The KiSS-1 gene encodes the peptide hormone kisspeptin, which acts as a principal positive regulator of the reproductive axis by directly stimulating GnRH neuron activity. To gain insight into a potential role for kisspeptin in integrating and relaying reproductively relevant stimuli to the GnRH system, we investigated changes in kisspeptin peptide expression associated with photoperiodic changes in reproductive state as well as pituitary and gonadal responses to peripheral kisspeptin injections. Seasonally breeding rodents undergo pronounced fluctuations in reproductive state in response to changing day lengths. In common with other rodent species, a majority of male Siberian hamsters (Phodopus sungorus) exhibit reproductive decline after exposure to short-day lengths. A subset of individuals fails to respond to day length information, however, and maintains their reproductive function. We exploited these individual differences to examine whether kisspeptin may act at the interface between external stimuli and the reproductive system. After extended exposure to short days, animals with a quiescent reproductive axis displayed a marked reduction in kisspeptin cell labeling in the anteroventral periventricular nucleus but robust kisspeptin-immunoreactive staining in the arcuate nucleus. In contrast, animals with functional reproductive systems displayed high numbers of kisspeptin-immunoreactive neurons in the anteroventral periventricular nucleus but a paucity of expression in the arcuate nucleus. Kisspeptin injections significantly elevated LH over preinjection levels regardless of photoperiod or reproductive state. Collectively, these findings suggest an important role for kisspeptin in coordinating and relaying environmentally relevant information to the reproductive axis as well as a role for this peptide in regulating seasonal changes in reproductive function.

To avoid breeding during unsuitable environmental or physiological circumstances, the reproductive axis adjusts its output in response to fluctuating internal and external conditions. The ability of the reproductive system to alter its activity appropriately in response to these cues has been well established. However, the means by which reproductively relevant cues are interpreted, integrated, and relayed to the reproductive axis remain less well specified. The neuropeptide kisspeptin has been shown to be a potent positive stimulator of the hypothalamo-pituitary-gonadal (HPG) axis, suggesting a possible neural locus for the interpretation/integration of these cues. Because a failure to inhibit reproduction during winter would be maladaptive for short-lived female rodents, female Siberian hamsters (Phodopus sungorus) housed in long and short days hamsters were examined. In long, 'summer' photoperiods, kisspeptin is highly expressed in the anteroventral periventricular nucleus (AVPV), with low expression in the arcuate nucleus (Arc). A striking reversal in this pattern is observed in animals held in short, 'winter' photoperiods, with negligible kisspeptin expression in the AVPV and marked staining in the Arc. Although all studies to date suggest that both populations act to stimulate the reproductive axis, these contrasting expression patterns of AVPV and Arc kisspeptin suggest disparate roles for these two cell populations. Additionally, we found that the stimulatory actions of exogenous kisspeptin are blocked by acyline, a gonadotropin-releasing hormone (GnRH) receptor antagonist, suggesting an action of kisspeptin on the GnRH system rather than pituitary gonadotropes. Finally, females held in short day lengths exhibit a reduced response to exogenous kisspeptin treatment relative to long-day animals. Together, these findings indicate a role for kisspeptin in the AVPV and Arc as an upstream integration center for reproductively-relevant stimuli and point to a dual mechanism of reproductive inhibition in which kisspeptin expression is reduced concomitant with reduced sensitivity of the HPG axis to this peptide.

Both competition for water and phenological variation are important determinants of plant community structure, but ecologists lack a synthetic theory for how they affect coexistence outcomes. We developed an analytically tractable model of water competition for Mediterranean annual communities and demonstrated that variation in phenology alone can maintain high diversity in spatially homogenous assemblages of water‐limited plants. We modelled a system where all water arrives early in the season and species vary in their ability to grow under drying conditions. As a consequence, species differ in growing season length and compete by shortening the growing season of their competitors. This model replicates and offers mechanistic explanations for patterns observed in empirical studies of how phenology influences coexistence among Mediterranean annuals. Additionally, we found that a decreasing, concave‐up trade‐off between growth rate and access to water can maintain high diversity under simple but realistic assumptions. High diversity is possible because: (1) later plants escape competition after their earlier season competitors have gone to seed and (2) early‐season species are more than compensated for their shortened growing season by a growth rate advantage. Together, these mechanisms provide an explanation for how phenologically variable annual plant species might coexist when competing only for water.

The increasing prevalence of high-severity wildfire in forests in the US state of California is connected to past forest management, but uncertainty remains regarding the differential effects of land ownership on these trends. To determine whether differing forest management regimes, inferred from land ownership, influence high-severity fire incidence, we assembled and analyzed a large dataset of 154 wildfires that burned a combined area of more than 971,000 ha in California. We found that where fires occurred, the odds of high-severity fire on "private industrial" lands were 1.8 times greater than on "public" lands and 1.9 times greater than on "other" lands (that is, remaining lands classified as neither private industrial nor public). Moreover, high-severity fire incidence was greater in areas adjacent to private industrial land, indicating this trend extends across ownership boundaries. Overall, these results indicate that prevailing forest management practices on private industrial timberland may increase high-severity fire occurrence, underscoring the need for cross-boundary cooperation to protect ecological and social systems.

Prescribed fire is a vital tool for mitigating wildfire hazard and restoring ecosystems in many western North American forest types. However, there can be considerable variability in fuel consumption from prescribed burns, which affects both hazard mitigation and emissions. In the present study, data from replicated, repeat-entry burns following a period of 100+ years of fire exclusion were used to provide a detailed quantification of fuel consumption as it varies by fuel type, size class, stand and prescribed burn number (first, second or third). Using model selection on a series of linear mixed-effects models, it was determined that total fuel load, proportion of overstorey pine, slope, canopy cover, basal area of live trees, burn number and stand influenced fuel consumption at a 0.04-ha scale. Specifically, overstorey pine composition had a positive effect on fuel consumption. Overall fuel consumption across the three burns averaged 45% of pre-burn fuel loads. Overall consumption was highest for the first burn at 65%, decreasing by 15–20% with each successive burn number. Fuel consumption was highly variable by fuel type, stand and tree species composition. This variability may be advantageous for managers seeking to foster structural diversity and resilience in forest stands.