Evolution of Litter Size: Proximate and Ultimate Mechanisms.

Relative reproductive success and failure are the ultimate determinants of Darwinian fitness. As such, reproductive traits and variations therein have an immediate and considerable impact on the evolutionary trajectory of lineages. Historically, significant attention has been paid to the ecological and evolutionary processes (ultimate factors) that shape the diversity and canalization of reproductive traits within groups to better our understanding of organismal diversity and population or species resilience.

Evolution in reproductive tempo and investment across the Peromyscus radiation.

Mammals display diverse reproductive strategies, however, the ultimate and proximate mechanisms that underlie this diversity and its composite traits remain poorly understood from both evolutionary and physiological perspectives. The Peromyscus genus of rodents, which is found throughout the north and central Americas, has diversified along life history gradients, varying both within and among species in reproductive strategies. This variation provides a useful model for studying reproductive diversity.

Impact of Chronic Prenatal Stress on Maternal Neuroendocrine Function and Embryo and Placenta Development During Early-to-Mid-Pregnancy in Mice.

Psychological stress, both leading up to and during pregnancy, is associated with increased risk for negative pregnancy outcomes. Although the neuroendocrine circuits that link the stress response to reduced sexual motivation and mating are well-described, the specific pathways by which stress negatively impacts gestational outcomes remain unclear. Using a mouse model of chronic psychological stress during pregnancy, we investigated 1) how chronic exposure to stress during gestation impacts maternal reproductive neuroendocrine circuitry, and 2) whether stress alters developmental outcomes for the fetus or placenta by mid-pregnancy.

Sex-Differences in Phenology: A Tinbergian Perspective.

Shifts in the timing of cyclic seasonal life-history events are among the most commonly reported responses to climate change, with differences in response rates among interacting species leading to phenological mismatches. Within a species, however, males and females can also exhibit differential sensitivity to environmental cues and may, therefore, differ in their responsiveness to climate change, potentially leading to phenological mismatches between the sexes. This occurs because males differ from females in when and how energy is allocated to reproduction, resulting in marked sex-differences in life-history timing across the annual cycle.