approach to examine whether or not we could detect pre-natal paternal effects on offspring TL. We found that zebra finch embryos fathered by old males have shorter telomeres than those produced by the same mothers but with younger fathers. Since variation in embryonic TL persists into post-natal life, and early life TL is predictive of longevity in this species, this experimental study demonstrates that a paternally driven pre-natal TL reduction could at least in part underlie the reduced lifespan of offspring from older parents

Does individual variation in metabolic phenotype predict fish behaviour and performance?

There is increasing interest in documenting and explaining the existence of marked intraspecific variation in metabolic rate in animals, with fishes providing some of the best-studied examples. After accounting for variation due to other factors, there can typically be a two to three-fold variation among individual fishes for both standard and maximum metabolic rate (SMR and MMR). This variation is reasonably consistent over time (provided that conditions remain stable), and its underlying causes may be influenced by both genes and developmental conditions. In this paper, current knowledge of the extent and causes of individual variation in SMR, MMR and aerobic scope (AS), collectively its metabolic phenotype, is reviewed and potential links among metabolism, behaviour and performance are described. Intraspecific variation in metabolism has been found to be related to other traits: fishes with a relatively high SMR tend to be more dominant and grow faster in high food environments, but may lose their advantage and are more prone to risk-taking when conditions deteriorate. In contrast to the wide body of research examining links between SMR and behavioural traits, very little work has been directed towards understanding the ecological consequences of individual variation in MMR and AS. Although AS can differ among populations of the same species in response to performance demands, virtually nothing is known about the effects of AS on individual behaviours such as those associated with foraging or predator avoidance. Further, while factors such as food availability, temperature, hypoxia and the fish's social environment are known to alter resting and MMRs in fishes, there is a paucity of studies examining how these effects vary among individuals, and how this variation relates to behaviour. Given the observed links between metabolism and measures of performance, understanding the metabolic responses of individuals to changing environments will be a key area for future research because the environment will have a strong influence on which animals survive predation, become dominant and ultimately have the highest reproductive success. Although current evidence suggests that variation in SMR may be maintained within populations via context-dependent fitness benefits, it is suggested that a more integrative approach is now required to fully understand how the environment can modulate individual performance via effects on metabolic phenotypes encompassing SMR, MMR and AS

Passive Evolution: Are the Faint Blue Galaxy Counts Produced by a Population of Eternally Young Galaxies?

A constant age population of blue galaxies, postulated in the model of Gronwall & Koo (1995), seems to provide an attractive explanation of the excess of very blue galaxies in the deep galaxy counts. Such a population may be generated by a set of galaxies with cycling star formation rates, or at the other extreme, be maintained by the continual formation of new galaxies which fade after they reach the age specified in the Gronwall and Koo model. For both of these hypotheses, we have calculated the luminosity functions including the respective selection criteria, the redshift distributions, and the number counts in the B_J and K bands. We find a substantial excess in the number of galaxies at low redshift (0 < z < 0.05) over that observed in the CFH redshift survey (Lilly et al. 1995) and at the faint end of the Las Campanas luminosity function (Lin et al. 1996). Passive or mild evolution fails to account for the deep galaxy counts because of the implications for low redshift determinations of the I-selected redshift distribution and the r-selected luminosity function in samples where the faded counterparts of the star-forming galaxies would be detectable.Comment: 11 pages, LaTeX type (aaspp4.sty), 3 Postscript figures, submitted to ApJ Letter

Primary neurons that express the L2/HNK-1 carbohydrate during early development in the zebrafish

