Review of Swallow Summer

The field season of 1995 (early May through late July) in western Nebraska is described in this book by the leading expert on cliff swallow (Petrochelidon pyrrhonota) behavior. This nontechnical introduction to the natural history of a colonial swallow was written for those who are interested in natural history or how field work is done. Brown\u27s stated goals are to describe the challenges and satisfaction of long-term field work and to tell the cliff swallow\u27s story (p xi). The book reads as part field notes (daily weather conditions, how many birds he caught and where), part personal diary (what frustrations with which assistant he experienced each day), and part historical account of his decade-and-a-half of research on cliff swallows

Periodic Cooling of Bird Eggs Reduces Embryonic Growth Efficiency

For many bird embryos, periodic cooling occurs when the incubating adult leaves the nest to forage, but the effects of periodic cooling on embryo growth, yolk use, and metabolism are poorly known. To address this question, we conducted incubation experiments on eggs of zebra finches (Taeniopygia guttata) that were frequently cooled and then rewarmed or were allowed to develop at a constant temperature. After 12 d of incubation, embryo mass and yolk reserves were less in eggs that experienced periodic cooling than in controls incubated constantly at 37.5C. Embryos that regularly cooled to 20C had higher mass-specific metabolic rates than embryos incubated constantly at 37.5C. Periodic cooling delayed development and increased metabolic costs, reducing the efficiency with which egg nutrients were converted into embryo tissue. Avian embryos can tolerate periodic cooling, possibly by adjusting their physiology to variable thermal conditions, but at a cost to growth efficiency as well as rate of development. This reduction in embryo growth efficiency adds a new dimension to the fitness consequences of variation in adult nest attentiveness

Evolutionary ecology of endocrine-mediated life-history variation in the garter snake Thamnophis elegans

The endocrine system plays an integral role in the regulation of key life-history traits. Insulin-like growth factor-1 (IGF-1) is a hormone that promotes growth and reproduction, and it has been implicated in the reduction of lifespan. IGF-1 is also capable of responding plastically to environmental stimuli such as resource availability and temperature. Thus pleiotropic control of life-history traits by IGF-1 could provide a mechanism for the evolution of correlated life-history traits in a new or changing environment. An ideal system in which to investigate the role of IGF-1 in life-history evolution exists in two ecotypes of the garter snake Thamnophis elegans, which derive from a single recent ancestral source but have evolved genetically divergent life-history characteristics. Snakes from meadow populations near Eagle Lake, California (USA) exhibit slower growth rates, lower annual reproductive output, and longer median adult lifespans relative to populations along the lakeshore. We hypothesized that the IGF-1 system has differentiated between these ecotypes and can account for increased growth and reproduction and reduced survival in lakeshore vs. meadow snakes. We tested for a difference in plasma IGF-1 levels in free-ranging snakes from replicate populations of each ecotype over three years. IGF-1 levels were significantly associated with adult body size, reproductive output, and season in a manner that reflects established differences in prey ecology and age/size-specific reproduction between the ecotypes. These findings are discussed in the context of theoretical expectations for a trade-off between reproduction and lifespan that is mediated by pleiotropic endocrine mechanisms

Maternal Effects Increase Within‐Family Variation in Offspring Survival

Maternal effects are environmental components of phenotypes that complicate relationships between natural selection and evolution because they often affect phenotypes and fitness simultaneously. We studied the effects of egg size variation on juvenile survival in a population of American coots (Fulica americana). We experimentally evaluated egg size variation at three levels: across the population, within natal nests, and within foster nests. Natal nests accounted for the most variation in population egg size. Within clutches, early-laid eggs were larger than later-laid eggs, with the exception of first-laid eggs, which were small. In the fostering experiment, posthatching survival was most strongly related to egg size relative to natal siblings and natal hatching order and less so to egg size within foster nests. These effects on survival were found even though young from natal nests were neither raised together nor raised by genetic parents. These results indicate that females allocate resources unequally among offspring such that offspring from larger, early-laid eggs have higher survival than offspring from smaller, laterlaid eggs, regardless of their size relative to foster siblings or to mean population egg size. These results suggest that egg size variation can be maintained through selection on maternal investment strategies and not on egg size per se