In zebrafish, many nerve pathways in both the CNS and periphery are pioneered by a small and relatively simple set of ‘primary’ neurons that arise in the early embryo. We now have used monoclonal antibodies to show that, as they develop, primary neurons of several functional classes express on their surfaces the L2/HNK-1 tetrasaccharide that is associated with a variety of cell surface adhesion molecules. We have studied the early labeling patterns of these neurons, as well as some non-neural cells, and found that the time of onset and intensity of immunolabeling vary specifically according to cell type. The first neuronal expression is by Rohon-Beard and trigeminal ganglion neurons, both of which are primary sensory neurons that mediate touch sensitivity. These cells express the epitope very strongly on their growth cones and axons, permitting study of their development unobscured by labeling in other cells. Both types initiate axogenesis at the same early time, and appear to be the first neurons in the embryo to do so. Their peripheral neurites display similar branching patterns and have similar distinctive growth cone morphologies. Their central axons grow at the same rate along the same longitudinal fiber pathway, but in opposite directions, and where they meet they appear to fasciculate with one another. The similarities suggest that Rohon-Beard and trigeminal ganglion neurons, despite their different positions, share a common program of early development. Immunolabeling is also specifically present on a region of the brain surface where the newly arriving trigeminal sensory axons will enter the brain. Further, the trigeminal expression of the antigen persists in growth cones during the time that they contact an individually identified central target neuron, the Mauthner cell, which also expresses the epitope. These findings provide descriptive evidence for possible roles of L2/HNK-1 immunoreactive molecules in axonal growth and synaptogenesis

Optimization of resource allocation can explain the temporal dynamics and honesty of sexual signals

In species in which males are free to dynamically alter their allocation to sexual signaling over the breeding season, the optimal investment in signaling should depend on both a male’s state and the level of competition he faces at any given time. We developed a dynamic optimization model within a game‐theoretical framework to explore the resulting signaling dynamics at both individual and population levels and tested two key model predictions with empirical data on three‐spined stickleback (Gasterosteus aculeatus) males subjected to dietary manipulation (carotenoid availability): (1) fish in better nutritional condition should be able to maintain their signal for longer over the breeding season, resulting in an increasingly positive correlation between nutritional status and signal (i.e., increasing signal honesty), and (2) female preference for more ornamented males should thus increase over the breeding season. Both predictions were supported by the experimental data. Our model shows how such patterns can emerge from the optimization of resource allocation to signaling in a competitive situation. The key determinants of the honesty and dynamics of sexual signaling are the condition dependency of male survival, the initial frequency distribution of nutritional condition in the male population, and the cost of signaling

Teachers Perception of Elementary School Principals Leadership Characteristics in Elementary Schools in Rural Southwest Virginia.

The characteristics of servant leaders as perceived by teachers who evaluated the leadership excellence of principals were the focus of this study. The essential ingredient of a leader was examined in all participating schools; the role of the principal was crucial to a school\u27s effectiveness and was widely acknowledged. Ten characteristics were discussed in the literature review. This dissertation was a quantitative study of teachers\u27 perceptions, as well as principals\u27 self-perceptions, of principals in rural Title I Schools located in southwest Virginia. The exploratory question that originated from this study was: Was there a significant difference between the mean score on the Metcalfe Leadership Questionnaire for teachers and their school principals for each of the 10 survey variables (listening, empathy, awareness, healing, persuasion, conceptualization, foresight, stewardship, commitment to the growth of people, and building community) for schools 1 through 17? In an attempt to answer this question, a Likert 5 scale survey was given to each principal regardless of years experience and teachers with at least 3 years of experience. This group of teachers was selected with the assumption that experienced teachers could better identify influential relationship that described true patterns in Title I schools. A one sample t-test was used to determine if differences existed between teachers\u27 means and their principal\u27s self-ratings. The results showed a significant difference in the teachers\u27 perceptions of their principal and the self-analysis by the principal in the servant-leadership characteristics as defined by Robert Greenleaf (1977). The null hypotheses relating to healing and persuasion were retained in more schools than rejected. The remaining 8 null hypotheses were rejected in more schools than retained. In most cases principals\u27 self-ratings were higher than the means of teachers rating them. In at least two schools principals generally rated themselves lower than their teachers